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Mbd4 inactivation increases Cright-arrowT transition mutations and promotes gastrointestinal tumor formation
Edmund Wong1, Kan Yang, Mari Kuraguchi
1Department of Cell Biology, Biostatistics Core, Albert Einstein Cancer Center, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
Abstract:
Mbd4 (methyl-CpG binding domain 4) is a novel mammalian repair enzyme that has been implicated biochemically in the repair of mismatched G-T residues at methylated CpG sites. In addition, the human protein has been shown to interact with the DNA mismatch repair protein MLH1. To clarify the role of Mbd4 in DNA repair in vivo and to examine the impact of Mbd4 inactivation on gastrointestinal (GI) tumorigenesis, we introduced a null mutation into the murine Mbd4 gene by gene targeting. Heterozygous and homozygous Mbd4 mutant mice develop normally and do not show increased cancer susceptibility or reduced survival. Although Mbd4 inactivation did not increase microsatellite instability (MSI) in the mouse genome, it did result in a 2- to 3-fold increase in C-->T transition mutations at CpG sequences in splenocytes and epithelial cells of the small intestinal mucosa. The combination of Mbd4 deficiency with a germ line mutation in the adenomatous polyposis coli (Apc) gene increased the tumor number in the GI tract and accelerated tumor progression. The change in the GI cancer phenotype was associated with an increase in somatic C-->T mutations at CpG sites within the coding region of the wild-type Apc allele. These studies indicate that, although inactivation of Mbd4 does not by itself cause cancer predisposition in mice, it can alter the mutation spectrum in cancer cells and modify the cancer predisposition phenotype.
Insights
Methyl-CpG binding domain 4 (Mbd4) deficiency increases C-->T mutations at CpG sites but does not cause cancer alone. However, Mbd4 inactivation accelerates gastrointestinal tumor progression in mice with Apc mutations.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Methyl-CpG binding domain 4 (Mbd4) is a mammalian DNA repair enzyme.
- Mbd4 is involved in repairing G-T mismatches at methylated CpG sites and interacts with MLH1.
- The in vivo role of Mbd4 in DNA repair and its impact on tumorigenesis remain unclear.
Purpose of the Study:
- To investigate the in vivo function of Mbd4 in DNA repair.
- To determine the effect of Mbd4 inactivation on gastrointestinal (GI) tumorigenesis.
- To analyze the mutation spectrum changes associated with Mbd4 deficiency.
Main Methods:
- Gene targeting was used to create Mbd4-null mutant mice.
- Analysis of cancer susceptibility, survival rates, microsatellite instability (MSI), and mutation spectra in Mbd4 mutant mice.
- Cross-breeding Mbd4-deficient mice with Apc (adenomatous polyposis coli) mutant mice to assess combined effects on GI tumorigenesis.
Main Results:
- Mice lacking Mbd4 (homozygous or heterozygous) developed normally without increased cancer susceptibility or reduced survival.
- Mbd4 inactivation led to a 2- to 3-fold increase in C-->T transition mutations at CpG sites in splenocytes and intestinal cells.
- Combined Mbd4 deficiency and Apc mutation significantly increased GI tumor number and accelerated tumor progression, associated with increased somatic C-->T mutations in the Apc gene.
Conclusions:
- Mbd4 inactivation alone does not predispose mice to cancer.
- Mbd4 deficiency alters the mutation spectrum, specifically increasing C-->T transitions at CpG sites.
- Mbd4 plays a role in modifying the cancer predisposition phenotype, particularly in the context of other cancer-associated mutations like those in Apc.