Interaction of the Type Ialpha PIPkinase with phospholipase D: a role for the local generation of phosphatidylinositol 4,5-bisphosphate in the regulation of PLD2 activity

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Abstract
Phosphoinositides are localized in various intracellular compartments and can regulate a number of intracellular functions, such as cytoskeletal dynamics and membrane trafficking. Phospholipase Ds (PLDs) are regulated enzymes that hydrolyse phosphatidylcholine (PtdCho) to generate the putative second messenger phosphatidic acid (PtdOH). In vitro , PLDs have an absolute requirement for higher phosphorylated inositides, such as phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5)P2]. Whether this lipid is able to regulate the activity of PLD in vivo is contentious. To examine this hypothesis we studied the relationship between PLD and an enzyme critical for the intracellular synthesis of PtdIns(4,5)P2: phosphatidylinositol 4‐phosphate 5‐kinase α (Type Iα PIPkinase). We find that both PLD1 and PLD2 interact with the Type Iα PIPkinase and that PLD2 activity in vivo can be regulated solely by the expression of this lipid kinase. Moreover, PLD2 is able to recruit the Type Iα PIPkinase to its intracellular location. We show that the physiological requirement of PLD enzymes for PtdIns(4,5)P2 is critical and that PLD2 activity can be regulated solely by the levels of this key intracellular lipid.