Role of peptide growth factors in the prostate: a review

Growth factors and epithelial-stromal interactions in prostate cancer development

Epithelial-stromal interactions are important not only in growth, development, and functional cytodifferentiation of the prostate but also in derangements of prostate gland such as BPH and prostate carcinoma. This chapter explores the roles of epithelium and stroma during this delicate process and highlights the role and mutual influence of each on the other. It also examines the importance of ECM in mediating the effects of androgens and drawn attention to estrogen and genetic factors in the process. During this process of epithelial-stromal interaction, growth factors play a central role in mediating the interactions. This chapter focuses on the role of several growth factors including epidermal growth factor, fibroblast growth factor, transforming growth factor alpha, transforming growth factor beta, insulin-like growth factor-1, vascular endothelial growth factor, nerve growth factor, platelet-derived growth factor, and hepatocyte growth factor. This chapter emphasizes the importance of epithelial-stromal interactions in tumorigenesis and highlights the switch of paracrine to autocrine mode during the process of carcinogenesis.

Novel strategies and therapeutics for the treatment of prostate carcinoma

BACKGROUND

An increased understanding of the biology of prostate carcinoma has led to the clinical evaluation of mechanism-based and targeted therapies. Modulating the immune system has been pursued through the use of both active and passive immunity as well as the ex vivo genetic manipulation of effector cells. A variety of gene therapies has been proposed not only to replace defective genes but to localize activation of prodrugs. Angiogenesis and tumor invasion also have been targeted, as have cell cycling and signal transduction. Strategies promoting apoptosis and augmenting differentiation are also under study.

METHODS

This study is a review of current clinical strategies using biologic, immunologic, and genetic approaches for the treatment of prostate carcinoma.

RESULTS

The clinical development of therapy targeting differentiation, apoptosis, cell signaling, angiogenesis, metastasis, immune surveillance, and others are in various stages of clinical development. A disease states model is used to discuss treatment groups, outcome measures, and other trial design elements in relation to specific therapeutic strategies.

CONCLUSIONS

Development of novel agents requires consideration of where in the natural history of the disease they should be applied. In addition, understanding the genetic and molecular alterations that occur as the disease progresses from a localized to a metastatic state, and from androgen dependence to independence, is necessary. Clinical trial design will require consideration of cytostatic and cytotoxic effects, the status of pathways not directly targeted, and potentially unexpected influences on prostate specific antigen expression by these agents.

Epithelial defect in prostates of Stat5a-null mice

The transcription factor Stat5a critically mediates prolactin (PRL)-induced mammary gland development and lactogenesis. PRL also stimulates growth and differentiation of prostate tissue. Specifically, hyperprolactinemia gives rise to prostate hyperplasia, and prostate size is reduced in PRL-deficient mice. We therefore investigated the importance of Stat5a for prostate development and function by examining Stat5a-null mice. The absence of Stat5a in mice was associated with a distinct prostate morphology characterized by an increased prevalence of local disorganization within acinar epithelium of ventral prostates. Affected acini were typically filled with desquamated, granular epithelial cells that had become embedded in dense, coagulated secretory material. These features were reminiscent of acinar cyst formation and degeneration frequently observed in human benign prostate hyperplasia, however, cystic changes in prostate acini of Stat5a-deficient mice were not associated with increased prostate size or morphologic hallmarks of epithelial hyperplasia. Instead, immunohistochemistry of the prostate-specific secretory marker, probasin, suggested that hypersecretory function of the epithelium could underlie local congestion and cyst formation in prostates of Stat5a-null mice. Serum testosterone and PRL levels were normal in Stat5a knockout mice, but prostate PRL receptor expression was reduced as determined by immunohistochemistry. Expression levels or activation states of other PRL signal transduction proteins, including Stat5b, Stat3, Stat1, ERK1, and ERK2 were not altered. The present study offers the first evidence for a direct role of Stat5a in the maintenance of normal tissue architecture and function of the mouse prostate.

Effects of androgens on the insulin-like growth factor system in an androgen-responsive human osteoblastic cell line

Although androgens have significant effects on bone metabolism, the mediators of their effects are still unclear. As the insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) have important effects on osteoblast proliferation and differentiation, we examined androgen effects on the IGF system in a conditionally immortalized human fetal osteoblastic cell line, hFOB/AR-6, which displays a mature osteoblastic phenotype and physiological levels of functional androgen receptors. The nonaromatizable androgen, 5alpha-dihydrotestosterone (5alphaDHT), and testosterone, but not dehydroepiandrosterone, increased IGF-I messenger RNA (mRNA) levels up to 4-fold in a dose (10(-12)-10(-6) M)- and time (2-72 h)-dependent fashion. These changes were prevented by the specific androgen receptor antagonist, hydroxyflutamide. In addition, 5alpha-DHT decreased IGFBP-4 mRNA and protein levels by 2- and 4-fold, respectively, and increased IGFBP-2 and -3 mRNA and protein levels by 6- and 7-fold (for mRNA) and 3- and 5-fold (for protein), respectively. hFOB/AR-6 cells expressed the type-I IGF receptor, but this was not regulated by 5alphaDHT. 5alphaDHT and IGFBP-3 specifically increased hFOB/AR-6 cell proliferation, and a monoclonal antibody specific for IGF-I blocked this effect. Thus, androgens increase the expression of IGF-I, IGFBP-2, and IGFBP-3, but decrease levels of the inhibitory IGFBP-4 in an androgen-responsive human osteoblastic cell line. Our data are consistent with the hypothesis that the effects of androgen on bone cells may be mediated at least in part by increases in IGF-I production and by differential regulation of IGFBPs.

Regulation of prostatic stromal cell growth and function by transforming growth factor beta (TGFbeta)

BACKGROUND

The majority of the overgrowth in benign prostatic hyperplasia (BPH) specimens is comprised of connective tissue. Factors that control stromal growth in the prostate are poorly understood; however, members of the transforming growth factor beta (TGFbeta) family may be of particular importance in the etiology of BPH.

