DNA mismatch repair and the DNA damage response
Introduction
In addition to its roles in editing replication errors and other functions (see other reviews in this issue and [3]), the MMR system is also implicated in the repair and cytotoxicity of a subset of DNA lesions caused by SN1 DNA alkylators, 6-thioguanine, fluoropyrimidines, cisplatin, UV light and certain environmental carcinogens that form DNA adducts (reviewed in [4], [5], [6], [7]). Defining the exact role of MMR in cell killing resulting from exposure to these DNA damaging agents is complicated by the sometimes broad spectrum of DNA damage and the convergence of multiple repair pathways such as base excision repair (BER), nucleotide excision repair (NER) and double-strand break (DSB) repair pathways and attendant DNA damage signaling pathways (see, e.g., [8], [9], [10], [11]). The SN1 DNA alkylators, e.g., N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), methylnitrosourea (MNU) and the chemotherapy drug temozolomide, methylate all four DNA bases producing a variety of potentially cytotoxic lesions that are substrates for BER. O6-methylguanine-DNA methyltransferase (MGMT) directly reverses O6meG and plays an important role in protecting against cytotoxic effects of SN1 alkylators and preventing tumor formation in vivo [7]. Not unexpectedly, there are numerous clinical implications, and these are discussed in this issue (minireviews by Begum, Heinen, Sijmons [7b–7d]).
In the case of SN1 DNA alkylators, the DDR requires components of the MMR system; the loss of functional MMR proteins, e.g., hMutSα (MSH2-MSH6) or hMutLα (MLH1-PMS2) gives rise to tolerance in which the persistence of potentially cytotoxic lesions is no longer linked to cell death. Tolerance to the SN1 class of DNA alkylating agents was first observed in Escherichia coli strains defective in MMR that exhibited greatly increased resistance to cell killing and was subsequently demonstrated in MMR-deficient mammalian cell lines some of which are almost two orders of magnitude more resistant to cell killing than comparable MMR-proficient cells (reviewed in [12]). In a similar vein, rare cells that survive exposure to alkylating agents oftentimes have accrued mutations that inactivate MMR [13]. Despite constituting only a small fraction of total alkylated DNA lesions, O6me-G is the key contributor to the mutagenic and cytotoxic effects of SN1 alkylators [14]. Low doses of MNNG induce a G2/M cell cycle arrest in the second cell cycle after exposure that is dependent on MMR proteins (reviewed in [15], [16]). A DDR signaling kinase, ATM and Rad3-related (ATR) is activated and licenses a G2/M cell cycle arrest mediated by downstream targets including the checkpoint kinases CHK1, CHK2, and SMC1 and cell division control 25 (CDC25) phosphatases. Apoptosis ensues directed in most cases by phosphorylation of p53 that also requires functional MutSα and MutLα [17].
Section snippets
The DNA damage response
The cellular responses to DNA damage are collectively termed the DNA damage response. The DDR engages signaling pathways that regulate the recognition of DNA damage, the recruitment of DNA repair factors, the initiation and coordination of DNA repair pathways, transit through the cell cycle and apoptosis [18]. The large number of human diseases and syndromes that arise from defects in components of the DNA damage response reflect the importance of the DDR for health and viability [19].
Three
Upstream events and activation of ATR
Recruitment of ATR and its constitutively interacting partner, ATR interacting protein (ATRIP), to damaged DNA was observed to be dependent on an interaction between ATRIP and replication protein A (RPA) bound to single-stranded DNA (ssDNA) [26]. Subsequent work has supported a model in which processing of DNA damage by various repair systems yields a common intermediate consisting of RPA-ssDNA, that, together with a ssDNA–dsDNA junction, serves to activate ATR [24], [27]. Such structures are
Downstream signaling from ATR
Following activation, ATR acts locally at sites of damage and more globally to phosphorylate a range of substrates that execute downstream functions regulating DNA replication origin firing, stabilizing or restarting replication forks, carrying out DNA repair, activating cell cycle checkpoints and signaling apoptosis [25], [27]. Although detailed understanding is not yet in hand, there is evidence of ATR’s involvement in the regulation of replication origin firing to minimize the collision of
DNA methylation and the DDR
A longstanding explanation for how O6meG triggers an MMR-dependent DDR is grounded in the targeting of MMR excision and resynthesis exclusively to the newly synthesized DNA strand (see the minireview by Kadyrova [76b]). DNA synthesis opposite O6meG by replicative polymerases or possibly utilizing a translesion synthesis (TLS) pathway and error-prone polymerases causes misincorporation and produces non-Watson-Crick base pairs including O6meG:T and O6meG:C. These mispairs are recognized by MutSα
Fluorouracil
Exposure of mammalian cells to fluoropyrimidines such as 5-fluorouracil (FU) or 5-fluoro-2′-deoxyuridine (FdU) also evinces a DDR that is dependent on the MutSα and MutLα MMR proteins [94], [95], [96]. FU is widely used in the treatment of a variety of solid tumors including colorectal tumors, and resistance is a challenge in the clinical setting (reviewed in [97]). Determining the mechanism of cell killing by FU is complicated as its metabolite, 5-fluoro-2′-deoxyuridine monophosphate, inhibits
Oxidative damage and DNA adducts
The primary repair pathway for oxidized DNA damage is BER utilizing specific DNA glycosylases that excise the damaged bases followed by cleavage at the abasic site by AP-endonuclease 1 and gap repair involving polβ (see, for example [107]). However, studies in E. coli, S. cerevisiae, murine embryonic fibroblasts and stem cells and human cancer cell lines support a role for MMR in the repair of oxidative DNA damage, specifically 7,8-dihydro-8-oxo-guanine (8-oxoG) mispairs [15], [108]. MMR can
Context and environment
Both the immediate and more global cellular environment can influence the DDR. Recent work reveals important links between MMR function/regulation and chromatin dynamics and the proteins that regulate chromatin structure (see the minireview by Li, [148b]) [149], [150], [151]. Lin and colleagues have examined the MMR-dependent DDR in human pluripotent stem cells (PSCs) exposed to MNNG and find a surprising result. In contrast to somatic cells exposed to MNNG alkylation damage that undergo a G2/M
Conclusions and future directions
The MMR system plays important roles in a number of cellular processes including the DDR. The challenges as have been noted above center on elucidating molecular mechanisms, exploring the interplay with other repair pathways and defining the effects of cellular and spatiotemporal context, all important for understanding fundamental processes relevant to cancer and therapeutic approaches. In vitro reconstitutions of a DDR that is activated by defined DNA damage and includes relevant repair
Acknowledgments
The authors are supported by the Division of Intramural Research of the National Institute of Diabetes and Digestive and Kidney Diseases, NIH.
References (161)
- et al.
DNA mismatch repair: molecular mechanism, cancer, and ageing
Mech. Ageing Dev.
(2008) - et al.
MBD4 and TDG: multifaceted DNA glycosylases with ever expanding biological roles
Mutat. Res.
(2013) Defective mismatch binding and a mutator phenotype in cells tolerant to DNA damage
Nature
(1993)- et al.
Apoptotic signaling in response to a single type of DNA lesion, O(6)-methylguanine
Mol. Cell
(2004) hMutSalpha- and hMutLalpha-dependent phosphorylation of p53 in response to DNA methylator damage
Proc. Natl. Acad. Sci. U. S. A.
(1999)- et al.
The ATM protein kinase: regulating the cellular response to genotoxic stress, and more
Nat. Rev. Mol. Cell Biol.
(2013) - et al.
The DNA-dependent protein kinase: a multifunctional protein kinase with roles in DNA double strand break repair and mitosis
Prog. Biophys. Mol. Biol.
(2014) - et al.
RPA-coated single-stranded DNA as a platform for post-translational modifications in the DNA damage response
Cell Res.
(2015) ATR autophosphorylation as a molecular switch for checkpoint activation
Mol. Cell
(2011)The Mre11-Rad50-Nbs1 complex mediates activation of TopBP1 by ATM
Mol. Biol. Cell
(2009)
DNA-PK phosphorylation of RPA32 Ser4/Ser8 regulates replication stress checkpoint activation, fork restart, homologous recombination and mitotic catastrophe
DNA Repair (Amst)
Distinct roles for DNA-PK, ATM and ATR in RPA phosphorylation and checkpoint activation in response to replication stress
Nucleic Acids Res.
RPA2 is a direct downstream target for ATR to regulate the S-phase checkpoint
J. Biol. Chem.
SUMOylation of ATRIP potentiates DNA damage signaling by boosting multiple protein interactions in the ATR pathway
Genes Dev.
PRP19 transforms into a sensor of RPA-ssDNA after DNA damage and drives ATR activation via a ubiquitin-mediated circuitry
Mol. Cell
Tel2 structure and function in the Hsp90-dependent maturation of mTOR and ATR complexes
Genes Dev.
