Differential regulation of CHOP translation by phosphorylated eIF4E under stress conditions.
Cells respond to environmental stress by inducing translation of a subset of mRNAs important for survival or apoptosis. CHOP, a downstream transcriptional target of stress-induced ATF4, is also regulated translationally in a uORF-dependent manner under stress. Low concentration of anisomycin induces CHOP expression at both transcriptional and translational levels. To study specifically the translational aspect of CHOP expression, and further clarify the regulatory mechanisms underlying stress-induced translation initiation, we developed a CMV promoter-regulated, uORF(chop)-driven reporter platform. Here we show that anisomycin-induced CHOP expression depends on phosphorylated eIF4E/S209 and eIF2alpha/S51. Contrary to phospho-eIF2alpha/S51, phospho-eIF4E/S209 is not involved in thapsigargin-induced CHOP expression. Studies using various kinase inhibitors and mutants uncovered that both the p38MAPK-Mnk and mTOR signaling pathways contribute to stress-responsive reporter and CHOP expression. We also demonstrated that anisomycin-induced translation is tightly regulated by partner binding preference of eIF4E. Furthermore, mutating the uORF sequence abolished the anisomycin-induced association of chop mRNA with phospho-eIF4E and polysomes, thus demonstrating the significance of this cis-regulatory element in conferring on the transcript a stress-responsive translational inducibility. Strikingly, although insulin treatment activated ERK-Mnk and mTOR pathways, and consequently eIF4E/S209 phosphorylation, it failed to induce phospho-eIF2alpha/S51 and reporter translation, thus pinpointing a crucial determinant in stress-responsive translation.
Chen
Yi-Jiun
YJ
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
Tan
Bertrand Chin-Ming
BC
Cheng
Ya-Yun
YY
Chen
Jin-Shin
JS
Lee
Sheng-Chung
SC
D000841:Anisomycin / Q000494:pharmacology; D002460:Cell Line; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D016366:Open Reading Frames; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D013312:Stress, Physiological / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases; D019284:Thapsigargin / Q000494:pharmacology; D051742:Transcription Factor CHOP / Q000096:biosynthesis / Q000235:genetics*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D015852:Eukaryotic Initiation Factor-2; D039561:Eukaryotic Initiation Factor-4E; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D051742:Transcription Factor CHOP; D019284:Thapsigargin; D000841:Anisomycin; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases