Abstract 2381: The effect of ERK5 inhibition in clear cell renal cell carcinoma

Abstract

Abstract Introduction Clear-cell renal cell carcinoma (ccRCC) is the most prevalent kidney cancer and is characterized by von Hippel-Lindau tumor suppressor gene (VHL) mutation. VHL protein acts in a ubiquitin ligase complex, mediating the proteasomal degradation of ubiquitinized proteins, including hypoxia-inducible factor (HIF). Therefore, HIF accumulates in VHL-defective cell lines. A recent study revealed that extracellular signal-regulated kinase 5 (ERK5) is degraded through the ubiquitin-proteasome system, in a process mediated by VHL and HIF. Our objectives were to examine the effects of ERK5 in ccRCC and to investigate ERK5 as a potential therapeutic target. Methods ERK5 expression was investigated in surgically resected ccRCC specimens using immunohistochemistry. To confirm that ERK5 is degraded by the VHL pathway, ERK5 levels were examined by western blotting in Caki-1 VHL wildtype renal cell carcinoma (RCC) cells and in A498 and A704 VHL-mutant RCC cells with or without the MG132 proteasome inhibitor. Furthermore, VHL-mutant cell lines were examined, with or without siRNA and XMD8-92-mediated ERK5 inhibition, to investigate the role of ERK5 in RCC cells using flow cytometry, MTS assays, and western blotting . Results In surgical specimens, RCC cells showed higher levels of ERK5 expression than did normal cells. In addition, MG132 enhanced ERK5 expression in wildtype cell lines, but not in VHL-mutant cell lines. Therefore, ERK5 degradation involves the VHL pathway. Furthermore, ERK5 inhibition resulted in increase of the sub-G1 population as observed by flow cytometry and cleaved RARP expression as seen by western blotting, indicating an increase in apoptotic cells. ERK5 inhibition also suppressed cell viability and downregulated p16 and Bcl-2 expression. Conclusion Our results show that ERK5 inhibition contributes to the downregulation of anti-apoptotic and cell cycle proteins and suggest that ERK5 is a promising therapeutic target for ccRCC. Citation Format: Hidenori Kanno, Sei Naito, Osamu Ichiyanagi, Norihiko Tsuchiya. The effect of ERK5 inhibition in clear cell renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2381. doi:10.1158/1538-7445.AM2017-2381