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van Ravesteyn TW, Dekker M, Riele HT. Mono- and Biallelic Replication-Coupled Gene Editing Discriminates Dominant-Negative and Loss-of-Function Variants of DNA Mismatch Repair Genes. J Mol Diagn 2024:S1525-1578(24)00131-4. [PMID: 38925454 DOI: 10.1016/j.jmoldx.2024.05.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Revised: 05/08/2024] [Accepted: 05/23/2024] [Indexed: 06/28/2024] Open
Abstract
Replication-coupled gene editing using locked nucleic acid-modified single-stranded DNA oligonucleotides (LMOs) can genetically engineer mammalian cells with high precision at single nucleotide resolution. Based on this method, oligonucleotide-directed mutation screening (ODMS) was developed to determine whether variants of uncertain clinical significance of DNA mismatch repair (MMR) genes can cause Lynch syndrome. In ODMS, the appearance of 6-thioguanine-resistant colonies upon introduction of the variant is indicative for defective MMR and hence pathogenicity. Whereas mouse embryonic stem cells (mESCs) hemizygous for MMR genes were used previously, we now show that ODMS can also be applied in wild-type mESCs carrying two functional alleles of each MMR gene. 6-Thioguanine resistance can result from two possible events: first, the mutation is present in only one allele, which is indicative for dominant-negative activity of the variant; and second, both alleles contain the planned modification, which is indicative for a regular loss-of-function variant. Thus, ODMS in wild-type mESCs can discriminate fully disruptive and dominant-negative MMR variants. The feasibility of biallelic targeting suggests that the efficiency of LMO-mediated gene targeting at a nonselectable locus may be enriched in cells that had undergone a simultaneous selectable LMO targeting event. This turned out to be the case and provided a protocol to improve recovery of LMO-mediated gene modification events.
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Affiliation(s)
- Thomas W van Ravesteyn
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Marleen Dekker
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Hein Te Riele
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, Amsterdam, The Netherlands.
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2
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Gallon R, Brekelmans C, Martin M, Bours V, Schamschula E, Amberger A, Muleris M, Colas C, Dekervel J, De Hertogh G, Coupier J, Colleye O, Sepulchre E, Burn J, Brems H, Legius E, Wimmer K. Constitutional mismatch repair deficiency mimicking Lynch syndrome is associated with hypomorphic mismatch repair gene variants. NPJ Precis Oncol 2024; 8:119. [PMID: 38789506 PMCID: PMC11126593 DOI: 10.1038/s41698-024-00603-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Accepted: 05/08/2024] [Indexed: 05/26/2024] Open
Abstract
Lynch syndrome (LS) and constitutional mismatch repair deficiency (CMMRD) are distinct cancer syndromes caused, respectively, by mono- and bi-allelic germline mismatch repair (MMR) variants. LS predisposes to mainly gastrointestinal and genitourinary cancers in adulthood. CMMRD predisposes to brain, haematological, and LS-spectrum cancers from childhood. Two suspected LS patients with first cancer diagnosis aged 27 or 38 years were found to be homozygous for an MMR (likely) pathogenic variant, MSH6 c.3226C>T (p.(Arg1076Cys)), or variant of uncertain significance (VUS), MLH1 c.306G>A (p.(Glu102=)). MLH1 c.306G>A was shown to cause leaky exon 3 skipping. The apparent genotype-phenotype conflict was resolved by detection of constitutional microsatellite instability in both patients, a hallmark feature of CMMRD. A hypomorphic effect of these and other variants found in additional late onset CMMRD cases, identified by literature review, likely explains a LS-like phenotype. CMMRD testing in carriers of compound heterozygous or homozygous MMR VUS may find similar cases and novel hypomorphic variants. Individualised management of mono- and bi-allelic carriers of hypomorphic MMR variants is needed until we better characterise the associated phenotypes.
