CYTOKINE-MEDIATED PROTEIN-KINASE-C ACTIVATION IS A SIGNAL FOR LINEAGEDETERMINATION IN BIPOTENTIAL GRANULOCYTE-MACROPHAGE COLONY-FORMING CELLS

Granulocyte macrophage colony-forming cells (GM-CFC) have the potentia l to develop into either macrophages and/or neutrophils. With a highly enriched population of these cells we have found that although GM-CFC are equally responsive to macrophage colony stimulating factor (M-CSF ) and stem cell factor (SCF) in terms of DNA synthesis, M-CSF stimulat ed the development of colonies containing macrophages in soft gel assa ys, while SCF promoted neutrophilic colony formation. When SCF and M-C SF were combined, mainly macrophage development was stimulated both in soft agar colony-forming assays and liquid cultures. An analysis of s ome potential signaling mechanisms associated with cytokine-mediated d evelopmental decisions in GM-CFC revealed that M-CSF, but not SCF, was able to chronically stimulate phosphatidylcholine breakdown and diacy lglycerol production, indicating that protein kinase C (PKC) may be in volved in the action of M-CSF Furthermore, M-CSF, but not SCF, can inc rease the levels of PKC alpha (PKC alpha) expression and stimulate the translocation of PKC alpha to the nucleus. When the PKC inhibitor, ca lphostin C, was added to GM-CFC cultured in M-CSF then predominantly n eutrophils were produced, conversely PKC activators added with SCF sti mulated macrophage development. The data indicate a role for PKC in M- CSF-simulated macrophage development from GM-CFC.