Nrdp1-mediated regulation of ErbB3 expression by the androgen receptor in androgen-dependent but not castrate-resistant prostate cancer cells.
ABSTRACT: Patients with advanced prostate cancer (PCa) are initially susceptible to androgen withdrawal (AW), but ultimately develop resistance to this therapy (castration-resistant PCa, CRPC). Here, we show that AW can promote CRPC development by increasing the levels of the receptor tyrosine kinase ErbB3 in androgen-dependent PCa, resulting in AW-resistant cell cycle progression and increased androgen receptor (AR) transcriptional activity. CRPC cell lines and human PCa tissue overexpressed ErbB3, whereas downregulation of ErbB3 prevented CRPC cell growth. Investigation of the mechanism by which AW augments ErbB3, using normal prostate-derived pRNS-1-1 cells, and androgen-dependent PCa lines LNCaP, PC346C, and CWR22 mouse xenografts, revealed that the AR suppresses ErbB3 protein levels, whereas AW relieves this suppression, showing for the first time the negative regulation of ErbB3 by AR. We show that AR activation promotes ErbB3 degradation in androgen-dependent cells, and that this effect is mediated by AR-dependent transcriptional upregulation of neuregulin receptor degradation protein-1 (Nrdp1), an E3 ubiquitin ligase that targets ErbB3 for degradation but whose role in PCa has not been previously examined. Therefore, AW decreases Nrdp1 expression, promoting ErbB3 protein accumulation, and leading to AR-independent proliferation. However, in CRPC sublines of LNCaP and CWR22, which strongly overexpress the AR, ErbB3 levels remain elevated due to constitutive suppression of Nrdp1, which prevents AR regulation of Nrdp1. Our observations point to a model of CRPC development in which progression of PCa to castration resistance is associated with the inability of AR to transcriptionally regulate Nrdp1, and predict that inhibition of ErbB3 during AW may impair CRPC development.
Project description:Prostate cancer (PCa) progression is regulated by the androgen receptor (AR); however, patients undergoing androgen-deprivation therapy (ADT) for disseminated PCa eventually develop castration-resistant PCa (CRPC). Results of previous studies indicated that AR, a transcription factor, occupies distinct genomic loci in CRPC compared with hormone-naïve PCa; however, the cause of this distinction was unknown. The E3 ubiquitin ligase Nrdp1 is a model AR target modulated by androgens in hormone-naïve PCa but not in CRPC. Using Nrdp1, we investigated how AR switches transcription programs during CRPC progression. The proximal Nrdp1 promoter contains an androgen response element (ARE); we demonstrated AR binding to this ARE in androgen-sensitive PCa. Analysis of hormone-naive human prostatectomy specimens revealed correlation between Nrdp1 and AR expression, supporting AR regulation of NRDP1 levels in androgen-sensitive tissue. However, despite sustained AR levels, AR binding to the Nrdp1 promoter and Nrdp1 expression were suppressed in CRPC. Elucidation of the suppression mechanism demonstrated correlation of NRDP1 levels with nuclear localization of the scaffolding protein filamin A (FLNA) which, as we previously showed, is itself repressed following ADT in many CRPC tumors. Restoration of nuclear FLNA in CRPC stimulated AR binding to Nrdp1 ARE, increased its transcription, and augmented NRDP1 protein expression and responsiveness to ADT, indicating that nuclear FLNA controls AR-mediated androgen-sensitive Nrdp1 transcription. Expression of other AR-regulated genes lost in CRPC was also re-established by nuclear FLNA. Thus, our results indicate that nuclear FLNA promotes androgen-dependent AR-regulated transcription in PCa, while loss of nuclear FLNA in CRPC alters the AR-regulated transcription program.
