Abstract
Insulin receptor substrate-2 (IRS-2) plays a critical role in the survival and function of pancreatic β-cells. Gene disruption of IRS-2 results in failure of the β-cell compensatory mechanism and diabetes. Nonetheless, the regulation of IRS-2 protein expression in β-cells remains largely unknown. Inducible nitric-oxide synthase (iNOS), a major mediator of inflammation, has been implicated in β-cell damage in type 1 and type 2 diabetes. The effects of iNOS on IRS-2 expression have not yet been investigated in β-cells. Here, we show that iNOS and NO donor decreased IRS-2 protein expression in INS-1/832 insulinoma cells and mouse islets, whereas IRS-2 mRNA levels were not altered. Interleukin-1β (IL-1β), alone or in combination with interferon-γ (IFN-γ), reduced IRS-2 protein expression in an iNOS-dependent manner without altering IRS-2 mRNA levels. Proteasome inhibitors, MG132 and lactacystin, blocked the NO donor-induced reduction in IRS-2 protein expression. Treatment with NO donor led to activation of glycogen synthase kinase-3β (GSK-3β) and c-Jun N-terminal kinase (JNK/SAPK) in β-cells. Inhibition of GSK-3β by pharmacological inhibitors or siRNA-mediated knockdown significantly prevented NO donor-induced reduction in IRS-2 expression in β-cells. In contrast, a JNK inhibitor, SP600125, did not effectively block reduced IRS-2 expression in NO donor-treated β-cells. These data indicate that iNOS-derived NO reduces IRS-2 expression by promoting protein degradation, at least in part, through a GSK-3β-dependent mechanism. Our findings suggest that iNOS-mediated decreased IRS-2 expression may contribute to the progression and/or exacerbation of β-cell failure in diabetes.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Acetylcysteine / analogs & derivatives
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Acetylcysteine / pharmacology
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Animals
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Anthracenes / pharmacology
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Cell Line, Tumor
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Cysteine Proteinase Inhibitors / pharmacology
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Enzyme Activation / drug effects
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Enzyme Activation / physiology
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Gene Expression Regulation / drug effects
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Gene Expression Regulation / physiology*
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Glycogen Synthase Kinase 3 / antagonists & inhibitors
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Glycogen Synthase Kinase 3 / genetics
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Glycogen Synthase Kinase 3 / metabolism*
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Glycogen Synthase Kinase 3 beta
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Humans
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Insulin Receptor Substrate Proteins / biosynthesis*
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Insulin Receptor Substrate Proteins / genetics
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Insulin-Secreting Cells / cytology
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Insulin-Secreting Cells / metabolism*
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Interferon-gamma / genetics
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Interferon-gamma / metabolism
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Interleukin-1beta / genetics
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Interleukin-1beta / metabolism
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JNK Mitogen-Activated Protein Kinases / antagonists & inhibitors
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JNK Mitogen-Activated Protein Kinases / genetics
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JNK Mitogen-Activated Protein Kinases / metabolism
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Leupeptins / pharmacology
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Mice
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Nitric Oxide Donors / pharmacology*
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Nitric Oxide Synthase Type II / genetics
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Nitric Oxide Synthase Type II / metabolism*
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Proteasome Endopeptidase Complex / genetics
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Proteasome Endopeptidase Complex / metabolism*
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Proteasome Inhibitors
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Rats
Substances
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Anthracenes
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Cysteine Proteinase Inhibitors
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IRS2 protein, human
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Insulin Receptor Substrate Proteins
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Interleukin-1beta
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Irs2 protein, mouse
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Irs2 protein, rat
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Leupeptins
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Nitric Oxide Donors
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Proteasome Inhibitors
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lactacystin
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pyrazolanthrone
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Interferon-gamma
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NOS2 protein, human
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Nitric Oxide Synthase Type II
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Nos2 protein, mouse
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Nos2 protein, rat
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GSK3B protein, human
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Glycogen Synthase Kinase 3 beta
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Gsk3b protein, mouse
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Gsk3b protein, rat
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JNK Mitogen-Activated Protein Kinases
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Glycogen Synthase Kinase 3
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Proteasome Endopeptidase Complex
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benzyloxycarbonylleucyl-leucyl-leucine aldehyde
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Acetylcysteine