Regulation of basal and luminal cell-specific cytokeratin expression in rat accessory sex organs. Evidence for a new class of androgen-repressed genes and insight into their pairwise control

Seasonal morphology and immunoreactivity of cytokeratin and atrial natriuretic peptide in dromedary camel poll glands

Poll glands are characteristic feature of dromedary camels; although they yield a yellowish offensive secretion, especially during rutting (breeding) season, their function is not yet exactly specified. The present study shows the seasonal morphology and immunoreactivity of cytokeratin (CK) and atrial natriuretic peptide (ANP) in the camel poll gland; the result could clearly specify the role of the gland in camel reproduction. Poll glands are compound tubulo-alveolar in structure. During rutting season, the secretory units showed wide lumina and simple squamous epithelium surrounded by myoepithelial cells; the lumina became narrower and the epithelium changed to simple cuboidal during non-rutting season. Many glandular lobules showed abundant interlobular connective tissue with fewer and smaller secretory units during non-rutting season compared to rutting season. Positive CK and ANP immunoreactivity was detected in the cytoplasm of epithelial cells of secretory units and ducts together with the myoepithelial cells and blood vessels. Although CK immunoreactivity was more intense during rutting season in comparison to non-rutting season, there was no seasonal variation in ANP immunoreactivity. During both seasons, while the glandular capsule, connective tissue septa, interstitium showed negative CK immunoreactions, they reacted moderately to ANP. In conclusion, the poll gland undergoes annual structural and functional changes which are suggested to correlate with the male seasonal sexual behaviour. Further, the biological role of CK and ANP proteins together with their immunohistochemical expression in the camel poll gland suggests a stimulatory effect in the glandular secretory cells, and hence, they might modify camel sexual activity.

RET-mediated glial cell line-derived neurotrophic factor signaling inhibits mouse prostate development

In humans and rodents, the prostate gland develops from the embryonic urogenital sinus (UGS). The androgen receptor (AR) is thought to control the expression of morphogenetic genes in inductive UGS mesenchyme, which promotes proliferation and cytodifferentiation of the prostatic epithelium. However, the nature of the AR-regulated morphogenetic genes and the mechanisms whereby AR controls prostate development are not understood. Glial cell line-derived neurotrophic factor (GDNF) binds GDNF family receptor α1 (GFRα1) and signals through activation of RET tyrosine kinase. Gene disruption studies in mice have revealed essential roles for GDNF signaling in development; however, its role in prostate development is unexplored. Here, we establish novel roles of GDNF signaling in mouse prostate development. Using an organ culture system for prostate development and Ret mutant mice, we demonstrate that RET-mediated GDNF signaling in UGS increases proliferation of mesenchyme cells and suppresses androgen-induced proliferation and differentiation of prostate epithelial cells, inhibiting prostate development. We also identify Ar as a GDNF-repressed gene and Gdnf and Gfrα1 as androgen-repressed genes in UGS, thus establishing reciprocal regulatory crosstalk between AR and GDNF signaling in prostate development.

Disruption of growth hormone signaling retards prostate carcinogenesis in the Probasin/TAg rat

We asked whether down-regulation of GH signaling could block carcinogenesis in the Probasin/TAg rat, a model of aggressive prostate cancer. The Spontaneous Dwarf rat, which lacks GH due to a mutation (dr) in its GH gene, was crossed with the Probasin/TAg rat, which develops prostate carcinomas at 100% incidence by 15 wk of age. Progeny were heterozygous for the TAg oncogene and homozygous for either the wild-type GH gene (TAg/Gh(+/+)) or the dr mutation (TAg/Gh(dr/dr)). Prostate tumor incidence and burden were significantly reduced, and tumor latency was delayed in TAg/Gh(dr/dr) rats relative to TAg/Gh(+/+) controls. At 25 wk of age, loss of GH resulted in a 20 and 80% decrease in the area of microinvasive carcinoma in the dorsal and lateral lobes, respectively. By 52 wk of age, invasive prostate adenocarcinomas were observed in all TAg/Gh(+/+) rats, whereas the majority of TAg/Gh(dr/dr) did not develop invasive tumors. Suppression of carcinogenesis could not be attributed to alterations in prostate expression of TAg or androgen receptor or changes in serum testosterone levels. As carcinogenesis progressed in TAg/Gh(+/+) rats, prostate GHR mRNA and protein expression increased significantly, but prostate IGF-I receptor mRNA and protein levels dropped. Furthermore, serum IGF-I and prostate IGF-I levels did not change significantly over the course of carcinogenesis. These findings suggest that GH plays a dominant role in progression from latent to malignant prostate cancer driven by the powerful probasin/TAg fusion gene in rats and suggest that GH antagonists may be effective at treating human prostate cancer.

