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-alpha and beta-isoforms were present, but PKC gamma-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-alpha and beta, a third PKC isoform appeared. This isoform was clearly distinct from rat PKC-alpha, beta, and gamma, immunologically. This isoform showed a distinctly lower Ca2+-requirement (3-mu-M) than that of PKC-alpha or beta (100-mu-M) and was more dependent on cardiolipin and phosphatidylethanolamine, compared with PKC-alpha, beta, and gamma. These results suggest that while the increases in the activities of PKC-alpha and beta 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.