Abstract 1435: Role of PRKD2 in HSP90- and hypoxia-mediated epithelial-to-mesenchymal transition

Abstract The protein kinase D (PRKD) family of serine/threonine kinases belongs to the calcium/calmodulin-dependent protein kinase superfamily and comprises three isoforms, PRKD1, PRKD2 and PRKD3. We have recently identified PRKD2 as a novel client of HSP90 chaperone in several cancer cell lines. Depletion of PRKD2 protein following pharmacologic inhibition of HSP90 was associated with tumor cell death in vitro and in vivo. Furthermore, abrogation of PRKD2 in cancer cells prevented hypoxia-induced accumulation and promoter activity of HIF-1a, an oxygen sensor also shown to be regulated by HSP90. Since, both HSP90 and hypoxia/HIF-1a regulate epithelial-to-mesenchymal transition (EMT), we sought to investigate the role played by PRKD2 in this process. Here we report that ectopic expression of PRKD2 was associated with a change in morphology, from epithelial polarized to a spindle-like phenotype, in lung and pancreatic cancer cells. This observation was associated with impaired E-cadherin and augmented vimentin protein levels. Pharmacologic inhibition of HSP90 was associated not only with PRKD2 degradation but also with decreased vimentin expression. However, the higher remaining PRKD2 levels after HSP90 inhibition of tumor cells expressing ectopic PRKD2 partially restored the vimentin expression suggesting a contribution of kinase to the chaperone-supported EMT. Incubation of cancer cells under low oxygen atmosphere showed decreased epithelial marker proteins and elevated vimentin levels, which was further enhanced by overexpressing PRKD2 suggesting that PRKD2 is involved in hypoxia-triggered EMT process. The fact that PRKD2 is able to interact with hypoxia-stabilized HIF-1a, which regulates EMT by controlling expression of Twist, a basic helix-loop-helix transcription factor reported to repress E-cadherin, suggests that PRKD2 may influence crucial EMT molecules via HIF-1a. Altogether, these findings 1) suggest PRKD2 as a crucial modulator of HSP90- and hypoxia-mediated EMT process, 2) suggest PRKD2 ablation through HSP90 inhibition as a potential therapeutic strategy in cancer with immediate implementation since several chaperone inhibitors are in clinical trials and 3) promote the intensification of designing specific PRKD2 inhibitors and their implementation in targeted therapy in human cancer. Citation Format: Ninel Azoitei, Alexander Becher, Kristina Diepold, Susanne Bobrovich, Cornelia Brunner, Gabriela Chiosis, Stefan Fröhling, van Lint Johan, Claudia Scholl, Thomas Seufferlein. Role of PRKD2 in HSP90- and hypoxia-mediated epithelial-to-mesenchymal transition. [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 1435. doi:10.1158/1538-7445.AM2015-1435