Induction of PUMA-α and down-regulation of PUMA-β expression is associated with benzo(a)pyrene-induced apoptosis in MCF-7 cells

Benzo(a)pyrene (BP) forms benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE)-DNA adducts in human breast adenocarcinoma MCF-7 cells, leading to p53 protein induction and phosphorylation. Although BP-induced apoptosis in rodent cells is known, it is still unclear in human cells. Here we have analyzed the effects of BP on p53 related apoptotic proteins, cell cycle and cell death in MCF-7 cells. PUMA-protein (p53 up-regulated modulator of apoptosis) levels were changed after BP exposure so that PUMA-α protein was statistically significantly increased whereas PUMA-β protein was statistically significantly decreased. PUMA-protein levels were also investigated in ZR-75-1 cells, where PUMA-α protein was statistically significantly increased. Cytochrome c, which is released from mitochondria during apoptosis to form the apoptosome, was increased in cytoplasmic fraction after BP exposure in MCF-7 cells. Increased apoptosis was also seen after 48 and 72 h BP exposure (2.5 and 5 μM). In addition, BP decreased dose dependently cell viability (2.5 and 5 μM) and increased ROS formation (1 and 10 μM). Our results suggest that PUMA-α protein is involved in BP-induced cell death most likely through a p53 dependent apoptotic pathway.