METHODS

Thirty-two low-passage stromal cultures were generated from human prostatectomy specimens. Their stromal origin was confirmed and expression of TGFbetas analyzed by duplex reverse transcription-polymerase chain reaction (RT-PCR). Challenge experiments were designed to study the effects of exogenous TGFbeta1 on stromal cell growth and synthesis of extracellular matrix components.

RESULTS

The expression of TGFbetas 1, 2, and 3 was demonstrated in all 32 cell strains. The stromal origin of the cell lines was confirmed. Exogenous TGFbeta1 added to stromal cultures resulted in inhibition of cell growth and increased production of type I collagen.

CONCLUSIONS

The prostatic stromal cell strains we have developed are a reliable mod- el for investigating prostatic connective tissue biology. The challenge experiments with TGFbeta1 provide further evidence for the involvement of TGFbetas in prostatic enlargement, as modulators of the extracellular matrix in the absence of growth stimulation.

Immunohistochemical comparative analysis of transforming growth factor alpha, epidermal growth factor, and epidermal growth factor receptor in normal, hyperplastic and neoplastic human prostates

Immunoreaction to TGF-alpha was limited to the basal epithelial cells of focal areas in the normal prostates. In benign prostatic hyperplasia (BPH) the immunostained areas were more widespread and immunolabelling was observed in both basal and columnar (secretory) cells of the epithelium. Some cells in the connective tissue stroma were also stained. In prostatic adenocarcinoma, epithelial immunostaining was even more extensive and intense than in BPH, and some stromal cells were also stained. Epidermal growth factor (EGF) immunostaining was only present in some basal cells in normal prostates. In BPH, this immunoreaction was strong in the basal cells and even stronger in the secretory cells. In prostatic cancer, the intensity of epithelial cell immunoreactivity was intermediate between that of normal prostates and that of BPH specimens. EGF-receptor immunostaining was focal and located in the basal cells in normal prostates. In BPH, labelling was also localized in basal cells but extended to wider areas. Some stromal cells appeared weakly labelled. In the prostatic carcinoma, both basal and columnar cells appeared stained and the number of immunolabelled stromal cells was higher than in BPH. The results presented suggest that, in normal conditions, EGF and TGF-alpha act as autocrine growth factors for the basal cells of the prostatic epithelium. In BPH this action is maintained and, in addition, the columnar cells start to secrete both factors which are bound by the basal cell receptors, giving rise to a paracrine regulation which probably overstimulates basal cell proliferation. In prostatic carcinoma, besides these regulatory mechanisms, the acquisition of EGF-receptors by the secretory cells develops an autocrine regulation which might induce their proliferation.

EGF induces the expression of matrilysin in the human prostate adenocarcinoma cell line, LNCaP

BACKGROUND

Matrix metalloproteinases (MMPs) are regulated both positively and negatively at the transcriptional level by a variety of growth factors, oncogenes, and tumor promoters. Induction of the MMP, matrilysin, by epidermal growth factor (EGF) was investigated in a human prostate cancer cell line.

METHODS

Secreted protein and messenger RNA were detected using Western and Northern methods, respectively. EGF receptor antibodies were used for neutralization of the EGF receptor to determine the role of the EGF growth factor family (EGF, transforming growth factor alpha (TGFalpha), or amphiregulin) in the basal induction of matrilysin.

RESULTS

EGF increased mRNA and secreted protein levels for the MMP matrilysin in LNCaP cells, in a concentration- and time-dependent manner. Transforming growth factor beta1 (TGFbeta1) had no inhibitory effect on the levels of mRNA or secreted protein induced by EGF in LNCaP cells. Decay of matrilysin mRNA after the addition of actinomycin D indicated that the half-life of matrilysin mRNA was not altered by EGF. Blocking with a neutralizing antibody to the EGF receptor did not alter the basal level of secreted matrilysin.

CONCLUSIONS

Exogenously added EGF increased matrilysin mRNA, perhaps at a transcriptional level. Growth factors, other than the members of the EGF family which act through the EGF receptor, may be involved in the regulation of the basal level of secreted matrilysin in LNCaP cells. Our data with LNCaP cells suggest that paracrine regulation of matrilysin expression in human prostate carcinoma cells could be via the EGF receptor.

Complex post-transcriptional regulation of EGF-receptor expression by EGF and TGF-alpha in human prostate cancer cells

The epidermal growth factor receptor (EGFR) plays an important role in the development and progression of prostate cancer and its overexpression is associated with decreased survival. With progression, prostate cancer cells switch from epidermal growth factor (EGF) to transforming growth factor alpha (TGF-alpha) synthesis, which contributes to autocrine growth and unrestrained proliferation. To define the molecular mechanisms involved in the regulation of EGFR expression by EGF and TGF-alpha we studied three human prostate cancer cell lines, androgen-responsive (LNCaP) and -unresponsive (DU145 and PC3). Here we show that TGF-alpha stabilized EGFR mRNA two- to threefold in all three cell lines, whilst EGF stabilized EGFR mRNA approximately twofold in LNCaP and DU145 cells, but not in PC3 cells. Both ligands increased EGFR transcription in LNCaP and DU145 cells, with less effect in PC3 cells. In all three cell lines EGF reduced total EGFR protein levels more than TGF-alpha, but this was associated with a greater increase in de novo protein synthesis with EGF compared to TGF-alpha. Only EGF, however, shortened EGFR protein stability (half-life decreased from 5 h to 120 min), resulting in rapid disappearance of newly synthesized EGFR protein. Both ligands increased total LNCaP and DU145 cell numbers. These studies demonstrate that the EGF- and TGF-alpha-induced upregulation of EGFR mRNA and protein in human prostate cancer cell lines is complex and occurs at multiple, transcriptional and post-transcriptional levels. Taken together, these data provide novel insight into the molecular mechanisms by which TGF-alpha would preferentially maintain an autocrine loop in human prostate cancer cells. Furthermore, this work suggests that in human prostate cancer cells ligand-specific differential intracellular trafficking of the EGFR plays a major role in regulating its expression.

