title: Chaperone hsp27 inhibits translation during heat shock by binding eIF4G and facilitating dissociation of cap-initiation complexes.
abstract: Inhibition of protein synthesis during heat shock limits accumulation of unfolded proteins that might damage eukaryotic cells. We demonstrate that chaperone Hsp27 is a heat shock-induced inhibitor of cellular protein synthesis. Translation of most mRNAs requires formation of a cap-binding initiation complex known as eIF4F, consisting of factors eIF4E, eIF4A, eIF4E kinase Mnk1, poly(A)-binding protein, and adaptor protein eIF4G. Hsp27 specifically bound eIF4G during heat shock, preventing assembly of the cap-initiation/eIF4F complex and trapping eIF4G in insoluble heat shock granules. eIF4G is a specific target of Hsp27, as eIF4E, eIF4A, Mnk1, poly(A)-binding protein, eIF4B, and eIF3 were not bound by Hsp27 and were not recruited into insoluble complexes. Dissociation of eIF4F was enhanced during heat shock by ectopic overexpression of Hsp25, the murine homolog of human Hsp27. Overexpression of Hsc70, a constitutive homolog of Hsp70, prevented loss of cap-initiation complexes and maintained eIF4G solubility. Purified Hsp27 specifically bound purified eIF4G in vitro, prevented in vitro translation, eliminated eIF4G interaction with protein binding factors, and promoted eIF4G insolubilization. These results therefore demonstrate that Hsp27 is a heat-induced inhibitor of eIF4F-dependent mRNA translation.
authors.affiliation: Department of Microbiology, New York University School of Medicine and Kaplan Cancer Center, New York, New York 10016 USA.
authors.forename: R
authors.initials: R
authors.lastname: Cuesta
authors.forename: G
authors.initials: G
authors.lastname: Laroia
authors.forename: R J
authors.initials: RJ
authors.lastname: Schneider
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D005455:Fluorescent Antibody Technique; D005982:Glutathione Transferase / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins; D055551:HSP27 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006367:HeLa Cells; D006360:Heat-Shock Proteins; D006358:Hot Temperature; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D009363:Neoplasm Proteins / Q000378:metabolism* / Q000502:physiology*; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D010957:Plasmids; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012315:RNA Caps; D012333:RNA, Messenger / Q000378:metabolism; D013696:Temperature; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D050883:HSC70 Heat-Shock Proteins; D055551:HSP27 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; C486113:Hsbp1 protein, mouse; C494372:Hspa8 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D010448:Peptide Initiation Factors; D012315:RNA Caps; D012333:RNA, Messenger; D005982:Glutathione Transferase; D010770:Phosphotransferases; C491395:MKNK1 protein, human; C106281:Mknk1 protein, mouse; D017346:Protein Serine-Threonine Kinases