Involvement of ATF3 in the negative regulation of iNOS expression and NO production in activated macrophages

Macrophage-associated nitric oxide (NO) production plays a crucial role in the pathogenesis of tissue damage. However, negative factors that regulate NO production remains poorly understood despite its significance of NO homeostasis. Here, we show that activating transcription factor 3 (ATF3), a transcriptional regulator of cellular stress responses, was strongly induced in activated macrophages and its depletion resulted in pronounced enhancement of inducible nitric oxide synthase (iNOS) gene expression and subsequently the induction of high levels of NO production. In response to lipopolysaccharide (LPS) and IFN-gamma, ATF3 inhibited transcriptional activity of NF-kappa B by interacting with the N-terminal (1-200 amino acids) of p65 and was bound to the NF-kappa B promoter, leading to suppression of iNOS gene expression. In addition, inhibitory effects of ATF3 on iNOS and NO secretion were suppressed by inhibitor of casein kinase II (CK2) activity or its knockdown. Moreover, the levels of ATF3 were highly elevated in established cecal ligation and puncture or LPS-injected mice, a model of endotoxemia. ATF3 is also elevated in peritoneal macrophages. Collectively, our findings suggest that ATF3 regulates NO homeostasis by associating with NF-kappa B component, leading to the repression of its transcriptional activity upon inflammatory signals and points to its potential relevance for the control of cell injuries mediated by NO during macrophage activation.