Growth factor involvement in progression of prostate cancer.
Little is currently known about the natural history of untreated prostate cancer. The discrepancy that exists between the prevalence of prostate cancer at autopsy and the clinical incidence of prostate cancer has been recognized for many years (1). The frequency of autopsydetected cancer has been reported to be 30-40% in men over the age of 50. In contrast to these autopsy prevalence studies, the lifetime probability that a man will be diagnosed clinically with prostate cancer is ~13%, and the probability of dying of prostate cancer is only ~3% (2). Despite these statistics, diagnosed prostate cancer is the most common cancer in men and the second highest cause of cancer death in men in Western society. In the US, >540 new cases are found daily, and the death rate is 104/day (3). At present, separating the individuals whose cancer will not progress from those with potentially fatal disease is not possible (4). Because no trial has examined the natural history of localized prostate cancers detected through screening for prostate-specific antigen (PSA)  this dilemma would be compounded in cancers detected through a screening program (5). Such cancers may have different natural histories from those that present clinically. Moreover, prostate cancers exhibit extreme heterogeneity with respect to grade and stage within individual tumors (6), making it difficult to determine their overall ability to progress. Although a number of characteristics of prostate cancer, including histological grade, tumor size, and ploidy (7), are useful in predicting biological activity, more reliable prognostic markers to identify individuals with potentially fatal forms of the disease are urgently needed. A better understanding of growth factors and the changes that occur in the androgen receptor (AR) should give some information in this regard (4).
Treatment for clinically detected prostate cancer includes watchful waiting, prostate surgery, or targeted irradiation. The latter two treatments can cure only cancer that is organ confined, yet up to 60% of patients present with metastases, particularly to the bone. Because determining the biological potential of localized cancers detected with any degree of certainty through screening is not possible, observation alone will result in a lost opportunity for cure in many patients; on the other hand, treatments such as radical prostatectomy or radiation therapy in such cases will necessarily overtreat many patients (8). Advanced prostate cancer with metastases to bone and other soft tissues also presents a difficult therapeutic problem (4). Management alternatives for advanced prostate cancer are palliative at best. Treatment for such cancers depends on the androgen requirement of prostate epithelial cells for growth and survival. Endocrine therapy leads to substantial periods of remission. However, it is ineffective once the tumors progress from androgen-dependent (AD), through androgen-sensitive (AS; these tumors do not require androgen for growth but proliferate more rapidly in its presence), to hormone refractory or androgen-independent (AI). This progression is almost inevitable in men after androgen ablation therapy. Total androgen ablation used in hormonally naive patients results in a median remission of about 24 months (4). Therapeutic alternatives in men who have progression of the disease after androgen ablation are very limited, with a median survival between 8 and 12 months.
The need to develop more effective therapy for these patients exists. A better understanding of growth factor pathways may provide an additional target for therapy in patients with advanced prostate cancer. This review focuses on the current state of knowledge of growth factor pathways in prostate cancer. The majority of data presented were derived from cancer cell lines without functional AR and from animal models. We thus warn the reader that such data may not be directly relevant to human prostate cancer. In addition, some of the data are based on single literature reports, and they need confirmation before definitive conclusions can be drawn.
Biological Properties of the Prostate Gland
The prostate gland is composed of epithelial cells, which form two layers and stromal cells. There are three types of epithelial cells: secretory glandular cells, nonsecretory basal cells, and neuroendocrine cells (9). The basal cells lack ARs, are AI, and are thought to be stem cells for secretory epithelial cells (10); the neuroendocrine cells may play a role in regulating the growth and function of the secretory cells (11). The stroma of the prostate is composed of smooth muscle cells, fibroblasts, lymphocytes, and neuromuscular tissue embedded in an extracellular matrix. Evidence suggests that epithelial-stromal interactions play an important role in normal prostatic morphogenesis (12). In normal tissue, such interactions are often paracrine with, for example, receptors for a particular growth factor present only on epithelial cells and production of the factor only by stromal cells. In cancer, some growth factor pathways become autocrine, enabling the epithelial cells, which express a growth factor and its receptor, to grow independently of stromal cells.
Various hypotheses to explain how malignant but not benign prostatic epithelial cells become AI have been proposed [reviewed in (13)]. These hypotheses are based on: (a) clonal selection of AI cells from a heterogeneous population of AD and AI cells by androgen ablation; (b) an adaptive theory, which proposes the presence of AD stem cells that can adapt to self-renewal in the absence of androgen; (c) the potential effects of small residual amounts of androgen, which can stimulate AS cells; and (d) changes in the AR, such as mutation, overexpression, or loss, that occur in some but not all cases of AI prostate cancer. Currently, determining which hypothesis is correct is not possible, but given that most prostate cancers are heterogeneous, it is likely that both clonal selection of preexisting AI cells and adaptive processes may contribute to AI progression. However, the findings described below make it clear that AI progression must also be mediated by growth-regulatory factors that function independently of androgen.
Both autocrine and paracrine growth factors are upregulated in AI prostate tumors and may replace androgen as the primary growth-stimulatory factors in cancer progression. This up-regulation may represent an adaptive response to androgen ablation in the growth regulation of AI tumors and is the basis for discussion in this review.
The AR in Prostate Cancer
Because androgen has been shown to regulate the expression of many prostatic growth factors and androgen ablation is the most common first-line treatment for prostate cancer patients [reviewed in (14)], no review on growth modulators of prostate cancer would be complete without some comment regarding the AR and its possible role in this disease.
The AR is a member of the steroid/thyroid hormone/ retinoic acid family of receptors that bind to specific hormone-responsive elements in target genes, thus regulating transcription [reviewed in (15)]. In the developing prostate, only the stromal cells express ARs, suggesting that androgen regulation of prostatic development is mediated via the stromal cells [reviewed in (16,17)]. In the normal adult prostate, AR expression is found mainly in the epithelium, but it is also identified in the stromal cells (16, 17). In contrast, in prostate cancer specimens, AR staining in the epithelium is heterogeneous, with a marked decrease in AR-positive cells occurring in less differentiated tumors, corresponding to the reported insensitivity to androgen observed in advanced prostate cancers (18,19). The reason for this altered expression of the AR and why some cells lose their AR is still not known.
Sequence analysis of the AR gene in prostate cancers has revealed that many tumors contain mutations (20-24). The resulting mutant proteins may be unable to bind androgen but remain constitutively activated, or they may bind androgen but be nonfunctional (15, 25). AR mutations in prostate cancers are commonly point mutations but may also reflect microsatellite instability. Point mutations have been identified in many prostate cancers, including the AS cell line LNCaP (20-22). In particular, a hot spot for mutation exists at codon 887 (ACT-GCT, Thr-Ala) in the hormone-binding domain of the gene. In LNCaP cells, this mutation enables the AR to bind progestogenic and estrogenic steroids, but it also causes a decreased affinity for androgen (23). Such abnormal binding may induce the transcription of genes out of context, thus upsetting the delicate balance of growth factors in the prostate and promoting cancer development.
Prostate cancer development has also been linked to a change in the number of repeats in the polymorphic CAG and GGC microsatellite in exon 1 of the AR gene (24-26). How this leads to prostate cancer development is not yet clear.
Prostate cancer cells have derived complex mechanisms that allow them to grow in the absence of androgen stimulation or in the presence of mutated or lost AR. Exposure of DU-145 AI prostate cancer cells transfected with an AR expression vector and a chloramphenicol acetyltransferase (CAT) reporter gene to keratinocyte growth factor (KGF), epidermal growth factor (EGF), or insulin-like growth factor 1 (IGF-1) could activate CAT gene expression in the absence of androgen (27). These data suggest that growth factors may activate AR in an androgen-deprived environment.
The Role of Growth Modulators in Prostate Cancer
Although the role of androgen is important, alone it is insufficient to maintain normal prostate homeostasis. This process also requires complex interactions between peptide growth factors and growth modulators that may be regulated either by androgen or independently by other factors (Table 1) (28-79). This renders the prostate gland very sensitive to any aberrations in growth factor or androgen expression. Therefore, it is not surprising that in prostate cancer the expression, regulation, and cell-related production of many of these growth modulators are altered (Table 1).
Alterations may take the form of up- or down-regulation of growth factors or their receptors or a change from paracrine to autocrine mediation of growth factor pathways. Alternatively, because many growth factor pathways send their messages to the cells via common signal transduction pathways, any mutations affecting signal transduction may affect several growth factor pathways simultaneously. Functional analysis of these potential changes is outside the scope of this review. Our focus is on growth factor families for which there is evidence to support a major role in normal and cancerous growth of the prostate. These families include the following: the fibroblast growth factor (FGF) family, the IGF family, EGF, and transforming growth factor a (TGF-[alpha]), all of which are predominantly stimulators of proliferation; retinoic acid, which causes differentiation and invasiveness; and the TGF-[beta] family and vitamin [D.sub.3], which are predominantly inhibitors of prostatic growth. Using evidence from human prostate cancer cell lines and animal models in vivo and in vitro, we will discuss the role that these factors play in normal prostate development and in cancer progression. Evidence obtained from clinical findings is often controversial, and many different models of prostate cancer have been studied in vivo and in vitro in an attempt to define more precisely the roles particular growth factors play in prostate cancer progression.
Models for Studies of Prostate Cancer
Prostate cancer rarely arises spontaneously in animals other than humans, and an ideal model for its study does not exist. Such a model would have a reasonably slow doubling time, be AD or AS, produce PSA, metastasize to lymph nodes and bone, and progress to an AI state after castration (80). The natural history of prostate cancer in humans varies widely in biological aggressiveness, androgen sensitivity, and histological appearance. Different models mimic various aspects of the clinical disease. Those most commonly used are summarized in Table 2 (81-111).
The rat prostate differs from the human gland in that it is divided into distinct individually encapsulated lobes (dorsal, ventral, and anterior), each of which has a separate set of compound ducts (111). The best known model of prostate cancer is the Dunning R-3327 rat prostatic adenocarcinoma model, derived by the passage of a spontaneous prostate tumor discovered at autopsy in a Copenhagen rat (81). Subcutaneously implanted tumors become palpable in ~60 days and histologically are well-differentiated adenocarcinomas with both glandular and stromal elements. Multiple sublines indicative of cancer progression have been developed [described in detail in (82)], including AS lines (H) and AI tumors (A subline), which lack 5[alpha]-reductase and ARs (83), and metastatic (84) sublines (Table 1).
Other rodent models include the hormone- or N-methyl-N-nitrosourea-induced Noble rat prostatic adenocarcinoma model (85, 86), Pollard rat tumors in Lobund-Wistar (L-W) rats derived from a spontaneous tumor (90, 91), spontaneous ACI rat prostate cancers in aging August X Copenhagen hybrids (93), and the Shionogi mouse mammary carcinoma model (95, 96), which produces both AD and AS wild-type tumors. In Shionogi mice, the proportion of AI stem cells in recurrent AI tumors has been shown to increase 500-fold, lending support for self-renewal of stem cells in the absence of androgen (113). These models have been described elsewhere in detail (13).
Thompson et al. (97) have developed a mouse prostate reconstitution (MPR) model that exploits the ability of fetal epithelial and stromal cells from the urogenital sinus to form a mature prostate gland when implanted under the renal capsule of adult mice. This model allows the study of paracrine interactions between cell compartments by introducing candidate genes for growth factors, oncogenes, or suppressor genes into the epithelial or fibroblast compartments derived from the fetal prostate gland and then combining and engrafting them under the renal capsule of syngeneic male mice.
HUMAN PROSTATE CANCER CELL LINES
Most human prostate cancer cell lines have been established from metastatic deposits, with the exception of PC-93 (98), grown from an AD primary tumor. However, PC-93 and other widely used lines, including PC-3 (99), DU-145 (100), and TSU-PR1 (114), are all Al; all lack ARs (with the possible exception of PC-93), PSA, and 5[alpha]-reductase; and all produce poorly differentiated tumors if inoculated into nude mice. The paucity of cell lines that are AD has made studies of the progression of prostate cancer using human material very difficult. However, metastatic sublines of PC-3 have been developed by injection of cells into nude mice via different routes, especially orthotopically (115).
The LNCaP cell line, established from a metastatic deposit in lymph node (100), is the only human prostate cancer cell line that demonstrates androgen sensitivity but not androgen dependence. After its initial characterization (100), several laboratories found that this line was poorly tumorigenic in nude mice unless coinoculated with tissue-specific mesenchymal or stromal cells (116) or Matrigel (117), suggesting that extracellular matrix and paracrine-mediated growth factors play a role in prostate cancer growth and site-specific metastasis (118). LNCaP cells grown in castrated mice that had progressed to the Al state were cultured to obtain new cell lines. The C-4 LNCaP (119) line produces PSA and a factor that stimulates PSA production, and the C4-2 line metastasizes to lymph nodes and bone after subcutaneous or orthotopic inoculation (102, 103). Another subline of LNCaP, LNCaP 104-R2, cultured in androgen-depleted medium for >100 passages, is stimulated by finasteride, causing some concern over the use of antiandrogens for the treatment of late-stage prostate cancer (104).
HUMAN XENOGRAFT MODELS
The CWR22 xenograft line is highly AD in vivo and relapses to an Al line, CWR22R, after androgen withdrawal (105), thus providing a useful model for studies of the progression of human prostate cancer. PC-82 is one of several xenograft lines established in Rotterdam. PC-82 and PC-EW are AD prostate cancer xenograft lines (106,107) that are useful for studying AR regulation (119). Honda and LuCap xenografts are also both AS (108, 109). The UCRU-PR-2 xenograft line, established from a patient with prostatc adenocarcinoma, is a small cell carcinoma of the prostate that secretes pro-opiomelano-corticotropinderived peptides (110, 111). Cell lines have not been established in vitro from these lines.
