Homotypic association between tumour-associated VHL proteins leads to the restoration of HIF pathway

Abstract

The von Hippel-Lindau (VHL) tumour suppressor gene encodes a substrate-specifying component of an E3 ubiquitin ligase that targets hypoxia-inducible factor (HIF) α subunits for degradation under normoxia. The VHL protein is composed of an N-terminal HIFα-binding β domain and a C-terminal α domain, which is necessary and sufficient for the formation of the E3 multiprotein enzyme. A large number of disease-causing mutations in either the α or β domain renders HIFα stable irrespective of oxygen tension, leading to the upregulation of numerous HIF-target genes, such as GLUT1 and VEGF. Here, we show that VHL forms a self-associated complex in vivo, but not in vitro, and demonstrate that coexpression of two different VHL missense mutants — one in the α domain and the other in the β domain — restores HIF-mediated gene expression profile. These findings indicate that VHL homotypic complexes can function in vivo in a complementary fashion to target HIFα for ubiquitin-mediated proteolysis, and potentially explain why VHL-associated tumours with a missense mutation-carrying VHL allele is almost invariably accompanied by a second VHL allele harbouring a gross truncation or deletion.