ARACHIDONIC-ACID INCREASES ACTIVATION OF NADPH OXIDASE IN MONOCYTIC U937 CELLS BY ACCELERATED TRANSLOCATION OF P47-PHOX AND CO-STIMULATION OF PROTEIN-KINASE-C

Arachidonic acid (AA) has been implicated as an important amphiphilic co-factor in the activation of reduced nicotinamide adenine dinucleoti de phosphate (NADPH) oxidase in neutrophils and reconstituted cell-fre e systems. To assess the role of AA in the activation of O-2(-) genera tion in monocytic cells, we studied pre-monocytic U937 cells different iated with 1,25-(OH)(2)-vitamin D-3 plus interferon-gamma (IFN-gamma). AA dose-dependently enhanced phorbol myristate acetate (PIMA)-stimula ted O-2(-) generation, with a maximum increase of 4.5-fold, through: ( 1) a more than 50% reduction of the lag-phase, defined as the time bet ween addition of PMA and detection of O-2(-); and (2) a more than 60% increase in the constant rate of O-2(-) generation. Reduction of the l ag phase was associated with increased protein kinase C (PKC)- indepen dent translocation of the cytosolic subunit of NADPH oxidase p47-phox to the cell membrane, whereas increased generation of O-2(-) correlate d with enhanced activation of PKC. The data indicate that AA increases activation of NADPH oxidase by accelerating its assembly and by co-st imulating PKC in monocytic U937 cells.