title: Cytosolic Hsp60 can modulate proteasome activity in yeast.
abstract: Hsp60, an essential oligomeric molecular mitochondrial chaperone, has been subject to rigorous basic and clinical research. With yeast as a model system, we provide evidence for the ability of cytosolic yHsp60 to inhibit the yeast proteasome. (i) Following biological turnover of murine Bax (a proteasome substrate), we show that co-expression of cytosolic yHsp60 stabilizes Bax, enhances its association with mitochondria, and enhances its killing capacity. (ii) Expression of yHsp60 in the yeast cytosol (yHsp60c) inhibits degradation of a cytosolic protein ΔMTS-Aco1 tagged with the degron SL17 (a ubiquitin-proteasome substrate). (iii) Conditions under which Hsp60 accumulates in the cytosol (elevated Hsp60c or growth at 37 °C) correlate with reduced 20 S peptidase activity in proteasomes purified from cell extracts. (iv) Elevated yHsp60 in the cytosol correlate with accumulation of polyubiquitinated proteins. (v) According to 20 S proteasome pulldown experiments, Hsp60 is physically associated with proteasomes in extracts of cells expressing Hsp60c or grown at 37 °C. Even mutant Hsp60 proteins, lacking chaperone activity, were still capable of proteasome inhibition. The results support the hypothesis that localization of Hsp60 to the cytosol may modulate proteasome activity according to cell need.
authors.affiliation: From the Department of Microbiology Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel and.
authors.forename: Bella
authors.initials: B
authors.lastname: Kalderon
authors.affiliation: From the Department of Microbiology Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel and.
authors.forename: Gleb
authors.initials: G
authors.lastname: Kogan
authors.affiliation: From the Department of Microbiology Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel and.
authors.forename: Ettel
authors.initials: E
authors.lastname: Bubis
authors.affiliation: From the Department of Microbiology Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel and the CREATE-NUS-HUJ Program, National University of Singapore, 138602 Singapore ophryp@ekmd.huji.ac.il.
authors.forename: Ophry
authors.initials: O
authors.lastname: Pines
mesh_terms: D000818:Animals; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D035941:Iron Regulatory Protein 1 / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D018834:Chaperonin 60; C504495:HSP60 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D051028:bcl-2-Associated X Protein; D046988:Proteasome Endopeptidase Complex; D035941:Iron Regulatory Protein 1
keywords: Heat Shock Protein (HSP); Mitochondria; Proteasome; Protein Targeting; Saccharomyces cerevisiae; Ubiquitylation (Ubiquitination)