Gene expression analysis in the ventral prostate of rats exposed to vinclozolin or procymidone

Vinclozolin and procymidone are antiandrogens that are thought to share a common androgen receptor (AR) mediated mechanism of action. This assessment is based primarily on morphological, AR binding, and in vitro transcriptional activation studies. Studies designed to evaluate the gene expression profiles induced by these compounds have the potential to provide further information to test this hypothesis. We have used targeted gene arrays to examine gene expression in the ventral prostate (VP) of 100-day old Sprague Dawley male rats exposed to either vinclozolin or procymidone. Animals were castrated and administered silastic implants with or without testosterone. A subset of testosterone treated animals was then dosed with 200 mg/kg of either fungicide in corn oil. Four treatment groups were used: castrated (C), testosterone (T), testosterone+vinclozolin (V), and testosterone+procymidone (P). Tissue from the VP was collected from six animals per group (3 animals per block x 2 blocks) at 20 h and at 4 days after the start of treatment. Total RNA was then isolated and gene expression analyzed using Clontech Atlas Rat 1.2 Toxicology arrays. When compared to group T, similar changes in gene expression were observed in groups C, P and V at both the 20 h and 4 day time points. After 20 h of treatment, 20 genes were similarly affected across these three treatment groups. Down-regulated genes included various molecular chaperones, the 11-kDa diazepam binding inhibitor, cyclin D1, and mitochondrial aspartate aminotransferase. Genes such as the androgen receptor, PTEN, and ERK2 were up-regulated. Three of the down-regulated genes, GRP78 (BiP), Dad1, and mitochondrial aspartate aminotransferase have been previously shown to be directly androgen regulated. Fifty-four genes were affected at 20 h, whereas, 311 genes were altered 4 days after the start of treatment. These observations, in part, may reflect regression of the VP at the later time point. These results support the hypothesis that procymidone and vinclozolin share a common mechanism or mode of action, a critical step in a cumulative risk assessment.

Chronic inflammation in benign prostate hyperplasia is associated with focal upregulation of cyclooxygenase-2, Bcl-2, and cell proliferation in the glandular epithelium

BACKGROUND

Chronic inflammation has been suggested to be linked to the development and progression of prostate cancer. An inflammatory microenvironment may support the development of malignancy by upregulation of proinflammatory cytokines and cyclooxygenase-2 (COX-2). Recent studies have suggested that COX-2 is upregulated in cancer and in proliferative inflammatory atrophy (PIA) of the prostate.

METHODS

Immunohistochemistry (IHC) was used to investigate the expression of COX-2 in prostate epithelium. The relationships between COX-2 expression and inflammatory cells, proliferation (proliferating cell nuclear antigen (PCNA) and Ki-67), and apoptosis (Bcl-2) were studied in 45 BPH samples.

RESULTS

COX-2 expression was detected in prostate luminal epithelial cells in all 45 samples studied. The overall percentage of COX-2 positive glands was 7.5%, distributed as 0.2% positive glands in normal prostate tissue, 25.7% in postatrophic hyperplasia (PAH), and 11.9% in simple atrophy (SA). The highest proliferation index was found in COX-2 positive stained epithelium. COX-2 expression was associated with Bcl-2 immunostaining in atrophic lesions (P < 0.0001). T lymphocytes and macrophages were the predominant inflammatory cells related to the COX-2 expression in prostate epithelium.

CONCLUSIONS

The data demonstrate that T lymphocytes and macrophages appeared to play an important role in the induction of COX-2 expression in prostate epithelium, which was associated with increased cell proliferation and possibly, due to overexpression of Bcl-2, apoptotic resistance. This suggests that pro-inflammatory cytokines released by adjacent inflammatory cells may induce COX-2 in the epithelial cells in prostate atrophic lesions. In addition, COX-2 expressing cells may be involved in the pathogenesis of prostate cancer.

Green fluorescent protein expression in germ-line transmitted transgenic zebrafish under a stratified epithelial promoter from keratin8

A zebrafish cDNA encoding a novel keratin protein was characterized and named keratin8, or krt8. krt8 expression was initiated at 4.5 hr postfertilization, immediately after the time of zygotic genome activation. The expression is limited to a single layer of envelope cells on the surface of embryos and, in later stages, it also appears in the innermost epithelial layer of the anterior- and posteriormost portions of the digestive tract. In adult, its expression was limited to the surface layer of stratified epithelial tissues, including skin epidermis and epithelia of mouth, pharynx, esophagus, and rectum but not in the gastral and intestinal epithelia. By using a 2.2-kb promoter from krt8, several stable green fluorescent protein (gfp) transgenic zebrafish lines were established. All of these transgenic lines displayed GFP expression in tissues mentioned above except for the rectum; therefore, the pattern of transgenic GFP expression is essentially identical to that of the endogenous krt8 mRNAs. krt8-GFP fusion protein was also expressed in zebrafish embryos under a ubiquitous promoter, and the fusion protein was capable of assembling into intermediate filaments only in the epithelia that normally expressed krt8 mRNAs, indicating the specificity of keratin assembly in vivo.

Prostatic luminal cell differentiation and prostatic steroid-binding protein (PBP) gene expression are differentially affected by neonatal castration

BACKGROUND

Although normal prostatic development is androgen-dependent, the prostate continues to grow in the neonate despite castration. However, the manner in which neonatal growth of the prostate occurs, in the absence of the testis, remains largely unknown. The purpose of this study was to examine the differentiation of prostatic epithelial cells after neonatal castration.

METHODS

Immunohistochemistry was utilized to detect the expression of differentiation products: basal-cell cytokeratin (CK 5), luminal-cell cytokeratin (CK 18), and prostatic steroid-binding protein (PBP), a ventral prostate-specific marker indicative of secretory function in luminal cells. The reverse transcription-polymerase chain reaction was used to detect transcription products of the three polypeptide subunits of PBP, designated C1, C2, and C3. Rats were castrated on day 5 after birth, and ventral prostates were collected on day 14. Dihydrotestosterone was injected (100 microg/animal every 2 days) in castrated animals to determine if PBP expression could be initiated by androgen.

RESULTS

Although no major effects of castration were detected on the differentiation of stromal or basal cells (which differentiate prior to day 5), castration had a pronounced effect on luminal-cell differentiation. Castration inhibited PBP protein expression, but did not affect the expression of luminal-cell cytokeratin (CK 18) protein. Furthermore, castration reduced C1, C2, and C3 transcription. Androgen replacement to castrated animals allowed for the initiation of PBP expression, although its onset was delayed.

CONCLUSIONS

These observations indicate that the testis is not necessary for prostatic luminal-cell differentiation, but is necessary for full expression of luminal-cell secretory phenotype. Furthermore, our study suggests that factors of testicular origin, in addition to androgen, are needed for proper timing of PBP expression. This investigation establishes that the cytological and the physiological differentiation of the rat prostate are differentially regulated.

