The Src Homology 2-Containing Inositol 5-Phosphatase 1 (SHIP1) is involved in CD32a signaling in human neutrophils

Abstract

Phosphatidylinositol(3,4,5)triphosphate (PtdIns(3,4,5)P 3) plays important signaling roles in immune cells, particularly in the control of activating pathways and of survival. It is formed by a family of phosphatidylinositol 3′-kinases (PI3Ks) which phosphorylate PtdIns(4,5)P 2 in vivo. In human neutrophils, the levels of PtdIns(3,4,5)P 3 increase rapidly at the leading edge of locomoting cells and at the base of the phagocytic cup during FcγR-mediated particle ingestion. Even though these, and other, data indicate that PtdIns(3,4,5)P 3 is involved in the control of chemotaxis and phagocytosis in human neutrophils, the mechanisms that regulate its levels have yet to be fully elucidated in these cells. We evaluated the potential implication of SHIP1 and PTEN, two lipid phosphatases that utilize PtdIns(3,4,5)P 3 as substrate, in the signaling pathways called upon in response to CD32a cross-linking. We observed that the cross-linking of CD32a resulted in a transient accumulation of PtdIns(3,4,5)P 3. CD32a cross-linking also induced the tyrosine phosphorylation of SHIP1, its translocation to the plasma membrane and its co-immunoprecipitation with CD32a. CD32a cross-linking had no effect on the level of serine/threonine phosphorylation of PTEN and did not stimulate its translocation to the plasma membrane. PP2, a Src kinase inhibitor, inhibited the tyrosine phosphorylation of SHIP1 as well as its translocation to the plasma membrane. Wortmannin, a PI3K inhibitor, had no effect on either of these two indices of activation of SHIP1. Our results indicate that SHIP1 is involved, in a Src kinase-dependent manner, in the early signaling events observed upon the cross-linking of CD32a in human neutrophils.