title: HspB8 chaperone activity toward poly(Q)-containing proteins depends on its association with Bag3, a stimulator of macroautophagy.
abstract: Mutations in HspB8, a member of the B group of heat shock proteins (Hsp), have been associated with human neuromuscular disorders. However, the exact function of HspB8 is not yet clear. We previously demonstrated that overexpression of HspB8 in cultured cells prevents the accumulation of aggregation-prone proteins such as the polyglutamine protein Htt43Q. Here we report that HspB8 forms a stable complex with Bag3 in cells and that the formation of this complex is essential for the activity of HspB8. Bag3 overexpression resulted in the accelerated degradation of Htt43Q, whereas Bag3 knockdown prevented HspB8-induced Htt43Q degradation. Additionally, depleting Bag3 caused a reduction in the endogenous levels of LC3-II, a key molecule involved in macroautophagy, whereas overexpressing Bag3 or HspB8 stimulated the formation LC3-II. These results suggested that the HspB8-Bag3 complex might stimulate the degradation of Htt43Q by macroautophagy. This was confirmed by the observation that treatments with macroautophagy inhibitors significantly decreased HspB8- and Bag3-induced degradation of Htt43Q. We conclude that the HspB8 activity is intrinsically dependent on Bag3, a protein that may facilitate the disposal of doomed proteins by stimulating macroautophagy.
authors.affiliation: Centre de Recherche en Cancérologie and Département de Médecine, Université Laval, Québec G1R 2J6, Canada.
authors.forename: Serena
authors.initials: S
authors.lastname: Carra
authors.affiliation: Centre de Recherche en Cancérologie and Département de Médecine, Université Laval, Québec G1R 2J6, Canada.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Seguin
authors.affiliation: Centre de Recherche en Cancérologie and Département de Médecine, Université Laval, Québec G1R 2J6, Canada.
authors.forename: Herman
authors.initials: H
authors.lastname: Lambert
authors.affiliation: Centre de Recherche en Cancérologie and Département de Médecine, Université Laval, Québec G1R 2J6, Canada. Electronic address: jacques.landry@med.ulaval.ca.
authors.forename: Jacques
authors.initials: J
authors.lastname: Landry
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D001343:Autophagy; D002460:Cell Line; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D000071058:Huntingtin Protein; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D051381:Rats
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C414431:BAG3 protein, human; C413214:HSPB8 protein, human; C086055:HTT protein, human; D006360:Heat-Shock Proteins; D000071058:Huntingtin Protein; D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; C097188:polyglutamine; D017346:Protein Serine-Threonine Kinases