Non-genomic effects of the androgen receptor and vitamin D agonist are involved in suppressing invasive phenotype of prostate cancer cells

Suppression of invasive phenotype is essential in developing new therapeutic tools to treat prostate cancer (PC). Evidence indicates that androgen-dependent (AD) prostate cancer cells are characterized by a lower malignant phenotype. We have demonstrated that transfection with an androgen receptor (AR) expression vector of the androgen-independent (AI) prostate cancer cell line PC3 decreases invasion of these cells through modulation of alpha6beta4 integrin expression, indicating a genotropic effect of androgens in inhibiting invasion ability of AD PC cells. Later on, we have shown that also a non-genotropic mechanism is involved in such an effect. By using immunoconfocal fluorescent microscopy, we demonstrated that AR in PC3-AR cells co-localizes with the EGFR receptors (EGFR) in PC3-AR cells. Co-immunoprecipitation studies both in PC3-AR cells and in the AD cell line LNCaP that physiologically express both receptors, confirm the occurrence of an interaction between of the two proteins. In PC3-AR cells, we demonstrated a disruption of EGFR signalling properties (reduced EGF-induced EGFR autotransphosphorylation, reduced EGF-stimulated PI3K activity as well as EGFR-PI3K interaction) contributing to the lower invasive phenotype of these cells. In another study, we investigated the effects of a new Vitamin D analogue, BXL628, on invasion in response to KGF in the androgen-independent PC cell line DU145. We found that the compound was able to reduce proliferation and invasion of the cells in response to the growth factor. In addition, we found that KGF-induced autotransphosphorylation of KGF receptor (KGFR) and PI3K activation were suppressed after short-term (5min) pre-treatment with the analogue before addition of KGF. Collectively, these studies demonstrate that a non-genotropic effect due to a direct interaction of the androgen receptor with EGFR and to a rapid effect of a Vitamin D agonist on KGFR may disrupt signalling of GF leading to decreased tumorigenicity and a less malignant phenotype of PC cells in vitro.     

Conditional expression of the androgen receptor induces oncogenic transformation of the mouse prostate

The androgen signaling pathway, mediated through the androgen receptor (AR), is critical in prostate tumorigenesis. However, the precise role of AR in prostate cancer development and progression still remains largely unknown. Specifically, it is unclear whether overexpression of AR is sufficient to induce prostate tumor formation in vivo. Here, we inserted the human AR transgene with a LoxP-stop-loxP (LSL) cassette into the mouse ROSA26 locus, permitting "conditionally" activated AR transgene expression through Cre recombinase-mediated removal of the LSL cassette. By crossing this AR floxed strain with Osr1-Cre (odd skipped related) mice, in which the Osr1 promoter activates at embryonic day 11.5 in urogenital sinus epithelium, we generated a conditional transgenic line, R26hAR(loxP):Osr1-Cre+. Expression of transgenic AR was detected in both prostatic luminal and basal epithelial cells and is resistant to castration. Approximately one-half of the transgenic mice displayed mouse prostatic intraepithelial neoplasia (mPIN) lesions. Intriguingly, four mice (10%) developed prostatic adenocarcinomas, with two demonstrating invasive diseases. Positive immunostaining of transgenic AR protein was observed in the majority of atypical and tumor cells in the mPIN and prostatic adenocarcinomas, providing a link between transgenic AR expression and oncogenic transformation. An increase in Ki67-positive cells appeared in all mPIN and prostatic adenocarcinoma lesions of the mice. Thus, we demonstrated for the first time that conditional activation of transgenic AR expression by Osr1 promoter induces prostate tumor formation in mice. This new AR transgenic mouse line mimics the human disease and can be used for study of prostate tumorigenesis and drug development.     

Nuclear exclusion of the androgen receptor by melatonin

Androgen receptors (AR) play a crucial role in androgen-mediated processes and prostate cancer progression. The pineal hormone melatonin attenuates the androgen-dependent growth of benign and cancer prostate epithelial cells in vitro and may reverse clinical resistance to androgen ablation therapy in patients progressing on gonadotropin releasing hormone (GnRH) analogue. Where along the AR cascade does melatonin act remains to be determined. The effects of melatonin on AR localization, level and activity were assessed using androgen-insensitive prostate carcinoma PC3 cells stably transfected with a wild-type AR-expressing vector (PC3-AR).AR was localized to the PC3-AR cell nucleus in the absence of dihydrotestosterone (DHT). Melatonin caused a robust exclusion of the AR from the cell nucleus to the cytoplasm. The nuclear export inhibitor, leptomycin B prevented this process. The exclusion was selective since melatonin had no such effect on the nuclear localization of estrogen receptors alpha (ERalpha) in these cells.Melatonin also caused nuclear exclusion of the AR in the presence of DHT. In addition, it attenuated androgen induced reporter gene activity in PC3 cells co-transfected with the human AR and AR reporter plasmids. Elevated androgen concentrations counteracted melatonin's effects. Melatonin did not decrease AR level or androgen binding in the cells.The nuclear localization of the AR is a hallmark of its cellular activity. These data point to AR nuclear exclusion as a possible mechanism to attenuate androgen responses in target tissues.     

A dominant-negative mutant of androgen receptor coregulator ARA54 inhibits androgen receptor-mediated prostate cancer growth.

The ligand-bound androgen receptor (AR) regulates target genes via a mechanism involving coregulators such as androgen receptor-associated 54 (ARA54). We investigated whether the interruption of the AR coregulator function could lead to down-regulation of AR activity. Using in vitro mutagenesis and a yeast two-hybrid screening assay, we have isolated a mutant ARA54 (mt-ARA54) carrying a point mutation at amino acid 472 changing a glutamic acid to lysine, which acts as a dominant-negative inhibitor of AR transactivation. In transient transfection assays of prostate cancer cell lines, the mt-ARA54 suppressed endogenous mutated AR-mediated and exogenous wild-type AR-mediated transactivation in LNCaP and PC-3 cells, respectively. In DU145 cells, the mt-ARA54 suppressed exogenous ARA54 but not other coregulators, such as ARA55-enhanced or SRC-1-enhanced AR transactivation. In the LNCaP cells stably transfected with the plasmids encoding the mt-ARA54 under the doxycycline inducible system, the overexpression of the mt-ARA54 inhibited cell growth and endogenous expression of prostate-specific antigen. Mammalian two-hybrid assays further demonstrated that the mt-ARA54 can disrupt the interaction between wild-type ARA54 molecules, suggesting that ARA54 dimerization or oligomerization may play an essential role in the enhancement of AR transactivation. Together, our results demonstrate that a dominant-negative AR coregulator can suppress AR transactivation and cell proliferation in prostate cancer cells. Further studies may provide a new therapeutic approach for blocking AR-mediated prostate cancer growth.     

L712V mutation in the androgen receptor gene causes complete androgen insensitivity syndrome due to severe loss of androgen function

Inability to respond to the circulating androgens is named as androgen insensitivity syndrome (AIS). Mutations in the androgen receptor (AR) gene are the most common cause of AIS. A cause and effect relationship between some of these mutations and the AIS phenotype has been proven by in vitro studies. Several other mutations have been identified, but need to be functionally validated for pathogenicity. Screening of the AR mutations upon presumptive diagnosis of AIS is recommended. We analyzed a case of complete androgen insensitivity syndrome (CAIS) for mutations in the AR gene. Sequencing of the entire coding region revealed C > G mutation (CTT–GTT) at codon 712 (position according to the NCBI database) in exon 4 of the gene, resulting in replacement of leucine with valine in the ligand-binding domain of the AR protein. No incidence of this mutation was observed in 230 normal male individuals analyzed for comparison. In vitro androgen binding and transactivation assays using mutant clone showed approximately 71% loss of ligand binding and about 76% loss of transactivation function. We conclude that CAIS in this individual was due to L712V substitution in the androgen receptor protein.     

Inflammatory Responses in a Benign Prostatic Hyperplasia Epithelial Cell Line (BPH-1) Infected with Trichomonas vaginalis

Trichomonas vaginalis causes the most prevalent sexually transmitted infection worldwide. Trichomonads have been detected in prostatic tissues from prostatitis, benign prostatic hyperplasia (BPH), and prostate cancer. Chronic prostatic inflammation is known as a risk factor for prostate enlargement, benign prostatic hyperplasia symptoms, and acute urinary retention. Our aim was to investigate whether T. vaginalis could induce inflammatory responses in cells of a benign prostatic hyperplasia epithelial cell line (BPH-1). When BPH-1 cells were infected with T. vaginalis, the protein and mRNA of inflammatory cytokines, such as CXCL8, CCL2, IL-1β, and IL-6, were increased. The activities of TLR4, ROS, MAPK, JAK2/STAT3, and NF-κB were also increased, whereas inhibitors of ROS, MAPK, PI3K, NF-κB, and anti-TLR4 antibody decreased the production of the 4 cytokines although the extent of inhibition differed. However, a JAK2 inhibitor inhibited only IL-6 production. Culture supernatants of the BPH-1 cells that had been incubated with live T. vaginalis (trichomonad-conditioned medium, TCM) contained the 4 cytokines and induced the migration of human monocytes (THP-1 cells) and mast cells (HMC-1 cells). TCM conditioned by BPH-1 cells pretreated with NF-κB inhibitor showed decreased levels of cytokines and induced less migration. Therefore, it is suggested that these cytokines are involved in migration of inflammatory cells. These results suggest that T. vaginalis infection of BPH patients may cause inflammation, which may induce lower urinary tract symptoms (LUTS).     

Androgen receptor transactivation assay using green fluorescent protein as a reporter

For screening of a large number of samples for androgenic activity, a robust system with minimal handling is required. The coding sequence for human androgen receptor (AR) was inserted into expression plasmid YEpBUbi-FLAG1, resulting in the plasmid YEpBUbiFLAG-AR, and the estrogen response element (ERE) on the reporter vector YRpE2 was replaced by an androgen response element (ARE), resulting in the plasmid YRpE2-ARE. Thus, a fully functional transactivation assay system with beta-galactosidase as a reporter gene could be created. Furthermore, green fluorescent protein (GFP) was introduced as an alternative reporter gene that resulted in a simplification of the whole assay procedure. For evaluation of both reporter systems, seven steroidal compounds with known AR agonistic properties (5 alpha-dihydrotestosterone, testosterone, androstenedione, 17 alpha-methyltestosterone, progesterone, epitestosterone, and d-norgestrel) were tested, and their potencies obtained in the different assays were compared. Furthermore, potencies from the transactivation assays were compared with IC(50) values obtained in radioligand binding assays. The newly developed androgen receptor transactivation assay is a useful tool for characterizing compounds with androgenic activity.     

A competitive inhibitor that reduces recruitment of androgen receptor to androgen-responsive genes

The androgen receptor (AR) has a critical role in the growth and progression of androgen-dependent and castration-resistant prostate cancers. To identify novel inhibitors of AR transactivation that block growth of prostate cancer cells, a luciferase-based high-throughput screen of ~160,000 small molecules was performed in cells stably expressing AR and a prostate-specific antigen (PSA)-luciferase reporter. CPIC (1-(3-(2-chlorophenoxy) propyl)-1H-indole-3-carbonitrile) was identified as a small molecule that blocks AR transactivation to a greater extent than other steroid receptors. CPIC inhibited AR-mediated proliferation of androgen-sensitive prostate cancer cell lines, with minimal toxicity in AR-negative cell lines. CPIC treatment also reduced the anchorage-independent growth of LAPC-4 prostate cancer cells. CPIC functioned as a pure antagonist by inhibiting the expression of AR-regulated genes in LAPC-4 cells that express wild-type AR and exhibited weak agonist activity in LNCaP cells that express the mutant AR-T877A. CPIC treatment did not reduce AR levels or alter its nuclear localization. We used chromatin immunoprecipitation to identify the site of action of CPIC. CPIC inhibited recruitment of androgen-bound AR to the PSA promoter and enhancer sites to a greater extent than bicalutamide. CPIC is a new therapeutic inhibitor that targets AR-mediated gene activation with potential to arrest the growth of prostate cancer.     

Triterpenes from Alisma orientalis act as androgen receptor agonists,progesterone receptor antagonists,and glucocorticoid receptor antagonists

Alisma orientalis, a well-known traditional medicine, exerts numerous pharmacological effects including anti-diabetes, anti-hepatitis, and anti-diuretics but its bioactivity is not fully clear. Androgen receptor (AR), progesterone receptor (PR), and glucocorticoid receptor (GR) are three members of nuclear receptor superfamily that has been widely targeted for developing treatments for essential diseases including prostate cancer and breast cancer. In this study, two triterpenes, alisol M 23-acetate and alisol A 23-acetate from Alisma orientalis were determined whether they may act as androgen receptor (AR), progesterone receptor (PR), or glucocorticoid receptor (GR) modulators. Indeed, in the transient transfection reporter assays, alisol M 23-acetate and alisol A 23-acetate transactivated AR in dose-dependent manner, while they transrepressed the transactivation effects exerted by agonist-activated PR and GR. Through molecular modeling docking studies, they were shown to respectively interact with AR, PR, or GR ligand binding pocket fairly well. All these results indicate that alisol M 23-acetate and alisol A 23-acetate from Alisma orientalis might possess therapeutic effects through their modulation of AR, PR, and GR pathways.     