RHINO forms a stoichiometric complex with the 9-1-1 checkpoint clamp and mediates ATR-Chk1 signaling
Cell Cycle
Claspin, a novel protein required for the activation of Chk1 during a DNA replication checkpoint response in Xenopus egg extracts
Mol. Cell
Tethering DNA damage checkpoint mediator proteins topoisomerase IIbeta-binding protein 1 (TopBP1) and Claspin to DNA activates ataxia-telangiectasia mutated and RAD3-related (ATR) phosphorylation of checkpoint kinase 1 (Chk1)
J. Biol. Chem.
Claspin operates downstream of TopBP1 to direct ATR signaling towards Chk1 activation
Mol. Cell. Biol.
The conserved C terminus of Claspin interacts with Rad9 and promotes rapid activation of Chk1
Cell Cycle
Rad17 phosphorylation is required for claspin recruitment and Chk1 activation in response to replication stress
Mol. Cell
The Mre11-Rad50-Nbs1 (MRN) complex has a specific role in the activation of Chk1 in response to stalled replication forks
Mol. Biol. Cell
Mismatch repair-dependent processing of methylation damage gives rise to persistent single-stranded gaps in newly replicated DNA
Genes Dev.
Mismatch repair-dependent iterative excision at irreparable O6-methylguanine lesions in human nuclear extracts
J. Biol. Chem.
RAD51D protects against MLH1-dependent cytotoxic responses to O6-methylguanine
DNA Repair (Amst)
Mammalian Exo1 encodes both structural and catalytic functions that play distinct roles in essential biological processes
Proc. Natl. Acad. Sci. U. S. A.
Mismatch repair-dependent metabolism of O(6)-methylguanine-containing DNA in Xenopus laevis egg extracts
DNA Repair (Amst)
MSH2 and ATR form a signaling module and regulate two branches of the damage response to DNA methylation
Proc. Natl. Acad. Sci. U. S. A.
Methylator-induced, mismatch repair-dependent G2 arrest is activated through Chk1 and Chk2
Mol. Biol. Cell
exo1-Dependent mutator mutations: model system for studying functional interactions in mismatch repair
Mol. Cell. Biol.
A mutation in EXO1 defines separable roles in DNA mismatch repair and post-replication repair
DNA Repair (Amst)
Exonuclease 1 (Exo1) is required for activating response to S(N) 1 DNA methylating agents
DNA Repair (Amst)
An Msh2 point mutation uncouples DNA mismatch repair and apoptosis
Cancer Res
Dominant effects of an Msh6 missense mutation on DNA repair and cancer susceptibility
Cancer Cell
DNA mismatch repair-dependent response to fluoropyrimidine-generated damage
J. Biol. Chem.
DNA mismatch repair (MMR)-dependent 5-fluorouracil cytotoxicity and the potential for new therapeutic targets
Br. J. Pharmacol.
5-Fluorouracil incorporated into DNA is excised by the Smug1 DNA glycosylase to reduce drug cytotoxicity
Cancer Res.
Role of DNA mismatch repair in apoptotic responses to therapeutic agents
Environ. Mol. Mutagen.
DNA damage responses in prokaryotes: regulating gene expression, modulating growth patterns, and manipulating replication forks
Cold Spring Harb. Perspect. Biol.
New insights into the mechanism of DNA mismatch repair
Chromosoma
Eukaryotic Mismatch Repair in Relation to DNA Replication
Annu. Rev. Genet.
DNA mismatch repair: functions and mechanisms
Chem. Rev.
Mechanisms and functions of DNA mismatch repair
Cell Res.
Balancing repair and tolerance of DNA damage caused by alkylating agents
Nat. Rev. Cancer
Targeting mismatch repair defects: a novel strategy for personalized cancer treatment
DNA Repair
Mismatch repair defects and Lynch syndrome: the role of the basic scientist in the battle against cancer
DNA Repair
Clinical aspects of hereditary mismatch repair gene mutations
DNA Repair
Protein oxidation and DNA repair inhibition by 6-thioguanine and UVA radiation
J. Invest. Dermatol.
Multiple forms of DNA damage caused by UVA photoactivation of DNA 6-thioguanine
Photochem. Photobiol.
Base excision repair: a critical player in many games
DNA Repair (Amst)
Mechanisms of tolerance to DNA damaging therapeutic drugs
Carcinogenesis
Postreplicative mismatch repair
Cold Spring Harb. Perspect. Biol.
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These authors made equal contributions.