Cadmium-induced apoptosis in murine fibroblasts is suppressed by Bcl-2

We investigated the induction of apoptosis by cadmium in NIH 3T3 murine fibroblasts. Apoptosis was triggered effectively by 10 muM CdCl(2) within 24 h under which conditions cell viability was reduced by 50%. Cadmium-induced apoptosis was demonstrated by both morphological and biochemical analysis. We have shown that cadmium concentrations of 5-20 muM caused nuclear fragmentation. Moreover, internucleosomal DNA fragmentation was evoked by 10-25 muM CdCl(2) within 24 h, as detected by the formation of ladder patterns in DNA electrophoresis. Since the induction of programmed cell death occurs together with modifications in the cell cycle, we examined the ability of cadmium to block cell divisions by using a 5-bromo-2-deoxy-uridine incorporation assay. Our results indicate that about 40% of treated cells are blocked in G(0)-G(1) phase when exposed to 10 muM cadmium for 27 h. Finally, we addressed the question of whether the effect of cadmium could be prevented by suppressing apoptosis. Over-expression of the anti-apoptotic protein Bcl-2 in NIH 3T3 cells protects against cadmium toxicity, thus suggesting a role for Bcl-2 in the regulation of cadmium-induced apoptosis.