A novel gene on human chromosome 2p24 is differentially expressed between androgen-dependent and androgen-independent prostate cancer cells

Identification of genes involved in the transition from androgen-dependent to androgen-independent prostate cancer is important to extend our current knowledge of the disease. Using differential display RT-PCR analysis between androgen-dependent and androgen-independent prostate cancer cells, we have identified a novel gene, designated GC109. GC109 harbours a putative Cys-His cluster, a nuclear localisation signal, a leucine zipper and a ret finger protein (rfp)-like domain. GC109 mRNA expression in normal human tissues was found not to be restricted to the prostate. However, using a variety of 15 human cancer cell lines, GC109 mRNA was preferentially expressed in androgen-dependent LNCaP-FGC, compared with androgen-independent LNCaP-LNO, DU145 and PC3 human prostate cancer cells. Finally, the GC109 gene was mapped on human chromosome 2p24. Based on its protein domain structure and chromosomal localisation, we hypothesise that GC109 may be involved in chromosomal rearrangements in prostate cancer.     

Prostate-specific antigen (PSA) promoter-driven androgen-inducible expression of sodium iodide symporter in prostate cancer cell lines

Currently, no curative therapy for metastatic prostate cancer exists. Causing prostate cancer cells to express functionally active sodium iodide symporter (NIS) would enable those cells to concentrate iodide from plasma and might offer the ability to treat prostate cancer with radioiodine. Therefore, the aim of our study was to achieve tissue-specific expression of full-length human NIS (hNIS) cDNA in the androgen-sensitive human prostatic adenocarcinoma cell line LNCaP and in subcell lines C4, C4-2, and C4-2b in vitro. For this purpose, an expression vector was generated in which full-length hNIS cDNA coupled to the prostate-specific antigen (PSA) promoter has been ligated into the pEGFP-1 vector (NIS/PSA-pEGFP-1). The PSA promoter is responsible for androgen-dependent expression of PSA in benign and malignant prostate cells and was therefore used to mediate androgen-dependent prostate-specific expression of NIS. In addition, two control vectors were designed, which consist of the pEGFP-1 vector containing the PSA promoter without NIS cDNA (PSA-pEGFP-1) and NIS cDNA without the PSA promoter (NIS-pEGFP-1). Prostate cancer cells were transiently transfected with each of the above-described expression vectors, incubated with or without androgen (mibolerone) for 48 h, and monitored for iodide uptake activity. In addition, stably transfected LNCaP cell lines were established for each vector. Prostate cells transfected with NIS/PSA-pEGFP-1 showed perchlorate-sensitive, androgen-dependent iodide uptake in a range comparable to that observed in control cell lines transfected with hNIS cDNA. Perchlorate-sensitive iodide uptake was not observed in cells transfected with NIS/PSA-pEGFP-1 and treated without androgen or in cells transfected with the control vectors. In addition, prostate cancer cell lines without PSA expression (PC-3 and DU-145) did not show iodide uptake activity when transfected with NIS/PSA-pEGFP-1. Western blotting of LNCaP and C4-2b cell membranes transfected with NIS/PSA-pEGFP-1 using a monoclonal antibody that recognizes the COOH-terminus of hNIS revealed a band with a molecular weight of 90,000 that was not detected in androgen-deprived cells or in cells transfected with the control vectors, as well as a minor band at Mr 150,000 in transiently transfected LNCaP cell membranes. In conclusion, tissue-specific androgen-dependent iodide uptake activity has been induced in prostate cancer cells by PSA promoter-directed NIS expression. This study represents an initial step toward therapy of prostate cancer with radioiodine.     

TMEFF2 is an androgen-regulated gene exhibiting antiproliferative effects in prostate cancer cells

We have identified a gene that is highly expressed in the androgen-dependent prostate cancer cell line, LNCaP. Sequence analysis revealed that it was identical to a recently cloned gene designated TMEFF2, which encodes a transmembrane protein containing an epidermal growth factor (EGF)-like motif and two follistatin domains. This gene was highly expressed only in primary samples of normal prostate and prostate cancer as well as normal brain. Expression of the gene was controlled by androgen as shown by dihydrotestosterone markedly increasing TMEFF2 expression in LNCaP cells. Also, androgen-dependent human prostate cancer xenografts (CWR22) expressed high levels of TMEFF2 and these levels markedly decreased by day 10 after castration of the mice. Furthermore, a large number of androgen-dependent xenografts (CWR22, LuCaP-35, LAPC-4AD, LAPC-9AD) exhibited higher levels of TMEFF2 mRNA than androgen-independent xenografts (CWR22R, LAPC-3AI, LAPC-4AI, LAPC-9AI). Ectopic expression of TMEFF2 in DU145 and PC3 cells resulted in their prominent inhibition of growth. Taken together, the results demonstrate that TMEFF2 is a androgen-regulated gene, which can suppress growth of prostate cancer cells and our xenograft data show that escape of prostate cancer cells from androgen modulation causes them to decrease their expression of this gene, which may result in their more malignant behavior.     

Thalidomide up-regulates prostate-specific antigen secretion from LNCaP cells

Thalidomide has been shown to have species- and metabolic-dependent antiangiogenic activity in vitro and in vivo, suggesting its potential in treating human angiogenesis-dependent pathologies such as solid tumors. Based on promising preclinical studies, thalidomide has entered phase II clinical trials for prostate, brain, breast cancer, and Kaposi's sarcoma. However, the antiangiogenic mechanism of action is largely unresolved, as are its effects on tumor-associated gene expression, cytokine secretion, etc. We have investigated the effects of thalidomide on: 1) the secretion of prostate-specific antigen (PSA) in a human androgen-dependent prostate cell line; 2) growth and viability of human prostate cells; and 3) differential gene expression profiles of thalidomide-treated vs untreated human prostate cells. A human androgen-dependent prostate carcinoma cell line (LNCaP) and a human androgen-independent prostate carcinoma cell line (PC-3) were incubated with thalidomide 0.6, 6, or 60 7g/mL for 5-6 days. Secreted PSA from LNCaP cells was measured using a commercial enzyme-linked immunosorbant assay. Cell viability studies were conducted in both LNCaP and PC-3 cells using the same thalidomide concentrations. Furthermore, the differential gene expression of thalidomide-treated LNCaP cells was compared to that of untreated control cells using a commercially available human cancer cDNA expression array system. Thalidomide-treated LNCaP cells demonstrated increased PSA/cell levels at all concentrations tested compared to untreated control cells. Thalidomide demonstrated a cytostatic effect in LNCaP cells but had no appreciable effect on PC-3 cell viability compared to untreated control cells. Comparison of cDNA expression arrays hybridized with thalidomide-treated LNCaP cDNA probes suggests that thalidomide may up- or downregulate expression of angiogenesis-related genes, i.e., vitronectin, but these differential effects require further verification. Thalidomide over a range of doses has demonstrated nontoxic, cytostatic activity in LNCaP cells and significant upregulation of LNCaP cell PSA secretion in vitro. Furthermore, preliminary data from cDNA nucleic acid arrays of thalidomide-treated LNCaP cells suggest that thalidomide upregulates a potential angiogenic modulatory protein, the vitronectin precursor, which may eventually link thalidomide's antiangiogenic activity with modulation of angiogenic vascular integrin pathways.     

Variations in activin receptor, inhibin/activin subunit and follistatin mRNAs in human prostate tumour tissues

The possible role of activin in the regulation of malignant prostatic growth was studied using RNAase protection assays of activin receptors, inhibin/activin subunits and follistatin mRNAs in the human prostatic carcinoma cell lines LNCaP-FGC, -R and -LNO, in human prostatic carcinoma xenografts and in human prostatic tissue. Activin receptor types IA (ActRIA), IB (ActRIB), IIA (ActRIIA) and IIB (ActRIIB) mRNAs were generally expressed in prostate epithelial cells, with significantly lower levels of ActRIB mRNA in prostate tumour material when compared to non-malignant tissue (P < 0.05; Mann-Whitney U-test). Inhibin/activin betaA- and betaB-subunit mRNA expression was also found in prostate tissue. Androgen-independent xenografts expressed significantly lower amounts of betaB-subunit mRNA when compared to androgen-dependent xenografts (P< 0.05). While betaB-subunit mRNA was expressed by LNCaP-FGC and -LNO cells, virtually no expression was found in the androgen-independent LNCaP-R line. Inhibin alpha-subunit mRNA levels were low or undetectable in all samples investigated. Follistatin mRNA was undetectable in LNCaP-sublines, while low levels were found in prostatic tissues. In androgen-independent LNCaP-R cells, activin inhibited cell growth in a dose-dependent manner. These results suggest that prostate tumour progression is accompanied by a decrease of the inhibitory effect of locally produced activin by either a decrease in the expression of activin betaB-subunit mRNA or by a decrease of ActRIB mRNA levels.     

Id-1 expression in androgen-dependent prostate cancer is negatively regulated by androgen through androgen receptor

This study discovered that Id-1 expression in androgen-dependent prostate cancer decreased immediately after androgen deprivation but increased after longer androgen deprivation both in vivo and in vitro. Id-1 expression in androgen-independent LNCaP cells was about 6 fold as that in their parental cells. As was the case with LNCaP cells, when androgen receptor (AR) was introduced into AR-negative PC-3 cells, dihydrotestosterone inhibited while flutamide increased Id-1 expression. Thus, Id-1 expression in androgen-dependent prostate cancer was negatively regulated by androgen in a receptor-dependent way. The re-increased Id-1 might partially contribute to the emergence of androgen-independent prostate cancer after longer androgen deprivation therapy.     

Response of prostate cancer to anti-Her-2/neu antibody in androgen-dependent and -independent human xenograft models.

Antibody to the Her-2/neu gene product has been shown to inhibit the growth of breast cancer cells overexpressing Her-2/neu and to have clinical utility in treating breast cancer. We studied a recombinant, humanized anti-Her-2/neu antibody (Herceptin) in preclinical models of human prostate cancer. The androgen-dependent CWR22 and LNCaP human prostate cancer xenograft models and androgen-independent sublines of CWR22 were used. Her-2/neu staining of the parental, androgen-dependent, and androgen-independent CWR22 tumors and LNCaP tumors demonstrated variable Her-2/neu expression. Herceptin was administered i.p. at a dose of 20 mg/kg twice weekly after the xenograft had been established. No effect of Herceptin on tumor growth was observed in any of the androgen-independent tumors; however, significant growth inhibition was observed in both of the androgen-dependent xenograft models, CWR22 (68% growth inhibition at the completion of the experiment; P = 0.03 for trajectories of the average tumor volume of the groups) and LNCaP (89% growth inhibition; P = 0.002). There was a significant increase in prostate-specific antigen (PSA) index (ng PSA/ml serum/mm3 tumor) in Herceptin-treated androgen-dependent groups compared with control (CWR22, 18-fold relative to pretreatment value versus 1.0-fold, P = 0.0001; LNCaP, 2.35-fold relative to pretreatment value versus 0.6-fold, P = 0.001). When paclitaxel (6.25 mg/kg s.c., five times/week) was given to animals with androgen-dependent and -independent tumors, there was growth inhibition in each group. Paclitaxel and Herceptin cotreatment led to greater growth inhibition than was seen for the agents individually. Thus, in these prostate cancer model systems, Herceptin alone has clinical activity only in the androgen-dependent tumor and has at least an additive effect on growth, in combination with paclitaxel, in both androgen-dependent and androgen-independent tumors. Response to Herceptin did not correlate with the PSA levels, because the PSA index markedly increased in the Herceptin-treated group, whereas it remained constant in the control group. These results suggest the utility of Herceptin in the treatment of human prostate cancer.     

Interleukin-17 receptor-like gene is a novel antiapoptotic gene highly expressed in androgen-independent prostate cancer

We have recently identified a new gene, interleukin-17 receptor-like (IL-17RL), which is expressed in normal prostate and prostate cancer. This investigation is focused on the role of IL-17RL in prostate cancer. We found that IL-17RL was expressed at significantly higher levels in several androgen-independent prostate cancer cell lines (PC3, DU145, cds1, cds2, and cds3) and tumors compared with the androgen-dependent cell lines (LNCaP and MLC-SV40) and tumors. In an in vivo model of human prostate tumor growth in nude mice (CWR22 xenograft model), IL-17RL expression in tumors was induced by androgen deprivation. The relapsed androgen-independent tumors expressed higher levels of IL-17RL compared with the androgen-dependent tumors. Overexpression of IL-17RL in tumor necrosis factor alpha (TNFalpha)-sensitive LNCaP cells inhibited TNFalpha-induced apoptosis by blocking activation of caspase-3 downstream to caspase-2 and caspase-8. Reciprocally, knocking down IL-17RL expression by small interfering RNA induced apoptosis in all the prostate cancer cell lines studied. Taken together, these results show that IL-17RL is a novel antiapoptotic gene, which may confer partially the property of androgen-independent growth of prostate cancer by promoting cell survival. Thus, IL-17RL is a potential therapeutic target in the treatment of prostate cancer.     

Deregulation of the Rho GTPase, Rac1, suppresses cyclin-dependent kinase inhibitor p21(CIP1) levels in androgen-independent human prostate cancer cells

Abnormally suppressed levels of cyclin-dependent kinase inhibitors (CKIs) are associated with aggressive androgen-independent prostate cancer and contribute to uncontrolled proliferation. The androgen-independent human prostate cancer cell lines, LNCaP-104R1, ALVA31 and PC-3, express low levels of the CKI, p21(CIP1), compared to the less-malignant, androgen-dependent LNCaP cells. We investigated the mechanism underlying this suppression by examining the role of Rho GTPases, signaling proteins that play important roles in cell cycle progression, at least in part through regulation of CKIs. Inhibition of Rac1 induced p21 expression in androgen-independent lines but had no effect on the higher p21 levels characteristic of LNCaP cells. This induction of p21 was functionally significant as evidenced by inhibition of cyclin-dependent kinase 2 activity and decreased cell proliferation. Conversely, overexpression of constitutively active Rac1 suppressed the higher p21 levels seen in LNCaP cells. Thus, Rac1 activity is both necessary and sufficient for suppression of p21 in prostate cancer cells. Furthermore, Rac1 activity was significantly higher in all three androgen-independent cell lines compared to LNCaP cells. Thus in three models of aggressive human prostate cancer, hyperactivity of Rac1 corresponds to suppressed levels of p21. These results are unique in describing a role for Rac1 in p21 regulation and may implicate the Rac1 signaling pathway as a potential therapeutic target for controlling prostate cancer cell growth following progression to androgen independence.     

Regulation of expression of Na+,K+-ATPase in androgen-dependent and androgen-independent prostate cancer.

The beta 1-subunit of Na+,K+-ATPase was isolated and identified as an androgen down-regulated gene. Expression was observed at high levels in androgen-independent as compared to androgen-dependent (responsive) human prostate cancer cell lines and xenografts when grown in the presence of androgens. Down-regulation of the beta 1-subunit was initiated at concentrations between 0.01 nM and 0.03 nM of the synthetic androgen R1881 after relatively long incubation times (> 24 h). Using polyclonal antibodies, the concentration of beta 1-subunit protein, but not of the alpha 1-subunit protein, was markedly reduced in androgen-dependent human prostate cancer cells (LNCaP-FGC) cultured in the presence of androgens. In line with these observations it was found that the protein expression of total Na+,K+-ATPase in the membrane (measured by 3H-ouabain binding) was also markedly decreased. The main function of Na+,K+-ATPase is to maintain sodium and potassium homeostasis in animal cells. The resulting electrochemical gradient is facilitative for transport of several compounds over the cell membrane (for example cisplatin, a chemotherapeutic agent experimentally used in the treatment of hormone-refractory prostate cancer). Here we observed that a ouabain-induced decrease of Na+,K+-ATPase activity in LNCaP-FGC cells results in reduced sensitivity of these cells to cisplatin-treatment. Surprisingly, androgen-induced decrease of Na+,K+-ATPase expression, did not result in significant protection against the chemotherapeutic agent.     

MicroRNA-616 induces androgen-independent growth of prostate cancer cells by suppressing expression of tissue factor pathway inhibitor TFPI-2

Expression of microRNA genes is profoundly altered in cancer but their role in the development of androgen-independent prostate cancer has received limited attention as yet. In this study, we report a functional impact in prostate cancer cells for overexpression of the microRNA miR-616, which occurred consistently in cells that were androgen-independent (AI) versus androgen-dependent (AD). miR-616 overexpression was confirmed in malignant prostate tissues as opposed to benign prostate specimens. Stable miR-616 overexpression in LNCaP cells by a lentiviral-based approach stimulated AI prostate cancer cell proliferation in vitro whereas concomitantly reducing androgen-induced cell growth. More importantly, miR-616 overexpressing LNCaP cells overcame castration resistance as shown by an enhanced ability to proliferate in vivo after bilateral orchiectomy. Conversely, antagonizing miR-616 in AI prostate cancer cells yielded opposite effects. Microarray profiling and bioinformatics analysis identified the tissue factor pathway inhibitor TFPI-2 mRNA as a candidate downstream target of miR-616. In support of this candidacy, we documented interactions between miR-616 and the 3'UTR of TFPI-2 and determined TFPI-2 expression to be inversely correlated to miR-616 in a series of prostate cell lines and clinical specimens. Notably, reexpression of TFPI-2 in LNCaP cells with stable miR-616 overexpression rescued the AD phenotype, as shown by a restoration of androgen dependence and cell growth inhibition. Taken together, our findings define a functional involvement for miR-616 and TFPI-2 in the development and maintenance of androgen-independent prostate cancer.     

Insulin-like growth factor binding protein-6 inhibits prostate cancer cell proliferation: implication for anticancer effect of diethylstilbestrol in hormone refractory prostate cancer

Diethylstilbestrol (DES) is a synthetic oestrogen, and its anticancer effects are exerted in androgen-dependent prostate cancer. The administration of DES decreases serum testosterone to castration levels. However, in androgen-independent prostate cancer patients, who are already orchiectomised, the administration of DES improves symptoms and decreases prostate-specific antigen (PSA). The mechanisms responsible for these direct inhibitory effects have been explained as biological actions not mediated by oestrogen receptors. We assessed the gene expression profiles of prostate cancer cells treated with DES, and investigated direct inhibitory effects of DES. DES inhibited the proliferation of LNCaP and PC-3 cells. cDNA microarray analysis showed that expression of many genes was downregulated by DES. However, insulin-like growth factor binding protein 6 (IGFBP-6) gene expression levels were upregulated in PC-3 cells. IGFBP-6 gene expression and protein levels significantly increased after DES treatment. Recombinant IGFBP-6 inhibited cell proliferation, and the inhibitory effect of DES was neutralised by anti-IGFBP-6 antibody. From the immunohistochemical analysis of IGFBP-6 using biopsy samples from androgen-independent prostate cancer, we found IGFBP-6 expression in androgen independent prostate cancer, and that DES treatment increased the IGFBP-6 staining intensity of the cancer cells in one sample. These findings suggested that DES induces IGFBP-6, which inhibits cell proliferation in an androgen-independent prostate cancer cell line, PC-3. IGFBP-6 therefore might be involved in the direct effects of DES in androgen-independent prostate cancer.