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/ þ 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 cirradiation, cisplatin, temozolomide and 5-fluorouracil (5-FU). This leads to increased clonogenic survival in vivo in Mbd4 À/À mice following exposure to either 5-FU or cisplatin. We next analysed the apoptotic response to 5-FU and temozolomide in doubly mutant Mbd4À/À 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 c-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.

Raltitrexed increases tumorigenesis as a single agent yet exhibits anti-tumor synergy with 5-fluorouracil in ApcMin/+ Mice1

“…Interestingly, recent reports indicate that deficiencies in DNA repair pathways confer cellular resistance to fluoropyrimidines, [38][39][40][41] suggesting that this class of drugs has effects at the level of DNA. Such effects likely derive from perturbation of nucleotide pools, misincorporation of nucleotides during DNA replication and/or repair, and apoptosis.…”

A human cancer-associated truncation of MBD4 causes dominant negative impairment of DNA repair in colon cancer cells

“…MBD4 has been shown in vitro to excise mismatched thymine (T) bases from oligo templates Petronzelli et al, 2000a, b), and mouse knockout models have found that in the absence of Mbd4, mutation frequency (MF) in vivo increases, mainly at methyl-CpG sites (Millar et al, 2002;Wong et al, 2002). MBD4 can also bind to MLH1 and Fas-associated death domain (FADD) proteins Screaton et al, 2003), and the small intestine of Mbd4 À/À mice shows reduced apoptosis in response to a variety of DNA-damaging agents (Cortellino et al, 2003;Sansom et al, 2003;Screaton et al, 2003). Absence of Mbd4 in mice also increases tumorigenicity in the tumour-susceptible APC min background (Millar et al, 2002;Wong et al, 2002).…”

Apoptosis and disease: a matter of cell fate

“…38 Mbd4 was essential for the normal apoptotic programme following DNA damage and Mbd4 deficiency can confer increased long-term clonogenic survival in vivo. 39 Clarke suggested that this might be a result of interaction with the death molecule FADD. A possible mechanism might be that Mbd4 retains FADD within the nucleus until DNA damage is recognised, whereupon FADD is released.…”