Nitric oxide inhibits execution of apoptosis at two distinct ATP-dependent steps upstream and downstream of mitochondrial cytochrome c release

The endogenous mediator nitric oxide (NO) blocked apoptosis of Jurkat cells elicited by stauro sporine, anti-CD95 or chemotherapeutics, and switched death to necrosis. The switch in the mode of cell death was dependent on the ATP loss elicited by NO. This affected two distinct steps of the apop· totic cascade. First, the release of cytochrome c from mitochondria was delayed by NO. Second, process ing of procaspases-317 to the active proteases was prevented even after cytochrome c had been re leased. Thus, NO interferes with execution steps of apoptosis both upstream and downstream of cyto chrome c release. © 1999 Academic Press Key Words: ATP; caspase; nitric oxide; apoptosis; necrosis; cytochrome c. Apoptosis is an evolutionary conserved form of cell death, that is essential for most multicellular organ isms to remove unwanted cells without disrupting tis sue organization, provoking scarring, and triggering inflammation [1,2]. Pharmacological intervention with caspase inhibitors [3], an increase of the intensity of the death-inducing stimulus [4], or depletion of intra cellular ATP [5,6] are known to preclude the execution of apoptosis. In many of the above cases, cell demise is not entirely prevented. but rather switched to necrosis, a mode of death often involving inflammation, scarring and prevention of tissue reconstitution [1]. The endogenous factors which decide on the switch ing of apoptosis to necrosis under pathological condi tions are still unknown. One potential candidate is nitric oxide (NO) which is produced in high concentra-I To whom correspondence should be addressed at Faculty o