Toxoplasma gondii inhibits ultraviolet light-induced apoptosis through multiple interactions with the mitochondrion-dependent programmed cell death pathway

Cells infected with the protozoan parasite Toxoplasma gondii are resistant to diverse apoptotic stimuli. In this study, we perform a detailed analysis of the manipulation of the mitochondrial arm of the apoptotic cascade by the parasite. Apoptosis was induced using irradiation with ultraviolet light (UV), and the kinetics of caspase activation, cytochrome c release and activation of the upstream signalling pathways were examined. The evidence clearly points to T. gondii targeting multiple steps in the transmission [inhibition of c-Jun N-terminal kinase (JNK) activation in response to UV], triggering (inhibition of cytochrome c release by affecting the balance of pro- and anti-apoptotic BCL-2 family members) and execution (inhibition of caspase 9 and caspase 3) phases of the apoptotic cascade. Interestingly, the multilevel pattern of inhibition that emerges suggests that the global inhibition of the mitochondrial arm of apoptosis is not likely to be contributed to by the small subset of mitochondria recruited to the T. gondii parasitophorous vacuole membrane.