Phospholipase C, protein kinase C, Ca²⁺/calmodulin-dependent protein kinase II, and redox state are involved in epigallocatechin gallate-induced phospholipase D activation in human astroglioma cells

We show that epigallocatechin-3 gallate (EGCG), a major component of green tea, stimulates phospholipase D (PLD) activity in U87 human astroglioma cells. EGCG-induced PLD activation was abolished by the phospholipase C (PLC) inhibitor and a lipase inactive PLC-γ1 mutant, which is dependent on intracellular or extracellular Ca²⁺, with the possible involvement of Ca ²⁺/calmodulin-dependent protein kinase II (CaM kinase II). EGCG induced translocation of PLC-γ1 from the cytosol to the membrane and PLC-γ1 interaction with PLD1. EGCG regulates the activity of PLD by modulating the redox state of the cells, and antioxidants reverse this effect. Moreover, EGCG-induced PLD activation was reduced by PKC inhibitors or down-regulation of PKC. Taken together, these results show that, in human astroglioma cells, EGCG regulates PLD activity via a signaling pathway involving changes in the redox state that stimulates a PLC-γ1 [Ins(1,4,5)P ₃-Ca²⁺]-CaM kinase II-PLD pathway and a PLC-γ1 (diacylglycerol)-PKC-PLD pathway.