高橋計画研究分担による成果が Journal of Biochemistry誌に掲載されました!

Replication across O6-methylguanine activates futile cycling of DNA mismatch repair attempts assisted by the chromatin-remodelling enzyme Smarcad1

Karin Shigenobu-Ueno, Reihi Sakamoto, Eiichiro Kanatsu, Yoshitaka Kawasoe, Tatsuro S Takahashi

Abstract
SN1-type alkylating reagents generate O6-methylguanine (meG) lesions that activate the mismatch repair (MMR) response. Since post-replicative MMR specifically targets the nascent strand, meG on the template strand is refractory to rectification by MMR and, therefore, can induce non-productive MMR reactions. The cycling of futile MMR attempts is proposed to cause DNA double-strand breaks in the subsequent S phase, leading to ATR-checkpoint-mediated G2 arrest and apoptosis. However, the mechanistic details of futile MMR cycling, especially how this reaction is maintained in chromatin, remain unclear. Using replication-competent Xenopus egg extracts, we herein establish an in vitro system that recapitulates futile MMR cycling in the chromatin context. The meG–T mispair, but not the meG–C pair, is efficiently targeted by MMR in our system. MMR attempts on the meG-strand result in the meG-to-A correction, whilst those on the T-strand induce iterative cycles of strand excision and resynthesis. Likewise, replication across meG generates persistent single-strand breaks on the daughter DNA containing meG. Moreover, the depletion of Smarcad1, a chromatin remodeller previously reported to facilitate MMR, impairs the retention of single-strand breaks. Our study thus provides experimental evidence that chromatin replication across meG induces futile MMR cycling that is assisted by Smarcad1.

Journal of Biochemistry, doi: 10.1093/jb/mvaf007. (2025)
https://academic.oup.com/jb/advance-article/doi/10.1093/jb/mvaf007/7989931