Abstract 4076: Taxanes inhibit the microtubule-dependent androgen receptor trafficking and signaling in prostate cancer
Authors: Thadani-Mulero Maria , Darshan Medha , Giannakakou Paraskevi 
Published: February 2011

Androgens (testosterone, DHT) control the development, differentiation and function of the prostate. Their principal action is to regulate gene expression through the androgen receptor (AR), a nuclear steroid hormone receptor, which translocates to the nucleus upon binding to its ligand and activates androgen response elements of target genes. This drives the growth and progression of prostate cancer (PC), the most commonly diagnosed cancer in males. Initial treatment involves androgen ablation, yet, these tumors eventually progress to a castrate-resistant state and taxanes represent the most effective class of anti-tumor agents to improve survival of CRPC patients. However, the molecular basis of taxane activity in prostate cancer is not fully elucidated.

Preliminary data from out lab has shown that taxane treatment of PC cells inhibits the ligand-induced nuclear localization of AR and subsequent activation of ARE-containing genes including PSA. We further show that AR colocalizes with the microtubule (MT) cytoskeleton by immunofluorescence followed by confocal microscopy. This result is further supported by co-immunoprecipitation and microtubule co-sedimentation assays that revealed the preferential association of the WT-AR to the MT polymer rather than tubulin dimers. Dynein, a minus-end directed MT motor protein involved in moving cargoes towards the nucleus, co-precipitated with AR and tubulin in untreated PC cells and at higher amounts following ligand induction, further implicating microtubule dynamics in AR trafficking and activity. To investigate whether AR binds MTs directly or via accessory proteins we plan to perform in vitro tubulin binding assays using purified MT protein and purified recombinant AR. We further plan on identifying the minimum AR domain that mediates microtubule binding. To that end we have generated deletion mutants of the AR, exogenously expressed them in PC3 cells stably expressing mCherry-tubulin and are in the process of testing their MT binding ability. To assess the role of microtubule dynamics in AR trafficking and nuclear translocation we performed live-cell confocal microscopy using PC3-mCherry-tubulin cells transfected with full length wild-type GFP-AR. This study revealed AR trafficking along the MTs and rapid AR nuclear accumulation within 30 min of R1881 (synthetic AR ligand) treatment. In contrast, taxol pre-treatment at concentrations that stabilized MTs attenuated the ligand-induced AR nuclear accumulation as well as the rate of AR's translocation to the nucleus, resulting in increased cytoplasmic sequestration of the receptor. Taken together we have identified a new mechanism of action for taxanes that involves the microtubule-dependent regulation of AR trafficking and downstream signalling. 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 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4076.