title: p58IPK is an inhibitor of the eIF2α kinase GCN2 and its localization and expression underpin protein synthesis and ER processing capacity.
abstract: One of the key cellular responses to stress is the attenuation of mRNA translation and protein synthesis via the phosphorylation of eIF2α (eukaryotic translation initiation factor 2α). This is mediated by four eIF2α kinases and it has been suggested that each kinase is specific to the cellular stress imposed. In the present study, we show that both PERK (PKR-like endoplasmic reticulum kinase/eIF2α kinase 3) and GCN2 (general control non-derepressible 2/eIF2α kinase 4) are required for the stress responses associated with conditions encountered by cells overexpressing secreted recombinant protein. Importantly, whereas GCN2 is the kinase that is activated following cold-shock/hypothermic culturing of mammalian cells, PERK and GCN2 have overlapping functions since knockdown of one of these at the mRNA level is compensated for by the cell by up-regulating levels of the other. The protein p58IPK {also known as DnaJ3C [DnaJ heat-shock protein (hsp) 40 homologue, subfamily C, member 3]} is known to inhibit the eIF2α kinases PKR (dsRNA-dependent protein kinase/eIF2α kinase 2) and PERK and hence prevent or delay eIF2α phosphorylation and consequent inhibition of translation. However, we show that p58IPK is a general inhibitor of the eIF2α kinases in that it also interacts with GCN2. Thus forced overexpression of cytoplasmic p58 delays eIF2α phosphorylation, suppresses GCN2 phosphorylation and prolongs protein synthesis under endoplasmic reticulum (ER), hypothermic and prolonged culture stress conditions. Taken together, our data suggest that there is considerable cross talk between the eIF2α kinases to ensure that protein synthesis is tightly regulated. Their activation is controlled by p58 and the expression levels and localization of this protein are crucial in the capacity the cells to respond to cellular stress via control of protein synthesis rates and subsequent folding in the ER.
authors.affiliation: *Centre for Molecular Processing and Protein Science Group, School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, U.K.
authors.forename: Anne
authors.initials: A
authors.lastname: Roobol
authors.affiliation: *Centre for Molecular Processing and Protein Science Group, School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, U.K.
authors.forename: Jo
authors.initials: J
authors.lastname: Roobol
authors.affiliation: †MRC Toxicology Unit, Hodgkin Building, PO Box 138, Lancaster Road, Leicester LE1 9HN, U.K.
authors.forename: Amandine
authors.initials: A
authors.lastname: Bastide
authors.affiliation: †MRC Toxicology Unit, Hodgkin Building, PO Box 138, Lancaster Road, Leicester LE1 9HN, U.K.
authors.forename: John R P
authors.initials: JR
authors.lastname: Knight
authors.affiliation: †MRC Toxicology Unit, Hodgkin Building, PO Box 138, Lancaster Road, Leicester LE1 9HN, U.K.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Willis
authors.affiliation: *Centre for Molecular Processing and Protein Science Group, School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, U.K.
authors.forename: C Mark
authors.initials: CM
authors.lastname: Smales
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D050956:HSP40 Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation / Q000502:physiology; D014176:Protein Biosynthesis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D050956:HSP40 Heat-Shock Proteins; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D019892:eIF-2 Kinase; C494651:DNAJC3 protein, human; C500846:Dnajc3 protein, mouse; C460640:EIF2AK3 protein, human; C529271:EIF2AK4 protein, human; C070634:Eif2ak4 protein, mouse