title: Degradation of an intramitochondrial protein by the cytosolic proteasome.
abstract: Mitochondrial uncoupling protein 2 (UCP2) is implicated in a wide range of pathophysiological processes, including immunity and diabetes mellitus, but its rapid degradation remains uncharacterized. Using pharmacological proteasome inhibitors, immunoprecipitation, dominant negative ubiquitin mutants, [corrected] cellular fractionation and siRNA techniques, we demonstrate the involvement of the ubiquitin-proteasome system in the rapid degradation of UCP2. Importantly, we resolve the issue of whether intramitochondrial proteins can be degraded by the cytosolic proteasome by reconstituting a cell-free system that shows rapid proteasome-inhibitor-sensitive UCP2 degradation in isolated, energised mitochondria presented with an ATP regenerating system, ubiquitin and 26S proteasome fractions. These observations provide the first demonstration that a mitochondrial inner membrane protein is degraded by the cytosolic ubiquitin-proteasome system.
authors.affiliation: MRC Mitochondrial Biology Unit, Hills Road, Cambridge CB2 0XY, UK.
authors.forename: Vian
authors.initials: V
authors.lastname: Azzu
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D002460:Cell Line; D002474:Cell-Free System; D003600:Cytosol / Q000378:metabolism; D004734:Energy Metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D018892:Proton-Motive Force; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D025801:Ubiquitin / Q000378:metabolism; D000071246:Uncoupling Protein 2
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D025801:Ubiquitin; C000604391:Ucp2 protein, rat; D000071246:Uncoupling Protein 2; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease