Androgen-independent epithelial cells of the rat ventral prostate

Prostate stem cells in the development of benign prostate hyperplasia and prostate cancer: emerging role and concepts

Benign Prostate hyperplasia (BPH) and prostate cancer (PCa) are the most common prostatic disorders affecting elderly men. Multiple factors including hormonal imbalance, disruption of cell proliferation, apoptosis, chronic inflammation, and aging are thought to be responsible for the pathophysiology of these diseases. Both BPH and PCa are considered to be arisen from aberrant proliferation of prostate stem cells. Recent studies on BPH and PCa have provided significant evidence for the origin of these diseases from stem cells that share characteristics with normal prostate stem cells. Aberrant changes in prostate stem cell regulatory factors may contribute to the development of BPH or PCa. Understanding these regulatory factors may provide insight into the mechanisms that convert quiescent adult prostate cells into proliferating compartments and lead to BPH or carcinoma. Ultimately, the knowledge of the unique prostate stem or stem-like cells in the pathogenesis and development of hyperplasia will facilitate the development of new therapeutic targets for BPH and PCa. In this review, we address recent progress towards understanding the putative role and complexities of stem cells in the development of BPH and PCa.

The path toward identifying prostatic stem cells

The concept that stem cells reside in prostate epithelia is well accepted and has led to significant efforts aimed at isolating and characterizing adult prostate stem/progenitor cells from both human and rodent prostate tissues. Understanding how prostatic stem and/or progenitor cells give rise to prostate epithelia during development and maintain homeostasis of the prostate gland in adulthood is a major research focus. Furthermore, the ability to identify and manipulate prostatic stem cells (PSCs) holds enormous promise for the development of new approaches to manage and treat prostate cancer. This review maps the pathways to identifying, isolating, characterizing, and understanding the differentiation capacity of PSCs.

Cell differentiation lineage in the prostate

Prostatic epithelium consists mainly of luminal and basal cells, which are presumed to differentiate from common progenitor/stem cells. We hypothesize that progenitor/stem cells are highly concentrated in the embryonic urogenital sinus epithelium from which prostatic epithelial buds develop. We further hypothesize that these epithelial progenitor/stem cells are also present within the basal compartment of adult prostatic epithelium and that the spectrum of differentiation markers of embryonic and adult progenitor/stem cells will be similar. The present study demonstrates that the majority of cells in embryonic urogenital sinus epithelium and developing prostatic epithelium (rat, mouse, and human) co-expressed luminal cytokeratins 8 and 18 (CK8, CK18), the basal cell cytokeratins (CK14, CK5), p63, and the so-called transitional or intermediate cell markers, cytokeratin 19 (CK19) and glutathione-S-transferase-pi (GSTpi). The majority of luminal cells in adult rodent and human prostates only expressed luminal markers (CK8, CK18), while the basal epithelial cell compartment contained several distinct subpopulations. In the adult prostate, the predominant basal epithelial subpopulation expressed the classical basal cell markers (CK5, CK14, p63) as well as CK19 and GSTpi. However, a small fraction of adult prostatic basal epithelial cells co-expressed the full spectrum of basal and luminal epithelial cell markers (CK5, CK14, CK8, CK18, CK19, p63, GSTpi). This adult prostatic basal epithelial cell subpopulation, thus, exhibited a cell differentiation marker profile similar to that expressed in embryonic urogenital sinus epithelium. These rare adult prostatic basal epithelial cells are proposed to be the progenitor/stem cell population. Thus, we propose that at all stages (embryonic to adult) prostatic epithelial progenitor/stem cells maintain a differentiation marker profile similar to that of the original embryonic progenitor of the prostate, namely urogenital sinus epithelium. Adult progenitor/stem cells co-express both luminal cell, basal cell, and intermediate cell markers. These progenitor/stem cells differentiate into mature luminal cells by maintaining CK8 and CK18, and losing all other makers. Progenitor/stem cells also give rise to mature basal cells by maintaining CK5, CK14, p63, CK19, and GSTpi and losing K8 and K18. Thus, adult prostate basal and luminal cells are proposed to be derived from a common pleuripotent progenitor/stem cell in the basal compartment that maintains its embryonic profile of differentiation markers from embryonic to adult stages.

Vasoactive intestinal peptide (VIP) stimulates rat prostatic epithelial cell proliferation

BACKGROUND

Androgens play a major role in supporting normal growth and functional maintenance in the prostate. However, this gland contains an array of neuroendocrine peptides that can play a regulatory role in its physiopathology. Among these peptides, one of the best studied is vasoactive intestinal peptide (VIP), which is abundant in autonomic nerves surrounding both human and rat prostatic acini. This neuropeptide may act through interaction with two types of high-affinity receptors, named VPAC(1) and VPAC(2) receptors. Another regulatory peptide, the pituitary adenylate cyclase-activating peptide (PACAP), interacts with these receptors with the same affinity as VIP, but binds with higher affinity to PAC(1) receptors. Human prostate tumors and rat prostate show a major presence of VPAC(1) receptors, whereas various findings suggest a role for VIP in prostatic development. Here we studied the effects of VIP on the proliferation of rat prostatic epithelial cells in culture.

