Superoxide Attenuates Macrophage Apoptosis by NF-κB and AP-1 Activation That Promotes Cyclooxygenase-2 Expression

Abstract

Macrophages are a major source of cytokines and proinflammatory radicals such as superoxide. These mediators can be both produced and utilized by macrophages in autocrine-regulatory pathways. Therefore, we studied the potential role of oxygen radical-regulatory mechanisms in reprogramming macrophage apoptosis. Preactivation of RAW 264.7 cells with a nontoxic dose of the redox cycler 2,3-dimethoxy-1,4-naphtoquinone (5 μM) for 15 h attenuated S-nitrosoglutathione (1 mM)-initiated apoptotic cell death and averted accumulation of the tumor suppressor p53, which is indicative for macrophage apoptosis. Preactivation with superoxide promoted cyclooxygenase-2 induction that was NF-κB and AP-1 mediated. NF-κB activation was confirmed by p50/p65-heterodimer formation, IκB-α degradation, and stimulation of a NF-κB luciferase reporter construct. Furthermore, a NF-κB decoy approach abrogated cyclooxygenase-2 (Cox-2) expression as well as inducible protection. The importance of AP-1 for superoxide-mediated Cox-2 expression and cell protection was substantiated by using the extracellular signal-regulated kinase-inhibitor PD98059 and the p38-inhibitor SB203580, which blocked Cox-2 expression. In corroboration, Cox-2 expression was hindered by a dominant-negative c-jun mutant (TAM67). Protection from apoptosis was verified in human macrophages with the notion that superoxide promoted Cox-2 expression, which in turn attenuated nitric oxide-evoked caspase activation. We conclude that the sublethal generation of oxygen radicals reprograms macrophages by NF-κB and AP-1 activation. The resulting hyporesponsiveness reveals an attenuated apoptotic program in association with Cox-2 expression.