The C-terminal flavin domain of gp91phox bound to plasma membranes of granulocyte-like X-CGD PLB-985 cells is sufficient to anchor cytosolic oxidase components and support NADPH oxidase-associated diaphorase activity independent of cytosolic phospholipase A2 regulation

Abstract

We have previously established a model of cytosolic phospholipase A(2) (cPLA(2))-deficient PLB-985 cells and demonstrated that cPLA(2)-generated arachidonic acid (AA) is essential for reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and NADPH-dependent diaphorase activity. The present study focuses on the C-terminal cytoplasmic domain of gp91(phox) (residues 283-570), which contains the NADPH binding and flavin adenine dinucleotide-reducing center, to determine if this portion is regulated by AA. The gp91(phox) C-terminal reductase domain was expressed in X-CGD PLB-985 cells lacking normal gp91(phox) (X-CGD PLB 91CT cells) and was detected in the plasma membrane. It appears to be bound electrostatically to the plasma membrane, as it is eluted by high salt. Permeabilized, granulocyte-like X-CGD PLB 91CT cells lacking cPLA(2) protein and activity, as well as AA release after stimulation, supported NADPH-dependent diaphorase activity after stimulation, similar to granulocyte-like X-CGD PLB 91CT cells. Normal translocation of p47(phox) and p67(phox) to the membrane fractions of both stimulated cell types indicated that the gp91(phox) C-terminal region is sufficient to anchor the cytosolic oxidase components to the membranes. cPLA(2) translocated to membranes and bound the assembled oxidase in granulocyte-like X-CGD PLB 91CT cells after stimulation. Therefore, the assembled membrane-bound oxidase complex encompassing the flavin domain of gp91(phox) provides a docking site for cPLA(2) but is not the site of AA-based regulation of oxidase activity.