Project description:Patients with recurrent prostate cancer are commonly treated with androgen withdrawal therapy (AWT); however, almost all patients eventually progress to castration resistant prostate cancer (CRPC), indicating failure of AWT to eliminate androgen-sensitive prostate cancer. The overall goal of these studies is to determine whether dual inhibition of the receptor tyrosine kinases epidermal growth factor receptor (EGFR) and HER2 would prolong the effectiveness of this treatment in prostate cancer.We used androgen-dependent LNCaP cells and its CRPC sublines LNCaP-AI and C4-2. Additional data were collected in pRNS-1-1 cells stably expressing a mutant androgen receptor (AR-T877A), and in nude mice harboring CWR22 tumors. Studies utilized EGFR inhibitors erlotinib and AG1478, and HER2 inhibitors trastuzumab and AG879.Dual EGFR/HER2 inhibition induced apoptosis selectively in androgen-sensitive prostate cancer cells undergoing AWT, but not in the presence of androgens, or in CRPC cells. We show that AWT alone failed to induce significant apoptosis in androgen-dependent cells, due to AWT-induced increase in HER2 and ErbB3, which promoted survival by increasing Akt phosphorylation. AWT-induced ErbB3 stabilized the AR and stimulated PSA, while it was inactivated only by inhibition of both its dimerization partners EGFR and HER2 (prostate cancer cells do not express ErbB4); but not the inhibition of any one receptor alone, explaining the success of dual EGFR/HER2 inhibition in sensitizing androgen-dependent cells to AWT. The effectiveness of the inhibitors in suppressing growth correlated with its ability to prevent Akt phosphorylation.These studies indicate that dual EGFR/HER2 inhibition, administered together with AWT, sensitize prostate cancer cells to apoptosis during AWT.
Project description:Prostate cancer (PCa) is the most common cancer and the second leading cause of cancer-related deaths of men in Western countries. Androgen deprivation therapy is initially successful, however eventually fails, and tumors progress to the more aggressive castration-resistant PCa (CRPC). Yet, androgen receptor (AR) usually remains as a major regulator of tumor cell proliferation in CRPC. Interleukin-23 (IL-23) was recently shown to promote the development of CRPC by driving AR transcription. Here we used the androgen-sensitive LNCaP, castration-resistant C4-2, and 22Rv1 cells. Interestingly, cellular senescence is induced in these human cell lines by treatment with the AR antagonists enzalutamide (ENZ) or darolutamide (ODM), which might be one underlying mechanism for inhibition of PCa cell proliferation. Treatment with IL-23 alone did not change cellular senescence levels in these cell lines, whereas IL-23 inhibited significantly cellular senescence levels induced by ENZ or ODM in both CRPC cell lines C4-2 and 22Rv1 but not in LNCaP cells. This indicates a response of IL-23 specific in CRPC cells. Generating LNCaP and C4-2 three-dimensional (3D) spheroids and treatment with AR antagonists resulted in the reduced spheroid volume and thus growth inhibition. However, the combination of AR antagonists with IL-23 did not affect the antagonist-mediated reduction of spheroid volumes. This observation was confirmed with proliferation assays using adherent monolayer cell cultures. Taken together, the data indicate that IL-23 treatment reduces the AR antagonists-induced level of cellular senescence of CRPC cells, which could be one possible mechanism for promoting castration resistance.
