The Major Replicative Histone Chaperone CAF-1 Suppresses the Activity of the DNA Mismatch Repair System in the Cytotoxic Response to a DNA-methylating Agent

Abstract

The DNA mismatch repair (MMR) system corrects DNA mismatches in the genome. It is also required for the cytotoxic response of O-methylguanine-DNA methyltransferase (MGMT)-deficient mammalian cells and yeast mgt1Δ rad52Δ cells to treatment with S1-type methylating agents, which produce cytotoxic O-methylguanine (O-mG) DNA lesions. Specifically, an activity of the MMR system causes degradation of irreparable O-mG-T mispair-containing DNA, triggering cell death; this process forms the basis of treatments of MGMT-deficient cancers with S1-type methylating drugs. Recent research supports the view that degradation of irreparable O-mG-T mispair-containing DNA by the MMR system and CAF-1-dependent packaging of the newly replicated DNA into nucleosomes are two concomitant processes that interact with each other. Here, we studied whether CAF-1 modulates the activity of the MMR system in the cytotoxic response to S1-type methylating agents. We found that CAF-1 suppresses the activity of the MMR system in the cytotoxic response of yeast mgt1Δ rad52Δ cells to the prototypic S1-type methylating agent N-methyl-N'-nitro-N-nitrosoguanidine. We also report evidence that in human MGMT-deficient cell-free extracts, CAF-1-dependent packaging of irreparable O-mG-T mispair-containing DNA into nucleosomes suppresses its degradation by the MMR system. Taken together, these findings suggest that CAF-1-dependent incorporation of irreparable O-mG-T mispair-containing DNA into nucleosomes suppresses its degradation by the MMR system, thereby defending the cell against killing by the S1-type methylating agent.

Nucleosomes around a mismatched base pair are excluded via an Msh2-dependent reaction with the aid of SNF2 family ATPase Smarcad1

“…6). It should also be noted that our genetic experiments are in good agreement with the data showing that CAF-1 is inhibitory for MMR (Kadyrova et al 2011;Schopf et al 2012;Rodriges Blanko et al 2016) and suppresses the cytotoxic activity of the MMR system upon treatment with a DNA-alkylating agent (Kadyrova et al 2016). Curiously, the genetic data suggest that yeast Fun30 is more important for MutSβ-dependent MMR than for MutSα-dependent MMR.…”

DNA mismatch repair in the context of chromatin

“…MMR proteins recognize and incise the O 6 -mG-T mispair, but cannot correct it, which leads to a futile repair cycle and, finally, apoptosis. Similar to its role in replication-coupled repair, CAF-1 also suppresses MMR activity in response to DNA methylating drugs by packaging DNA that contains O 6 -mG-T mispairs into nucleosomes to prevent it from degrading [6], which may lead to cell resistance to methylating agents, such as methyl-nitronitrosoguanidine (MNNG). Similarly, Smarcad1 may sensitize cells to methylating agents by promoting MMRmediated cytotoxic responses.…”

“…Indeed, recent studies have indicated that trimethylation of histone H3 lysine 36 (H3K36me3) plays a role in MMR by recruiting MutSα to replicating chromatin [5]. In addition, chromatin assembly/remodeling factors also interact with MMR proteins to coordinate MMR and nucleosome formation [6,7].…”

Human MutLγ, the MLH1–MLH3 heterodimer, is an endonuclease that promotes DNA expansion

“…The relaxed 3-nt loop-containing ccDNA and the relaxed control homoduplex ccDNA were prepared using the gapped form of the plasmid pAH1A (73) according to previously described procedures (17,74). To prepare the 3-nt loop-containing ccDNA a phosphorylated 39-mer oligonucleotide with the sequence 5′-GCTACCGTCCTCGAAGCTAGCTCCGCATCGGAGTCGACG-3′ (the 3-nt loop sequence is underlined) was utilized.…”