METHODS

We studied the [(3)H]-thymidine uptake by rat prostatic epithelial cells in culture, characterized previously by using biomarkers such as cytokeratin and vimentin. In these cells we tested the effect of VIP and PACAP-27 on two different signaling pathways, the cyclic AMP (cAMP) and the inositol phosphate (IPs).

RESULTS

The rat prostatic cells in culture were cytokeratin (5,6,8) and vimentin positive, indicating that the culture was predominantly epithelial. The proliferation curves showed that the cells followed different states of growth: a quiescent, an exponential proliferative, and a steady state. Cyclic AMP production, but not inositol phosphate production, was increased in the presence of VIP and PACAP-27, which suggests the expression of VPAC(1) and/or VPAC(2) receptors primarily. VIP significantly increased prostatic cell proliferation in a bimodal manner, as shown for dibutyryl cyclic AMP (dbcAMP), which suggests that the effect of VIP upon prostatic proliferation is cAMP-dependent.

CONCLUSIONS

Here, we demonstrate that VIP increased [(3)H]thymidine uptake by rat prostatic epithelial cells in culture, conceivably by the activation of the adenylate cyclase.

Androgen independence of primary epithelial cultures of the prostate is associated with a down-regulation of androgen receptor gene expression

BACKGROUND

Epithelial cells cultured from prostatic acini do not demonstrate significant (P > 0.05) growth response to the testosterone metabolite dihydrotestosterone (DHT) at concentrations of 0.001-10.0 nM. In addition, the nonsteroidal antiandrogen hydroxyflutamide (HO-F) does not influence primary epithelial cell proliferation in this concentration range.

METHODS

Northern blotting carried out with an androgen reception (AR)-specific cDNA probe indicated that the extent of AR gene expression in six unpassaged primary prostatic epithelial cell cultures was insufficient to elicit a detectable signal upon autoradiography. However, RT/PCR analysis of total RNA using two sets of intron-spanning androgen receptor (AR) primers demonstrates the presence of full-length receptor transcripts in two BPH-derived epithelial cell cultures (BPH1 and BPH2) as well as a carcinoma-derived culture (CaP1).

RESULTS

AR-positive LNCaP cells transfected with the AR reporter plasmid pMMTV/SPAP exhibit significant increases (P < 0.05) in SPAP production upon treatment with DHT. pMMTV/SPAP-transfected primary epithelial cells exhibit no such response when pulsed with either androgen or anti-androgen.

CONCLUSIONS

These results indicate that the lack of significant AR gene expression underlies the androgen independence of primary prostatic epithelial cell cultures.

An edgewise look at basal epithelial cells: three-dimensional views of the rat prostate, mammary gland and salivary gland

Wholemount immunocytochemical staining was used to visualize basal and luminal epithelial-cell-specific cytokeratin and smooth muscle alpha-actin expression in the developing and adult rat prostate, in the pregnant rat mammary gland and adult rat salivary gland. The stained samples were examined using an Edge R400 3D microscope. Images were collected in both single-image and stereo-pair formats. Prostatic basal epithelial cells were found to have a cell body covering an area of 52-62 microns 2. The mean footprint size of basal cells was not significantly different between prostatic lobes. Basal epithelial cells were most dense in the anterior and most sparse in the ventral prostatic lobes. Basal epithelial cells had a large body with many processes, which spread around the duct and projected between luminal cells towards the lumen. These processes closely approached their counterparts from adjacent basal cells. In the developing prostate the differentiation of the basal cells from undifferentiated epithelial cords was observed at the region of ductal widening associated with canalization. Following castration prostatic basal epithelial cells became more closely packed, though the size of individual cells was not significantly changed. There was a two-to four-fold increase in basal cell density by 7 days after surgery. Most prostatic luminal cells were found to have hexagonal bases though some were pentagonal in shape. Luminal cells had a mean basal area of 50 microns 2. In the prostate immunocytochemical staining against smooth muscle alpha-actin revealed discrete bands of muscle surrounding individual prostatic ducts. In the mammary and salivary glands the epithelium was organized into an alveolar arrangement. In the salivary gland a single basal epithelial cell covered the top of each alveolus with processes arranged down the side of the structure. In the mammary gland several basal cells were draped over each alveolus. The mammary and salivary gland basal cells expressed smooth muscle alpha-actin, indicating their myoepithelial phenotype. The organization of the mammary and salivary gland basal cells placed them in an ideal position to squeeze the alveolar structures.

