High glucose, high insulin, and their combination rapidly induce laminin-beta1 synthesis by regulation of mRNA translation in renal epithelial cells.
Laminin is a glycoprotein that contributes to renal extracellular matrix expansion in diabetes. We investigated regulation of laminin-beta1 synthesis in murine renal proximal tubular epithelial cells by 30 mmol/l glucose (high glucose), 1 nmol/l insulin (high insulin), and their combination (high glucose+high insulin), simulating conditions observed during progression of type 2 diabetes. Compared with 5 mmol/l glucose and no insulin (control), high glucose alone, high insulin alone, or high glucose+high insulin together increased laminin-beta1 chain protein synthesis within 5 min, lasting for up to 60 min with no change in laminin-beta1 mRNA levels. Cycloheximide, but not actinomycin-D, abrogated increased laminin-beta1 synthesis. High glucose, high insulin, and high glucose+high insulin stimulated phosphorylation of 4E-BP1, a repressor binding protein for eukaryotic initiation factor 4E (eIF4E), that was dependent on activation of phosphatidylinositol 3-kinase, Akt, and mammalian target of rapamycin. High glucose, high insulin, and high glucose+high insulin also promoted release of eIF4E from 4E-BP1, phosphorylation of eIF4E, and increase in eIF4E association with eIF4G, critical events in the initiation phase of mRNA translation. High glucose, high insulin, and high glucose+high insulin increased Erk phosphorylation, which is an upstream regulator of eIF4E phosphorylation, and PD098059, which is a MEK inhibitor that blocks Erk activation, abolished laminin-beta1 synthesis. This is the first demonstration of rapid increment in laminin-beta1 synthesis by regulation of its mRNA translation by cells exposed to high glucose, high insulin, or high glucose+high insulin.
Mariappan
Meenalakshmi M
MM
Department of Medicine, MC7882, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
Feliers
Denis
D
Mummidi
Srinivas
S
Choudhury
Goutam Ghosh
GG
Kasinath
Balakuntalam S
BS
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039642:Eukaryotic Initiation Factors; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology*; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D007684:Kidney Tubules / Q000166:cytology* / Q000378:metabolism; D007797:Laminin / Q000096:biosynthesis*; D051379:Mice; D010446:Peptide Fragments / Q000096:biosynthesis*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects*; D013997:Time Factors
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004338:Drug Combinations; C499527:Eif4ebp1 protein, mouse; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007328:Insulin; D007797:Laminin; D010446:Peptide Fragments; D010750:Phosphoproteins; C459079:laminin beta1 (925-933); D048049:Extracellular Signal-Regulated MAP Kinases; D005947:Glucose