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 β-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 β-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 β-cells to glucosamine resulted in reduction in glucose- and insulin-stimulated insulin biosynthesis, which in RIN β-cells was associated with impairment in insulin-stimulated insulin receptor substrate-1 (IRS-1) phosphorylation at Tyr608 and Tyr628, 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 β-cells exposed to high glucose exhibited increased c-Jun N-terminal kinase (JNK) and ERK1/2 activi...