Transdifferentiation of NRP-152 rat prostatic basal epithelial cells toward a luminal phenotype: regulation by glucocorticoid, insulin-like growth factor-I and transforming growth factor-beta

The role of basal epithelial cells in prostatic function, development and carcinogenesis is unknown. The ability of basal prostatic epithelial cells to acquire a luminal phenotype was explored in vitro using the NRP-152 rat dorsal-lateral prostate epithelial cell line as a model system. NRP-152, which was spontaneously immortalized and clonally derived, is an androgen-responsive and nontumorigenic cell line that has a basal cell phenotype under normal growth conditions. However, when placed in mitogen-deficient media, these cells undergo a dramatic morphological change to a luminal phenotype. Under these growth-restrictive conditions, immunocytochemical analysis shows that NRP-152 cells acquire the luminal markers Z0-1 (a tight-junction associated protein), occludin (integral tight-junction protein), and cytokeratin 18, and lose the basal markers cytokeratins 5 and 14. Total protein and mRNA levels of cytokeratins 8, 18, c-CAM 105 (the calcium-independent cell adhesion molecule) and Z0-1, as detected by western and/or northern blot analyses, respectively, are induced, while cytokeratin 5 and 15 are lost, and occludin is unchanged. Concomitant with this differentiation, expression of transforming growth factor-beta2 (TGF-beta2), TGF-beta3, and TGF-beta receptor type II (TbetaRII) is induced, while those of TGF-beta1 and TbetaRI remain essentially unchanged. Mitogens, such as insulin-like growth factor-I and dexamethasone inhibit luminal differentiation, while exogenous TGF-beta induces such differentiation. These data together with TGF-beta neutralization experiments using pan-specific antibody implicate an important role for autocrine TGF-beta in the induction of the luminal differentiation.

Regulation of rat DOC-2 gene during castration-induced rat ventral prostate degeneration and its growth inhibitory function in human prostatic carcinoma cells

Androgen is a mitogen as well as a morphogen for prostatic epithelium. However, the detailed mechanisms of these distinct androgenic actions have not yet been delineated. Therefore, we employed differential display PCR to unveil any potential genes that may be involved in these processes. In this study, we report the isolation and characterization of two alternative splicing forms (p82 and p59) of C9 complementary DNA, the rat homolog of the human deletion of ovarian carcinoma 2 (DOC-2) gene and mouse p96 phosphoprotein, from rat ventral prostate (VP). We found that C9 was up-regulated in rat VP after castration, suggesting that C9 may be regulated by androgen receptor directly or indirectly during prostate degeneration. A similar regulatory pattern was also observed in both the seminal vesicle and dorsolateral prostate, but not in the coagulating gland or other androgen-independent organs. Immunohistochemical analysis of rat VP demonstrated that C9 is detected in the basal epithelia and surrounding stromal cells after prolonged castration. Ribonuclease protection assay and Western blot analysis revealed that p59 is the predominant C9 isoform in rat VP. To unveil the function of C9 in cell growth, we transfected p59 complementary DNA into the C4-2 cells, a derivative of the LNCaP prostatic carcinoma cell line. The p59 stable transfectants exhibited a slower growth rate and an increase in the cell fraction in the G1 phase under our experimental conditions. These data indicate that C9-p59 has growth inhibitory activity for prostatic epithelial cells. Taken together, our results suggest that C9 is up-regulated during prostate degeneration process and may play an active role in the proliferation and differentiation of prostatic epithelium.

Cytokeratin expression patterns in the rat respiratory tract as markers of epithelial differentiation in inhalation toxicology. I. Determination of normal cytokeratin expression patterns in nose, larynx, trachea, and lung

