Ras GTPase is essential for Fas-mediated activation of phospholipase D in A20 cells

Abstract

In an attempt to explore the Fas downstream factor contributing to the activation of phospholipase D, we have investigated the possible involvement of a small GTP binding protein Ras in signaling events that were triggered by Fas crosslinking. Upon adenoviral expression of dominant negative mutant of Ras(n17Ras), an increase in phospholipase D activity by anti-Fas monoclonal antibody was diminished. Also, the Fas-downstream signaling events triggered by Fas cross-linking such as the activation of phosphatidylcholine-specific phospholipase C, the increase in diacylglycerol level and the translocation of protein kinase C to membrane fraction, were all reduced by N17Ras expression. When parellel experiments were performed with manumycin-A, a Ras farnesyltransferase inhibitor, almost identical inhibitory effects on Fas downstream signaling were exhibited. These data suggest that Ras GTPase is essential in transmitting phospholipase D activation signal induced by Fas cross- linking and is located at phosphatidylcholine-specific phospholipase C upstream in Fas signaling cascades.