Selective mRNA translation during eIF2 phosphorylation induces expression of IBTKα

• Published in: Molecular biology of the cell Vol. 25; no. 10; pp. 1686 - 1697
• Main Authors: Baird, Thomas D., Palam, Lakshmi Reddy, Fusakio, Michael E., Willy, Jeffrey A., Davis, Christopher M., McClintick, Jeanette N., Anthony, Tracy G., Wek, Ronald C.
• Format: Journal Article
• Language: English
• Published: United States The American Society for Cell Biology 15.05.2014
• Subjects: Activating Transcription Factor 4 - genetics; Animals; Base Sequence; Carrier Proteins - biosynthesis; Carrier Proteins - genetics; Caspase 3 - metabolism; Caspase 7 - metabolism; Cell Division - genetics; Cell Line; Cell Survival - genetics; eIF-2 Kinase - genetics; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum Stress - genetics; Gene Expression Regulation; Hep G2 Cells; Humans; Mice; Molecular Sequence Data; Open Reading Frames - genetics; Phosphorylation; Protein Biosynthesis - genetics; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; RNA Interference; RNA, Messenger - genetics; RNA, Small Interfering; Transcription Factor CHOP - genetics; Transcription Initiation Site; Transcriptional Activation - genetics; Unfolded Protein Response - genetics
• ISSN: 1059-1524; 1939-4586; 1939-4586
• DOI: 10.1091/mbc.e14-02-0704

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.