Cytokeratin (CK) polypeptides constitute the intermediate filament cytoskeleton of epithelial cells. The patterns of CK expression can be regarded as specific markers for the epithelial differentiation status. Our objective was to map the cell type-specific CK expression patterns at all representative sites of the respiratory tract of untreated rats to use as a base for the detection of inhalation exposure-related differentiation changes. Using routine paraffin-embedded sections and a panel of well-characterized monoclonal antibodies for immunohistochemistry, we obtained CK staining patterns as follows. Nasal cavity: respiratory epithelium CK18, CK19 (basal, ciliated, nonciliated cells), CK14, and/or CK15 (basal and nonciliated cells); olfactory epithelium CK18 (basal, mid, apical zones and Bowman's glands), CK14, and CK15 (basal zone); squamous epithelium of ventral meatus CK14, CK15 (basal and suprabasal cells), CK1, 10/11, and CK13 (suprabasal cells); glands and columnar epithelia of vomeronasal organ and nasolacrimal duct CK7 and CK13 in addition to respiratory epithelial CK pattern. Trachea: similar to nasal respiratory epithelium with pronounced CK15 and additional CK7. Larynx: CK14, CK15 (basal, ciliated, nonciliated cells), CK8, CK18, CK19 (not in basal cells), CK4, and CK13 (cuboidal and squamoid cells of ventral half). Lung: bronchial epithelium CK14 and CK15 (basal cells only); bronchial and alveolar epithelium CK7, CK8, CK18, and CK19; bronchiolar epithelium similar but less CK8 and no CK7; pleural mesothelium CK7, CK8, and CK19. This inventory of complex CK expression patterns provides the basis for investigating test substance-related effects in inhalation toxicology, e.g., cigarette smoke-induced changes.

Cytokeratin 8 is a suitable epidermal marker during zebrafish development

We have cloned and characterized the zebrafish (Danio rerio) homologous cytokeratin 8 (zf-K8) cDNA. This cytokeratin belongs to the gene family of intermediate filaments and it is a component of the cytoskeleton of epithelial cells. Gene expression analysis during embryonic development and at adult stages presented here revealed that zf-K8 mRNA is inherited maternally and that it is present in the oocyte, the zygote and in the cleavage stage embryo. After mid blastula transition this gene is expressed in all surface cells, notably in those of the enveloping layer (EVL) and of the periderm, as well as in a subpopulation of the deep cells (DEL) presumed to be intestinal progenitors. During later embryonic stage zf-K8 mRNA is strongly expressed in the developing pectoral fin. In adult zebrafish, the zf-K8 gene is not only expressed in simple epithelia such as the colorectal intestine, but also, in contrast to other vertebrates, it is present in stratified skin and differentiated fins. These observations suggest that the zf-K8 gene is an appropriate epidermal marker during zebrafish ontogenesis.

Phosphorylation of human keratin 8 in vivo at conserved head domain serine 23 and at epidermal growth factor-stimulated tail domain serine 431

Dynamic phosphorylation is one mechanism that regulates the more than 20 keratin type I and II intermediate filament proteins in epithelial cells. The major type II keratin in "simple type" glandular epithelia is keratin 8 (K8). We used biochemical and mutational approaches to localize two major in vivo phosphorylation sites of human K8 to the head (Ser-23) and tail (Ser-431) domains. Since Ser-23 of K8 is highly conserved among all type II keratins, we also examined if the corresponding Ser-59 in stratified epithelial keratin 6e is phosphorylated. Mutation of K6e Ser-59 abolished its phosphorylation in 32PO4-labeled baby hamster kidney cell transfectants. With regard to K8 phosphorylation at Ser-431, it increases dramatically upon stimulation of cells with epidermal growth factor (EGF) or after mitotic arrest and is the major K8 phosphorylated residue after incubating K8 immunoprecipitates with mitogen-activated protein or cdc2 kinases. A monoclonal antibody that specifically recognizes phosphoserine 431-K8 manifests increased reactivity with K8 and recognizes reorganized K8/18 filaments after EGF stimulation. Our results suggest that in vivo serine phosphorylation of K8 and K6e within the conserved head domain motif is likely to reflect a conserved phosphorylation site of most if not all type II keratins. Furthermore, K8 Ser-431 phosphorylation occurs after EGF stimulation and during mitotic arrest and is likely to be mediated by mitogen-activated protein and cdc2 kinases, respectively.

