Cytoplasmic Hsp70 promotes ubiquitination for endoplasmic reticulum-associated degradation of a misfolded mutant of the yeast plasma membrane ATPase, PMA1.
Cells have a variety of strategies for dealing with misfolded proteins. Heat shock response involves transcriptional induction of chaperones to promote and/or correct folding, and also activation of the ubiquitin/proteasome system to degrade defective proteins. In the secretory pathway, it is primarily luminal misfolded or unassembled proteins that trigger the unfolded protein response which, like heat shock, induces chaperones and components of the endoplasmic reticulum (ER)-associated degradation (ERAD) pathway. To understand cellular response to a misfolded polytopic membrane protein of the secretory pathway, we studied Pma1-D378S, a model ERAD substrate. Expression of misfolded Pma1 induces heat shock response in the absence of increased temperature. Overexpression of HSF1, the transcription factor that mediates heat shock response, increases degradation of Pma1-D378S without temperature upshift. Nevertheless, efficient Pma1-D378S degradation occurs in an hsf1 mutant that maintains basal transcription levels but cannot mediate transcriptional activation. Thus, heat shock protein induction enhances but is not necessary for ERAD. The Ssa group of cytoplasmic Hsp70 chaperones is required for ERAD of both Pma1-D378S and another transmembrane ERAD substrate, Ste6*. In the absence of Ssa chaperones, ubiquitination of both substrates is impaired, resulting in stabilization. We suggest a role for Hsp70 cytoplasmic chaperones in recognition by the endoplasmic reticulum-associated ubiquitination machinery.
Han
Sumin
S
Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
Liu
Yu
Y
Chang
Amy
A
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response / Q000502:physiology; D008954:Models, Biological; D020125:Mutation, Missense; D017510:Protein Folding; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D004268:DNA-Binding Proteins; D006023:Glycoproteins; C067168:HSF1 protein, S cerevisiae; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C489277:STE6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases