title: MBD4 deficiency reduces the apoptotic response to DNA-damaging agents in the murine small intestine.
abstract: MBD4 was originally identified through its methyl binding domain, but has more recently been characterized as a thymine DNA glycosylase that interacts with the mismatch repair (MMR) protein MLH1. In vivo, MBD4 functions to reduce the mutability of methyl-CpG sites in the genome and mice deticient in MBD4 show increased intestinal tumorigenesis on an Apc(Min/+) background. As MLH1 and other MMR proteins have been functionally linked to apoptosis, we asked whether MBD4 also plays a role in mediating the apoptotic response within the murine small intestine. Mice deficient for MBD4 showed significantly reduced apoptotic responses 6 h following treatment with a range of cytotoxic agents including gamma-irradiation, cisplatin, temozolomide and 5-fluorouracil (5-FU). This leads to increased clonogenic survival in vivo in Mbd4(-/-) mice following exposure to either 5-FU or cisplatin. We next analysed the apoptotic response to 5-FU and temozolomide in doubly mutant Mbd4(-/-), Mlh1(-/-) mice but observed no additive decrease. The results imply that MBD4 and MLH1 lie in the same pathway and therefore that MMR-dependent apoptosis is mediated through MBD4. MBD4 deficiency also reduced the normal apoptotic response to gamma-irradiation, which we show is independent of Mlh1 status (at least in the murine small intestine), so suggesting that the reliance upon MBD4 may extend beyond MMR-mediated apoptosis. Our results establish a novel functional role for MBD4 in the cellular response to DNA damage and may have implications for its role in suppressing neoplasia.
authors.affiliation: Cardiff School of Biosciences, Cardiff University, PO Box 911, Cardiff CF10 3US, UK.
authors.forename: Owen James
authors.initials: OJ
authors.lastname: Sansom
authors.forename: Joanna
authors.initials: J
authors.lastname: Zabkiewicz
authors.forename: Stefan Mark
authors.initials: SM
authors.lastname: Bishop
authors.forename: Jackie
authors.initials: J
authors.lastname: Guy
authors.forename: Adrian
authors.initials: A
authors.lastname: Bird
authors.forename: Alan Richard
authors.initials: AR
authors.lastname: Clarke
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002945:Cisplatin / Q000633:toxicity; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000633:toxicity; D004706:Endodeoxyribonucleases / Q000172:deficiency* / Q000235:genetics; D005472:Fluorouracil / Q000633:toxicity; D007413:Intestinal Mucosa / Q000187:drug effects / Q000473:pathology*; D007421:Intestine, Small / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D000077204:Temozolomide
chemical_list: D000970:Antineoplastic Agents; D003606:Dacarbazine; D004706:Endodeoxyribonucleases; C492249:Mbd4 protein, mouse; D002945:Cisplatin; D005472:Fluorouracil; D000077204:Temozolomide