Common inhibitory serine sites phosphorylated by IRS-1 kinases, triggered by insulin and inducers of insulin resistance.
The Insulin Receptor Substrate (IRS) proteins are key players in insulin signal transduction and are the best studied targets of the insulin receptor. Ser/Thr phosphorylation of IRS proteins negatively modulates insulin signaling; therefore, the identification of IRS kinases and their target Ser phosphorylation sites is of physiological importance. Here we show that in Fao rat hepatoma cells, the IkappaB kinase beta (IKKbeta) is an IRS-1 kinase activated by selected inducers of insulin resistance, including sphingomyelinase, ceramide, and free fatty acids. Moreover, IKKbeta shares a repertoire of seven potential target sites on IRS-1 with protein kinase C zeta (PKCzeta), an IRS-1 kinase activated both by insulin and by inducers of insulin resistance. We further show that mutation of these seven sites (Ser-265, Ser-302, Ser-325, Ser-336, Ser-358, Ser-407, and Ser-408) confers protection from the action of IKKbeta and PKCzeta when they are overexpressed in Fao cells or primary hepatocytes. This enables the mutated IRS proteins to better propagate insulin signaling. These findings suggest that insulin-stimulated IRS kinases such as PKCzeta overlap with IRS kinases triggered by inducers of insulin resistance, such as IKKbeta, to phosphorylate IRS-1 on common Ser sites.
Herschkovitz
Avia
A
Department of Molecular Cell Biology, The Weizmann Institute of Science, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel.
Liu
Yan-Fang
YF
Department of Molecular Cell Biology, The Weizmann Institute of Science, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel.
Ilan
Erez
E
Institute of Biochemistry, Food Science, and Nutrition, Faculty of Agricultural, Food, and Environmental Quality, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel.
Ronen
Denise
D
Department of Molecular Cell Biology, The Weizmann Institute of Science, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel.
Boura-Halfon
Sigalit
S
Department of Molecular Cell Biology, The Weizmann Institute of Science, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel.
Zick
Yehiel
Y
Department of Molecular Cell Biology, The Weizmann Institute of Science, The Hebrew University of Jerusalem, P. O. Box 12, Rehovot 76100, Israel. Electronic address: yehiel.zick@weizmann.ac.il.
D000818:Animals; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D008297:Male; D010750:Phosphoproteins / Q000737:chemistry / Q000502:physiology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012694:Serine / Q000737:chemistry*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D000099221:Protein Kinase C zeta
D005230:Fatty Acids, Nonesterified; D051550:I-kappa B Kinase; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011493:Protein Kinase C; D012694:Serine; D013108:Sphingomyelin Phosphodiesterase; D000099221:Protein Kinase C zeta; C526292:IRS1 protein, human; C526296:Irs1 protein, rat