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Affiliation(s)
- Richard Gallon
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK.
| | | | | | | | - Esther Schamschula
- Institute of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria
| | - Albert Amberger
- Institute of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria
| | - Martine Muleris
- Département de Génétique, AP-HP.Sorbonne Université, Hôpital Pitié-Salpêtrière, Paris, France
- Inserm UMRS_938, Sorbonne Université, Centre de Recherche Saint Antoine, Paris, France
| | - Chrystelle Colas
- Département de Génétique, Institut Curie, Paris, France
- INSERM U830, Université de Paris, Paris, France
| | - Jeroen Dekervel
- Department of Digestive Oncology, University Hospital Leuven, Leuven, Belgium
| | - Gert De Hertogh
- Department of Pathology, University Hospital Leuven, Leuven, Belgium
| | | | | | | | - John Burn
- Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Hilde Brems
- Centre for Human Genetics, University Hospital Leuven, Leuven, Belgium
| | - Eric Legius
- Centre for Human Genetics, University Hospital Leuven, Leuven, Belgium
| | - Katharina Wimmer
- Institute of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria.
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3
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Fatemi N, Tu SJ, Chung CC, Moghadam PK, Mojarad EN, Sadeghi A, Totonchi M, Aghdaei HA, Chang JG. Whole exome sequencing identifies MAP3K1, MSH2, and MLH1 as potential cancer-predisposing genes in familial early-onset colorectal cancer. Kaohsiung J Med Sci 2023; 39:896-903. [PMID: 37314251 DOI: 10.1002/kjm2.12715] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 05/01/2023] [Accepted: 05/21/2023] [Indexed: 06/15/2023] Open
Abstract
The incidence of early-onset colorectal cancer (CRC), which affects people under 50, is increasing for unknown reasons. Additionally, no underlying genetic cause is found in 20%-30% of patients suspected of having familial CRC syndrome. Whole exome sequencing (WES) has generated evidence for new genes associated with CRC susceptibility, but many patients remain undiagnosed. This study applied WES in five early-onset CRC patients from three unrelated families to identify novel genetic variants that could be linked to rapid disease development. Furthermore, the candidate variants were validated using Sanger sequencing. Two heterozygote variations, c.1077-2A>G and c.199G>A, were found in the MSH2 and the MLH1 genes, respectively. Sanger sequencing analysis confirmed that these (likely) pathogenic mutations segregated in all the affected families' members. In addition, we identified a rare heterozygote variant (c.175C>T) with suspected pathogenic potential in the MAP3K1 gene; formally the variant is of uncertain significance (VUS). Our findings support the hypothesis that CRC onset may be oligogenic and molecularly heterogeneous. Larger and more robust studies are needed to understand the genetic basis of early-onset CRC development, combined with novel functional analyses and omics approaches.
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Affiliation(s)
- Nayeralsadat Fatemi
- Basic and Molecular Epidemiology of Gastrointestinal Disorders Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Siang-Jyun Tu
- Center for Precision Medicine, China Medical University Hospital, Taichung, Taiwan
| | - Chin-Chun Chung
- Center for Precision Medicine, China Medical University Hospital, Taichung, Taiwan
| | - Pardis Ketabi Moghadam
- Gastroenterology and Liver Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Ehsan Nazemalhosseini Mojarad
- Gastroenterology and Liver Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Amir Sadeghi
- Gastroenterology and Liver Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mehdi Totonchi
- Basic and Molecular Epidemiology of Gastrointestinal Disorders Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
- Department of Genetics, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran
| | - Hamid Asadzadeh Aghdaei
- Basic and Molecular Epidemiology of Gastrointestinal Disorders Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Jan-Gowth Chang
- Center for Precision Medicine, China Medical University Hospital, Taichung, Taiwan
- Department of Bioinformatics and Medical Engineering, Asia University, Taichung, Taiwan
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4
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Abildgaard AB, Nielsen SV, Bernstein I, Stein A, Lindorff-Larsen K, Hartmann-Petersen R. Lynch syndrome, molecular mechanisms and variant classification. Br J Cancer 2023; 128:726-734. [PMID: 36434153 PMCID: PMC9978028 DOI: 10.1038/s41416-022-02059-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 10/31/2022] [Accepted: 11/02/2022] [Indexed: 11/27/2022] Open
Abstract
Patients with the heritable cancer disease, Lynch syndrome, carry germline variants in the MLH1, MSH2, MSH6 and PMS2 genes, encoding the central components of the DNA mismatch repair system. Loss-of-function variants disrupt the DNA mismatch repair system and give rise to a detrimental increase in the cellular mutational burden and cancer development. The treatment prospects for Lynch syndrome rely heavily on early diagnosis; however, accurate diagnosis is inextricably linked to correct clinical interpretation of individual variants. Protein variant classification traditionally relies on cumulative information from occurrence in patients, as well as experimental testing of the individual variants. The complexity of variant classification is due to (1) that variants of unknown significance are rare in the population and phenotypic information on the specific variants is missing, and (2) that individual variant testing is challenging, costly and slow. Here, we summarise recent developments in high-throughput technologies and computational prediction tools for the assessment of variants of unknown significance in Lynch syndrome. These approaches may vastly increase the number of interpretable variants and could also provide important mechanistic insights into the disease. These insights may in turn pave the road towards developing personalised treatment approaches for Lynch syndrome.
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Affiliation(s)
- Amanda B Abildgaard
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Sofie V Nielsen
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
| | - Inge Bernstein
- Department of Surgical Gastroenterology, Aalborg University Hospital, Aalborg, Denmark
- Institute of Clinical Medicine, Aalborg University Hospital, Aalborg University, Aalborg, Denmark
| | - Amelie Stein
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Kresten Lindorff-Larsen
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
| | - Rasmus Hartmann-Petersen
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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5
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Bruekner SR, Pieters W, Fish A, Liaci AM, Scheffers S, Rayner E, Kaldenbach D, Drost L, Dekker M, van Hees-Stuivenberg S, Delzenne-Goette E, de Konink C, Houlleberghs H, Dubbink H, AlSaegh A, de Wind N, Förster F, te Riele H, Sixma T. Unexpected moves: a conformational change in MutSα enables high-affinity DNA mismatch binding. Nucleic Acids Res 2023; 51:1173-1188. [PMID: 36715327 PMCID: PMC9943660 DOI: 10.1093/nar/gkad015] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 12/30/2022] [Accepted: 01/12/2023] [Indexed: 01/31/2023] Open
Abstract
The DNA mismatch repair protein MutSα 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 MutSα 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.
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Affiliation(s)
| | | | - Alexander Fish
- Division of Biochemistry, Netherlands Cancer Institute and Oncode Institute, 1066 CX Amsterdam, The Netherlands
| | - A Manuel Liaci
- Structural Biochemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584CH Utrecht, The Netherlands
| | - Serge Scheffers
- Division of Biochemistry, Netherlands Cancer Institute and Oncode Institute, 1066 CX Amsterdam, The Netherlands
| | - Emily Rayner
- Department of Human Genetics, Leiden University Medical Center, PO Box 9600 2300RC Leiden, The Netherlands
| | - Daphne Kaldenbach
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | - Lisa Drost
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | - Marleen Dekker
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | | | - Elly Delzenne-Goette
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | - Charlotte de Konink
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | - Hellen Houlleberghs
- Division of Tumor Biology and Immunology, Netherlands Cancer Institute, 1066CX Amsterdam, The Netherlands
| | - Hendrikus Jan Dubbink
- Department of Pathology, Erasmus Medical Center, PO Box 2040 3000CA Rotterdam, The Netherlands
| | - Abeer AlSaegh
- Sultan Qaboos Comprehensive Cancer Care and Research Center, PO Box 787, 117 Muscat, Oman
| | - Niels de Wind
- Department of Human Genetics, Leiden University Medical Center, PO Box 9600 2300RC Leiden, The Netherlands
| | - Friedrich Förster
- Structural Biochemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584CH Utrecht, The Netherlands
| | - Hein te Riele
- Correspondence may also be addressed to Hein te Riele. Tel: +31 20 512 2084;
| | - Titia K Sixma
- To whom correspondence should be addressed: Tel: +31 20 512 1959;
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6
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Rayner E, Tiersma Y, Fortuno C, van Hees-Stuivenberg S, Drost M, Thompson B, Spurdle AB, de Wind N. Predictive functional assay-based classification of PMS2 variants in Lynch Syndrome. Hum Mutat 2022; 43:1249-1258. [PMID: 35451539 PMCID: PMC9545740 DOI: 10.1002/humu.24387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 04/07/2022] [Accepted: 04/20/2022] [Indexed: 11/21/2022]
Abstract
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 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).
