Abstract
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.
Highlights
Prostate cancer (PCa) is the second leading cause of cancer related deaths in American men [1] and elevated androgen receptor (AR) signaling facilitates PCa growth
Androgen deprivation therapy (ADT) was designed to deplete systemic androgen levels and suppress AR signaling in hormone dependent PCa cells [2]
Our previous findings demonstrated that NADPH oxidases (NOX)-4 and NOX-5, Prx-1, and the oxidative stress-induced transcription factors Nrf1 and Nrf2 are differentially expressed in LNCaP and C4-2B cells [36]
Summary
Prostate cancer (PCa) is the second leading cause of cancer related deaths in American men [1] and elevated androgen receptor (AR) signaling facilitates PCa growth. Androgen deprivation therapy (ADT) was designed to deplete systemic androgen levels and suppress AR signaling in hormone dependent PCa cells [2]. CRPC cells retain both AR expression and function [2,3]. Understanding the mechanisms of persistent AR function in CRPC cells despite ADT will aid in developing therapeutic strategies that suppress PCa recurrence. Dihydrotestosterone (DHT) is a potent androgen that stimulates AR mediated transactivation at the androgen response element (ARE), present on promoters of numerous genes important in PCa cell growth [4]. The classical AR transactivation pathway is often bypassed in CRPC cells where persistent AR function occurs despite low androgen levels [5,6]
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