Crosstalk between ARF6 and protein kinase Cα in FcγRI-mediated activation of phospholipase D1

Abstract

Fc receptors play a pivotal role linking the cellular and humoral arms of the immune system [1–3]. Our previous studies have shown that the human high-affinity immunoglobulin G receptor FcγRI couples to a novel intracellular signaling pathway requiring phospholipase D activation [4]. The mechanisms that regulate receptor coupling to phospholipase D in intact cells are poorly understood but involve small molecular weight GTPases and protein kinase C [5–7]. Here, we show that immune complex aggregation of FcγRI stimulates the association of phospholipase D1 with ARF6 and protein kinase Cα. Surprisingly, PKCα activity per se is not required. Rather, all of the FcγRI-mediated increase in PKC activity requires phospholipase D1, as treatment of cells with butan-1-ol (0.3%) or specific downregulation of phospholipase D1 using antisense oligonucleotides inhibits FcγRI-coupled PKC activation. Moreover, treatment of cells with butan-1-ol or phospholipase D1 antisense oligonucleotides inhibits translocation of PKCδ, -ϵ, and -ζ but had no effect on the association of PKCα or ARF6 with phospholipase D1. These data indicate that association with ARF6 and PKCα plays a role in coupling FcγRI to phospholipase D1 activation and that PLD1 lies upstream of all FcγRI-mediated PKC activity.