Role of calcineurin in neurons and immune cells

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Calcineurin, a serine/threonine phosphatase 2B, plays an important role in T cell signaling through a transcription factor NF-AT (nuclear factor of activated T cell). We reported previously that calcineurin directly dephosphorylated a pro-apoptotic protein Bad, one of Bcl-2 family member, as well as Bcl-2. Two critical phosphorylation sites S24 and S70 of Bcl-2 were reported to be induced in a certain cancer. For the further analysis of these phosphorylation sites, we prepared the specific antibody against S24P or S70P by synthetic peptides. The antibody against the phosphorylated S70 can detect phosphorylated Bcl-2 at 10 - 50% tumor cells in 10 different tissues of human breast cancer. This antibody also detected the Bcl-2 kinase activity which was induced by anti-cancer agent, Taxol or steroid, dexamethazone, and completely inhibited by both actinomycin D and cycloheximide. This results suggest that Bcl-2 kinase might be de novo synthesised after stimulation.We recently found that th … More e novel function of calcineurin involved in neuronal cell death pathway in rat forebrain ischemic models, in which ischemic reperfusion leads to brain damages in CA1 sector of the hippocampus and the forebrain}. Dephosphorylation of Bad and the release of cytochrome c from mitochondria were detected in CA1, but not in CA3 or in DG after 24 hours of ischemia. The calcineurin activity increased 4 folds in these regions 1 hour after ischemia, and then gradually reached a maximal level (6 folds) at 24 hours later. Pre-treatment with CsA or FK506 suppressed the calcineurin activity in each region. The area of high T2WI (T2-weighted image) in diffusion MRI appeared in the putamen and the hippocampal region 6-12 hours after ischemia. Seven days after ischemia, the areas of high T2WI appeared strongly in forebrain and CA1, which were consisted of massive dead cells and slight edema in pathological staining and EM. Surprisingly, CsA totally (over 95%) suppressed the delayed neuronal cell death and edema while Fk506 effected only 40 - 50% of them.Cyclophilin D expressed in mitochondria was reported to regulate cytochrome c release by protecting MPT (mito-chondrial permeability transition) pores. Our results suggest that CsA has the strong neuroprotective effect through suppression of both calcineurin and cyclophilin D. Moreover, CsA can be applied to treat ischemic brain damages caused by cerebral infarction, embolism and hemorrhages. Less