Mitochondrial outer membrane permeabilization (MOMP) and release of mitochondrial intermembrane proteins like cytochrome c are critical steps in the control of apoptosis. Previous work has shown that MOMP depends on the functionally redundant multidomain proapoptotic proteins, Bak and Bax. Here we demonstrate that Bak and Bax are functionally non-redundant during Neisseria gonorrhoeae (Ngo)- and cisplatin-induced apoptosis. While the activation of Bak is caspase independent Bax activation needs Bak and active caspases. Silencing of either Bak or Bax resists both Ngo- and cisplatin- but not TNFalpha-induced apoptosis. Activation of Bak is required to release cytochrome c from the mitochondria; however, Bax is still required to activate effector caspases. Thus, both Bak and Bax are necessary to accomplish DNA damage and Ngo-induced apoptosis.
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