Jun Ho Lee, Young Mi Kim, Nam Wook Kim, Jie Wan Kim, Erk Her, Bo Kyung Kim, Jong Hyun Kim, Sung Ho Ryu, Jong Woo Park, Dong Wan Seo, Jeung Whan Han, Michael A. Beaven, and Wahn Soo Choi
From the Department of Immunology and Department of Physiology, College of Medicine, Konkuk University, Chungju, Korea; College of Pharmacy, Duksung Women''s University, Seoul, Korea; Division of Molecular and Life Sciences, Pohang University of Science and Technology, Korea; College of Pharmacy, Sungkyunkwan University, Suwon, Korea; and Laboratory of Molecular Immunology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD.
Mast cells are responsible for IgE-mediated allergic reactions. Phospholipase D1 (PLD1) and PLD2 regulate mast cell activation, but the mechanisms remain unclear. Here we show that PLD2 associates with and promotes activation of Syk, a key enzyme in mast cell activation. Antigen stimulation resulted in increased association and colocalization of Syk with PLD2 on the plasma membrane as indicated by coimmunoprecipitation and confocal microscopy. This association was dependent on tyrosine phosphorylation of Syk but not on PLD2 activity. In vitro, PLD2 interacted via its Phox homology (PX) domain with recombinant Syk to induce phosphorylation and activation of Syk. Furthermore, overexpression of PLD2 or catalytically inactive PLD2K758R enhanced antigen-induced phosphorylations of Syk and its downstream targets, the adaptor proteins LAT and SLP-76, while expression of a PLD2 siRNA blocked these phosphorylations. Apparently, the interaction of PLD2 with Syk is an early critical event in the activation of mast cells.