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 2-ALPHA KINASE

Depletion of endoplasmic reticulum (ER) Ca2+ perturbs protein folding and processing within the organelle while inhibiting translational ini tiation through activation of the double-stranded RNA-activated eukary otic initiation factor (eIF)-2 alpha kinase (PKR) (Prostko, C. R., Dho lakia, J. N., Brostrom, M. A., and Brostrom, C. O. (1995) J. Biol. Che m. 270, 6211-6215). The glucose-regulated stress protein (GRP) chapero nes are subsequently induced, We now report that sodium arsenite, a pr ototype for stressors fostering cytoplasmic protein misfolding, also i nhibits translational initiation through activation of PKR while subse quently inducing the heat shock protein (HSP) chaperones, Arsenite nei ther mobilized ER-associated Ca2+ nor slowed peptide chain elongation, Various HSP-inducing chemicals caused rapid phosphorylation of eIF-2 alpha. When incubated with double-stranded RNA, extracts derived from arsenite-treated cells displayed greater degrees of phosphorylation of PKR and eIF-2 alpha than did control extracts. Cells overexpressing a dominant negative PKR mutation resisted translational inhibition and eIF-2 alpha phosphorylation in response to ER or cytoplasmic stressors , Induction of either the HSP or GRP chaperones was accompanied by dev elopment of translational tolerance to either Ca2+-mobilizing agents o r arsenite, Following induction of the HSPs by arsenite, cells remaine d susceptible to induction of the GRPs by Ca2+-mobilizing agents. Conv ersely, cells possessing induced GRP contents in response to Ca2+-mobi lizing 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.