Dept. of Molecular Microbiology and Immunology
Oregon Health & Science University
ER-associated, ubiquitin-proteasome system (UPS)-mediated degradation of the wild-type gap junction protein connexin32 (WT Cx32) is inhibited by mild forms of cytosolic stress at a step prior to its dislocation into the cytosol. We show that the same conditions (a 30 min, 42Â°C heat shock or oxidative stress induced by arsenite) also reduce the ER-associated turnover of disease causing mutants of Cx32 and 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.
School of Medicine
Kelly, Sean M., "Regulation of ubiquitin-proteasome system-mediated degradation by cytosolic stress" (2007). Scholar Archive. 789.