Retinoic Acid-Specific Induction of a Protein Kinase C Isoform during Differentiation of HL-60 Cells

Human promyelocytic leukemia cells (HL-60) were treated with several differentiation inducers, then the changes in the activity of cytosolic protein kinase C (PKC) isoforms were examined by hydroxylapatite chromatography and the species of the isoforms were determined immunologically. In three undifferentiated HL-60 cell lines examined, PKC α and β isoforms were present, but PKC γ isoform was not detected. When the cells were induced by dimethylsulfoxide, dibutyryl cAMP, or nicotinamide to differentiate into granulocytes, these two PKC isoforms each increased to about 2- to 3-fold. When retinoic acid was used as the inducer, in addition to PKC α and β, a third PKC isoform appeared. This isoform was clearly distinct from rat PKC α, β, and γimmunologically. This isoform showed a distinctly lower Ca2+-requirement (3μM) than that of PKC α or β (100 μM.) and was more dependent on cardiolipin and phosphatidylethanolamine, compared with PKC α, β, and γ. These results suggest that while the increases in the activities of PKC α and β isoforms are common in the differentiation program initiated by several inducers, including retinoic acid, the emergence of an unclassified PKC isoform is a retinoic acid-specific process.