Activation of mRNA translation in rat cardiac myocytes by insulin involves multiple rapamycin-sensitive steps.
Insulin acutely activates protein synthesis in ventricular cardiomyocytes from adult rats. In this study, we have established the methodology for studying the regulation of the signaling pathways and translation factors that may be involved in this response and have examined the effects of acute insulin treatment on them. Insulin rapidly activated the 70-kDa ribosomal S6 kinase (p70 S6k), and this effect was inhibited both by rapamycin and by inhibitors of phosphatidylinositol 3-kinase. The activation of p70 S6k is mediated by a signaling pathway involving the mammalian target of rapamycin (mTOR), which also modulates other translation factors. These include the eukaryotic initiation factor (eIF) 4E binding proteins (4E-BPs) and eukaryotic elongation factor 2 (eEF2). Insulin caused phosphorylation of 4E-BP1 and induced its dissociation from eIF4E, and these effects were also blocked by rapamycin. Concomitant with this, insulin increased the binding of eIF4E to eIF4G. Insulin also activated protein kinase B (PKB), which may lie upstream of p70 S6k and 4E-BP1, with the activation of the different isoforms being in the order alpha>beta>gamma. Insulin also caused inhibition of glycogen synthase kinase 3, which lies downstream of PKB, and of eEF2 kinase. The phosphorylation of eEF2 itself was also decreased by insulin, and this effect and the inactivation of eEF2 kinase were attenuated by rapamycin. The activation of overall protein synthesis by insulin in cardiomyocytes was substantially inhibited by rapamycin (but not by inhibitors of other specific signaling pathways, e.g., mitogen-activated protein kinase), showing that signaling events linked to mTOR play a major role in the control of translation by insulin in this cell type.
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Department of Anatomy and Physiology, Medical Sciences Institute, University of Dundee, Dundee DD1 5EH, United Kingdom.
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D000367:Age Factors; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002352:Carrier Proteins; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D039561:Eukaryotic Initiation Factor-4E; D005419:Flavonoids / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D008715:Methionine / Q000378:metabolism / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D020652:Peptide Elongation Factor 2 / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism; D010649:Phenylalanine / Q000378:metabolism / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology*; D013462:Sulfur Radioisotopes; D014316:Tritium
D002352:Carrier Proteins; D002867:Chromones; C499526:Eif4ebp1 protein, rat; D004791:Enzyme Inhibitors; D039561:Eukaryotic Initiation Factor-4E; D005419:Flavonoids; D007004:Hypoglycemic Agents; D007166:Immunosuppressive Agents; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D020652:Peptide Elongation Factor 2; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D013462:Sulfur Radioisotopes; D014316:Tritium; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D010649:Phenylalanine; D008715:Methionine; D038341:Glycogen Synthase Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus