Activation of the hexosamine pathway leads to phosphorylation of insulin receptor substrate-1 on Ser307 and Ser612 and impairs the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin insulin biosynthetic pathway in RIN pancreatic beta-cells.
Many adverse effects of glucose were attributed to its increased routing through the hexosamine pathway (HBP). There is evidence for an autocrine role of the insulin signaling in beta-cell function. We tested the hypothesis that activation of the HBP induces defects in insulin biosynthesis by affecting the insulin-mediated protein translation signaling. Exposure of human pancreatic islets and RIN beta-cells to glucosamine resulted in reduction in glucose- and insulin-stimulated insulin biosynthesis, which in RIN beta-cells was associated with impairment in insulin-stimulated insulin receptor substrate-1 (IRS-1) phosphorylation at Tyr(608) and Tyr(628), which are essential for engaging phosphatidylinositol 3-kinase (PI 3-kinase). These changes were accompanied by impaired activation of PI 3-kinase, and activation of Akt/mammalian target of rapamycin/phosphorylated heat- and acid-stable protein-1/p70S6 kinase pathway. RIN beta-cells exposed to high glucose exhibited increased c-Jun N-terminal kinase (JNK) and ERK1/2 activity, which was associated with increased IRS-1 phosphorylation at serine (Ser)(307) and Ser(612), respectively, that inhibits coupling of IRS-1 to the insulin receptor and is upstream of the inhibition of IRS-1 tyrosine phosphorylation. Azaserine reverted the stimulatory effects of high glucose on JNK and ERK1/2 activity and IRS-1 phosphorylation at Ser(307) and Ser(612). Glucosamine mimicked the stimulatory effects of high glucose on JNK and ERK1/2 activity and IRS-1 phosphorylation at Ser(307) and Ser(612). Inhibition of JNK and MAPK kinase-1 activity reverted the negative effects of glucosamine on insulin-mediated protein synthesis. These results suggest that activation of the HBP accounts, in part, for glucose-induced phosphorylation at Ser(307) and Ser(612) of IRS-1 mediated by JNK and ERK1/2, respectively. These changes result in impaired coupling of IRS-1 and PI 3-kinase, and activation of the Akt/mammalian target of rapamycin/phosphorylated heat- and acid-stable protein-1/p70S6 kinase pathway.
Dipartimento di Medicina Sperimentale e Clinica, Università di Catanzaro-Magna Graecia, Via Tommaso Campanella, 115, 88100 Catanzaro, Italy.
Francesco
F
Andreozzi
Cristina
C
D'Alessandris
Massimo
M
Federici
Emanuela
E
Laratta
Silvia
S
Del Guerra
Stefano
S
Del Prato
Piero
P
Marchetti
Renato
R
Lauro
Francesco
F
Perticone
Giorgio
G
Sesti
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005944:Glucosamine / Q000494:pharmacology; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology; D006595:Hexosamines / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000096:biosynthesis / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007515:Islets of Langerhans / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis* / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000502:physiology; D011494:Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics; D012694:Serine / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005944:Glucosamine; D005947:Glucose; D006595:Hexosamines; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D012694:Serine; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine; C087000:EIF4EBP1 protein, human; C499526:Eif4ebp1 protein, rat; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C546842:MTOR protein, human; C546845:mTOR protein, rat; C494918:AKT1 protein, human; C494920:Akt1 protein, rat