Effect of an inhibitory factor for protein kinase C on cell growth of leukemic cells

A factor which inhibits protein kinase C has been detected in normal human lymphocytes and leukemia cells obtained from some untreated patients with lymphoblastic leukemia. The partially purified inhibitory factor obtained from normal human lymphocytes depressed the growth of K562 cells and HL-60 cells, while it also suppressed DNA synthesis of these cells in a dose-dependent manner. The inhibitory factor was not able to suppress the DNA synthesis, however when it was added to the medium 12 hours after the culture. The inhibitory factor also reduced the phosphorylation of endogenous proteins, mainly Mr 80,000, 40,000 and 38,000. These results suggest that the inhibitory factor is closely related to the cell proliferation of various cells through the suppression of protein kinase C activity.