Project description:Background:As deregulation of androgen receptor (AR) signaling target genes is associated with tumorigenesis and the development of prostate cancer (PCa), AR signaling is the primary therapeutic target for PCa. Although patients initially responses to first-line androgen deprivation therapies (ADTs), most of them with advanced PCa progress to lethal castration-resistant prostate cancer (CRPC). Recent studies have suggested the molecular mechanisms by which AR elicit the robust up-regulation of the FKBP51 gene. We suggest that restored expression of FKBP51 gene, modulated by androgen receptor splicing variant 7 (AR-V7) which replaces full length androgen receptor (AR-FL) in androgen ablation status, promotes CRPC progression through activating NF-?B signaling. Methods:Immunohistochemistry assays were used to detect the expression of AR-V7, FKBP51 and NF-?B signaling correlated proteins in CRPC tissues. An androgen ablation resistant PCa cell line model established by Long-term culturing in androgen depleted medium, named androgen-independent LNCaP (LNCaP-AI) cells, were used to dynamically monitor FKBP51 expression during the process of androgen dependent PCa cells transforming into androgen-independent cells, as well as its association with NF-?B signal pathway. LNCaP-AI cell line was determined to express AR-V7 protein continuously. Luciferase reporter assays and DNA pull down were used to determine the association between AR-V7 and FKBP51. Results:Our results suggested that CRPC patients with AR-V7 high expression tend to have higher expression of FKBP51 and enhanced NF-?B signaling compared with AR-V7 negative patients. Knockdown of AR-V7 or FKBP51 in LNCaP-AI cells attenuated the level of p-NF-?B (Ser536) and androgen-resistant cells growth. Luciferase reporter assays and DNA pull down results indicated that FKBP51 was transcriptionally promoted by AR-V7 in absence of androgen, which enhanced NF-?B signaling. Conclusions:Because of upregulation of AR-V7 in androgen-independent PCa cells, increasing of FKBP51 induced NF-?B signaling, leading to progression of CRPC.
Project description: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.
Project description:Prostate cancer (PCa) growth is mainly driven by androgen receptor (AR), and tumors that initially respond to androgen deprivation therapy (ADT) or AR inhibition usually relapse into a more aggressive, castration-resistant PCa (CRPC) stage. Circulating growth hormone (GH) has a permissive role in PCa development in animal models and in human PCa xenograft growth. As GH and GH receptor (GHR) are both expressed in PCa cells, we assessed whether prostatic GH production is linked to AR activity and whether GH contributes to the castration-resistant phenotype. Using online datasets, we found that GH is highly expressed in human CRPC. We observed increased GH expression in castration-resistant C4-2 compared with castration-sensitive LNCaP cells as well as in enzalutamide (MDV3100)-resistant (MDVR) C4-2B (C4-2B MDVR) cells compared with parental C4-2B. We describe a negative regulation of locally produced GH by androgens/AR in PCa cells following treatment with AR agonists (R1881) and antagonists (enzalutamide, bicalutamide). We also show that GH enhances invasive behavior of CRPC 22Rv1 cells, as reflected by increased migration, invasion, and anchorage-independent growth, as well as expression of matrix metalloproteases. Moreover, GH induces expression of the AR splice variant 7, which correlates with antiandrogen resistance, and also induces insulinlike growth factor 1, which is implicated in PCa progression and ligand-independent AR activation. In contrast, blockade of GH action with the GHR antagonist pegvisomant reverses these effects both in vitro and in vivo. GH induction following ADT or AR inhibition may contribute to CRPC progression by bypassing androgen growth requirements.
Project description:The major challenge in castration-resistant prostate cancer (CRPC) remains the ability to predict the clinical responses to improve patient selection for appropriate treatments. The finding that androgen deprivation therapy (ADT) induces alterations in the androgen receptor (AR) transcriptional program by AR coregulators activity in a context-dependent manner, offers the opportunity for identifying signatures discriminating different clinical states of prostate cancer (PCa) progression. Gel electrophoretic analyses combined with western blot showed that, in androgen-dependent PCa and CRPC in vitro models, the subcellular distribution of spliced and serine-phosphorylated heterogeneous nuclear ribonucleoprotein K (hnRNP K) isoforms can be associated with different AR activities. Using mass spectrometry and bioinformatic analyses, we showed that the protein sets of androgen-dependent (LNCaP) and ADT-resistant cell lines (PDB and MDB) co-immunoprecipitated with hnRNP K varied depending on the cell type, unravelling a dynamic relationship between hnRNP K and AR during PCa progression to CRPC. By comparing the interactome of LNCaP, PDB, and MDB cell lines, we identified 51 proteins differentially interacting with hnRNP K, among which KLK3, SORD, SPON2, IMPDH2, ACTN4, ATP1B1, HSPB1, and KHDRBS1 were associated with AR and differentially expressed in normal and tumor human prostate tissues. This hnRNP K?AR-related signature, associated with androgen sensitivity and PCa progression, may help clinicians to better manage patients with CRPC.
