SENSITIVITY OF INSULIN-SECRETING RIN-M5F CELLS TO UNDERGOING APOPTOSIS BY THE PROTEIN-KINASE-C INHIBITOR STAUROSPORINE

This study shows the sensitivity of insulin-secreting RIN m5F cells to undergoing apoptosis without modifying intracellular free calcium concentrations. The culture of cells in the absence of serum during 6 h failed to produce spontaneous DNA fragmentation. However, when cultures were carried out in the presence of the putative protein kinase C inhibitor staurosporine (1 μM), cells underwent apoptosis. Tumor-promoting phorbol ester failed to inhibit this effect. The presence of the chemotherapeutic drug bleomycin (0.6 mg/ml) in the culture medium reproduced the same pattern of cleaved DNA in nucleosomal pieces. Lower doses of staurosporine (0.1-1 nM) inhibited DNA synthesis but were unable to trigger apoptosis in 6 h culture. Higher doses of staurosporine (0.1-1 μM), which abolished DNA synthesis almost completely, were needed to trigger apoptosis. Short incubation of RIN m5F cells in the presence of staurosporine did not produce any change in the concentration of intracellular calcium or in the integrity of the plasma membrane. These results suggest the involvement of protein kinase C in RIN m5F cell survival. © 1993 Academic Press, Inc.