Rajendra V. Deshpande

GRANULOCYTE COLONY-STIMULATING FACTOR-INDUCED ACTIVATION OF PROTEIN KINASE-C IN MYELOID CELLS

Granulocyte colony stimulating factor (G‐CSF) regulates survival, proliferation, differentiation, and activation of myeloid cells. It binds to a high affinity receptor (G‐CSF‐R) expressed on myeloid cells, for which the signal transduction mechanisms other than protein tyrosine kinase (PTK) activation have not been completely identified. We explored the potential involvement of protein kinase‐C (PKC) in G‐CSF‐R signal transduction. In this report, we provide direct evidence of PKC activation by G‐CSF‐R. G‐CSF treatment of peripheral blood neutrophils, granulocytic cell lines (HL‐60, NFS‐60, KG‐1), and monocytic cell lines (WEHI‐3B,U‐937) resulted in PKC activation. Chelerythrine chloride and HA‐100, an isoquinolinesulfonamide derivative, the specific inhibitors of PKC, 1,2‐Bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetra‐acetic acid (BAPTA), a chelator of intracellular calcium, and 3,4,5‐trimethoxybenzoic acid 8‐(diethylamino)‐octyl ester (TMB‐8), an inhibitor of intracellular calcium release, blocked G‐CSF‐induced PKC activation in HL‐60 cells, and reduced CD11b upregulation in neutrophils, but did not affect ligand‐binding or down‐modulation of G‐CSF‐R. Methyl 2,5‐dihydroxycinnamate (MDHC), a potent inhibitor of protein tyrosine kinases (PTK), also inhibited PKC activation in response to G‐CSF treatment, suggesting that PKC activation may occur downstream of PTK activation. Our results demonstrate the involvement of PKC in G‐CSF‐R signal transduction, and suggest a common signaling pathway in myeloid cells of granulocytic and monocytic lineages. J. Cell. Biochem. 66:286–296, 1997.