Studies on the relationship between protein kinase C and differentiation of human promyelocytic leukemia cells induced by retinoic acid.

We studied the differentiation of acute promyelocytic leukemia (APL) cells in 14 patients with APL. After the induction by retinoic acid (RA) the mature cells rose to 60 +/- 11.8% compared to 0.7 +/- 1% of the control, while the promyelocytes declined to 8.7 +/- 6.4% (93.3 +/- 5.6% in the control group). Protein kinase C (PKC) activity was significantly increased to 149.3 +/- 156.2 pmol/mg per min compared to 47 +/- 40.9 of the control (p less than 0.01). In HL-60 cells, the activity of PKC increased also from 52.3 +/- 35 to 129.2 +/- 64.6 pmol/mg per min (n = 10, p less than 0.01) after the induction of differentiation with RA. If the leukemia cells were pretreated with a kind of PKC inhibitor such as trifluoperazine, the increase of PKC activity was inhibited, and the rate of nitroblue tetrazolium reduction decreased from 89.9 +/- 7.7% to 62 +/- 25% (n = 6, p less than 0.01) and the mature cells reduced from 63.1 +/- 11.7% to 19.7 +/- 12.2% (p less than 0.01). We presumed that the activity of PKC is closely related to the differentiation of human promyelocytic leukemia cells induced by all-trans-retinoic acid.