BPH-1通过分泌PGE2上调前列腺间质细胞ERRα的表达

摘要 雌激素受体相关受体α（estrogen receptor-related receptor α,ERRα）是一类可以直接或间接参与雌激素应答反应的孤儿核受体,它与雌激素受体（estrogen receptor）在结构上有很强的同源性．雌激素效应在良性前列腺增生（benign prostatic hyperplasis,BPH）的发生和发展中起着重要的作用．通常,孤儿核受体的转录活性多受一些非经典激素如维生素A衍生物、前列腺素类、固醇的调控．本文研究前列腺上皮细胞分泌的活性因子对间质细胞ERRα表达调控的分子机制．收集前列腺增生上皮细胞系BPH-1和前列腺癌上皮细胞系DU-145的条件培养液（condition medium,CM）培养的间质细胞,采用实时定量RT-PCR和Western 印迹法检测前列腺间质细胞（prostate stromal cells,PrSCs）中ERRα的表达,筛选CM中影响ERRα表达的活性因子．研究结果显示,BPH-1的CM可以上调ERRα的表达,而DU-145的CM对ERRα的表达没有影响;BPH-1中合成前列腺素E2 (prostaglandin E2, PGE2)的限速酶——环氧合酶2（cyclooxygenase-2, COX-2）的mRNA表达水平和PGE2的分泌水平明显高于DU-145中COX-2表达水平和PGE2分泌水平;用经添加COX-2抑制剂NS-398的培养液处理BPH-1,其CM中PGE2的浓度明显下降,并失去了对ERRα表达的上调作用;添加PGE2可上调间质细胞中ERRα的表达．结果表明,BPH-1通过分泌PGE2促进间质细胞ERRa的表达,提示：在良性前列腺增生的发生和发展中,上皮细胞的旁分泌作用可促进间质细胞由ERRα介导的雌激素效应．     

Pomegranate polyphenols down-regulate expression of androgen-synthesizing genes in human prostate cancer cells overexpressing the androgen receptor

Prostate cancer is dependent on circulating testosterone in its early stages and is treatable with radiation and surgery. However, recurrent prostate tumors advance to an androgen-independent state in which they progress in the absence of circulating testosterone, leading to metastasis and death. During the development of androgen independence, prostate cancer cells are known to increase intracellular testosterone synthesis, which maintains cancer cell growth in the absence of significant amounts of circulating testosterone. Overexpression of the androgen receptor (AR) occurs in androgen-independent prostate cancer and has been proposed as another mechanism promoting the development of androgen independence. The LNCaP-AR cell line is engineered to overexpress AR but is otherwise similar to the widely studied LNCaP cell line. We have previously shown that pomegranate extracts inhibit both androgen-dependent and androgen-independent prostate cancer cell growth. In this study, we examined the effects of pomegranate polyphenols, ellagitannin-rich extract and whole juice extract on the expression of genes for key androgen-synthesizing enzymes and the AR. We measured expression of the HSD3B2 (3beta-hydroxysteroid dehydrogenase type 2), AKR1C3 (aldo-keto reductase family 1 member C3) and SRD5A1 (steroid 5alpha reductase type 1) genes for the respective androgen-synthesizing enzymes in LNCaP, LNCaP-AR and DU-145 human prostate cancer cells. A twofold suppression of gene expression was considered statistically significant. Pomegranate polyphenols inhibited gene expression and AR most consistently in the LNCaP-AR cell line (P=.05). Therefore, inhibition by pomegranate polyphenols of gene expression involved in androgen-synthesizing enzymes and the AR may be of particular importance in androgen-independent prostate cancer cells and the subset of human prostate cancers where AR is up-regulated.     

Modulation of the tumor cell death pathway by androgen receptor in response to cytotoxic stimuli

Despite an initial response from androgen deprivation therapy, most prostate cancer patients relapse to a hormone-refractory state where tumors still remain dependent on androgen receptor (AR) function. We have previously shown that AR breakdown correlates with the induction of cancer cell apoptosis by proteasome inhibition. However, the involvement of AR in modulating the cell death pathway has remained elusive. To investigate this, we used an experimental model consisting of parental PC-3 prostate cancer cells that lack AR expression and PC-3 cells stably overexpressing wild type AR gene. Here, we report that both chemotherapeutic drugs (cisplatin) and proteasome inhibitors induced caspase-3-associated cell death in parental PC-3 cells whereas non-caspase-3 associated cell death in PC3-AR cells. The involvement of AR in modulating tumor cell death was further confirmed in PC-3 cells transiently expressing AR. Consistently, treatment with the clinically used proteasome inhibitor Bortezomib (Velcade/PS-341) of (AR+) LNCaP prostate cancer cells caused AR cleavage and cell death with low levels of caspase activation. However, co-treatment with Bortezomib and the AR antagonist Bicalutamide (Casodex) caused significant decrease in AR expression associated with an increase in caspase-3 activity in both LNCaP and PC3-AR cells. Thus our results provide compelling evidence for involvement of AR in deciding types of tumor cell death upon cytotoxic stimuli, and specifically, blockade of AR activities could change necrosis to apoptosis in tumor cells. Our findings may help guide clinicians based on AR status in the design of favorable treatment strategies for prostate cancer patients.     

Opposite effects of alternative TZF spliced variants on androgen receptor

We previously demonstrated that testicular zinc-finger protein (TZF) was a corepressor of the androgen receptor (AR). In the present study, we further showed that TZF-L, an alternative spliced variant of TZF, enhanced transactivation function of AR. Deletion analysis of TZF-L revealed that its N-terminus, which almost corresponded to that of TZF, but not its C-terminus was able to interact with AR. Additional analysis suggested that TZF and TZF-L were able to form both homodimers and heterodimers. TZF-L inhibited the homodimer formation of TZF and the intranuclear dot formation of TZF. We propose that in the unique regulation system of AR-mediated transactivation, two spliced isoforms of TZF act as coactivator and corepressor, respectively.     

Capsaicin, a component of red peppers, induces expression of androgen receptor via PI3K and MAPK pathways in prostate LNCaP cells

In this study, capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) induced an increase in the cell viability of the androgen-responsive prostate cancer LNCaP cells, which was reversed by the use of the TRPV1 antagonists capsazepine, I-RTX and SB 366791. In further studies we observed that capsaicin induced a decrease in ceramide levels as well as Akt and Erk activation. To investigate the mechanism of capsaicin action we measured androgen (AR) receptor levels. Capsaicin induced an increase in the AR expression that was reverted by the three TRPV1 antagonists. AR silencing by the use of siRNA, as well as blocking the AR receptor with bicalutamide, inhibited the proliferative effect of capsaicin.     

DU-145 and PC-3 human prostate cancer cell lines express androgen receptor: implications for the androgen receptor functions and regulation

The majority of human prostate cancer cell lines, including the two "classical" cell lines DU-145 and PC-3, are reported to be androgen receptor (AR)-negative. However, other studies have provided evidence that the DU-145 and PC-3 cell lines express AR mRNA. These contradictory observations prompted us to investigate whether DU-145 and PC-3 cell lines express the androgen receptor. Using antipeptide antibodies directed against three distinct regions of the human AR protein and an improved method to detect AR protein in immunoblotting, we report that DU-145 and PC-3 cell lines express AR protein. We found that the relative levels of the AR mRNA and protein that were detected in DU-145 and PC-3 cell lines were lower than the LNCaP, an AR-positive cell line. Moreover, the antibody directed against the non-variant region (amino acids 299-315), but not the variant N- or C-terminal region (amino acids 1-20 and 900-919, respectively) of the human AR protein, detected the expression of AR in all prostate cancer cell lines. Notably, treatment of these cell lines with dihydrotestosterone (DHT) resulted in measurable increases in the AR protein levels and considerable nuclear accumulation. Although, treatment of DU-145 and PC-3 cells with DHT did not result in stimulation of the activity of an AR-responsive reporter, knockdown of AR expression in PC-3 cells resulted in decreases in p21(CIP1) protein levels, and a measurable decrease in the activity of the p21-luc-reporter. Our observations demonstrate the expression of AR protein in DU-145 and PC-3 prostate cancer cell lines.