title: Topoisomerase II-mediated DNA cleavage and mutagenesis activated by nitric oxide underlie the inflammation-associated tumorigenesis.
abstract: OBJECTIVE
  Both cancer-suppressing and cancer-promoting properties of reactive nitrogen and oxygen species (RNOS) have been suggested to play a role in tumor pathology, particularly those activities associated with chronic inflammation. Here, we address the impact of nitric oxide (NO) on the induction of DNA damage and genome instability with a specific focus on the involvement of topoisomerase II (TOP2). We also investigate the contribution of NO to the formation of skin melanoma in mice.
  
  
  RESULTS
  Similar to the TOP2-targeting drug, etoposide (VP-16), the NO-donor, S-nitrosoglutathione (GSNO), induces skin melanomas formation in 7,12-dimethyl- benz[a]anthracene (DMBA)-initiated mice. To explore the mechanism(s) underlying this NO-induced tumorigenesis, we use a co-culture model system to demonstrate that inflamed macrophages with inducible NO synthase (iNOS) expression cause γ-H2AX activation, p53 phosphorylation, and chromosome DNA breaks in the target cells. Inhibitor experiments revealed that NO and TOP2 isozymes are responsible for the above described cellular phenotypes. Notably, NO, unlike VP-16, preferentially induces the formation of TOP2β cleavable complexes (TOP2βcc) in cells. Moreover, GSNO induced TOP2-dependent DNA sequence rearrangements and cytotoxicity. Furthermore, the incidences of GSNO- and VP-16-induced skin melanomas were also observed to be lower in the skin-specific top2β-knockout mice. Our results suggest that TOP2 isozymes contribute to NO-induced mutagenesis and subsequent cancer development during chronic inflammation.
  
  
  CONCLUSIONS
  We provide the first experimental evidence for the functional role of TOP2 in NO-caused DNA damage, mutagenesis, and carcinogenesis. Notably, these studies contribute to our molecular understanding of the cancer-promoting actions of RNOS during chronic inflammation.
authors.affiliation: Department and Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Yu-Chen
authors.initials: YC
authors.lastname: Yang
authors.forename: Han-Yi E
authors.initials: HY
authors.lastname: Chou
authors.forename: Tang-Long
authors.initials: TL
authors.lastname: Shen
authors.forename: Wei-Jer
authors.initials: WJ
authors.lastname: Chang
authors.forename: Pei-Han
authors.initials: PH
authors.lastname: Tai
authors.forename: Tsai-Kun
authors.initials: TK
authors.lastname: Li
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000378:metabolism*; D018920:Coculture Techniques; D053837:DNA Cleavage / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology; D045325:HCT116 Cells; D018922:HL-60 Cells; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000503:physiopathology; D051379:Mice; D018345:Mice, Knockout; D016296:Mutagenesis / Q000187:drug effects / Q000235:genetics; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D026422:S-Nitrosoglutathione / Q000494:pharmacology
chemical_list: D020030:Nitric Oxide Donors; D011725:Pyridines; C431843:tris(2-pyridylmethyl)amine; D009569:Nitric Oxide; D015127:9,10-Dimethyl-1,2-benzanthracene; D026422:S-Nitrosoglutathione; D005047:Etoposide; D004250:DNA Topoisomerases, Type II