JAK1 EXPRESSION IS REQUIRED FOR MEDIATING INTERLEUKIN-4 INDUCED TYROSINE PHOSPHORYLATION OF INSULIN-RECEPTOR SUBSTRATE AND STATE SIGNALING MOLECULES

The Jak1, Jak2, Jak8, and Fes tyrosine kinases have been demonstrated to undergo tyrosine phosphorylation in response to interleukin (IL)-4 stimulation in different cell systems. However, it is not clear which, if any, of these kinases are responsible for initiating IL-4-induced tyrosine phosphorylation of intracellular substrates in vivo, In the p resent study, we have utilized a mutant Jak1-deficient HeLa cell line, E1C3, and its parental Jakl-expressing counterpart, 1D4, to analyze t he role of Jak1 in mediating IL-8-induced tyrosine phosphorylation eve nts, IL-4 treatment rapidly induced tyrosine phosphorylation of insuli n receptor substrate (IRS)-1 and IRS-2 in 1D4 but not in E1C3 cells. I L-4-mediated tyrosine phosphorylation of State was pronounced in 1D4 c ells, while no IL-4-induced State phosphorylation was detected in E1C3 cells. IL-4 also induced State DNA binding activity from lysates of 1 D4 but not E1C3 cells utilizing a radiolabeled immunoglobulin heavy ch ain germline epsilon promotor sequence (I epsilon) in an electrophoret ic mobility shift assay, Reconstitution of Jak1 expression in E1C3 cel ls restored the ability of IL-4 to induce IRS and Stat6 tyrosine phosp horylation, These results provide evidence that Jak1 expression is req uired for mediating tyrosine phosphorylation and activation of crucial molecules involved in IL-4 signal transduction.