Dissociation of protein kinase C activation from phorbol ester-induced maturation of HL-60 leukemia cells

Abstract

The role of C-kinase in the induction of maturation of HL-60 promyelocytic leukemia cells was examined using two activators of this kinase, 12-O-tetradecanoyl phorbol 13-acetate (TPA) and 1-oleoyl-2-acetylglycerol (OAG). At 10(-8) M, a concentration that induced maturation, TPA effectively stimulated C-kinase activity in cell-free preparations by increasing the affinity of the enzyme for Ca2+. Similar activation was observed with 20 micrograms/ml of OAG. At these concentrations, addition of either compound to intact cells stimulated the phosphorylation of cellular proteins. Treatment with TPA resulted in an increased phosphorylation of 14 proteins, 9 of which also changed in response to OAG. In addition to the effects on protein phosphorylation, TPA and OAG both affected choline lipid metabolism. TPA at 10(-8) M stimulated the incorporation of [methyl-3H]choline into phosphatidylcholine, sphingomyelin, and lysophosphatidylcholine. OAG at 20 micrograms/ml had quantitatively similar effects on the labeling of the former two lipids, but did not affect incorporation of choline into lysophosphatidylcholine. Despite the similar biochemical effects of TPA and OAG, the diglyceride was unable to induce HL-60 cell maturation as measured by inhibition of cell growth, development of nonspecific esterase activity, phagocytosis, adherence of cells to plastic, and loss of transferrin receptor activity. The lack of effect is not due to metabolism of OAG; maturation could not be induced by treating cells with fresh OAG every 2 h for a period of 12 h. These results suggest a dissociation of the activation of C-kinase and the induction of HL-60 cell maturation by TPA.