Abstract 3486: Dissecting the mechanism of AR-v7 nuclear translocation in prostate cancer
Authors: Kim Seaho , Jamalruddin Mohd Azrin , Portella Luigi , Giannakakou Paraskevi 
Published: July 2016

Abstract
Continuous androgen receptor (AR) signaling is the key driver of castration-resistant prostate cancer (CRPC), despite prior androgen deprivation therapy (ADT). Potent, next-generation AR signaling inhibitors, such as abiraterone and enzalutamide have been recently added to the standard of care in the treatment of prostate cancer. However, resistance to these drugs inevitably emerges and is mediated by adaptive mechanisms that restore AR function, in the form of constitutively active, ligand-independent AR-variant (AR-V) overexpression. The microtubule-targeting drugs Docetaxel (DTX) and Cabazitaxel (CTX) are the only chemotherapy that significantly improves survival of CRPC patients. We have shown that full-length AR (AR-fl) binds microtubules (MTs) via its hinge domain, and utilizes them as tracks to facilitate its nuclear translocation. Taxanes keep AR-fl inactive in the cytoplasm as a result of MT stabilization. Of the two most prevalent AR-Vs, ARv567 contains the hinge region and is sensitive to taxane treatment while AR-v7, expressed in 60% of CRPC patients, lacks the hinge region and does not depend on MTs for its nuclear translocation. Therefore, ARv7 nuclear translocation is MT-independent and neither taxane treatment nor the disruption of dynein motor complex inhibited its nuclear localization. Thus, AR-v7 expression confers taxane resistance in vivo, in addition to next-generation AR inhibitors. Hence, inhibition of AR-v7 nuclear translocation and activity is critical to overcome drug resistance to current therapeutic modalities. However, the mechanism of ARv7 nuclear translocation is not clearly understood. Previously, we showed that ARv7 exhibited faster kinetics of nuclear translocation compared to AR-fl. Additionally, AR-v7 nuclear import is independent of the importin-α/β pathway, which is utilized by the MT-dependent, AR-fl and ARv567. Upon disruption of the Ran-GTPase nuclear import pathway, by overexpression of the catalytic mutant Q69L form of Ran, we observed that the nuclear import of both AR-fl and AR-V567 was significantly impaired, while ARv7 nuclear import was only partially affected. In this study, we hypothesized that molecular dynamics of AR nuclear import and export determines overall spatiotemporal localization of AR and its activity. To test this hypothesis, we generated photo-convertible AR-fl and AR-Vs (AR-v567 and AR-v7) fused to mEos4b construct, which enables us to track protein mobilization in the region of interest after photo-conversion in live cells. We are currently studying the nuclear import and export kinetics of both AR-fl and AR variants (AR-v567 and AR-v7) alone and in combination using the photo-conversion methodology. Elucidation of the distinct pathway(s) that mediate ARv7 nuclear import and/or export will allow the rationale design of effective ARv7 inhibitors or the development of co-targeting strategies in combination with taxanes and AR signaling inhibitors.
Citation Format: Seaho Kim, Mohd Azrin Jamalruddin, Luigi Portella, Paraskevi Giannakakou. Dissecting the mechanism of AR-v7 nuclear translocation in prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3486.