Abstract 3451: Distinct nuclear translocation mechanism of androgen receptor variant ARv7
Authors: Kim Seaho , Portella Luigi , Giannakakou Paraskevi 
Published: August 2015

Abstract
Next generation androgen receptor (AR) inhibitors (abiraterone, enzalutamide) are used to treat metastatic prostate cancer (mCRPC) patients with a response rate of 20∼40%. The presence of androgen receptor variants has emerged as one of the mechanisms of resistance to these drugs. Specifically, the ARv7 and Arv567 splice variants lacking the ligand-binding domain are constitutively active in the nucleus, and have been identified in mCRPC patients. Recently, ARv7 expression in circulating tumor cells (CTCs) from mCRPC patients was correlated with resistance to abiraterone and enzalutamide. Following androgen deprivation therapy (ADT), CRPC patients receive taxane chemotherapy as first and second line of treatment. We have recently shown that AR utilizes microtubules and the dynein motor protein as transportation system for its nuclear translocation and activity and that taxanes inhibit AR signaling downstream of microtubule stabilization. Furthermore, we identified that the AR hinge region mediates binding to MTs; this region is present in ARv567, but missing from ARv7. Thus, the ARv7 does not bind MTs, its nuclear localization is not affected by taxane treatment or dynein motor complex disruption while its expression confers taxane resistance in vivo. Collectively these data suggest that ARv7 confers resistance to both ADT and taxanes, which represent the most important therapeutic modalities in CRPC. To this end, elucidation of the molecular mechanism of ARv7 nuclear translocation is extremely critical for the design of new targeted therapies to treat more than 60% of mCRPC patients who do not respond to current treatment options. To monitor the dynamics of ARv nuclear localization, we used fluorescence recovery after photobleaching (FRAP) assay and measured the time kinetics of ARv nuclear translocation. Our results indicated that ARv7 translocates to the nucleus significantly faster as compared to AR-wt and ARv567. In addition, since AR-wt utilizes the importin-α/β to translocate to the nucleus we used importazole, a tool compound blocking importin-β activity, and measured the dynamics of ARv translocation. We found that importazole was effective in inhibiting AR-wt and ARv567 nuclear import, but had no such effect on ARv7 nuclear accumulation. Currently, we are investigating the novel molecular mechanism of ARv7 nuclear translocation including the involvement of Ran-GTPase and the identification of the putative non-canonical nuclear localization signal. Overall, our data demonstrate that ARv7 utilizes a different nuclear translocation mechanism as compared with AR-wt and ARv567. Elucidation of this mechanism will be invaluable in order to design an alternative therapeutic modality to halt AR signaling which eventually will open new avenues to treat large subset of mCRPC patients who show resistance to current treatments.
Citation Format: Seaho Kim, Luigi Portella, Paraskevi Giannakakou. Distinct nuclear translocation mechanism of androgen receptor variant ARv7. [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 3451. doi:10.1158/1538-7445.AM2015-3451