Estrogen regulation of nuclear matrix-intermediate filament proteins in human breast cancer cells

The tissue matrix consists of linkages and interactions of the nuclear matrix, cytoskeleton, and extracellular matrix. This system is a dynamic structural component of the cell that organizes and processes structural and functional information to maintain and coordinate cell function and gene expression. We have studied estrogen regulation of nuclear matrix associated proteins, including the intimately connected cytoskeletal intermediate filaments, in T-47D5 human breast cancer cells. Three proteins (identified as cytokeratins 8, 18, and 19) present in the nuclear matrix-intermediate filament fraction (NM-IF) of cells grown in estrogen-replete conditions were dramatically reduced when the cells were grown in acute (1 week) estrogen-depleted conditions. Replacing estrogen in the medium of acute estrogen-depleted cells restored expression of these proteins. T-47D5 cells that are chronically depleted of estrogen (T5-PRF) are estrogen-nonresponsive in culture. These cells overexpressed these three proteins, compared to parent cells grown in the presence of estrogen. Treatment of the T5-PRF cells with estrogen did not lead to further up-regulation of these proteins. Treating T-47D5 cells in estrogen-replete conditions with the antiestrogens 4-hydroxytamoxifen and ICI 164 384 (100 nM, 3 days) resulted in a significant reduction in these proteins, while no effect was seen in long-term chronic estrogen-depleted T-47D5 cells. In conclusion, we have identified NM-IF proteins (cytokeratins 8, 18, and 19) in human breast cancer cells that are estrogen regulated and may play a role in estrogen action in human breast cancer cells.

Keratinocyte growth factor and its receptor are involved in regulating early lung branching

Lung branching morphogenesis depends on mesenchymal-epithelial tissue interactions. Keratinocyte growth factor (KGF) has been implicated to be a regulator of these tissue interactions. In the present study, we investigated the role of KGF in early rat lung organogenesis. Reverse transcriptase-polymerase chain reaction analysis revealed KGF mRNA expression in the mesenchymal component of the 13-day embryonic lung, while message for KGF receptor (KGFR) was expressed in the epithelium, confirming the paracrine nature of KGF/KGFR axis. Antisense KGF oligonucleotides inhibited DNA synthesis of embryonic lung explants. This inhibitory effect of antisense KGF was partially reversed by the addition of exogenous KGF. Recombinant KGF was mitogenic for 13-day isolated embryonic lung epithelial cells. Medium conditioned by 13-day lung mesenchymal cells also stimulated DNA synthesis of 13-day embryonic lung epithelial cells. This stimulatory effect was partially abrogated by a neutralizing KGF antibody. The number of terminal buds of lung explants cultured in the presence of antisense KGF oligonucleotides was significantly reduced compared to control explants. Exogenous KGF partially abrogated the inhibitory effect of antisense KGF on early lung branching. Sense or scrambled KGF oligonucleotides had no inhibitory effect on lung growth and branching. Addition of neutralizing KGF antibodies to the explants also reduced the degree of branching, while non-immune IgG and neutralizing acidic FGF antibodies had no effect. Explants incubated with antisense oligonucleotides targeted to the initiation site of translation of both the splice variants of the fibroblast growth factor receptor-2 (FGFR2) gene, KGFR and bek, exhibited a similar reduction in lung branching as observed with antisense KGF oligonucleotides. Antisense KGFR-specific oligonucleotides dramatically inhibited lung branching, while exposure of explants to antisense bek-specific oligonucleotides resulted in reduced branching albeit to a lesser degree than that observed with antisense KGFR-specific oligonucleotides. Neither sense nor scrambled KGFR-specific oligonucleotides had any effect on early lung branching. These results suggest that the KGF/KGFR system has a critical role in early lung organogenesis.

Establishment of immortalized alveolar type II epithelial cell lines from adult rats

We developed methodology to isolate and culture rat alveolar Type II cells under conditions that preserved their proliferative capacity, and applied lipofection to introduce an immortalizing gene into the cells. Briefly, the alveolar Type II cells were isolated from male F344 rats using airway perfusion with a pronase solution followed by incubation for 30 min at 37 degrees C. Cells obtained by pronase digestion were predominantly epithelial in morphology and were positive for Papanicolaou and alkaline phosphatase staining. These cells could be maintained on an extracellular matrix of fibronectin and Type IV collagen in a low serum, insulin-supplemented Ham's F12 growth medium for four to five passages. Rat alveolar epithelial cells obtained by this method were transformed with the SV40-T antigen gene and two immortalized cell lines (RLE-6T and RLE-6TN) were obtained. The RLE-6T line exhibits positive nuclear immunostaining for the SV40-T antigen and the RLE-6TN line does not. PCR analysis of genomic DNA from the RLE-6T and RLE-6TN cells demonstrated the T-antigen gene was present only in the RLE-6T line indicating the RLE-6TN line is likely derived from a spontaneous transformant. After more than 50 population doublings, the RLE-6T cells stained positive for cytokeratin, possessed alkaline phosphatase activity, and contained lipid-containing inclusion bodies (phosphine 3R staining); all characteristics of alveolar Type II cells. The RLE-6TN cells exhibited similar characteristics except they did not express alkaline phosphatase activity. Early passage RLE-6T and 6TN cells showed a near diploid chromosome number.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal control of apoptosis: the rat prostate gland as a model system

Because of the large proportion of cells that undergoes apoptosis in response to castration and because of the predictable time in which apoptosis occurs subsequent to castration of an adult male, the rat ventral prostate gland provides a superior model system in which to study the process of apoptosis in vivo. This model system has already proven to be one of the more fertile systems for the identification of specific gene products that have the potential to effect apoptosis. Unfortunately, this in vivo system has limited usefulness for the types of genetic manipulations required to prove the role of any given gene product in the onset and procession of apoptosis. Direct genetic manipulation of a living tissue remains a goal of molecular biology-based therapies, especially for peripheral tissues such as the prostate gland. Appropriate in vitro (cell culture) models in which to study androgen-regulated apoptosis of prostate cells are currently unavailable because prostate epithelial cells, once established in culture, are no longer dependent on androgenic steroids. In the future, genetic approaches involving gene targeting through transgenic mouse technology may provide the kind of information needed to evaluate the role of individual gene products in prostate cell apoptosis.

Derivation of androgen-independent human LNCaP prostatic cancer cell sublines: role of bone stromal cells

A model of human prostate cancer was established to study cellular interaction between prostate cancer and bone stroma in vivo. In this model, subcutaneous co-injection of 2 non-tumorigenic human cell lines--LNCaP, a prostate cancer cell line, and MS, a bone stromal cell-line--into intact adult male mice resulted in formation of carcinomas that secreted prostate-specific antigen (PSA), a clinically useful human serum prostate cancer marker. In castrated hosts, upon cellular interaction with bone fibroblasts, we observed the progression of these tumors from an androgen-dependent (AD) to an androgen-independent state (AI). We derived 4 LNCaP cell sublines from the chimeric LNCaP/MS tumors: the M subline from intact hosts and the C4, C4-2 and C5 sublines from castrated hosts. The LNCaP sublines had chromosomal markers similar to those of the parental LNCaP cells and distinctly different from those of the MS bone stromal cell line. Although the parental and derived cell lines expressed similar steady-state levels of ornithine decarboxylase transcript, the sublines expressed 5- to 10-fold higher basal steady-state levels of PSA transcript than did the parental LNCaP cell line. The LNCaP sublines formed 13- to 26-fold more soft-agar colonies than the parental LNCaP cell line. The sublines became tumorigenic, yielding an incidence of tumors in intact athymic mice of 7-75%. The LNCaP sublines C4 and C5 (but not the parental and M cell line) formed tumors in castrated hosts when co-injected with bone fibroblasts. A second-generation LNCaP subline, C4-2, was derived from a chimeric tumor induced by co-inoculating castrated mouse with C4 cells and MS cells. We found that C4-2 subline was tumorigenic when inoculated into castrated hosts in the absence of inductive fibroblasts. Moreover, C4-2 was the only subline capable of forming soft-agar colonies when cultured in serum-free medium. In comparison with the parental LNCaP cells, the C4-2 subline expressed lower steady-state levels of androgen receptor (AR) protein and mRNA transcript and lost its androgen responsiveness in vitro. Our results suggest that certain genetic traits of prostate cancer cells may be selected or altered through an "adaptive" mechanism that involves cellular interaction with the bone stromal cells.