Functional inactivation of the von Hippel-Lindau (
VHL) tumor suppressor protein is linked to the development of several forms of
cancer as well as oncogenic progression like sporadic renal clear-cell
carcinomas (RCC). Despite the critical role played by VHL in destruction of
hypoxia-inducible factor α (HIFα) via
ubiquitin-mediated proteolysis, very little is known about the post-translational modification which regulates VHL activity. Our previous study showed that the SUMO
E3 ligase PIASy interacts with VHL and induces VHL SUMOylation on
lysine residue 171 (Cai et al, PLoS ONE, 2010, 5(3):e9720). Here we further report that VHL also undergoes ubiquitylation on both
lysine residues 171 and 196, which is blocked by PIASy. Moreover, using a VHL-SUMO1 or
ubiquitin fusion
protein, we found that ubiquitylated VHL is localized predominantly in the cytoplasm, while SUMOylated VHL results in increased VHL protein stability and nuclear redistribution. Interestingly, substitution of
lysine 171 and 196 to
arginine of VHL abrogates its inhibitory function on the transcriptional activity of HIFα, and tube formation in vitro. This demonstrates that post-translational modifications like ubiquitylation and SUMOylation contributes to VHL protein stability and nucleocytoplasmic shuttling, and that the overall function of VHL in
tumor suppression may require a precise and dynamically regulated process which involves
protein modification.