During the past several years, major advances have been made in understanding how reactive oxygen species (ROS) and nitrogen species (RNS) participate in signal transduction. Identification of the specific targets and the chemical reactions involved still remains to be resolved with many of the signaling pathways in which the involvement of reactive species has been determined. Our understanding is that ROS and RNS have second messenger roles. While cysteine residues in the thiolate (ionized) form found in several classes of signaling proteins can be specific targets for reaction with H 2 O 2 and RNS, better understanding of the chemistry, particularly kinetics, suggests that for many signaling events in which ROS and RNS participate, enzymatic catalysis is more likely to be involved than non-enzymatic reaction. Due to increased interest in how oxidation products, particularly lipid peroxidation products, also are involved with signaling, a review of signaling by 4-hydroxy-2-nonenal (HNE) is included. This article focuses on the chemistry of signaling by ROS, RNS, and HNE and will describe reactions with selected target proteins as representatives of the mechanisms rather attempt to comprehensively review the many signaling pathways in which the reactive species are involved. Keywords signaling; glutathione; thioredoxin; oxidants; reactive oxygen species; thiols; peroxide; nitric oxide; peroxynitrite; 4-hydroxynonenal; cysteine; hydrogen peroxide; protein tyrosine phosphatase; reactive nitrogen species; eNOS; iNOS; nNOS; soluble guanylate cyclase; cGMP; tyrosine nitration; fatty acid nitration; NO-heme; NO-metal complexes; nitrite; protein kinase C; ERK; JNK; p38MAPK; tyrosine kinase receptors; calcium OVERVIEW OF SIGNALING BY REACTIVE SPECIESUnderstanding of the roles of reactive oxygen species (ROS), reactive nitrogen species (RNS) and the lipid peroxidation product, 4-hydroxy-2-nonenal (HNE) in signaling has evolved rapidly during the last decade. This has been markedly helped by identification of the specific targets in signaling pathways. In previous reviews, we defined how ROS, H 2 O 2 in particular,

Summaryc-Myc is a transcription factor that is implicated in many cellular processes including proliferation, apoptosis and cancers. Recently, c-Myc was shown to be involved in regulation of glutamate cysteine ligase through E-box sequences. This investigation examined whether c-Myc also regulates phase II genes through interaction with the electrophile response element (EpRE). Experiments were conducted in human bronchial epithelial cells using si-RNA to knock down c-Myc. RT-PCR and reporter assays were used to measure transcription and promoter activity. c-Myc downregulated transcription and promoter activity of phase II genes.

The transcription factors that bind to EpRE elements play a key role in the regulation of phase II genes. In this study, we examined whether c-Jun, a partner of Nrf2 in binding to EpRE, requires phosphorylation by JNK for binding and transcriptional activation. We used chromatin immunoprecipitation assays (ChIP) to measure recruitment of transcription factors to EpRE sequences in nqo2, gclc and gclm, western analysis for phosphorylation of JNK, and EpRE driven reporters along with a JNK specific inhibitor peptide to determine the potential importance of c-Jun phosphorylation. Human bronchial epithelial (HBE1) and human hepatoma (HepG2) cells were exposed to 4-hydroxy-2-nonenal (HNE) and differences in regulation of the same EpRE sequences examined. We found binding of c-Jun to EpRE sequences increased subsequent to HNE exposure in HepG2 cells; however, in HNE-exposed HBE1 cells, binding of only phosphorylated c-Jun to the three EpRE sequences increased. Despite the increase in binding of phosphorylated c-Jun, reporter assays for EpREs showed that inhibition of c-Jun phosphorylation had variable effects on basal and HNE-induced transcription of gclc and gclm in HBE1 cells. Thus, in terms of its role in mediating HNE-induction of EpRE-mediated transcription, c-Jun appears to be a partner of Nrf2 and while its phosphorylated form may predominate in one cell type versus another, the effect of phosphorylation of c-Jun on transcription can vary with the gene. This contrasts markedly with the well-established requirement for phosphorylation of c-Jun in the activation of AP-1/TRE mediated transcription.

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Pentachlorophenol (PCP) is used in industrial and domestic applications, including as a biocide and a wood preservative. Metabolism of PCP undergoes oxidative dechlorination, forming tetrachlorocatechol (TCC) and tetrachlorohydroquinone (TCHQ). Both sodium azide (NaN(3)) and TCC appear naturally in soil. None of them are cytotoxic by themselves or facilitate autooxidation. Here, we show that their combination leads to synergistic cytotoxicity (>6 log bacterial killing) to Escherichia coli. The rate of oxygen consumption in a cell-free system showed that NaN(3) increases TCC oxidation by 520-fold. The synergism coefficient to cells was calculated as 96 or greater, and we have shown the formation of a new compound. It is suggested that the intermediate species, o-tetrachlorosemiquinine, and an unknown, nitrogen-centered free radical, both visualized by electron-spin resonance, are harmful species responsible for the synergistic cytotoxicity of TCC/NaN(3), rather than the endproduct formed during the reaction. Desferrioxamine and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide offered nearly complete protection, but through radical scavenging rather than through chelating properties. The mechanism of damage for TCC compared to its analogue, TCHQ, were investigated, and whereas the cellular damage of TCHQ/NaN(3) is through a site-specific mechanism, in the case of TCC/NaN(3) it is through the accumulation of the component(s) in the bacterial cell membrane, eventually leading to dysfunction, as evidenced by electron microscopy.