TRANSGENIC MOUSE MODELS
Fusion of tissue-specific promoter elements to oncogenes has been used to target expression of the oncoprotein to a given organ, sometimes with the development of cancer in that organ. The use of a viral promoter with the oncogene INT2 causes benign hyperplasia of the prostate in transgenic mice (49), whereas TGF-[alpha] expressed under the control of a metallothionine gene promoter produced prostate epithelial hyperplasia and focal dysplasia resembling carcinoma in situ (121). Regulatory elements of the rat probasin gene have been shown to target hormonally regulated expression of heterologous genes in the prostates of transgenic mice (122). Two new transgenic models have excellent potential for studies of prostate cancer progression. These are C3(1)/SV40 large T antigen transgenic mice, which show a progression to cancer from intraepithelial neoplasia (123), and the TRAMP (transgenic adenocarcinoma mouse prostate) model, in which metastases develop (124).
Growth Factor Families Important in Prostate Cancer
The growth factor families involved in prostate cancer progression are shown in Table 1. Some of these families appear to play a more major role in prostate cancer progression than others. Their characteristics are described in Table 3 (51,125-144).
THE TGF-[beta] FAMILY
Three proteins of the TGF-[beta] superfamily, TGF-[beta]1, TGF-[beta]2, and TGF-[beta]3, are expressed during prostate development and in the adult prostate in both normal and malignant tissue (125, 126). More distantly related peptides, including the activins and inhibins, are not discussed here. The TGF-[beta] family is highly conserved between species (145). TGF-[beta]1 predominates in all tissues, whereas the expression of TGF-[beta]2 and TGF-[beta]3 is more tissue-restricted (126, 127, 146). However, all three isoforms share a multiplicity of biological effects (126). TGF-[beta]s induce angiogenesis in wound healing (41); stimulate the synthesis of extracellular matrix components such as collagen, fibronectin, proteoglycans, and integrins; and also can inhibit extracellular matrix formation through down-regulation of a wide variety of proteases (42, 145). TGF-[beta]s also can induce proliferation of mesenchyme cells and can act as growth inhibitors of epithelial cells (147) and as important immunoregulatory molecules (43).
How TGF-[beta]1 works on prostrate cancer cells is unclear. TGF-01 binds to the TGF-[beta]2 receptor (TbetaR-II), which recruits the TGF-[beta]I receptor (TbetaR-I) to initiate a signal transduction cascade. Although TbetaR-I and TbetaR-II are transmembrane serine-threonine kinases (129), they can trigger decreases in the expression of members of the Src family of tyrosine kinases (130), affecting protein tyrosine kinase signaling and hence growth regulation (131). TGF-[beta]3 receptor (TbetaR-III) plays a more indirect role because it delivers ligands to the signaling receptors (132). TGF-01 prevents phosphorylation of the retinoblastoma gene product (149) that is involved in cellular proliferation and should, therefore, inhibit proliferation. Thus, in the nondiseased prostate, TGF-[beta] is believed to play a role in regulating cell growth through its antiproliferative effects because it can inhibit the mitogenic effects of EGF/TGF-[alpha] on epithelial cells (28) and of basic FGF (bFGF) on stromal cells (29).
TGF-[beta]1, TGF-[beta]2, and TGF-[beta]3 are important for fetal prostate development and are expressed at high concentration in 17-day murine urogenital sinus mesenchyme but not in the epithelium. In adult mice, only TGF-[beta]1 is increased, with the highest concentrations observed during epithelial duct formation (30). The expression of TGF-[beta]1 and its receptor are negatively regulated by androgen in the prostate. In apparently healthy rats, expression of TGF-[beta] and TbetaR-I and TbetaR-II is upregulated within 24 h after castration and has been linked to programmed cell death in the prostate (31). In tumors, androgen withdrawal results in increased TGF-01 and receptor concentrations in both rat Dunning R3327 PAP (31) and human PC-82 prostatic cancer cells (32). Increasing expression of TGF-[beta]1 appears to be important in prostate cancer progression, but its exact role remains uncertain (125). In humans, increased mRNA and protein expression of both epithelial cell-specific and, to a lesser extent, stromal cell expression of intracellular TGF-[beta]1 is associated with prostate cancer progression (33, 34). Moreover, serum TGF-[beta]1 concentrations in patients with lymph node and/or distant metastases were markedly higher than in patients with localized disease but did not differ substantially among localized cancers as to tumor extension (35). Similarly, increased TGF-[beta]1 expression is associated with increasing malignancy in the mouse MPR model (36) and, in particular, in metastatic versus primary cell lines (37). Moreover, transfection of TGF-[beta]1 into rat R3327-MATLyLu prostate cancer cells resulted in larger, less necrotic, and more metastatic cells than controls (38).
Not only is expression of TGF-[beta]1 increased with prostate cancer progression, but secretion also occurs. A factor involved in TGF-[beta]1 secretion (150, 151), the latent TGF-01 high molecular weight complex, is associated with a latent binding protein (150) that is not expressed in prostate cancer (150). This suggests the possibility that progression of this disease is associated with TGF-[beta]1 switching from an autocrine/paracrine to a juxtacrine mode of action. This is reflected by secretion of TGF-[beta]1 by the human AI cell lines DU-145 and PC-3 but not by the AS LNCaPs (152). Less information is available on the other TGF-[beta] isoforms in prostate cancer. The PC-3 cells do not respond to TGF-[beta]2 (153), indicating that an autocrine pathway is not present. Studies in the MPR model show that TGF-[beta]3 but not TGF-[beta]2 concentrations are increased in carcinomas (36). These observations may reflect increased TGF-[beta]1 concentrations given that TGF-[beta]1 has been shown to up-regulate the expression of TGF-[beta]2 and TGF-[beta]3 in many epithelial and stromal cell lines (154).
Studies of human prostate cancer cell lines suggest that changes in sensitivity to TGF-[beta]1 may play a role in prostate cancer progression, but different results are obtained in clinical samples and in rodent cells. TGF-[beta]1 inhibits the proliferation of AI PC-3 and DU-145 cells in a dose-dependent manner but not the proliferation of AS LNCaP cells (39). TGF-[beta] insensitivity in LNCaP cells has been attributed to a genetic change in their TGF-[beta] receptor I gene (39) and can be reversed by transfection with the wild-type type I receptor gene (39). However, in clinical samples of prostate cancer, an inverse correlation between the loss of expression of TbetaR-I and TbetaR-II and tumor grade is observed (40). This could provide a potential mechanism for prostate cancer cells to escape the growth-inhibitory effects of TGF-[beta]. In the rodent models, sensitivity to TGF-[beta] growth inhibition is lost with tumor progression. In the R3227 Dunning model, functional TbetaR-I and TbetaR-II, as well as decreasing sensitivity to TGF-[beta]1, are found in advanced prostate carcinoma cells (41), whereas metastatic cell lines derived from the MPR model secrete but do not respond to TGF-[beta]1 (37). This suggests the role of TGF-[beta] in the progression of prostate cancer cell lines from rodent and human cancers.
TGF-[beta] can modulate extracellular matrix proteins and has effects on bone-derived cells, suggesting the possibility that it may promote the spread of prostate cancer cells and provide a suitable milieu in bone for metastatic growth. TGF-[beta] can induce type IV collagenase matrix metalloproteinase-9 and plasminogen activator inhibitor 1 in mouse prostate-derived cell lines (37) and procollagen I[alpha]-chain mRNA in human osteoblast-like cells (131). TGF-[beta]1 also stimulates adhesion of PC-3 cells to bone matrix proteins, possibly via the [alpha]2 [beta]1 integrin receptor (155) and the migration of human osteoblasts (44).
In summary, the role of TGF-[beta] in the prostate is highly complex (Fig. 1). In the nondiseased prostate, TGF-[beta] can counterbalance the mitogenic effects of various growth factors, thus having a role in growth regulation. Moreover, its expression and that of its receptors is associated with castration-induced prostate cell apoptosis. In cancer, TGF-[beta] expression is increased as prostate cancer progresses. It can be secreted and may show autocrine rather than paracrine regulation, although its autocrine role is as yet unexplained. The sensitivity of prostate cancer cells from different species to respond to TGF-[beta] varies, in one case, because of genetic changes in the receptor. TGF-[beta] also has the capacity to modulate matrix metalloprotease production and to stimulate adhesion of prostate cancer cells to bone cells, providing a possible role in prostate cancer cell metastases. Given its role in angiogenesis and as an immunoregulatory molecule, the secretion of TGF-[beta] by prostate cancer cells could have important effects on the cancer cell environment.
[FIGURE 1 OMITTED]
EGF AND TGF-[alpha]
EGF and TGF-[alpha] are two structurally and functionally related peptides (Table 3) that signal through the same 170-kDa EGF receptor, a transmembrane tyrosine kinase (133, 134). Consequently, their biological activities overlap and include roles in embryogenesis, cell differentiation, and angiogenesis (135).
Prostatic fluids from nondiseased human prostates contain large amounts of EGF (64), which appears to be an important regulator for normal growth in both rat and human prostate (156). Human prostate epithelial cells require EGF in serum-free medium for growth in primary culture (157), and nondiseased human fetal prostatic fibroblasts can replicate in response to this cytokine (65). Immunohistochemical studies on nondiseased and benign prostatic tissue have shown that TGF-[alpha] expression occurs predominantly in the stroma, whereas its receptor is expressed by epithelial cells, suggesting a paracrine/ juxtacrine mode of regulation (72).
Prostatic cell EGF expression is regulated by androgen. Castration of mice or rats results in a marked decrease in EGF expression (66, 67), which can be restored by testosterone administration. There is some evidence that TGF-[alpha] may also be androgen-related. Castration of rats, followed by androgen-induced regrowth, results several days later in increased TGF-[alpha] mRNA (67); because of the timing, this may reflect the induction of other regulatory factors by androgen.
Increased expression of EGF/TGF-[alpha] has been linked to prostate cancer development. A slight but important rise in EGF protein expression is observed in the epithelial cells of prostate cancer specimens (68, 69), and similarly, TGF-[alpha] protein concentrations are raised in human prostate cancers in comparison with benign tissue (70, 71). In many tumors, TGF-[alpha] and epithelial growth factor receptor (EGFR) are coexpressed in the epithelial cells, suggesting a switch from paracrine to autocrine regulation (72).
These studies are supported by findings in vitro using human prostate cancer cell lines. LNCaP cells are stimulated in vitro (158) and in vivo (159) by EGF and TGF-[alpha]; in LNCaP cells undergoing AI progression, the EGFR is up-regulated (160). Both LNCaP and DU-145 cell lines secrete EGF, with 14-fold higher expression in the DU-145 line (161, 162). Interestingly, although both lines express single EGF-binding sites of similar high affinities, LNCaP cells exhibit markedly enhanced DNA synthesis in response to exogenous EGF compared with DU-145 cells, suggesting that locally produced EGF may be an important regulator of cell proliferation in the AS cells compared with AI cancer cells (163). Similarly, changes in TGF-[alpha] expression are observed in human prostate cancer cell lines. The AI lines PC-3 and DU-145 express higher concentrations of TGF-[alpha] mRNA than do LNCaP cells (164), but at the protein level, PC-3 cells express the least TGF-[alpha], whereas DU-145 cells express the most (165). However, PC-3 cells are more sensitive to TGF-[alpha]-induced proliferation than DU-145 cells, although they express lower concentrations of EGFR (165). The differential sensitivity of prostate cancer cells to TGF-[alpha] suggests that the autocrine loop involving TGF-[alpha] in prostate cancer cell lines may be further regulated by other unknown factors.
The importance of these findings may relate to the ability of EGF to enhance prostate tumor cell invasion. EGF increased the invasive capacity of PC-3 cells in a Boyden chamber microinvasion assay. This was associated with increased expression of urokinase plasminogen activator, a serine protease, mRNA, and protein (73).
Because both EGF and TGF-[alpha] bind to the EGFR, regulation of receptor expression is mandatory to an understanding of prostate cancer development and progression. In the nondiseased prostate, EGFR expression is largely confined to the basal cell layers (166-168), whereas in human cancer cell lines, EGFR expression is increased with increasing malignancy. Thus, the AI DU145 prostate cancer cells express 10-fold more EGFR than do AS LNCaP cells (163). Results from immunohistochemistry of human prostatic tumors are inconclusive. Some studies reported no difference in EGFR expression between nondiseased and malignant cells (168); others noted a decrease in EGFR expression in advanced malignancy compared with nondiseased tissue (166,167), whereas still other reports described an increased EGFR mRNA and protein expression in secretory epithelial cells that is associated with advanced cancer (166) or with increasing tumor grade (169) but not with patient survival (170). Such discrepancies may relate to differences in methodology, or they may reflect heterogeneity between prostate tumors in relation to EGFR expression.
EGFR expression in nondiseased prostate tissues appears to be under negative androgen regulation. Prostate biopsies from patients with benign hyperplasia show substantially increased EGFR expression after androgen withdrawal (171). Likewise in rats, castration induces increased EGFR expression with a return to normal concentrations after administration of dihydrotestosterone (65), whereas exposure of LNCaP cells to the synthetic androgen, R1881, up-regulates EGFR expression from 11500 to 28 500 sites/cell (172). However, the LNCaP data may be affected by the presence of a mutated AR in these cells (23). Taken together, these data suggest the possibility that the regulation of EGFR by androgen may be disrupted in prostate cancer. What impact this has on the actions of the EGFR ligands, EGF and TGF-[alpha], remains to be elucidated.
In summary, in the nondiseased prostate, EGF appears to be an important regulator of growth (173), and its expression is positively regulated by androgen, whereas that of EGFR is negatively regulated by androgen. TGF-[alpha] is predominantly expressed in a paracrine fashion by nondiseased prostate stroma. In prostate cancer, EGFR expression is up-regulated with progression as judged from prostate cancer cell lines, but evidence from clinical trials leaves its role controversial. However, up-regulation of EGF, TGF-[alpha], and EGFR suggest their autocrine expression in advanced cancer. Increased EGF expression appears to be associated with the invasive ability of prostate cancer cells.
The FGF family consists of nine structurally related heparin-binding peptides that share 40-55% amino acid homology (174). Four genes have been identified that encode distinct high affinity ([K.sub.d] = [10.sup.-11] mol/L) receptors for FGFs, fibroblast growth factor receptor 1 (FGFR-1), FGFR-2, FGFR-3, and FGFR-4 (175). Each encodes transmembrane receptor tyrosine kinases, derived from alternative mRNA splicing, that give rise to the potential of multiple binding combinations for each FGF peptide (176). These receptors also differ in their affinity for each member of the FGF family. The FGFs show different cellular locations. Some forms are secreted, and others are located in the nucleus (176,177). Three members of this family, bFGF (FGF-2), acidic FGF (aFGF or FGF-1), and KGF (FGF-7) have been implicated in prostate cancer.
bFGF is encoded by a 36-kb single copy gene (178,179) with four variants from alternative splicing (Table 3). Differing intracellular locations suggest different biological functions (175). Despite no signal sequence (178), bFGF has been found cell-associated or deposited into the basement membrane (176), with its release possibly due to cell injury in vivo.
bFGF is synthesized by a wide variety of cell types, including epithelial cells, stromal cells (45), macrophages (180), and endothelial cells (181). Its biological functions include a role in angiogenesis, tissue development and differentiation (182, 183), and the ability to modulate neural function (184).
Prostatic stromal and epithelial cells actively synthesize bFGF (45). However, in the nondiseased prostate, only the stromal cells express the bFGF receptor and thus respond to this growth factor, suggesting that bFGF plays an important role in maintaining prostatic mesenchymal homeostasis (46). Human fetal prostatic fibroblasts have also been shown to proliferate in response to bFGF (185), which can overcome the TGF-[beta]1 inhibition of these cells (186). Some conflict concerning the response of the bFGF pathway to androgen exists. In 7-day-old rats, castration results in decreased bFGF expression, with increased bFGF mRNA 16 h after exposure of regressed prostate to androgen (187). In AS LNCaP cells, androgen causes an increase in bFGF expression (188), whereas other human prostatic cancer cell lines produce bFGF independently of androgen (189). Similarly, AI cells from Shionogi mice produce a bFGF-like protein (190). These data suggest that production of bFGF becomes AI as cancer progresses.
Further evidence of a role for the bFGF pathway in prostate cancer progression comes from studies in the Dunning tumor model (48). A switch in exon IIIb (which has a high affinity for KGF) of the FGFR gene to exon IIIc (with a high affinity for bFGF and aFGF) occurs in malignant epithelial cells as they become independent of their requirement for stroma (48). This suggests that prostate cancer progression may be associated with a switch from stromal autocrine bFGF regulation to epithelial autocrine regulation. It has been proposed that bFGF may enable the epithelial cell to metastasize by promoting angiogenesis in the malignant tumor. These studies are supported by findings in human prostate cancer cell lines. The AS LNCaP cell line produces very low concentrations of bFGF and FGFR (47) compared with the AI cell lines PC-3 and DU-145 (47). However, the data are confusing; although LNCaP and DU-145 cells proliferate in response to bFGF, the more malignant PC-3 cells do not (47). As with the rat model, this suggests that some form of autocrine regulation of bFGF by epithelial cells may be an important step in prostate cancer progression.
Because bFGF is angiogenic, its increased production in late stage prostate cancer may promote angiogenesis, allowing tumors to grow and metastasize (50). The acquisition of metastatic ability in prostate cancer has been correlated with increasing microvessel density (191, 192), implying that angiogenic ability is necessary for metastasis to occur.
In summary, bFGF appears to be produced in an autocrine fashion by nondiseased prostate stromal cells and is important for maintaining their homeostasis. As cancer occurs and progresses, the production of bFGF becomes independent of androgen and becomes regulated in an autocrine fashion by prostate cancer epithelial cells. The ability to produce bFGF may stimulate angiogenesis, allowing the cells to metastasize.
aFGF (Table 3) is important in the development of the prostate in rats, but it has not been detected in human prostatic tissues. In 6- to 8-week-old rats, expression is confined to epithelial cells and is increased, but it declines at 14 weeks and cannot be detected by 35 weeks (51). Epithelial and mesenchymal cells from nondiseased rat prostate and various grades of rat prostate tumors exhibit specific aFGF membrane receptor sites (52). In the Dunning model, aFGF alone is expressed only by stromal cells of the slow-growing AD R3327PAP tumor, whereas fastgrowing metastatic AT-3 cells express both aFGF and bFGF (52). This suggests that, in rat models of prostate cancer, progression is associated with a switch in regulation of aFGF from paracrine to autocrine control.
Another member of the FGF family, KGF (140), is important in prostate development (Table 3). In the rodent prostate, KGF is expressed and secreted by nondiseased stromal cells, but only epithelial cells express the BEK/ FGFR-2 receptor gene that binds KGF, suggesting that this cytokine controls epithelial cell proliferation in a paracrine manner (53). The BEK receptor has been shown to require an interaction with heparan sulfate proteoglycans to facilitate binding to its ligands (54). Serum-free organ culture of neonatal rat ventral prostates, which express both KGF and BEK receptor mRNA, has been developed as a model to study prostate development (193). The addition of an anti-KGF antibody could inhibit testosterone-induced branching in this model, and in testosteronefree conditions, KGF could mimic the effects of the hormone. These data suggest that, in the developing prostate, KGF may act as a paracrine mediator of androgen action. An important and similar role for KGF has also been implicated in the human prostate. KGF and its receptor are expressed in the stromal and epithelial cells, respectively, and in both fetal and adult nondiseased prostates (55). This cytokine is also a potent mitogen for nondiseased human prostatic epithelial cells in vitro (141, 194) and promotes the growth of these cells under serum-free conditions (195).
In human prostatic carcinomas, in situ hybridization studies have shown increased expression of the KGF gene and receptor in epithelial cells of high-grade carcinomas but not in benign hyperplasia of the prostate, suggesting a switch from a paracrine to an autocrine loop (55, 56).
In summary, multiple autocrine and potentially intracrine ligand-receptor loops result from alterations within the FGF-FGFR family, which may underlie the autonomy of malignant tumor cells. bFGF and KGF appear to be produced by nondiseased prostate stromal cells in an autocrine and paracrine fashion, respectively, and are important for maintaining prostate homeostasis. As cancer occurs and progresses, the production of bFGF becomes independent of androgen and becomes regulated in an autocrine fashion by prostate cancer epithelial cells. The ability to produce bFGF may stimulate angiogenesis, allowing the cells to metastasize. Although aFGF appears to have a role in the rat prostate, its importance in the human prostate has not been ratified. The production of KGF by prostate stromal cells appears to control epithelial cell proliferation in a paracrine manner, but in human prostate cancer, autocrine production of KGF accompanies the progression to AI disease.
IGFs are polypeptide growth factors with functional homology to insulin, but in contrast to insulin, these proteins are locally produced by a wide variety of tissues. Regulation of their production and function is extremely complex. There are two IGF peptides, IGF-1 and IGF-2, two cell surface receptors (the type 1 IGF receptor family and the type 2 IGF receptor), and at least six specific high-affinity binding proteins, IGF-BP-1 through IGF-BP-6, that regulate IGF availability and are in turn regulated by a group of IGF-BP proteases that cleave IGF-BPs to modulate IGF action (Table 3).
In the nondiseased prostate, IGFs are produced only by stromal cells, but normal epithelial cells express IGF-1 receptors and secrete predominantly IGF-BP-4. However, they also secrete IGF-BP-2, IGF-BP-3, and IGF-BP-6, suggesting a paracrine mode of regulation (58, 59). Some controversy concerning the IGF loop in prostate cancer exists. Some authors (74) have shown that DU-145 cells can proliferate in response to IGF-1 but do not produce this protein, suggesting maintenance of the paracrine mode of action of IGFs in prostate cancer. However, others (196) describe autocrine production of IGF-1 in PC-3, DU-145, and a subline of LNCaP cells, all of which were reported to grow in serum-free medium, secrete IGF-1, and display constitutively autophosphorylated IGF-1 receptors. The LNCaP cell line also proliferates in response to IGF-1 but does not produce it; however, this only occurs in synergy with dihydrotestosterone (197). IGF-1 may act directly through the AR pathway (27) and in turn may be regulated through an EGF autocrine growth regulatory loop (74). IGF-2 protein secretion has been detected in all three human prostate cancer cell lines, and under serum-free conditions, as described above, each can produce IGF-1 (196). This suggests that the capacity for autocrine production of EGFs by prostatic epithelial cells exists, and that this production may play a role in prostate cancer development.
This situation is even more complicated, however, because changes in the expression of the IGF-BPs are observed in all of these lines. For instance, PC-3 cells express large amounts of IGF-BP-2 and IGF-BP-3 and less IGF-BP-4, whereas LNCaP cells express only IGF-BP-2 (60). Thus, dysregulation of the IGF-BP system may be associated with prostate cancer development (Fig. 2). Constitutively autophosphorylated IGF-1 receptors are also displayed by the PC-3, DU-145, and LNCaP cell lines (196), but proliferation in response to IGF in these cell lines appears to be regulated by the autocrine secretion of IGF-BPs (74). In serum-free culture, DU-145 cells produce IGF-BP-1, but the addition of an antibody that binds this protein inhibits the effects of IGF-1 (74). There is also evidence that some IGF-BPs may be under androgen regulation. PC-3 cells stably transfected with an active AR construct do not produce IGF-BP-3 and proliferate in response to IGF-1 or IGF-2, in contrast to untransfected cells. PSA, a serine protease that is up-regulated by androgen, can cleave IGF-BP-3 (61), and the nerve growth factor [gamma]-subunit, which has high sequence homology with PSA, also has this capacity (198). This could release IGFs locally to stimulate prostate cancer cell growth. These data have been interpreted to suggest that androgen may indirectly modulate IGF-induced proliferation of prostate cancer cells by regulating IGF-BP-3 production (62).
In prostate cancer patients, serum IGF-BP-2 is increased; this is related to a rise in PSA concentrations, suggesting that the prostate is the source of IGF-BP-2 production (61). Because PSA is a protease for IGF-BP-3, it likely that the rise in PSA may be related to lowered concentrations of IGF-BP-3 in prostate cancer patients (61).
A potential role for the IGFs in prostate cancer progression is in the development of bone metastasis. Both IGF-1 and IGF-2 mRNA transcripts have been detected in nondiseased human osteoblast-like cells (199) and appear to have an important role in bone formation (63). Interestingly, studies have shown that factors that decrease the activity of IGF-BP-3, such as dexamethasone, also inhibit bone formation (63), suggesting an important role for IGF-BP-3 in the formation of bone metastasis in advanced prostate cancer.
[FIGURE 2 OMITTED]
In summary, the IGFs appear to have an important role in the development of prostate cancer. This can be achieved by modulation of paracrine pathways, which occur in the nondiseased prostate, to autocrine pathways, seen in prostate cancer cell lines, and also by modulation of the concentrations of different IGF-BPs that are differentially expressed in the normal condition vs cancer. Androgen appears to regulate the expression of some of these IGF-BPs, and PSA, which is androgen-regulated, particularly can cleave IGF-BP-3. The local release of IGFs in distant tissues as a result of cleavage of IGF-BP-3 may allow prostate cancer growth as metastatic deposits.
RETINOIC ACID (RA) AND VITAMIN [D.sub.3]
Strong evidence suggests that dietary factors can affect the incidence of prostate cancer (200). Two such factors are RA (vitamin A) and 1,25-dihydroxyvitamin D (vitamin [D.sub.3]). RA can induce the differentiation of a wide variety of cells and elicit changes in growth factor protein and receptor expression (201-203). The active form of vitamin [D.sub.3], 1,25-dihydroxyvitamin D, affects calcium and phosphate homeostasis (204, 205) and is an important modulator of proliferation and differentiation in both nondiseased and malignant cells (206, 207). Recent evidence suggests a role for these chemical hormones in regulating the proliferation and differentiation of prostate cancer cells.
RA has marked but different effects on different human prostate cancer cells in vitro. LNCaP cells are induced to differentiate in response to RA in the presence or absence of androgens (208). DU-145 cells are growthinhibited by 13-cis-retinoic acid (209). In contrast, RA induces increased invasiveness of PC-3 cells by up-regulating urokinase plasminogen activator expression, suggesting that in more advanced tumors, RA may promote disease progression (210). The different cell responses to RA may relate to their differences in AR expression. RA can inhibit the binding capacity of the LNCaP AR (which is mutated) by 30-40% (211), whereas PC-3 cells lack an AR.
A deficiency in vitamin D has been proposed to increase the risk of prostate cancer (212). This result is still controversial because a comparison of serum concentrations of vitamin D metabolites between prostate cancer patients and age-matched controls showed no substantial differences (213). However, a striking difference between black and white men in the allelic frequencies of the gene encoding a vitamin [D.sub.3] binding protein has been reported, raising the possibility that this protein may be important in indicating risk of prostate cancer development (214).
