Tumor-selective killing by selenite in patient-matched pairs of normal and malignant prostate cells

BACKGROUND

Selenium compounds have been shown to induce apoptosis in a variety of human prostate cancer cell lines. However, the effects of selenium have yet to be examined in normal and malignant cells derived from the same individual. Selenite metabolism consumes glutathione (GSH) and produces superoxide. The generation of reactive oxygen species is an important mechanism in selenite-induced apoptosis.

METHODS

Three patient-matched pairs of primary prostatic epithelial cell cultures from normal and cancer were evaluated for their response to selenite. Apoptosis was measured and the differential response of normal and cancer cells was correlated with the expression of bcl-2, bax, GSH, and manganese superoxide dismutase (MnSOD).

RESULTS

The cancer-derived cells were significantly more sensitive to selenite-induced apoptosis than the corresponding normal cells. Tumor-selective killing was not observed in cells treated with selenomethionine. The ratio of bcl-2:bax was decreased in the cancer-derived cells treated with selenite. Total GSH concentrations were similar in paired normal and cancer cells. Therefore, differences in GSH content do not appear to play a role in tumor-selective killing by selenite. Superoxide is a by-product of selenite metabolism and normal cells showed increased MnSOD expression and SOD activity compared to the cancer-derived cells. Prostate cancer cells treated with the MnSOD mimetic, MnTMPyP, were protected against the cytotoxic effects of selenite.

CONCLUSIONS

Higher MnSOD expression in normal cells may play an important role in eliminating superoxide radicals produced as a result of selenite metabolism and contribute to the tumor-selective killing by selenite in prostate cancer.

Tumor-suppression function of transcription factor USF2 in prostate carcinogenesis

Although the transcription factor USF2 has been implicated in the regulation of cellular growth and proliferation, it is unknown whether alterations in USF2 contribute to tumorigenesis and tumor development. We examined the role of USF2 in prostate tumorigenesis. Western blot analysis revealed markedly decreased USF2 levels in three androgen-independent prostate cancer cell lines, PC-3, DU145, and M12, as compared to nontumorigenic prostate epithelial cells or the androgen-dependent cell line, LNCaP. Ectopic expression of USF2 in PC-3 cells did not affect the cell proliferation rate of PC-3 cells on plastic surfaces. However, it dramatically decreased anchorage-independent growth of PC-3 cells in soft agar (90-98% inhibition) and the invasion capability (80% inhibition) of PC-3 cells in matrix gel assay. Importantly, expression of USF2 in PC-3 cells inhibited the tumorigenicity of PC-3 cells in an in vivo nude mice xenograft model (80-90% inhibition). These results suggest that USF2 has tumor-suppression function. Consistent with its function in tumor suppression, we found that the USF2 protein is present in normal prostate epithelial cells but absent in 18 of 42 (43%) human prostate cancer tissues (P = 0.015). To further examine the functional role of USF2 in vivo, we generated mice with genetic deletion of USF2 gene. We found that USF2-null mice displayed marked prostate hyperplasia at a young age, suggesting that USF2 is involved in the normal growth and differentiation of prostate. Together, these studies demonstrate that USF2 has tumor-suppressor function and plays a role in prostate carcinogenesis.

Primary cell cultures as models of prostate cancer development

This review focuses on primary cultures of human prostatic epithelial cells and their applications as models of normal and malignant biological behavior. Current abilities to culture cells from normal tissues, from premalignant dysplastic lesions (prostatic intraepithelial neoplasia), from primary adenocarcinomas, and from metastases are described. Evidence for representation of the interrelated cells of the normal prostatic epithelium--stem cells, basal epithelial cells, secretory epithelial cells, transit amplifying cells and neuroendocrine cells--in primary cultures is presented. Comparisons between normal and cancer-derived primary cultures are made regarding biological activities relevant to carcinogenesis, such as proliferation, apoptosis, differentiation, senescence, adhesion, migration, invasion, steroid hormone metabolism, other metabolic pathways and angiogenesis. Analyses of tumor suppressor activity, differential gene expression and cytogenetics in primary cultures have revealed changes relevant to prostate cancer progression. Preclinical studies with primary cultures have provided information useful for designing new strategies for chemoprevention, chemotherapy, cytotoxin therapy, radiation therapy, gene therapy and imaging. While the behavior of normal primary cultures is often used as a basis for comparison with established, immortal prostate cancer cell lines, the most informative studies are performed with donor-matched pairs of normal and malignant primary cultures, grown under identical conditions. Challenges that remain to be addressed if the full potential of primary cultures as a model system is to be realized include isolation, culture and characterization of stem cells, improved methodology to induce or maintain a fully differentiated, androgen-responsive phenotype, and identification of cell surface antigens or other markers with which to purify pure populations of live cancer or premalignant cells apart from non-malignant epithelial cells prior to culture.

Re-evaluation of inhibin alpha subunit as a tumour suppressor in prostate cancer

Inhibin is a member of the TGF-beta superfamily of growth and differentiation factors and a tumor suppressor. Consistent with the tumor suppressive function of the inhibin alpha subunit in prostate cancer, we reported a loss of gene expression due to DNA hypermethylation and loss of heterozygosity (LOH) as well as down regulation of inhibin alpha subunit immunoreactivity. Paradoxically, an expanded study to evaluate the prognostic significance of inhibin alpha subunit expression in men with prostate cancer resulted in a contradictory outcome, whereby an up-regulation of subunit expression was recorded. In seeking a more comprehensive explanation for all data sets, we offer a unifying hypothesis. We propose that the tumor suppressor activities of the inhibin alpha subunit dominate in non-malignant tissue, but its oncogenic activities emerge during tumorigenesis. An explanation such as this, involving a switch in gene function from being tumor suppressive to pro-oncogenic, may account for the discrepant findings in other types of cancer.

Preferential production of latent transforming growth factor ?-2 by primary prostatic epithelial cells and its activation by prostate-specific antigen

Three mammalian isoforms of transforming growth factor-beta (TGFbeta) are known, TGFbeta1, 2, and 3, that have non-overlapping functions during development. However, their specific roles in cancers such as prostate cancer are less clear. Here we show that primary cultures of prostatic epithelial cells preferentially produce and activate the latent TGFbeta2 isoform. Paired cultures of normal and malignant prostate cells from prostate cancer patients produced predominantly the TGFbeta2 isoform, with 30- to 70-fold less TGFbeta1. By mono-Q ion exchange chromatography, three major peaks of latent TGFbeta2 activity were observed corresponding to the known small latent TGFbeta2 complex, the known large latent TGFbeta2 complex and a novel eluting peak of latent TGFbeta2. Although prostate cells are known to activate latent TGFbeta, the mechanism for activation is currently unclear. We investigated whether prostate specific antigen (PSA), a serine protease used as a clinical marker for prostate cancer, could play a role in the activation of latent TGFbeta. Unlike plasmin, a known activator of both latent TGFbeta1 and 2, PSA specifically activated the recombinant small latent form of TGFbeta2, but not TGFbeta1. Prostate epithelial cells, therefore, preferentially produce the TGFbeta2 isoform and PSA, a protease produced by the prostate, specifically targets the activation of this TGFbeta isoform. PSA-mediated activation of latent TGFbeta2 may be an important mechanism for autocrine TGFbeta regulation in the prostate and may potentially contribute to the formation of osteoblastic lesions in bone metastatic prostate cancer.

Elevated Expression of Inhibin α in Prostate Cancer

PURPOSE

Less than 50% of men who undergo radical prostatectomy for prostate cancer are cured of disease. We evaluate tumor expression of inhibin alpha, a putative tumor suppressor, and the related protein, follistatin, to determine whether expression correlated with failure to be cured by surgery.

MATERIALS AND METHODS

Tissues were selected from an archival collection of 379 prostatectomy specimens from men with followup of at least 5 years after surgery. Since previous studies showed that such men with only Gleason grade 3 cancer had a greater than 95% chance of no biochemical recurrence (increase in serum prostate specific antigen), our investigation was confined to 174 men with 2% or greater grade 4/5 cancer. These men had an intermediate rate of failure, providing an opportunity to analyze the potential contribution of inhibin alpha or follistatin to progression. Intensity of immunohistochemical labeling for inhibin alpha and follistatin in each cancer was compared with that in normal glands within the same tissue section.

RESULTS

The majority of cases showed more intense expression of inhibin alpha in cancer than in normal glands. Those individuals whose cancers had the most elevated expression of inhibin alpha had a higher risk of recurrence, although this association was not statistically significant. Follistatin was expressed equivalently in normal and cancer cells in the majority of cases and did not correlate with recurrence.

CONCLUSIONS

Our finding that inhibin alpha is frequently overexpressed in high grade prostate cancer suggests that the role of inhibin alpha as a tumor suppressor needs to be reevaluated. Furthermore, assessment of inhibin alpha as a serum marker of prostate cancer, as used to diagnose ovarian cancer, may be warranted.

The role of vitamin D and retinoids in controlling prostate cancer progression

Prostate cancer is a leading cause of cancer-related deaths in many countries. Premalignant lesions and invasive cancer occur more frequently in the prostate than in any organ other than the skin. Yet, the incidence of clinically detected prostate cancer is much lower than the histopathological incidence. The slow growth of prostate cancer and the low incidence of clinically manifest disease in some geographical locations or racial/ethnic groups suggest that prostate cancer can be controlled, perhaps by dietary factors. Vitamin D and retinoids have emerged as leading candidates both to prevent and to treat prostate cancer. Many of the activities of these compounds, established from epidemiological studies, research with cell culture and animal models, and clinical trials, are consistent with tumor suppressor effects. However, retinoids may have additional tumor enhancer properties that balance or negate anti-cancer activity. This perhaps explains the overall lack of protective effects of vitamin A compounds against prostate cancer found in epidemiological studies, and the minimal efficacy of retinoids in clinical trials to treat prostate cancer. While current efforts focus on developing strategies to use vitamin D compounds to control prostate cancer, the possibility exists that prostate cancer cells may become resistant to tumor suppressor effects of vitamin D. Analyses of experimental model systems show that prostate cancer cells become less sensitive to vitamin D through loss of receptors or signaling molecules that mediate vitamin D's actions, or through changes in metabolic enzymes that synthesize or degrade vitamin D compounds. The potential promise of exploiting vitamin D to control prostate cancer is tempered by the possibility that prostate cancer, perhaps even at early stages, may develop mechanisms to escape tumor suppressor activities of vitamin D and/or retinoids.

Role of glutathione depletion and reactive oxygen species generation in apoptotic signaling in a human B lymphoma cell line

The primary objective of this study was to determine the sequence of biochemical signaling events that occur after modulation of the cellular redox state in the B cell lymphoma line, PW, with emphasis on the role of mitochondrial signaling. L-Buthionine sulphoximine (BSO), which inhibits gamma glutamyl cysteine synthetase (gammaGCS), was used to modulate the cellular redox status. The sequence and role of mitochondrial events and downstream apoptotic signals and mediators was studied. After BSO treatment, there was an early decline in cellular glutathione (GSH), followed by an increase in reactive oxygen species (ROS) production, which induced a variety of apoptotic signals (detectable at different time points) in the absence of any external apoptotic stimuli. The sequence of biochemical events accompanying apoptosis included a 95% decrease in total GSH and a partial (25%) preservation of mitochondrial GSH, without a significant increase in ROS production at 24h. Early activation and nuclear translocation of the nuclear factor kappa B subunit Rel A was observed at approximately 3h after BSO treatment. Cytochrome c release into the cytosol was also seen after 24h of BSO treatment. p53 protein expression was unchanged after redox modulation for up to 72 h, and p21waf1 independent loss of cellular proliferation was observed. Surprisingly, a truncated form of p53 was expressed in a time-dependent manner, beginning at 24h after BSO incubation. Irreversible commitment to apoptosis occurred between 48 and 72 h after BSO treatment when mitochondrial GSH was depleted, and there was an increase in ROS production. Procaspase 3 protein levels showed a time-dependent reduction following incubation with BSO, notably after 48 h, that corresponded with increasing ROS levels. At 96 h, caspase 3 cleavage products were detectable. The pan-caspase inhibitor zVADfmk, partially blocked the induction of apoptosis at 48 h, and was ineffective after 72 h. PW cells could be rescued from apoptosis by removing them from BSO after up to 48, but not 72 h incubation with BSO. Mitochondrial transmembrane potential (DeltaPsi(m)) remained intact in most of the cells during the 72 h observation period, indicating that DeltaPsi(m) dissipation is not an early signal for the induction of redox dependent apoptosis in PW cells. These data suggest that a decrease in GSH alone can act as a potent early activator of apoptotic signaling. Increased ROS production following mitochondrial GSH depletion, represents a crucial event, which irreversibly commits PW cells to apoptosis.

Genetic polymorphisms in the androgen receptor and type II 5 alpha-reductase genes in prostate enlargement

PURPOSE

We examined the association of androgen receptor gene cytosine-adenine-guanine (CAG) repeat length and the 2 single nucleotide polymorphisms A49T and V89L in the type II 5 alpha-reductase gene with prostate enlargement measured as the weight of the surgically removed prostate.

MATERIALS AND METHODS

A total of 68 men with a prostate weighing 80 gm. or greater were compared with 197 controls with a prostate weighing less than 80 gm. These men had undergone radical prostatectomy between 1992 and 1996. DNA was extracted from archival prostate tissue uninvolved with cancer and genotyped for 3 polymorphic markers. The effects of genetic variants and clinicopathological variables on prostate enlargement risk were estimated by logistic regression.

RESULTS

The age adjusted odds ratio estimate of prostate enlargement risk in men with 23 or greater versus 20 or fewer CAG repeats was 0.41 (95% confidence interval 0.19 to 0.89). This risk reduction was consistently found when an alternative prostate enlargement definition and subject restriction were used. No consistent association with prostate enlargement risk was observed for A49T or V89L polymorphisms.

CONCLUSIONS

Our finding further supports the hypothesis that the shorter CAG repeat length of the androgen receptor gene is related to prostate enlargement.

Prostatic expression of hensin, a protein implicated in epithelial terminal differentiation

OBJECTIVES

Hensin induces terminal differentiation in rabbit kidney collecting tubule cells. Rabbit hensin and human DMBT1 result from alternative splicing of the same gene. The human DMBT1 gene is located on chromosome 10q25-26, a region often deleted in prostate cancer. In this study we examined the potential role of this gene in terminal differentiation of prostate, as well as its role in prostatic carcinogenesis.

METHODS

We searched for deletions of this gene in prostatic cells cultured from cancer and benign tissues using PCR and cDNA cloning. The expression of hensin/DMBT1 in cultured cells and during prostate development was characterized by immunochemistry.

RESULTS

No deletions of hensin/DMBT1 similar to those found in glioblastomas, lung and esophageal cancers were observed in prostate cancer or BPH cells. Hensin/DMBT1 protein was localized in intracellular vesicles of epithelial cells in neonatal and 6-week-old mouse prostates. By 6 weeks, hensin/DMBT1 began to localize in the basal lamina of the prostate and vas deferens. In matured 6-month-old prostates, there was extensive deposition of hensin/DMBT1 in the basal lamina.

CONCLUSIONS

There is no evidence that hensin/DMBT1 is implicated in prostatic carcinogenesis. The localization of hensin/DMBT1 during maturation raises the possibility that hensin/DMBT1 is involved in terminal differentiation of the prostate and vas deferens.

Characterization of cultured human prostatic epithelial cells by cluster designation antigen expression

Cultured prostatic epithelial cells have been extensively studied as a model of prostate biology. What is the lineage relationship of the cultured cells to the epithelial cell types in tissue? How different are cultured cells derived from tumor tissue to those derived from benign tissue? Expression of cluster designation (CD) cell surface molecules has been shown to be useful in characterizing cells according to lineage. A CD profile was therefore generated for cultured human prostatic epithelial cells and compared with those previously established for basal and luminal epithelial cells in the prostate. Presence of CD44, CD49b, CD49f, and CD104 and absence of CD57 suggests that cultured cells were derived from basal cells of prostatic tissues. However, expression of certain CD antigens characteristic of luminal epithelial cells was also observed in subpopulations of cultured cells. The pattern of CD antigens in cultured cells reflects a phenotype similar to that of transit-amplifying cells that have been described in the prostate. Several CD antigens were found expressed by both cultured prostatic epithelial and stromal cells, and are probably associated with cell proliferation. The CD profiles of cultured epithelial cell strains derived from normal compared with malignant tissues were notably similar to each other and to that of the prostate cancer cell line PC-3. We conclude that cells in culture retain expression of certain lineage-characteristic CD antigens. Furthermore, CD antigens can define subpopulations of cells with differential gene expression.

Rationale for combination ketoconazole/ vitamin D treatment of prostate cancer

The high rate of progression of prostate cancer after androgen deprivation therapy mandates that new strategies be developed. Adjuvant therapy combined with androgen deprivation may slow or prevent progression. Ketoconazole plus calcitriol therapy is an example of 1 such a combination with a mechanistic basis for synergistic activity. Ketoconazole is commonly used as a second-line androgen deprivation therapy. This imidazole derivative is an inhibitor of P-450 enzymes, including those involved in steroidogenesis. Other P-450 enzymes that are inhibited by ketoconazole include 1alpha-hydroxylase and 24-hydroxylase, which metabolize vitamin D. Growth inhibition of prostate cancer cells by vitamin D depends on levels of the active metabolite, 1,25-dihydroxyvitamin D(3) (calcitriol). The enzyme 24-hydroxylase converts calcitriol to less active products. The inhibition of 24-hydroxylase by ketoconazole maintains the magnitude and duration of response to calcitriol. Combined ketoconazole/calcitriol therapy might therefore potentiate the antitumor activity of calcitriol. Because androgen-independent prostate cancer cells often remain responsive to growth inhibition by calcitriol, it is also possible that calcitriol would slow or prevent development of androgen-independent cancer growth. Another consideration is that ketoconazole blocks 1alpha-hydroxylase activity, which is the key enzyme that creates calcitriol in the body. Therefore, patients receiving ketoconazole therapy are likely to be deficient in vitamin D. The detrimental consequences of vitamin D deficiency in these patients would also be alleviated by the addition of calcitriol to the therapeutic regimen.

Activation of EphA receptor tyrosine kinase inhibits the Ras/MAPK pathway

Interactions between Eph receptor tyrosine kinases (RTKs) and membrane-anchored ephrin ligands critically regulate axon pathfinding and development of the cardiovascular system, as well as migration of neural cells. Similar to other RTKs, ligand-activated Eph kinases recruit multiple signalling and adaptor proteins, several of which are involved in growth regulation. However, in contrast to other RTKs, activation of Eph receptors fails to promote cell proliferation or to transform rodent fibroblasts, indicating that Eph kinases may initiate signalling pathways that are distinct from those transmitted by other RTKs. Here we show that stimulation of endogenous EphA kinases with ephrin-A1 potently inhibits the Ras/MAPK cascade in a range of cell types, and attenuates activation of mitogen-activated protein kinase (MAPK) by receptors for platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF). In prostatic epithelial cells and endothelial cells, but not fibroblasts, treatment with ephrin-A1 inhibits cell proliferation. Our results identify EphA kinases as negative regulators of the Ras/MAPK pathway that exert anti-mitogenic functions in a cell-type-specific manner.

Reduced 1alpha-hydroxylase activity in human prostate cancer cells correlates with decreased susceptibility to 25-hydroxyvitamin D3-induced growth inhibition

Evidence from epidemiological, molecular, and genetic studies suggests a role for vitamin D in the development and/or progression of prostate cancer. In experimental models and clinical trials, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] was shown to exert antiproliferative, prodifferentiating, and antimetastatic/invasive effects on prostatic epithelial cells. Because the direct clinical application of 1,25(OH)2D3 is limited by the major side effect of hypercalcemia, we investigated the potential therapeutic utility of its less calcemic precursor, 25-hydroxyvitamin D3 [25(OH)D3], which is converted locally within the prostate to 1,25(OH)2D3 by 1alpha-hydroxylase. Quantification of 1alpha-hydroxylase activity in human prostatic epithelial cells by enzyme-substrate reaction analyses revealed a significantly decreased activity in cells derived from adenocarcinomas compared with cells derived from normal tissues or benign prostatic hyperplasia (BPH). In growth assays, we found that 25(OH)D3 inhibited growth of normal or BPH cells similarly to 1,25(OH)2D3. In contrast, in primary cultures of cancer cells and established cell lines, the antiproliferative action of 25(OH)D3 was significantly less pronounced than that of 1,25(OH)2D3. Our results indicate that growth inhibition by 25(OH)D3 depends on endogenous 1alpha-hydroxylase activity, and that this activity is deficient in prostate cancer cells. This finding has ramifications for both the prevention and therapy of prostate cancer with vitamin D compounds.

SMAD3 represses androgen receptor-mediated transcription

The androgen-signaling pathway is important in the growth and progression of prostate cancer. Androgen ablation therapy, which may result in programmed cell death, is often used to treat advanced prostate cancer. The growth-promoting effects of androgen are mediated mostly through the androgen receptor (AR). Transforming growth factor beta (TGF-beta) plays critical roles in controlling prostate cell proliferation, differentiation, and apoptosis. Normal transcripts and proteins of TGF-beta receptors are frequently lost in prostate cancer cells, especially in advanced stages of the disease. However, the mechanisms by which TGF-beta inhibits proliferation and induces apoptosis in prostate cancer cells is not clear. We investigated the molecular mechanism by which TGF-beta inhibits transcriptional activation mediated by AR. Using transient transfection systems, we demonstrated that Smad3 specifically represses transcriptional activation mediated by AR on two natural androgen-responsive promoters. This repression is transmitted through TGF-beta signaling and can be regulated by other Smad proteins. A protein-protein interaction between AR and Smad3 was identified in vitro and in vivo, and the transcription activation domain of AR and the MH2 of Smad3 were identified as being responsible for binding. Additional functional experiments showed that the repression of AR by Smad3 is mediated solely through the MH2 domain. These results provide fresh insight for understanding the mechanism by which TGF-beta regulates the androgen-signaling pathway in prostate cancer cells.

Basic science of hormonal therapy for prostate cancer

New developments in molecular and cellular biology are rapidly increasing knowledge of the mechanisms of androgen action in the prostate. Molecular profiling of recurrent cancer after androgen deprivation therapy has revealed genetic changes related to cell survival and proliferation. It is now clear that loss of the androgen receptor (AR) does not explain androgen-independent growth of a majority of recurrent cancers. Rather, overexpression, mutation, and ligand-independent activation of the AR may confer enhanced sensitivity to androgen or other growth factors. Therefore, the term "androgen-independent" is often a misnomer. This emerging concept is the basis of novel strategies to prevent or slow recurrence.

Cultured stromal cells: an in vitro model of prostatic mesenchymal biology

BACKGROUND

Initial efforts to develop in vitro models to study prostatic biology focused on the culture and characterization of epithelial cells. Recently, attention has turned towards inclusion of stromal cells in experimental systems.

METHODS

Improved methods to isolate and culture stromal cells have been developed. An array of markers are employed to characterize subtypes of stromal cells, with particular interest in smooth muscle differentiation.

RESULTS

Defined, serum-free media are available for certain experimental applications. Conditions that promote smooth muscle differentiation have been identified. Investigators have characterized hormonal and peptide factors that regulate the growth of prostatic stromal cells, and have also described paracrine factors produced by stromal cells that influence epithelial biology.

CONCLUSIONS

Prostatic stromal-cell cultures are now widely employed by a large number of investigators for a diverse array of experimental purposes. While further refinement is required to obtain model systems that fully mimic in vivo processes, the availability of stromal- and epithelial-cell cultures provides a valuable resource for studying normal prostatic biology as well as benign prostatic hyperplasia (BPH) and cancer.

Brefeldin A induces p53-independent apoptosis in primary cultures of human prostatic cancer cells

PURPOSE

The objective of this study was to investigate growth-inhibitory and apoptotic activity of the experimental antitumor drug, brefeldin A (BFA), on primary cultures of human epithelial cells derived from prostatic adenocarcinomas.

MATERIALS AND METHODS

Clonal assays were performed to evaluate the effects of BFA on growth of prostatic cancer cell strains. Loss of cell viability in response to BFA was assessed by trypan blue exclusion. Induction of apoptosis by BFA was evaluated by morphologic criteria, electrophoretic assay of DNA fragmentation, and a cell death ELISA. Immunoblots were used to monitor p53 and pRB expression in response to BFA.

RESULTS

BFA was growth-inhibitory at a half-maximal concentration of 5 ng./ml. (18 nM). Morphological manifestations of apoptosis were evident by 24 hours of treatment. Cell viability declined and the cell death ELISA indicated an 18-fold increase in apoptosis in BFA-treated versus untreated cells at 48 hours. DNA fragmentation was also seen at 48 hours. Levels of p53 were not altered by BFA, but pRB was maintained in a hypophosphorylated state by BFA treatment.

CONCLUSIONS

BFA is a potent inducer of apoptosis in prostatic cancer cells via a p53-independent mechanism. Cells derived from low-grade as well as high-grade cancers responded similarly to BFA. Since p53-mediated pathways of apoptosis may frequently be abrogated in prostatic cancer cells, agents such as BFA that induce p53-independent cell death may be promising candidates for chemotherapeutic agents.

Vitamin D and prostate cancer risk

Prostate cancer is a progressive, multistep disease which presents many stages for intervention. Microscopic cancer is found in the prostate beginning by age 30 in about 20% of men, and the incidence increases steadily so that by the time a man is 90 years old, he has almost a 100% chance of having cancer in his prostate. Independent, multiple foci of cancer are present in the majority of prostate specimens, and the incidence of premalignant lesions is even higher than that of cancer. Yet, despite the high incidence of microscopic cancer, only 8% of men in the US present with clinically significant disease during their lifetime. Furthermore, only 3% of men in the US die of prostate cancer. In no other human cancer is there such disparity between the high incidence of microscopic malignancy and the relatively low death rate. Thus, there are many windows of opportunity for control of prostate cancer. Evidence from diverse areas of study - epidemiologic, molecular, genetic, cellular, animal models, and clinical trials - suggests that vitamin D may be an effective preventive agent against prostate cancer.

