DNA replication and repair are critical processes for all living organisms to ensure faithful duplication and transmission of genetic information.
Flap endonuclease 1 (Fen1), a structure-specific nuclease, plays an important role in multiple
DNA metabolic pathways and maintenance of
genome stability. Human FEN1 mutations that impair its
exonuclease activity have been linked to
cancer development. FEN1 interacts with multiple
proteins, including proliferation cell
nuclear antigen (
PCNA), to form various functional complexes. Interactions with these
proteins are considered to be the key molecular mechanisms mediating FEN1's key
biological functions. The current challenge is to experimentally demonstrate the
biological consequence of a specific interaction without compromising other functions of a desired
protein. To address this issue, we established a mutant mouse model harboring a FEN1 point mutation (F343A/F344A, FFAA), which specifically abolishes the FEN1/
PCNA interaction. We show that the FFAA mutation causes defects in
RNA primer removal and long-patch base excision repair, even in the heterozygous state, resulting in numerous DNA breaks. These breaks activate the G2/M checkpoint
protein, Chk1, and induce near-
tetraploid aneuploidy, commonly observed in human
cancer, consequently elevating the transformation frequency. Consistent with this, inhibition of
aneuploidy formation by a Chk1 inhibitor significantly suppressed the cellular transformation. WT/FFAA FEN1 mutant mice develop
aneuploidy-associated
cancer at a high frequency. Thus, this study establishes an exemplary case for investigating the
biological significance of
protein-
protein interactions by knock-in of a point mutation rather than knock-out of a whole gene.