Crosstalk between ARF6 and protein kinase C alpha in Fc gamma RI-mediated activation of phospholipase D1

Fc receptors play a pivotal role linking the cellular and humoral arms of t he immune system [1-3], Our previous studies have shown that the human high -affinity immunoglobulin G receptor Fc gamma RI couples to a novel intracel lular signaling pathway requiring phospholipase D activation [4], The mecha nisms that regulate receptor coupling to phospholipase D in intact cells ar e poorly understood but involve small molecular weight GTPases and protein kinase C [5-7], Here, we show that immune complex aggregation of Fc gamma R I stimulates the association of phospholipase D1 with ARF6 and protein kina se C alpha. Surprisingly, PKC alpha activity per se is not required. Rather , all of the Fc gamma RI-mediated increase in PKC activity requires phospho lipase D1, as treatment of cells with butan-1-ol (0.3%) or specific downreg ulation of phospholipase D1 using antisense oligonucleotides inhibits Fc ga mma RI-coupled PKC activation. Moreover, treatment of cells with butan-1-ol or phospholipase D1 antisense oligonucleotides inhibits translocation of P KC delta, -epsilon, and -zeta but had no effect on the association of PKCa or ARF6 with phospholipase D1. These data indicate that association with AR F6 and PKCa plays a role in coupling Fc gamma RI to phospholipase D1 activa tion and that PLD1 lies upstream of all Fc gamma RI-mediated PKC activity.