Mitochondria play no roles in Mn(II)-induced apoptosis in HeLa cells

Manganese(II) has been shown to exhibit catalase-like activity under physio logical conditions. In the course of studies to test the antioxidant activi ty of Mn(II) on HeLa cells, it was observed at high concentrations; (1-2 mM ) that Mn(II) also induced apoptosis, as judged by changes in cell morpholo gy, caspase-3 activation, cleavage of poly(ADP) ribose, and DNA condensatio n. However, in contrast to established mechanisms,the Mn(II)-induced apopto sis is associated with an increase rather than a decrease in mitochondrial inner-membrane potential, as monitored by the fluorescent probe tetra methy l rhodamine ethyl ester. Based on immunochemical analysis, Mn(II)-induced a poptosis does not lead to the release of cytochrome c into the cytosol. The se and other measurements show that treatment with Mn(II) leads to enhancem ent of the mitochondrial "membrane mass," has no effect on mitochondrial vo lume, and does not affect the permeability transition pore. Together, these results support the view that Mn(II)-induced apoptosis occurs by a heretof ore unrecognized mechanism. In addition, it was demonstrated that Mn(II) tr eatment leads to an increase in the production of reactive oxygen species ( peroxides) and to the induction of the manganese superoxide dismutase and c atalase activities but has no effect on the Cu,Zn-superoxide dismutase leve l.