The arachidonic acid‐binding protein S100A8/A9 promotes NADPH oxidase activation by interaction with p67^phoxand Rac‐2

Abstract

The Ca2+- and arachidonic acid-binding S100A8/A9 protein complex was recently identified by in vitro studies as a novel partner of the phagocyte NADPH oxidase. The present study demonstrated its functional relevance by the impaired oxidase activity in neutrophil-like NB4 cells, after specific blockage of S100A9 expression, and bone marrow polymorphonuclear neutrophils from S100A9-/- mice. The impaired oxidase activation could also be mimicked in a cell-free system by pretreatment of neutrophil cytosol with an S100A9-specific antibody. Further analyses gave insights into the molecular mechanisms by which S100A8/A9 promoted NADPH oxidase activation. In vitro analysis of oxidase activation as well as protein-protein interaction studies revealed that S100A8 is the privileged interaction partner for the NADPH oxidase complex since it bound to p67phox and Rac, whereas S100A9 did interact with neither p67phox nor p47phox. Moreover, S100A8/A9 transferred the cofactor arachidonic acid to NADPH oxidase as shown by the impotence of a mutant S100A8/A9 complex unable to bind arachidonic acid to enhance NADPH oxidase activity. It is concluded that S100A8/A9 plays an important role in phagocyte NADPH oxidase activation.

The NLRP3 inflammasome functions as a driver of the myelodysplastic syndrome phenotype

“…S100A8/S100A9 heterodimers activate both NF-kB and NLRP3 inflammasome assembly via a NOX/ROS-dependent mechanism. 23,[44][45][46] Intracellularly, S100A8/9 heterodimers serve as a scaffold for the membrane assembly and activation of the NOX complex, 47,48 which generates ROS via transfer of electrons across membranes to generate superoxide. 49 As also shown here, NOX regulates both priming and activation of NLRP3 inflammasomes, including the activation of caspase-1 and IL-1b secretion.…”

Imbalance of Clara cell-mediated homeostatic inflammation is involved in lung metastasis

“…Inhibition of S100A8 abrogated myeloid cell infiltration into pneumonic lungs that requires transendothelial and transepithelial cell migration to reach the pathogens (Kerkhoff et al, 1999;Ryckman et al, 2003;Vogl et al, 2004;Raquil et al, 2008). Bacteriocidal reactive oxygen species production is regulated by the interaction of S100A8 and cofactors of Nox2, such as p67 and Rac2 (Kerkhoff et al, 2005) or a direct binding between TLR4 and Nox4 (Park et al, 2004). TLR4 and another proposed endogenous ligand hyaluronan have been shown to regulate lung injury and repair (Jiang et al, 2005).…”

A Regulated Adaptor Function of p40phox: Distinct p67phoxMembrane Targeting by p40phoxand by p47phox

“…We confirmed AA can trigger membrane translocation of p47 phox , through interactions involving its PX domain and SH3 domain and that this enables cotranslocation of p67 phox (Figures 4 and 6). Other reports suggest exogenous AA has indirect effects on Nox2 activation through downstream AA-derived mediators Kerkhoff et al, 2005;Kim and Dinauer, 2006). Direct involvement of cPLA 2 in human Nox2 activation (neutrophils, PLB-985 cells, or monocytes) has been demonstrated using inhibitors or antisense molecules targeted to cPLA 2 (Dana et al, 1994;Li and Cathcart, 1997;Dana et al, 1998;Zhao et al, 2002).…”