The localization of transforming growth factor alpha and epidermal growth factor receptor in stromal and epithelial compartments of developing human prostate and hyperplastic, dysplastic, and carcinomatous lesions

Cooperative effects of EGF, FGF, and TGF-β1 in prostate stromal cells are different from responses to single growth factors

AIMS

Stromal growth is critical for prostate enlargement during benign prostatic hyperplasia (BPH). While responses of prostate cells to single growth factors have been well characterized, responses to multiple growth factors at once are poorly understood. Here, we examined the effects of combinations between epidermal growth factor (EGF), fibroblast growth factor (FGF), and transforming growth factor-β1 (TGF-β1) in human prostate stromal cells.

MAIN METHODS

EGF, FGF, and TGF-β1 were applied to WPMY-1 cells, an immortalized, non-malignant line of stromal cells from the human prostate. Hypertrophic responses were assessed by protein/DNA ratio, and cyclin D1 mRNA by RT-PCR. Expression of EGF, FGF, and TGF-β1 and their receptors in human prostate tissue was analyzed by RT-PCR, Western blot, and fluorescence staining.

KEY FINDINGS

Hypertrophic responses to single growth factors and combinations were similar. Combinations showed additive effects on cyclin D1 mRNA. Combination of EGF with TGF-β1, but not EGF or TGF-β1 alone, caused assembly of cells to a new two-dimensional structure, being characterized by dense aggregates connected by branches of few cells. EGF and TGF-β1 were detected together in human prostates. Receptors for EGF and TGF-β colocalized on stromal cells in human prostates.

SIGNIFICANCE

Responses of prostate stromal cells to combinations of EGF, FGF, and TGF-β1 may be quantitatively different, qualitatively different, or similar to responses to single growth factors. The combination of EGF and TGF-β1, but not EGF or TGF-β1 alone, induces aggregation of prostate stromal cells, which may be relevant for morphogenesis.

MAP Kinases and Prostate Cancer

The three major mitogen-activated protein kinases (MAPKs) p38, JNK, and ERK are signal transducers involved in a broad range of cell functions including survival, apoptosis, and cell differentiation. Whereas JNK and p38 have been generally linked to cell death and tumor suppression, ERK plays a prominent role in cell survival and tumor promotion, in response to a broad range of stimuli such as cytokines, growth factors, ultraviolet radiation, hypoxia, or pharmacological compounds. However, there is a growing body of evidence supporting that JNK and p38 also contribute to the development of a number of malignances. In this paper we focus on the involvement of the MAPK pathways in prostate cancer, including the less-known ERK5 pathway, as pro- or antitumor mediators, through their effects on apoptosis, survival, metastatic potential, and androgen-independent growth.

EGF promotes the shedding of soluble E-cadherin in an ADAM10-dependent manner in prostate epithelial cells

During the progression of prostate cancer, the epithelial adhesion molecule E-cadherin is cleaved from the cell surface by ADAM15 proteolytic processing, generating an extracellular 80kDa fragment referred to as soluble E-cadherin (sE-cad). Contrary to observations in cancer, the generation of sE-cad appears to correlate with ADAM10 activity in benign prostatic epithelium. The ADAM10-specific inhibitor INCB8765 and the ADAM10 prodomain inhibit the generation of sE-cad, as well as downstream signaling and cell proliferation. Addition of EGF or amphiregulin (AREG) to these untransformed cell lines increases the amount of sE-cad shed into the conditioned media, as well as sE-cad bound to EGFR. EGF-associated shedding appears to be mediated by ADAM10 as shRNA knockdown of ADAM10 results in reduced shedding of sE-cad. To examine the physiologic role of sE-cad on benign prostatic epithelium, we treated BPH-1 and large T immortalized prostate epithelial cells (PrEC) with an sE-cad chimera comprised of the human Fc domain of IgG(1), fused to the extracellular domains of E-cadherin (Fc-Ecad). The treatment of untransformed prostate epithelial cells with Fc-Ecad resulted in phosphorylation of EGFR and downstream signaling through ERK and increased cell proliferation. Pre-treating BPH-1 and PrEC cells with cetuximab, a therapeutic monoclonal antibody against EGFR, decreased the ability of Fc-Ecad to induce EGFR phosphorylation, downstream signaling, and proliferation. These data suggest that ADAM10-generated sE-cad may have a role in EGFR signaling independent of traditional EGFR ligands.

Gene expression changes are age-dependent and lobe-specific in the brown Norway rat model of prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is an age-related enlargement of the prostate, characterized by increased proliferation of stromal and epithelial cells. Despite its prevalence, the etiology of BPH is unknown.

METHODS

The Brown Norway rat is a model for age-dependent, lobe-specific hyperplasia of the prostate. Histological analyses of the dorsal and lateral lobes from aged rats reveal focal areas characterized by increased numbers of luminal epithelial cells, whereas the ventral lobe is unaffected. This study examined differential gene expression by lobe and age in the Brown Norway rat prostate. The objective was to identify genes with different levels of expression in the prostate lobes from 4-month (young) and 24-month (old) animals, and to subsequently link changes in gene expression to mechanisms of prostate aging.

RESULTS

The number of age-dependent differentially expressed genes was greatest in the dorsal compared to the ventral and lateral lobes. Minimal redundancy was observed among the differentially expressed genes in the three lobes. Age-related changes in the expression levels of 14 candidate genes in the dorsal, lateral and ventral lobes were confirmed by quantitative RT-PCR. Genes that exhibited age-related differences in their expression were associated with proliferation, oxidative stress, and prostate cancer progression, including topoisomerase II alpha (Topo2a), aurora kinase B (Aurkb), stathmin 1 (Stmn1), and glutathione S-transferase pi. Immunohistochemistry for Topo2a, Aurkb, and Stmn1 confirmed age-related changes in protein localization in the lateral lobe of young and aged prostates.

CONCLUSION

These findings provide clues to the molecular events associated with aging in the prostate.

Immunohistochemical Evaluation of H-R3 a Novel Humanized Monoclonal Antibody That Neutralizes the EGF-receptor

The epidermal growth factor receptor (EGF-R) is an important growth regulator of epithelial cancer cells, overexpressed by several human tumors and scantly detectable in most normal tissues. The introduction of monoclonal antibodies (Mabs) and more recently engineered humanized Mabs have greatly expanded the therapeutic potential of this modality of cancer treatment. The present study was designed to compare the specificity of the murine and humanized anti-EGF-R Mabs. Biotinylated Mabs were tested in samples of fetal and adult normal and neoplastic tissues by ABC peroxidase method. All fetal tissues studied were positive for both Mabs, showing 2 different staining patterns, one homogeneous and finely granular in cytoplasm and another grosser with intense labeling in both membrane and cytoplasm. A similar recognition pattern was exhibited in adult normal tissues, where an intense reactivity was also evidenced in skin, tongue, gastrointestinal tract, renal tubules, and breast gland epithelium. In tissues from genitourinary and central nervous system, a faint staining was demonstrate, whereas those from cardiovascular and lymphoid tissues proved to be negative. These Mabs exhibited a heterogeneous and strong membrane and cytoplasm staining in neoplastic cells from lung, breast, and head and neck cancer. On the basis of these results, we conclude that the humanized (h-R3) and murine (egf/r3) anti-EGF-R Mabs show a very similar immunohistochemical pattern of recognition of fetal, adult, and neoplastic tissues. Also h-R3 Mab is a novel candidate for the development of an immunotherapeutic approach suitable for the treatment of tumors with EGF-R overexpression.

Epithelial Phenotypes in the Developing Human Prostate

An intermediate population has been identified among prostate glands called transiently amplifying (TA) cells, which are characterized by coexpression of basal and luminal cytokeratins (CKs), high proliferation, and lack of p27 expression. These cells are rare in the normal adult prostate and increase in pretumoral conditions, but their importance in the developing gland remains unknown. We analyzed fetal prostates for the expression of CKs (5/6, 18, 19) and factors involved in proliferation and apoptosis: p63, Ki67, p27, epidermal growth factor (EGFR), Bcl2, androgen receptor (AR). Immunostaining was performed on a tissue microarray, including 40 prostates from fetuses aged 13-42 weeks and normal prostate tissue from 10 adults. In both solid buds and the basal compartment of canalized glands, cells expressed p63, CK5/6, CK19, CK18, BCL2, EGFR and were p27 negative. Luminal cells of fetal canalized glands continue to express CK19, EGFR, and BCL2, without p27 expression. In contrast, adult epithelial luminal cells showed diffuse AR and p27 expression, without CK19, BCL2, and EGFR staining. Proliferation was high and diffuse in fetal glands and rare and restricted to basal cells in adult glands. These results indicate that most fetal epithelial prostatic cells exhibit the phenotype of TA cells, suggesting their regulatory function in prostate development.

Complete loss of PTEN expression as a possible early prognostic marker for prostate cancer metastasis

The EGF/IGF growth factors are potent mitogens that regulate cell proliferation and cell survival and are involved in prostate cancer development. Using laser microdissection technology and real-time PCR, together with immunohistochemistry, we have explored the growth factor and integrin dependent PI3-kinase/PTEN/Akt signalling pathway in prostate cell lines and tumour samples by analysing EGF-R, IGF1-R, ILK, beta3 integrin, PTEN and p-Akt protein expression. We provide evidence that loss of PTEN expression rather than upregulated EGF/IGF1 receptor expression was responsible for increased p-Akt in neoplastic prostate cells. We therefore compared PTEN expression in patient biopsies at first time diagnosis recruited prospectively (Study I, 112 patients) and patients with confirmed metastasis recruited retrospectively from the Luxembourg cancer registry (Study II, 42 patients). In Study I, loss of PTEN expression at first time diagnosis was found in 26 of 112 patients (23%). In Study II, 25 of the 42 patients (59%) with lymph node metastasis had complete loss of PTEN expression in both the neoplastic glands of the prostate and the invasive prostate cancer cells in the lymph node, and of these 13 (52%) exhibited already loss of PTEN expression at first diagnosis. These findings demonstrate that loss of PTEN expression is an important factor in progression towards metastatic disease and could potentially serve as an early prognostic marker for prostate cancer metastasis.

Oxytocin and the human prostate in health and disease

Oxytocin is a peptide hormone produced by the neurohypophysis. The discovery that the peptide is produced locally within the male and female reproductive tracts has raised the possibility that oxytocin may have paracrine and autocrine actions outside of the nervous system. Oxytocin and its receptor have been identified in the human prostate. The prostate is an androgen-dependent organ whose function is to secrete components of the seminal fluid. Oxytocin has been shown to modulate contractility of prostate tissue and also to regulate local concentrations of the biologically active androgens. Oxytocin has also been shown to regulate cell growth. Prostate disease is common and results from abnormal growth of the gland. Oxytocin concentrations are altered in both benign and malignant prostate diseases and in vitro studies suggest that the peptide may be involved in the pathophysiology of these diseases.

Epidermal growth factor receptor (ErbB1) expression in prostate cancer progression: correlation with androgen independence

BACKGROUND

The role of the epidermal growth factor receptor (ErbB1) in the progression of prostate cancer is incompletely understood.

METHODS

Tissue microarrays from hormone-naive and advanced androgen-independent tumors were used to investigate the role of ErbB1 in prostate cancer progression.

