The Ca2+ signal as common target of three different proteins involved in the apoptotic process.

Ca2+ signal plays a fundamental role in modulating a diverse range of cellular responses including muscle contraction, exocytosis, motility, fertilization, proliferation and apoptosis. Therefore, several proteins involved in this wide range of biological processes “manipulate” intracellular Ca2+ to (dis)regulate these events. To analyse Ca2+ homeostasis at the subcellular level, we employed the Ca2+-sensitive photoprotein aequorin, targeted to defined intracellular locations (organelles, such as mitochondria, endoplasmic reticulum, and cytoplasmic regions). Using this experimental approach, we investigated multiple effects on Ca2+ dynamics of three different proteins: i) the role of 66 KDa isoform of Shc (p66Shc) on the alterations of mitochondrial Ca2+ homeostasis observed after oxidative stress, and elucidation of specific signalling route leading to its mitochondrial import. ii) The tumor suppressor protein Fhit sensitizes the low-affinity Ca2+ transporters of mitochondria, enhancing Ca2+ uptake into the organelle both in intact and in permabilized cells, and potentiating the effect of apoptotic agents. iii) The proto-oncogene Akt, a potent inhibitor of apoptosis, reduces Ca2+ release from the ER induced either by agonist stimulation or by apoptotic stimuli and this alteration of ER Ca2+ content and release, reduces significantly cellular sensitivity to Ca2+ mediated proapoptotic stimulation. Taken together these data remark the practical useful of Ca2+-dynamics investigation as a “reporter system” to understand different molecular mechanisms of different proteins and may provide ways to act on various biological processes, especially on apoptotic cell death and its derangement in cancer.