Tumor Necrosis Factor α-induced Phosphorylation of Insulin Receptor Substrate-1 (IRS-1)

Abstract

Tumor necrosis factor-␣ (TNF) has been suggested to be the mediator of insulin resistance in infection, tumor cachexia, and obesity. We have previously shown that TNF diminishes insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1). The current work examines potential mechanisms that mediate this event. TNF effect on IRS-1 in Fao hepatoma cells was not associated with a significant reduction in insulin receptor tyrosine kinase activity as measured in vitro but impaired the association of IRS-1 with phosphatidylinositol 3-kinase, localizing TNF impact to IRS-1. TNF did not increase protein-tyrosine phosphatase activity and protein-tyrosine phosphatase inhibition by vanadate did not change TNF effect on IRS-1 tyrosine phosphorylation, suggesting that protein-tyrosine phosphatases are not involved in this TNF effect. In contrast, TNF increased IRS-1 phosphorylation on serine residues, leading to a decrease in its electrophoretic mobility. TNF effect on IRS-1 tyrosine phosphorylation was not abolished by inhibiting protein kinase C using staurosporine, while inactivation of Ser/Thr phosphatases by calyculin A and okadaic acid mimicked it. Our data suggest that TNF induces serine phosphorylation of IRS-1 through inhibition of serine phosphatases or activation of serine kinases other than protein kinase C. This increased serine phosphorylation interferes with insulin-induced tyrosine phosphorylation of IRS-1 and impairs insulin action.

Free fatty acid-induced muscle insulin resistance and glucose uptake dysfunction: Evidence for PKC activation and oxidative stress-activated signaling pathways

“…To test this hypothesis in our model, we applied the proteomic approach to study the key protein components involved in the C2C12 insulin resistance model, following FFA chronic treatment. We used the comparative proteomic analysis to screen for different kinases (75), phosphatases [27] and phosphosite proteins [31]. The phosphosite screen clearly showed a significant increase in the phosphorylation of PKCα (122%), PKCβ (631%), PKCδ (351%), and PKCε (698%) isoforms in cells treated with oleate but only alpha (80%) and delta (51%) in cells pretreated with palmitate.…”

“…PKC activation has been implicated in several studies of insulin resistance and diabetes and even in the absence of lipid oversupply [11,25,26]. The inhibitory effects of PKC on insulin signaling may at least in part be explained by the more recently identified role of the serine/ threonine phosphorylation of IRS-1, which has been implicated in the inhibition of its tyrosine phosphorylation [26,27].…”

Sphingomyelinase and Ceramide Stimulate the Expression of Inducible Nitric-oxide Synthase in Rat Primary Astrocytes

“…N GMethyl-L-arginine, FPT inhibitor II, and antibodies against mouse macrophage iNOS were obtained from Calbiochem. [␥- 32 Isolation and Maintenance of Astrocytes and C 6 Glial Cells-Astrocytes were prepared from rat cerebral tissue as described by McCarthy and DeVellis (14). Cells were maintained in DMEM/F-12 containing 10% fetal bovine serum.…”

Differential Regulation by Tumor Necrosis Factor-α of β1-, β2-, and β3-Adrenoreceptor Gene Expression in 3T3-F442A Adipocytes

“…Subsequent studies have indicated that, through the p55 TNF receptor (58), TNF-␣ can interfere with the insulin signaling pathway by impairing insulin-induced tyrosine phosphorylation of both the insulin receptor and insulin receptor substrate-1 (IRS-1) (59 -63). It has been shown that a serine phosphorylation of IRS-1 (64,65) converts this protein into an inhibitor of the insulin receptor tyrosine kinase activity. In contrast with these investigators, Stephens et al (66) have very recently suggested that the primary mechanism for TNF-␣-induced insulin resistance was rather the reduced mRNA transcription of several genes involved in the insulin-stimulated glucose transport.…”