Rac2 is an essential regulator of neutrophil nicotinamide adenine dinucleotide phosphate oxidase activation in response to specific signaling pathways

Rac2 is a hematopoietic-specific Rho family GTPase implicated as an important constituent of the NADPH oxidase complex and shares 92% amino acid identity with the ubiquitously expressed Rac1. In bone marrow (BM) neutrophils isolated from rac2^-/- mice generated by gene targeting, we previously reported that PMA-induced superoxide production was reduced by about 4-fold, which was partially corrected in TNF-α-primed BM neutrophils and in peritoneal exudate neutrophils. We investigated receptor-mediated activation of the NADPH oxidase in the current study, finding that superoxide production in rac2^-/- BM and peritoneal exudate neutrophils was normal in response to opsonized zymosan, reduced to 22% of wild type in response to IgG-coated SRBC, and almost absent in response to fMLP. In wild-type murine BM neutrophils, phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, and Akt was induced by PMA or fMLP, which was decreased in rac2^-/- neutrophils for ERK1/2 and p38. Activation of p38 by either opsonized zymosan or IgG-coated SRBC was similar in wild-type and rac2^-/- cells. Inhibition of ERK1/2 or p38 activation using either PD98059 or SB203580, respectively, had only a modest effect on fMLP-elicited superoxide production and no effect on the PMA-induced response. These data provide genetic evidence supporting an important role for Rac2 in regulating neutrophil NADPH oxidase activation downstream of chemoattractant and Fcγ receptors. The effect of Rac2 deficiency on superoxide production is probably exerted through multiple pathways, including those independent of mitogen-activated protein kinase activation.