RESULTS

ErbB1 expression in tumor tissues was strongly associated with hormone-refractory status (odds ratio = 6.67, 95% CI = (2.6, 17.4), P = 0.0001). However, ErbB1 overexpression was not a statistically significant covariate in a multivariate proportional hazards model for biochemical failure of hormone-naïve prostate cancer. Moreover, ErbB1 overexpression was not associated with tumor differentiation (P = 0.44), positive margins (P = 0.53), seminal vesicle invasion (P = 0.69), extraprostatic extension (P = 0.10), or preoperative PSA (P = 0.18) in the hormone-naïve group.

CONCLUSIONS

These findings are consistent with a model in which ErbB1 expression increases during the development of the androgen-independent state, and suggest that drugs targeted toward ErbB signaling could be of therapeutic relevance in the management of advanced prostatic carcinoma.

The epidermal growth factor receptor signaling network in head and neck carcinogenesis and implications for targeted therapy

Improved understanding of the molecular signaling pathways that mediate cellular transformation has led to the development of novel strategies for the treatment of cancer. The epidermal growth factor receptor (EGFR), a transmembrane protein with intrinsic tyrosine kinase activity, transduces important signals from the surface of epithelial cells to the intracellular domain. Aberrant signaling through EGFR plays a key role in the carcinogenesis of squamous cell carcinomas of the head and neck (SCCHN). SCCHN tend to express high levels of EGFR, and the degree of expression correlates with poor clinical outcome. Since EGFR is present at much higher levels in cancerous lesions than in normal epithelial tissue, the receptor has been implicated as a highly specific therapeutic target for the treatment of SCCHN. EGFR can be abrogated at the extracellular level using either monoclonal antibodies or toxin conjugates that compete with the natural ligand at the binding site of the receptor, and targeting of the EGFR intracellular domain has been achieved by specific inhibitors of tyrosine kinase activity. Antisense strategies use synthesized DNA or RNA oligonucleotides to block the translation of the mRNA sequences that code for the production of the EGFR or other proteins with a role in EGFR-mediated cell signaling. Clinical evaluation of EGFR-specific monoclonal antibodies and tyrosine kinase inhibitors has demonstrated limited toxicity in SCCHN patients, and concurrent administration with standard cytotoxic therapies has produced additive or synergistic antitumor effects.

Epidermal growth factor receptor–related peptide inhibits growth of PC-3 prostate cancer cells

Interference with the activation of growth factor receptors, specifically epidermal growth factor receptor (EGFR), represents a promising strategy for the development of novel and selective anticancer therapies. We reported that EGFR-related peptide (ERRP), a recently isolated negative regulator of EGFR, could be a potential therapeutic agent for colorectal cancer. To determine whether ERRP could potentially be a therapeutic agent for prostate carcinoma, we examined the effect of recombinant ERRP on the growth of the prostate cancer cell line PC-3 in vitro. Events of the EGFR signal transduction pathways were also examined. ERRP caused a marked inhibition of cell growth in a dose- and time-dependent manner and also induced apoptosis. The latter was evidenced by increased number of apoptotic cells, activation of caspase-3, and cleavage of poly(ADP-ribose)polymerase. The transforming growth factor-α–induced stimulation of cell growth and activation of EGFR was also inhibited by ERRP. These changes were accompanied by a concomitant attenuation of activation of Akt and mitogen-activated protein kinases as well as basal and transforming growth factor-α–induced activation of nuclear factor-κB. Inhibition of EGFR activation by ERRP could be partly attributed to increased sequestration of EGFR ligands. In summary, our data show that ERRP inhibits the growth of prostate cancer cells by attenuating EGFR signaling processes. ERRP could potentially be an effective therapeutic agent for prostate cancer.