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Affiliation(s)
- Emily Rayner
- Dept. of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Yvonne Tiersma
- Dept. of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.,Princess Maxima Center for child oncology, Utrecht, the Netherlands
| | | | | | - Mark Drost
- Dept. of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.,Dept. of Clinical Genetics, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Bryony Thompson
- Department of Pathology, Royal Melbourne Hospital, Parkville, VIC, Australia
| | | | - Niels de Wind
- Dept. of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
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7
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8
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Gallon R, Gawthorpe P, Phelps RL, Hayes C, Borthwick GM, Santibanez-Koref M, Jackson MS, Burn J. How Should We Test for Lynch Syndrome? A Review of Current Guidelines and Future Strategies. Cancers (Basel) 2021; 13:406. [PMID: 33499123 PMCID: PMC7865939 DOI: 10.3390/cancers13030406] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 01/18/2021] [Accepted: 01/20/2021] [Indexed: 12/13/2022] Open
Abstract
International guidelines for the diagnosis of Lynch syndrome (LS) recommend molecular screening of colorectal cancers (CRCs) to identify patients for germline mismatch repair (MMR) gene testing. As our understanding of the LS phenotype and diagnostic technologies have advanced, there is a need to review these guidelines and new screening opportunities. We discuss the barriers to implementation of current guidelines, as well as guideline limitations, and highlight new technologies and knowledge that may address these. We also discuss alternative screening strategies to increase the rate of LS diagnoses. In particular, the focus of current guidance on CRCs means that approximately half of Lynch-spectrum tumours occurring in unknown male LS carriers, and only one-third in female LS carriers, will trigger testing for LS. There is increasing pressure to expand guidelines to include molecular screening of endometrial cancers, the most frequent cancer in female LS carriers. Furthermore, we collate the evidence to support MMR deficiency testing of other Lynch-spectrum tumours to screen for LS. However, a reliance on tumour tissue limits preoperative testing and, therefore, diagnosis prior to malignancy. The recent successes of functional assays to detect microsatellite instability or MMR deficiency in non-neoplastic tissues suggest that future diagnostic pipelines could become independent of tumour tissue.
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Affiliation(s)
| | | | | | | | | | | | | | - John Burn
- Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK; (P.G.); (R.L.P.); (C.H.); (G.M.B.); (M.S.-K.); (M.S.J.)
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9
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Jia X, Burugula BB, Chen V, Lemons RM, Jayakody S, Maksutova M, Kitzman JO. Massively parallel functional testing of MSH2 missense variants conferring Lynch syndrome risk. Am J Hum Genet 2021; 108:163-175. [PMID: 33357406 PMCID: PMC7820803 DOI: 10.1016/j.ajhg.2020.12.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 12/03/2020] [Indexed: 12/20/2022] Open
Abstract
The lack of functional evidence for the majority of missense variants limits their clinical interpretability and poses a key barrier to the broad utility of carrier screening. In Lynch syndrome (LS), one of the most highly prevalent cancer syndromes, nearly 90% of clinically observed missense variants are deemed “variants of uncertain significance” (VUS). To systematically resolve their functional status, we performed a massively parallel screen in human cells to identify loss-of-function missense variants in the key DNA mismatch repair factor MSH2. The resulting functional effect map is substantially complete, covering 94% of the 17,746 possible variants, and is highly concordant (96%) with existing functional data and expert clinicians’ interpretations. The large majority (89%) of missense variants were functionally neutral, perhaps unexpectedly in light of its evolutionary conservation. These data provide ready-to-use functional evidence to resolve the ∼1,300 extant missense VUSs in MSH2 and may facilitate the prospective classification of newly discovered variants in the clinic.
