Inducible nitric-oxide synthase and NO donor induce insulin receptor substrate-1 degradation in skeletal muscle cells.
Chronic inflammation plays an important role in insulin resistance. Inducible nitric-oxide synthase (iNOS), a mediator of inflammation, has been implicated in many human diseases including insulin resistance. However, the molecular mechanisms by which iNOS mediates insulin resistance remain largely unknown. Here we demonstrate that exposure to NO donor or iNOS transfection reduced insulin receptor substrate (IRS)-1 protein expression without altering the mRNA level in cultured skeletal muscle cells. NO donor increased IRS-1 ubiquitination, and proteasome inhibitors blocked NO donor-induced reduction in IRS-1 expression in cultured skeletal muscle cells. The effect of NO donor on IRS-1 expression was cGMP-independent and accentuated by concomitant oxidative stress, suggesting an involvement of nitrosative stress. Inhibitors for phosphatidylinositol-3 kinase, mammalian target of rapamycin, and c-Jun amino-terminal kinase failed to block NO donor-induced IRS-1 reduction, whereas these inhibitors prevented insulin-stimulated IRS-1 decrease. Moreover iNOS expression was increased in skeletal muscle of diabetic (ob/ob) mice compared with lean wild-type mice. iNOS gene disruption or treatment with iNOS inhibitor ameliorated depressed IRS-1 expression in skeletal muscle of diabetic (ob/ob) mice. These findings indicate that iNOS reduces IRS-1 expression in skeletal muscle via proteasome-mediated degradation and thereby may contribute to obesity-related insulin resistance.
Sugita
Hiroki
H
Department of Anesthesia and Critical Care, Massachusetts General Hospital, Shriners Hospital for Children, Harvard Medical School, Boston, Massachusetts 02129, USA.
Fujimoto
Masaki
M
Yasukawa
Takashi
T
Shimizu
Nobuyuki
N
Sugita
Michiko
M
Yasuhara
Shingo
S
Martyn
J A Jeevendra
JA
Kaneki
Masao
M
D000818:Animals; D002460:Cell Line; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D032342:Muscle Cells / Q000166:cytology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D020030:Nitric Oxide Donors; D010750:Phosphoproteins; D025801:Ubiquitin; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D019869:Phosphatidylinositol 3-Kinases; D046988:Proteasome Endopeptidase Complex