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The phagocyte reduced nicotinamide adenine dinucleotide phosphate oxidase is a multiprotein enzyme that catalyzes the production of microbicidal oxidants. Although oxidase assembly involves association of several membrane and cytosolic oxidase proteins, one of the cytosolic cofactors, p67phox, appears to play a more prominent role in final activation of the enzyme complex. Based on the importance of p67phox, we investigated transcriptional regulation of the p67phox gene [neutrophil cytosolic factor 2 (NCF2)] and demonstrated previously that activator protein-1 (AP-1) was essential for basal transcriptional activity. As p67phox can be up-regulated by tumor necrosis factor alpha (TNF-alpha), which activates AP-1, we hypothesized that TNF-alpha might regulate NCF2transcription via AP-1. In support of this hypothesis, we show here that NCF2 promoter-reporter constructs are up-regulated by TNF-alpha but only when AP-1 factors were coexpressed. Consistent with this observation, we also demonstrate that NCF2 mRNA and p67phox protein are up-regulated by TNF-alpha in various myeloid cell lines as well as in human monocytes. It was surprising that mutagenesis of the AP-1 site in NCF2 promoter constructs did not eliminate TNF-alpha induction, suggesting additional elements were involved in this response and that AP-1 might play a more indirect role. Indeed, we used NCF2 promoter-deletion constructs to map a novel TNF-alpha-responsive region (TRR) located between -56 and -16 bp upstream of the translational start site and demonstrated its importance in vivo using transcription factor decoy analysis. Furthermore, DNase footprinting verified specific binding of factor(s) to the TRR with AP-1 binding indirectly to this region. Thus, we have identified a novel NCF2 promoter/enhancer domain, which is essential for TNF-alpha-induced up-regulation of p67phox.

The cytosolic NADPH oxidase cofactor p67(phox) has been shown to be one of the limiting factors in assembly and activation of this multi-protein enzyme complex and, therefore, must be highly regulated at the transcriptional level. In the present studies, we have further characterized the promoter for human p67(phox). Genomic sequence upstream of the translational start site (TLS; 2 kb) was cloned, and RACE was used to identify and compare the transcriptional start site (TSS) in two myeloid cell lines, HL-60 and PLB-985. Two major TSS were identified within the first intron for both cell lines, and one transcript isolated from PLB-985 cells started approximately 34 bp 5' of exon 1 and contained no intron 1 sequence. To identify regulatory regions of the promoter, a luciferase reporter was used to assay a series of promoter deletion constructs. The greatest transcriptional activity was observed for fragments containing at least 500 bp upstream of the TLS. Sequence analysis of the p67(phox) promoter revealed consensus binding sites for previously described transcription factors including AP-1 and PU.1. Site-directed mutagenesis of the AP-1 site demonstrated that this site was essential for basal transcription. EMSA, competition, and super-shift assays showed that this site was specifically recognized by nuclear factors of the AP-1 family. EMSA analysis and promoter-reporter assays with the PU.1 consensus sites at positions -176, -283, and -328 demonstrate that PU.1 binds the site at position -283 with high affinity. Mutagenesis of any one of the PU.1 sites reduced the basal transcriptional activity by approximately 50%, demonstrating that, although none of these sites is singularly responsible for the basal transcriptional activity, all three sites play some role in the transcriptional activity of the p67(phox) promoter. In support of this conclusion, mutagenesis of all three sites completely abrogated transcriptional activity.