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10
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van Ravesteyn TW, Arranz Dols M, Pieters W, Dekker M, te Riele H. Extensive trimming of short single-stranded DNA oligonucleotides during replication-coupled gene editing in mammalian cells. PLoS Genet 2020; 16:e1009041. [PMID: 33119594 PMCID: PMC7595315 DOI: 10.1371/journal.pgen.1009041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2019] [Accepted: 08/10/2020] [Indexed: 11/19/2022] Open
Abstract
Through transfection of short single-stranded oligodeoxyribonucleotides (ssODNs) small genomic alterations can be introduced into mammalian cells with high precision. ssODNs integrate into the genome during DNA replication, but the resulting heteroduplex is prone to detection by DNA mismatch repair (MMR), which prevents effective gene modification. We have previously demonstrated that the suppressive action of MMR can be avoided when the mismatching nucleotide in the ssODN is a locked nucleic acid (LNA). Here, we reveal that LNA-modified ssODNs (LMOs) are not integrated as intact entities in mammalian cells, but are severely truncated before and after target hybridization. We found that single additional (non-LNA-modified) mutations in the 5’-arm of LMOs influenced targeting efficiencies negatively and activated the MMR pathway. In contrast, additional mutations in the 3’-arm did not affect targeting efficiencies and were not subject to MMR. Even more strikingly, homology in the 3’-arm was largely dispensable for effective targeting, suggestive for extensive 3’-end trimming. We propose a refined model for LMO-directed gene modification in mammalian cells that includes LMO degradation. The first step of many gene editing approaches in mammalian cells is to generate a targeted DNA lesion. By administering a repair template as second step, endogenous DNA repair mechanisms can be misled to introduce specific gene variants. However, subtle gene modification can also be achieved with high precision through a one-action protocol in the absence of DNA breaks. We have shown before that short single-stranded DNA molecules (LMOs) are very useful to introduce and study genetic variants that may predispose patients to cancer. While LMOs are known to integrate into the genome during DNA replication, the precise mechanism is poorly understood. We targeted mouse embryonic stem cells with differently designed LMOs to examine their effectiveness and editing outcomes. Based on these results we conclude that the two LMO termini are processed at different moments during the gene editing process. While the 3’-arm is degraded prior to LMO binding to the target site, the 5’-arm is degraded afterwards. Counterintuitively we also observe that partial degradation of the 3’-arm increases targeting efficiencies. Taken together our data provides novel mechanistic insight into our understanding of replication-coupled gene editing and may guide future LMO design strategies.
