Hormones – Cytokines – Signalling
Kidney International (2001) 59, 866–875; doi:10.1046/j.1523-1755.2001.059003866.x
Insulin regulation of protein translation repressor 4E-BP1, an eIF4E-binding protein, in renal epithelial cells
Basant K Bhandari, Denis Feliers, Senthil Duraisamy, Jennifer L Stewart, Anne-Claude Gingras, Hanna E Abboud, Goutam Ghosh Choudhury, Nahum Sonenberg and Balakuntalam S Kasinath
Department of Medicine, University of Texas Health Science Center, and GRECC, South Texas Veterans Health Care System, San Antonio, Texas, USA; and Department of Biochemistry, McGill Cancer Center, McGill University, Montreal, Quebec, Canada
Correspondence: B. S. Kasinath, M.D., Division of Nephrology, Mail code 7882, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA. E-mail: kasinath@uthscsa.edu
Received 2 May 2000; Revised 6 September 2000; Accepted 28 September 2000.
Abstract
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.
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.
Keywords:
cell signaling, eukaryotic initiation factor 4E binding protein-1, tubular epithelial cells, MAP kinase, protein synthesis, type 2 diabetes, proximal tubule cell
Abbreviations:
ATP, adenosine 5'-triphosphate; 4E-BP1, 4E binding protein-1; eIF4E, eukaryotic initiation factor 4E; FKBP, FK binding protein; FRAP, FKBP12 and rapamycin associated protein; IRS, insulin receptor substrate; MAP kinase, mitogen-activated protein kinase; MBP, myelin basic protein; mTOR, mammalian target of rapamycin; PHAS, phosphorylated heat and acid stable protein; PI 3-kinase, phosphatidylinositol 3-kinase; PIK, phosphoinositide kinase related; PTE, proximal tubule epithelial; RAFT1, rapamycin and 12-kD FK506 binding protein target-1; TBST, Tris buffered saline containing Tween 20; UTR, untranslated region