Most evidence concerning the role of vitamin [D.sub.3] in prostate cancer comes from studies of prostate cancer cell lines. The human lines DU-145, PC-3, and LNCaP all express receptors for vitamin [D.sub.3], with PC-3 showing the greatest binding capacity (215). Proliferation of LNCaP and PC-3 cells is inhibited by vitamin [D.sub.3] (215, 216), and proliferation of DU-145 is inhibited only by analogs of vitamin [D.sub.3] (217). In LNCaP cells, exposure to vitamin [D.sub.3] can neutralize the proliferative effects of androgens, suggesting that it is a strong inhibitor of epithelial cell proliferation (208). Vitamin [D.sub.3] can up-regulate expression of IGF-BP-6 mRNA in a dose-dependent manner in all three human prostate cancer cell lines (216), suggesting that it may modulate growth via the IGF axis. In Lobund/ Wistar rats, growth of a nontumorigenic AS epithelial cell line derived from the dorsal-lateral prostate is inhibited by vitamin [D.sub.3], whereas its AI tumorigenic counterpart is insensitive to these effects (217). Taken together, these results suggest that vitamin [D.sub.3] may act as a growth modulator of prostate epithelial cell proliferation, but that its inhibitory effects may be lost in late-stage prostate cancer.
A recent study has shown that prostate cancer may be associated with vitamin D receptor gene polymorphism. Race-adjusted combined analysis showed that men who were homozygous for the t allele (shown to correlate with higher serum concentrations of the active form of vitamin D) have only one-third of the risk of developing prostate cancer requiring prostatectomy compared with men who were heterozygotes or homozygous for the T allele (218). Because this is a single study, credence awaits confirmation, but this appears to suggest that vitamin D is an important determinant of prostate cancer risk and could lead to strategies for chemoprevention.
The vitamin D receptor is thought to act as a heterodimer with the retinoid X receptor, suggesting functional interactions between 1,25-dihydroxyvitamin [D.sub.3] and retinoids (219). The combination of 1,25-dihydroxyvitamin [D.sub.3] and 9-cis-retinoic acid was shown to act synergistically in inhibiting the growth of LNCaP cells.
In summary, different activities of RA on different cancer cell lines leave its potential role in controlling prostate cancer in doubt. The ability of RA to differentiate LNCaP cells has exciting potential for control of the disease, but its ability to increase invasiveness of PC-3 cells would argue against its use. However, Phase I clinical trials on the use of liarozole, which binds to the cytochrome P450-dependent hydroxylating enzymes involved in RA catabolism (220), and Phase II trials of all-trans-RA for control of hormone-refractory prostate cancer are in progress (221). Moreover, the use of liarozole fumarate, a compound that blocks the cytochrome P450-dependent catabolism of RA and which has been successful in reducing both AD and AI tumor growth in the Dunning rat model, has been proposed (222). The progression of prostate cancer to androgen independence is accompanied by a loss in sensitivity to the antiproliferative effects of vitamin [D.sub.3]. Hence this vitamin could be of therapeutic benefit in patients with early disease but not once progression to late-stage disease has occurred.
INTERACTIONS OF GROWTH FACTOR PATHWAYS IN PROSTATE CANCER
The IGF axis appears to be under the control of other growth factor pathways. EGF, FGF, and TGF-[beta] have been shown to regulate the expression of the IGFs and their binding proteins. Antibodies to EGFR inhibit the secretion of IGF-BP (74) and the growth-promoting effects of IGF-1. The addition of bFGF to the human osteoblast cell line MC3T-E1 inhibits IGF-1 and IFG-2 mRNA and IGF-BP-2, IGF-BP-4, IGF-BP-5, and IGF-BP-6 concentrations (223), whereas TGF-[beta] can increase the expression of IGF-1 mRNA in nondiseased human osteoblast-like cells (224). Moreover, as mentioned previously, vitamin [D.sub.3] can upregulate expression of IGF-BP-6 mRNA in a dose-dependent manner in LNCaP, PC-3, and DU-145 prostate cancer cells (216). This suggests that the interactions of the IGFs and their binding proteins with other cytokines may in some way regulate prostate growth. Additionally, any changes to this complex IGF regulatory system may promote prostate cancer development. Moreover, several growth factor pathways including IGF-1, KGF, and EGF can aberrantly activate the AR in the absence of androgen, suggesting that the androgen-signaling chain may be activated by growth factors in an androgen-depleted environment (27).
These findings suggest that up-regulation of growth factor production and, in particular, the appearance of several autocrine pathways in prostate epithelial cells (Table 4), apparently bypassing any requirement for stromal cells, may represent an adaptive response to androgen ablation in the growth regulation of AI tumors. Future studies may lead to targeted therapy for patients with advanced prostate cancer, using an understanding of the changes that occur in growth factor pathways as prostate cancer progresses (225). A recent example of a possible antigrowth factor treatment is the use of suramin (225), which has antiproliferative effects against prostate cancer cells in vitro. The mode of action of suramin is unclear, but it may be mediated by its ability to disrupt the cellular energy balance of prostate cancer cells (226, 227). There are conflicting reports about the ability of suramin to interfere with growth factor pathways; it can inhibit the growth-stimulating effects of exogenous testosterone and bFGF (228), but it is not counteracted by 10-fold excesses of exogenous growth factors in vitro (229), and the effects are reversible. Suramin is a polysulfonated naphthylurea with substantial activity in prostate cancer. When high dosages of suramin were used in 38 patients with hormone-refractory prostate cancer, declines in serum PSA of >75% were obtained in 38% of patients, and measurable disease response was observed in 35% of patients (225, 230). Although preliminary studies on the effects of growth factor receptor inhibitors and neural peptide inhibitors on prostate cancer cells in vitro are very impressive, no definite conclusions regarding the efficacy or clinical applicability can yet be made. Understanding growth factors will help novel and innovative therapeutic approaches, but it will obviously require much refinement before being translated from bench to bedside.
S. Bennett was supported by the Cancer Council of New South Wales. We thank Mirella Daja, Paul Jackson, and Sean Downing for critical reading of the manuscript.
(1.) Seidman H, Mushinski MH, Gelb SK, Silverberg E. Probabilities of eventually developing or dying of cancer: United States. Cancer J Clin 1985;35:36-56.
(2.) Coates M, Armstrong B. Cancer in NSW. Incidence and Mortality 1994:58-9.
(3.) Boring CC, Squires TS, Tong T, Montgomery S. Cancer statistics, 1994. Cancer J Clin 1990;44:7-26.
(4.) McNeal JE, Bostwick DG, Kindrachuk RA, Redwine EA, Freiha FS, Stamey TA. Patterns of progression in prostate cancer. Lancet 1986;i:60-3.
(5.) Rosen MA. Impact of PSA screening on the natural history of prostate cancer. Urology 1995;46:757-68.
(6.) Aikara M, Wheeler TM, Ohori M, Scardino PT. Heterogeneity of prostate cancer in radical prostatectomy specimens. Urology 1994;43:60-7.
(7.) van den Ouden D, Tribukait B, Blom JHM, Fossa SD, Kurth KH, ten Kate FJ, et al. Deoxyribonucleic acid ploidy of core biopsies and metastatic lymph nodes of prostate cancer patients: impact on time to progression. The European Organization for Research and Treatment of Cancer Genitourinary Group. J Urol 1993;150: 400-6.
(8.) Chodak GW, Thisted RA, Gerber GS, Johansson JE, Adolfsson J, Jones GW, et al. Results of conservative management of clinically localised prostate cancer. N Engl J Med 1994;330:242-8.
(9.) Coffey DS. The molecular biology of the prostate. In: Lepor H, Lawson RK, eds. Prostate diseases. Philadelphia: Saunders, 1993:28-56.
(10.) Bonkhoff H, Remberger K. Differentiation pathways and histogenetic aspects of normal and abnormal prostatic growth: a stem cell model. Prostate 1996;28:98-106.
(11.) Coffey DS. The molecular biology, endocrinology and physiology of the prostate and seminal vesicles. In: Walsy PC, Refik AB, Stamey TA, Vaughan ED, eds. Campbell's urology, 6th ed. Philadelphia: Saunders, 1992:221-51.
(12.) Cunha GR, Donjacour AA, Cooke PS, Mee S, Bigsby RM, Higgins SJ, Sugimura Y. The endocrinology and developmental biology of the prostate. Endocr Rev 1987;8:338-62.
(13.) Gleave ME, Hsieh J-T. Animal models in prostate cancer. In: Raghavan D, Scher HI, Leibel SA, Lange PH, eds. Principles and practice of genitourinary oncology. Philadelphia: Lippincott-Raven Publishers, 1997:367-78.
(14.) Catalona WJ. Management of cancer of the prostate. N Engl J Med 1994;331:996-1004.
(15.) Lubahn DB, Joseph DR, Sar M, Tan J, Higgs HN, Larson RE, et al. The human androgen receptor: complementary deoxyribonucleic acid cloning, sequence analysis and gene expression in prostate. Mol Endocrinol 1988;2:1265-75.
(16.) Lee C. Role of androgen in prostate growth and regression: stromal-epithelial interaction. Prostate 1996;6(Suppl):52-6.
(17.) Chung LWK, Gleave ME, Hsieh J, Hong SJ, Zhau HE. Reciprocal mesenchymal-epithelial interaction affecting prostate tumor growth and hormonal responsiveness. Cancer Surv 1991;11: 91-119.
(18.) Sadi MV, Walsh PC, Barrack ER. Immunohistochemical study of androgen receptors in metastatic prostate cancer. Comparison of receptor content and response to hormonal therapy. Cancer 1991;67:3057-64.
(19.) Chodak GW, Kranc DM, Puy LA, Takeda H, Johnson K, Chang C. Nuclear localization of androgen receptor in heterogeneous samples of normal prostate, hyperplastic and neoplastic human prostate. J Urol 1992;147:798-803.
(20.) Bentel JM, Tilley WD. Androgen receptors in prostate cancer. J Endocrinol 1996;151:1-11.
(21.) Taplin ME, Bubley GJ, Shuster TD, Frantz ME, Spooner AE, Ogata GK, et al. Mutations of the androgen receptor gene in metastatic androgen-independent prostate cancer. N Engl J Med 1995;332: 1393-8.
(22.) Gaddipati JP, Mcleod DG, Heidenbery H B, Seterhen IA, Finger MJ, Moul JW. Frequent detection of codon 877 mutations in the androgen receptor gene in advanced prostate cancer. Cancer Res 1994;54:2861-4.
(23.) Veldscholte J, Voorhorst-Ogink MM, Bolt-de Vries J, van Rooji HCJ, Trapman J, Mulder E. Unusual specificity of the androgen receptor in the human prostate tumour cell line LNCaP: high affinity for progestogenic and estrogenic steroids. Biochim Biophys Acta 1990;1052:187-94.
(24.) Schoenberg MP, Hakimi JM, Wang S, Bova GS, Epstein JI, Fishbeck KH, et al. Microsatellite mutation (CAG 24-18) in the androgen receptor in human prostate cancer. Biochem Biophys Res Commun 1994;198:74-80.
(25.) Rundlett SE, Wu XP, Miesfeld RL. Functional characterizations of the androgen receptor confirm that the molecular basis of androgen action is transcriptional regulation. Mol Endocrinol 1990;4:7211-5.
(26.) Simental JA, Sar M, Lane MV, French FS, Wilson EM. Transcriptional activation and nuclear targeting signals of the human androgen receptor. J Biol Chem 1991;226:510-8.
(27.) Culig Z, Hobisch A, Cronauer MV, Radmayr C, Trapman J, Hittmair A, et al. Androgen receptor activation in prostatic tumour cell lines by a insulin-like growth factor-1, keratinocyte growth factor, and epidermal growth factor. Cancer Res 1994;54:5474-8.
(28.) Schuurmans AL, Bolt J, Mulder E. Androgens and transforming growth factor beta modulate the growth response to epidermal growth factor in human prostatic tumor cells (LNCaP). Mol Cell Endocrinol 1988;60:101-4.
(29.) Story MT, Hopp KA, Meier D. Regulation of basic fibroblast growth factor expression by transforming growth factor beta in cultured human prostate stroma cells. Prostate 1996;28:21926.
(30.) Timme TL, Truong LID, Slavin KM, Kadmon D, Park SH, Thompson TC. Mesenchymal-epithelial interactions and transforming growth factor-beta 1 expression during normal and abnormal prostatic growth. Microsc Res Tech 1995;30:333-41.
(31.) Landstrom M, Eklov S, Colosetti P, Nilsson S, Damber JE, Bergh A, Funa K. Estrogen induces apoptosis in a rat prostatic adenocarcinoma: association with an increased expression of TGF-beta 1 and its typed and type-II receptors. Int J Cancer 1996;67: 573-9.
(32.) Kyprianou N, English HF, Davidson NE, Isaacs JT. Programmed cell death during regression of the PC-82 human prostate cell line following androgen ablation. Cancer Res 1990;90:374853.
(33.) Roberts AB, Sporn MB. Transforming growth factors. Cancer Surv 1985;4:683-705.
(34.) Truong LID, Kadmon D, McCune BK, Flanders KC, Scardino PT, Thompson TC. Association of transforming growth factor beta 1 with prostate cancer. Hum Pathol 1993;24:4-9.
(35.) Kahehi Y, Oka H, Mitsumori K, Itoh N, Ogawa 0, Yoshida 0. Elevation of serum transforming growth factor-[beta]1 level in patients with metastatic prostate cancer. Urol Oncol 1996;2: 131-5.
(36.) Merz VW, Miller GJ, Krebs T, Timme TL, Kadmon D, Park SH, et al. Elevated transforming growth factor beta 1 and beta 3 mRNA levels are associated with ras+myc-induced carcinomas in re constituted mouse prostate: evidence for a paracrine role during progression. Mol Endocrinol 1991;5:503-13.
(37.) Sehgal I, Baley PA, Thompson TC. Transforming growth factor beta 1 stimulates contrasting responses in metastatic versus primary mouse prostate cancer-derived cell lines in vitro. Cancer Res 1996;56:3359-65.
(38.) Steiner MS, Barrack ER. Transforming growth factor-beta 1 overproduction in prostate cancer: effects on growth in vivo and in vitro. Mol Endocrinol 1992;6:15-25.
(39.) Kim IY, Ahn HJ, Zelner DJ, Shaw JW, Sensibar JA, Kim JH, et al. Genetic changes in transforming growth factor beta (TGF-beta) receptor type 1 gene correlates with insensitivity to TGF-beta 1 in human prostate cancer. Cancer Res 1996;56:44-8.
(40.) Kim IY, Ahn H-J, Zelner DJ, Shaw JW, Lang S, Kato M, et al. Loss of expression of transforming growth factor [beta] type I and type II receptors correlates with tumor grade in human prostate cancer tissues. Clin Cancer Res 1996;2:1255-61.
(41.) Steiner MS, Anthony CT, Metts J, Moses HL. Prostate cancer cells lose their sensitivity to TGF[beta]1 growth inhibition with tumor progression. Urol Oncol 1995;1:252-62.
(42.) Roberts AB, Heine UI, Flanders KC, Sporn MB. Transforming growth factor-[beta]. Major role in regulation of extracellular matrix. Part IV. Developmental biology of collagen. Ann N Y Acad Sci 1990;580:225-32.
(43.) McCartney-Francis N, Mizel D, Wong H, Wahl L, Wahl S. Transforming growth factor beta (TGF-[beta]) as an immunoregulatory molecule. FASEB J 1988;2:A875.
(44.) Lind M, Deleuran B, Thestrup-Pedersen K, Soballe K, Eriksen EF, Bunger C. Chemotaxis of human osteoblasts. Effects of osteotropic growth factors. Acta Pathol Microbiol Immunol Scand 1995;103:140-6.
(45.) Sherwood ER, Fong C-J, Lee C, Kozlowsski JM. Basic fibroblast growth factor: a potential mediator of stromal growth in the human prostate. Endocrinology 1992;130:2955-63.
(46.) Story MT, Livingston B, Baeton L, Swartz SJ, Jacobs SC, Begun FP, et al. Cultured human prostate-derived fibroblasts produce a factor that stimulates their growth with properties indistinguish able from basic fibroblast growth factor. Prostate 1989;15:35565.
(47.) Nakamoto T, Chang C, Li A, Chodak GW. Basic fibroblast growth factor in human prostate cancer cells. Cancer Res 1992;52: 571-7.
(48.) Yan G, Fukabori Y, McBride G, Nikolaropolous S, McKeehan WL. Exon switching and activation of stromal and embryonic fibroblast growth factor (FGF)-FGF receptor genes in prostate epithelial cells accompany stromal independence and malignancy. Mol Cell Biol 1993;13:4513-22.
(49.) Muller WJ, Lee FS, Dickson C, Peters G, Pattengale P, Leder P. The int-2 gene product acts as an epithelial growth factor in transgenic mice. EMBO J 1990;9:907-13.
(50.) Folkman J. What is the evidence that tumours are angiogenesis dependent? J Natl Cancer Inst 1990;82:4-6.
(51.) Mansson PE, Adams P, Kan M, McKeehan WL. Heparin-binding growth factor gene expression and receptor characteristics in normal rat prostate and two transplantable rat prostatic tumors. Cancer Res 1989;49:2485-94.
(52.) McKeehan WL. Growth factor receptors and prostate cell growth. Cancer Surv 1991;11:165-75.
(53.) Yan G, Fukabori Y, Nikolaropoulos S, Wang F, McKeehan WL. Heparin-binding keratinocyte growth factor is a candidate stromal-to epithelial-cell andromedin. Mol Endocrinol 1992;6: 2123-8.
(54.) Mansukhani A, Dell'Era P, Moscatelli D, Kombluth S, Hanafusa H, Basilico C. Characterization of the murine BEK fibroblast growth factor (FGF) receptor: activation by three members of the FGF family and requirement for heparin. Proc Natl Acad Sci U S A 1992;89:3305-9.
(55.) McGarvey TW, Sterans ME. Keratinocyte growth factor and receptor mRNA expression in benign and malignant human prostate. Exp Mol Pathol 1995;63:52-62.
(56.) Leung HY, Metaa P, Gray LB, Collins AT, Robson CN, Neal DE. Keratinocyte growth factor expression in hormone insensitive prostate cancer. Oncogene 1997;15:1115-20.
(57.) Schmitt JF, Hearn MT, Risbridger GP. Expression of fibroblast growth factor-8 in adult rat tissues and human prostate carcinoma cells. J Steroid Biochem Mol Biol 1996;57:173-8.
(58.) Cohen P, Peehl DM, Lamson G, Rosenfeld R. Insulin-like growth factors (Gift's) IGF receptors, and IGF binding proteins in primary cultures of prostate epithelial cells. J Clin Endocrinol Metab 1991;73:401-7.
(59.) Bourdon C, Rowdier G, Lechevallier E, Mottet N, Barenton B, Sultan C. Secretion of insulin-like growth factors and their binding proteins by human normal and hyperplastic prostatic cells in primary culture. J Clin Endocrinol Metab 1996;81:612-7.
(60.) Kimura G, Kasuya J, Giannini S, Honda Y, Mohan S, Kawachi M, et al. Insulin-like growth factor (IGF) system components in human prostatic cancer cell lines, LNCaP, DU145, and PC-3 cell. Int J Urol 1996;3:39-46.
(61.) Kanety H, Madjar Y, Dagen Y, Levi J, Papa MZ, Pariente C, et al. Serum insulin-like growth factor-binding protein-2 (IGFBP-2) is increased and IGFBP-3 is decreased in patients with prostate cancer: correlation with serum prostate-specific antigen. J Clin Endocrinol Metab 1993;77:229-33.
(62.) Marcelli M, Haidacher SJ, Plymate SR, Birnbaum RS. Altered growth and insulin-like growth factor-binding protein-3 production in PC-3 prostatic carcinoma cells stably transfected with a constitutively active androgen receptor complementary deoxyribonucleic acid. Endocrinology 1995;136:1040-8.
(63.) Chevalley T, Strong DD, Mohan S, Baylink DJ, Linkhart TA. Evidence for a role of insulin-like growth factor binding proteins in glucocorticoid inhibition of normal human osteoblast-like cell proliferation. Eur J Endocrinol 1996;134:591-601.
(64.) Gregory J, Willshire IR, Kavanagh JP, Blacklock NJ, Chowdury S, Richards RC. Urogastrone-epidermal growth factor concentrations in prostatic fluid of normal individuals and patients with benign prostatic hypertrophy. Clin Sci 1986;70:359-63.
(65.) St. Arnaud R, Poyet P, Walker P, Labrie F. Androgens modulate epidermal growth factor expression in the rat ventral prostate. Mol Cell Endocrinol 1988;56:21-7.
(66.) Hiramatsu M, Kashinmata M, Minami N, Sato A, Murayama M. Androgenic regulation of epidermal growth factor in the mouse ventral prostate. Biochem Int 1988;17:311-7.
(67.) Nishi N, Oya H, Matsumoto K, Nakamura T, Miyanaka H, Wada F. Changes in gene expression of growth factors and their receptors during castration-induced involution and androgen-induced regrowth of rat prostates. Prostate 1996;28:139-52.
(68.) Fowler JE, Tau LK, Ghosh L. Epidermal growth factor and prostatic carcinoma: an immunohistochemical study. J Urol 1988;139:857-61.
(69.) Yang Y, Chisholm GD, Habib FK. Epidermal growth factor and transforming growth factor alpha concentrations in BPH and cancer of the prostate: their relationship with tissue androgen levels. Br J Cancer 1993;67:152-5.
(70.) Harper ME, Goddard L, Glynne-Jones E, Wilson DW, Price-Thomas M, Peeling WB, Griffiths K. An immunochemical analysis of TGF-alpha expression in benign and malignant prostate. Prostate 1993;23:9-23.
(71.) Glynne-Jones E, Goddard L, Harper ME. Comparative analysis of mRNA and protein expression for epidermal growth factor receptor and ligands relative to the proliferative index in human prostate tissue. Hum Pathol 1996;27:688-94.
(72.) Cohen DW, Simak R, Fair WR, Melded J, Scher HI, Cordon-Cardo C. Expression of transforming growth factor-alpha and the epidermal growth factor receptor in human prostatic tissue. J Urol 1994;152:2120-4.
(73.) Jarrad DF, Blitz BF, Smith RC, Patai BL, Rukstalis DB. Effects of epidermal growth factor on prostate cancer line PC-3 growth and invasion. Prostate 1994;24:46-53.
(74.) Kimura G, Kasuya J, Giannini S, Honda Y, Mohan S, Kawachi M, et al. Insulin-like growth factor (IGF) system components in human prostatic cancer cell lines: LNCaP, DU145 and PC-3 cells. Int J Urol 1996;3:39-46.
(75.) Harris SE, Harris MA, Mahy P, Wozney J, Feng JQ, Mundy GR. Expression of bone morphogenetic protein messenger RNAs by normal rat and human prostate and prostate cancer cells. Prostate 1994;24:204-11.
(76.) Graham CW, Lynch JH, Djakiew D. Distribution of nerve growth factor-like protein and nerve growth factor receptor in human benign prostatic hyperplasia and prostatic adenocarcinoma. J Urol 1992;147:1444-7.
(77.) Pflug BR, Onoda M, Lynch JH, Djakiew D. Reduced expression of the low affinity nerve growth factor receptor in benign and malignant human prostate tissue and loss of expression in four human metastatic prostate tumor cell lines. Cancer Res 1992; 52:5403-6.
(78.) Twillie DA, Eisenberger MA, Carducci MA, Hseih WS, Kim WY, Simons JW. Interleukin-6, a candidate mediator of human prostate cancer morbidity. Urology 1995;45:542-9.
(79.) Siegsmund MJ, Yamazaki H, Pastan I. Interleukin 6 receptor mRNA in prostate carcinomas and benign prostate hyperplasia. J Urol 1994;151:1396-9.
(80.) Coffey DS, Isaacs JT. Requirement for an idealized animal model of prostatic cancer. Prog Clin Biol Res 1980;37:379-88.
(81.) Dunning WR. Prostate cancer in the rat. Natl Cancer Inst Monogr 1963;12:351-69.
(82.) Isaacs JT. Development and characteristics of the available animal models for the study of prostate cancer. In: Coffey DS, Bruchovsky N, Gardner WH, Resnick MI, Karr JP, eds. Current approaches to the study of prostate cancer. New York: Alan R. Liss, 1987:513-75.
(83.) Voigt W, Feldman M, Dunning WF. 5[alpha]-Dihydrotestosterone-binding proteins and androgen sensitivity in prostatic cancer of Copenhagen rats. Cancer Res 1975:35:1840-6.
(84.) Isaacs JT, Isaacs WB, Feitz WFJ, Scheres J. Establishment and characterization of seven Dunning rat prostatic cancer cell lines and their use in developing methods for predicting metastatic abilities of prostatic cancers. Prostate 1986;9:261-81.
(85.) Noble RL, Hoover L. The classification of transplantable tumors in Nb rats controlled by estrogen from dormancy to autonomy. Cancer Res 1975;35:2935-41.
(86.) Noble RL. The development of prostatic adenocarcinoma in the Nb rat following prolonged sex hormone administration. Cancer Res 1977;37:1929-33.
(87.) Drago JR, Goldman LB, Gerswin ME. Chemotherapeutic and hormonal considerations of the Nb rat prostatic adenocarcinoma model. Prog Clin Biol Res 1980;37:325-63.
(88.) Drago JR, Curley RM, Sipio J. Nb rat prostatic adenocarcinoma model: metastasis. Anticancer Res 1985;5:193-6.
(89.) Chung LWK, Chang SM, Bell C, Zhau HE, Ro JY, von Eschenbach AC. Co-inoculation of tumorigenic rat prostate mesenchymal cells with nontumorigenic epithelial cells results in the development of carcinosarcoma in syngeneic and athymic animals. Int J Cancer 1989;43:1179-87.
(90.) Pollard M. Spontaneous prostate adenocarcinomas in aged germfree Wistar rats. J Natl Cancer Inst 1973;51:1235-41.
(91.) Pollard M, Luckert P. Prostate cancer in a Sprague-Dawley rat. Prostate 1985;6:389-93.
(92.) Cohen MB, Heidger PM, Lubaroff DM. Gross and microscopic pathology of induced prostatic complex tumors arising in Lobund-Wistar rats. Cancer Res 1994;54:626-8.
(93.) Shain SA, McCullough B, Segaloff A. Spontaneous adenocarcinomas of the ventral prostate of aged AXC rats. J Natl Cancer Inst 1975;55:177-80.
(94.) Shain SA, Boesel RW, Kalter SS, Heberling RL. AXC rat prostatic adenocarcinoma: initial characterization of testosterone regulation of hormone receptors of cultured cancer cells and derived tumors. J Natl Cancer Inst 1981;66:565.
(95.) Minesita T, Yamaguchi K. An androgen-dependent mouse mammary tumor. Cancer Res 1964;25:1168-75.
(96.) Bruchovsky N. The metabolism of testosterone and dihydrotestosterone and tumor growth in vivo. Biochem J 1972;127:56175.
(97.) Thompson TC, Southgate J, Kitchener, Land H. Multistage carcinogenesis induced by ras and myc oncogenes in a reconstituted organ. Cell 1989;56:917-30.
(98.) Claas FHJ, van Steenbrugge GJ. Expression of HLA-like structures on a permanent human tumor line PC-93. Tissue Antigens 1983;21:227-32.
(99.) Kaighn M. Shakar Narayan K, Ohnuki Y, Lechner J, Jones L. Establishment and characterization of a human prostatic carcinoma cell line (PC-3). Invest Urol 1979;17:16-23.
(100.) Mickey D, Stone K, Wunderli H, Mickey G, Vollmer R, Paulson D. Hetero-transplantation of a human prostatic adenocarcinoma cell line in nude mice. Cancer Res 1977;37:4049-58.
(101.) Horoszewicz J, Leong S, Chu T, Wajsman Z, Friedman M, Papsidero L, et al. The LNCaP cell line: a new model for studies on human prostatic carcinoma. Prog Clin Biol Res 1980;37: 115-32.
(102.) Wu H-C, Hsieh JT, Gleave ME, Brown NM, Pathak S, Chung LW. Derivation of androgen-independent LNCaP prostate cancer sublines: role of bone stromal cells. Int J Cancer 1994;57:406-12.
(103.) Thalmann GN, Anezinis PE, Chang SH, Ahau HE, Kim EE, Hopwood VL, et al. Androgen-independent cancer progression and bone metastasis in the LNCaP model of human prostate cancer. Cancer Res 1994;54:2577-81.
(104.) Umekita Y, Hiipakka RA, Kokontis JM, Liao S. Human prostate tumor growth in athymic mice: inhibition by androgens and stimulation by finasteride. Proc Natl Acad Sci U S A 1996;93: 11802-7.
(105.) Nagablushan M, Miller CM, Pretlow TP, Giaconia JM, Edgehouse NL, Schwartz S, et al. CWR22: the first human prostate cancer xenograft with strongly androgen-dependent and relapsed strains both in vivo and in soft agar. Cancer Res 1996;56: 3042-6.
(106.) Hoehn W, Schroeder F, Riemann J, Joebsis A, Hermanek P. Human prostatic adenocarcinoma: some characteristics of a serially transplantable line in nude mice (PC-82). Prostate 1980; 1:95-104.
(107.) van Weerden WM, van Kreuningen A, Elissen NM, Vermeij M, de Jong FH, van Steenbrugge GJ, Schroder FH. Castration induced changes in morphology, androgen levels and proliferation activity of human prostate tissue grown in athymic nude mice. Prostate 1993;23:149-63.
(108.) Ito Y, Nakazato Y. A new serially transplantable human prostatic cancer (Honda) in nude mice. J Urol 1984;132:384-7.
(109.) Bladou F, Vessella RL, Buhler KR, Ellis WJ, True LID, Lange PH. Cell proliferation and apoptosis during prostatic tumor xenograft involution and regrowth after castration. Int J Cancer 1996;67: 785-90.
(110.) Pittman S, Russell PJ, Jelbart ME, Wass J, Raghavan D. Flow cytometric and karyotypic analysis of a primary small cell carcinoma of the prostate: a xenografted cell line. Cancer Genet Cytogenet 1987;26:165-9.
(111.) Jelbart M, Russell PJ, Fullerton M, Russell P, Funder J, Raghavan D. Ectopic hormone production by a prostatic small cell carcinoma xenograft line. Mol Cell Endocrinol 1988;55:167-72.
(112.) Cunha GR, Fujii H, Neubauer BL, Shannon JM, Sawyer L, Reese BA. Epithelial-mesenchymal interactions in prostate development. I, Morphological observations of prostatic induction by urogenital sinus mesenchyme in epithelium of adult rodent urinary bladder. J Cell Biol 1983;96:1662-70.
(113.) Rennie PS, Bruchovsky N, Coldman AJ. Loss of androgen-dependence is associated with an increase in tumorigenic stem cells and resistance to cell-death genes. J Steroid Biochem Mol Biol 1990;37:843-7.
(114.) lizumi T, Yazaki T, Kanoh S, Kondo I, Koiso K. Establishment of a new prostatic carcinoma cell (TSU-PR1). J Urol 1987;137: 1304-6.
(115.) Pettaway CA, Pathak S, Greene G, Ramirez E, Wilson MR, Killion JJ, Fidler IJ. Selection of highly metastatic variants of different human prostatic carcinomas using orthotopic implantation in nude mice. Clin Cancer Res 1996;2:1627-36.
(116.) Gleave ME, Hsieh JT, Gao CA, von Eschenbach AC, Chung LWK. Acceleration of human prostate cancer growth in vivo by factors produced by prostate and bone fibroblasts. Cancer Res 1991; 51:3753-61.
(117.) Gleave ME, Hsieh JT, von Eschenbach AC, Chung LWK. Prostate and bone fibroblasts induce human prostate cancer growth in vivo: implications for bidirectional stromal-epithelial interactions in prostate carcinoma growth and metastasis. J Urol 1992;147: 1151-9.
(118.) Chung LWK, Gleave ME, Hsieh JT, Hong SJ, Zhau HE. Reciprocal mesenchymal-epithelial interaction affecting prostate cancer growth and hormonal responsiveness. Cancer Surv 1991;11: 91-121.
(119.) Hsieh JT, Wu H-C, Gleave ME, von Eschenbach AC, Chung LW. Autocrine regulation of PSA gene expression in a human prostatic cancer (LNCaP) subline. Cancer Res 1993;53:2852-7.
(120.) Ruizeveld de Winter JA, van Weerden WM, Faber PW, van Steenbrugge GJ, Trapman J, Brinkmann AO, van der Kwast TH. Regulation of androgen receptor expression in the human heterotransplantable prostate carcinoma PC-82. Endocrinology 1992;131:3045-50.
(121.) Sandgren EP, Leutteke NC, Palmiter RD, Brinster RL, Lee DD. Overexpression of TGFalpha in transgenic mice: induction of epithelial hyperplasia, pancreatic metaplasia, and carcinoma of the breast. Cell 1990;61:1121-35.
(122.) Greenberg NM, de Mayo F, Finegold MJ, Medina D, Tilley WD, Aspinall JO, et al. Prostate cancer in a transgenic mouse. Proc Natl Acad Sci U S A 1995;92:3439-43.
(123.) Shibata MA, Ward JM, Devor DE, Liu ML, Green JE. Progression of prostatic intraepithelial neoplasia to invasive carcinoma in C3 (1)/SV40 large T antigen transgenic mice: histopathological and molecular biological alterations. Cancer Res 1996;56:4894-903.
(124.) Gingrich JR, Barrios RJ, Morton RA, Boyce BF, De Mayo FJ, Finegold MJ, et al. Metastatic prostate cancer in a transgenic mouse. Cancer Res 1996;56:4096-102.
(125.) Roberts AB, Sporn MB. The transforming growth factor betas. In: Sporn MB, Roberts AB, eds. Peptide growth factors and their receptors: handbook of experimental pharmacology. Volume 95-1. Heidelberg: Springer-Verlag, 1990:419-72.
(126.) Merz VW, Arnold AM, Studer UE. Differential expression of transforming growth factor-beta 1 and beta 3 as well as c-fos mRNA in normal human prostate, benign prostatic hyperplasia and prostatic cancer. World J Urol 1994;12:96-8.
(127.) Graycar JL, Miller DA, Arrick BA, Lyons RM, Moses HL, Derynck R. Human transforming growth factor-beta 3; recombinant expression, purification and biological activities in comparison with transforming growth factors-beta 1 and -beta 2. Mol Endocrinol 1989;3:1977-86.
(128.) Miller DA, Pelton RW, Derynck R, Moses HL. Transforming growth factor beta. Ann N Y Acad Sci 1990;593:208-17.
(129.) Chen R, Ebner R, Derynck R. Inactivation of the type II receptor reveals two receptor pathways for the diverse TGF-[beta] activities. Science 1993;260:1335-8.
(130.) Atfi A, Drobetsky E, Boissonneault M, Chapdelaine A, Chevalier
S. Transforming growth factor beta down-regulates src family protein tyrosine kinase signalling pathways. J Biol Chem 1994; 269:30688-93.
(131.) Sietzer U, Batge B, Acil Y, Muller PK. Transforming growth factor beta 1 influences lysyl hydroxylation of collagen I and reduces steady-state levels of lysyl hydroxylase mRNA in human osteoblast-like cells. Eur J Clin Invest 1995;25:959-66.
(132.) Miyazono K. TGF-beta receptors and signal transduction. Int J Hematol 1997;65:97-104.
(133.) Massague J. Transforming growth factor-alpha. A model for membrane-anchored growth factors. J Biol Chem 1990;265: 21393-6.
(134.) Carpenter G, Cohen S. Epidermal growth factor. J Biol Chem 1990;265:7709-12.
(135.) Ulrich A, Coussens L, Hayflick JS, Dull TJ, Gray A, Tam AW, et al. Human epidermal growth factor receptor cDNA sequence and aberrant expression of the amplified gene in A431 epidermoid carcinoma cells. Nature 1984;309:418-24.
(136.) Florkiewicz RZ, Baird A, Gonzalez AM. Multiple forms of bFGF: differential nuclear and cell surface localization. Growth Factors 1991;4:265-75.
(137.) Renko M, Quarto N, Morimoto T, Rifkin DB. Nuclear and cytoplasmic localization of different basic fibroblast growth factor species. J Cell Physiol 1990;144:108-14.
(138.) D'Amore PA. Modes of FGF release in vivo and in vitro. Cancer Metastasis Rev 1990;9:227-38.
(139.) Gimenez-Gallego G, Rodkey J, Bennett C, Rios-Candelore M, Disalvo J, Thomas K. Brain-derived acidic fibroblast growth factor: complete amino acid sequence and homologies. Science 1985;230:1385-8.
(140.) Yan GC, Nikolaropolous S, Wang F, McKeehan WL. Sequence of rat keratinocyte growth factor (heparin-binding growth factor 7). In Vitro Cell Dev Biol 1991;27A:437-8.
(141.) Finch PW, Rubin JS, Miki A. Human KGF is a FGF-related with properties of a paracrine effector of epithelial cells. Science 1989;245:752-5.
(142.) Daughady WH, Rotwein P. Insulin-like growth factors 1 and 11, peptide, messenger ribonucleic acid and gene structures, serum and tissue concentrations. Endocr Rev 1989;10:68-91.
(143.) Czech MP. Signal transmission by the insulin-like growth factors. Cell 1989;59:235-8.
(144.) Rosenfeld RG, Lamson GL, Hung P. Insulin-like growth factor binding proteins. Recent Prog Horm Res 1990;46:99-163.
(145.) Wilding G. Response of prostate cancer cells to peptide growth factors: transforming growth factor-[beta]. Cancer Surv 1991;11: 147-62.
(146.) Derynck R, Lindquist PB, Lee A, Wen D, Tamm J, Graycar JL, et al. A new type of transforming growth factor-beta, TGF-beta 3. EMBO J 1988;7:3737-43.
(147.) Edwards DR, Murphy G, Reynolds JJ, Whitham SE, Docherty AJ, Angel P, Heath JK. Transforming growth factor beta modulates the expression of collagenase and metalloproteinase inhibitor. EMBO J 1989;6:1899-1904.
(148.) Battegay EJ, Raines EW, Seifert RA, Bowen-Pope DF, Ross R. TGF-beta induces bimodal proliferation of connective tissue cells via complex control of an autocrine PDGF loop. Cell 1990;53: 515-29.
(149.) Laiho M, DeCaprio JA, Ludlow JW, Livingstone DM, Massague J. Growth inhibition by TGF-[beta] linked to suppression of retinoblastoma protein phosphorylation. Cell 1990;62:175-85.
(150.) Miyazono K, Olofsson A, Colosetti P, Heldin CH. The role of the latent TGF-beta-1 binding protein in the assembly and secretion of TGF-beta 1. EMBO J 1991;10:1091-101.
(151.) Eklov S, Funa K, Nordgen H, Olofsson A, Kanzaki T, Miyazono K, Nilsson S. Lack of the latent transforming growth factor beta binding protein in malignant but not benign prostatic tissue. Cancer Res 1993;53:3193-7.
(152.) Wilding G, Zugmeier G, Knabbe C, Flanders K, Gelmann E. Differential effects of transforming growth factor beta on human prostate cancer cells in vitro. Mol Cell Endocrinol 1989;62:7987.
(153.) Ikeda T, Lioubin MN, Marquardt H. Human transforming growth factor type [beta] 2: production by a prostatic adenocarcinoma cell line, purification and initial characterization. Biochemistry 1987; 26:2406-10.
(154.) Bascom CC, Wolfshohl JR, Coffey RJ Jr, Madisen L, Webb NR, Purchio AR, et al. Complex regulation of transforming growth factor beta 1 and beta 2. Mol Cell Biol 1989;9:5508-15.
(155.) Kostenuik PJ, Singh G, Orr FW. Transforming growth factor beta upregulates the integrin-mediated adhesion of human prostatic carcinoma cells to type I collagen. Clin Exp Metastasis 1997; 15:41-52.
(156.) McKeehan WL, Adams PS, Rosser MP. Direct mitogenic effects of insulin, epidermal growth factor, glucocorticoid, cholera toxin, unknown pituitary factors and possibly prolactin, but not androgen, on normal rat prostate epithelial cells in serum-free primary cell culture. Cancer Res 1984;44:1998-2010.
