Functional androgen receptor confers sensitization of androgen-independent prostate cancer cells to anticancer therapy via caspase activation

Mechanism of Notch1‑saRNA‑1480 reversing androgen sensitivity in human metastatic castration‑resistant prostate cancer

The aim of the present study was to explore the mechanism by which Notch1-small activating (sa)RNA restored androgen sensitivity in human metastatic castration-resistant prostate cancer (CRPC). After transfection of Notch1-saRNA-1480 in PC3 cells, the expression of Notch1 and androgen receptor (AR) was investigated by reverse transcription quantitative PCR (RT-qPCR) and western blotting. Furthermore, the protein expression level of vascular endothelial growth factor (VEGF) was measured. Then, flow cytometry was used to analyze the cell cycle and apoptosis after transfection. Moreover, the migration and invasion ability of PC3 cells were assessed by transwell assays. Then, angio-genesis experiments were conducted to analyze the abilities of PC3 cells to form blood vessels. Furthermore, in vivo experiments detected the antitumor activity of Notch1-saRNA-1480. The mRNA and protein expression levels of Notch1 were significantly increased after transfection, while the expression levels of AR and VEGF were decreased. After transfection, the cell cycle was arrested at the G0/G1 checkpoint. Notch1-saRNA-1480 significantly increased the proportion of apoptotic cells after transfection. In addition, transwell assay results showed that PC3 cell migration and invasion were inhibited. The total vessel length was significantly decreased based on angiogenesis experiments, which indicated that PC3 cell angiogenesis was inhibited. In vivo experiments showed that Notch1-saRNA-1480 could inhibit tumor growth and volume. The protein expression of Notch1, AR, VEGF receptor 2 (VEGFR2) and VEGF in tumor tissues was consistent with in vitro levels. Notch1-saRNA-1480 could significantly inhibit the proliferation of PC3 cells in vitro and the growth of tumors in vivo, which is associated with the inhibition of the AR and VEGF pathways.

Quality of Life and Sexual Health in the Aging of PCa Survivors

Prostate cancer (PCa) is the most common malignancy in elderly men. The progressive ageing of the world male population will further increase the need for tailored assessment and treatment of PCa patients. The determinant role of androgens and sexual hormones for PCa growth and progression has been established. However, several trials on androgens and PCa are recently focused on urinary continence, quality of life, and sexual function, suggesting a new point of view on the whole endocrinological aspect of PCa. During aging, metabolic syndrome, including diabetes, hypertension, dyslipidemia, and central obesity, can be associated with a chronic, low-grade inflammation of the prostate and with changes in the sex steroid pathways. These factors may affect both the carcinogenesis processes and treatment outcomes of PCa. Any treatment for PCa can have a long-lasting negative impact on quality of life and sexual health, which should be assessed by validated self-reported questionnaires. In particular, sexual health, urinary continence, and bowel function can be worsened after prostatectomy, radiotherapy, or hormone treatment, mostly in the elderly population. In the present review we summarized the current knowledge on the role of hormones, metabolic features, and primary treatments for PCa on the quality of life and sexual health of elderly Pca survivors.

Nrf1 and Nrf2 transcription factors regulate androgen receptor transactivation in prostate cancer cells

Despite androgen deprivation therapy (ADT), persistent androgen receptor (AR) signaling enables outgrowth of castration resistant prostate cancer (CRPC). In prostate cancer (PCa) cells, ADT may enhance AR activity through induction of oxidative stress. Herein, we investigated the roles of Nrf1 and Nrf2, transcription factors that regulate antioxidant gene expression, on hormone-mediated AR transactivation using a syngeneic in vitro model of androgen dependent (LNCaP) and castration resistant (C4-2B) PCa cells. Dihydrotestosterone (DHT) stimulated transactivation of the androgen response element (ARE) was significantly greater in C4-2B cells than in LNCaP cells. DHT-induced AR transactivation was coupled with higher nuclear translocation of p65-Nrf1 in C4-2B cells, as compared to LNCaP cells. Conversely, DHT stimulation suppressed total Nrf2 levels in C4-2B cells but elevated total Nrf2 levels in LNCaP cells. Interestingly, siRNA mediated silencing of Nrf1 attenuated AR transactivation while p65-Nrf1 overexpression enhanced AR transactivation. Subsequent studies showed that Nrf1 physically interacts with AR and enhances AR’s DNA-binding activity, suggesting that the p65-Nrf1 isoform is a potential AR coactivator. In contrast, Nrf2 suppressed AR-mediated transactivation by stimulating the nuclear accumulation of the p120-Nrf1 which suppressed AR transactivation. Quantitative RT-PCR studies further validated the inductive effects of p65-Nrf1 isoform on the androgen regulated genes, PSA and TMPRSS2. Therefore, our findings implicate differential roles of Nrf1 and Nrf2 in regulating AR transactivation in PCa cells. Our findings also indicate that the DHT-stimulated increase in p65-Nrf1 and the simultaneous suppression of both Nrf2 and p120-Nrf1 ultimately facilitates AR transactivation in CRPC cells.

Androgen receptor (AR) expression in prostate cancer and progression of the tumor: Lessons from cell lines, animal models and human specimens

Prostate cancer (PC) is among the most frequent causes of death for cancer in men in western countries. In about 30% of cases, the disease is very aggressive rapidly leading to a metastatic disease. In these cases, prostatectomy is not possible and the patient is usually directed to androgen deprivation therapy (ADT) which is only palliative as a castration resistant PC (CRPC) usually develops within 2-3 years of treatment. At present there are no prognostic markers of PC progression. The role of the androgen receptor (AR) in initiation and development of PC is well established and documented. In particular, it is now recognized that androgens actions are mediated by an integration of classical (genomic) and non-classical (extragenomic) activity of AR. The picture about AR and PC become less clear when CRPC is considered. Indeed, the role of AR in the progression of PC and in CRPC is controversial. Results of studies on the role of AR in the progression of PC in cell lines, xenografts, animal models and even clinical specimens are conflicting reflecting the high heterogeneity of PC. Recent evidence in AR conditional KO in mouse models of PC shows possible contrasting roles of AR depending on its location in the two (epithelial or stromal) compartments of PC. Here, we review this evidence and report preliminary data of a study performed in microdissected areas of epithelia and stromal compartments of human PC.

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.

Androgen regulation of prostate cancer: where are we now?

BACKGROUND

Androgens play an essential role in the development and differentiation of the prostate gland; their contribution to pathological conditions, such as benign prostatic hyperplasia and prostate cancer (PC), remains unclear.

AIM

We reviewed relationships between androgens and the prostate both in physiological and pathological conditions.

MATERIAL AND METHODS

A systematic search of published evidence was performed using Medline (1969 to September 2010).

RESULTS

Androgen-dependency of prostate growth is evident only in the hypogonadal condition, but not in the eugonadal state (the "saturation hypothesis"). There is unequivocal evidence that reducing androgen signaling to the hypogonadal range can reduce PC growth and patient symptoms. At physiological testosterone concentration there is no link between androgen levels and PC risk. In addition, different strategies of androgen deprivation (ADT) for advanced PC are only palliative and rarely cure patients. Preliminary evidence indicates that a low androgen milieu is associated with tumor aggressiveness. Transition to androgen-independence is complex and involves both selection and outgrowth of preexisting androgen resistant clones, as well as adaptative upregulation of genes that help the cancer cells to survive and grow after ADT. Because androgens are essential for the regulation of fat distribution, insulin sensitivity, and lipid and bone metabolism, recent publications have highlighted the concept that ADT may also be involved with an increase in overall, as well as cardiovascular, morbidity and mortality.

CONCLUSIONS

While ADT still represents a cornerstone for the palliative therapy of a small fraction of aggressive PC, a "misuse and/or abuse" of ADT should be avoided.

Recyclable single-stranded DNA template for synthesis of siRNAs

RNA interference is a post-transcriptional silencing mechanism triggered by the bioavailability and/or exogenous introduction of double-stranded RNA (dsRNA) into cells. Here we describe a novel method for the synthesis of siRNA in a single vessel. The method employs in vitro transcription and a single-stranded DNA (ssDNA) template and design, which incorporates upon self-annealing, two promoters, two templates, and three loop regions. Using this method of synthesis we generated efficacious siRNAs designed to silence both exogenous and endogenous genes in mammalian cells. Due to its unique design the single-stranded template is easily amenable to adaptation for attachment to surface platforms for synthesis of siRNAs. A siRNA synthesis platform was generated using a 3' end-biotinylated ssDNA template tethered to a streptavidin coated surface that generates stable siRNAs under multiple cycles of production. Together these data demonstrate a unique and robust method for scalable siRNA synthesis with potential application in RNAi-based array systems.

PI3K/Akt-dependent transcriptional regulation and activation of BMP-2-Smad signaling by NF-kappaB in metastatic prostate cancer cells

BACKGROUND

Bone morphogenetic proteins (BMPs) exert osteoinductive effects in prostate cancer (PC) via uncharacterized mechanisms. In this study, we investigated whether the nuclear transcription factor NF-kappaB, implicated in PC metastasis, is involved in transcriptional regulation and activation of BMP-2 or BMP-4/Smad signaling in PC cells.

METHODS

NF-kappaB inhibition was achieved by IkappaBalpha super-repressor adenoviral vector and activation was monitored by EMSA and reporter assays. BMP expression and activation was measured by PCR and reporter assays. Promoter binding assay was performed by chromatin immunoprecipitation (ChIP) assay. Smad1/5/8 phosphorylation was measured by Western blot analysis.

RESULTS

PCR and chimeric BMP-2 and BMP-4 luciferase assays demonstrate that NF-kappaB confers robust and selective activation of BMP-2 in p65 overexpressing or rhTNF-alpha-stimulated PC cells. Inhibition of NF-kappaB significantly reduced transcript levels and autocrine production of BMP-2 by rhTNF-alpha stimulated C4-2B cells and to a lesser extent by the parental LNCaP cells. Selective inhibition of PI3K/Akt suppressed the NF-kappaB-induced BMP-2 promoter activity. Furthermore, suppression of NF-kappaB activation decreased the transcript levels and BMP-2-induced phosphorylation of Smad1/5/8, critical downstream targets of BMP-2 signaling in PC cells. Notably, the activation of BMPRII by BMP-2 is required for modulation of Smad activation by NF-kappaB in PC cells. Based on ChIP analysis, the transcriptional regulation of BMP-2 gene by NF-kappaB may be partially attributed to binding to kappab site on the BMP-2 promoter.

CONCLUSIONS

The data suggest that PI3K/Akt-NF-kappaB axis may promote PC bone metastasis in part by regulating transcription and activation of the BMP-2-Smad signaling cascade in osteotropic PC cells.

Unique bisphenol A transcriptome in prostate cancer: novel effects on ERbeta expression that correspond to androgen receptor mutation status

BACKGROUND

Prostatic adenocarcinomas are dependent on androgen receptor (AR) activity for growth and progression, and therapy for disseminated disease depends on ablation of AR activity. Recurrent tumors ultimately arise wherein AR has been re-activated. One mechanism of AR restoration is via somatic mutation, wherein cells containing mutant receptors become susceptible to activation by alternative ligands, including bisphenol A (BPA). In tumors with specific AR mutations, BPA promotes therapeutic bypass, suggesting significant negative impact to the clinical management of prostate cancer.

OBJECTIVE

Our goal was to determine the mechanism of BPA action in cancer cells carrying BPA-responsive AR mutants.

METHODS

The molecular signature of BPA activity in prostate cancer cells harboring mutant AR was delineated via genetic microarray analysis. Specificity of BPA action was assessed by comparison with the molecular signature elicited by dihydrotestosterone (DHT).

RESULTS

BPA and DHT elicited distinct transcriptional signatures in prostate cancer cells expressing the BPA-responsive mutant AR-T877A. BPA dramatically attenuated estrogen receptor beta (ERbeta) expression; this finding was specific to prostate tumor cells in which BPA induces cellular proliferation.

CONCLUSIONS

BPA induces a distinct gene expression signature in prostate cancer cells expressing somatic AR mutation, and a major molecular consequence of BPA action is down-regulation of ERbeta. Since ERbeta functions to antagonize AR function and AR-dependent proliferation, these findings reveal a novel mechanism by which BPA likely regulates cellular proliferation. Future investigation directed at dissecting the importance of ERbeta in the proliferative response to BPA will establish the contribution of this event to adverse effects associated with human exposure.

An androgen-independent androgen receptor function protects from inositol hexakisphosphate toxicity in the PC3/PC3(AR) prostate cancer cell lines

BACKGROUND

Inositol hexakisphosphate (IP6) is a phytochemical exhibiting anticancer activity. Because few prostate cancer (PCa) cell lines have been used to study IP6, we assessed its efficacy in a panel of PCa cell lines.

METHODS AND RESULTS

Using WST-1 assays we observed that, although androgens did not modulate its efficacy, IP6 was more active in androgen receptor (AR) negative cells than in AR-positive cells. Stable expression of the AR in PC3 cells (PC3(AR)) decreased the response to IP6, which was reversed by an AR-targeting siRNA. Furthermore, AR expression in PC3 cells resulted in significantly reduced caspase-3 activation (P < 0.001) and DNA fragmentation (P < 0.05) in response to IP6. Similarly, although treatment with IP6 caused the upregulation of NF-kappaB-responsive (IkappaB-alpha, IRF-2) and p53/E2F-responsive genes (Puma, Noxa) in PC3 cells, this increase was reduced in PC3AR cells (P < 0.01).

CONCLUSION

We conclude that resistance to IP6 can be linked to a ligand-independent AR function.

Molecular characterization of an improved vector for evaluation of the tumor suppressor versus oncogene abilities of the androgen receptor

BACKGROUND

There is a growing body of evidence demonstrating that the function of the ligand-occupied androgen receptor (AR) within the nuclei of normal prostatic epithelial cells acts as a tumor suppressor gene. This is in contrast to the well-documented ability of the AR within prostate cancer cells to function as an oncogene. Thus, many groups are attempting to understand the biochemistry and signaling cascade differences involved in the switching of AR from a tumor suppressor to an oncogene.

METHODS

To do this, of plasmid vectors for transgenic expression of AR are very useful. AR negative PC-3 human prostate cancer cells were transfected with a plasmid containing the full length coding sequence of AR without its 5'- or 3'-untranslated regions (UTRs) (i.e., pSG5-AR).

RESULTS

Transgenic expression of the AR protein results in profound growth inhibition which is not relieved by the addition of ligand. A new expression vector for the AR, pAR-IRES-EGFP, has been constructed that contains full-length 5'-UTR which includes the identified translation regulatory regions, the full length coding sequence and the partial 3'-UTR, which includes the identified post-transcriptional regulatory regions. When PC-3 cells were transfected with the pAR-IRES-EGFP vector, it was found that transgenic AR protein expression was not growth inhibitory until ligand was added.

CONCLUSIONS

These pSG5-AR versus pSAR-IRES-EGFP clones are being studied to determine the molecular pathways explaining their different response to AR and ligand.

Molecular characterization of the commonly used human androgen receptor expression vector, pSG5-AR

BACKGROUND

pSG5-AR is a commonly used androgen receptor (AR) expression vector. However, a detailed molecular characterization of this construct has not been published. In this study, we describe the molecular organization of the above plasmid and analyze the AR transcript coded by the above construct.

METHODS

pSG5-AR was sequenced by the standard dideoxy sequencing method. The obtained sequence was analyzed by the DS Gene software.

RESULTS

A molecular map of the pSG5-AR plasmid as well as a map of the AR insert is provided. The AR transcript from pSG5-AR is lacking significant portions of the 5'- and 3'-untranslated region (UTR) and contains shorter than average CAG and GGC repeats.

CONCLUSIONS

The above characteristics of the pSG5-AR are significant and may result in different regulation pattern of expression of the expressed AR in comparison to the endogenous gene. Such a conclusion is based on the knowledge that post-transcriptional regulation plays an important role in controlling the levels of AR in a cell. Such regulation is controlled by the regulatory elements within the 5'- and 3'-UTRs of the AR transcript. In addition, this vector might be coding for an AR with a different transactivational capacity than the endogenous AR gene. The transactivational activity of AR was shown to be affected by the size of the trinucleotide-repeat-regions (CAG and GGC) within the gene.