Binding of epidermal growth factor by human normal, hypertrophic, and carcinomatous prostate

The α1-adrenoceptor-mediated human hyperplastic prostate cells proliferation is impaired by EGF receptor inhibition

Benign prostatic hyperplasia (BPH) is an aging-related and progressive disease linked to an up-regulation of α₁-adrenoceptors. The participation of EGF receptors (EGFR) in the GPCRs' signalosome has been described but so far data about the contribution of these receptors to prostatic stromal hyperplasia are scanty. We isolated and cultured vimentin-positive prostate stromal cells obtained from BPH patients. According to intracellular Ca²⁺ measurements, cell proliferation and Western blotting assays, these cultured hyperplastic stromal cells express functional α_1-adrenoceptors and EGFR, and proliferate in response to the α_1-adrenoceptor agonist phenylephrine. Interestingly, in these cells the inhibition of EGFR signaling with GM6001, CRM197, AG1478 or PD98059 was associated with full blockage of α₁-adrenoceptor-mediated cell proliferation, while cell treatment with each inhibitor alone did not alter basal cell growth. Moreover, the co-incubation of AG1478 (EGFR inhibitor) with α_1A/α_1D-adrenoceptor antagonists showed no additive inhibitory effect. These findings highlight a putative role of EGFR signaling to α₁-adrenoceptor-mediated human prostate hyperplasia, suggesting that the inhibition of this transactivation cascade could be useful to reduce BPH progression.

NPM1 silencing reduces tumour growth and MAPK signalling in prostate cancer cells

The chaperone nucleophosmin (NPM1) is over-expressed in the epithelial compartment of prostate tumours compared to adjacent healthy epithelium and may represent one of the key actors that support the neoplastic phenotype of prostate adenocarcinoma cells. Yet, the mechanisms that underlie NPM1 mediated phenotype remain elusive in the prostate. To better understand NPM1 functions in prostate cancer cells, we sought to characterize its impact on prostate cancer cells behaviour and decipher the mechanisms by which it may act. Here we show that NPM1 favors prostate tumour cell migration, invasion and colony forming. Furthermore, knockdown of NPM1 leads to a decrease in the growth of LNCaP-derived tumours grafted in Nude mice in vivo. Such oncogenic-like properties are found in conjunction with a positive regulation of NPM1 on the ERK1/2 (Extracellular signal-Regulated Kinases 1/2) kinase phosphorylation in response to EGF (Epidermal Growth Factor) stimulus, which is critical for prostate cancer progression following the setting of an autonomous production of the growth factor. NPM1 could then be a target to switch off specifically ERK1/2 pathway activation in order to decrease or inhibit cancer cell growth and migration.

Action, localization and structure-function relationship of growth factors and their receptors in the prostate

Whereas the direct action of sex steroids, namely of androgens, on prostate cell division was questioned as early as in the 1970s, and remains so, the interest in prostatic growth factors (GFs) is rather recent but has expanded tremendously in the last five years. This lag period can be partly explained by the fact that, at the time, androgen receptors had just been discovered, and newly developed hormonal regimens or strategies to treat patients with prostate carcinoma (PCa) or epithelioma had generated great enthusiasm and hopes in the medical and scientific community. Another point to consider was the difficulty in maintaining prostate tissues in organ cultures and the relative novelty of culturing prostate epithelial cells in monolayers. Failures of sex steroids to elicit a direct positive response on prostate cell divisionin vitro, as seenin vivo, were interpreted as resulting from inappropriate models or culture conditions. However, the increasing number of reports confirming the lack of mitogenic activity of sex steroidsin vitro, coupled with the powerful mitogenic activity of GFs displayed in other systems, the discovery of GF receptors (GF-Rs), and the elucidation of their signalling pathways showing sex steroid receptors as potential substrates of GF-activated protein kinases gradually led to an increased interest in the putative role of GFs in prostate physiopathology. Of utmost importance was the recognition that hormone refractiveness was responsible for PCa progression, and for the poor outcome of patients with advanced disease under endocrine therapies. This problem remains a major issue and it raises several key questions that need to be solved at the fundamental and clinical levels.

Magmas expression in neoplastic human prostate

Magmas, is a 13-kDa mitochondrial protein which is ubiquitously expressed in eukaryotic cells. It was identified as a granulocyte-macrophage-colony stimulating factor (GM-CSF) inducible gene in hematopoietic cells and has a key role in the transport of mitochondrial proteins in yeast. Because GM-CSF receptor levels are elevated in prostate cancer, Magmas expression was examined in normal and neoplastic tissue. Magmas protein levels were barely detectable in non-neoplastic prostate glands. Increased amounts were observed in some samples of intraepithelial neoplasia. Approximately one half of the adenocarcinoma samples examined had weak Magmas expression, while the remainder had intermediate to high levels. The increased Magmas observed in malignant tissue was a result of higher protein expression and not from changes in mitochondrial content. Interestingly, in some patients, the normal prostate tissue had more Magmas message than the malignant portion. The results indicated that Magmas expression in prostate cancer is heterogeneous and independent of clinical stage and Gleason score. Further studies are needed to determine if Magmas expression has prognostic significance in prostate cancer.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Targeted inhibition of the epidermal growth factor receptor-tyrosine kinase by ZD1839 (?Iressa?) induces cell-cycle arrest and inhibits proliferation in prostate cancer cells

The epidermal growth factor (EGF) plays a role in the development of prostate cancer, which becomes essential after androgen resistance has emerged. The EGF receptor (EGFR) is therefore a potential target for anticancer therapy. We evaluated the effects of ZD1839 ('Iressa'), an orally active EGFR-tyrosine kinase inhibitor, on prostate cancer cell lines. The effects of ZD1839 were evaluated on the anchorage dependent and independent growth of androgen-responsive (LNCaP) and androgen-independent (DU145 and PC3) cells by a cell proliferation assay, cell counting, and soft agar analysis. Flow cytometric analysis and Western blotting were used to assess the effects on the cell-cycle and on protein expression levels, respectively. ZD1839 caused a dose- and time-dependent growth inhibition in all three cell lines. A dose-dependent supra-additive increase in growth inhibition was observed when ZD1839 was combined with the antiandrogen flutamide or ionizing radiation (IR). The antiproliferative effect of ZD1839 was mainly cytostatic and associated with a block in the G(0)/G(1) phase of the cell-cycle, evident after about 12 h of treatment. In the DU145 cells this block was associated with an increase in expression of the CDK inhibitor p27(Kip1), both in the cytoplasmic and nuclear fractions. The increase in p27(Kip1) was not evident in the LNCaP and PC3 cells. No changes were observed in the expression of cyclin D1 protein. These results demonstrate the antiproliferative effects of ZD1839 on the growth of prostate cancer cells and suggest that inhibition of EGFR-associated signal transduction pathway might represent a promising novel therapeutic strategy for the treatment of prostate cancer.

