Activation of the phosphatidylinositol 3-kinase serine kinase by IFN-alpha.
During engagement of the type I IFN receptor, IRS-1 is phosphorylated on tyrosine and associates with the p85 regulatory subunit of the phosphatidylinositol (PI) 3'-kinase, which is a dual-specificity enzyme possessing both lipid and serine kinase activities. We sought to determine whether treatment of cells with IFN-alpha activates the PI 3'-kinase serine kinase. 32P-labeling experiments and phosphoaminoacid analysis of immunoprecipitated IRS-1 protein demonstrated that, in addition to tyrosine phosphorylation, IFN-alpha induces its phosphorylation on serine residues. In vitro kinase assays on alphaIRS-1 immunoprecipitates also demonstrated IFN-alpha-dependent serine phosphorylation of IRS-1, suggesting that the protein associates with an IFN-alpha-regulated serine kinase. Furthermore, IFN-alpha-dependent phosphorylation of IRS-1 was detected in in vitro kinase assays on alpha p85 immunoprecipitates, and was inhibited by pretreatment of cells with the specific PI 3'-kinase inhibitor wortmannin, consistent with a regulatory role of the PI 3'-kinase serine kinase on the phosphorylation of the protein. Treatment of cells with wortmannin also inhibited the phosphorylation of the p85 subunit of PI 3'-kinase and the type I IFN-regulated activation of the Map kinase, but had no inhibitory effect on the IFN-alpha-induced activation of Tyk-2 and Jak-1 kinases nor on the activation of Stat-1, Stat-2, and Stat-3. Taken all together, these data establish that the PI 3'-kinase serine kinase is activated by IFN-alpha and may play an important role in the transmission of type I IFN receptor-generated signals.
Uddin
S
S
Department of Medicine, University of Illinois at Chicago, 60607, USA.
Fish
E N
EN
Sher
D A
DA
Gardziola
C
C
White
M F
MF
Platanias
L C
LC
D000730:Androstadienes / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D015459:Leukemia-Lymphoma, Adult T-Cell; D009101:Multiple Myeloma; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation / Q000187:drug effects; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D016898:Interferon-alpha; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin