Abstract 5051: Androgen receptor-mediated regulation of p14ARF transcription in prostate tumor cells

Abstract

Abstract The p14ARF tumor suppressor is often deleted or silenced in malignancies. Prostate tumors are an exception, where p14 expression is elevated. To understand this phenomenon, we assessed the expression of p53 pathway members, which are most effected by p14ARF. The expression of androgen receptor (AR), a pivotal prostate cancer regulator, which is also affected by p14arf and MDM2 was analyzed as well. The studies used archival prostate tumor tissues obtained from prostatectomies performed at the Veterans Affairs-Northern California Health Care System in Mather California between 1996 and 2002 to better define the relationship between these interrelated networks. A prostate tumor tissue array consisting of 78 tumors of differing stages and grades was constructed to evaluate correlations between multiple parameters. Immunohistochemical studies assessed expression of the proliferation marker Ki67, p53, MDM2, MDM4, p14ARF, and the AR in the nuclear and cytoplasmic compartments of tumor and adjacent cells. p53, MDM4, p14ARF and AR were detected in nuclear and cytoplasmic compartments of tumor and non-tumor cells, but were predominantly nuclear. MDM2 expression was primarily cytoplasmic in tumor cells. Multivariate analysis of the immunohistochemical markers identified a strong correlation between expression of p14ARF and AR. Studies utilizing the prostate CWR22 xenograft and LNCaP cell line models revealed that castration or androgen deprivation resulted in reduced p14arf levels and that this effect correlated with a precipitous decline in E2F1-3a levels. In a reciprocal analysis, RB ablation enhanced p14ARF transcription, arguing that the E2F/RB pathway mediates AR-dependent p14ARF expression. However, we also identified an AR binding site located ∼40 KB upstream of the p14ARF gene. Chromatin immunoprecipitation (ChIP) studies showed that in prostate cells this site was bound by AR. ChIP studies also revealed E2F1 and E2F3 were present at the p14ARF promoter. Together, the studies argue p14ARF is a direct transcriptional target of AR and that AR and E2F collaborate to promote p14ARF expression. . Citation Format: Maria Mudryj, Salma Siddiqui, Stephen J. Libertini, Alan P. Lombard, Benjamin Mooso, Leandro D'Abronzo, Frank Melgoza, Alexander Borowsky, Christiana Drake, LiHong Qi, Paramita M. Ghosh. Androgen receptor-mediated regulation of p14ARF transcription in prostate tumor cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5051. doi:10.1158/1538-7445.AM2015-5051