Androgen and retinoic acid interaction in LNCaP cells, effects on cell proliferation and expression of retinoic acid receptors and epidermal growth factor receptor

BACKGROUND

Modulation of the expression of retinoic acid receptors (RAR) alpha and gamma in adult rat prostate by testosterone (T) suggests that RAR signaling events might mediate some of the androgen effects on prostate cells.

METHOD

In this study, we examined the interactions between T and retinoic acid (RA) in cell growth of human prostate carcinoma cells, LNCaP, and their relationship with the expression of RAR and epidermal growth factor receptor (EGF-R).

RESULTS

Both T and RA, when administered alone, stimulated 3H-thymidine incorporation in LNCaP cells in a dose-dependent manner; the effect of each agent was reciprocally attenuated by the other agent. Testosterone treatment of LNCaP cells also resulted in dose dependent, biphasic increases in RAR alpha and gamma mRNAs; increases paralleled that of 3H-thymidine incorporation and were attenuated by the presence of 100 nM RA. These results suggest a link between RAR signaling and the effect of T on LNCaP cell growth. Gel electrophoretic mobility shift assays revealed the presence of putative androgen responsive element (ARE) in the promoter region of RAR alpha gene, suggesting that a direct AR-DNA interaction might mediate the effects of T on RAR alpha gene. Furthermore, treatment of LNCaP cells with 20 nM T resulted in an increase in EGF-R. In contrast, EGF-R was suppressed by 100 nM RA that also suppressed the effect of T.

CONCLUSIONS

Current results demonstrate interactions between T and RA in the expression of RARs and cell growth in LNCaP cells. The presence of putative ARE in the promoter of the RAR alpha gene suggests that AR-DNA interaction might mediate the effects of T on RAR alpha gene. The opposite effects of T and RA on the expression of RAR and EGF-R suggest that signal events of these receptors might be involved in the interaction between T and RA in the control of LNCaP cell growth.

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.

Endocrine treatment in prostate cancer

Over its natural course, prostate cancer is a heterogeneous tumour with a generally slow but constant rate of growth. The androgen dependence of the prostate gland was demonstrated more than half a century ago by the landmark studies of Professor C. Huggins and colleagues. They established that androgens are implicated not only in growth regulation of the normal gland but also in the pathogenesis of prostate cancer, and that this malignant tissue retains some degree of androgen dependence. This concept was supported by studies of symptomatic clinical cancer, with androgen ablative therapy bringing relief to the patient in more than 80% of the cases. The classical treatment consisted of either bilateral orchiectomy, or administration of diethylstilbestrol (DES). Other forms of therapy followed, involving successive waves of new compounds that either withdrew androgen support from the cancer or blocked the androgens from their receptors in the prostate cancer cells. Chronologically, the progestagens can be well recognised, with one in particular: The successful derivative, cyproterone acetate (CPA). There also have been a number of oral vs. parenteral estrogens, the development of the luteinizing hormone-releasing hormone agonists (LH-RHA), the introduction of the non-steroidal anti-androgens characterised by flutamide and casodex, and more recently, the introduction of the LH-RHA. Moreover, there have been multiple possible forms of combination treatment to obtain maximal androgen blockade (MAB). However, no major differences in treatment outcome have been reported during the last 5 decades and most treatment choices have been based on tradition, associated side effects, the preferences of a particular doctor and patient, together with economic considerations. Furthermore, endocrine treatment has never been shown to cure clinical prostate cancer, which consequently has led to initiatives to defer endocrine treatment or to use it intermittently or use it as a form of neo-adjuvant or adjuvant treatment with surgery or radiotherapy. The history of endocrine therapy is replete with clinical trials that do not represent the patient population in general, and these trials share the clinical fact that they ignore the 20% to 30% of all patients who lack an initial response to a given endocrine treatment. Thus, it is no wonder that prognostic factors determine the outcome more than the treatment itself. Important to current endocrine treatment, however, is the shift to earlier stages of prostate cancer at initial diagnosis. Integration of endocrine treatment at this earlier phase in the pathogenesis of prostate cancer will substantially alter the treatment strategy in relation to long-term benefit with regard to survival, associated side effects, and costs. This complex adjustment is enhanced by recent discoveries in the molecular biology of the prostate which show, on the one hand, that the dihydrotestosterone-androgen receptor (DHT-AR) complex is important in the regulation of gene expression, but also that a number of intrinsic factors (e.g., peptide growth regulatory factors) can, through various paracrine, autocrine or intracrine interactions, exercise a major influence on cellular homeostasis and the regulation of prostatic growth.

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.

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.

Comparative analysis of epidermal growth factor receptor mRNA levels in normal, benign hyperplastic and carcinomatous prostate

Epidermal growth factor receptor (EGFR), a mediator of mitogenic activity of epidermal growth factor and transforming growth factor-alpha, has been shown to be associated with tumour progression. We have detected a level of EGFR transcript in normal, hyperplastic (BPH) and carcinomatous (CaP) prostate tissues by cytoplasmic dot hybridization. Our results show that the majority of CaP cases (62% of untreated cases and 71% of treated cases) were positive for EGFR mRNA while about 50% of normal and BPH cases were positive for EGFR mRNA. The level of EGFR transcript was significantly higher in the untreated CaP group as compared to the normal group (P < 0.05), while the difference in the normal and BPH groups was not statistically significant.

