The regulatory subunits of PI3Kγ control distinct neutrophil responses

Neutrophils, which migrate toward inflamed sites and kill pathogens by producing reactive oxygen species (ROS), are important in the defense against bacterial and fungal pathogens, but their inappropriate regulation causes various chronic inflammatory diseases. Phosphoinositide 3-kinase gamma (PI3K gamma) functions downstream of proinflammatory G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs) in neutrophils and is a therapeutic target. In neutrophils, PI3K gamma consists of a p110 gamma catalytic subunit, which is activated by the guanosine triphosphatase Ras, and either a p84 or p101 regulatory subunit. Loss or inhibition of p110 gamma or expression of a Ras-insensitive variant p110 gamma (p110 gamma(DASAA/DASAA)) impairs PIP3 production, Akt phosphorylation, migration, and ROS formation in response to GPCR activation. The p101 subunit binds to, and mediates PI3K gamma activation by, G protein beta gamma subunits, and p101(-/-) neutrophils have a similar phenotype to that of p110 gamma(-/-) neutrophils, except that ROS responses are normal. We found that p84(-/-) neutrophils displayed reduced GPCR-stimulated PIP3 and Akt signaling, which was indistinguishable from that of p101(-/-) neutrophils. However, p84(-/-) neutrophils produced less ROS and exhibited normal migration in response to GPCR stimulation. These data suggest that p84-containing PI3K gamma controls GPCR-dependent ROS production. Thus, the PI3K gamma regulatory subunits enable PI3K gamma to mediate distinct neutrophil responses, which may occur by targeting PIP3 signaling into spatially distinct domains.