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 6 -methylguanine-DNA methyltransferase (MGMT)deficient mammalian cells and yeast mgt1 rad52 cells to treatment with S n 1-type methylating agents, which produce cytotoxic O 6 -methylguanine (O 6 -mG) DNA lesions. Specifically, an activity of the MMR system causes degradation of irreparable O 6 -mG-T mispair-containing DNA, triggering cell death; this process forms the basis of treatments of MGMT-deficient cancers with S n 1-type methylating drugs. Recent research supports the view that degradation of irreparable O 6 -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 S n 1-type methylating agents. We found that CAF-1 suppresses the activity of the MMR system in the cytotoxic response of yeast mgt1 rad52 cells to the prototypic S n 1-type methylating agent N-methyl-N-nitro-Nnitrosoguanidine. We also report evidence that in human MGMT-deficient cell-free extracts, CAF-1-dependent packaging of irreparable O 6 -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 6 -mG-T mispair-containing DNA into nucleosomes suppresses its degradation by the MMR system, thereby defending the cell against killing by the S n 1-type methylating agent.