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Affiliation(s)
- Thomas W. van Ravesteyn
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands
| | - Marcos Arranz Dols
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands
| | - Wietske Pieters
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands
| | - Marleen Dekker
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands
| | - Hein te Riele
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands
- * E-mail:
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11
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Djursby M, Madsen MB, Frederiksen JH, Berchtold LA, Therkildsen C, Willemoe GL, Hasselby JP, Wikman F, Okkels H, Skytte AB, Nilbert M, Wadt K, Gerdes AM, van Overeem Hansen T. New Pathogenic Germline Variants in Very Early Onset and Familial Colorectal Cancer Patients. Front Genet 2020; 11:566266. [PMID: 33193653 PMCID: PMC7541943 DOI: 10.3389/fgene.2020.566266] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 08/24/2020] [Indexed: 12/30/2022] Open
Abstract
A genetic diagnosis facilitates personalized cancer treatment and clinical care of relatives at risk, however, although 25% of colorectal cancer cases are familial, around 95% of the families are genetically unresolved. In this study, we performed gene panel analysis on germline DNA of 32 established or candidate colorectal cancer predisposing genes in 149 individuals from either families with an accumulation of colorectal cancers or families with only one sporadic case of very early onset colorectal cancer (≤40 years at diagnosis). We identified pathogenic or likely pathogenic genetic variants in 10.1% of the participants in genes such as APC, POLE, MSH2 or PMS2. The MSH2 variant, c.2168C>T, p.(Ser723Phe) was previously described as a variant of unknown significance, but we have now reclassified it to be likely pathogenic. The POLE variant, c.1089C>A, p.(Asn363Lys) was identified in a patient with three metachronous colorectal cancers from age 28 and turned out to be de novo. One pathogenic PMS2 variant was novel. We also identified a number of highly interesting variants of unknown significance in APC, BUB1, TP53 and RPS20. The RPS20 variant is novel and was found in a large Amsterdam I positive family with a multi tumor phenotype including 12 cases of CRC from as early as age 24. This variant was found to segregate with cancer in the family and multiple in silico tools predict it to be pathogenic. Our data further support the shift from phenotypic-based cancer panels to large panels including all established genes involved in hereditary cancer syndromes or (targeted) whole genome sequencing. Additionally, identification of a likely disease-predisposing variant in RPS20 expands the phenotypic spectrum of RPS20-related cancers and emphasize that this gene is relevant to include in colorectal cancer gene panels.
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Affiliation(s)
- Malene Djursby
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Majbritt B Madsen
- Center for Genomic Medicine, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Jane H Frederiksen
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Lukas A Berchtold
- Center for Genomic Medicine, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Christina Therkildsen
- The Danish HNPCC Register, Clinical Research Centre, Copenhagen University Hospital, Hvidovre, Denmark
| | - Gro L Willemoe
- Department of Pathology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Jane P Hasselby
- Department of Pathology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Friedrik Wikman
- Department of Molecular Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Henrik Okkels
- Section of Molecular Diagnostics, Department of Clinical Chemistry, Aalborg University Hospital, Aalborg, Denmark
| | - Anne-Bine Skytte
- Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark
| | - Mef Nilbert
- The Danish HNPCC Register, Clinical Research Centre, Copenhagen University Hospital, Hvidovre, Denmark
| | - Karin Wadt
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Anne-Marie Gerdes
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Thomas van Overeem Hansen
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
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12
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Singh AK, Talseth-Palmer B, McPhillips M, Lavik LAS, Xavier A, Drabløs F, Sjursen W. Targeted sequencing of genes associated with the mismatch repair pathway in patients with endometrial cancer. PLoS One 2020; 15:e0235613. [PMID: 32634176 PMCID: PMC7340288 DOI: 10.1371/journal.pone.0235613] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 06/19/2020] [Indexed: 01/28/2023] Open
Abstract
Germline variants inactivating the mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2 cause Lynch syndrome that implies an increased cancer risk, where colon and endometrial cancer are the most frequent. Identification of these pathogenic variants is important to identify endometrial cancer patients with inherited increased risk of new cancers, in order to offer them lifesaving surveillance. However, several other genes are also part of the MMR pathway. It is therefore relevant to search for variants in additional genes that may be associated with cancer risk by including all known genes involved in the MMR pathway. Next-generation sequencing was used to screen 22 genes involved in the MMR pathway in constitutional DNA extracted from full blood from 199 unselected endometrial cancer patients. Bioinformatic pipelines were developed for identification and functional annotation of variants, using several different software tools and custom programs. This facilitated identification of 22 exonic, 4 UTR and 9 intronic variants that could be classified according to pathogenicity. This study has identified several germline variants in genes of the MMR pathway that potentially may be associated with an increased risk for cancer, in particular endometrial cancer, and therefore are relevant for further investigation. We have also developed bioinformatics strategies to analyse targeted sequencing data, including low quality data and genomic regions outside of the protein coding exons of the relevant genes.
