The NF-κB p65 and p50 homodimer cooperate with IRF8 to activate iNOS transcription

Abstract

BackgroundInducible nitric oxide synthase (iNOS) metabolizes L-arginine to produce nitric oxide (NO) which was originally identified in myeloid cells as a host defense mechanism against pathogens. Recent studies, however, have revealed that iNOS is often induced in tumor cells and myeloid cells in the tumor microenvironment. Compelling experimental data have shown that iNOS promotes tumor development in certain cellular context and suppresses tumor development in other cellular conditions. The molecular mechanisms underlying these contrasting functions of iNOS is unknown. Because iNOS is often induced by inflammatory signals, it is therefore likely that these contrasting functions of iNOS could be controlled by the inflammatory signaling pathways, which remains to be determined.MethodsiNOS is expressed in colon carcinoma and myeloid cells in the tumor microenvironment. Colon carcinoma and myeloid cell lines were used to elucidate the molecular mechanisms underlying iNOS expression. Chromatin immunoprecipitation and electrophoretic mobility shift assay were used to determine the IFNγ-activated pSTAT1 and NF-κB association with the chromatin DNA of the nos2 promoter.ResultsWe show here that iNOS is dramatically up-regulated in inflammed human colon tissues and in human colon carcinoma as compared to normal colon tissue. iNOS is expressed in either the colon carcinoma cells or immune cells within the tumor microenvironment. On the molecular level, the proinflammatory IFNγ and NF-κB signals induce iNOS expression in human colon cancer cells. We further demonstrate that NF-κB directly binds to the NOS2 promoter to regulate iNOS expression. Although neither the IFNγ signaling pathway nor the NF-κB signaling pathway alone is sufficient to induce iNOS expression in myeloid cells, IFNγ and NF-κB synergistically induce iNOS expression in myeloid cells. Furthermore, we determine that IFNγ up-regulates IRF8 expression to augment NF-κB induction of iNOS expression. More interestingly, we observed that the p65/p65 and p50/p50 homodimers, not the canonical p65/p50 heterodimer, directly binds to the nos2 promoter to regulate iNOS expression in myeloid cells.ConclusionsIFNγ-induced IRF8 acts in concert with NF-κB to regulate iNOS expression in both colon carcinoma and myeloid cells. In myeloid cells, the NF-κB complexes that bind to the nos2 promoter are p65/p65 and p50/p50 homodimers.

DNA methylation protects against cisplatin-induced kidney injury by regulating specific genes, including interferon regulatory factor 8

“…The target genes of Irf8 include Fas, Bax, FLIP, STAT1 and iNOS, suggesting an essential role of Irf8 in apoptosis. 58-62 Consistently, knockdown of Irf8 attenuated cisplatin-induced apoptosis in RPTC cells (Figure 7). Thus, hypomethylation of Irf8 during cisplatin-induced AKI may lead to the up-regulation of this pro-apoptotic transcription factor for tubular cell injury and death.…”

All-Trans Retinoic Acid Modulates TLR4/NF-κB Signaling Pathway Targeting TNF-αand Nitric Oxide Synthase 2 Expression in Colonic Mucosa during Ulcerative Colitis and Colitis Associated Cancer

“…It was reported that several key genes in the inflammatory process such as NF- κ B provide a mechanistic link between inflammation and cancer [45–48]. Activation of TLRs and TNFR leads to NF- κ B activation and induced the expression of many proinflammatory molecules including NO synthase 2 (iNOS) [49, 50]. A growing number of studies have reported the key role of TLR4/NF- κ B/TNF- α signaling to promote tumor growth in experimental models of colitis associated cancer [44, 51–53], whereas data from human CAC are rare.…”

SETD1B Activates iNOS Expression in Myeloid-Derived Suppressor Cells

“…In myeloid cells, particularly in macrophages, TNFα and LPS/TLR ligands-activated NF-κB is a major regulator of iNOS expression (27, 28, 42, 43). NF-κB, once activated by LPS or TNFα, can activate iNOS expression (28, 44). The p65 and p50 homodimers of the canonical NF-κB directly binds to the nos2 promoter region to activate nos2 transcription in myeloid cells (28).…”

“…NF-κB, once activated by LPS or TNFα, can activate iNOS expression (28, 44). The p65 and p50 homodimers of the canonical NF-κB directly binds to the nos2 promoter region to activate nos2 transcription in myeloid cells (28). In addition to NF-κB, inflammatory cytokines such as IFN-γ have also been shown to regulate iNOS expression (27, 45).…”