title: Calcineurin promotes hypoxia-inducible factor 1alpha expression by dephosphorylating RACK1 and blocking RACK1 dimerization.
abstract: Oxygen homeostasis represents an essential organizing principle of metazoan evolution and biology. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of transcriptional responses to changes in O2 concentration. HIF-1 is a heterodimer of HIF-1alpha and HIF-1beta subunits. O2-dependent degradation of the HIF-1alpha subunit is mediated by prolyl hydroxylase, von Hippel-Lindau protein (VHL)/Elongin-C E3 ubiquitin ligase, and the proteasome. O2-independent degradation of HIF-1alpha is regulated by the competition of RACK1 and HSP90 for binding to HIF-1alpha. RACK1 binding results in the recruitment of the Elongin-C E3 ubiquitin ligase, leading to VHL-independent ubiquitination and degradation of HIF-1alpha. In this report, we show that calcineurin inhibits the ubiquitination and proteasomal degradation of HIF-1alpha. Calcineurin is a serine/threonine phosphatase that is activated by calcium and calmodulin. The phosphatase activity of calcineurin is required for its regulation of HIF-1alpha. RACK1 binds to the catalytic domain of calcineurin and is required for HIF-1alpha degradation induced by the calcineurin inhibitor cyclosporine A. Elongin-C and HIF-1alpha each bind to RACK1 and dimerization of RACK1 is required to recruit Elongin-C to HIF-1alpha. Phosphorylation of RACK1 promotes its dimerization and dephosphorylation by calcineurin inhibits dimerization. Serine 146 within the dimerization domain is phosphorylated and mutation of serine 146 impairs RACK1 dimerization and HIF-1alpha degradation. These results indicate that intracellular calcium levels can regulate HIF-1alpha expression by modulating calcineurin activity and RACK1 dimerization.
authors.affiliation: Vascular Program, Institute for Cell Engineering, Department of Pharmacology and Molecular Sciences, Mass Spectronomy Proteomics Facility, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Ye V
authors.initials: YV
authors.lastname: Liu
authors.forename: Maimon E
authors.initials: ME
authors.lastname: Hubbi
authors.forename: Fan
authors.initials: F
authors.lastname: Pan
authors.forename: Karin R
authors.initials: KR
authors.lastname: McDonald
authors.forename: Malini
authors.initials: M
authors.lastname: Mansharamani
authors.forename: Robert N
authors.initials: RN
authors.lastname: Cole
authors.forename: Jun O
authors.initials: JO
authors.lastname: Liu
authors.forename: Gregg L
authors.initials: GL
authors.lastname: Semenza
mesh_terms: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002460:Cell Line; D016572:Cyclosporine / Q000494:pharmacology; D019281:Dimerization; D000075065:Elongin; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis*; D009363:Neoplasm Proteins / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects / Q000502:physiology; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000378:metabolism
chemical_list: C497396:ARNT protein, human; D002147:Calmodulin; C000616395:ELOC protein, human; D000075065:Elongin; D004791:Enzyme Inhibitors; C497442:HIF1A protein, human; D018841:HSP90 Heat-Shock Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009363:Neoplasm Proteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D014157:Transcription Factors; D025801:Ubiquitin; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D016572:Cyclosporine; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D019703:Calcineurin; D046988:Proteasome Endopeptidase Complex; D019204:GTP-Binding Proteins; C497446:VHL protein, human; D010100:Oxygen; D002118:Calcium