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

Phospholipase C-delta 1 (PLC delta 1) is the most fundamental form of the eukaryotic PLC and thought to play important roles in the regulation of cells. We previously reported that PLC delta 1 shuttles between the cytoplasm and nucleus, and an influx of Case triggers the nuclear import of PLC delta 1 via Ca2+-dependent interaction with importin beta 1, although the physiological meaning of this is unclear. Here we have examined the distribution of PLC delta 1 using primary cultures of rat hippocampal neurons. Treatment of 7DIV neurons with ionomycin or thapsigargin caused the nuclear localization of PLC delta 1 as has been observed in other cell lines. Similar results were obtained with neurons treated with glutamate, suggesting that the nuclear localization of PLC delta 1 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-PLC delta 1 facilitated ionomycin-induced nuclear shrinkage in embryonic fibroblasts derived from PLC delta 1 gene-knockout mice (PLC delta 1KO-MEF). By contrast, an E341A mutant that cannot bind with importin beta 1 and be imported into the nucleus by ionomycin and also lacks enzymatic activity did not cause nuclear shrinkage in PLC delta 1KO-MEF. Nuclear translocation and the PLC activity of PLC delta 1, therefore, may regulate the nuclear shape by controlling the nuclear scaffold during stress-induced cell death caused by high levels of Ca2+. (C) 2010 Elsevier Ireland Ltd. All rights reserved.