Abstract 2064: Regulation of the VHL tumor suppressor protein in hypoxia and through the cell cycle

Abstract

Abstract The von Hippel-Lindau (VHL) gene is a classical tumor suppressor and is inactivated in patients with von Hippel-Lindau disease, as well as the majority of patients with sporadic clear cell renal carcinoma (RCC). The VHL protein (pVHL) is an E3 ubiquitin ligase with many functions, including regulating the hypoxia response as well as microtubule stability. While the involvement of pVHL in targeting of HIF alpha subunits for ubiquitin-mediated degradation is well documented, less is understood about regulation of pVHL itself. We determined pVHL levels under normoxic (room air, 21% oxygen) and hypoxic (1% oxygen) conditions and found that pVHL levels decreased in hypoxia. VHL protein half-life was similar in cells cultured in normoxia or hypoxia, suggesting that pVHL expression is regulated through a post-transcriptional mechanism. Down regulation of pVHL in hypoxia suggests a novel and complementary mechanism to account for stabilization of HIF alpha subunits. While pVHL-negative RCC cells progress through the cell cycle when cultured in hypoxia, isogenic pVHL-expressing RCC exhibited hypoxia-induced arrest in G1 phase of the cell cycle. We also determined pVHL levels during cell cycle progression and found that pVHL levels were decreased levels during mitosis and G1. The anaphase promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that is active during late M phase and G1 through the association with the activators, Cdh1 and Cdc20. Cdh1 and Cdc20 bind to APC/C target proteins through recognition of Destruction box consensus sequences. Such sequences are found in pVHL, suggesting that pVHL may be a target for APC/C ubiquitylation. We found that pVHL physically bound to Cdh1, that Cdh1 knockdown was associated with increased pVHL levels, that Cdh1 overexpression was associated with decreased pVHL levels and increased polyubiquitylation pVHL, and that these activities were dependent on pVHL Destruction box sequences. Our results indicate that pVHL is a novel substrate of APC/C-Cdh1. 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 2064. doi:10.1158/1538-7445.AM2011-2064