Mechanistic Study Of The Function Of P53-independent Signaling Pathway In MMS-induced Cell Apoptosis

Methyl methanesulfonate (MMS) has been shown to induce apoptosis in various cell types through p53-dependent pathways. Nevertheless, pharmacological and genetic blockade of p53functions results in similar or delayed sensitivity to MMS treatment, suggesting the presence of p53-independent apoptotic mechanisms.To understand the p53-independent mechanisms that are engaged during MMS-induced apoptosis, we established MMS-induced apoptotic cell models using p53-deficient HI299and Hep3B cells. Our results demonstrated that MMS at concentrations of50,100,200,400and800μM induced the formation of gammaH2AX foci, and that at higher concentrations,400and800μM, MMS treatment led to apoptosis in the two cell lines. This apoptotic cell death was concurrent with the loss of mitochondrial membrane potential, nuclear-cytosolic translocation of active Caspase2, release of Cytochrome c from mitochondria, and the cleavage of Caspase9,Caspase3and PARP. However, MMS-induced DNA damage failed to stabilize the p53family members TAp73and DNp73.These results demonstrated a p53-and p73-independent mechanism for MMS-induced apoptosis that involves the nuclear-cytosolic translocation of active Caspase2as well as the mitochondria-mediated pathway.