14-3-3{eta} Amplifies Androgen Receptor Actions in Prostate Cancer.

PURPOSE: Androgen receptor abundance and androgen receptor-regulated gene expression in castration-recurrent prostate cancer are indicative of androgen receptor activation in the absence of testicular androgen. Androgen receptor transactivation of target genes in castration-recurrent prostate cancer occurs in part through mitogen signaling that amplifies the actions of androgen receptor and its coregulators. Herein we report on the role of 14-3-3eta in androgen receptor action. Experimental Design and RESULTS: Androgen receptor and 14-3-3eta colocalized in COS cell nuclei with and without androgen, and 14-3-3eta promoted androgen receptor nuclear localization in the absence of androgen. 14-3-3eta interacted with androgen receptor in cell-free binding and coimmunoprecipitation assays. In the recurrent human prostate cancer cell line, CWR-R1, native endogenous androgen receptor transcriptional activation was stimulated by 14-3-3eta at low dihydrotestosterone concentrations and was increased by epidermal growth factor. Moreover, the dihydrotestosterone- and epidermal growth factor-dependent increase in androgen receptor transactivation was inhibited by a dominant negative 14-3-3eta. In the CWR22 prostate cancer xenograft model, 14-3-3eta expression was increased by androgen, suggesting a feed-forward mechanism that potentiates both 14-3-3eta and androgen receptor actions. 14-3-3eta mRNA and protein decreased following castration of tumor-bearing mice and increased in tumors of castrate mice after treatment with testosterone. CWR22 tumors that recurred 5 months after castration contained 14-3-3eta levels similar to the androgen-stimulated tumors removed before castration. In a human prostate tissue microarray of clinical specimens, 14-3-3eta localized with androgen receptor in nuclei, and the similar amounts expressed in castration-recurrent prostate cancer, androgen-stimulated prostate cancer, and benign prostatic hyperplasia were consistent with androgen receptor activation in recurrent prostate cancer. CONCLUSION: 14-3-3eta enhances androgen- and mitogen-induced androgen receptor transcriptional activity in castration-recurrent prostate cancer. (Clin Cancer Res 2009;15(24):7571-81).