Signaling through the epidermal growth factor receptor during the development of malignancy

The epidermal growth factor receptor (EGFR) is overexpressed and/or constitutively activated in a variety of human malignancies. Detection of increased expression levels of EGFR in cancer and the association between overexpression and decreased patient survival has led to the development of several therapeutic strategies to target this receptor. The results of early-phase clinical trials to date suggest that targeting EGFR alone may not be sufficient to eradicate established tumors. This limited antitumor efficacy as monotherapy has led to combining EGFR inhibitors with chemotherapy or radiation therapy for advanced disease, or incorporating EGFR inhibition to cancer prevention approaches. This review will discuss the role of EGFR signaling in carcinogenesis and the rationale for EGFR inhibition as a clinical prevention and treatment strategy.

Epidermal growth factor, neurotrophins and the metastatic cascade in prostate cancer

Although cancer of the prostate (CaP) is the most commonly occurring cancer in males, there are major limitations in its diagnosis and long-term cure. Consequently, understanding the molecular mechanisms involved in the progression of CaP is of particular importance for production of pharmacological and biological agents to manage the disease. The development of the normal prostate is regulated by stromal-epithelial interactions via endocrine and paracrine factors, such as androgens and growth factors, which act as precise homeostatic regulators of cellular proliferation. Importantly, after a period of hormonal therapy, CaP shifts from an androgen-dependent to an androgen-independent state with a concomitant switch from paracrine to autocrine growth factor stimulation and subsequent upregulation of growth factor expression. Thus, growth factors and their receptors have a pivotal role in CaP. This is emphasized by current evidence obtained from clinical specimens as well as several in vitro and in vivo models strongly suggesting that epidermal growth factor and the neurotrophins (nerve growth factor, brain derived neurotrophin factor, neurotrophin-3 and neurotrophin-4/5) together with their tyrosine kinase receptors could play a very significant role in CaP progression.

Novel Therapeutic Molecular Targets for Prostate Cancer: The mTor Signaling Pathway and Epidermal Growth Factor Receptor

PURPOSE

The scientific rationale and existing evidence for the use of novel molecular targets in the chemoprevention of cancer are reviewed, with special attention to prostate cancer.

MATERIALS AND METHODS

A search for relevant literature on basic science and clinical trials was conducted using PubMed/MEDLINE.

RESULTS

The emergence of molecularly targeted therapies for advanced malignancies creates an important opportunity to examine these agents for the chemoprevention of prostate cancer. Two critical targets in the proliferation and malignant transformation of normal cells, the PI3/Akt signal transduction pathway and the epidermal growth factor receptor, are currently the focus of several novel investigational therapies that are in late stage phase II and phase III studies.

CONCLUSIONS

Research to date supports consideration of these novel molecular targets as future agents in the chemoprevention of prostate cancer.

Involvement of Growth Factor Receptors of the Epidermal Growth Factor Receptor Family in Prostate Cancer Development and Progression to Androgen Independence

The development of prostate cancer and the progression from a normal prostate epithelium to androgen-dependent cancer and eventually to hormone-refractory prostate cancer is a multistep process involving several changes in the function of different growth-regulatory signals. In the past 10 years, conflicting results on epidermal growth factor receptor (EGFR) family expression in prostate cancer have been reported. These differences may result from technical differences, lack of standardization of immunohistochemical assays, or different scoring methodologies. Recently, 4 studies have shown experimental evidence of a role of the EGFR family, particularly ErbB-2, in the development of prostate cancer and, more specifically, in the progression to hormone-refractory clinical behavior. These 4 studies were similar in some relevant aspects, such as the patient population. In fact, the patients in each study were divided into 3 groups that represent the progression of prostate cancer. In 3 of 4 studies, a statistically significant increase in ErbB-2 expression was detected by immunohistochemistry in the progression from hormone-dependent to hormone-independent disease. The expression of EGFR was also evaluated in 1 of the 4 studies. In a recent report from our group, a significant increase in EGFR expression was observed in patients treated with radical surgery, in patients who received hormonal therapy as primary therapy before radical prostatectomy, and, finally, in patients with metastatic and hormone-refractory disease. It has been proposed that EGFR family receptors and androgen receptors function synergistically in the absence of androgen suggesting cross-talk between the ErbB-2 and androgen receptor pathways, and that mitogen-activated protein kinase and phosphatidylinositol 3-kinase can be considered the transduction pathways. Finally, clinical trials are currently in progress in patients with prostate cancer testing novel agents that selectively interfere with these receptors, such as trastuzumab, an anti- ErbB-2 monoclonal antibody, and gefitinib (ZD1839, Iressa), a small-molecule selective EGFR tyrosine kinase inhibitor.

