Activation of phospholipase Dl by direct interaction with ADP-ribosylation factorl and RalA

Activation of phospholipase D (PLD) has been reported as a critical step in numerous cellular pathways, including exocytosis, membrane trafficking, and the regulation of mitosis. PLD1 is known to be activated by ADP ribosviation factor 1 (ARF1). We report here that ARF1 coimmunoprecipitates with PLD1 and that the ARFl-dependent PLD activation is induced by the direct interaction between ARF1 and PLD1, We found that RalA, another member of the small GTP-binding proteins, synergistically enhances the ARFl-deporidont PLD activity with an EC50 of about 30nM. Using in vitro binding assay, wo show that ARF1 and RalA directly interact with different sites of PLD 1. There suits suggest that the independent interactions of RalA and ARF1 with PLDl are responsible for the synergistic activation. The interaction of PLDl with other PLD-activatiiig factors including RhoA and PKC-a wiil be also presented and discussed.