Glycosaminoglycans in the three lobes of the rat prostate following castration and testosterone treatment

Androgen dependence of glycosaminoglycans (GAGs) in the prostate was studied using tissue from intact (sham control), castrated, and androgen-treated castrated rats. GAGs from the ventral, dorsal, and lateral lobes of the prostate were isolated and characterized by cellulose electrophoresis using appropriate GAG standards and enzymatic digestion or nitrous acid hydrolysis. Androgen deprivation was initiated by castration and rats were sacrificed at various time intervals after 7 days castration. After castration, the total GAG content decreased in three prostate lobes. At day 7 after castration, the total hyaluronic acid (HA) content decreased by 74% (ventral lobe) and 34% (lateral lobe) compared with the sham control. No effect was observed for HA content in the dorsal lobe. Castration decreased the total heparan sulphate (HS), dermatan sulphate (DS), and chondroitin sulphate (CS) contents in the three prostate lobes at 0 days of treatment, except for the CS content in the dorsal and lateral lobes. Androgen replacement increased the total GAG contents in the three prostate lobes. At 14 days of testosterone propionate treatment, there were 9-, 6.8-, 4.1- and 3.7-fold increases in HA, HS, DS, and CS, respectively, in the ventral lobe. These increases were more rapid and profound in the ventral than in the dorsal and lateral lobes. These findings indicate that all GAGs are regulated by androgen and there may be lobe-specific differences in their regulation. This could be a function of the heterogeneous populations of cells in each lobe.

Establishment and characterization of an immortalized but non-transformed human prostate epithelial cell line: BPH-1

This report describes the development and characterization of an epithelial cell line (BPH-1) from human prostate tissue obtained by transurethral resection. Primary epithelial cell cultures were immortalized with SV40 large T antigen. One of the isolated clones was designated BPH-1. These cells have a cobblestone appearance in monolayer culture and are non-tumorigenic in nude mice following subcutaneous injection or subrenal capsule grafting. They express the SV40 large T antigen and exhibit increased levels of p53, as determined by immunocytochemistry. Cytogenetic analysis by G-banding demonstrated an aneuploid karyotype with a modal chromosome number of 76 (range 71 to 79, n = 28) and 6 to 8 marker chromosomes. Some structurally rearranged chromosomes were observed, but the Y chromosome was normal. The expressed cytokeratin profile was consistent with a prostatic luminal epithelial cell. This profile was the same as that of primary prostatic epithelial cultures from which the BPH-1 cells were derived. In serum-free culture in plastic dishes epidermal growth factor (EGF), transforming growth factor (TGF)-alpha, fibroblast growth factor (FGF) 1 (aFGF), and FGF 7 (KGF) induced increased proliferation in these cells whereas FGF 2 (bFGF), TGF-beta 1, and TGF-beta 2 inhibited proliferative activity. Testosterone had no direct effect on the proliferative rate of BPH-1 cells. 5 alpha-Reductase, 3 alpha-hydroxysteroid oxidoreductase, and 17 beta-hydroxy-steroid oxidoreductase activities were detected in BPH-1 cells. Expression of androgen receptors and the secretory markers, prostate specific antigen and prostatic acid phosphatase, were not detectable by immunocytochemistry, biochemical assay, or RT-PCR analysis.

Castration rapidly results in a major reduction in epithelial cell numbers in the rat prostate, but not in the highly differentiated Dunning R3327 prostatic adenocarcinoma

Rats with implanted highly differentiated Dunning R3327PAP prostatic tumors were castrated, and at 3, 7, and 14 days thereafter, the effects on tumor volume, epithelial cell numbers, and sizes were quantified using morphometrical methods. The castration response on these parameters was also examined in the normal prostate of the same rats. Castration resulted in a rapid decrease in organ volume, epithelial cell number, and size in the normal prostate, and morphological signs of epithelial cell death (apoptosis) were observed. Tumor growth and mitotic index were reduced, but there were no signs of increased apoptosis, and cell numbers remained fairly constant in the Dunning tumors during the study period. It is concluded that the castration-induced inhibition of tumor growth is caused by factors other than tumor cell death.

Active cell death in hormone-dependent tissues

Active cell death (ACD) in hormone-dependent tissues such as the prostate and mammary gland is readily induced by hormone ablation and by treatment with anti-androgens or anti-estrogens, calcium channel agonists and TGF beta. These agents induce a variety of genes within the hormone-dependent epithelial cells including TRPM-2, transglutaminase, poly(ADP-ribose) polymerase, Hsp27 and several other unidentified genes. Not all epithelial cells in the glands are equally sensitive to the induction of ACD. In the prostate, the secretory epithelial cells that are sensitive to hormone ablation are localized in the distal region of the prostatic ducts, and are in direct contact with the neighboring stroma. In contrast, the epithelial cells in the proximal regions of the ducts are more resistant to hormone ablation, probably because the permissive effects of the stroma are attenuated by the presence of the basal epithelial cells, which are intercalated between the epithelium and stroma. The underlying biology of ACD in prostate and mammary glands, and its relevance to hormone resistance, is discussed in this review.

