Lectin-induced activation of plasma membrane NADPH oxidase in cholesterol-depleted human neutrophils

The gp91phox subunit of flavocytochrome 10558 is the catalytic core of the phagocyte plasma membrane NADPH oxidase. Its activation occurs within lipid rafts and requires translocation of four subunits to flavocytochrome b(558). gp91 phox is the only glycosylated subunit of NADPH oxidase and no data exist about the structure or function of its glycans. Glycans, however, bind to lectins and this can stimulate NADPH oxidase activity. Given this information, we hypothesized that lectin-gp91 phox interactions would facilitate the assembly of a functionally active NADPH oxidase in the absence of lipid rafts. To test this, we used lectins with different carbohydrate-binding specificity to examine the effects on H2O2 generation by human neutrophils treated with the lipid raft disrupting agent methyl-beta-cyclodextrin (M beta CD). M beta CD treatment removed membrane cholesterol, caused changes in cell morphology, inhibited lectin-induced cell aggregation, and delayed lectin-induced assembly of the NADPH oxidase complex. More importantly, M beta CD treatment either stimulated or inhibited H2O2 production in a lectin-dependent manner. Together, these results show selectivity in lectin binding to gp91phox, and provide evidence for the biochemical structures of the gp91phox glycans. Furthermore, the data also indicate that in the absence of lipid rafts, neutrophil NADPH oxidase activity can be altered by these select lectins. (C) 2011 Elsevier Inc. All rights reserved.