Cystosarcoma phyllodes of the prostate with rhabdomyoblastic differentiation

A 36-year-old man presented with recurrent urinary obstruction and an enlarged, partially cystic prostate tumour on ultrasonography. Microscopically, the tumour was composed of cystically dilated ducts with leaf-like stromal projections in the lumen. A portion of the stroma was very cellular with atypia and a high mitotic rate. In addition, there was a small focus with well differentiated rhabdomyoblasts. This case is the second description of a cystosarcoma phyllodes of the prostate with rhabdomyoblasts differentiation. With radical surgery and chemotherapy only partial remission could be obtained.

Controlling tumor-derived and vascular endothelial cell growth: role of the 4Ff2 cell surface antigen

We have isolated a monoclonal antibody, clone betaE11, which recognizes an antigen that is highly abundant on the surface of mitotic vascular endothelial cells and tumor cells. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting, expression of this 190-kd antigen is approximately threefold higher in mitotic versus interphase endothelial cells. Treatment of tumor cells with an antibody to the betaE11 antigen inhibits their growth in a dose-dependent manner in vitro with maximal inhibition at an antibody concentration of 1 microg/ml. Different tumor cell lines demonstrate varying sensitivities to anti-betaE11 with the following order of growth inhibition: colon > prostate = glioma > melanoma = fibroblast > breast > liver. Furthermore, the betaE11 antigen localizes to regions of prostatic intraductal neoplasia in paraffin-embedded sections. Mass spectrometry of the cell-derived betaE11 protein and V8-protease fingerprint analysis indicate that the betaE11 antigen is nearly identical to the 4F2 heavy chain antigen, a cell surface protein that has been implicated in cell activation and proliferation. Expression of the betaE11 antigen during mitosis functionally links it to a fundamental aspect of cell proliferation, and its spatial localization on the surface of both proliferating endothelium and tumor cells demonstrates its potential for tumor immunotherapy.

Differential expression of c-erb B2/neu, epidermal growth factor receptor, cytokeratin 8, and the prostatic steroid-binding protein gene in rat ventral prostate during postnatal development

BACKGROUND

The development and progression of prostate neoplasia may recapitulate the early developmental pattern of expression of genes in the prostate. The study of prostate development may, therefore, provide insights into the molecular mechanisms important in prostate neoplasia and reveal new markers.

METHODS

We compared postnatal expression of four genes: neu and epidermal growth factor receptor genes (EGFR), androgen-upregulated in the ventral prostate of adult rats (C-3), and androgen-repressed (CK8) in Sprague-Dawley rats. In situ hybridization was performed on prostate frozen sections collected on postnatal days 1, 5, 10, 15, 20, 30, and 60 from five rats per day. Staining intensities for antisense probes specific for each gene were determined relative to day 1 intensity.

RESULTS

Growth factor receptors including neu and EGFR may be coordinately regulated in the basal-cell population during prostate development. CK8 and C-3 show evidence of similar androgen regulation during development.

CONCLUSIONS

CK8 and C-3 have distinct patterns of expression in the postnatal period of development and these genes may be good markers of differentiation. Both neu and EGFR may be involved in androgen-independent growth of basal cell population in prostate. Prostate 47:164-171, 2001.

