title: Regulation of ubiquitin-proteasome system mediated degradation by cytosolic stress.
abstract: ER-associated, ubiquitin-proteasome system (UPS)-mediated degradation of the wild-type (WT) gap junction protein connexin32 (Cx32) is inhibited by mild forms of cytosolic stress at a step before its dislocation into the cytosol. We show that the same conditions (a 30-min, 42 degrees C heat shock or oxidative stress induced by arsenite) also reduce the endoplasmic reticulum (ER)-associated turnover of disease-causing mutants of Cx32 and the cystic fibrosis transmembrane conductance regulator (CFTR), as well as that of WT CFTR and unassembled Ig light chain. Stress-stabilized WT Cx32 and CFTR, but not the mutant/unassembled proteins examined, could traverse the secretory pathway. Heat shock also slowed the otherwise rapid UPS-mediated turnover of the cytosolic proteins myoD and GFPu, but not the degradation of an ubiquitination-independent construct (GFP-ODC) closely related to the latter. Analysis of mutant Cx32 from cells exposed to proteasome inhibitors and/or cytosolic stress indicated that stress reduces degradation at the level of substrate polyubiquitination. These findings reveal a new link between the cytosolic stress-induced heat shock response, ER-associated degradation, and polyubiquitination. Stress-denatured proteins may titer a limiting component of the ubiquitination machinery away from pre-existing UPS substrates, thereby sparing the latter from degradation.
authors: Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239, USA.
authors: Sean M
authors: SM
authors: Kelly
authors: Judy K
authors: JK
authors: Vanslyke
authors: Linda S
authors: LS
authors: Musil
mesh_terms: D000818:Animals; D016466:CHO Cells; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D006358:Hot Temperature; D009154:Mutation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D021381:Protein Transport; D013379:Substrate Specificity; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D017630:Connexins; D025801:Ubiquitin; D018698:Glutamic Acid; D046988:Proteasome Endopeptidase Complex
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