IDENTIFICATION OF INTERLEUKIN-2 RECEPTOR-ASSOCIATED TYROSINE KINASE P116 AS NOVEL LEUKOCYTE-SPECIFIC JANUS KINASE

Janus tyrosine kinase (JAK) has recently been linked to signal transdu ction by cytokine receptors of the hematopoietin family. We have recen tly described a 116-kDa tyrosine kinase (p116) present in interleukin- 2 (IL-2) receptor complexes in human YT cells that showed functional c haracteristics of a JAK kinase. These included receptor association, r apid and transient tyrosine phosphorylation kinetics in response to li gand, and in vitro autophosphorylating tyrosine kinase activity (Kirke n, R. A., Rui, H., Evans, G. A., and Farrar, W. L. (1993) J. Biol. Che m. 268, 22765-22770). Here we extend these observations by demonstrati ng structural homologies between IL-2-modulated p116 and prolactin-mod ulated JAK2 in the rat T cell line Nb2. These include similar net char ge as determined by nonequilibrium pH gradient electrofocusing and rel ated primary structure based upon phosphopeptide mapping of V8 proteas e-digested hyperphosphorylated proteins. This putative JAK kinase unde rwent marked tyrosine phosphorylation in response to IL-2, IL-4, and I L-7, lymphoid growth factors that use the common IL-2 receptor gamma-c hain, but not in response to prolactin. Furthermore, polyclonal antise ra to JAK1, JAK2, or tyrosine kinase 2 did not recognize either rat or human p116. However, we identified the IL-2-modulated p116 as the rec ently cloned novel leukocyte Janus kinase, L-JAK, using an antiserum t o a peptide corresponding to the COOH terminus of human L-JAK.