Prostate plasma membrane receptor: a hypothesis

Based on 50 years of emerging knowledge about and changing views of prostate biochemistry and physiology and especially on the belief that there is an underlying mechanism of androgen control, the hypothesis is developed and tested that the rates of proliferation, biosynthesis, metabolism, and secretion are modulated through the hormone-sensitive Na, K-ATPase of the plasma membrane. These preliminary experiments, constituting a novel synthesis of technologies from endocrinology, intermediary metabolism, and membrane transport, attempt to explain the extraordinary production and secretion of citrate and how this may be coupled to sustaining prostate cell number and function. Attention is focused on learning where androgen is bound and how it interacts with the Na,K-ATPase. Both the dissimilar properties of epithelial and stromal cells in the separate regions of the acinus and the changing environment of growth factors in which these cells are bathed help account for their unlike reactivities during development and ongoing mature function. Little wonder that one hormone can have so many effects!

Morphologic and regulatory aspects of prostatic function

Current concepts of the structural and functional organization of the human prostate are presented and are related to endocrine principles which have been studied in experimental animals. Based on embryological and histological studies, the internal structure of the human prostate gland is divided into four subdivisions: 1. the anterior nonglandular fibromuscular stroma. 2. the periurethral portion, 3. the peripheral zone, and 4. the central zone. The central zone which accounts for 25% of the gland, is formed by a wedge-shaped group of ducts, arising close to the orifices of the ejaculatory ducts and is surrounded by the peripheral zone (75% of the gland). The functional interdependence and relationship between the stroma and the epithelium observed during embryological development, postnatal maturation and under certain pathological conditions, has led to the concept of a functional prostatic unit, which is useful for the explanation of prostatic growth and the expression of specific genes. There is growing evidence of a functional heterogeneity within the prostatic secretory duct system, with a concentration of estrogen-sensitive cells close to the urethra, and a relatively long persistence of undifferentiated nonsecretory acini at the peripheral tips of the gland ducts close to the dorsal capsule until late puberty. Secretory and proliferative activities of the gland are strictly androgen-dependent. Of particular importance with respect to glandular and stromal proliferation are the recent reports on the presence of different growth factors in the prostate. Hormonally induced imbalances in the system of growth factor production, androgen- and estrogen-dependence and general ageing of the cells have to be taken into consideration in understanding various prostatic pathologies such as benign prostatic hyperplasia and prostate cancer.

Does the lack of regression-associated mRNA expression render a rat ventral prostate epithelial cell line androgen independent?

A series of rapidly dividing epithelial (RDE) cell lines have been isolated from primary cultures of rat ventral prostate (RVP) epithelial cells. Unlike androgen-dependent secretory epithelial cells, the RDE cells in culture do not express the androgen-dependent secretory proteins, nor do they express the androgen-repressed cell death sequences (TRPM-2) found in the epithelial cells during prostatic regression. Screening of a cDNA clone library established from RDE cell mRNA has yielded a number of RDE cell-specific sequences. One of these, RDE-.25 is a 250-base mRNA. The sequence of RDE-.25 shows considerable homology with the rat growth hormone gene and two murine oncogene sequences. We believe that the absence of androgen-repressed cell death sequence expression confers androgen independence for survival and growth, while the expression of RDE-.25 may represent an autocrine growth stimulus which greatly increases the rate of cell division in these cells.

Separation of mature rat ventral prostate epithelial and fibroblast cells

Several techniques for the separation of rat ventral prostate cells, using density gradient centrifugation or mechanical means have been published, yielding fibroblast and epithelial cell populations of varying purities and viability. These techniques are often tedious, yield relatively limited numbers of cells, demand considerable technical expertise, and result in the isolation of cells of limited viability. Two techniques for the isolation and establishment of epithelial and fibroblast cell cultures from mature rat ventral prostate are described here. Collagenase/trypsin digestion of the tissue yields a single-cell suspension of both cell types that are separated on Percoll isopycnic centrifugation gradients. A continuous gradient system allows for the separation of a greater number of cells with very high degrees of purity. A second technique based on a step-gradient system produces reproducible subfractionation of the epithelial cell component of the prostate within a considerable shorter period of time. An improved medium for plating epithelial and fibroblast cells has also been developed. The separated cells are plated on collagen and/or fibronectin-coated dishes in a serum-free plating medium that is later replaced with a serum containing growth medium. The plating medium greatly increases the plating efficiency of the isolated cell types, particularly the epithelial cells.