Calcium fluxes cause nuclear shrinkage and the translocation of phospholipase C-δ1 into the nucleus

Phospholipase C-δ1 (PLCδ1) is the most fundamental form of the eukaryotic PLC and thought to play important roles in the regulation of cells. We previously reported that PLCδ1 shuttles between the cytoplasm and nucleus, and an influx of Ca2+ triggers the nuclear import of PLCδ1 via Ca2+-dependent interaction with importin β1, although the physiological meaning of this is unclear. Here we have examined the distribution of PLCδ1 using primary cultures of rat hippocampal neurons. Treatment of 7DIV neurons with ionomycin or thapsigargin caused the nuclear localization of PLCδ1 as has been observed in other cell lines. Similar results were obtained with neurons treated with glutamate, suggesting that the nuclear localization of PLCδ1 plays some roles in excitotoxicity associated with ischemic stress. Generally, cells undergoing ischemic or hypoxic cell death show nuclear shrinkage. We confirmed that a massive influx of Ca2+ caused similar results. Furthermore, overexpression of GFP-PLCδ1 facilitated ionomycin-induced nuclear shrinkage in embryonic fibroblasts derived from PLCδ1 gene-knockout mice (PLCδ1KO-MEF). By contrast, an E341A mutant that cannot bind with importin β1 and be imported into the nucleus by ionomycin and also lacks enzymatic activity did not cause nuclear shrinkage in PLCδ1KO-MEF. Nuclear translocation and the PLC activity of PLCδ1, therefore, may regulate the nuclear shape by controlling the nuclear scaffold during stress-induced cell death caused by high levels of Ca2+.