MBD4 deficiency reduces the apoptotic response to DNA-damaging agents in the murine small intestine.
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.
Sansom
Owen James
OJ
Cardiff School of Biosciences, Cardiff University, PO Box 911, Cardiff CF10 3US, UK.
Zabkiewicz
Joanna
J
Bishop
Stefan Mark
SM
Guy
Jackie
J
Bird
Adrian
A
Clarke
Alan Richard
AR
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
D000970:Antineoplastic Agents; D003606:Dacarbazine; D004706:Endodeoxyribonucleases; C492249:Mbd4 protein, mouse; D002945:Cisplatin; D005472:Fluorouracil; D000077204:Temozolomide