Enhanced CpG Mutability and Tumorigenesis in MBD4-Deficient Mice

Abstract
The mammalian protein MBD4 contains a methyl-CpG binding domain and can enzymatically remove thymine (T) or uracil (U) from a mismatched CpG site in vitro. These properties suggest that MBD4 might function in vivo to minimize the mutability of 5-methylcytosine by removing its deamination product from DNA. We tested this hypothesis by analyzing Mbd4 −/− mice and found that the frequency of of C → T transitions at CpG sites was increased by a factor of three. On a cancer-susceptibleApc Min/+ background,Mbd4 −/− mice showed accelerated tumor formation with CpG → TpG mutations in the Apc gene. Thus MBD4 suppresses CpG mutability and tumorigenesis in vivo.