C5a reduces formyl peptide-induced actin polymerization and phosphatidylinositol(3,4,5)trisphosphate formation, but not phosphatidylinositol (4,5) bisphosphate hydrolysis and superoxide production, in human neutrophils.

We investigated phospholipid signal transduction, calcium flux, O2- anion production and actin polymerization after stimulation with the C fragment and chemoattractant, C5a, and then determined how C5a pretreatment affected subsequent responses to formyl peptide in human neutrophils. We have previously demonstrated that the novel lipids, phosphatidylinositol trisphosphate (PIP3) and phosphatidylinositol(3,4)P2 (PI(3,4)P2), rise transiently in neutrophils after activation with formyl peptide. Furthermore, the rise in PIP3 parallels actin polymerization. In this study, neutrophils activated with C5a exhibited two distinct G protein-dependent signal pathways involving different phosphoinositides: 1) [32P]PI(4,5)P2 hydrolysis and [32P]PA production, and 2) the transient formation of D-3-phosphorylated phosphoinositides, [32P]PIP3 and [32P]PI(3,4)P2. When neutrophils were preincubated with C5a for 5 min before stimulation with formyl peptide, [32P]PI(4,5)P2 hydrolysis was unchanged, and [32P]PA production and O2- formation were slightly enhanced compared with controls stimulated with formyl peptide in the absence of C5a. In contrast, [32P]PIP3 production, right angle light scatter, and actin polymerization were all reduced 35 to 40%. Therefore, these data support the hypothesis that PIP3 plays a role in chemotaxis but not superoxide formation.