Interferon-dependent activation of the serine kinase PI 3'-kinase requires engagement of the IRS pathway but not the Stat pathway.
Several signaling pathways are activated by interferon alpha (IFNalpha) in hematopoietic cells, including the Jak-Stat and the insulin receptor substrate (IRS) pathways. It has been previously shown that IFNalpha activates the phosphatidylinositol (PI) 3'-kinase via an interaction of the p85 subunit of PI 3'-kinase with IRS proteins. Other studies have proposed that Stat-3 also functions as an adapter for p85. We sought to identify the major pathway that regulates IFNalpha activation of the PI3'-kinase in hematopoietic cells. Our data demonstrate that IFNalpha induces the interaction of p85 with IRS-1 or IRS-2, but not Stat-3, in various hematopoietic cell lines in which IRS-1 and/or IRS-2 and Stat-3 are activated by IFNalpha. In addition, inhibition of PI 3'-kinase activity by preincubation of cells with the PI 3'-kinase inhibitor LY294002 does not affect IFN-dependent formation of SIF complexes that contain Stat-3. To determine whether phosphorylation of tyrosine residues in the IFN receptor is required for activation of the PI 3'-kinase, we performed studies using mouse L929 fibroblasts transfected with mutated human IFNAR1 and/or IFNAR2 subunits of the Type I IFN receptor, lacking tyrosine phosphorylation sites. The serine kinase activity of the PI-3K was activated by human IFNalpha in these cells, suggesting that phosphorylation of the Type I IFN receptor is not essential for PI3K activation. We then determined whether IFNalpha activates the Akt kinase, a known downstream target for PI 3'-kinase that mediates anti-apoptotic signals. Akt was activated by insulin or IGF-1, but not IFNalpha, in the IFNalpha-sensitive U-266 myeloma cell line. Altogether, our data establish that the IRS pathway and not the Stat pathway, is the major pathway regulating engagement of PI 3'-kinase in hematopoietic cells. Furthermore, the selective activation of Akt by insulin/IGF-1 suggests the existence of distinct regulatory activities of PI3'-kinase in growth factor versus interferon signaling.
Uddin
S
S
Section of Hematology-Oncology, University of Illinois at Chicago, Chicago, Illinois 60607-7173, USA.
Majchrzak
B
B
Wang
P C
PC
Modi
S
S
Khan
M K
MK
Fish
E N
EN
Platanias
L C
LC
D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D016898:Interferon-alpha / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D053633:Receptor, Interferon alpha-beta; D017471:Receptors, Interferon / Q000378:metabolism*; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism
D004268:DNA-Binding Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D016898:Interferon-alpha; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D053633:Receptor, Interferon alpha-beta; D017471:Receptors, Interferon; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; C507964:IFNAR1 protein, human; C508033:IFNAR2 protein, human; C526297:IRS2 protein, human; C508032:Ifnar1 protein, mouse; C508034:Ifnar2 protein, mouse; C526298:Irs2 protein, mouse; C494086:STAT3 protein, human; C494918:AKT1 protein, human