Regulation of androgen receptor localization in prostate cancer cells

• Main Author: Saporita, Anthony J
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2006
• Subjects: Molecular biology; Oncology
• ISBN: 9780542908392; 0542908395

The physiological consequences of androgen action are mediated by the androgen receptor (AR), a transcription factor that has instrumental roles in prostate development and prostate cancer progression. The ligand-dependent trafficking of AR is a critical determinant in its role in gene regulation. Unliganded AR is localized to the cytoplasm and translocates to the nucleus when it binds hormone. In the nucleus AR acts as a transcription factor through binding to androgen-response elements. These studies have identified a leptomycin B-insensitive nuclear export signal (NES) in the ligand-binding domain of AR, which we have designated NESAR. NESAR is necessary and sufficient for the cytoplasmic localization of AR. NES AR is functionally conserved in other steroid receptors. Mutagenesis studies suggest that multiple regions within NESAR are involved in regulating cytoplasmic localization. The following model describes the mechanism by which NESAR may function within AR: In the absence of ligand, NESAR is dominant over the NLS in the DBD and hinge region and AR is localized to the cytoplasm. In the presence of ligand, NES AR is repressed and AR is localized to the nucleus. Androgen-refractory prostate cancer is characterized by AR activation despite androgen ablation. Ligand-independent nuclear localization of AR is observed in androgen-refractory C4-2 prostate cancer cells. NESAR remains functional in C4-2 cells, suggesting that nuclear localization of AR is not due to a deficiency in nuclear export. Analysis of AR mutants impaired in ligand-binding indicates that the nuclear localization of AR in C4-2 cells is truly androgen-independent. The hsp90 inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), inhibits basal PSA expression and disrupts the ligand-independent nuclear localization of AR at doses much lower than required to inhibit androgen-induced nuclear import. The research presented in this dissertation contributes to the understanding of androgen receptor action in the prostate and in prostate cancer progression. The identification of NESAR provides a basis for the cytoplasmic localization of AR in the absence of hormone and insight into the ligand-dependent regulation of AR trafficking. The disruption of ligand-independent nuclear localization of AR by 17-AAG implicates Hsp90 in androgen-refractory prostate cancer and suggests that 17-AAG may be a useful therapeutic agent for this disease.