Nuclear Localization of Phospholipase D1 Mediates the Activation of Nuclear Protein Kinase C and Extracellular Signal-regulated Kinase Signaling Pathways*

Recent studies highlight the existence of a nuclear lipid metabolism related to cellular proliferation. However, the importance of nuclear phosphatidylcholine (PC) metabolism is poorly understood. Therefore, we were interested in nuclear PC as a source of second messengers and, particularly, nuclear localization of PC-specific phospholipase D (PLD). In the present study we have identified the nuclear localization sequence (NLS) of PLD1 whose mutation abolished its nuclear import. Recently, we reported that caspase-mediated cleavage of PLD1 generates the N-terminal fragment (NF-PLD1) and C-terminal fragment (CF-PLD1). Here we show that CF-PLD1 but not NFPLD1, is exclusively imported into the nucleus via its functional NLS, whereas only some portions of intact PLD1 were localized into the nucleus. The NLS of intact PLD1 or CFPLD1 is required for interaction with importin, which is known to mediate nuclear import. The amount of intact PLD1 or CF-PLD1 translocated into nucleus is correlated with its binding affinity with importin. Ultimately, nuclear localization of intact PLD1 but not CF-PLD1 mediates the activation of nuclear protein kinase C and extracellular signal-regulated kinase signaling pathways. Taken together, we propose that nuclear localization of PLD1 via the NLS and its interaction with importinmay provide new insights on the functional role of nuclear PLD1 signaling.