Protein kinase C activation promotes cell survival in mature lymphocytes prone to apoptosis.

The putative protein kinase C (PKC) inhibitors polymyxin B and staurosporine were used to test the influence of PKC activity on the viability of lymphocytes. The cytotoxic effect of polymyxin B was characterized and it was found to be both time and dose dependent, with an LD50 in micromolar range, and counteracted by phorbol myristate acetate (PMA). To explore further the possible mechanism of action involved in polymyxin B-induced cell death, PKC activity and intracellular calcium were measured in polymyxin B-challenged lymphocytes. Polymyxin B inhibited PKC activity in both resting (25% inhibition) and PMA-stimulated (50% inhibition) cells, and increased intracellular calcium without disruption of the plasma membrane, a signal which is known to trigger apopotosis. Additionally, a number of experiments were conducted to assess the effect of staurosporine on PKC activity, cell growth, cell death and survival of mature lymphocytes. Staurosporine inhibited PKC activity in a dose-dependent manner (Ki close to 1 microM) and this effect correlated to some extent with the inhibition of [3H]thymidine incorporation and the breakdown of DNA into oligonucleosome-sized fragments. These results support the hypothesis that PKC is involved in the survival of mature lymphocytes undergoing apoptosis.