The DNA mismatch repair protein MutS alpha recognizes wrongly incorporated DNA bases and initiates their correction during DNA replication. Dysfunctions in mismatch repair lead to a predisposition... Show moreThe DNA mismatch repair protein MutS alpha recognizes wrongly incorporated DNA bases and initiates their correction during DNA replication. Dysfunctions in mismatch repair lead to a predisposition to cancer. Here, we study the homozygous mutation V63E in MSH2 that was found in the germline of a patient with suspected constitutional mismatch repair deficiency syndrome who developed colorectal cancer before the age of 30. Characterization of the mutant in mouse models, as well as slippage and repair assays, shows a mildly pathogenic phenotype. Using cryogenic electron microscopy and surface plasmon resonance, we explored the mechanistic effect of this mutation on MutS alpha function. We discovered that V63E disrupts a previously unappreciated interface between the mismatch binding domains (MBDs) of MSH2 and MSH6 and leads to reduced DNA binding. Our research identifies this interface as a 'safety lock' that ensures high-affinity DNA binding to increase replication fidelity. Our mechanistic model explains the hypomorphic phenotype of the V63E patient mutation and other variants in the MBD interface. Show less
Rayner, E.; Tiersma, Y.; Fortuno, C.; Hees-Stuivenberg, S. van; Drost, M.; Thompson, B.; ... ; Wind, N. de 2022
The large majority of germline alterations identified in the DNA mismatch repair (MMR) gene PMS2, a low-penetrance gene for the cancer predisposition Lynch syndrome, represent variants of uncertain... Show moreThe large majority of germline alterations identified in the DNA mismatch repair (MMR) gene PMS2, a low-penetrance gene for the cancer predisposition Lynch syndrome, represent variants of uncertain significance (VUS). The inability to classify most VUS interferes with personalized healthcare. The complete in vitro MMR activity (CIMRA) assay, that only requires sequence information on the VUS, provides a functional analysis-based quantitative tool to improve the classification of VUS in MMR proteins. To derive a formula that translates CIMRA assay results into the odds of pathogenicity (OddsPath) for VUS in PMS2 we used a set of clinically classified PMS2 variants supplemented by inactivating variants that were generated by an in cellulo genetic screen, as proxies for cancer-predisposing variants. Validation of this OddsPath revealed high predictive values for benign and predisposing PMS2 VUS. We conclude that the OddsPath provides an integral metric that, following the other, higher penetrance, MMR proteins MSH2, MSH6 and MLH1 can be incorporated as strong evidence type into the upcoming criteria for MMR gene VUS classification of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP). Show less
Temviriyanukul, P.; Hees-Stuivenberg, S. van; Delbos, F.; Jacobs, H.; Wind, N. de; Jansen, J.G. 2012
Replicative polymerases (Pols) arrest at damaged DNA nucleotides, which induces ubiquitination of the DNA sliding clamp PCNA (PCNA-Ub) and DNA damage signaling. PCNA-Ub is associated with the... Show moreReplicative polymerases (Pols) arrest at damaged DNA nucleotides, which induces ubiquitination of the DNA sliding clamp PCNA (PCNA-Ub) and DNA damage signaling. PCNA-Ub is associated with the recruitment or activation of translesion synthesis (TLS) DNA polymerases of the Y family that can bypass the lesions, thereby rescuing replication and preventing replication fork collapse and consequent formation of double-strand DNA breaks. Here, we have used gene-targeted mouse embryonic fibroblasts to perform a comprehensive study of the in vivo roles of PCNA-Ub and of the Y family TLS Pols η, ι, κ, Rev1 and the B family TLS Polζ in TLS and in the suppression of DNA damage signaling and genome instability after exposure to UV light. Our data indicate that TLS Pols ι and κ and the N-terminal BRCT domain of Rev1, that previously was implicated in the regulation of TLS, play minor roles in TLS of DNA photoproducts. PCNA-Ub is critical for an early TLS pathway that replicates both strongly helix-distorting (6-4) pyrimidine-pyrimidone ((6-4)PP) and mildly distorting cyclobutane pyrimidine dimer (CPD) photoproducts. The role of Polη is mainly restricted to early TLS of CPD photoproducts, whereas Rev1 and, in particular, Polζ are essential for the bypass of (6-4)PP photoproducts, both early and late after exposure. Thus, structurally distinct photoproducts at the mammalian genome are bypassed by different TLS Pols in temporally different, PCNA-Ub-dependent and independent fashions. Show less
Temviriyanukul, P.; Hees-Stuivenberg, S. van; Delbos, F.; Jacobs, H.; Wind, N. de; Jansen, J.G. 2012
DNA lesions, induced by genotoxic compounds block the processive replication fork but can be bypassed by specialized translesion synthesis (TLS) DNA Polymerases (Pols). TLS safeguards the... Show moreDNA lesions, induced by genotoxic compounds block the processive replication fork but can be bypassed by specialized translesion synthesis (TLS) DNA Polymerases (Pols). TLS safeguards the completion of replication, albeit at the expense of nucleotide substitution mutations. We studied the in vivo role of individual TLS Pols in cellular responses to benzo[a]pyrene diolepoxide (BPDE), a polycyclic aromatic hydrocarbon, and 4-hydroxynonenal (4-HNE), a product of lipid peroxidation. To this aim, we used mouse embryonic fibroblasts with targeted disruptions in the TLS-associated Pols η, ι, κ and Rev1, as well as in Rev3, the catalytic subunit of TLS Polζ. After exposure, cellular survival, replication fork progression, DNA damage responses (DDR), and the induction of micronuclei was investigated. The results demonstrate that Rev1, Rev3 and, to a lesser extent, Polη are involved in TLS, DDR and the prevention of DNA breaks, in response to both agents. Conversely, Polκ and the N-terminal BRCT domain of Rev1 are specifically involved in TLS of BPDE-induced DNA damage. We furthermore describe a novel role of Polι in TLS of 4-HNE-induced DNA damage in vivo. We hypothesize that different sets of TLS polymerases act on structurally different genotoxic DNA lesions in vivo, thereby suppressing genomic instability associated with cancer. Our experimental approach may provide a significant contribution in delineating the molecular bases of the genotoxicity in vivo of different classes of DNA damaging agents. Show less