Regulation of EGF-receptor expression by EGF and TGF alpha in epidermoid cancer cells is cell type-specific

The epidermal growth factor receptor (EGF-R) and its major ligands EGF and transforming growth factor alpha (TGF alpha) play an important role in the development of multiple human tumors. However, little is known of the comparative effects of each ligand on the regulation of EGF-R expression. To investigate this issue we used two similar human epidermoid cancer cell lines that overexpress EGF-Rs (KB and A431). In KB cells, EGF and TGF alpha increased EGF-R mRNA and protein levels by 2-3 fold over 8 h, associated with a greater than 4-fold stabilization of EGF-R mRNA half-life. EGF and TGF alpha also increased transcription of EGF-R mRNA 2-3-fold in KB cells. In contrast, EGF and TGF alpha only minimally increased EGF-R mRNA and protein in A431 cells, without changing EGF-R mRNA half-life. Basal EGF-R mRNA half-life was 2 fold greater in A431 cells than in KB cells (6-7 h versus 2-3 h), whilst the half-life of a mutant 2.6 kb EGF-R mRNA present in A431 cells, which lacks the 3-untranslated region (3'-UTR), was 2 fold greater than the full-length EGF-R mRNA. RNA gel-shift studies demonstrated that KB and A431 cells contain cytoplasmic proteins that bind specifically to an AU-rich sequence from the 3'-UTR of EGF-R mRNA. Taken together, these results demonstrate that in KB cells EGF and TGF alpha upregulate EGF-R expression at both transcriptional and post-transcriptional levels. The identification of AU-rich EGF-R mRNA-specific RNA-binding proteins from epidermoid cancer cells that overexpress EGF-Rs suggests that regulated RNA-protein interactions involving this region may play a central role in modulating EGF-R mRNA stability.

Epidermal growth factor receptor activation in androgen-independent but not androgen-stimulated growth of human prostatic carcinoma cells

These studies were undertaken to assess the relative expression and autocrine activation of the epidermal growth factor receptor (EGFR) in normal and transformed prostatic epithelial cells and to determine whether EGFR activation plays a functional role in androgen-stimulated growth of prostate cancer cells in vitro. EGFR expression was determined by Western blot analysis and ELISA immunoassays. Immunoprecipitation of radiophosphorylated EGFR and evaluation of tyrosine phosphorylation was used to assess EGFR activation. The human androgen-independent prostate cancer cell lines PC3 and DU145 exhibited higher levels of EGFR expression and autocrine phosphorylation than normal human prostatic epithelial cells or the human androgen-responsive prostate cancer cell line LNCaP. PC3 and DU145 cells also showed higher levels of autonomous growth under serum-free defined conditions. Normal prostatic epithelial cells expressed EGFR but did not exhibit detectable levels of EGFR phosphorylation when cultured in the absence of exogenous EGF. Addition of EGF stimulated EGFR phosphorylation and induced proliferation of normal cells. LNCaP cells exhibited autocrine phosphorylation of EGFR but did not undergo significant proliferation when cultured in the absence of exogenous growth factors. A biphasic growth curve was observed when LNCaP cells were cultured with dihydrotestosterone (DHT). Maximum proliferation occurred at 1 nM DHT with regression of the growth response at DHT concentrations greater than 1 nM. However, neither EGFR expression nor phosphorylation was altered in LNCaP cells after androgen stimulation. In addition, DHT-stimulated growth of LNCaP cells was not inhibited by anti-EGFR. These studies show that autocrine activation of EGFR is a common feature of prostatic carcinoma cells in contrast to normal epithelial cells. However, EGFR activation does not appear to play a functional role in androgen-stimulated growth of LNCaP cells in vitro.

Epidermal growth factor-related peptides in human prostatic fluid: sources of variability in assay results

BACKGROUND

Prostatic fluid (PF) provides a unique medium for noninvasive evaluation of critical growth and differentiation signals in the prostatic microenvironment. The purpose of this study was to establish the feasibility of measuring two prostatic mitogens, epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) in PF, and specifically to quantify extraneous variability attributable to the assay itself, sample handling, or biological variation within an individual over time.

METHODS

PF was collected by transrectal massage from consecutive patients attending a urology clinic. Pooled PF and individual samples from 25 men with stable benign prostatic hyperplasia (BPH) were analyzed for EGF and TGF-alpha by radioimmunoassay and for total protein.

RESULTS

Reproducibility was adequate at dilutions as low as 1:50 (2-microliter pooled sample) and 1:5 (20 microliters) for EGF and TGF-alpha, respectively. Results were not affected by freeze-thaw cycles, time in storage, or protease inhibition in fresh PF. EGF and TGF-alpha were detectable in 100% and 92% of individual men, with respective means of 152 and 0.2 ng/ml. Correlations between two samples obtained from the same man within 12 months were highly significant (EGF r = 0.89, TGF-alpha r = 0.71). Protein concentrations were consistent over time; expression of either peptide per weight of protein rather than per volume did not improve within-man correlation. Between-man variability far exceeded within-man variability for both peptides, and was estimated to account for 84% and 61% of the total variability in EGF and TGF-alpha, respectively. There was no correlation between EGF and TGF-alpha in the same samples.

CONCLUSIONS

We conclude that men with BPH secrete consistent and distinct levels of EGF-related peptides in PF, and that these levels can be detected with acceptable sensitivity and precision by radioimmunoassay (RIA). Measurement of TGF-alpha, which has not been reported previously, requires a relatively larger sample.

Luteinizing hormone-releasing hormone antagonist Cetrorelix (SB-75) and bombesin antagonist RC-3940-II inhibit the growth of androgen-independent PC-3 prostate cancer in nude mice

BACKGROUND

Hormones like bombesin (BN)/gastrin-releasing peptide (GRP) and luteinizing hormone-releasing hormone (LH-RH) and growth factors such as epidermal growth factor (EGF) might be involved in the relapse of prostate cancer under androgen ablation therapy. Interference with receptors for BN/GRP, LH-RH, or EGF might provide a therapeutic approach to inhibit tumor growth of androgen-independent prostate cancer.

METHODS

LH-RH antagonist Cetrorelix (SB-75) and the BN/GRP antagonist RC-3940-II were tested for their effects on the growth of the androgen-independent PC-3 human prostate cancer cell line xenografted into nude mice. Tumor growth, serum hormone levels, and receptor concentrations for BN/GRP and EGF were measured.

RESULTS

When the treatment was started, tumor volume in all groups was 70-80 mm3. After 4 weeks, tumor volume in the control animals injected with saline was 871 +/- 233 mm3 and that of animals treated with Cetrorelix only 197 +/- 61 mm3. The BN/GRP antagonist RC-3940-II also significantly reduced PC-3 tumor volume in nude mice to 122 +/- 20 mm3. The combination of Cetrorelix and RC-3940-II produced no additional inhibition. High-affinity receptors for EGF were detected in the tumor membranes and their number was significantly decreased after administration of Cetrorelix or RC-3940-II.

CONCLUSIONS

These findings demonstrate that LH-RH antagonists and BN/GRP antagonists inhibit the growth of the androgen-independent prostate cancer cell line PC-3 in vivo. Both analogs may exert a direct inhibitory effect on tumor growth through a down-regulation of EGF receptors.

