Inhibition of phosphatidylinositol 4-kinase results in a significant reduced respiratory burst in formyl-methionyl-leucyl-phenylalanine-stimulated human neutrophils

The effects of phenylarsine oxide and a monoclonal antibody directed against type II phosphatidylinositol 4-kinase (PI4K) on the N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated respiratory burst and the PI4K activity in neutrophils were investigated. Fluorescence microscopic imaging showed that the antibody labeled with IANBD amide (N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)ethylenediamine) could enter into the cytosol possibly by endocytosis. It was found that the antibody inhibited the fMLP-stimulated respiratory burst but had little effect on the phorbol myristate acetate-activated respiratory burst in neutrophils, whereas phenylarsine oxide inhibited both. It was found that even at higher concentration, the antibody could not completely inhibit the cell response. Using cells preincubated with human immunoglobulin G of the same concentration as the control, the maximal inhibition of the fMLP-stimulated respiratory burst by the antibody against type II PI4K was found to be about 70%, whereas the PI4K activity was inhibited by only about 40%. The discrepancy in depressing the cell response and the enzyme activity may be the result of depletion of the phosphatidylinositol 4,5-bisphosphate or phosphatidylinositol 3,4,5-trisphosphate pools during the incubation of cells with the antibody. Both the 40% inhibition of PI4K activity and 70% depression of the respiratory burst by the type II PI4K antibody may imply that at least 40% of the phosphatidylinositol 4,5-biphosphate was synthesized promptly by all forms of PI4K and phosphatidylinositol-4-phosphate 5-kinase in the fMLP-activated cells. The results suggest that PI4K plays a central role in either phospholipase C or PI3K signaling and that PI3K, PI4K, and phosphatidylinositol 4-phosphate 5-kinase must be considered as an integrated family for the phosphatidylinositol 3,4,5-trisphosphate initiated signaling.