AN ACTIVATED PROTEIN-KINASE-C-ALPHA GIVES A DIFFERENTIATION SIGNAL FOR HEMATOPOIETIC PROGENITOR CELLS AND MIMICS MACROPHAGE-COLONY-STIMULATING FACTOR-STIMULATED SIGNALING EVENTS

Highly enriched, bipotent, hematopoietic granulocyte macrophage colony -forming cells (GM-CFC) require cytokines for their survival, prolifer ation, and development. GM-CFC will form neutrophils in the presence o f the cytokines stem cell factor and granulocyte colony-stimulating fa ctor, whereas macrophage colony-stimulating factor leads to macrophage formation, Previously, we have shown that the commitment to the macro phage lineage is associated with lipid hydrolysis and translocation of protein kinase C alpha (PKC alpha) to the nucleus. Here we have trans fected freshly prepared GM-CFC with a constitutively activated form of PKC alpha, namely PKAC, in which the regulatory domain has been trunc ated. Greater than 95% of the transfected cells showed over a twofold increase in PKC alpha expression with the protein being located primar ily within the nucleus. The expression of PKAC caused macrophage devel opment even in the presence of stimuli that normally promote only neut rophilic development. Thus, M-CSF-stimulated translocation of PKC alph a to the nucleus is a signal associated with macrophage development in primary mammalian hematopoietic progenitor cells, and this signal can be mimicked by ectopic PKAC, which is also expressed in the nucleus.