Comparative studies of the mitogenic effects of epidermal growth factor and transforming growth factor-alpha and the expression of various growth factors in neoplastic and non-neoplastic prostatic cell lines

BACKGROUND

The role of growth factors in prostate cell growth has been investigated as these peptides may be involved in the autonomous growth of hormone-independent prostate cancer.

METHODS

Responses of neoplastic (PC-3 and CPA) and non-neoplastic (CAPE) prostatic cell lines to epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) were determined using clonogenic and growth curve analysis. The constitutive expression of EGF, TGF-alpha, and TGF-beta 1-3 mRNA was examined using Northern blotting and EGF and TGF-alpha protein levels were determined immunohistochemically.

RESULTS

Growth curve and clonogenic analysis indicated that EGF and TGF-alpha were mitogenic in each cell line. The magnitude of the clonogenic response varied between the cell lines, with CPA cells showing the greatest growth increases. CPA cells also displayed the highest levels of EGF and TGF-alpha mRNA and protein. TGF-beta 1 mRNA was detected in the order of magnitude, PC-3 > CPA > CAPE. Furthermore, PC-3 and CPA cells expressed TGF-beta 3 and TGF-beta 2 transcripts respectively. In each cell line, the expression of any growth factor mRNA was not affected by exogenous EGF.

CONCLUSIONS

The growth responses of the cell lines to EGF and TGF-alpha did not correlate with their constitutive levels of EGF and TGF-alpha mRNA and protein, thus whilst growth factors may be important in malignant cell growth, other pathways may also be involved in the autocrine regulation of cell proliferation.

The expression of receptors for estrogen and epithelial growth factor in the male rabbit prostate and prostatic urethra following castration

In the lower urinary tract of the male rabbit, estrogen receptors (ERs) are restricted to the urethra and the prostatic stroma. At present, the function of ERs in these tissues is not known. Epithelial growth factor (EGF) stimulates proliferation of epidermal and epithelial tissues, and several animal studies have indicated that EGF is regulated by estrogen. On this background, we have studied the effect of castration on the expression of ERs and EGF receptors in the rabbit prostatic urethra and prostate. Twelve male rabbits were studied fourteen days after castration, and eight normal rabbits were included as controls. In the control group, ERs were found in the urothelial lining and lamina propria of the prostatic urethra, and in the prostatic stroma. EGF receptors were demonstrated in the epithelial lining of the prostatic urethra and the glandular epithelium of the prostate. Following castration, the expression of ERs, assessed as the increase in the number of positively stained specimens, increased significantly in the lamina propria of the prostatic urethra and the prostatic stroma. EGF receptor expression increased significantly in the epithelial lining of the prostatic urethra. In the prostate, the increase was not significant. The results give no support to the view that ERs play role in the regulation of EGF receptors in the rabbit prostatic urethra nor the prostate.

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.

Differential gene expression of transforming growth factors alpha and beta, epidermal growth factor, keratinocyte growth factor, and their receptors in fetal and adult human prostatic tissues and cancer cell lines

OBJECTIVES

Recent studies have shown that growth factors may play a role in the etiology of benign prostatic hyperplasia (BPH) and prostatic carcinoma. Several growth factors have been reported to be expressed by prostatic tissues, but these growth factors have never been examined in human fetal prostate and compared with adult prostates and cancer cell lines. The present study was designed to investigate the messenger ribonucleic acid (mRNA) expression of transforming growth factor (TGF)-alpha, TGF-beta 1, TGF-beta 2, TGF- beta 3, keratinocyte growth factor (KGF), epidermal growth factor (EGF), EGF receptor (EGF-R), and KGF receptor (KGF-R) in human fetal and adult prostatic tissues and cancer cell lines by reverse-transcriptase-polymerase chain reaction-(RT-PCR) using specific oligonucleotide primers.

METHODS

Total RNA was extracted from human fetal and adult prostates (BPH tissues) and cancer cell lines. The gene expression of these growth factors and their receptors was determined by RT-PCR using specific oligonucleotide primers.

RESULTS

The results of these experiments suggest that: (1) human fetal prostate expressed mRNA transcripts for TGF-alpha, TGF-beta 1, TGF-beta 2, TGF-beta 3, and EGF. However, KGF, KGF-R, and EGF-R mRNA were not expressed by human fetal prostate; (2) human adult prostate (BPH tissues) showed mRNA transcripts for all growth factors and their receptors except KGF-R; (3) human BPH-1 cell lines expressed mRNA transcripts for TGF-alpha, TGF-beta 1, TGF-beta 2, TGF-beta 3, EGF, and KGF-R, but not for EGF-R and KGF growth factors; (4) human primary prostate cancer cell line (ND-1) showed mRNA transcripts for all growth factors except EGF and KGF; and (5) human prostate cancer cell lines (LNCaP, DU-145, PC-3) expressed mRNA transcripts for all growth factors except KGF, which was absent in all cell lines. However, KGF-R mRNA was absent in the PC-3 prostate cancer cell line.

CONCLUSIONS

These results suggest that the differential gene expression for various growth factors and their receptors in human fetal and adult prostatic tissues and cancer cell lines may be important in understanding the role of these factors in the pathophysiology of prostatic diseases.

EGF receptor signaling enhances in vivo invasiveness of DU-145 human prostate carcinoma cells

Carcinomas of the prostate and other lineages often present an autocrine stimulatory loop acting via the EGF receptor (EGFR). We have recently shown that EGFR-mediated signals enhance DU-145 prostate carcinoma cell transmigration of an extracellular matrix in vitro, and that this increased invasiveness was independent of proteolytic degradation of the matrix (Xie et al., 1995, Clin Exp Metastasis, 13, 407). To determine whether up-regulated EGFR signaling promotes tumor progression in vivo and to define the EGFR-induced cell property responsible, we inoculated athymic mice with genetically-engineered DU-145 cells. Parental DU-145 cells and those transduced to overexpress a full-length wild type (WT) EGFR formed tumors and metastasized to the lung when inoculated in the prostate and peritoneal cavity. The WT DU-145 tumors were more invasive. DU-145 cells expressing a mitogenically-active, but motility-deficient (c'973) EGFR formed small, non-invasive tumors without evidence of metastasis. All three sublines demonstrated identical, EGFR-dependent rates of cell growth in vitro, suggesting that the differential invasiveness was not due to altered growth rates. To determine whether cell motility may be, in part, responsible for tumor invasiveness, we treated WT DU-145 intraperitoneal tumors with a pharmacologic agent (U73122) which blocks EGFR-mediated cell motility but not mitogenesis. Under this treatment regimen, the WT DU-145 cells formed tumors of similar numbers and size to those formed without treatment; however, these tumors were much less invasive. These data suggest that EGFR-mediated cell motility is an important mechanism involved in tumor progression, and that this cell property may represent a novel target to limit the spread of tumors.