(157.) Peehl DM, Wong S, Bazinet M, Stamey TA. In vitro studies of human prostatic epithelial cells. Attempts to identify distinguishing features of malignant cells. Growth Factors 1989;1:237-50.
(158.) Schuurmans ALG, Bolt J, Mulder E. Androgen receptor-mediated growth and epidermal growth factor receptor induction in human prostate cell lines LNCaP. Urol Int 1989;44:71-6.
(159.) Chung LW, Li W, Gleave ME, Sikes RA, Zhau HE, Bandyk MG, et al. Human prostate cancer model: roles of growth factors and extracellular matrices. J Cell Biochem Suppl 1992;16:99-105.
(160.) Wu H-C, Hsieh JT, Gleave ME, Chung LWK. Characterization of growth and differentiation-associated gene activities during the progression of prostate cancer from androgen-responsive to androgen-refractory status [Abstract]. Cancer Res 1992;33: 1651.
(161.) Connolly JM, Rose DP. Production of epidermal growth factor and transforming growth factor-alpha by the androgen-responsive LNCaP human prostate cancer cell line. Prostate 1990;16:20918.
(162.) Connolly JM, Rose DP. Secretion of epidermal growth factor and related polypeptides by the Du145 human prostate cell line. Prostate 1989;15:177-86.
(163.) MacDonald A, Habib FK. Divergent responses to epidermal growth factor in hormone sensitive and insensitive human prostate cancer cell lines. Br J Cancer 1992;65:177-82.
(164.) Ching KZ, Ramsay E, Pettigrew N, D'Cunha R, Jason M, Dodd JG. Expression of mRNA for epidermal growth factor, transforming growth factor-alpha and their receptors in human prostate tissue and cell lines. Mol Cell Biochem 1993;126:151-8.
(165.) Carruba G, Leake RE, Rinaldi F, Chalmers D, Comito L, Sorci C, et al. Steroid-growth factor interaction in human prostate cancer. 1, Short-term effects of transforming growth factors on growth of human prostate cancer cells. Steroids 1994;59:412-20.
(166.) Roberston CN, Roberson KM, Herzberg AJ, Kerns BJ, Dodge RK, Paulson DF. Differential immunoreactivity of transforming growth factor alpha in benign, dysplastic and malignant prostatic tissue. Surg Oncol 1994;3:237-42.
(167.) MacDonald A, Habib FK. Divergent responses to epidermal growth factor in hormone sensitive and insensitive human prostate cancer cell lines. Br J Cancer 1992;65:177-82.
(168.) Fox SB, Persad RA, Coleman N, Day CA, Silcocks PB, Collins CC. Prognostic value of c-erb-2 and epidermal growth factor receptor in stage A1 (T1a) prostatic carcinoma. Br J Urol 1994;74:21420.
(169.) Turkeri LN, Sakr WA, Wydes SM, Grignon DJ, Pontes JE, Macoska JA. Comparative analysis of epidermal growth factor receptor expression and protein product in benign, pre-malignant, and malignant prostatic tissue. Prostate 1994;25:199-205.
(170.) Morris GL, Dodd JG. Epidermal growth factor receptor mRNA levels in human prostatic tumors and cell lines. J Urol 1990; 143:1272-4.
(171.) Fiorelli G, DeBellis A, Longo A, Pioli P, Constantini A, Giannini S, et al. Growth factors in the human prostate. J Steroid Biochem Mol Biol 1991;40:199-205.
(172.) Schuurmans AL, Bolt J, Veldscholte J, Mulder E. Regulation of growth of LNCaP prostate tumor cells by growth factors and steroid hormones. J Steroid Biochem Mol Biol 1991;40:193-7.
(173.) Culig Z, Hobisch A, Cronauer MV, Radmayr C, Hittmair A, Zhang J, et al. Regulation of prostatic growth and function by peptide growth factors. Prostate 1996;28:392-405.
(174.) Eisemann A, Ahn JA, Graziani G, Ronick SR, Ron D. Alternative splicing generates at least five different isoforms of the human basic-EGF receptor [published erratum appears in Oncogene 1991;6:2379] Oncogene 1991;6:1195-202.
(175.) Johnson DE, Lu H, Chen H, Werner S, Williams LT. The human fibroblast growth factor receptor genes: a common structural arrangement underlies the mechanisms for generating receptor forms that differ in their third immunoglobulin domain. Mol Cell Biol 1991;11:4627-34.
(176.) Werner S, Duan DR, De Vies C, Peters KG, Johnson DE, Williams LT. Differential slicing in the extracellular region of fibroblast growth factor receptor 1 generates receptor variants with different ligand-binding specificities. Mol Cell Biol 1992;12:82-8.
(177.) Woodward WR, Nishi R, Meshul CK, Williams TE, Coulombe M, Eckenstein FP. Nuclear and cytoplasmic localization of basic fibroblast growth factor in astrocytes and CA2 hippocampal neurons. J Neurosci 1992;12:142-52.
(178.) Abraham JA, Whang JL, Tumolo A, Mergia A, Freidman J, Gospodarowicz D, Fiddes JC. Human basic fibroblast growth factor: nucleotide sequence and genomic organisation. EMBO J 1986; 5:2523-8.
(179.) Shibata F, Baird A, Florkiewicz RZ. Functional characterization of the human basic fibroblast growth factor gene promoter. Growth Factors 1991;4:277-87.
(180.) Baird A, Esch F, Bohlen P, Ling N, Gospodarowicz D. Isolation and partial characterization of an endothelial cell growth factor from the bovine kidney: homology with basic fibroblast growth factor. Regul Pept 1985;12:201-13.
(181.) Schweigerer L, Nuefeld G, Freidman J. Capillary endothelial cells express basic fibroblast growth factor, a mitogen which promotes their own growth. Nature 1987;325:257-9.
(182.) Slack JM, Darlington BG, Heath JK, Godsave SF. Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature 1987;326:197-200.
(183.) Chamberlain, CG, McAvoy JW. Evidence that fibroblast growth factor promotes lens fibre differentiation. Curr Eye Res 1987;6: 1165-8.
(184.) Schubert D, Ling N, Baird A. Multiple influences of a heparinbinding growth factor on neuronal development. J Cell Biol 1987;104:635-43.
(185.) Luo D, Lin Y, Liu X, Qin Z, Zhao C, Zhang Y, Yu Z. Effect of prostatic growth factor, basic fibroblast growth factor, epidermal growth factor and steroids on the proliferation of human fetal prostatic fibroblast. Prostate 1996;28:352-8.
(186.) Story MT, Hopp KA, Meier DA, Begun FP, Lawson RK. Influence of transforming growth factor beta 1 and other growth factors on basic fibroblast growth factor level and proliferation of cultured human prostate-derived fibroblasts. Prostate 1993;22:183-97.
(187.) Katz AE, Benson MC, Wise GJ, Olsson CA, Bandyk MG, Sawczuk IS, et al. Gene activation during the early phase of androgen-stimulated rat prostate regrowth. Cancer Res 1989;49:5889-94.
(188.) Zuck B, Goepfert C, Nedlin-Chittka A, Short K, Voight KID, Knabbe C. Regulation of fibroblast growth factor-like proteins in the androgen-responsive human prostate cell line, LNCaP. J Steroid Biochem Mol Biol 1992;41:659-63.
(189.) Geller J, Sionit LR, Baird A, Kohls M, Connors KM, Hoffman RM. In vivo and in vitro effects of androgen on fibroblast growth factor-2 concentration in the human prostate. Prostate 1994; 25:206-9.
(190.) Sato N, Watabe Y, Suzuki H, Shimazaki J. Progression of androgen-sensitive mouse tumor (Shionogi carcinoma 115) to androgen-insensitive tumor after long-term removal of testosterone. Jpn J Cancer Res 1993;84:1300-8.
(191.) Weidner N, Carroll PR, Flas J, Blumenfeld W, Folkman J. Tumor angiogenesis correlates with metastasis in invasive prostate cancer. Am J Pathol 1993;43:401-9.
(192.) Brawn PN. The dedifferentiation of prostate carcinoma. Cancer 1983;53:246-51.
(193.) Sugimura Y, Foster BA, Hom YK, Lipschutz JH, Rubin JS, Finch PW, et al. Keratinocyte growth factor (KGF) can replace testosterone in the ductal branching morphogenesis of the rat ventral prostate. Int J Dev Biol 1996;40:941-51.
(194.) Story MT, Hopp KA, Molter M, Meier DA. Characteristics of FGF-receptors expressed by stromal and epithelial cells cultured from normal and hyperplastic prostates. Growth Factors 1994; 10:269-80.
(195.) Peehl DM, Wong ST, Rubin JS. KGF and EGF differentially regulate the phenotype of prostatic epithelial cells. Growth Regul 1996;6:22-31.
(196.) Pietrzkowski Z, Mulholland G, Gomella IL, Jameson BA, Wernicke D, Baserga R. Inhibition of growth of prostatic cancer cell lines by peptide analogues of insulin-like growth factor 1. Cancer Res 1993;53:1102-6.
(197.) Iwamura M, Sluss PM, Casamento JB, Cockett ATK. Insulin-like growth factor 1: action and receptor characteristics in human prostatic cancer cell lines. Prostate 1993;22:243-52.
(198.) Rajah R, Bhala A, Nunn SE, Peehl DM, Cohen P. 7S nerve growth factor is an insulin-like growth factor-binding protein protease. Endocrinology 1996:137:2676-82.
(199.) Okazaki R, Conover CA, Harris SA, Spelsberg TC, Riggs BL. Normal human osteoblast-like cells consistently express genes for insulin-like growth factors 1 and 11, but transformed osteoblast cell lines do not. J Bone Miner Res 1995;10:788-95.
(200.) Kaul L, Heshmat M, Kovi J, Jackson MA, Jackson MG, Jones GW, Enterline JP, Worrell RG, Perry SL. The role of diet in prostate cancer. Nutr Cancer 1987;9:123-8.
(201.) Rogers MB, Rosen V, Wozney JM, Gudas U. Bone morphogenic proteins -2 and -4 are involved in the retinoic acid-induced differentiation of embryonal carcinoma cells. Mol Biol Cell 1992; 3:189-96.
(202.) Glick AB, Flander KC, Danielpour D, Yuspa SH. Retinoic acid induces transforming growth factor beta 2 in cultured keratinocytes and mouse epidermis. Cell Regul 1989;1:87-97.
(203.) Schofield PN, Ekstrom TJ, Granerus M, Engstrom W. Differentiation associated modulation of K-FGF expression in a human teratocarcinoma cell line and in primary germ cell tumours. FEBS Lett 1991;280:8-10.
(204.) Reichel H, Norman AW. Systemic effects of vitamin D. Annu Rev Med 1989;40:71-8.
(205.) Norman AW, Roth J, Orch L. The vitamin D endocrine system. Steroid metabolism, hormone receptors and biological response. Endocr Rev 1982;3:331-66.
(206.) Feldman D, Skowronski RJ, Peehl DM. Vitamin D, prostate cancer. Adv Exp Med Biol 1995;375:53-63.
(207.) Pols HAP, Birkenhager JC, Foekens JA, Van Leeuwen JPTM. Vitamin D. A modulator of cell proliferation and differentiation. J Steroid Biochem 1190;37:873-6.
(208.) Esquenet E, Swinnen JV, Heyns, Verhoeven G. Control of LNCaP proliferation and differentiation: actions and interactions of androgens, 1a,25-dihdroxycholecalciferol, all-trans retinoic acid, 9-cis retinoic acid and phenylacetate. Prostate 1996;28:18294.
(209.) Dahiya R, Boyle B, Park HD, Kurhanewicz J, Macdonald JM, Narayan P. 13-cis-Retinoic acid-mediated growth inhibition of DU-145 human prostate cancer cells. Biochem Mol Biol Int 1994:32:1-12.
(210.) Liu DF, Rabbani SA. Induction of urinary plasminogen activator by retinoic acid results in increased invasiveness of human prostate cancer cells PC-3. Prostate 1995;27:269-76.
(211.) Young CY, Murtha PE, Andrews PE, Lindzey JK, Tindall DJ. Antagonism of androgen action in prostate tumor cells by retinoic acid. Prostate 1994;25:39-45.
(212.) Schwartz GG, Hulka BS. Is vitamin D deficiency a risk factor for prostate cancer? [Hypothesis]. Anticancer Res 1990;10:130712.
(213.) Braun MM, Helzlsouer KJ, Hollis BW, Comstock GW. Prostate cancer and prediagnostic levels of serum vitamin D metabolites. Cancer Causes Control 1995;6:235-9.
(214.) Corder EH, Freidman GD, Vogelman JH, Orentreich N. Seasonal variation in vitamin D, vitamin D binding protein and dehydroepiandrosterone: risk of prostate cancer in black and white men. Cancer Epidemiol Biomark Prev 1995;4:655-9.
(215.) Skowronski RJ, Peehl DM, Feldman D. Vitamin D, prostate cancer: 1,25-dihydroxy vitamin [D.sub.3] receptor and actions in human prostate cancer cell lines. Endocrinology 1993;132:195260.
(216.) Drivdahl RH, Loop SM, Andress DL, Ostenson RC. IGF-binding proteins in human prostate tumor cells: expression and regulation by 1,25-dihydroxyvitamin. Prostate 1995;26:72-9.
(217.) Danielpour D, Kadomatsu K, Anzano MA, Smith JM, Sporn MB. Development and characterisation of nontumorigenic and tumorigenic epithelial cell lines from rat dorsal-lateral prostate. Cancer Res 1994;54:3413-21.
(218.) Taylor JA, Hirvonen A, Watson M, Pittman G, Mohler JL, Bell DA. Association of prostate cancer with vitamin D receptor gene polymorphism. Cancer Res 1996;56:4108-10.
