Phospholipase Cδ1 associates with importin β1 and translocates into the nucleus in a Ca2+-dependent manner

Phospholipase C (PLC)δ1 shuttles between the nucleus and the cytoplasm. Here, we demonstrate that treatment of MDCK cells and PC12 cells with ionomycin causes nuclear accumulation of ectopically expressed and endogenous PLCδ1, respectively, suggesting that signals that increase [Ca2+]i trigger nuclear translocation. To clarify the molecular mechanisms involved in this translocation, we have examined whether PLCδ1 binds with importins. PLCδ1 interacted with importin β1 in a Ca2+-dependent manner in vitro even in the absence of importin α. A PLCδ1 mutant E341A, which lacks Ca2+-binding to the catalytic core, did not show this interaction at any physiological Ca2+ concentration and did not translocate into the nucleus after ionomycin treatment when expressed in MDCK cells. These results suggested that the nuclear import of PLCδ1 is mediated by its Ca2+-dependent interaction with importin β1.