Incorporation of 5-chlorocytosine into mammalian DNA results in heritable gene silencing and altered cytosine methylation patterns

103

Significance Our study investigates chemical damage associated with chronic inflammation and relates these macromolecular damage products to inflammatory bowel disease activity. Using mice as a model system, we show that chronic inflammatory responses that are common to mice and humans produce similar types and quantities of damage products in both species. Additional analysis of signaling molecules in the serum and tissue of diseased samples highlights the role of the innate immune response in the overall pathology of inflammatory bowel disease.

Section: Discussionmentioning

confidence: 87%

Chemical and cytokine features of innate immunity characterize serum and tissue profiles in inflammatory bowel disease

Knutson

Mangerich

Zeng

et al. 2013

103

“…Interestingly, one of the mechanisms that leads to microsatellite instability is inhibition of MLH1 expression, a key mismatch repair protein, by hypermethylation (59). As mentioned earlier, one biochemical feature of 5ClC, when present in CpG islands, is the ability to induce DNA hypermethylation (25,60). Therefore, we speculate that signature 6 (and/or signature H) may reflect both the mutagenic and the epigenetic features of genomic 5ClC accumulation and thus represent the mutational signature of neutrophil-driven chronic inflammation (Fig.…”

Section: The Mechanistic Link Between Chronic Inflammation and Geneticmentioning

confidence: 95%

“…So far, research on 5ClC has focused on the lesion's ability to interact with DNA methyl transferases (22)(23)(24) when 5ClC is part of a CpG island; this interaction was shown to lead to changes in DNA methylation patterns (25). However, there are no reports affirming the ability of 5ClC to induce genetic changes directly during the replication or repair of genomic DNA.…”

mentioning

confidence: 99%

Intrinsic mutagenic properties of 5-chlorocytosine: A mechanistic connection between chronic inflammation and cancer

Fedeles

Freudenthal

Yau

et al. 2015

During chronic inflammation, neutrophil-secreted hypochlorous acid can damage nearby cells inducing the genomic accumulation of 5-chlorocytosine (5ClC), a known inflammation biomarker. Although 5ClC has been shown to promote epigenetic changes, it has been unknown heretofore if 5ClC directly perpetrates a mutagenic outcome within the cell. The present work shows that 5ClC is intrinsically mutagenic, both in vitro and, at a level of a single molecule per cell, in vivo. Using biochemical and genetic approaches, we have quantified the mutagenic and toxic properties of 5ClC, showing that this lesion caused C→T transitions at frequencies ranging from 3-9% depending on the polymerase traversing the lesion. X-ray crystallographic studies provided a molecular basis for the mutagenicity of 5ClC; a snapshot of human polymerase β replicating across a primed 5ClC-containing template uncovered 5ClC engaged in a nascent base pair with an incoming dATP analog. Accommodation of the chlorine substituent in the template major groove enabled a unique interaction between 5ClC and the incoming dATP, which would facilitate mutagenic lesion bypass. The type of mutation induced by 5ClC, the C→T transition, has been previously shown to occur in substantial amounts both in tissues under inflammatory stress and in the genomes of many inflammation-associated cancers. In fact, many sequence-specific mutational signatures uncovered in sequenced cancer genomes feature C→T mutations. Therefore, the mutagenic ability of 5ClC documented in the present study may constitute a direct functional link between chronic inflammation and the genetic changes that enable and promote malignant transformation.5-chloro-deoxycytidine | hypochlorite | myeloperoxidase | inflammatory bowel disease | carcinogenesis

“…Further, chlorination-derived damage products have also been associated with other inflammatory conditions, such as higher levels of 5-chlorouracil in human atherosclerotic tissue (40) and dihalogenated 2′-deoxycytidine in lungs and livers of mice treated with proinflammatory lipopolysaccharaide (41). It has been observed that 5-Cl-dC mimics 5-methyl-dC and induces inappropriate DNMT1 methylation within CpG sequences (9,42,43), which may result in altered cytosine methylation patterns that could affect the expression of tumor suppressor genes and initiate carcinogenesis (9,42,43). Localized oxidation chemistry also appears to play an important role in the spectrum of DNA and RNA lesions.…”

Section: )mentioning

confidence: 99%

Infection-induced colitis in mice causes dynamic and tissue-specific changes in stress response and DNA damage leading to colon cancer

Mangerich

Knutson

Parry³

et al. 2012

208

294

Helicobacter hepaticus -infected Rag 2 -/- mice emulate many aspects of human inflammatory bowel disease, including the development of colitis and colon cancer. To elucidate mechanisms of inflammation-induced carcinogenesis, we undertook a comprehensive analysis of histopathology, molecular damage, and gene expression changes during disease progression in these mice. Infected mice developed severe colitis and hepatitis by 10 wk post-infection, progressing into colon carcinoma by 20 wk post-infection, with pronounced pathology in the cecum and proximal colon marked by infiltration of neutrophils and macrophages. Transcriptional profiling revealed decreased expression of DNA repair and oxidative stress response genes in colon, but not in liver. Mass spectrometric analysis revealed higher levels of DNA and RNA damage products in liver compared to colon and infection-induced increases in 5-chlorocytosine in DNA and RNA and hypoxanthine in DNA. Paradoxically, infection was associated with decreased levels of DNA etheno adducts. Levels of nucleic acid damage from the same chemical class were strongly correlated in both liver and colon. The results support a model of inflammation-mediated carcinogenesis involving infiltration of phagocytes and generation of reactive species that cause local molecular damage leading to cell dysfunction, mutation, and cell death. There are strong correlations among histopathology, phagocyte infiltration, and damage chemistry that suggest a major role for neutrophils in inflammation-associated cancer progression. Further, paradoxical changes in nucleic acid damage were observed in tissue- and chemistry-specific patterns. The results also reveal features of cell stress response that point to microbial pathophysiology and mechanisms of cell senescence as important mechanistic links to cancer.