Insulin regulation of protein translation repressor 4E-BP1, an eIF4E-binding protein, in renal epithelial cells.
BACKGROUND
Augmented protein translation by insulin involves activation of eukaryotic initiation factor 4E (eIF4E) that follows release of eIF4E from a heterodimeric complex by phosphorylation of its inhibitory binding protein, 4E-BP1. We examined insulin regulation of 4E-BP1 phosphorylation in murine proximal tubular epithelial cells.


RESULTS
Insulin (1 nmol/L) increased de novo protein synthesis by 58 +/- 11% (P < 0.001). Insulin also augmented 4E-BP1 phosphorylation and phosphatidylinositol 3-kinase (PI 3-kinase) activity in antiphosphotyrosine immunoprecipitates. This could be prevented by PI 3-kinase inhibitors, Wortmannin, and LY294002. Insulin also activated Akt that lies downstream of PI 3-kinase. Rapamycin abrogated 4E-BP1 phosphorylation in response to insulin, suggesting involvement of mammalian target of rapamycin (mTOR), a kinase downstream of Akt. Insulin-stimulated phosphorylation of 4E-BP1 was also inhibited by PD098059, implying involvement of Erk-1/-2 mitogen-activated protein (MAP) kinase. An increase in Erk-1/-2 type MAP kinase activity by insulin was directly confirmed in an immunokinase assay and was found to be PI 3-kinase dependent.


CONCLUSIONS
In proximal tubular epithelial cells, insulin augments 4E-BP1 phosphorylation, which is PI 3-kinase and mTOR dependent. The requirement for Erk-1/-2 MAP kinase activation for 4E-BP1 phosphorylation by insulin suggests a cross-talk between PI 3-kinase and Erk-1/-2-type MAP kinase pathways.
Department of Medicine, University of Texas Health Science Center, San Antonio, Texas 78299-3900, USA.
B K
BK
Bhandari
D
D
Feliers
S
S
Duraisamy
J L
JL
Stewart
A C
AC
Gingras
H E
HE
Abboud
G G
GG
Choudhury
N
N
Sonenberg
B S
BS
Kasinath
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007328:Insulin / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007328:Insulin; D020928:Mitogen-Activated Protein Kinases; D010448:Peptide Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine; C499527:Eif4ebp1 protein, mouse; C546843:mTOR protein, mouse