Project description:Prostate cancer (PCa) is the second leading cause of cancer-related death in males in the United States. Majority of prostate cancers are originally androgen-dependent and sensitive to androgen-deprivation therapy (ADT), however, most of them eventually relapse and progress into incurable castration-resistant prostate cancer (CRPC). Of note, the activity of androgen receptor (AR) is still required in CRPC stage. The mitotic kinase polo-like kinase 1 (Plk1) is significantly elevated in PCa and its expression correlates with tumor grade. In this study, we assess the effects of Plk1 on AR signaling in both androgen-dependent and androgen-independent PCa cells. We demonstrate that the expression level of Plk1 correlated with tumorigenicity and that inhibition of Plk1 caused reduction of AR expression and AR activity. Furthermore, Plk1 inhibitor BI2536 down-regulated SREBP-dependent expression of enzymes involved in androgen biosynthesis. Of interest, Plk1 level was also reduced when AR activity was inhibited by the antagonist MDV3100. Finally, we show that BI2536 treatment significantly inhibited tumor growth in LNCaP CRPC xenografts. Overall, our data support the concept that Plk1 inhibitor such as BI2536 prevents AR signaling pathway and might have therapeutic potential for CRPC patients.
Project description:Expression of androgen receptor (AR) in prostate cancer (PCa) is heterogeneous but the functional significance of AR heterogeneity remains unclear. Screening ~200 castration-resistant PCa (CRPC) cores and whole-mount sections (from 89 patients) reveals 3 AR expression patterns: nuclear (nuc-AR), mixed nuclear/cytoplasmic (nuc/cyto-AR), and low/no expression (AR<sup>-/lo</sup>). Xenograft modeling demonstrates that AR<sup>+</sup> CRPC is enzalutamide-sensitive but AR<sup>-/lo</sup> CRPC is resistant. Genome editing-derived AR<sup>+</sup> and AR-knockout LNCaP cell clones exhibit distinct biological and tumorigenic properties and contrasting responses to enzalutamide. RNA-Seq and biochemical analyses, coupled with experimental combinatorial therapy, identify BCL-2 as a critical therapeutic target and provide proof-of-concept therapeutic regimens for both AR<sup>+/hi</sup> and AR<sup>-/lo</sup> CRPC. Our study links AR expression heterogeneity to distinct castration/enzalutamide responses and has important implications in understanding the cellular basis of prostate tumor responses to AR-targeting therapies and in facilitating development of novel therapeutics to target AR<sup>-/lo</sup> PCa cells/clones.
Project description:Epigenetic factors play critical roles in prostate cancer (PCa) development. However, how they contribute to neuroendocrine differentiation (NED) and castration-resistant PCa (CRPC) is not fully understood. Using bioinformatics and biochemical approaches to analyze cell-based models of NED and CRPC, we found a cluster of epigenetic factors whose expression is downregulated during NED and upregulated in CRPC (i.e. follow a Down-Up pattern). Two histone demethylases within this cluster, PHF8 and KDM3A, are post-transcriptionally regulated by c-MYC through miR-22, which targets both PHF8 and KDM3A. We also found that the c-MYC/miR-22/PHF8 axis is downstream of androgen receptor (AR) signaling in CRPC cells. The co-expression of PHF8 with AR in clinical CRPC samples, normal mouse prostate, and adenocarcinomas of the prostate during PCa progression in a transgenic (TRAMP) mouse model supports the connection between PHF8 and AR. Knockdown of PHF8 impedes cell cycle progression in CRPC cells and has more profound effects on their growth than on the parental LNCaP cell line. Furthermore, PHF8 knockdown sensitizes LNCaP-Abl cells to the AR antagonist enzalutamide. Our data reveal novel mechanisms that underlie the regulation of PHF8 and KDM3A during NED and in CRPC, and support the candidacy of PHF8 as a therapeutic target in CRPC.