Abstract 1709: Activation of androgen signaling axis by NF-kappaB2/p52

Abstract INTRODUCTION: Castration-resistant progression of prostate cancer occurs in >80% of patients after failure of hormonal therapy but the underlying mechanisms are incompletely understood. Emerging evidence implies that ligand-independent activation of the androgen receptor (AR) is of critical importance during this process. Our previous studies show that the levels of NF-κB2/p52 are elevated in prostate cancer cells and that active NF-κB2/p52 promotes prostate cancer cell growth in vitro and in vivo. In this study, we examined the role of NF-κB2/p52 in the aberrant activation of the AR during castration resistant progression, in contrast to the interaction between the AR and RelA/p65. METHODS: The effects of NF-κB2/p52 on cell survival, growth and androgen responsiveness were examined in prostate cancer cells. Modulation of LNCaP tumor growth by p52 was examined in intact and castrated male nude mice. Effect of p52 or p65 on AR activation was examined using luciferase assays, EMSA, ChIP assays and ELISA. RESULTS: Expression of NF-κB2/p52 enhanced androgen-sensitive LNCaP human CaP cell growth and clonogenic ability in androgen-deprived conditions in vitro. LNCaP cells expressing p52 exhibited protection from apoptotic cell death and cell cycle arrest induced by androgen-deprivation. Adenoviral mediated p52 expression in LNCaP cells induced tumor growth in castrated male nude mice. NF-κB/p52 induced the activation of the AR resulting in increased transactivation of AR-responsive genes such as PSA and NKX3.1 in a ligand-independent manner. NF-κB2/p52 enhanced nuclear translocation and transactivation of AR by interacting with its N-terminal domain and enhanced the recruitment of co-activators like p300 to the promoters of AR-dependent genes. These results were confirmed in 3 different prostate cancer cell lines: LAPC-4 (wild type AR), LNCaP (mutant AR) and C4-2 (androgen-insensitive). Transfection of p52 into LAPC-4 and LNCaP cells (which express low levels of p52) showed increased activation of the endogenous AR. Downregulation of endogenous p52 in C4-2 cells resulted in abrogation of AR constitutive activation. In contrast, we observed that p65 exhibited transcriptional repression of the AR, and did not induce expression of AR-responsive genes, PSA and NKX3.1. CONCLUSIONS: These findings demonstrate that overexpression of NF-κB2/p52 induces castration-resistant growth and aberrant activation of the AR in LNCaP cells. NF-κB2/p52 may promote castration resistant progression by activating the AR under conditions of androgen deprivation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1709.