Stepwise genetic changes associated with progression of nontumorigenic HPV-18 immortalized human prostate cancer-derived cell line to a malignant phenotype

Cytogenetics, fluorescence in situ hybridization (FISH), and comparative genomic hybridization (CGH) were used to identify genes that are involved in the development and progression of prostate cancer. For that purpose, we chose a cell line established in vitro from a prostatic adenocarcinoma which was nontumorigenic in nude mice and followed its progression to a tumorigenic cell line. Stepwise changes were observed in the cell line as it became tumorigenic. The composite karyotype at the nontumorigenic stage (CA-HPV-10) was 68 approximately 77,XXY,-(1, 9, 13, 14, 19, 22),+(4, 5, 11, 18, 20, 21),+(del(1) (q23q31)=M1 (two copies), +der(9)t(1;9)(q24 approximately q31;p23)=M5(two copies), der(14)t(14;?)(q10;?)=M17 in the majority of metaphases. These two derivative chromosomes were also observed a previous study. Our CGH analysis clearly showed that this deleted region in M1 is, in fact, translocated with derivative M5 and, in reality, is amplified. The cell line established from nodule (SCID 5019 p11), showed a number of new changes, as described; however, the most significant change was amplification of the 8q23 approximately qter region, harboring c-myc. This region was translocated with chromosomes 2, 4, and 16 as der(2)t(2;8)(q33;q23)=M12, der(4)t(4;8)(q34;q23)=M11, and der(16)t(8;16)(q24;q21)=M9. We deduce from our study that amplification of c-myc and other genes in the 8q23 approximately qter region were important in progression but did not lead to tumorigenicity. The population that became tumorigenic (SCID 5019 II) showed almost all of the same changes in the karyotype as observed in the nodular cell line; the only significant change was the appearance of der(11)t(4;11)(q32;q22)=M7 and the addition of another copy of t(3q;7p)=M2. These new changes lead to loss of chromosomes 3p, 4pter approximately q34, 6, 7q21 approximately qter, 11q22 approximately qter, and 18q, and gain of 3q, 7p, 8q23 approximately qter, and 11pter approximately q22, before the cell line became tumorigenic. The clonal selection of the population is proven by the presence of a number of the same derivative chromosomes in both the nodular and tumorigenic cell line. As it progressed to tumorigenicity, some of the same changes observed in the original study re-appear at different stages of malignancy, although it was absent in the nontumorigenic cell line. These are: der(16)t(8;16)(q24;q21)=M9 in the nodular cell line and der(11)t(4;11)(q32;q22)=M7 in the tumorigenic cell line. In our system, amplification of c-myc and other genes in der(2)t(2;8)(q33;q23)=M12,der(4) t(4;8)(q34;q23)=M11 together with the presence of der(16)t(8;16)(q24;q21)=M9 and der(11)t(4;11)(q32;q22)=M5 makes the cell line tumorigenic. It is either nontumorigenic, with the presence of a marker equivalent to der(16)=M9 and der(11)=M7 observed in the original study, and only nodular (SCID 5019 p11, present study), with the presence of number of markers with c-myc amplification (M9, M11, and M12). There is accumulation of all the above-mentioned changes in the same cell before it becomes tumorigenic.

1alpha,25-dihydroxyvitamin D3 inhibits prostate cancer cell growth by androgen-dependent and androgen-independent mechanisms

We recently reported that 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] inhibits the growth of the LNCaP human prostate cancer cell line by an androgen-dependent mechanism. In the present study we examined the actions and interactions of 1,25-(OH)2D3 and the androgen 5alpha-dihydrotestosterone (DHT) on two new human prostate cancer cell lines (MDA), MDA PCa 2a and MDA PCa 2b. Scatchard analyses revealed that both cell lines express high affinity vitamin D receptors (VDRs) with a binding affinity (Kd) for [3H]1,25-(OH)2D3 of 0.1 nM. However, the MDA cell lines contain low affinity androgen receptors (ARs) with a Kd of 25 nM for [3H]DHT binding. This is 50-fold lower than the AR in LNCaP cells (Kd = 0.5 nM). Their response to DHT is greatly reduced; 2a cells do not respond to 100 nM DHT, and 2b cells show a modest response at that high concentration. 1,25-(OH)2D3 causes significant growth inhibition in both MDA cell lines, greater (for 2b cells) or lesser (for 2a cells) than that in the LNCaP cell line. Moreover, 1,25-(OH)2D3 significantly up-regulates AR messenger RNA in all three cell lines, as shown by Northern blot analysis. The growth inhibitory effect of 1,25-(OH)2D3 on LNCaP cells is blocked by the pure antiandrogen, Casodex, as we previously reported. However, Casodex (at 1 microM) did not block the antiproliferative activity of 1,25-(OH)2D3 in MDA cells. In conclusion, the growth inhibitory action of 1,25-(OH)2D3 in the MDA cell lines appears to be androgen independent, whereas the actions of 1,25-(OH)2D3 in LNCaP cells are androgen dependent. Most importantly, the MDA cell lines, derived from a bone metastasis of human prostate carcinoma, remain sensitive to 1,25-(OH)2D3, a finding relevant to the therapeutic application of vitamin D and its low calcemic analogs in the treatment of advanced prostate cancer.

Glucocorticoids can promote androgen-independent growth of prostate cancer cells through a mutated androgen receptor

The androgen receptor (AR) is involved in the development, growth and progression of prostate cancer (CaP). CaP often progresses from an androgen-dependent to an androgen-independent tumor, making androgen ablation therapy ineffective. However, the mechanisms for the development of androgen-independent CaP are unclear. More than 80% of clinically androgen-independent prostate tumors show high levels of AR expression. In some CaPs, AR levels are increased because of gene amplification and/or overexpression, whereas in others, the AR is mutated. Nonetheless, the involvement of the AR in the transition of CaP to androgen-independent growth and the subsequent failure of endocrine therapy are not fully understood. Here we show that in CaP cells from a patient who failed androgen ablation therapy, a doubly mutated AR functioned as a high-affinity cortisol/cortisone receptor (ARccr). Cortisol, the main circulating glucocorticoid, and its metabolite, cortisone, both equally stimulate the growth of these CaP cells and increase the secretion of prostate-specific antigen in the absence of androgens. The physiological concentrations of free cortisol and total cortisone in men greatly exceed the binding affinity of the ARccr and would activate the receptor, promoting CaP cell proliferation. Our data demonstrate a previously unknown mechanism for the androgen-independent growth of advanced CaP. Understanding this mechanism and recognizing the presence of glucocorticoid-responsive AR mutants are important for the development of new forms of therapy for the treatment of this subset of CaP.

p16INK4A mediates cyclin dependent kinase 4 and 6 inhibition in senescent prostatic epithelial cells

The senescence checkpoint constrains the proliferative potential of normal cells in culture to a finite number of cell doublings. In this study, we investigated the mechanism of cyclin dependent kinase (cdk) inhibition in senescent human prostatic epithelial cells (HPECs). Progression of HPECs from early passage to senescence was accompanied by a gradual loss of cells in S phase and an accumulation of cells containing 2N DNA. Furthermore, G1-S phase-associated kinase activities progressively diminished with increasing cell passage. In senescent HPECs, cdk4 and cyclin E1- and A-associated kinases were catalytically inactive. In contrast to observations in senescent fibroblasts, levels of the kinase inhibitor protein (KIP) inhibitor p21CIP1 diminished over the proliferative life span of HPECs. p27KIP1 levels fell as cells approached senescence, and the association of both p21CIP1 and p27KIP1 with cdk4/6 complexes was decreased. However, the level of cyclin E1-associated KIP molecules was unaltered as cells progressed into senescence. Progression to senescence was accompanied by a progressive increase in both the level of p16(INK4A) and in its association with cdk4 and cdk6. As HPECs approached senescence, cdk4- and cdk6-bound p16(INK4A) showed a shift to a slower mobility due to a change in its phosphorylation profile. As p16(INK4A) increased in cdk4 and cdk6 complexes, there was a loss of cyclin D1 binding. The altered phosphorylation of p16(INK4A) in senescent prostatic epithelial cells may facilitate its association with cdk4 and cdk6 and play a role in the inactivation of these kinases.

Transforming growth factor-beta induces growth inhibition and IGF-binding protein-3 production in prostatic stromal cells: abnormalities in cells cultured from benign prostatic hyperplasia tissues

The IGF axis has been implicated in the pathogenesis of benign prostatic hyperplasia (BPH) via the paracrine action of IGFs and IGF-binding proteins (IGFBPs). In this study, we examined the regulation of cell growth and IGFBP-3 secretion by transforming growth factor-beta (TGF-beta) in prostatic stromal cell (PC-S) cultures from histologically normal tissues and tissues from BPH. PC-S cultures were treated with varying doses of TGF-beta1. Forty-eight hour conditioned media (CM) from these cultures were subjected to Western immunoblotting and ligand blotting for detection and quantification of IGFBPs. IGFBPs-2, -3 and -4 were detected in the CM from normal PC-S cultures. In CM from BPH PC-S, IGFBP-3 levels were 2-fold lower at baseline than in the normal PC-S CM, in addition to the differences in IGFBPs-2 and -5 which we have previously reported. In response to TGF-beta1, a 15-fold increase in the levels of IGFBP-3 was observed in normal PC-S CM, while a mere 2-fold increase was observed in BPH PC-S CM (P<0.001). These findings were confirmed by specific immunoblotting and immunocytochemistry. IGFBP-3 mRNA levels detected by Northern blotting of total RNA extracted from similar cultures showed the induction of IGFBP-3 expression by TGF-beta1 in normal PC-S and its lack of induction in BPH PC-S. Cell growth inhibition in response to TGF-beta1 correlated with the IGFBP-3 concentrations found in CM. Normal PC-S showed a 60% decrease in cell number after 10 days in media with 1 ng/ml TGF-beta1, compared with the untreated control. The decrease in proliferation observed in comparably treated BPH cells was only 20% (P<0.001). In conclusion, BPH PC-S had a reduced IGFBP-3 response to TGF-beta1 and demonstrated decreased TGF-beta1-induced growth inhibition relative to normal PC-S. We hypothesize that in normal PC-S, TGF-beta exerts its anti-proliferative effects by stimulating the production of IGFBP-3, which acts as an inhibitory factor, either by inhibiting IGFs or directly by interacting with cells, and that this process is altered in BPH PC-S.