Molecular biology of prostatic intraepithelial neoplasia

High-grade PIN is the most likely precursor of prostatic adenocarcinoma, according to virtually all available evidence to date. The clinical importance of recognizing PIN is based on its strong association with prostatic carcinoma. PIN has a high predictive value as a marker for adenocarcinoma. Its identification in biopsy specimens of the prostate warrants further search for concurrent invasive carcinoma. PIN is associated with progressive abnormalities of phenotype and genotype intermediate between normal prostatic epithelium and cancer, indicating impairment of cell differentiation and regulatory control with advancing stages of prostatic carcinogenesis. There is progressive gain or loss of a wide variety of biomarkers, including morphometric markers, differentiation markers, stromal markers, growth factors and associated receptors, oncogenes, tumor suppressor genes, and chromosomes. Abnormalities in expression of most biomarkers are amplified in the progression from high-grade PIN to localized cancer, metastatic cancer, and hormone-refractory cancer. Oncogenesis of prostatic carcinoma probably occurs through the selection of several genetic changes, each modifying the expression or function of genes controlling cell growth and differentiation. Further studies are needed to evaluate the function and prognostic value of oncogene expression in the normal, preneoplastic, and neoplastic prostate.

Regulation of prostatic growth and function by peptide growth factors

Polypeptide growth factors are positive and negative regulators of prostatic growth and function. Expression and biological effects of epidermal growth factor (EGF), transforming growth factors (TGFs) alpha and beta, fibroblast growth factors (FGFs), and insulin-like growth factors (IGFs) in the prostate have been extensively studied. EGF and TGF alpha, which share the same receptor, are strong mitogens for prostatic epithelial and stromal cells. Their paracrine mode of action in normal tissue and early-stage tumors is apparently altered towards an autocrine stimulation in hormone-independent tumors, which gain the ability to produce TGF alpha by themselves. TGF beta has a dual role in the regulation of prostatic growth. It inhibits growth of prostatic epithelial cells in culture and mediates programmed cell death after androgen withdrawal. However, advanced prostatic carcinomas become insensitive to the inhibitory effect of TGF beta. Several members of the FGF family have been identified in the prostate. They are mainly or exclusively expressed in the stromal cells, and stimulate the epithelial cells. In the rat Dunning tumor model, progression is accompanied by distinct changes in the expression of FGFs and their receptors. In the hyperplastic tissue, basic FGF (bFGF) is accumulated. This growth factor is also a potent angiogenic inducer, expression of which may determine the metastatic capability of a tumor. IGFs are paracrine growth stimulators in the normal and hyperplastic prostate. It is still under consideration whether prostatic cancer cells gain the ability to produce IGF-I by themselves and thus shift to an autocrine mode of IGF-I stimulation. Growth factors also interact with the androgen-signaling pathway. IGF-I in particular, other growth factors as well, can activate the androgen receptor.

In vitro invasiveness of DU-145 human prostate carcinoma cells is modulated by EGF receptor-mediated signals

Prostate carcinomas often present an autocrine stimulatory loop in which the transformed cells both express the EGF receptor (EGFR) and produce activating ligands (TGF alpha and EGF forms). Up-regulated EGFR signalling has been correlated with tumor progression in other human neoplasia; however, the cell behaviour which is promoted remains undefined. To determine whether an EGFR-induced response contributes to cell invasiveness, we transduced DU-145 human prostate carcinoma cells with either a full-length (WT) or a mitogenically-active but motility-deficient truncated (c'973) EGFR. The DU-145 Parental and two transgene sublines all produced EGFR and TGF alpha, but the transduced WT and c'973 EGFR underwent autocrine downregulation to a lesser degree, with more receptor remaining intact. DU-145 cells transduced with WT EGFR transmigrated a human amniotic basement membrane matrix (Amgel) to a greater extent than did Parental DU-145 cells (175 +/- 22%). Cells expressing the c'973 EGFR invaded through the Amgel only to about two thirds the extent of the Parental cells (62 +/- 23%). A monoclonal antibody which prevents ligand-induced activation of EGFR decreased the invasiveness of WT-expressing cells by half and Parental cells by a fifth, but had little effect on the invasiveness of c'973-expressing cells; with the result that in the presence of antibody, all three cell lines transmigrated the Amgel to the same extent. The different levels of invasiveness between the three sublines were independent of cell proliferation. These findings demonstrated that EGFR-mediated signals increase tumor cell invasiveness and suggested that domains in the carboxy-terminus are required to signal invasiveness. As an initial investigation into the mechanisms underlying the EGFR-mediated enhanced invasiveness, we determined whether these cells presented different collagenolytic activity, as the major constituents of Amgel are collagen types I and IV. All three sublines secreted easily detectable levels of gelatin-directed proteases and TIMP-1, with WT cells secreting equivalent or lower levels of proteases. The proteolytic balance in these cells did not correlate with invasiveness. These data suggest that the TGF alpha-EGFR autocrine loop promotes invasiveness and that this is accomplished by signalling cell properties other than differential secretion of collagenolytic activity.

Epidermal growth factor-related peptides and the epidermal growth factor receptor in normal and malignant prostate

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) are two closely related peptides that interact with cell-surface epidermal growth factor receptors (EGFR) to induce receptor tyrosine phosphorylation and activation of intracellular signal-transduction pathways. EGF appears to be the predominant EGF-related growth factor in the normal prostate and in benign prostatic hyperplasia (BPH). Evidence indicates that EGF and TGF alpha are important for maintainence of the structural and functional integrity of the benign prostatic epithelium. The EGF-related peptides are primarily localized to the secretory epithelium of the benign prostate, and their production and secretion is augmented by the presence of circulating androgens. EGFR are located in the basal/neuroendocrine (NE) compartment of the benign prostate and exhibit relatively androgen-independent expression. The EGF-related peptides and EGFR are also present in neoplastic prostatic tissues. There is currently no direct evidence to implicate EGFR activation in the pathogenesis of BPH. However, the EGF-related peptides appear to play a functional role in the growth of prostatic carcinoma cells, with TGF alpha being the predominant growth factor. Numerous investigators have demonstrated the functional significance of a TGF alpha/EGFR-mediated autocrine growth pathway in cultured prostatic carcinoma cells. Studies of cultured prostate cancer cells, but not normal epithelial cells, demonstrate constitutive activation of EGFR. Androgen-independent cancer cells exhibit more EGFR expression and phosphorylation than do androgen-responsive prostate cancer cells. Most studies indicate that EGFR do not play a functional role in androgen-stimulated growth of prostate cancer cells. Several studies have correlated EGFR expression with increased nuclear size and tumor dedifferentiation. Future studies should focus on determining both the prognostic significance of EGFR expression and whether manipulation of EGFR-mediated growth can be exploited for therapeutic benefit in human prostate cancer.

Recurrent cytogenetic alterations of prostate carcinoma and amplification of c-myc or epidermal growth factor receptor in subclones of immortalized PNT1 human prostate epithelial cell line

To develop an experimental prostate cancer model, we immortalized normal human prostate adult epithelial cells with SV40 large-T antigen. Two sublines were derived in culture, namely PNT1A and PNT1B. They retained the characteristics of prostate epithelial cells, but did not clone in soft agarose. PNT1A occasionally formed undifferentiated adenocarcinoma tumors in nude mice, but only in the presence of matrigel. PNT1A and PNT1B displayed common cytogenetic alterations: a 10q arm deletion, which is a recurrent alteration in prostate carcinoma, chromosome losses and a translocation involving chromosome 5. An extensive study of oncogenic alterations occurring in these cells showed that PNT1A displayed c-myc gene amplification, forming an hsr on chromosome 4, as well as gene amplification, forming an hsr on chromosome 4, as well as c-myc mRNA overexpression, with a faster doubling time (25 hr); moreover, it seemed less sensitive to EGF than PNT1B. PNT1B had a doubling time identical to that of normal cells (48 hr) but displayed EGF receptor gene amplification accompanied by an increased number of EGF binding sites and sensitivity to EGF. Because both cell lines displayed cytogenetic and oncogenic alterations found in prostate cancer, as well as differing malignant potentials, they represent an interesting model for studying the progression of prostate tumors.

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.

Epidermal growth factor receptor content in rat prostatic adenocarcinoma: effects of endocrine treatment

Epidermal growth factor receptor (EGF-R) was studied in Dunning prostatic cancer models using competitive binding assays and solution hybridization assay. EGF-R-binding capacity and mRNA were demonstrated in a hormone-sensitive R3327 prostatic tumor from both control and castrated animals while no such activity was found in the hormone-independent AT-1 tumors. Castration induced no quantitative changes in the EGF-R. Estrogen treatment induced a significant reduction of the binding capacity of EGF-R and its mRNA. It was concluded that EGF-R is present in the androgen-sensitive Dunning prostatic tumor models (R3327), but that the androgen-insensitive, undifferentiated AT-1 tumor lacks EGF-R expression. Endocrine treatment has no significant effect on the EGF-R in these tumor models.

Zonal biochemical and morphological characteristics in BPH

OBJECTIVE

To compare androgen, oestrogen, progesterone and epidermal growth factor receptor concentrations in the transition zone and peripheral zone of the prostate in benign prostatic hyperplasia (BPH), and to relate these findings to epithelial and stromal composition.

PATIENTS AND METHODS

Tissue from both the transition and peripheral zone of the prostate was obtained from 26 patients undergoing transurethral prostatectomy for benign prostatic obstruction and used for both receptor binding studies and morphometric analysis. Androgen receptor (AR), oestrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor (EGFR) concentrations were assayed by saturation binding with a competitive inhibitor. The epithelial, stromal and luminal composition of the tissue was determined using a Zeiss AxioHOME microscope workstation.

RESULTS

The epithelial content was significantly greater in the transition zone than in the peripheral zone. No overall zonal difference in AR concentration was detected; however, when values were expressed relative to the epithelial component, the AR content was significantly higher in the peripheral zone. Conversely, overall EGFR concentrations were significantly greater in the transition zone, although not when expressed per unit epithelium. Higher concentrations of oestrogen receptor were measured in the transition zone per unit stroma. No zonal difference in PR was detected. However, there was a significant correlation between AR and PR in the peripheral zone and between EGFR and AR in the transition zone.

CONCLUSION

These data demonstrate that receptor concentrations should be related to tissue composition. Concentrations of AR were higher in the peripheral zone epithelium than in transition zone epithelium, suggesting greater androgen dependence. This may be important in determining its greater propensity for malignancy. Although EGFR concentrations were greater in the transition zone, there was no zonal difference after correction for the amount of epithelium. Finally, higher concentrations of ER were detected in the transition zone stroma which may reflect important zonal differences in regulating growth and provides further evidence of a role for oestrogens in BPH.

Analysis of cell death and cell proliferation in embryonic stages, normal adult, and aging prostates in human and animals

Homeostasis in the prostate is recognized to be maintained by a complex interplay between the opposing actions of cell proliferation and cell death. Growth regulatory factors that promote or inhibit cell proliferation and promote cellular death have been identified in the prostate. The integration of these forces involves cellular cooperation between the prostatic stroma and epithelium. Hormone-regulated production of growth regulatory factors by one cell type may determine growth stimulation, inhibition, or cell death in a reciprocal cell partner. Imbalance between net cell proliferation and net cell death rates may result in abnormal growth leading to BPH. Additional study of the growth regulatory factors associated with distal vs. proximal epithelial cells and stroma and comparison of growth factor expression by the neonatal, postnatal growing, adult quiescent, and aging prostates will likely provide further insight into the regulation of prostate cell division and death.

Comparative analysis of epidermal growth factor receptor gene expression and protein product in benign, premalignant, and malignant prostate tissue

In order to more clearly define the status of epidermal growth factor receptor (EGFR) in prostate cancer, expression of EGFR transcript and protein was analyzed in paired samples of benign and malignant tissues from 30 radical prostatectomy specimens. Prostate tumors and high grade prostatic intraepithelial neoplasias (PINs) expressed significantly less EGFR protein than benign tissues or low grade PINs (P < 0.001). Expression of EGFR mRNA was analyzed in a subset of the same samples, and was higher in more prostate tumors than benign specimens (P < 0.05). However, differences in mean mRNA expression between malignant and benign tissues were not significant. EGFR mRNA was expressed at moderate or low levels in equivalent numbers of PIN lesions. These results suggest that, although EGFR mRNA expression is somewhat elevated in prostate tumors, EGFR protein expression may be down-regulated in the same malignant tissues. Furthermore, our data demonstrate phenotypic similarity between prostate tumors and high grade PIN at the level of EGFR protein expression.

