Protein disulfide isomerase redox-dependent association with p47(phox): evidence for an organizer role in leukocyte NADPH oxidase activation.

ABSTRACT

Mechanisms of leukocyte NADPH oxidase regulation remain actively investigated. We showed previously that vascular and macrophage oxidase complexes are regulated by the associated redox chaperone PDI. Here, we investigated the occurrence and possible underlying mechanisms of PDI-mediated regulation of neutrophil NADPH oxidase. In a semirecombinant cell-free system, PDI inhibitors scrRNase (100 µg/mL) or bacitracin (1 mM) near totally suppressed superoxide generation. Exogenously incubated, oxidized PDI increased (by ~40%), whereas PDIred diminished (by ~60%) superoxide generation. No change occurred after incubation with PDI serine-mutated in all four redox cysteines. Moreover, a mimetic CxxC PDI inhibited superoxide production by ~70%. Thus, oxidized PDI supports, whereas reduced PDI down-regulates, intrinsic membrane NADPH oxidase complex activity. In whole neutrophils, immunoprecipitation and colocalization experiments demonstrated PDI association with membrane complex subunits and prominent thiol-mediated interaction with p47(phox) in the cytosol fraction. Upon PMA stimulation, PDI was mobilized from azurophilic granules to cytosol but did not further accumulate in membranes, contrarily to p47(phox). PDI-p47(phox) association in cytosol increased concomitantly to opposite redox switches of both proteins; there was marked reductive shift of cytosol PDI and maintainance of predominantly oxidized PDI in the membrane. Pulldown assays further indicated predominant association between PDIred and p47(phox) in cytosol. Incubation of purified PDI (>80% reduced) and p47(phox) in vitro promoted their arachidonate-dependent association. Such PDI behavior is consistent with a novel cytosolic regulatory loop for oxidase complex (re)cycling. Altogether, PDI seems to exhibit a supportive effect on NADPH oxidase activity by acting as a redox-dependent enzyme complex organizer.