Vascular endothelial growth factor-C expression in human prostatic carcinoma and its relationship to lymph node metastasis

Lymph node dissemination is a major prognostic factor in human cancer. However, the molecular mechanisms underlying lymph node metastasis are poorly understood. Recently, vascular endothelial growth factor-C (VEGF-C) was identified as a ligand for VEGF receptor-3 (VEGFR-3/Flt-4) and the expression of VEGFR-3 was found to be highly restricted to the lymphatic endothelial cells. In this report, we investigated the expression of VEGF-C and VEGFR-3 in human prostatic carcinoma tissue by using in situ hybridization and immunohistochemical staining respectively. Expression of VEGF-C mRNA in prostatic carcinoma was significantly higher in lymph node-positive group than in lymph node-negative group. In addition, the number of VEGFR-3-positive vessels was increased in stroma surrounding VEGF-C-positive prostatic carcinoma cells. These results suggest that the expression of VEGF-C in prostatic carcinoma cells is implicated in the lymph node metastasis.

Effects of pituitary hormones on the prostate

BACKGROUND

Although essential, androgens alone are not sufficient to induce normal growth and functionality of the prostate. Nonandrogenic hormones must also be involved in the proliferation of the prostate cancer cells which do not respond to antiandrogenic therapy and which thus become androgen-independent. Prolactin, but also growth hormone and luteinizing hormone, are potentially able to act on both normal and abnormal prostatic cells.

METHODS

In this review we summarize data from the literature concerning the physiological and pathological implications of prolactin, growth hormone, and luteinizing hormone on the prostate.

RESULTS

In rodent prostates, prolactin and growth hormone can induce a variety of effects independently of androgens (e.g., transactivation of certain genes, or synthesis of the major secretion products). Moreover, hyperprolactinemia is responsible for inflammation and dysplasia of the gland, while growth hormone promotes the development of prostate tumors in vivo in the mouse and rat. Growth hormone acts on the gland directly, through prostatic growth hormone receptors, and/or indirectly via the stimulation of insulin-like growth factor-I (IGF-I) synthesis in the liver. Luteinizing hormone receptor is expressed in rat and human prostates. Luteinizing hormone increases the amount of various transcripts in the rat prostate through an androgen-independent pathway.

CONCLUSIONS

Prolactin, growth hormone, and luteinizing hormone, alone or synergistically with androgens, play physiologically significant roles in the normal prostate. The involvement of these hormones in the development of benign prostatic hyperplasia and prostatic carcinoma is an issue that needs to be addressed.

Prostate stroma: physiology

BACKGROUND

The separate structural and functional activities of the prostatic stroma were only recently discovered and are still poorly understood.

METHODS

This review summarizes recent literature on the structure, and on the angiogenic, contractile, proliferative, and secretory activities mediated by the prostatic stroma and its agents.

RESULTS

The stroma undergirds the acinar epithelium through its fibromuscular substance. Neovascularization of its hypoxic cells, a process driven by cytokines, especially vascular endothelial growth factor, provides fuel for glycolytic empowerment of smooth muscle contraction, growth, and secretion. Signals from the stromal complement of cholinergic and adrenergic fibers, modulated by also-elaborated nitric oxide, provide tight regulation of uroflow. Apparently, autonomic control is independent of that of the powerful endothelin, secreted by the epithelium. Superimposed on these intrinsic elements of prostatic stromal control are the effects of steroid hormones and their effectors.

CONCLUSIONS

The illumination of the stroma's role in prostatic physiology, coupled with advances in knowledge of its pharmacology, should aid in our understanding, management, and prevention of prostatic disease.

Age-dependent and lobe-specific spontaneous hyperplasia in the brown Norway rat prostate

We showed previously that exogenously administered testosterone caused age- and lobe-specific overgrowth of the prostate in Brown Norway rats. A common feature observed in testosterone-treated animals was cell hypertrophy in each of the ventral, dorsal, and lateral lobes of both young (6 mo old) and old (24 mo old) rats. By contrast, hyperplasia was seen only in the dorsal and lateral lobes of old rats treated with testosterone. These observations prompted us to examine whether age- and lobe-specific overgrowth might also occur in untreated rats as a consequence of the endogenous hormonal milieu. To this end, blood and prostates were collected from a large number (25-30 rats per group) of 4- to 6-mo-old (young) and 21- to 24-mo-old (old) Brown Norway rats. Both serum testosterone (-45%) and estradiol (-22%) concentrations decreased significantly with age, but the greater magnitude of the decrement in testosterone relative to estradiol led to a reduction in the serum testosterone:estradiol ratio. Paradoxically, although the prostate is androgen dependent, the wet weight, protein, and DNA contents increased significantly with age in the dorsal and lateral lobes of old rats despite the decrease in testosterone level. Histologic examination revealed that the increased weights and DNA contents of the dorsal and lateral lobes in old rats coincided with an increased number of epithelial cells in the distal and intermediate segments of these lobes, indicative of hyperplasia but independent of change in cell size. Taken together, these results show a spontaneous age-related overgrowth of cells in the dorsal and lateral prostatic lobes of old Brown Norway rats despite diminished serum testosterone concentrations. The aging Brown Norway rat, therefore, may be a useful model for studies of some aspects of the pathogenesis underlying spontaneous age-related prostatic hyperplasia.

Insulin-like growth factor-I and -II in human benign prostatic hyperplasia: relationship with binding proteins 2 and 3 and androgens

In prostatic tissue, androgen action may be mediated by growth factors such as insulin-like growth factor-I (IGF-I) and II (IGF-II), which are mitogenic for prostatic cells and modulate the stroma-epithelium interaction. IGF-binding proteins (IGFBPs) have an autocrine and/or paracrine role in regulating the local actions of the IGFs. In this study, testosterone, dihydrotestosterone (DHT), 3 alpha androstanediol (3 alpha diol), IGF-I, IGF-II, IGFBP2, and IGFBP3 concentrations were evaluated in human benign prostatic hyperplasia (BPH) tissue. Samples of prostate tissue were removed by suprapubic prostatectomy from twelve BPH patients. Androgen tissue levels were determined by radioimmunoassay after purification on celite microcolumns. IGF-I, IGFBP2, and IGFBP3 were measured by radioimmunoassay, and IGF-II by immunoradio metric assay, after acidification and chromatography on Sep-pak C18 Cartridges for IGF-I and IGF-II. Androgen concentrations, expressed in ng/g tissue (mean +/- SE), were 0.51 +/- 0.05 for testosterone, 5.3 +/- 0.16 for DHT, and 1.1 +/- 0.07 for 3 alpha diol. IGF-I, IGF-II, IGFBP2, and IGFBP3 levels were 24 +/- 3.7, 121 +/- 14 ng/g tissue and 0.44 +/- 0.05 and 1.2 +/- 0.17 micrograms/g tissue, respectively. No correlation between IGF-I, androgens, and IGFBPs was found. IGF-II was positively correlated with DHT (r = 0.78; p = 0.003) and 3 alpha diol (r = 0.66; p = 0.021) but not with IGFBPs. These data suggest that in BPH, DHT modulates the IGF system by increasing IGF-II without modifying IGFBPs. Therefore, the stroma-epithelium interaction, which plays an important role in prostatic growth, may be regulated by DHT through IGF-II.

Osteopontin stimulates a subpopulation of quiescent human prostate epithelial cells with high proliferative potential to divide in vitro

BACKGROUND

Osteopontin (OPN) is a secreted extracellular matrix (ECM) protein found in bone, as well as associated with epithelial cells. The main objective of these studies was to test in vitro the hypothesis that interaction with OPN stimulates proliferation of a quiescent subpopulation of prostate epithelial cells with high proliferative potential.

METHODS

To simulate conditions that restrict proliferation and inhibit terminal differentiation of basal cells in vivo, control cultures grew on substrate coated with collagen (CO) or fibronectin (FN), in medium containing low levels of growth factors.

RESULTS

Under growth-restricting conditions, most prostate epithelial cells with high proliferative potential, seeded in control secondary cultures, were quiescent within the time frame of the studies, as indicated by the small number of large colonies in these cultures. Growing prostate epithelial cells (PR) under the same growth-restricting conditions, but on substrate coated with OPN instead of CO or FN, stimulated proliferation of a subpopulation of single cells with high proliferative ability as indicated by: 1) dose-dependent increase in the percentage of single cells incorporating bromodeoxyuridine, i.e., proliferating PR; and 2) subsequent dose-dependent increase in the percentage of large colonies. The OPN effect was not merely due to preferential attachment to OPN, because PR attachment to OPN, CO, or FN was identical. PR attachment to OPN was inhibited in the presence of GRGDTP or an antibody against the integrin subunit alphav, but not in the presence of an RGES peptide or a nonspecific IgG.

CONCLUSIONS

Integrin-mediated OPN/PR interaction stimulates proliferation of a quiescent subpopulation of prostate epithelial cells with high proliferative potential, possibly stem cells.

Developmental and hormonal regulation of transforming growth factor-alpha and epidermal growth factor receptor gene expression in isolated prostatic epithelial and stromal cells

Androgen has an important role in development of the prostate, and the actions of androgen are mediated, in part, by locally produced growth factors. These growth factors are postulated to mediate stromal-epithelial interaction in the prostate to maintain normal tissue physiology. Transforming growth factor-alpha (TGF-alpha) is one of the growth factors that can stimulate prostatic growth. The expression of TGF-alpha is thought to be regulated by androgen. The expression of epidermal growth factor receptor (EGFR), which is the receptor of TGF-alpha and EGF, also may be regulated by androgen. The hormonal and developmental regulation of TGF-alpha and EGFR messenger RNA (mRNA) levels in isolated epithelial and stromal cells from rat ventral prostate was investigated. The expression of mRNA for TGF-alpha and EGFR was analyzed by a quantitative RT-PCR (QRT-PCR) procedure developed. Observations from this assay demonstrated that both epithelial and stromal cells expressed the mRNA for TGF-alpha and EGFR. TGF-alpha mRNA expression was constant during postnatal, pubertal, and adult development of the prostate. EGFR mRNA expression was elevated at the midpubertal period and decreased with age. After castration of 60-day-old adult rats, both TGF-alpha and EGFR mRNA were significantly enhanced. TGF-alpha mRNA expression was stimulated by EGF in stromal cells (4.5-fold increase) but was not changed by any treatment in epithelial cells. EGFR mRNA levels were stimulated by EGF and keratinocyte growth factor treatment and inhibited by testosterone treatment in epithelial cells. Stromal cell EGFR mRNA levels were not affected by any treatment. Both testosterone and EGF stimulated incorporation of 3H-thymidine into prostatic stromal and epithelial cells. Anti-TGF-alpha antibody significantly inhibited testosterone-stimulated 3H-thymidine incorporation into stromal cells and epithelial cells. Immunocytochemical localization of TGF-alpha and EGFR demonstrated expression on the luminal surface of epithelial cells within prostatic ducts, and minimal expression was observed in stromal cells. Results indicate that testosterone does not directly regulate TGF-alpha mRNA levels but does inhibit EGFR mRNA levels. Interestingly, anti TGF-alpha antibody suppressed the effect of testosterone on 3H-thymidine incorporation into prostatic stromal and epithelial cells. This finding suggests that testosterone may act indirectly on prostatic cells to influence TGF-alpha actions. TGF-alpha mRNA levels were influenced by EGF in stromal cells only, and EGFR mRNA levels were influenced by testosterone, EGF, and keratinocyte growth factor in epithelial cells. These observations suggest that regulation of TGF-alpha and EGFR is distinct between the cell types. In conclusion, a network of hormonally controlled growth factor-mediated stromal-epithelial interactions is needed to maintain prostate development and function.

NGF-beta, NE-cells and prostatic cancer cell lines. A study of neuroendocrine expression in the human prostatic cancer cell lines DU-145, PC-3, LNCaP, and TSU-pr1 following stimulation of the nerve growth factor-beta

Neuroendocrine (NE) cells are present in both benign and malignant human prostate. However, their function is poorly understood, mainly due to the lack of suitable experimental models. The nerve growth factor-beta (NGF-beta) promotes the rat pheochromocytoma cell line PC-12 to differentiate into neuronal like cells. We have studied the effect of NGF-beta on four human prostate cancer cell lines, LNCaP, DU-145, PC-3, and TSU-pr1. NGF-beta stimulates the growth rate in all these cell lines, but does not induce a neuronal phenotype. NE tumour markers (chromogranin A [CgA] and chromogranin B[CgB]) could not be demonstrated by immunocytochemistry (CgA and CgB), Northern blotting (CgA), or ELISA techniques (CgA), neither in control nor in NGF-beta stimulated cells. Consequently, other experimental models have to be sought in the study of NE cells in the human prostate.

Detection and epitope mapping of immunoreactive human endothelin-1 using ELISA and a surface plasmon resonance-based biosensor

A surface plasmon resonance-based biosensor (BIA technology) and enzyme-linked immunosorbent assays (ELISA) have been used for detecting and characterizing human endothelin (ET), a potent vasoactive 21 amino acid polypeptide. Antibodies produced against the isoform ET-1 and its C-terminal eptapeptide ET-1(15-21) have been characterized with respect to their binding capacity to the two isoforms ET-1 and ET-3, the non-secreted portion of the precursor molecule Big.ET-1(22-38), the C-terminal of ET-1, six analogues of ET-1(16-21) each containing a substitution with Ala of a single amino acid in positions 16-21, respectively, and three synthetic cyclic peptides mimicking the N-terminal portion of ET-1. Antibodies reacting with ET-1 also bound to ET-1(16-21) and, with less affinity, to ET-3 but did not cross-react with Big.ET-1(22-38). Ala substitution in positions 16, 17 and 19 of ET-1(16-21) hardly affected the antibody binding capacity of ET-1(16-21), whereas Ala substitution of Asp18, Ile20 and, in particular, Trp21, inhibited its immunoreactivity. The C-terminus thus represents an immunodominant epitope in ET-1 and is important for antibody binding. Epitope mapping using as antibody pairs polyclonal anti-ET-1 and monoclonal anti-ET-1(15-21) antibodies indicated the presence of another immunogenic domain in the N-terminal portion of the molecule. There was excellent agreement between the epitopes determined using ELISA and BIA analyses.

Effect of fibroblastic growth factors (FGF) on steroid UDP-glucuronosyltransferase expression and activity in the LNCaP cell line

It is now widely accepted that factors other than androgens are crucial in the normal and abnormal growth of the prostate. In addition to hormones, many polypeptide growth factors, including the fibroblast growth factor family (FGF), can act as potent mitogens on cell proliferation. The FGF family of growth factors are essential factors for both normal and abnormal proliferation of prostate cells. To study the effect of FGFs on steroid glucuronidation, we used the human prostate cancer LNCaP cell line which is known to be stimulated by FGF resulting in increased cell proliferation. LNCaP cells express steroid metabolizing enzymes including uridine diphosphoglucuronosyltransferases (UGTs). In addition, LNCaP cells treated with dihydrotestosterone (DHT) and epidermal growth factor (EGF) express differential levels of the human UGT2B15 and UGT2B17 transcripts. In the present study, we examined the possible interaction between FGF and steroid UGT enzymes. Results show a dose dependent inhibition of DHT glucuronide (DHT-G) formation following treatment (6 days) with acidic FGF (aFGF) and basic FGF (bFGF). When cells were treated with 10 ng/ ml of FGFs, we observed 33 and 51% inhibition of glucuronidation activity using aFGF and bFGF respectively. Ribonuclease protection analyses revealed a 2 and 3 fold increase of UGT2B15 mRNA expression following treatment with aFGF (50 ng/ml) and bFGF (10 ng/ml) respectively. However, a slight decrease in UGT2B17 transcripts was observed, demonstrating a differential regulation. Since a reduction in the glucuronidation of DHT or its 5alpha-reduced metabolites may contribute to an increase in intraprostatic androgen levels, down-regulation of UGTs by growth factors such as FGFs may increase the proliferation of androgen-dependent tumors.

Differences in prostate and adipose tissue basic fibroblast growth factor: analysis of preliminary results

OBJECTIVES

Basic fibroblast growth factor (bFGF or FGF-2) is mitogenic to human prostate epithelial and stromal cells, and it is reported to be elevated in the serum and urine of patients with various cancers, including prostate cancer. Obesity, with increased body fat, is a risk factor for prostate cancer through unknown mechanisms. Because adipose tissue is a source of FGF-2, we determined the quantity and quality of activity of FGF-2 in omental adipose tissue and compared it with normal and cancerous prostate tissues.

METHODS

Using heparin-Sepharose chromatography, we extracted proteins from human omental adipose tissue, adenocarcinoma of the prostate, and benign prostatic hypertrophic (BPH) tissues. Each of the mitogenic proteins eluted with NaCl concentrations between 1.4 M and 1.8 M, similar to control FGF-2. Using FGF-2 antisera (which inhibited the mitogenic activity of the proteins), we performed Western blot analysis to confirm their homology to FGF-2. We also assessed recovery, mitogenicity, and angiogenicity of each of the proteins using thymidine incorporation into human umbilical vein endothelial cells and the chorioallantoic membrane assay.

RESULTS

There was greater recovery of FGF-2 from omental adipose tissue compared with cancerous or BPH homogenates (40 micrograms [2.0 micrograms/g] versus 25 micrograms [1.25 micrograms/g] and 20 micrograms [1.0 microgram/g], respectively). Moreover. FGF-2 from adipose tissue had greater mitogenic activity (96.2% versus 74.8% and 54%; P < 0.05) and a greater angiogenic activity (5.1 vessels versus 2.9 and 1.8 vessels; P < 0.05) on the chorioallantoic assay.

CONCLUSIONS

We suggest that human omental adipose tissue FGF-2 may demonstrate greater mitogenic and angiogenic activity than either BPH or prostate cancer tissue FGF-2. It is not known whether FGF-2 from adipose tissue qualitatively or quantitatively may underlie the relationship between obesity and prostate cancer.

