Insulin resistance contributes importantly to the pathophysiology of type 2 diabetes mellitus. One mechanism mediating insulin resistance may involve the phosphorylation of serine residues in insulin receptor substrate-1 (IRS-1), leading to impairment in the ability of IRS-1 to activate downstream phosphatidylinositol 3-kinase-dependent pathways. Insulin-resistant states and serine phosphorylation of IRS-1 are associated with the activation of the inhibitor kappaB kinase (IKK) complex. However, the precise molecular mechanisms by which IKK may contribute to the development of insulin resistance are not well understood. In this study, using phosphospecific antibodies against rat IRS-1 phosphorylated at Ser(307) (equivalent to Ser(312) in human IRS-1), we observed serine phosphorylation of IRS-1 in response to TNF-alpha or calyculin A treatment that paralleled surrogate markers for IKK activation. The phosphorylation of human IRS-1 at Ser(312) in response to tumor necrosis factor-alpha was significantly reduced in cells pretreated with the IKK inhibitor 15 deoxy-prostaglandin J(2) as well as in cells derived from IKK knock-out mice. We observed interactions between endogenous IRS-1 and IKK in intact cells using a co-immunoprecipitation approach. Moreover, this interaction between IRS-1 and IKK in the basal state was reduced upon IKK activation and increased serine phosphorylation of IRS-1. Data from in vitro kinase assays using recombinant IRS-1 as a substrate were consistent with the ability of IRS-1 to function as a direct substrate for IKK with multiple serine phosphorylation sites in addition to Ser(312). Taken together, our data suggest that IRS-1 is a novel direct substrate for IKK and that phosphorylation of IRS-1 at Ser(312) (and other sites) by IKK may contribute to the insulin resistance mediated by activation of inflammatory pathways.
We have not found any resources mentioned in this publication.
SciCrunch® is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch® will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to SciCrunch®, however this is not currently a free service.