Differential immunoreactivity of transforming growth factor alpha in benign, dysplastic and malignant prostatic tissues

Immunohistochemical examination of radical prostatectomy specimens from 57 patients was performed to determine the differential expression of transforming growth factor alpha in the human prostate. In addition, epidermal growth factor receptor (EGFr) immunoreactivity was assessed in each case. Stromal versus epithelial staining was determined for each histological subtype: benign prostatic hypertrophy (BPH), prostatic intra-epithelial neoplasia (PIN), and prostatic cancer (CaP) by a single pathologist reviewer. TGFa staining was predominant in stroma while EGFr was localized to the epithelial basal cell layer. Immunoreactivity of both TGFa (P = 0.002) and EGFr (P < 0.001) revealed a significant reduction in CaP compared to BPH or PIN. Autocrine stimulation of EGFr by TGFa or other unrecognized factors may be present in CaP. Conversely, altered stromal influence of CaP via TGFa may be present. These observations could form the basis for future cancer therapeutic strategies using antagonist factors.

Prognostic value of c-erbB-2 and epidermal growth factor receptor in stage A1 (T1a) prostatic adenocarcinoma

OBJECTIVE

To determine whether the presence or absence of the oncoproteins epidermal growth factor receptor (EGFR) and c-erbB-2 could predict tumour behaviour.

PATIENTS AND METHODS

Tissue from 45 stage A1 (T1a) prostatic adenocarcinomas from patients with a mean age of 65 years were immunostained for EGFR (12E) and c-erbB-2 (NCL-CB11). Their expression in the tumour and surrounding benign hyperplastic epithelium was correlated with each other and with survival.

RESULTS

Forty percent (18 of 45) and 36% (16 of 45) of patients respectively were EGFR and c-erbB-2 positive in the tumour. Expression of these tyrosine kinase oncogenes was not confined to the tumour and the surrounding hyperplastic prostate was also positive for EGFR in 76% (34/45) of patients and for c-erbB-2 in 16% (11 of 45). EGFR and c-erbB-2 expression was weakly associated in both benign and malignant epithelium. Statistical analysis of survival showed that tumour c-erbB-2 expression was associated with a significantly worse prognosis (exact two tailed P = 0.0316), whereas no significant association was observed between EGFR expression and survival (P = 0.737).

CONCLUSION

As c-erbB-2 expression increases the rate of dying by 4.2 times, recording its expression by these tumours may be useful in selecting patients who would benefit from treatment in stage A1 (T1a) disease.

Overexpression of human epidermal growth factor receptor and c-erbB-2 by neuroendocrine cells in normal prostatic tissue

OBJECTIVE

It has been suggested that prostatic neuroendocrine (NE) cells play an important role in the growth and differentiation of the prostate by secreting various neuropeptides and serotonin. However, the mechanism by which NE cells themselves are regulated is virtually unknown. In the present study we evaluated the expression of the human epidermal growth factor receptor (EGFR) family (HER) in prostatic NE cells.

METHODS

Formalin-fixed, paraffin-embedded tissue sections from twenty radical prostatectomy specimens were immunostained with validated rabbit polyclonal antibodies raised against human EGFR and c-erbB-2, using the streptavidin-peroxidase enzyme conjugate method.

RESULTS

A strong immunoreactivity was observed with both antibodies in the cytosol of a few epithelial cells. These cells frequently had a dendritic appearance and were located in the acini and ducts. The EGFR-positive cells were predominant in most cases. Double immunostaining revealed the colocalization of both antigens with chromogranin A, a polypeptide that is expressed by most NE cells. Moreover, EGFR and c-erbB-2 appeared to be colocalized as well as independently expressed by different subpopulations of NE cells.

CONCLUSIONS

The results suggest that prostatic NE cells might be regulated by the HER protein family, probably, in a ligand-specific fashion. This is the first report identifying a potential pathway regulating prostatic NE cells.

Etiopathogenesis: Hypothesis and Confirmation of Experimental Research

After a review of the latest points of view about the etiopathogenesis of prostatic hyperplasia; i.e. hormonal growth factors, McNeal's theory of reawakening, theories based on the involvement of staminal cells, and the correlation between BPH and prostatic cancer, the authors report their practical experience on this subject. Since 1989 they have prepared in-vitro cultures, standardized the methodology and obtained an “immortalized” cell clone named U285. These cells have been cultivated with different concentrations of testosterone and growth factors. Analyses were performed by direct observation, providing cytologic and immunochemical preparations for morphologic characterization, and using the Frame cytotoxity test to determine the proliferative index. From a preliminary survey of results it seems that the DHT does not affect multiplication of the cells, but takes part in the differentiation process, becoming an agent of well-being and not a real growth factor. The EGF would appear to be efficacious only at high dosage with non differentiation and growth of immature cells. Suramine, a growth factor antagonist, and Finasteride, an inhibitor of the 5 alpha reductase enzyme, were utilized to explain the micro-endocrinology mechanisms at the origin of these processes.

Effect of epidermal growth factor on prostate cancer cell line PC3 growth and invasion

Elevated levels of epidermal growth factor (EGF) and epidermal growth factor receptor (EGF-R) have been demonstrated in prostate cancer cell lines and clinical specimens suggesting a role for polypeptide growth factors in prostate tumor cell growth and invasion. To more clearly define the role of EGF in prostate cancer invasion, we undertook a series of studies utilizing the PC3 prostate cancer cell line, an aggressive, hormone-independent cell line derived from a metastatic lesion. No statistical differences were noted in the growth of PC3 cells under serum-free conditions when EGF (10(-10) M-10(-8) M) or monoclonal anti-EGF-R antibody (10(-11) M-10(-8) M) were added. Utilizing the Boyden chamber microinvasion assay, EGF supplemented cells demonstrated a statistically significant augmentation in invasion (P < 0.05) when compared to control cells at each time point in the study. With increasing length of exposure to EGF, the number of concentrations that produced significant invasion increased: day 1 (10(-8) M), day 3 (10(-8), 10(-9) M), and day 5 (10(-7), 10(-8), 10(-10) M). Northern blot analysis of EGF supplemented cells revealed an increase in expression of urokinase plasminogen activator (uPA) RNA, a serine protease involved in the regulation of pericellular proteolysis and membrane degradation. Protein analysis confirmed these findings. Statistically significant inhibition of invasion by anti-uPA antibodies was demonstrated for EGF-stimulated and PC3 control cells. Our results demonstrate that certain concentrations of EGF augment invasion in the PC3 cell line. This enhancement of invasion occurs in part by an overproduction of uPA, an extracellular protease. These findings suggest that the autocrine production of EGF may potentiate tumor cell invasion.