Calcium signaling in prostate cancer cells: evidence for multiple receptors and enhanced sensitivity to bombesin/GRP

BACKGROUND

Cellular calcium is an important second messenger for growth regulation. We sought to identify potentially important receptors on prostate tumor cells by screening over 20 agonists for their ability to increase intracellular free calcium ([Ca2+]i) in several human prostate tumor cell lines.

METHODS

Intracellular calcium mobilization was detected using fura-2.

RESULTS

We found bombesin, GRP, ATP/UTP, lysophosphatidic acid, thrombin, endothelin, histamine, and bradykinin increased [Ca2+]i in the advanced tumor cell lines DU-145, PC3, and PPC-1. Bombesin failed to elevate [Ca2+]i in an immortalized human prostate cell line. Rank-order of potency studies suggested the presence of P2U nucleotide receptors for ATP/UTP on prostate epithelial cells. Potency studies also revealed GRP > > bombesin > > neuromedin B at elevating [Ca2+]i in responding tumor cells.

CONCLUSIONS

These findings indicate that androgen independent prostate tumor cell lines express multiple receptors capable of elevating intracellular calcium, and suggest that GRP receptors may be selectively expressed and/or coupled to calcium signaling during prostate tumor progression. Calcium sensitive cellular events may therefore contribute to the progression of prostate cancer.

Coregulatory effects of epidermal growth factor, dihydrotestosterone, and prolactin on benign human prostatic hyperplasia tissue culture proliferation

BACKGROUND

A variety of hormones have demonstrated effects on prostatic tissue growth dynamics. Our goal was to define the effect of dihydrotestosterone (DHT), epidermal growth factor (EGF), and prolactin (PRL) on prostate cellular proliferation.

METHODS

Thirty benign human prostatic hyperplasias (BPH) were maintained 48 hr as in vitro cultures. Culture media were supplemented with EGF, DHT, and PRL alone and in combinations. Proliferation was assessed by labeling with tritiated thymidine.

RESULTS

The proliferative response of individual BPH cultures was heterogeneous. DHT and EGF tended to have a greater proliferative effect than PRL, both in terms of the percent cultures responding and the magnitude of the response. PRL antagonized EGF-induced proliferative effects. EGF- and PRL-mediated effects correlated with each other, while DHT-mediated effects did not correlate with either those of PRL or EGF.

CONCLUSIONS

The proliferative response of individual BPH to DHT, EGF, and PRL, alone or in combination, is too variable to define a predictable response to their influence. Our methodology represents a technique with the capacity to define therapeutic potential for individual cases.

Change in morphological and functional cytodifferentiation induced by seminal vesicle mesenchyme in cell suspensions of rat Dunning prostatic adenocarcinoma cells

Previous experiments have shown that seminal vesicle mesenchyme (SVM) can induce small 0.5 mm fragments of the rat Dunning tumor (DT) to undergo secretory differentiation with a concomitant reduction in tumorigenesis. In the present experiments Dunning tumor epithelial cells (DTE) were purified from DT cell suspensions by Percoll gradient centrifugation and recombined with neonatal rat SVM. The resultant tissue recombinants (SVM + DTE) were grafted under the renal capsule of male athymic mice and grown for 2 months. Under these conditions SVM induced the DTE to exhibit a highly differentiated secretory phenotype by forming ducts lined with tall columnar epithelial cells or large clear cells with pale cytoplasm. Undifferentiated epithelial cells of the parental DT were rarely observed in these tissue recombinants. The loss of tumorigenicity in SVM + DTE recombinants was associated with a striking reduction of epithelial 3H-thymidine labeling index in SVM + DTE recombinants (DT = 8.31%; SVM + DTE recombinants = 1.10%). Differences in putative secretory proteins were also observed by SDS-PAGE in SVM + DTE recombinants in comparison with DT. Testosterone metabolism was examined in epithelial cells recovered from grafts of DT vs. SVM + DTE tissue recombinants by thin layer chromatography and revealed that the major metabolite produced by DTE was androstenedione, whereas in epithelium isolated from SVM + DTE tissue recombinants the major androgen metabolite was 5alpha-DHT. Thus, after induction by SVM the DTE metabolized androgens in a pattern similar to the normal rat dorsal prostate. The SVM-induced changes in DTE suggest the possibility that emerging or established carcinomas might be regulated at least in part by their connective tissue microenvironment.

Expression of transforming growth factor beta 1 (TGF beta 1), -beta 2, and- beta 3 by cultured human prostate cells

Transforming growth factor beta s (TGF beta s) are members of a superfamily of polypeptides that control cell cycle progression and a variety of other cellular activities. TGF beta family members, -beta 1, -beta 2, and -beta 3, have been identified in prostate. The levels of expression of these TGF beta isotypes have been reported to vary with the pathologic state of the prostate. While the significance of these observations remains to be elucidated there is little doubt that TGF beta s play an important role in controlling growth of the prostate. The prostatic cells expressing TGF beta s have not been identified. This information would provide insight into the physiologic role of TGF beta s and suggest ways that growth control may be altered in prostate disease. We used stromal (PS) and epithelial (PE) cells, cultured from normal human prostate and benign prostatic hyperplasia (BPH), to study the effect of TGF beta s on cell proliferation and TGF beta transcript and protein expression. The proliferation of PS and PE was inhibited by pM quantities of TGF beta 1, -beta 2, and -beta 3. Both cell types expressed transcripts for all three TGF beta isotypes, but PS primarily secreted TGF beta 1, whereas PE secreted more TGF beta 2 than TGF beta 1. These observations suggest that TGF beta s are antiproliferative agents in vivo, and that the stroma is the source of TGF beta 1 while the epithelium is the major source of TGF beta 2 in prostate. There were no significant differences in the growth response to TGF beta s, the TGF beta-isotype expressed, or the amount of TGF beta secreted by cells cultured from normal prostate or BPH.

Inhibition of human prostate cancer cells growth by gossypol is associated with stimulation of transforming growth factor-beta

Gossypol (GP), an antifertility agent in males, is also capable of inhibiting the proliferation of a wide range of cancer cells in vivo and in vitro. Thus, in this study we investigated the effect of GP on the growth of human androgen-independent prostate cancer cell line (PC3). The results showed that GP acts as a potent inhibitor of PC3 cells as determined by thymidine incorporation assay and flow cytometric analysis. Flow cytometry revealed that treatment of PC3 cells with GP resulted in a dose- and time-dependent accumulation of cells in the GO/GI phase with a concomitant decrease in cells progressing to the S and G2/M phase. These data support our thymidine incorporation results which indicated that GP is a potent inhibitor of PC3 cells. By ribonuclease protection assay, we also investigated the effect of GP on transforming growth factor-beta 1 (TGF-beta 1) gene expression in PC3 cells. Interestingly, the stimulatory effect of GP on TGF-beta 1 gene expression correlates well with its inhibitory effect on PC3 cell DNA synthesis and its ability to arrest cells in GO/G1 phase. Based on these data, it can be concluded that GP is a potent inhibitor of prostate cancer cell growth that acts by arresting cells in GO/G1 phase and that this inhibitory effect may be mediated by TGF-beta 1.

Androgen receptor expression in prostatic dysplasia (prostatic intraepithelial neoplasia) in the human prostate: an immunohistochemical and in situ hybridization study

To evaluate the role of androgens in the pathogenesis of prostatic dysplasia, we compared the localization of androgen receptor (AR) in proliferative and nonproliferative cells in normal and dysplastic acini. Basal cells, the only proliferating cells identified in normal acini, contained AR mRNA but lacked an immunodetectable receptor. Both AR mRNA and immunodetectable receptor were present, however, in secretory and stromal cells. Androgen receptor localization in dysplastic lesions was identical to normal but here the proliferative marker Ki-67 was found in both basal and secretory cells. Our findings suggest that androgens do not directly initiate the division of basal cells, the putative precursors of secretory cells. Instead, the hormone may act through its fully translated receptor to mainly mediate the differentiation of secretory cells. The presence of both AR and Ki-67 in dysplastic secretory cells may indicate an abnormal direct androgen-mediated proliferation in this compartment. This is consistent with previous evidence that secretory cell differentiation is impaired in dysplasia.

Matrilysin expression in the involuting rat ventral prostate

Matrilysin (PUMP-1) is a member of the matrix metalloproteinase (MMP) family of extracellular matrix degrading enzymes that has been found to be overexpressed in human prostate cancer. The rat ventral prostate (RVP) following castration has been used as a model for both tissue involution and apoptosis. Northern analysis and in situ hybridization were used to determine the time course and localization of matrilysin during 8 days of RVP involution. Northern analysis revealed that the 1.2 kb matrilysin mRNA was undetectable in normal RVP. An increase in the steady-state levels of matrilysin mRNA was observed 5 days after castration, and the levels began to decline by 8 days after castration. The mRNAs for tissue inhibitor of metalloproteinase-1 and urokinase-type plasminogen activator also showed a time-dependent induction during the course of involution. Localization of matrilysin by in situ hybridization indicated that the mRNA was produced by epithelial cells of the involuting RVP. The matrilysin message was observed in a small number of glands within the whole RVP. Matrilysin protein was present in the RVP and peaked 3 days after castration. The combination of proteinase genes expressed in the RVP following castration indicate that the MMP and serine protease families of enzymes may interact during tissue remodeling of the RVP following castration.

Tyrosine kinase inhibitor as a novel signal transduction and antiproliferative agent: prostate cancer

In prostate cancer cells, the binding of peptide growth factors to specific receptors increases tyrosine kinases (TK) activity to regulate cell proliferation, cell differentiation, and signaling processes. To determine whether inhibition of receptor TK activity inhibits tumor growth, we studied the effects of a tyrosine kinase inhibitor, RG-13022 (tyrphostin), on cultured human prostate cancer cells. RG-13022 significantly inhibited TGF alpha-induced phosphorylation of EGF receptor (EGFR). This compound inhibited TGF alpha-stimulated [3H]thymidine incorporation in a dose-dependent manner with IC50 being 30 microM. Clonogenicity in soft agar was reduced in the presence of RG-13022. Inhibitory effects were also observed in androgen-positive LNCaP cells and androgen-negative PC3 cells. RG-13022 not only inhibited TGF alpha-induced growth but also growth stimulated by epidermal growth factor (EGF), acidic fibroblast growth factor (aFGF) and serum. In addition, RG-13022 also blocked androgen-stimulated cell proliferation, suggesting that functioning TK pathways are required for androgen-induced growth. This novel synthetic inhibitor may be useful in providing a new strategy for future therapeutic intervention for prostate cancer.

Expression of fibroblast growth factor-8 in adult rat tissues and human prostate carcinoma cells

Androgens are essential for normal prostatic and testicular function. However, paracrine and/or autocrine actions of a number of growth factors have been implicated in the function of these tissues. A recent addition to the fibroblast growth factor family, the so called androgen-induced growth factor (AIGF) or fibroblast growth factor-8 (FGF-8), has been proposed to be under strict androgen regulation and induction in the mouse mammary carcinoma cell line SC3. FGF-8, therefore, may have a local role in the prostate, which is known to be an androgen-responsive organ. This study reports, for the first time, the presence of FGF-8 mRNA in normal adult rat tissues (heart, brain, lung, kidney, testis, prostate and ovary), using an optimised reverse transcription and nested polymerase chain reaction (RT-PCR) procedure, although androgen-dependent FGF-8 expression was not demonstrated in these adult tissues. Consistent with the oncogenic characteristics of FGF-8, the corresponding mRNA was detected in the human prostate tumour cell lines LNCaP and DU145. Because the DU145 cell line is known to be androgen-independent, and the expression of FGF-8 mRNA in cultured LNCaP cells also occurred in the absence of exogenous androgens, it can be concluded that the expression of FGF-8 mRNA in these human cell lines, in the rat prostate and in other rat tissues is not under the regulation of androgens as hitherto proposed.

Dual regulation of the epidermal growth factor family of growth factors in breast cancer by sex steroids and protein kinase C

There has been increased interest in the last few years in seeking a better understanding of the local regulation of polypeptide growth factors by systemic hormones, such as sex steroids and by polypeptide hormones. Growth factors and systemic hormones play pivotal roles in hormone-regulated cancers such as breast cancer. In this review, we discuss the regulation of members of the epidermal growth factor (EGF) family by sex steroids and by regulators of the polypeptide hormone signal transduction enzyme termed protein kinase C (PKC). Regulation of the EGF family of genes will be discussed as a model system to evaluate interactions between these two important types of regulatory pathways in breast cancer.

Influence of dihydrotestosterone, epidermal growth factor, and basic fibroblast growth factor on the cell kinetics of the PC3, DU145, and LNCaP prostatic cancer cell lines: relationship with DNA ploidy level

The cell kinetics (percentage of cells in the S+G2 phases of the cell cycle) and the DNA ploidy levels (nuclear DNA content) were determined in 108 samples each of the PC3, DU145, and LNCaP prostate cancer models. This was carried out by means of the digital cell image analysis of Feulgen-stained nuclei. Two to three hundred cell nuclei were analyzed for each of the 324 samples under study. The three cell lines were submitted to experimental conditions including the addition of dihydrotestosterone (DHT), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF), either alone or in combination, to the culture media. The results show that under the present culture conditions, the PC3 cell line was DHT-, EGF- and bFGF-insensitive. In contrast to what is generally reported in the literature, the DU145 cell line was DHT- and EGF-sensitive under the present culture conditions, but bFGF-insensitive. The LNCaP cell line was DHT-sensitive, but EGF- and bFGF-insensitive. While mainly tetraploid, the three cell lines nevertheless exhibited a significant level of heterogeneity in their nuclear DNA content distributions. Indeed, the proportions of non-tetraploid (diploid, hyperdiploid, triploid, hypertriploid, hypertetraploid, polymorphic) DNA histograms were 14% in the PC3, 16% in the DU145, and 29% in the LNCaP cell lines. These results suggest that the DNA ploidy level would not influence the hormone sensitivity level in the cell lines since they had significantly distinct hormone sensitivity profiles while remaining mainly tetraploid.

Urinary basic fibroblast growth factor in patients with bladder cancer and benign prostatic hypertrophy

OBJECTIVE

To investigate the role of urinary measurements of an angiogenic factor, basic fibroblast growth factor (bFGF), in the assessment of patients with bladder cancer.

PATIENTS AND METHODS

Urine from 83 patients was assayed using a commercially available ELISA for bFGF. Thirty-eight patients had a bladder tumour and 21 had a history of bladder cancer but no disease at the time of testing. Twenty-four patients acted as controls, 16 of whom were about to undergo transurethral resection of the prostate (TURP) for benign prostatic hypertrophy (BPH) and eight who had no urological disease.

RESULTS

Median urinary bFGF was higher in patients with active bladder cancer than in those with a clear cystoscopy (5.20 and 2.13 ng/g creatinine, respectively; P < 0.005). Median urinary bFGF was also elevated in patients about to undergo TURP (4.52 ng/g creatinine). Using a threshold value of 6.0 ng/g creatinine, the sensitivity of the test for detecting cancer was 42% and specificity was 88%. At a threshold value of 4.0 ng/g the sensitivity was 62% and the specificity 70%.

CONCLUSION

The relationship between urinary basic FGF and the presence of bladder cancer was significant. The test is not sufficiently sensitive or specific to use as a screening test for bladder cancer but may be very useful in monitoring the effectiveness of systemic therapies in bladder cancer. Elevated levels of bFGF in the urine of patients about to undergo TURP suggests a role for bFGF in the pathogenesis of BPH.

Benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a pathologic disorder that develops in response to the action of dihydrotestosterone on the aging prostate and to changes in stromal and epithelial cells in this exocrine gland. The current therapies for this disorder are chosen after other causes for irritative and obstructive symptoms have been excluded and the status of the urinary tract has been assessed. This evaluation includes a detailed medical history, a thorough genitourinary and neurological examination, assessment of serum prostate specific antigen and creatinine levels, as well as a urinalysis. A urodynamic evaluation consisting of a combined pressure-flow study is required if the diagnosis of obstruction is to be made. Patients with minimal symptoms and normal test results require no therapy. Mild to moderate symptoms can be controlled, at least temporarily, with alpha-adrenergic blockers such as terazosin or doxazosin. A subset of BPH patients with obstructive symptoms respond to the 5 alpha-reductase inhibitor finasteride. Early results with minimally invasive treatments such as laser prostatectomies, hyperthermia, and ultrasonic and radiofrequency ablation appear encouraging for those with moderate symptoms of prostatism. Severe symptoms, urinary retention, gross hematuria, recurrent urinary tract infections, bladder calculi, and hydronephrosis or renal insufficiency warrant transurethral incision, resection, vaporization, or open prostatectomy (for very large neoplasms). Although the morbidities of these latter surgical therapies are not insignificant, these treatments offer the best and most durable results for relief of obstruction and amelioration of symptoms.

Sex steroids and epidermal growth factor in benign prostatic hyperplasia (BPH)

Androgens provide the primary signal for the onset of DNA synthesis and cell division in normal prostate and benign prostatic hyperplasia (BPH). It is possible, however, that androgen mitogenic activity is in part indirect and mediated by peptide growth factors. In LNCaP cell lines, R1881 added to DCC-FCS medium increases DNA, epidermal growth factor (EGF) and EGF receptor (EGFR) levels: the antiandrogen hydroxy-flutamide prevents the increase of the growth factor and increases its receptor. In BPH tissue removed by transvesical prostatectomy, DHT, testosterone, 3 alpha-androstanediol and nuclear androgen receptors (AR) show a positive linear correlation with EGF: treatment with flutamide decreases significantly the EGF production. Androgens, therefore, represent important modulatory factors of prostatic EGF release. Moreover, androgens and EGF downregulate EGFR, which is probably internalized into the cell and degraded by lisosomes: in fact, a negative linear correlation between EGF, nuclear AR and the high- and low-affinity binding of EGFR is observed. These findings support the hypothesis that the growth-promoting effects of androgens in the prostate are in part mediated by peptide growth factors. The inhibitory effect of antiandrogens on prostatic cell proliferation may be the result of the decreased androgenic support and decreased EGF release and expression.