Cadmium-induced apoptosis in lymphoblastoid cell line: involvement of caspase-dependent and -independent pathways

Abstract

Cadmium is a widely used heavy metal that causes severe damage to many organs including liver, kidney and lung. Cadmium toxicity has been described as in vitro and in vivo apoptosis but its molecular mechanisms are not fully understood. In this study, we used the human lymphoblastoid cell line Boleth to characterise cadmium-induced apoptosis further, using sub-lethal (10 microM) and lethal (IC50: 350 microM) doses. At lethal concentration, we observed features of apoptosis between 6 and 8 h after treatment: maturation of caspases 3 and 8, poly(ADP-ribose)polymerase (PARP) cleavage and DNA fragmentation. In order to determine the role of the MAPKs in this process, we investigated p38, ERK1/2 and c-Jun NH2-terminal kinases (JNK) phosphorylation: at lethal concentration, all these pathways were rapidly activated, but no decrease in the apoptotic rate was seen on inhibition of these kinases with drugs. Chemical inhibitors of caspases 3 and 8 blocked cleavage of PARP but not cell death, suggesting the existence of a caspase-independent death. We found that cadmium depolarised membrane potential in less than 1 h, as determined with DiOC6 dye. Interestingly, mitochondrial alteration led to the translocation of apoptosis-inducing factor (AIF) to the nucleus, where we observed chromatin condensation and possibly DNA fragmentation. These results suggest that cadmium-induced apoptosis can occur in the Boleth cell line through caspase-dependent and -independent pathways, independently of activation of major MAPKs.