Protein tyrosine kinases in granulocyte colony stimulating factor receptor signal transduction, myeloid cell proliferation, and neutrophil activation

Granulocyte colony-stimulating factor (G-CSF) plays an important role in the growth and maturation of granulocytic precursor cells. Although the interaction between G-CSF and its receptor (G-CSF-R) is an obligatory event during proliferation and differentiation of myeloid cells, the signal transduction mechanisms leading to these effects are not completely known. We investigated the kinetics of protein tyrosine kinase (PTK) activation in G-CSF-R signal transduction in myeloid leukemic cell lines and peripheral blood neutrophils. G-CSF treatment of myeloid cell-lines (HL-60, KG-1, NFS-60) and neutrophils resulted in a rapid increase in PTK activity. This induction was inhibited by an anti-G-CSF monoclonal antibody and various PTK-specific inhibitors. PTK activity was important for proliferation of myeloid cells; its inhibition resulted in decreased proliferation and clonogenicity of these cells. PTK-induction was not involved in G-CSF-R expression, internalization or recycling, but was partially responsible for up-regulation of CD11b expression on neutrophils. In contrast to neutrophilic cell-lines, the myelo-monocytic cell lines (U-937, WEHI-3B) showed no change in PTK levels in response to G-CSF. The results indicate that the G-CSF-R-mediated PTK up-regulation may be a neutrophil-lineage-restricted signal, and that PTK may play an important role in the proliferation of neutrophil-precursors and functional activation of mature neutrophils.