Abstract 2163: Microtubule-dependent regulation of a constitutively active androgen receptor splice variant
Authors: Thadani-Mulero Maria , Plymate Stephen R. , Giannakakou Paraskevi 
Published: June 2012

Prostate cancer progression is dependent on androgens and can be suppressed by androgen ablation. Androgen deprivation provides palliation but not cure in men with prostate cancer, and the disease progresses to a castrate-resistant stage (CRPC), which is often accompanied by molecular alterations in the androgen receptor (AR). Recently, an AR splice variant lacking the ligand binding domain was found in human prostate tissue. This AR variant (ARv567) was not expressed in normal prostate epithelium, suggesting that the presence of a constitutively active splice variant of the AR arises following castration and plays a role in the progression of prostate cancer.

Work from our lab shows that taxanes, used in CRPC treatment, impair the ligand-induced nuclear accumulation of full-length AR (AR-FL) and hence its transcriptional activity. We also show that AR trafficking towards the nucleus occurs along microtubules (MTs) with the aid of the dynein motor protein using a variety of assays including co-immunoprecipitation, immunofluorescence and microtubule co-sedimentation. In order to identify the minimum AR domain that mediates MT binding we have generated deletion mutants of the AR, and are testing their MT binding ability both in cells and in vitro.

We have extended these studies to the clinically relevant AR splice variant ARv567, and showed that it binds MTs as evidenced by microtubule co-sedimentation assays and live cell imaging. Next we sought to determine the dynamics of AR-FL and variant nuclear accumulation in relation to taxane-induced MT stabilization. To do so we microinjected GFP-tagged AR-FL or GFP-tagged ARv567 into the nucleus of PC3 cells stably expressing mCherry tubulin and monitored the effect of taxane treatment on MT dynamics and AR nuclear translocation using live-cell confocal microscopy. This study revealed rapid AR-FL nuclear accumulation within 30 min of R1881 treatment, while it did not induce further nuclear accumulation of the variant, consistent with the lack of ligand binding domain in ARv567. On the other hand, taxane pre-treatment attenuated the nuclear accumulation of both AR-FL and ARv567, suggesting that functional MTs are required for AR's nuclear transport in a ligand independent manner.

Interestingly, we observed that the presence of the variant sensitizes cells to taxane treatment as seen by greater decreases in tumor volumes in response to taxanes in xenografts expressing variant vs those with AR-FL. Taken together, these data, reveal a new mechanism of regulation of AR activity in prostate cancer. Further elucidation of this mechanism may help us better understand the molecular basis of clinical response to taxane treatment in CRPC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2163. doi:10.1158/1538-7445.AM2011-2163