(219.) Blutt SE, Allegretto EA, Pike JW, Weigel NL. 1,25-Dihydroxyvitamin [D.sub.3] and 9-cis-retinoic acid act synergistically to inhibit the growth of LNCaP prostate cells and cause accumulation of cells in G1. Endocrinology 1997:138:1491-7.
(220.) Seldmon EJ, Trump DL, Kreis W, Hall SW, Kurman MR, Ouyang SP, et al. Phase I/II dose-escalation study of liarozole in patients with stage D, hormone-refractory carcinoma of the prostate. Ann Surg Oncol 1995;2:550-6.
(221.) Trump DL, Smith DC, Stiff D, Adedoyin A, Day R, Bahnson RR, et al. A phase II trial of all-trans-retinoic acid in hormone-refractory prostate cancer: a clinical trial with detailed pharmacokinetic analysis. Cancer Chemother Pharmacol 1997;39:349-56.
(222.) De Coster R, Wouters W, Bruynseels J. P450-dependent enzymes as targets for prostate cancer therapy. J Steroid Biochem Mol Biol 1996;56:133-43.
(223.) Hurley MA, Abrue C, Hakeda Y. Basic fibroblast growth factor regulates IGF-1 binding proteins in the clonal osteoblastic cell line MC3T3 E1. J Bone Miner Res 1995;10:222-30.
(224.) Okazaki R, Durham SK, Riggs BL, Conover CA. Transforming growth factor-beta and forskolin increase all classes of insulin-like growth factor-1 transcripts in normal human osteoblast-like cells. Biochem Biophys Res Commun 1995;207:963-70.
(225.) Konety BR, Getzenberg RH. Novel therapies for advanced prostate cancer. Semin Urol Oncol 1997;15:33-42.
(226.) Rago R, Mitchen J, Cheng AL, Oberley T, Wilding G. Disruption of cellular energy balance by suramin in intact prostatic carcinoma cells, a likely anti proliferative mechanism. Cancer Res 1991;51: 6629-35.
(227.) Rago RP, Brazy PC, Wilding G. Disruption of mitochondrial function by suramin measured by rhodamine 123 retention and oxygen consumption in intact DU145 prostate carcinoma cells. Cancer Res 1992;52:6953-5.
(228.) La Rocca RV, Danesi R, Cooper MR, Jamis-Dow CA, Ebing MW, Linehan WM, Myers CE. Effect of suramin on human prostate cancer cells in vitro. J Urol 1991;145:393-8.
(229.) Peehl DM, Wong ST, Stamey TA. Cytostatic effects of suramin on prostate cancer cells cultured from primary tumors. J Urol 1991;145:624-30.
(230.) Myers C, Cooper M, Stein C, LaRocca R, Walther MM, Weiss G, et al. Suramin: a novel growth factor antagonist with activity in hormone-refactory metastatic prostate cancer. J Clin Oncol 1992;10:875-7.
PAMELA J. RUSSELL,  * SUZANNE BENNETT,  and PHILLIP STRICKER 
 Oncology Research Centre, Prince of Wales Hospital, High Street, Randwick, New South Wales, Australia, 2031 and Division of Medicine, University of New South Wales, Kensington, New South Wales 2052, Australia.  Department of Urology, St. Vincent's Hospital, 438 Victoria St., Darling-hurst, New South Wales 2010, Australia.
 Nonstandard abbreviations: PSA, prostate-specific antigen; AR, androgen receptor; AD, androgen dependent; AS, androgen sensitive; AI, androgen independent; KGF, keratinocyte growth factor; EGF, epidermal growth factor; IGF, insulin-like growth factor; IGF-BP, high-affinity IGF-specific binding protein; FGF, fibroblast growth factor; TGF, transforming growth factor; MPR, mouse prostate reconstitution; TbetaR, transforming growth factor-/3 receptor; bFGF, basic fibroblast growth factor; EGFR, epidermal growth factor receptor; FGFR, fibroblast growth factor receptor; aFGF, acidic fibroblast growth factor; and RA, retinoic acid.
* Address correspondence to this author at: Oncology Research Centre, Villa 1, Prince of Wales Hospital, High Street, Randwick, New South Wales 2031, Australia. Fax 61 2 9382 2629; e-mail P.Russell@usnw.edu.au.
Received November 6, 1997; revision accepted December 5, 1997.
Table 1. Role of growth factors in normal prostate and in prostate cancer progression. Expression (a) and regulation in Growth factor normal prostate TGF-[beta] 1, 2, and 3 Rats/humans: expressed by PE and PM, a2; TGF-bs counterbalance mitogenic effects of other growth factors; expression associated with castration- induced apoptosis (28-32) bFGF Expressed by PE and PS but receptor only in PS, a1; maintains homeostasis (45, 46) aFGF Rats: role in early prostate epithelial development (51) KGF Rats/humans: involved in ductal branching of fetal prostate; paracrine production by PS, receptor (BEK) on PE; [a.sup.+] (53-55) FGF-8 Androgen-regulated FGF detected by PCR in rat prostate (57) IGF-1, IGF-2, and IGFs produced by PS; IGF-type I IGF-BPs receptors are on PE; PE secrete IGF-BP-2, -3, -4, and -6 (58, 59) EGF, TGF-[alpha]/EGFR EGF found in prostatic fluids, suggesting a regulatory role; TGF-[alpha] production by PS, but EGFR on PE; EGF and TGF-[alpha] production is [a.sup.+] but EGFR expression is [a.sup.-] (64-67) BMP Rats/humans: BMP 2, 3, 4, and 6 present in prostate tissue (75) NGF NGF protein is localized in PS, receptors on PE (76) IL-6 IL-6 is present in normal serum and in primary prostate epithelial cell cultures (78) Growth factor Expression and regulation in prostate cancer TGF-[beta] 1, 2, and 3 Expression of members of TGF-[beta] family correlates with responsiveness to androgens and is associated with abnormal growth; TGF-[beta]1 and -[beta]3 up-regulated; may be secreted with autocrine regulation; sensitivity to TGF-[beta] inhibition is lost with tumor progression (33-41) bFGF Bone fibroblasts from PC patients stimulate LNCaP tumor formation in vivo, involving bidirectional bFGF activity; expression is higher in AI than in AS human cell lines (47); switch from PS autocrine to PE autocrine expression occurs in rat and human PC (47, 48); in Dunning rat PC, AI is accompanied by a switch in exon IIIc of the FGF-r2 gene, changing ligand from KGF to bFGF in epithelial cells (48); antisense bFGF causes Dunning AT3 cells to form smaller, more slowly growing tumors in vivo; MMTV-Int-2 transgenic mice show proliferation of PE cells (49) aFGF Rats: expression changes with progression from PS in slow-growing tumors to PE in more aggressive tumors (52) KGF Human: switch to autocrine production by PE tumor cells (55, 56) FGF-8 Detected by PCR in LNCaP and AI DU-145 cells, suggesting that it is not androgen regulated (57) IGF-1, IGF-2, and PE shows autocrine regulation of IGF IGF-BPs pathways in absence of serum; dysregulation of IGF-BP production in cell lines and patients (60, 61) EGF, TGF-[alpha]/EGFR Both EGF and TGF-a expression are up-regulated in human cancers (68-71); switch from paracrine to autocrine production by PE (72) BMP BMP 3 predominates in rat tumors and varies in concentration in human cell lines (75) NGF Expression of NGF is reduced, and that of receptors is lost with cancer progression (77) IL-6 IL-6 is high in prostate cancer cell lines; receptors appear to be up-regulated in prostate cancer patients, with autocrine production (79) Growth Factor Possible role in metastasis TGF-[beta] 1, 2, and 3 Causes osteoblast migration, angiogenesis, immunosuppression (42-44) bFGF bFGF regulates protease expression, e.g., urokinase-type plasminogen activator, collagenase, which may be involved in metastatic cascade; bFGF is highly angiogenic (50) aFGF Not defined KGF Not defined FGF-8 Not defined IGF-1, IGF-2, and IGFs may promote bony metastases; IGF-BPs PSA cleaves IGF-BP-3, resulting in release of IGFs in distant tissues (61-63) EGF, TGF-[alpha]/EGFR EGF enhances cell invasion by induction of tumor proteases (73); EGF can regulate the IGF axis (74) BMP May be produced at metastatic sites and stimulate bone formation (75) NGF Not defined IL-6 (a) PE, expression in prostate epithelial cells; PS, expression in prostate mesenchymal/stromal cells. Androgen regulation is notated as negative ([a.sup.-]) or positive ([a.sup.+]). BMP, bone morphogenetic protein; NGF, nerve growth factor; IL-6, interleukin 6. Table 2. Models of prostate cancer. Animal Model Androgen sensitivity AR Rats Copenhagen Dunning H line, AS; + R-3327 A line, AI; - MAT-Ly-Lu, AI; - MAT-Ly, AI - Noble Noble AD and AI lines Lobund-Wistar Pollard AD and AI (L-W) lines August X ACI Copenhagen Mice DD/S Shionogi AD and AI + mammary lines carcinoma C57BL/6 MPR RM-6 line, (renal capsule) AI Human cell lines PC-93 AI ? PC-3 AI ? DU-145 AI ? LNCaP Parent line, Mutated AS; C4 line, AI; C4-2 line, AI; P104-R2 line Human CWR22 AD ? xenograft lines CWR22R AI ? PC-82 AD + PC-EW AD + Honda AD + LuCaP AS + PR-2 ? ? Animal 5[alpha]-reductase Comments References Rats Copenhagen + Various sublines 81-82 - reflect PC progression; - metastatic (liver/lung); 83 - metastatic (liver); 84 Noble Chronic hormones 85-88 induce PCs; stroma plus epithelial cells required for 89 tumorigenicity Lobund-Wistar Spontaneous tumor; 90 (L-W) tumors induced by 91, 92 testosterone or N-methyl-N-nitrosourea administration August X Spontaneous PC in 93, 94 Copenhagen ventral lobe; old rats Mice + DD/S Extensively used for 95, 96 studying intermittent hormonal ablation therapy C57BL/6 Overexpression of myc 97 and ras in stromal and epithelial cells from urogenital sinus allows analysis ? of paracrine/autocrine pathways Human cell - Established from lines primary AD 98 - Established from 99 Mutated prostate cancer 100 metastases 101 102 103 Stimulated by finasteride 104 Human xenograft lines 105 106 + 107 108 Small cell carcinoma 109 of prostate 110, 111 Table 3. Characteristics of growth factors/receptor pathways in prostate cancer. Factor/Receptor Isoforms/Size, human, mature form TGF-[beta] TGF-[beta]1, 44.3 kDa 390 aa TGF-[beta]2, 47.8 kDa 414 aa TGF-[beta]3, 47.3 kDa 410 aa TGF-[beta] receptors TbetaR-I, 53 kDa 505 aa TbetaR-II, 68 kDa 565aa TbetaR-III EGF 6 kDa, 53 aa TGF-[alpha] 6 kDa, 50 aa bFGF 4 variants 18, 21, 21.5, and 22.5 kDa, all 155aa aFGF 17.5 kDa, 155 aa KGF 19 kDa IGF IGF-1, 70 aa IGF-2, 7.5 kDa, 60aa IGF receptors Type I, 1367aa; Type II IGF-BP Types 1-6, 24-43 kDa, all 200-300 aa Factor/Receptor Biological activity TGF-[beta] Requires proteolytic cleavage TGF-[beta] receptors Transmembrane serine-threonine kinases Membrane proteoglycan EGF Secreted by normal and tumor cells TGF-[alpha] Secreted by tumor cells bFGF No signal sequence aFGF No signal sequence KGF Has signal sequence IGF Cause prostate cell proliferation IGF receptors IGF-BP Regulate IGFs by modulating their receptor access Factor/Receptor Comments References TGF-[beta] TGF-[beta]1 and 2 are homodimers of 125, 126 25 kDa protein; 75% homologous TGF-[beta]3 is a heterodimer, 80% 127, 128 homology to TGF-[beta]2 TGF-[beta] receptors Trigger decreases in expression of 129-131 src tyrosine-kinases Does not transduce signals but 132 binding of TGF-[beta] activates other receptors EGF Share 35% homology; signal 133, 134 through same EGF receptor (170 TGF-[alpha] kDa, 1210 aa) 135 bFGF 18 kDa protein found in cytosol; 136-138 others nuclear aFGF On chromosome 5; 55% homology 51, 139 with bFGF KGF 30-40% homology with other FGFs 140, 141 IGF 142 IGF receptors Type I binds IGF-1 with higher 143 affinity than IGF-2; type II prefers IGF-2 IGF-BP 144 aa, amino acids; kDa, kilodaltons; b, basic; a, acidic. Table 4. Expression of growth factors and their receptors in human prostate cancer cell lines. Presence in human prostate cancer cell line Secreted growth factor/Receptor LNCaP DU-145 PC-3 EGF/TGF-[alpha]/EGFR +/+ +/+ ?/+ TGF-[beta]/Receptor -/- +/+ +/+ IGF-1/IGFr type +/+ +/+ +/+ 1 IGF-2/IGFr type +/- +/- ?/- 2 bFGF/bFGFr -/+ +/+ +/+ Autocrine loops for granulocyte-macrophage-colony stimulating factor, macrophage-colony stimulating factor, and interleukin 6 also exist for each line. IGFr, insulin-like growth factor receptor; bFGFr, basic fibroblast growth factor receptor; +, factor or receptor expressed; and -, factor or receptor not expressed.
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|Author:||Russell, Pamela J.; Bennett, Suzanne; Stricker, Phillip|
|Date:||Apr 1, 1998|
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