The Bmx tyrosine kinase is activated by IL-3 and G-CSF in a PI-3K dependent manner

Cytoplasmic protein tyrosine kinases play crucial roles in signaling, ia a variety of cell surface receptors, The Bmx tyrosine kinase, a member of the Tec family, is expressed in hematopoietic cells of the granulocytic and monocytic lineages. Here we show that Bmx is catalytically activated by interleukin-3 (IL-3) and granulocyte-colony stimulating factor (G-CSF) receptors, Activation of Ems required phosphatidylinositol 3-kinase (PI-3K) as demonstrated by the ability of PI-3K inhibitors to block the activation signal. A green fluorescent protein (GFP) tagged Bmx nas translocated to cellular membranes upon co-expression of a constitutively active form of PI-3K, further indicating a role for PI-3K in signaling upstream of Ems. The expression of wild type Bmx in 32D myeloid progenitor cells resulted in apoptosis in the presence of G-CSF, while cells expressing a kinase dead mutant of Bmx differentiated into mature granulocytes. However, Bmx did not modulate IL-3-dependent proliferation of the cells. These results demonstrate distinct effects of Ems in cytokine induced proliferation and differentiation of myeloid cells, and suggest that the stage specific expression of Ems is critical for the differentiation of myeloid cells.