Regulation of TNF-induced Oxygen Radical Production in Human Neutrophils: Role of Delta-PKC

In human neutrophils, TNF-elicited O(2)(-) production requires adherence and integrin activation. How this cooperative signaling between TNFRs and integrins regulates O(2)(-) generation has yet to be fully elucidated. Previously, we identified delta-PKC as a critical early regulator of TNF signaling in adherent neutrophils. In this study, we demonstrate that inhibition of delta-PKC with a dominant-negative delta-PKC TAT peptide resulted in a significant delay in the onset time of TNF-elicited O(2)(-) generation but had no effect on Vmax, indicating an involvement of delta-PKC in the initiation of O(2)(-) production. In contrast, fMLP-elicited O(2)(-) production in adherent and nonadherent neutrophils was delta-PKC-independent, suggesting differential regulation of O(2)(-) production. An important step in activation of the NADPH oxidase is phosphorylation of the cytosolic p47phox component. In adherent neutrophils, TNF triggered a time-dependent association of delta-PKC with p47phox, which was associated with p47phox phosphorylation, indicating a role for delta-PKC in regulating O(2)(-) production at the level of p47phox. Activation of ERK and p38 MAPK is also required for TNF-elicited O(2)(-) generation. TNF-mediated ERK but not p38 MAPK recruitment to p47phox was delta-PKC-dependent. delta-PKC activity is controlled through serine/threonine phosphorylation, and phosphorylation of delta-PKC (Ser643) and delta-PKC (Thr505) was increased significantly by TNF in adherent cells via a PI3K-dependent process. Thus, signaling for TNF-elicited O(2)(-) generation is regulated by delta-PKC. Adherence-dependent cooperative signaling activates PI3K signaling, delta-PKC phosphorylation, and delta-PKC recruitment to p47phox. delta-PKC activates p47phox by serine phosphorylation or indirectly through control of ERK recruitment to p47phox.