Vascular endothelial growth factor induces protein synthesis in renal epithelial cells: a potential role in diabetic nephropathy.
BACKGROUND
Vascular endothelial growth factor (VEGF) is an important determinant of ocular complications of diabetes. Its potential role in diabetic renal disease has not been extensively studied.


METHODS
We employed mice with streptozotocin-induced type 1 diabetes and db/db mice with type 2 diabetes to study the regulation of renal VEGF. Studies of VEGF regulation of protein synthesis were performed using proximal tubular epithelial (MCT) cells in culture.


RESULTS
A nearly three-fold increase of VEGF165 expression in the renal cortex was seen, coinciding with renal hypertrophy in mice with either type 1 or type 2 diabetes. VEGF increased de novo protein synthesis and induced significant hypertrophy in MCT cells. VEGF stimulation of protein synthesis was dependent on tyrosine phosphorylation of the type 2 VEGF receptor and phosphatidylinositol 3-kinase (PI 3-kinase) activity. Activity of Akt was increased two- to three-fold by VEGF. Expression of dominant-negative Akt showed that Akt activation was also needed for VEGF-induced protein synthesis and cell hypertrophy. As PI 3-kinase-Akt axis regulates initial events in protein translation, these events were examined in the context of VEGF regulation of protein synthesis. VEGF stimulated eukaryotic initiation factor 4E-binding protein (4E-BP1) phosphorylation, which was dependent on activation of PI 3-kinase and Akt. Stable transfection with 4E-BP1 Thr37,46-Ala37,46 mutant abolished the VEGF-induced de novo protein synthesis and cell hypertrophy.


CONCLUSIONS
VEGF augments protein synthesis and induces hypertrophy in MCT cells in a PI 3-kinase- and Akt-dependent manner. Phosphorylation of Thr37,46 in 4E-BP1 is required for VEGF-induced protein synthesis and hypertrophy in MCT cells. These data suggest a role for VEGF in the pathogenesis of diabetic renal disease.
Senthil
Duraisamy
D
South Texas Veterans' Health Care System and Department of Medicine, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Choudhury
Goutam Ghosh
GG
McLaurin
Colby
C
Kasinath
Balakuntalam S
BS
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism* / Q000473:pathology; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism* / Q000473:pathology; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D039642:Eukaryotic Initiation Factors; D006984:Hypertrophy; D007668:Kidney / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D042461:Vascular Endothelial Growth Factor A; C499527:Eif4ebp1 protein, mouse