NO Inhibits Cytokine-Induced iNOS Expression and NF-κB Activation by Interfering With Phosphorylation and Degradation of IκB-α

Abstract

Abstract-Nitric oxide (NO) is known to have antiatherogenic and anti-inflammatory properties, but its effects on the cytokine-induced nuclear factor-kappa B (NF-B) activation pathway in relation to the regulation of inducible nitric oxide synthase (iNOS) gene in vascular smooth muscle cells (VSMCs) remain elusive. To elucidate the roles of NO in the regulation of cytokine-induced NF-B activation and consequent iNOS gene expression, we studied the effects of synthases (NOSs). Three distinct isozymes of NOS have been identified to date: 2 Ca 2ϩ /calmodulin-dependent constitutive isozymes dominantly expressed in the brain and endothelium, and a Ca 2ϩ -independent, cytokine-inducible isozyme (iNOS). 1 iNOS produces large amounts of NO in response to bacterial lipopolysaccharides (LPS) and certain cytokines in a variety of cells, including vascular smooth muscle cells (VSMCs). 2 NO possesses diverse physiological properties, such as vasodilation, neurotransmission, and mediation of immune responses. 1 High-output NO produced by iNOS in VSMCs not only causes inhibition of cell proliferation but apoptosis of VSMCs as well. 3,4 Therefore, regulation of iNOS gene expression has been implicated in the pathogenesis of vascular remodeling and atherosclerosis. 5 Many of the biological effects of NO have been attributed to cGMP generation via the stimulation of soluble guanylate cyclase, although a cGMP-independent mechanism is also involved in its diverse actions.The promoter region of the rat and mouse iNOS gene contains several potential cis-elements for the binding of different transcription factors, among which 2 putative binding sites for nuclear factor-kappa B (NF-B) exist in the upstream (GGGGATTTTCC, nucleotides Ϫ965 to Ϫ955: NF-Bu) and downstream (GGGGACTCTCC, nucleotides Ϫ107 to Ϫ97: NF-Bd) regions. [6][7][8] The sequence of NF-Bd is unique in that it is found only in murine and human iNOS genes. It has been shown that a key region of the promoter activity in mediation of LPS inducibility resides in the NF-Bd region in mouse macrophages. 6,7 However, its role in mediation of iNOS expression in response to cytokines in VSMCs remains largely unknown.NF-B complexes function as a pleiotropic regulator of many genes modulating immunologic and inflammatory pro-

Catalytic consumption of nitric oxide by 12/15- lipoxygenase: Inhibition of monocyte soluble guanylate cyclase activation

“…Under basal conditions, ⅐ NO plays a central role in maintaining vascular homeostasis (56)(57)(58)(59). Thus, stimulation of ⅐ NO consumption by monocytes will contribute to proatherogenic conditions by increasing leukocyte adhesion and margination.…”

Nitric oxide: a key regulator of myeloid inflammatory cell apoptosis

“…124 Alternatively, transcriptional induction and stabilisation of the inhibitory molecule IkB, that keeps NF-kB sequestered in the cytoplasm, may account for the inhibition of NF-kB activity. 125 Furthermore, it has been reported that NO inhibits NF-kB activation in rat vascular smooth muscle cells via a cGMP-independent inhibition of the phosphorylation and proteasomal degradation of I-kB, 126 and inhibition of the proteasome by NO has additionally been demonstrated by Glockzin et al 127 in macrophages. The result of such inhibition would be downregulation of survival factors under the control of this transcription factor, such as the antiapoptotic Bcl-2 family members.…”

Nuclear transcription factor-κB as a target for cancer drug development

“…Examples include aspirin, 230,231 (sodium salicylate), ibuprofen, 232 nitric oxide, [233][234][235] prostoglandin A1, 236 sanguinarine, 237 and YopJ (encoded by Yersinia pseudotuberculosis). 238 Recently, 4-hydroxy-2-nonenal, a lipid peroxidation product, has been shown to block phosphorylation by direct inhibition of IKK.…”