Insulin regulation of protein translation repressor 4E-BP1, an eIF4E-binding protein, in renal epithelial cells

Kidney Int. 2001 Mar;59(3):866-75. doi: 10.1046/j.1523-1755.2001.059003866.x.

Abstract

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.

Methods and 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carrier Proteins / metabolism
  • Cell Cycle Proteins
  • Cells, Cultured
  • Epithelial Cells / metabolism
  • Eukaryotic Initiation Factor-4E
  • Eukaryotic Initiation Factors
  • Insulin / pharmacology*
  • Kidney Tubules, Proximal / cytology
  • Kidney Tubules, Proximal / metabolism*
  • Mice
  • Mitogen-Activated Protein Kinases / metabolism
  • Peptide Initiation Factors / metabolism
  • Phosphatidylinositol 3-Kinases / physiology
  • Phosphoproteins / metabolism*
  • Phosphoproteins / physiology
  • Phosphorylation
  • Protein Biosynthesis
  • Protein Kinases / physiology
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / physiology
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • Tyrosine / metabolism

Substances

  • Carrier Proteins
  • Cell Cycle Proteins
  • Eif4ebp1 protein, mouse
  • Eukaryotic Initiation Factor-4E
  • Eukaryotic Initiation Factors
  • Insulin
  • Peptide Initiation Factors
  • Phosphoproteins
  • Proto-Oncogene Proteins
  • Tyrosine
  • Protein Kinases
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases