Tyrosine 966 of jak2 interacts with multiple proteins implicated in mitogenic signaling

Janus kinases (Jaks) play critical roles in transducing growth and differentiation signals from the ligand activated cytokine receptor complex to the cell nucleus. Studies in a variety of cytokine receptor systems show the correlation between the activation of Jak kinases and cell proliferation. We found that tyrosine 966 of Jak2, which is conserved among all four Jak family members, may be responsible for interaction with and activation of downstream proteins that were involved in mitogenic signaling. Mutation of Y966 into phenylalanine in the framework of a EGFR-Jak2 chimeric resulted in diminished level of EGF-induced c-Myc and pim-1 expression, as compared to the wild type chimeric in 32D cells. A synthetic phosphopeptide corresponding to sequence around Y966 could pull down several proteins that are known to be involved in cytokine signaling, whereas the nonphosphopeptide of the same sequence could not. They included PLCyl, PLC-y2, StatS, She, HCP, Pyruvate Kinase and several unknown proteins. Our results suggest that Jak kinase may directly interact with and phosphorylate some of these proteins. Once activated by tyrosine phosphorylation, they may contribute to the mitogenic responses induced by cytokines.