Caspase-2: a possible trigger of apoptosis induced in A-549 tumor cells by ZnPc photodynamic treatment

Photodynamic therapy applied to cell cultures represents a widely accepted experimental method to investigate molecular mechanisms that lead to apoptotic cell death. In this context the subcellular localization of photosensitizers seems to be a significant factor in order to determine the apoptotic pathway that could be activated. We have characterized the experimental conditions that induce apoptotic cell death in A-549 cells incubated with ZnPc and irrradiated with red light. Previously we have found that in this cell line the drug is localized in the Golgi apparatus after 3-h incubation. Indirect immunofluorescence analysis of the events that lead to apoptosis made possible the detection of caspase-2 activation in the Golgi region immediately after photodynamic treatments. A few minutes later, the morphology of this organelle starts to disrupt and just 6 h after treatment the nuclei appear affected showing the fragmented appearance typical of apoptotic cell death. From this results we assume that following the photodynamic treatment of A-549 cells with ZnPc, the activation of caspase-2 in the Golgi apparatus could begin to initiate immediately the apoptotic process.