FANCD2 counteracts O-methylguanine-induced mismatch repair-dependent apoptosis.

Background: Sn1-type alkylating agents methylate the oxygen atom on guanine bases thereby producing O-methylguanine. This modified base could pair with thymine and cytosine, resulting in the formation of O-methylguanine/thymine mismatch during DNA replication, recognized by the mismatch repair (MMR) complex, which then initiates the DNA damage response and subsequent apoptotic processes. In our investigation of the molecular mechanisms underlying MMR-dependent apoptosis, we observed FANCD2 modification upon the activity of alkylating agent N-methyl-N-nitrosourea (MNU).

Bloom syndrome DNA helicase mitigates mismatch repair-dependent apoptosis.

Generation of O-methylguanine (O-meG) by DNA-alkylating agents such as N-methyl N-nitrosourea (MNU) activates the multiprotein mismatch repair (MMR) complex and the checkpoint response involving ATR/CHK1 and ATM/CHK2 kinases, which may in turn trigger cell cycle arrest and apoptosis. The Bloom syndrome DNA helicase BLM interacts with the MMR complex, suggesting functional relevance to repair and checkpoint responses. We observed a strong interaction of BLM with MMR proteins in HeLa cells upon treatment with MNU as evidenced by co-immunoprecipitation as well as colocalization in the nucleus as revealed by dual immunofluorescence staining.