title: Inhibition of translational initiation by activators of the glucose-regulated stress protein and heat shock protein stress response systems. Role of the interferon-inducible double-stranded RNA-activated eukaryotic initiation factor 2alpha kinase.
abstract: Depletion of endoplasmic reticulum (ER) Ca2+ perturbs protein folding and processing within the organelle while inhibiting translational initiation through activation of the double-stranded RNA-activated eukaryotic initiation factor (eIF)-2alpha kinase (PKR) (Prostko, C. R., Dholakia, J. N., Brostrom, M. A., and Brostrom, C. O. (1995) J. Biol. Chem. 270, 6211-6215). The glucose-regulated stress protein (GRP) chaperones are subsequently induced. We now report that sodium arsenite, a prototype for stressors fostering cytoplasmic protein misfolding, also inhibits translational initiation through activation of PKR while subsequently inducing the heat shock protein (HSP) chaperones. Arsenite neither mobilized ER-associated Ca2+ nor slowed peptide chain elongation. Various HSP-inducing chemicals caused rapid phosphorylation of eIF-2alpha. When incubated with double-stranded RNA, extracts derived from arsenite-treated cells displayed greater degrees of phosphorylation of PKR and eIF-2alpha than did control extracts. Cells overexpressing a dominant negative PKR mutation resisted translational inhibition and eIF-2alpha phosphorylation in response to ER or cytoplasmic stressors. Induction of either the HSP or GRP chaperones was accompanied by development of translational tolerance to either Ca2+-mobilizing agents or arsenite. Following induction of the HSPs by arsenite, cells remained susceptible to induction of the GRPs by Ca2+-mobilizing agents. Conversely, cells possessing induced GRP contents in response to Ca2+-mobilizing agents readily induced the HSPs in response to arsenite. It is concluded that the two chaperone systems function independently except for their mutual suppression of PKR.
authors.affiliation: Department of Pharmacology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
authors.forename: C O
authors.initials: CO
authors.lastname: Brostrom
authors.forename: C R
authors.initials: CR
authors.lastname: Prostko
authors.forename: R J
authors.initials: RJ
authors.lastname: Kaufman
authors.forename: M A
authors.initials: MA
authors.lastname: Brostrom
mesh_terms: D016475:3T3 Cells; D000818:Animals; D018053:Arsenites / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007372:Interferons / Q000494:pharmacology*; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects*; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D017670:Sodium Compounds / Q000494:pharmacology; D019892:eIF-2 Kinase
chemical_list: D018053:Arsenites; D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D017670:Sodium Compounds; C017947:sodium arsenite; D007372:Interferons; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D002118:Calcium