Two mutations identified in the androgen receptor of the new human prostate cancer cell line MDA PCa 2a

PURPOSE

We have characterized the androgen receptor (AR) in a new human prostate cancer cell line, MDA PCa 2a, that has recently been established from a bone metastasis of a patient whose cancer exhibited androgen-independent growth.

MATERIALS AND METHODS

Androgen responsiveness of these cells was assessed by measuring the effect of DHT and R1881 on cell growth and PSA secretion. Scatchard analysis was used to characterize the affinity and abundance of AR protein. Using a PCR based strategy, genomic DNA of the entire coding region of AR gene was sequenced to identify possible mutations.

RESULTS

These cells express abundant AR (Nmax = 685 +/- 149 fmol./mg. protein), but the AR binding affinity (Kd) for DHT is only 25 nM, approximately 50-fold lower affinity than the mutated AR in LNCaP prostate cancer cells (Kd = 0.5 nM) or the wildtype AR in MCF-7 breast cancer cells (Kd = 0.4 nM). Two mutations, L701H and T877A, were identified in the ligand binding domain of the AR gene. Compared with LNCaP cells, the new cell line is significantly less responsive to DHT and R1881 as well as to other androgens such as testosterone, androstenedione, and DHEA. Similar to LNCaP cells, the ligand specificity of the AR in MDA PCa 2a cells appears to be relaxed and non-androgens such as progesterone and estradiol act as agonists although with less potency than in LNCaP cells. Interestingly, in the absence of androgens, the new cell line expresses 15-fold higher baseline levels of PSA than LNCaP.

CONCLUSIONS

Two mutations were identified in the AR gene of the MDA PCa 2a cell line that are likely responsible for the decreased androgen sensitivity and altered ligand specificity observed in these cells. Thus, this new cell line with partial androgen responsiveness and PSA expression can serve as a functionally relevant model system of bone metastatic prostate cancer, and can be used to investigate the role of AR mutations in prostate cancer and its progression to androgen independence.

Altered growth regulation and loss of response to retinoic acid accompany tumorigenic transformation of prostatic cells

In vitro models of human prostatic carcinogenesis are increasingly available and include representatives of normal, immortal, tumorigenic and metastatic phenotypes. In this study, growth regulation of immortal, but non-tumorigenic, human papillomavirus-transformed prostatic epithelial cells was compared to that of their tumorigenic variants. These variants were created either by exposure to a carcinogen or by passage through mice. In all cases, tumorigenic cells retained responsiveness to a potent mitogen, epidermal growth factor, and to a potent growth inhibitory factor, 1,25-dihydroxyvitamin D3. Responses to other growth regulatory factors were altered. One set of transformants, CA-HPV-10 and its tumorigenic variants 5019 and 5019IIc, lost their requirement for insulin-like growth factor. Another set, RWPE-1 and its tumorigenic variant 129Nu5002-1 Tu, became unresponsive to growth inhibition by transforming growth factor-beta. The only alteration uniquely correlated with the tumorigenic phenotype was loss of response to retinoic acid. This factor, which inhibits growth of normal and immortal but non-tumorigenic prostatic epithelial cells, had no effect on tumorigenic 129Nu5002-1 Tu cells. We previously reported that conversion of an SV40-immortalized prostatic epithelial cell line to tumorigenicity by introduction of the ras oncogene also resulted in loss of responsiveness to growth inhibitory activity of retinoic acid. 129Nu5002-1 Tu cells, which do not have an altered ras gene, gained the same phenotype. This suggests that loss of inhibition by retinoic acid may be a critical element in the tumorigenic conversion of prostatic epithelial cells.

Induction of androgen receptor by 1alpha,25-dihydroxyvitamin D3 and 9-cis retinoic acid in LNCaP human prostate cancer cells

We have recently shown that 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] inhibits proliferation of LNCaP cells, an androgen-responsive human prostate cancer cell line. Also, 1,25-(OH)2D3 increases androgen receptor (AR) abundance and enhances cellular responses to androgen in these cells. In the current study, we have investigated the mechanism by which 1,25-(OH)2D3 regulates AR gene expression and the involvement of AR in the 1,25-(OH)2D3- and 9-cis retinoic acid (RA)-mediated growth inhibition of LNCaP cells. Northern blot analyses demonstrated that the steady-state messenger RNA (mRNA) level of AR was significantly increased by 1,25-(OH)2D3 in a dose-dependent manner. Time-course experiments revealed that the increase of AR mRNA by 1,25-(OH)2D3 exhibited delayed kinetics. In response to 1,25-(OH)2D3, AR mRNA levels were first detected to rise at 8 h and reached a maximal induction of 10-fold over the untreated control at 48 h; the effect was sustained at 72 h. Furthermore, the induction of AR mRNA by 1,25-(OH)2D3 was completely abolished by incubation of cells with cycloheximide, a protein synthesis inhibitor. 1,25-(OH)2D3 was unable to induce expression of an AR promoter-luciferase reporter. Together, these findings indicate that the stimulatory effect of 1,25-(OH)2D3 on AR gene expression is indirect. Western blot analyses showed an increase of AR protein in 1,25-(OH)2D3-treated cells. This increased expression of AR was followed by 1,25-(OH)2D3-induced inhibition of growth in LNCaP cells. Similar to 1,25-(OH)2D3, 9-cis RA also induced AR mRNA expression, and the effect of both hormones was additive. Moreover, 1,25-(OH)2D3 and 9-cis RA acted synergistically to inhibit LNCaP cell growth. These antiproliferative effects of 1,25-(OH)2D3 and 9-cis RA, alone or in combination, were blocked by the pure AR antagonist, Casodex. In conclusion, our results demonstrate that growth inhibition of LNCaP cells by 1,25-(OH)2D3 and 9-cis RA is mediated by an AR-dependent mechanism and preceded by the induction of AR gene expression. This finding, that differentiating agents such as vitamin D and A derivatives are potent inducers of AR, may have clinical implications in the treatment of prostate cancer.

Defined medium for normal adult human prostatic stromal cells

Stromal-epithelial interactions are pivotal in many aspects of prostatic biology. A defined culture system is critical for the investigation of factors that regulate the growth and differentiation of human prostatic stromal cells. We have identified conditions which promote stromal cell attachment and proliferation in serum-free medium. MCDB 201, originally developed for the clonal growth of chick embryo fibroblasts, proved to be a superior basal medium of those that we tested. Supplementation of MCDB 201 with basic fibroblast growth factor (FGF), insulin-like growth factor (IGF), and platelet-derived growth factor (PDGF) permitted attachment and exponential growth of cells throughout a 7-d period with an initial inoculum as low as 10(3) cells per well of a 96-well microtiter dish. Using these assay conditions, we subsequently verified that basic FGF and IGF, but not PDGF, were required for optimal growth. No activity was found for heparin, transferrin, or the androgen R1881. Epidermal growth factor (EGF) didn't stimulate growth when added to medium containing basic FGF and IGF, but was moderately stimulatory when added to basal medium alone. Cholera toxin inhibited growth. This simple and efficient culture medium provides a suitable assay system for more extensive studies of growth regulation and differentiation of human prostatic stromal cells, and will provide the basis for future development of a defined medium that supports clonal growth. Characterization of stromal-epithelial interactions will be facilitated by the use of this defined culture system for stromal cells in conjunction with the serum-free culture systems previously developed for human prostatic epithelial cells.

Basic FGF, EGF, and PDGF modify TGFbeta-induction of smooth muscle cell phenotype in human prostatic stromal cells

BACKGROUND

We investigated the ability of a variety of growth factors to regulate the differentiation of prostatic fibroblasts into smooth muscle cells.

METHODS

Smooth muscle actin levels were monitored by immunoblot analysis and immunocytochemistry. Proliferation was measured in clonal growth assays and by cell counts.

RESULTS

We determined that TGFbeta inhibited proliferation and induced smooth muscle differentiation of stromal cells derived from prostatic adenocarcinomas, as we previously reported for cells derived from the normal peripheral zone. Basic FGF, EGF, TGFalpha, and PDGF, but not IGF, retinoic acid, 1,25-dihydroxyvitamin D3, or androgen, attenuated induction of differentiation by TGFbeta, by a mechanism apparently unrelated to proliferation.

CONCLUSIONS

Regulation of growth and differentiation occurs equivalently in prostatic stromal cells derived from adenocarcinomas and normal peripheral zone. TGFbeta is a potent inducer of the smooth muscle phenotype. Basic FGF, EGF and/or TGFalpha, and PDGF attenuate TGFbeta's activity, and promote a fibroblastic phenotype. Our studies provide an in vitro model system in which fibroblastic or smooth muscle cells can be promoted, maintained, and investigated in a defined manner. The results suggest that the ratio of fibroblasts to smooth muscle cells in the stroma reflects the relative levels of growth factors, which may be altered in diseased states.

Expression of prostatic factors measured by reverse transcription polymerase chain reaction in human papillomavirus type 18 deoxyribonucleic acid immortalized prostate cell lines

OBJECTIVES

To investigate expression of the prostatic markers prostate-specific antigen (PSA), prostate-specific membrane antigen (PSM), and the androgen receptor (AR) after human papillomavirus (HPV) type 18 deoxyribonucleic acid (DNA) transfection and subsequent immortalization of human prostate epithelial cells.

METHODS

Recently, two human prostate epithelial cell lines were established by HPV transformation: PZ-HPV-7, derived from normal peripheral zone (PZ) tissue, and CA-HPV-10, derived from high Gleason grade adenocarcinoma. Expression of PSA was studied by the reverse transcription polymerase chain reaction (RT-PCR), because in preliminary studies using immunocytochemistry and Northern blotting, no PSA expression was found. PSM was analyzed by RT-PCR and nested RT-PCR. These analyses included primary human prostate cell strains. Furthermore, androgen-supplemented methylthiazol tetrazolium (MTT) growth assays were performed and expression of AR was studied by immunocytochemistry. Prostate carcinoma cell lines LNCaP and PC-346C were included as positive controls and breast carcinoma cell line MCF-7 as a negative control.

RESULTS

Both cell lines exhibited low levels of RNA for PSA and PSM in comparison with cell lines LNCaP and PC-346C. AR expression by immunocytochemistry was negative using monoclonal antibody F39.4 and polyclonal antibody SP-197. In an androgen-supplemented environment, growth rates of both HPV immortalized cell lines were not stimulated in contrast to LNCaP.

CONCLUSIONS

RNA transcripts of PSA and PSM were detected by RT-PCR in HPV immortalized prostate epithelial cell lines PZ-HPV-7 and CA-HPV-10. The expression of prostate-specific markers may further validate the utility of this stepwise transformation model of human prostate carcinogenesis.

Expression and characterization of recombinant type 2 3 alpha-hydroxysteroid dehydrogenase (HSD) from human prostate: demonstration of bifunctional 3 alpha/17 beta-HSD activity and cellular distribution

In androgen target tissues, 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) may regulate occupancy of the androgen receptor (AR) by catalyzing the interconversion of 5alpha-dihydrotestosterone (5alpha-DHT) (a potent androgen) and 3alpha-androstanediol (a weak androgen). In this study, a 3alpha-HSD cDNA (1170 bp) was isolated from a human prostate cDNA library. The human prostatic 3alpha-HSD cDNA encodes a 323-amino acid protein with 69.9%, 84.1%, 99.4%, and 87.9% sequence identity to rat liver 3alpha-HSD and human type 1, type 2, and type 3 3alpha-HSDs, respectively, and is a member of the aldo-keto reductase superfamily. The close homology with human type 2 3alpha-HSD suggests that it is either identical to this enzyme or a structural allele. Surprisingly, when the recombinant protein was expressed and purified from Escherichia coli, the enzyme did not oxidize androsterone when measured spectrophotometrically, an activity previously assigned to recombinant type 2 3alpha-HSD using this assay. Complete kinetic characterization of the purified protein using spectrophotometric, fluorometric, and radiometric assays showed that the catalytic efficiency favored 3alpha-androstanediol oxidation over 5alpha-DHT reduction. Using [14C]-5alpha-DHT as substrate, TLC analysis confirmed that the reaction product was [14C]-3alpha-androstanediol. However, in the reverse reaction, [3H]-3alpha-androstanediol was oxidized first to [3H]-androsterone and then to [3H]-androstanedione, revealing that the expressed protein possessed both 3alpha- and 17beta-HSD activities. The 17beta-HSD activity accounted for the higher catalytic efficiency observed with 3alpha-androstanediol. These findings indicate that, in the prostate, type 2 3alpha-HSD does not interconvert 5alpha-DHT and 3alpha-androstanediol but inactivates 5alpha-DHT through its 3-ketosteroid reductase activity. Levels of 3alpha-HSD mRNA were measured in primary cultures of human prostatic cells and were higher in epithelial cells than stromal cells. In addition, elevated levels of 3alpha-HSD mRNA were observed in epithelial cells derived from benign prostatic hyperplasia and prostate carcinoma tissues. Expression of 3alpha-HSD was not prostate specific, since high levels of mRNA were also found in liver, small intestine, colon, lung, and kidney. This study is the first complete characterization of recombinant type 2 3alpha-HSD demonstrating dual activity and cellular distribution in the human prostate.

Selection of human cervical epithelial cells that possess reduced apoptotic potential to low-oxygen conditions

Since human papillomavirus (HPV) infection is strongly associated with cervical neoplasia and tumor hypoxia has prognostic significance in human cervical carcinomas, we examined the relationship between hypoxia and apoptosis in human cervical epithelial cells expressing high-risk HPV type 16 oncoproteins. In vitro, hypoxia stimulated both p53 induction and apoptosis in primary cervical epithelial cells infected with the HPV E6 and E7 genes but not in cervical fibroblasts infected with E6 and E7. Furthermore, cell lines derived from HPV-associated human cervical squamous cell carcinomas were substantially less sensitive to apoptosis induced by hypoxia, indicating that these cell lines have acquired additional genetic alterations that reduced their apoptotic sensitivity. Although the process of long-term cell culturing resulted in selection for subpopulations of HPV oncoprotein-expressing cervical epithelial cells with diminished apoptotic potential, the exposure of cells to hypoxia greatly accelerated the selection process. These results provide evidence for the role of hypoxia-mediated selection of cells with diminished apoptotic potential in the progression of human tumors and can in part explain why cervical tumors that possess low pO2 values are more aggressive.

1alpha,25-dihydroxyvitamin D3 actions in LNCaP human prostate cancer cells are androgen-dependent

We and others have recently shown that 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] significantly inhibits cell proliferation and increases secretion of prostate-specific antigen (PSA) in LNCaP cells, an androgen-responsive human prostate cancer cell line. The present study was designed to investigate the possible interactions between 1,25-(OH)2D3 and androgens in the regulation of LNCaP cellular function. LNCaP cell growth was dose-dependently inhibited by 1,25-(OH)2D3 (60% inhibition at 10 nM) when cells were cultured in medium supplemented with FBS (FBS medium). 1,25-(OH)2D3-treated cells showed a 5-fold increase in PSA secretion, similar to the increase seen in dihydrotestosterone (DHT)-treated cells. In combination, 1,25-(OH)2D3 and DHT synergistically enhanced PSA secretion 22-fold. This synergistic effect was even greater when cells were cultured in medium supplemented with charcoal-stripped serum (CSS medium), where endogenous steroids are substantially depleted. Under these conditions, 1,25-(OH)2D3 and DHT together stimulated PSA secretion up to 50-fold over the untreated control. Radioligand binding assays and Western blot analyses showed that the androgen receptor (AR) content was increased significantly by 1,25-(OH)2D3 at 48 h. Furthermore, the steady-state mRNA level of AR was up-regulated approximately 2-fold by 1,25-(OH)2D3 at 24 h. When cells were grown in CSS medium, 1,25-(OH)2D3 alone no longer inhibited cell growth or induced PSA secretion. Titration experiments revealed that the addition of DHT at 1 nM to the medium restored the antiproliferative activity of 1,25-(OH)2D3. Conversely, an antiandrogen, Casodex, completely blocked 1,25-(OH)2D3 antiproliferative and PSA stimulation activities when cells were cultured in FBS medium. In conclusion, these results demonstrate that the antiproliferative and PSA induction activities of 1,25-(OH)2D3 in LNCaP cells are dependent upon androgen action and that AR up-regulation by 1,25-(OH)2D3 likely contributes to the synergistic actions of 1,25-(OH)2D3 and DHT in these cells.

Loss of response to epidermal growth factor and retinoic acid accompanies the transformation of human prostatic epithelial cells to tumorigenicity with v-Ki-ras

Growth factor-independent proliferation and loss of response to differentiation factors are believed to be critical elements in carcinogenesis. We have developed an in vitro model of human prostatic carcinogenesis by the introduction of SV40 DNA into normal prostatic epithelial cells to create a transformed, immortal cell line, pRNS-1-1. This non-tumorigenic cell line responded similarly to normal prostatic epithelial cells to most growth- and differentiation-regulatory factors, with the notable exception of loss of response to the inhibitory factor 1,25-dihydroxyvitamin D3. In this study, we describe the introduction of the ras oncogene into pRNS-1-1 cells to create a tumorigenic cell line, pRNS-1-1/ras. In addition to an attenuated response to 1,25-dihydroxyvitamin D3, these cells also became unresponsive to retinoic acid and gained the ability to undergo clonal proliferation in the absence of epidermal growth factor (EGF). EGF-independent growth could not be linked to the production of autocrine transforming growth factor-alpha, but instead was likely due to sustained signaling by the ras oncogene, bypassing ligand-activation of the EGF receptor. Ligand-independent proliferation, coupled with the loss of response to the growth-inhibitory and differentiation agent retinoic acid, may be important elements in the conversion of human prostatic epithelial cells to tumorigenicity.

Decreased expression of Wilms' tumor gene WT-1 and elevated expression of insulin growth factor-II (IGF-II) and type 1 IGF receptor genes in prostatic stromal cells from patients with benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a common proliferative disorder of unknown etiology. We have previously documented that the insulin-like growth factor (IGF) axis is critical for prostate cell growth and is abnormal in BPH. The type 1 IGF receptor (IGF-1R) is constitutively expressed by most body tissues and plays a significant role in regulating cell proliferation, consistent with the role of its ligands (IGF-I and IGF-II) as important mitogenic factors. The Wilms' tumor gene product (WT-1) is a tumor suppressor that has been shown to be altered in rare kidney tumors and is known to regulate IGF-II and IGF-1R. We investigated the possibility that the expression of prostatic WT-1, IGF-1R, and IGF-II genes is altered in patients with BPH. We utilized primary cultures of prostatic stromal cells grown from normal (n = 9) and hyperplastic (n = 9) surgical specimens and analyzed WT-1, IGF-1R, and IGF-II messenger RNA levels. In all of the BPH cell strains, WT-1 expression (measured by RT-PCR and RNase protection assays) was strikingly lower than that found in normal strains (0-20% of normal, mean 14% of normal, P < 0.01). The expression of both the IGF-1R (300% of normal, P < 0.05) and IGF-II (1000% of normal, P < 0.01) messenger RNAs was higher in BPH strains as compared with normal strains. No changes were seen in stromal cell strains derived from prostatic adenocarcinoma. Thus, in cultured human prostatic stromal cell strains from patients with BPH, decreased WT-1 gene expression is associated with increases in the expression of the IGF-1R and IGF-II genes that are known transcriptional targets of WT-1. These findings indicate that reduced expression of the WT-1 tumor suppressor gene and elevated IGF-1R and IGF-II gene expression may be involved in the pathophysiology of prostatic hyperplasia, implying a new role for the Wilms' tumor gene in nonmalignant states.

Human papillomavirus detection by polymerase chain reaction in benign and malignant prostate tissue is dependent on the primer set utilized

OBJECTIVES

Prior investigations evaluating the presence of human papillomavirus (HPV) in prostatic tissue by polymerase chain reaction (PCR) technology have yielded detection rates of 0% to 100%. Contamination by viral DNA from prostatic urethral colonization or less than optimal laboratory conditions have been suggested to explain this discrepancy. In addition, the various investigations have differed in the specific oligonucleotide primers utilized for amplification and, therefore, have searched for different segments of the viral genome. The objective of this study is to address these differences.

METHODS

Forty-one archival radical prostatectomy specimens were evaluated, identifying areas of normal and abnormal histology. Meticulous technique was used during tissue acquisition, histologic confirmation, DNA isolation, PCR amplification, polyacrylamide gel electrophoresis, and staining. Primers for a 126- and 99-base pair (bp) fragment of the E6 portion of HPV 16 as well as a consensus primer for the L1 portion of the papillomavirus genome were utilized.

RESULTS

Of the normal prostatic tissues, 13.5% (5/37) contained the 126-bp E6 viral DNA as did 33.3% (7/21) of benign prostatic hyperplasia (BPH) samples, 25% (5/20) of dysplasia, 18.2% (2/11) of Gleason grades 1 and 2 adenocarcinoma, 25.9% (7/27) of Gleason grade 3 adenocarcinoma, and 6.7% (1/15) of Gleason grade 4 adenocarcinoma. Sections from the urethras of the prostatectomy specimens contained viral DNA in 31.7% (13/41). Viral detection was variable among different specimens in the same patient. With amplification for the 99-bp fragment of HPV 16, 1 of 37 normal (2.7%), 2 of 21 BPH (9.5%), 1 of 20 dysplasia (5.0%), and 2 of 53 cancer (3.8%) specimens revealed HPV DNA. In none of the specimens was DNA amplified using primers for a 450-bp fragment of the L1 portion of HPV.

CONCLUSIONS

Previously published discrepancies in HPV detection may be solely due to the differences in primer sets utilized.

Acid-activated insulin-like growth factor binding protein protease activity of cathepsin D in normal and malignant prostatic epithelial cells and seminal plasma

In this study, we demonstrate insulin-like growth factor binding protein (IGFBP) acid proteolysis in conditioned media (CM) from normal and malignant primary cultures of prostatic epithelial cells, prostatic cell lines, and in seminal plasma. We further demonstrate the absence of such activity in CM from prostatic stromal cells. Radio-labeled IGFBPs (1-6) were incubated with various acidified CM and seminal plasma. None of these media showed IGFBP proteolytic activity at neutral pH, but all CM from prostatic epithelial cells (PC-E) demonstrated strong IGFBP proteolysis at acidic pH. No acid-activated proteolysis was observed in the CM from stromal cell cultures. In order to ascertain the role of cathepsin D, anti-cathepsin antibodies were used to immunodeplete the media of the selected enzymes prior to incubation with IGFBPs. Depletion of cathepsin D greatly reduced the proteolytic activity of the PC-E CM. Additionally, purified cathepsin D yielded a digestion pattern identical to that produced by prostatic cell CM and seminal plasma, following acidic incubation with IGFBP-3. Remarkably, the proteolytic pattern generated by seminal plasma, when incubated with IGFBP-3 at neutral pH, corresponded to that produced by prostate-specific antigen (PSA), demonstrating the interpolation of both neutral and acid proteases from prostate cells into seminal plasma. In conclusion, prostatic epithelial cells secrete acid-specific IGFBP protease(s) related to cathepsin D. Although no significant statistical difference was observed in the degree of acid-specific proteolysis in the media from normal versus malignant primary epithelial cell cultures, physiological characteristics of the malignant state might facilitate increased cathepsin D activity. We suspect this proteolysis may play a role in prostatic cell proliferation and invasive tumor growth.

Induction of smooth muscle cell phenotype in cultured human prostatic stromal cells

Stromal cells are key regulators of growth and differentiation in the adult human prostate. Alterations in the stroma are believed to initiate the development of benign prostatic hyperplasia, and stromal-epithelial interactions may have a role in malignant progression. The prostatic stroma is composed of two major cell types, smooth muscle cells and fibroblasts. Cell cultures from the prostatic stroma have been established by several investigators, but the phenotype of these cells has not been extensively characterized and it is not clear whether they are fibroblastic or smooth muscle-like. In this study, the response of stromal cells cultured from normal prostatic tissues to transforming growth factor-beta (TGF beta) was investigated. We confirmed a previous report that TGF beta inhibited the growth of prostatic stromal cells in serum-containing medium, and showed that inhibition also occurred in serum-free medium. Growth inhibition by TGF beta was irreversible after 24 to 72 h of exposure. In the absence of TGF beta, cells were fibroblastic and expressed vimentin and fibronectin but little alpha-smooth muscle actin. After 3 days of exposure to 1 ng/ml of TGF beta, the majority of cells expressed alpha-smooth muscle actin and desmin, as demonstrated by immunocytochemistry and immunoblot analysis. This effect was specific and alpha-smooth muscle actin was not induced by two other growth-inhibitory factors, retinoic acid or 1,25-dihydroxyvitamin D3. These results suggest that TGF beta is an important regulator of growth and differentiation of prostatic stromal cells and that a smooth muscle cell phenotype is promoted in the presence of TGF beta.

Parathyroid hormone-related protein is not an autocrine growth factor for normal prostatic epithelial cells

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is the primary factor responsible for humoral hypercalcemia of malignancy. The hypercalcemic actions of PTHrP occur via stimulation of renal distal tubular calcium reabsorption and increased osteoclastic bone resorption. These effects of PTHrP are thought to be mediated through a common parathyroid hormone (PTH)/PTHrP receptor. In addition to the well-established role of PTHrP in bone remodeling, PTHrP is believed to be an important mediator of cellular growth and differentiation in a number of nonbony tissues. We recently demonstrated abundant expression of PTHrP in normal and malignant human prostatic tissues, and in cultured prostatic epithelial cells.

METHODS

In vitro assays were used to test growth-regulatory activity of synthetic and endogenous PTHrP peptides on normal prostatic epithelial cells.

RESULTS

No growth-regulatory activity could be demonstrated.

CONCLUSIONS

PTHrP is not an autocrine growth factor for normal prostatic epithelial cells.

Prostate specific antigen cleaves parathyroid hormone-related protein in the PTH-like domain: inactivation of PTHrP-stimulated cAMP accumulation in mouse osteoblasts

PURPOSE

To determine whether parathyroid hormone-related protein (PTHrP) is a substrate of prostate-specific antigen (PSA) and how the biological activity of PTHrP may be altered by cleavage with PSA.

MATERIALS AND METHODS

Prostate-specific antigen cleavage of recombinant human PTHrP 1-141 was conducted in vitro at 37C and analyzed by SDS-PAGE. Five rounds of automated amino-terminal amino acid sequence analysis were performed on blotted PSA-cleaved PTHrP peptide fragments to determine the PSA cleavage sites. The mouse osteoblast cell line MC3T3-E1 was used to test whether PSA cleavage of PTHrP 1-141 altered its ability to stimulate cAMP production.

RESULTS

Prostate-specific antigen was found to specifically cleave PTHrP 1-141 in a time- and dose-dependent manner. Cleavage of PTHrP 1-141 by PSA generated fragments on Coomassie-stained acrylamide gels that migrated with mobilities that corresponded to 19.5, 17, 15 and < 7 kd. The preferred PSA cleavage site of PTHrP 1-141 was determined to be at the carboxyl-terminus of phenylalanine 23, consistent with chymotryptic-like enzymatic activity of PSA. Cleavage of PTHrP by PSA completely abolished the ability of PTHrP to stimulate cAMP production.

CONCLUSIONS

Cleavage of PTHrP 1-141 by PSA carboxyl-terminal to phenylalanine 23 represents a unique pattern of PTHrP processing that may be specific to the prostate. Prostate-specific antigen inactivation of the cAMP-inducing activity of PTHrP 1-141 demonstrates that PSA cleavage regulates the biological activity of PTHrP. These results have implications for the role of PTHrP in prostate cancer metastasis to bone and its subsequent regulation of bone remodeling. Study of the biological activities of the PSA-generated PTHrP peptides identified in this study merits further investigation.

Role of prostatic basal cells in the regulation and suppression of human prostate cancer cells

Cytokeratin expression in normal and malignant prostatic tissue indicates a loss of basal epithelial cells in cancer. We investigated the ability of basal-like prostatic epithelial cells to inhibit the growth of prostatic cancer cells. Human prostate LNCaP cells were grown in medium with or without 10 nM dihydrotestosterone (DHT) on plastic culture dishes or on extracellular matrix derived from basal-like epithelial cells (primary cultures derived from normal peripheral zone of the prostate) that were grown with or without 10 nM DHT. Colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays were used to assess the growth of LNCaP cells. On plastic dishes, growth of LNCaP cells was increased 5-10% by the presence of DHT in the medium. On matrix derived from basal-like cells that were grown in the absence of DHT, growth of LNCaP cells with or without DHT was similar to that on plastic. However, on matrix derived from basal-like cells that were grown with DHT, growth of LNCaP cells was suppressed when compared to all other culture conditions (P < 0.01). To determine whether basal-like cells could alter the function of LNCaP cells, we measured prostate-specific antigen (PSA) mRNA expression with the use of comparative RT-PCR. We found a significant decrease in the mature PSA transcript in cells grown on matrix derived from basal-like cells that were grown with DHT. The expression of PSA transcript was not altered in LNCaP cells that were grown on matrix derived from basal-like cells that were grown in the absence of DHT. Furthermore, using differential display of mRNA, we demonstrated that there were induction and suppression of multiple unique transcripts in the LNCaP cells when grown on the various culture conditions. To determine a possible mechanism for these observations. We used a dot blot immunoassay for several known inhibitory factors. We determined that DHT can induce the basal-like cells to secrete transforming growth factor-beta (TGF-beta 1), and that TGF-beta 1 can inhibit the proliferation of LNCaP cells in a dose dependent manner. We conclude that basal-like epithelial cells, in the presence of DHT, secrete an extracellular matrix o matrix associated factor(s), e.g. TGF-beta 1, that suppresses proliferation and function of prostate cancer cells. Our data suggest that the disappearance of the basal cell layer may be a prerequisite for the progression of prostatic neoplasia.

7S nerve growth factor is an insulin-like growth factor-binding protein protease

Insulin-like growth factor (IGF)-binding protein (IGFBP) proteases modulate IGF action by cleaving IGFBPs into fragments with lower affinity to IGFs, thereby increasing the levels of free IGFs. We have previously documented that prostate-specific antigen (PSA), a serine protease of the kallikrein family, is an IGFBP-3 protease. In this study, we characterized the potential IGFBP proteolytic activity of nerve growth factor (NGF gamma-subunit), which shares high sequence homology with PSA. [125I]IGFBP-3 was cleaved by NGF (but not other kallikreins) at a 3-fold lower concentration than that of PSA, thus proving NGF to be a more potent IGFBP protease than PSA. NGF-generated, lower mol wt IGFBP-3 fragments, detected by immunoblotting and cross-linking to IGFs, had a lower affinity to IGFs than intact IGFBP-3. Unlike PSA, which cleaves primarily IGFBP-3 and -5, NGF also displayed potent proteolytic activity against IGFBP-4 and -6. These data suggest that NGF may be involved in the growth of cells by more than one mechanism. In addition to binding to its receptors, NGF is capable of cleaving IGFBPs and, thus, enhancing IGF action. This synergistic action between NGF and IGF may have important implications on cell growth, development, and repair in the brain and other tissues.

Keratin 19 in the adult human prostate: tissue and cell culture studies

Keratin 19 is found primarily in simple epithelia. In mammary epithelia, keratin 19 was localized to a subset of luminal cells, suggesting that keratin 19-negative cells may be the proliferative compartment of the secretory cell lineage. The structural and functional similarities of prostate and breast led us to examine keratin 19 expression in the prostate. Immunohistochemical studies revealed that keratin 19 expression was heterogeneous and frequently occurred in basal as well as in luminal cells of normal, dysplastic, and benign hyperplastic tissues. Keratin 19 was observed in cancer, but usually in a minority of cells. This was in dramatic contrast to invasive breast cancers, which are reportedly uniformly positive for keratin 19. Prostatic epithelial cells cultured from tissues of all histologies expressed keratin 19. In summary, keratin 19 does not obviously correlate with any epithelial cell lineage or phenotype in the prostate.

Parathyroid hormone--related protein (PTHrP) is an epidermal growth factor-regulated secretory product of human prostatic epithelial cells

Parathyroid hormone-related protein (PTHrP) has previously been shown to be expressed in human prostatic tissue and in prostatic cancer cell lines. In the present study, PTHrP immunoreactivity was detected in the glandular epithelium of normal prostate and benign prostatic hyperplasia (BPH), as well as in prostatic adenocarcinoma (CaP). Epithelial cell cultures derived from normal, BPH, and CaP tissues were also stained by antibodies against PTHrP, and northern analysis revealed multiple transcripts of PTHrP in the cellular RNA. PTHrP (1-34) was measurable by radioimmunoassay (RIA) in media conditioned by the prostatic epithelial cell cultures, and PTHrP accumulated in conditioned media during a 72 hr time course. Addition of complete growth medium to starved cells resulted in increased PTHrP mRNA levels by 1 hr, with maximal stimulation at 8-24 hr. Several individual factors contained in the complete growth medium were tested for their ability to regulate PTHrP expression. Epidermal growth factor (EGF) was the major inducer of PTHrP expression, while cholera toxin, bovine pituitary extract, hydrocortisone, and insulin had minimal or no effect on PTHrP transcript levels. Since each of these factors is growth stimulatory, the unique ability of EGF to induce PTHrP is apparently unrelated to mitogenicity. 1,25-Dihydroxyvitamin D3[1,25(OH)2D3], an inhibitor of PTHrP expression in several other cell types, had no effect on steady-state levels of PTHrP mRNA expressed by epithelial cells in complete growth medium, although prostate cells have vitamin D receptors and are responsive to 1,25(OH)2D3 in other ways. Our results indicate that PTHrP expression is not confined to the neuroendocrine cells of the human prostate and that our culture system can be used as a model to investigate the role of PTHrP in the prostate.

KGF and EGF differentially regulate the phenotype of prostatic epithelial cells

Previous studies indicate that keratinocyte growth factor (KGF) acts as a paracrine factor in the prostatic epithelium and epidermal growth factor (EGF) acts as an autocrine factor. In serum-free medium, KGF or EGF promoted similar growth of human prostatic epithelial cells. Response to two growth-inhibitory factors (suramin and transforming growth factor-beta), and expression of keratins and prostate-specific antigen (PSA), were similar with either mitogen. However, colonies in medium with KGF were very compact with extensive intercellular bonds, whereas colonies with EGF consisted of widely-separated cells. Growth was decreased to a greater extent by deletion of growth factors from medium with KGF versus EGF, and retinoic acid was 10-fold more potent at inducing growth inhibition and differentiation-associated keratin with KGF compared with EGF. We conclude that regulation of growth and differentiation in the prostate might vary depending on the availability of KGF versus EGF.