title: 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) alpha subunits for degradation under normoxia. The VHL protein is composed of an N-terminal HIFalpha-binding beta domain and a C-terminal alpha domain, which is necessary and sufficient for the formation of the E3 multiprotein enzyme. A large number of disease-causing mutations in either the alpha or beta domain renders HIFalpha 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 alpha domain and the other in the beta domain -- restores HIF-mediated gene expression profile. These findings indicate that VHL homotypic complexes can function in vivo in a complementary fashion to target HIFalpha 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.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Chung
authors.forename: A M
authors.initials: AM
authors.lastname: Roberts
authors.forename: J
authors.initials: J
authors.lastname: Chow
authors.forename: N
authors.initials: N
authors.lastname: Coady-Osberg
authors.forename: M
authors.initials: M
authors.lastname: Ohh
mesh_terms: D019943:Amino Acid Substitution; D001859:Bone Neoplasms / Q000473:pathology; D002292:Carcinoma, Renal Cell / Q000473:pathology; D045744:Cell Line, Tumor; D019281:Dimerization; D000075065:Elongin; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology*; D007680:Kidney Neoplasms / Q000473:pathology; D020125:Mutation, Missense; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D012516:Osteosarcoma / Q000473:pathology; D010100:Oxygen / Q000378:metabolism; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary / Q000235:genetics; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D043743:Ubiquitin-Protein Ligase Complexes / Q000737:chemistry / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000502:physiology*; D015854:Up-Regulation; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D000075065:Elongin; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009363:Neoplasm Proteins; D014157:Transcription Factors; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; C497446:VHL protein, human; D010100:Oxygen