Journal Article

Both base excision repair and <i>O<sup>6</sup></i>-methylguanine-DNA methyltransferase protect against methylation-induced colon carcinogenesis

Stefan Wirtz, Georg Nagel, Leonid Eshkind, Markus F. Neurath, Leona D. Samson and Bernd Kaina

in Carcinogenesis

Volume 31, issue 12, pages 2111-2117
Published in print December 2010 | ISSN: 0143-3334
Published online August 2010 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgq174

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Methylating agents are widely distributed environmental carcinogens. Moreover, they are being used in cancer chemotherapy. The primary target of methylating agents is DNA, and therefore, DNA repair is the first-line barrier in defense against their toxic and carcinogenic effects. Methylating agents induce in the DNA O6-methylguanine (O6MeG) and methylations of the ring nitrogens of purines. The lesions are repaired by O6-methylguanine-DNA methyltransferase (Mgmt) and by enzymes of the base excision repair (BER) pathway, respectively. Whereas O6MeG is well established as a pre-carcinogenic lesion, little is known about the carcinogenic potency of base N-alkylation products such as N3-methyladenine and N3-methylguanine. To determine their role in cancer formation and the role of BER in cancer protection, we checked the response of mice with a targeted gene disruption of Mgmt or N-alkylpurine-DNA glycosylase (Aag) or both Mgmt and Aag, to azoxymethane (AOM)-induced colon carcinogenesis, using non-invasive mini-colonoscopy. We demonstrate that both Mgmt- and Aag-null mice show a higher colon cancer frequency than the wild-type. With a single low dose of AOM (3 mg/kg) Aag-null mice showed an even stronger tumor response than Mgmt-null mice. The data provide evidence that both BER initiated by Aag and O6MeG reversal by Mgmt are required for protection against alkylation-induced colon carcinogenesis. Further, the data indicate that non-repaired N-methylpurines are not only pre-toxic but also pre-carcinogenic DNA lesions.

Journal Article.  4859 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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