Expression and chromosomal assignment of a novel protein-tyrosine kinase gene related to the insulin receptor family.

There is growing evidence in recent literature for the involvement of protein-tyrosine phosphorylation in the early events of leukocyte activation. Interleukin-3 (IL-3), a growth factor essential for the growth of hematopoietic stem cells, myeloid cells, and possibly early lymphoid cells induces rapid phosphorylation of several cellular proteins in different IL-3-dependent cells (B. Isfort and J. Ihle, personal communication; [1]). One of the early events in T-cell activation is the tyrosine phosphorylation of a component of the T-cell antigen receptor [2]. Macrophage proliferation in response to M -CSF is mediated through the activation of the tyrosine kinase moiety of its receptor, the c-fms proto-oncogene [3). The protein-tyrosine kinases described to date are either transmembrane proteins having an extracellular ligand binding domain [3 8] or cytoplasmic proteins related to the v-src oncogene [911]. Most of these proteins are expressed in a wide variety of cells and tissues; few are tissue specific [12]. Previous studies have suggested that lymphokines may mediate hematopoietic cell survival via