Effect of somatostatin analog RC-160 and bombesin/gastrin releasing peptide antagonist RC-3095 on growth of PC-3 human prostate-cancer xenografts in nude mice

Nude mice bearing xenografts of the androgen-independent human prostate-cancer cell line PC-3 were treated for 4 weeks with somatostatin analog RC-160, bombesin/gastrin-releasing peptide (GRP) antagonist (RC-3095), or the combination of both peptides. In the first experiment, treatment was started when the tumors measured approximately 10 mm3. Tumor volumes and weights were reduced by about 40% by RC-160 or RC-3095 administered by s.c. injections at doses of 100 micrograms/day/animal and 20 micrograms/day/animal respectively. The combination of RC-3095 with RC-160 did not further potentiate suppression of tumor growth, but histologically the ratio of apoptotic and mitotic indices was significantly higher in the groups treated with the combination than in the other groups. Serum gastrin levels were significantly reduced in all treated groups. Therapy with RC-160 or the combination also significantly decreased serum growth-hormone levels. Specific high-affinity binding sites for bombesin, somatostatin and epidermal growth factor (EGF) were found on the tumor membranes. Receptors for EGF were significantly down-regulated by treatment with RC-3095, RC-160 and a combination of both analogs. Tumors from mice treated with RC-160 showed a significant increase in maximal binding capacity for somatostatin as compared with control tumors, demonstrating the absence of down-regulation. In the second experiment, treatment was started when the tumors were well developed and measured approximately 90 mm3. No significant reduction in volume, weight and growth rate of tumors was found in the groups treated with RC-160 or RC-3095. Our results suggest that somatostatin analog RC-160 and bombesin/GRP antagonist RC-3095 can inhibit the growth of androgen-independent prostate cancer when the therapy is started at an early stage of tumor development.

Relationship between epidermal growth factor and its receptor in human benign prostatic hyperplasia

Human benign prostatic hyperplasia (BPH) samples were analyzed to evaluate the presence of immunoreactive epidermal growth factor (irEGF) and EGF receptor (EGFR). In all BPH samples examined both peptide and its receptor were present. Scatchard analysis of binding data of [125I]EGF showed two classes of binding sites with high and low affinity. Intratissular irEGF concentrations showed a significant inverse linear correlation with EGFR levels. Two groups of samples can be identified: the first showing high irEGF concentrations and low levels of EGF binding sites; the second low irEGF and high concentrations of EGFR. The simultaneous presence of EGF and its receptor in BPH samples indicates that this growth factor may act in an autocrine/paracrine manner in human prostatic tissue. The inverse relationship between EGF and the two sites of EGFR lead one to hypothesize that EGF itself could play a central role in determining receptor cell surface availability.

Growth factors and their receptors as determinants in the proliferation and metastasis of human prostate cancer

Prostate adenocarcinoma, the most common tumor occurring among North American men, preferentially metastasizes to bone, where it characteristically forms osteoblastic lesions. The following growth regulatory factors are expressed in some human prostate cancers and/or established cell lines: epidermal growth factor (EGF), transforming growth factor alpha, transforming growth factor beta, basic fibroblast growth factor (bFGF), and insulin-like growth factor. Some of these, especially EGF, bFGF, and TGF-beta, are also implicated in growth regulation in normal and benign hyperplastic prostates. Although evidence from in vitro study of the small number of prostate cell lines available demonstrates that these growth regulatory pathways are exploited by some of these cells, direct in vivo evidence is limited. The development of human prostate cancer cell lines which grow and metastasize in immune-deficient rodents is an advance which now permits experimental analysis of the role of these growth factors in prostatic metastasis, particularly to bone. The progression and metastasis of human prostate cancer results from the complex interactions of multiple growth factors, androgens, and cellular communication, which form a dynamic network. Continued progress in the study and treatment of this disease will require new conceptual frameworks as well as successful application of the techniques of molecular and cellular biology.

Somatostatin analog RC-160 and bombesin/gastrin-releasing peptide antagonist RC-3095 inhibit the growth of androgen-independent DU-145 human prostate cancer line in nude mice

Nude mice bearing xenografts of the androgen-independent human prostate cancer DU-145 were treated for 4-5 weeks with somatostatin analog RC-160 or the bombesin/gastrin-releasing peptide (GRP) antagonist RC-3095. Tumor growth in animals treated with somatostatin analog RC-160 at a dose of 100 micrograms/day s.c. was significantly inhibited within 14 days of the start of the experiment. At necropsy, in mice given RC-160, tumor weight and volume were significantly decreased compared with control mice. Treatment with RC-3095 at a dose of 20 micrograms/day s.c. also suppressed tumor growth, the inhibition being significant after 2 weeks, but the reduction in tumor volume and weight was smaller than that produced by RC-160. Therapy with RC-160 significantly decreased serum growth hormone and gastrin levels. Specific binding sites for bombesin, somatostatin and epidermal growth factor (EGF) were found in the DU-145 tumor membranes. Receptors for EGF were significantly down-regulated after therapy with RC-3095 and RC-160. The finding that somatostatin analog RC-160 and bombesin/GRP antagonist RC-3095 inhibit the growth of androgen-independent prostate tumors in mice might be of practical importance for human prostate cancer therapy.

Oncogenes in prostate cancer. An update

Oncogenes have been implicated in the carcinogenic development of many diverse types of human malignancies. For some cancers, the expression of specific oncogenes has been shown to have diagnostic or prognostic value. By contrast currently, no oncogene has been correlated conclusively with the initiation or progression of prostate cancer. The ras oncogene has been investigated the most thoroughly for its involvement in prostate cancer, but ras does not appear to play a significant role in the development of this malignancy. Several years ago, limited studies hinted at the possibility of overexpression of the myc oncogene and aberrant expression of the sis oncogene in prostate cancer, but additional studies to clarify the involvement of these oncogenes have not been done. Oncogenic activity of growth factors or growth factor receptors in prostate cancer has been suggested but not amply demonstrated. Current dogma indicates that oncogenes exist in prostate cancer, but these will be identified only by more intensive investigation.