New concepts in the pathology of prostatic epithelial carcinogenesis

The development of drugs to prevent prostate cancer is underway, yet monitoring the potential efficacy of these agents during clinical trials relies on measuring intermediate endpoints. In this review, various candidate markers are presented that are under different stages of evaluation as intermediate endpoint biomarkers. In addition, the near future will bring an unprecedented wave of new potential biomarkers. For instance, through genomics-based methods many new genes are being discovered whose altered expression may be involved in different phases of prostate cancer development and progression. In the development of rational approaches for selecting which of these untested biomarkers may be useful to measure systematically, there must be an improved understanding of the mechanisms of prostatic carcinogenesis. We submit that this improved understanding will come through new knowledge of the biology of normal prostate epithelial cells, the determination of the precise target cells of transformation, and how their growth regulation is genetically and epigenetically perturbed during the phases of initiation and progression. In this review, therefore, we also present our recent immune-mediated oxidant injury and regeneration hypothesis of why and how the prostate is targeted for carcinogenesis.

Heparin-binding epidermal growth factor-like growth factor is an autocrine mediator of human prostate stromal cell growth in vitro

PURPOSE

The physiological mechanisms by which soluble mediators of cell proliferation and survival alter expansion of the prostatic stroma in benign prostatic hyperplasia are poorly understood. We recently identified heparin-binding epidermal growth factor like growth factor (HB-EGF) as a product predominantly of the smooth muscle cell compartments of the adult human prostate. We assess the potential role of this growth factor as a stromal cell regulator.

MATERIALS AND METHODS

Primary cultures of desmin and alpha-actin positive human prostate stromal cells were shown to express several cell associated HB-EGF isoforms as well as the primary cognate HB-EGF receptor, ErbB1/HER1, suggesting the existence of an autocrine or juxtacrine regulatory loop. The related receptor tyrosine kinase, ErbB2/HER2, was also expressed as assessed by reverse transcriptase (RT) polymerase chain reaction (PCR). HB-EGF messenger RNA levels in human prostate stromal cells increased modestly (70%) in response to a repetitive mechanical stimulus, a lower response than has been reported for neonatal rat bladder smooth muscle cells, in which HB-EGF was originally identified as a mechanically responsive gene.

RESULTS

HB-EGF, epidermal growth factor and basic fibroblast growth factor stimulated human prostate stromal cell growth, while a specific antagonist of HB-EGF, [Glu52]-diphtheria toxin/CRM197, inhibited human prostate stromal growth in serum-free medium by a mechanism that did not involve increased apoptosis. A function blocking antibody against CD9/DRAP27/MRP-1, a cell surface binding partner of the membrane form of HB-EGF, also stimulated human prostate stromal cell proliferation.

CONCLUSIONS

HB-EGF is an endogenously produced human prostate stromal cell growth factor and, thus, may have a role as a physiologically relevant autocrine or juxtacrine mediator of stromal expansion in benign prostatic hyperplasia.

PSK, a novel STE20-like kinase derived from prostatic carcinoma that activates the c-Jun N-terminal kinase mitogen-activated protein kinase pathway and regulates actin cytoskeletal organization

Degenerate polymerase chain reaction against conserved kinase catalytic subdomains identified 15 tyrosine and serine-threonine kinases expressed in surgically removed prostatic carcinoma tissues, including six receptor kinases (PDGFBR, IGF1-R, VEGFR2, MET, RYK, and EPH-A1), six non-receptor kinases (ABL, JAK1, JAK2, TYK2, PLK-1, and EMK), and three novel kinases. Several of these kinases are oncogenic, and may function in the development of prostate cancer. One of the novel kinases is a new member of the sterile 20 (STE20) family of serine-threonine kinases which we have called prostate-derived STE20-like kinase (PSK) and characterized functionally. PSK encodes an open reading frame of 3705 nucleotides and contains an N-terminal kinase domain. Immunoprecipitated PSK phosphorylates myelin basic protein and transfected PSK stimulates MKK4 and MKK7 and activates the c-Jun N-terminal kinase mitogen-activated protein kinase pathway. Microinjection of PSK into cells results in localization of PSK to a vesicular compartment and causes a marked reduction in actin stress fibers. In contrast, C-terminally truncated PSK (1-349) did not localize to this compartment or induce a decrease in stress fibers demonstrating a requirement for the C terminus. Kinase-defective PSK (K57A) was unable to reduce stress fibers. PSK is the first member of the STE20 family lacking a Cdc42/Rac binding domain that has been shown to regulate both the c-Jun N-terminal kinase mitogen-activated protein kinase pathway and the actin cytoskeleton.

Amphiregulin is coordinately expressed with heparin-binding epidermal growth factor-like growth factor in the interstitial smooth muscle of the human prostate

Peptide growth factors have been proposed as mediators of smooth muscle-epithelial cell interactions in the human prostate; however, the identity of these molecules has not been established. In this study, we compared expression levels of messenger RNAs (mRNAs) encoding the epidermal growth factor (EGF) receptor-related receptor tyrosine kinases (ErbB1 through 4), the six EGF receptor ligands, EGF, transforming growth factor (TGF)-alpha, amphiregulin (ARG), HB-EGF, betacellulin, and epiregulin, and the related molecule heregulin-alpha, in a series of 10 prostate tissue specimens. Only EGF showed a disease-specific association, with increased mRNA levels in four of five PCa specimens in comparison to matched normal tissue from the same subject. In contrast, ARG and HB-EGF mRNAs showed a coordinate pattern of expression in 7/10 specimens that was distinct from all other growth factor or receptor genes examined and from mRNAs for prostate specific antigen, the androgen receptor and GAPDH, a house-keeping enzyme. Analysis of an additional series of benign prostatic hyperplasia and prostate cancer specimens from 60 individuals confirmed that ARG and HB-EGF mRNA levels varied in a highly coordinate manner (r = 0.93; P < 0.0001) but showed no association with disease. ARG was immunolocalized largely to interstitial smooth muscle cells (SMC), previously identified as the site of synthesis of HB-EGF in the prostate, while the cognate ARG and HB-EGF receptor, ErbB1, was localized exclusively to ductal epithelial cells and carcinoma cells. Although ARG was a relatively poor mitogen for Balb/c3T3 cells in comparison to HB-EGF, it was similar in potency to HB-EGF in stimulating human prostate epithelial cell growth, suggesting that prostate epithelia may be a physiologic target for ARG in vivo. Expression of both ARG and HB-EGF mRNAs was induced in cultured prostate SMC by fibroblast growth factor-2, a human prostate SMC mitogen linked to prostate disease. These findings indicate that ARG and HB-EGF are likely to be key mediators of directional signaling between SMC and epithelial cells in the human prostate and appear to be coordinately regulated.

Prolactin receptor expression in the developing human prostate and in hyperplastic, dysplastic, and neoplastic lesions

In situ hybridization and immunohistochemistry were used to localize and compare the expression of the long form of the human prolactin receptor in fetal, prepubertal, and adult prostate. Results were then compared with hyperplastic, dysplastic, and neoplastic lesions. Both receptor message and protein were predominately localized in epithelial cells of the fetal, neonatal, prepubertal, and normal adult prostate. In hyperplastic lesions the expression of the receptor was unchanged with respect to normal epithelial cells. Irrespective of grade, markedly enhanced expression of the receptor was evident in dysplastic lesions. In lower Gleason grade carcinomas the intensity of receptor signal at the message and protein levels approximated that found in normal prostatic epithelium. However, in foci within higher grade cancers, receptor expression appeared diminished. Results from our study suggest that prolactin action plays a role in the development and maintenance of the human prostate and may also participate in early neoplastic transformation of the gland. Diminution of receptor expression in high grade neoplasms could reflect the emergence of a population of cells that are no longer responsive to the peptide hormone.