title: Selective mRNA translation during eIF2 phosphorylation induces expression of IBTKα.
abstract: Disruption of protein folding in the endoplasmic reticulum (ER) triggers the unfolded protein response (UPR), a transcriptional and translational control network designed to restore protein homeostasis. Central to the UPR is PKR-like ER kinase (PERK/EIF2AK3) phosphorylation of the α subunit of eIF2 (eIF2α∼P), which represses global translation coincident with preferential translation of mRNAs, such as activating transcription factor 4 (ATF4) and C/EBP-homologous protein (CHOP), that serve to implement UPR transcriptional regulation. In this study, we used sucrose gradient ultracentrifugation and a genome-wide microarray approach to measure changes in mRNA translation during ER stress. Our analysis suggests that translational efficiencies vary over a broad range during ER stress, with the majority of transcripts being either repressed or resistant to eIF2α∼P, whereas a notable cohort of key regulators are subject to preferential translation. From the latter group, we identified the α isoform of inhibitor of Bruton's tyrosine kinase (IBTKα) as being subject to both translational and transcriptional induction during eIF2α∼P in both cell lines and a mouse model of ER stress. Translational regulation of IBTKα mRNA involves stress-induced relief of two inhibitory upstream open reading frames in the 5'-leader of the transcript. Depletion of IBTKα by short hairpin RNA reduced viability of cultured cells coincident with increased caspase 3/7 cleavage, suggesting that IBTKα is a key regulator in determining cell fate during the UPR.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Baird
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202.
authors.forename: Lakshmi Reddy
authors.initials: LR
authors.lastname: Palam
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Fusakio
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202Investigative Toxicology, Lilly Research Laboratories, Indianapolis, IN 46285.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Willy
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Davis
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202.
authors.forename: Jeanette N
authors.initials: JN
authors.lastname: McClintick
authors.affiliation: Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ 08901.
authors.forename: Tracy G
authors.initials: TG
authors.lastname: Anthony
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202 rwek@iu.edu.
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Wek
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000235:genetics*; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP / Q000235:genetics; D024363:Transcription Initiation Site; D015533:Transcriptional Activation / Q000235:genetics; D056811:Unfolded Protein Response / Q000235:genetics*; D019892:eIF-2 Kinase / Q000235:genetics*
chemical_list: D051701:Activating Transcription Factor 4; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D053148:Caspase 3; D053179:Caspase 7; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C081452:Atf4 protein, mouse; C497250:Ddit3 protein, mouse; C000594398:IBtk protein, mouse; C531557:eIF2alpha kinase, mouse; C505524:Casp7 protein, mouse