title: Sti1 regulation of Hsp70 and Hsp90 is critical for curing of Saccharomyces cerevisiae [PSI+] prions by Hsp104.
abstract: Although propagation of Saccharomyces cerevisiae prions requires Hsp104 protein disaggregating activity, overproducing Hsp104 "cures" cells of [PSI(+)] prions. Earlier evidence suggests that the Hsp70 mutant Ssa1-21 impairs [PSI(+)] by a related mechanism. Here, we confirm this link by finding that deletion of STI1 both suppresses Ssa1-21 impairment of [PSI(+)] and blocks Hsp104 curing of [PSI(+)]. Hsp104's tetratricopeptide repeat (TPR) interaction motif was dispensable for curing; however, cells expressing Sti1 defective in Hsp70 or Hsp90 interaction cured less efficiently, and the Hsp90 inhibitor radicicol abolished curing, implying that Sti1 acts in curing through Hsp70 and Hsp90 interactions. Accordingly, strains lacking constitutive or inducible Hsp90 isoforms cured at reduced rates. We confirm an earlier finding that elevating free ubiquitin levels enhances curing, but it did not overcome inhibition of curing caused by Hsp90 defects, suggesting that Hsp90 machinery is important for the contribution of ubiquitin to curing. We also find curing associated with cell division. Our findings point to crucial roles of Hsp70, Sti1, and Hsp90 for efficient curing by overexpressed Hsp104 and provide evidence supporting the earlier suggestion that destruction of prions by protein disaggregation does not adequately explain the curing.
authors.affiliation: Laboratory of Biochemistry and Genetics, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Reidy
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Masison
mesh_terms: D002455:Cell Division; D005800:Genes, Fungal; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018942:Macrolides / Q000494:pharmacology; D009154:Mutation; D010454:Peptide Termination Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011328:Prions / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018942:Macrolides; D010454:Peptide Termination Factors; D011328:Prions; C090869:SSA3 protein, S cerevisiae; C542289:STI1 protein, S cerevisiae; C068068:SUP35 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C070972:HsP104 protein, S cerevisiae; C035359:monorden