DNA mismatch repair-induced double-strand breaks

Abstract

Escherichia coli dam mutants are sensitized to the cytotoxic action of base analogs, cisplatin and Nmethyl-N'-nitro-N-nitrosoguanidine (MNNG), while their mismatch repair (MMR)-deficient derivatives are tolerant to these agents. We showed previously, using pulse field gel electrophoresis, that MMR-mediated double-strand breaks (DSBs) are produced by cisplatin in dam recB (Ts) cells at the non-permissive temperature. We demonstrate here that the majority of these DSBs require DNA replication for their formation, consistent with a model in which replication forks collapse at nicks or gaps formed during MMR. DSBs were also detected in dam recB(Ts) ada ogt cells exposed to MNNG in a dose-and MMR-dependent manner. In contrast to cisplatin, the formation of these DSBs was not affected by DNA replication and it is proposed that two separate mechanisms result in DSB formation. Replication-independent DSBs arise from overlapping base excision and MMR repair tracts on complementary strands and constitute the majority of detectable DSBs in dam recB (Ts) ada ogt cells exposed to MNNG. Replication-dependent DSBs result from replication fork collapse at O 6 -meG base pairs undergoing MMR futile cycling and are more likely to contribute to cytotoxicity. This model is consistent with the observation that fast-growing dam recB (Ts) ada ogt cells, which have more chromosome replication origins, are more sensitive to the cytotoxic effect of MNNG than the same cells growing slowly.

Rapid induction of chromatin-associated DNA mismatch repair proteins after MNNG treatment

“…Another recent study has demonstrated that MNNG induces replicationindependent DSBs in a dose and MMR-dependent manner, and does not require DNA replication. These replication-independent DSBs are proposed to be the result of overlapping BER and MMR tracts on complementary DNA strands [60]. Our experimental approach may also indicate increased DSB damage that is located at sites on the chromatin not associated with lesions recognized by MMR.…”

DNA mismatch repair: Molecular mechanism, cancer, and ageing

“…In E. coli, homologous recombination is required for resistance to methylating agents that give rise to MMR-dependent DSBs. In dam recB(Ts) ada ogt cells exposed to MNNG, a subset of these DSBs are replication-dependent, and likely to be the primary contributor to cytotoxicity (Nowosielska and Marinus, 2008). Rapidly dividing cells were more sensitive to killing by MNNG than slowly growing cells consistent with a futile cycling model.…”

Activation-Induced Cytidine Deaminase-Dependent DNA Breaks in Class Switch Recombination Occur during G1 Phase of the Cell Cycle and Depend upon Mismatch Repair

“…If excision continued until a SSB on the opposite strand is reached, a DSB would be formed. A similar model has been proposed for Escherichia coli dam cells exposed to the methylating agent MNNG, in which DSBs arise when MMR excision on one strand encounters a nick generated by APE on the other (47). Depending on the orientation of the SSBs relative to each other, some DSBs created by MMR activity will be blunt and some will have 5Ј or 3Ј overhangs.…”