Stimulation of protein synthesis, eukaryotic translation initiation factor 4E phosphorylation, and PHAS-I phosphorylation by insulin requires insulin receptor substrate 1 and phosphatidylinositol 3-kinase.
Insulin rapidly stimulates protein synthesis in a wide variety of tissues. This stimulation is associated with phosphorylation of several translational initiation and elongation factors, but little is known about the signaling pathways to these events. To study these pathways, we have used a myeloid progenitor cell line (32D) which is dependent on interleukin 3 but insensitive to insulin because of the very low levels of insulin receptor (IR) and the complete lack of insulin receptor substrate (IRS)-signaling proteins (IRS-1 and IRS-2). Expression of more IR permits partial stimulation of mitogen-activated protein kinase by insulin, and expression of IRS-1 alone mediates insulin stimulation of the 70-kDa S6 kinase (pp70S6K) by the endogenous IR. However, expression of both IR and IRS-1 is required for stimulation of protein synthesis. Moreover, this effect requires activation of phosphatidylinositol 3-kinase (PI3K), as determined by wortmannin inhibition and the use of an IRS-1 variant lacking all Tyr residues except those which activate PI3K. Stimulation of general protein synthesis does not involve activation by IRS-1 of GRB-2-SOS-p21ras or SH-PTP2, since IRS-1 variants lacking the SH2-binding Tyr residues for these proteins are fully active. Nor does it involve pp70S6K, since rapamycin, while strongly inhibiting the synthesis of a small subset of growth-regulated proteins, only slightly inhibits total protein synthesis. Recruitment of mRNAs to the ribosome is enhanced by phosphorylation of eIF4E, the cap-binding protein, and PHAS-I, a protein that specifically binds eIF4E. The behavior of cell lines containing IRS-1 variants and inhibition by wortmannin and rapamycin indicate that the phosphorylation of both proteins requires IRS-1-mediated stimulation of PI3K and pp70S6K but not mitogen-activated protein kinase or SH-PTP2.
Mèndez
R
R
Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, Shreveport 71130, USA.
Myers
M G
MG
White
M F
MF
Rhoads
R E
RE
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D039561:Eukaryotic Initiation Factor-4E; D051380:GRB2 Adaptor Protein; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010448:Peptide Initiation Factors / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases
D048868:Adaptor Proteins, Signal Transducing; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D051380:GRB2 Adaptor Protein; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010448:Peptide Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D011506:Proteins; D012333:RNA, Messenger; D011972:Receptor, Insulin; D019893:Ribosomal Protein S6 Kinases; C087000:EIF4EBP1 protein, human; C495948:GRB2 protein, human; C526292:IRS1 protein, human; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human