Evidence of In Vivo Peroxynitrite Formation in Patients With Colorectal Carcinoma, Higher Plasma Nitrate/Nitrite Levels, and Lower Protection Against Oxygen Free Radicals

158

106

The release of cytochrome c from mitochondria is a crucial step in apoptosis, resulting in the activation of the caspase proteases. A further consequence of cytochrome c release is the enhanced mitochondrial production of superoxide radicals (O 2 . ), which are converted to hydrogen peroxide by manganese-superoxide dismutase. Recently, we showed that cytochrome c is a potent catalyst of 2,7-dichlorofluorescin oxidation to the fluorescent 2,7-dichlorofluorescein by these species, leading to the conclusion that 2,7-dichlorofluorescein fluorescence is a reflection of cytosolic cytochrome c concentration rather than "reactive oxygen species" levels (Burkitt, M. J., and Wardman, P.

Section: Traces B and D)mentioning

confidence: 87%

Evidence for the Role of a Peroxidase Compound I-type Intermediate in the Oxidation of Glutathione, NADH, Ascorbate, and Dichlorofluorescin by Cytochrome c/H2O2

Lawrence

Jones

Wardman

et al. 2003

158

106

“…In colorectal cancer augmented expression of iNOS is evident in infiltrating mononuclear cells but characteristically also in tumor epithelial cells (23,25). Notably, increased levels of nitrotyrosine residues can be detected in the colonic tumor microenvironment indicative of enhanced NOS activity (23,30). Although the role of iNOS in tumor biology may depend on the type of cancer and on the amount of NO being produced in an In addition, cells were mock-transfected for control conditions or IL-22 (20 ng/ml)/IFN␥ (10 ng/ml) stimulations that were performed in the absence of STAT3-siRNA or control siRNA, respectively.…”

Section: Discussionmentioning

confidence: 99%

The Interleukin-22/STAT3 Pathway Potentiates Expression of Inducible Nitric-oxide Synthase in Human Colon Carcinoma Cells

Ziesché

Bachmann

Kleinert

et al. 2007

105

Interleukin (IL)2 -22 is a newly described member of the IL-10 family of cytokines that is produced by T and NK cells under conditions of immunoactivation. Initiation of the Jak1/Tyk2/ signal transducer and activator of transcription (STAT) 3 pathway appears to be the major mode of IL-22 signal transduction (1-4), although activation of STAT1 (5, 6), mitogen-activated protein kinases (5-7), nuclear factor B (NF-B) (8), activator protein-1 (8), and protein kinase B (6) has been related to this cytokine under specific conditions. IL-22 signaling is established by binding of the cytokine to its heterodimeric receptor complex consisting of IL-22R1 and IL-10R2 (2, 3). Because IL-10R2 is a ubiquitous protein, cellular IL-22 responsiveness is mainly determined by expression of the IL-22R1 receptor chain. Interestingly, IL-22R1 expression is restricted to nonleukocytic cells (9 -11). Therefore, IL-22 appears to be unique among a vast array of cytokines in that this protein is incapable of mediating autocrine or paracrine functions between leukocytes but is rather specialized to transmit information between leukocytes and the nonleukocytic cell compartment. This distinctive biological characteristic essentially discriminates IL-22 from another major activator of the STAT3 signaling system, namely IL-6 (12). Cell types identified to be responsive to IL-22 include synoviocytes (7), pancreatic acinar cells (11), hepatocytes (5, 13, 14), colonic epithelial myofibroblasts (8), and in particular cells of epithelial origin such as keratinocytes (10,15), lung carcinoma cells (16), and colon carcinoma cells (6,17). Proteins that have been reported to be inducible by IL-22 include pro-inflammatory and pro-angiogenic mediators such as IL-8 and enzymes that are involved in cell migration and tissue remodeling such as matrix metalloprotease-1 and -3 (6, 8), effector molecules of innate immunity such as ␤-defensins (10), and immunosuppressive modulators such as IL-10 (17) and SOCS proteins (17, 18). IL-22-induced STAT3 has been associated with induction of the acute phase response (13), with proliferation, and with protection from cell death (6, 14). Interestingly, constitutive activation of the STAT3 pathway is characteristic for numerous human malignancies. Based on the capabilities of this transcription factor to inhibit apoptosis and to promote cell proliferation, STAT3 is actually considered an oncogenic protein (12,19,20).Inducible nitric-oxide synthase (iNOS) and its volatile enzymatic product nitric oxide (NO) have been identified as potential promoters of tumor growth in a variety of human neoplasia, among other colorectal cancers (20 -24). The ability of iNOS to * This work was supported by Deutsche Forschungsgemeinschaft Grants GK1172 Biologicals and SFB 553. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.

“…In addition, peroxynitrite plays a major role in carcinogenesis and tumor progression leading to peroxynitrite-dependent modification of proteins, in particular in patients with colorectal and breast carcinoma (43,44,58). Moreover, different enzymes such as cytochromes P450 (38,39) and glutathione S-transferase (40) have been shown to be inhibited by peroxynitrite.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, evidence is accumulating from studies in vitro and in vivo that peroxynitrite is generated during carcinogenesis and promotes this process, in particular for colon and breast cancer (30,(42)(43)(44). As stated above, NAT1 has been shown to be highly expressed in normal and cancerous human breast tissue (17).…”

Section: From the ‡Cnrs-unité Mixte De Recherche 7000 Faculté De Médmentioning

confidence: 99%

Peroxynitrite Irreversibly Inactivates the Human Xenobioticmetabolizing Enzyme Arylamine N-Acetyltransferase 1 (NAT1) in Human Breast Cancer Cells

Dairou

Atmane

Rodrigues‐Lima

et al. 2004

Arylamine N-acetyltransferases (NATs) play an important role in the detoxification and metabolic activation of a variety of aromatic xenobiotics, including numerous carcinogens. Both of the human isoforms, NAT1 and NAT2, display interindividual variations, and associations between NAT genotypes and cancer risk have been established. Contrary to NAT2, NAT1 has a ubiquitous tissue distribution and has been shown to be expressed in cancer cells. Given that the activity of NAT1 depends on a reactive cysteine that can be a target for oxidants, we studied whether peroxynitrite, a highly reactive nitrogen species involved in human carcinogenesis, could inhibit the activity of endogenous NAT1 in MCF7 breast cancer cells. We show here that exposure of MCF7 cells to physiological concentrations of peroxynitrite and to a peroxynitrite generator (3-morpholinosydnonimine Nethylcarbamide, or SIN1) leads to the irreversible inactivation of NAT1 in cells. Further kinetic and mechanistic analyses using recombinant NAT1 showed that the enzyme is rapidly (k inact ‫؍‬ 5 ؋ 10 4 M ؊1 ⅐s ؊1 ) and irreversibly inactivated by peroxynitrite. This inactivation is due to oxidative modification of the catalytic cysteine. We conclude that the reducing cellular environment of MCF7 cells does not sufficiently protect NAT1 from peroxynitrite-dependent inactivation and that only high concentrations of reduced glutathione could significantly protect NAT1. Thus, cellular generation of peroxynitrite may contribute to carcinogenesis and tumor progression by weakening key cellular defense enzymes such as NAT1.