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

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Abstract
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 Ca2+/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)P3‐Ca2+]–CaM kinase II–PLD pathway and a PLC‐γ1 (diacylglycerol)–PKC–PLD pathway.