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Affiliation(s)
- Ashish Kumar Singh
- Department of Medical Genetics, St. Olavs Hospital, Trondheim, Norway
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, NTNU—Norwegian University of Science and Technology, Trondheim, Norway
| | - Bente Talseth-Palmer
- Department of Medical Genetics, St. Olavs Hospital, Trondheim, Norway
- School of Biomedical Science and Pharmacy, Faculty of Health and Medicine, University of Newcastle and Hunter Medical Research Institute, Newcastle, Australia
- Department of Research and Development, Møre og Romsdal Hospital Trust, Molde, Norway
| | - Mary McPhillips
- NSW Health Pathology, Molecular Medicine, John Hunter Hospital, Newcastle, NSW, Australia
| | | | - Alexandre Xavier
- School of Biomedical Science and Pharmacy, Faculty of Health and Medicine, University of Newcastle and Hunter Medical Research Institute, Newcastle, Australia
| | - Finn Drabløs
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, NTNU—Norwegian University of Science and Technology, Trondheim, Norway
| | - Wenche Sjursen
- Department of Medical Genetics, St. Olavs Hospital, Trondheim, Norway
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, NTNU—Norwegian University of Science and Technology, Trondheim, Norway
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13
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Šimčíková D, Heneberg P. Refinement of evolutionary medicine predictions based on clinical evidence for the manifestations of Mendelian diseases. Sci Rep 2019; 9:18577. [PMID: 31819097 PMCID: PMC6901466 DOI: 10.1038/s41598-019-54976-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 11/21/2019] [Indexed: 12/28/2022] Open
Abstract
Prediction methods have become an integral part of biomedical and biotechnological research. However, their clinical interpretations are largely based on biochemical or molecular data, but not clinical data. Here, we focus on improving the reliability and clinical applicability of prediction algorithms. We assembled and curated two large non-overlapping large databases of clinical phenotypes. These phenotypes were caused by missense variations in 44 and 63 genes associated with Mendelian diseases. We used these databases to establish and validate the model, allowing us to improve the predictions obtained from EVmutation, SNAP2 and PoPMuSiC 2.1. The predictions of clinical effects suffered from a lack of specificity, which appears to be the common constraint of all recently used prediction methods, although predictions mediated by these methods are associated with nearly absolute sensitivity. We introduced evidence-based tailoring of the default settings of the prediction methods; this tailoring substantially improved the prediction outcomes. Additionally, the comparisons of the clinically observed and theoretical variations led to the identification of large previously unreported pools of variations that were under negative selection during molecular evolution. The evolutionary variation analysis approach described here is the first to enable the highly specific identification of likely disease-causing missense variations that have not yet been associated with any clinical phenotype.
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Affiliation(s)
- Daniela Šimčíková
- Charles University, Third Faculty of Medicine, Prague, Czech Republic
| | - Petr Heneberg
- Charles University, Third Faculty of Medicine, Prague, Czech Republic.
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14
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Houlleberghs H, Dekker M, Lusseveld J, Pieters W, van Ravesteyn T, Verhoef S, Hofstra RMW, Te Riele H. Three-step site-directed mutagenesis screen identifies pathogenic MLH1 variants associated with Lynch syndrome. J Med Genet 2019; 57:308-315. [PMID: 31784484 DOI: 10.1136/jmedgenet-2019-106520] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 10/12/2019] [Accepted: 10/16/2019] [Indexed: 12/30/2022]
Abstract
BACKGROUND Inactivating mutations in the MLH1 DNA mismatch repair (MMR) gene underlie 42% of Lynch syndrome (LS) cases. LS is a cancer predisposition causing early onset colorectal and endometrial cancer. Nonsense and frameshift alterations unambiguously cause LS. The phenotype of missense mutations that only alter a single amino acid is often unclear. These variants of uncertain significance (VUS) hinder LS diagnosis and family screening and therefore functional tests are urgently needed. We developed a functional test for MLH1 VUS termed 'oligonucleotide-directed mutation screening' (ODMS). METHODS The MLH1 variant was introduced by oligonucleotide-directed gene modification in mouse embryonic stem cells that were subsequently exposed to the guanine analogue 6-thioguanine to determine whether the variant abrogated MMR. RESUTS In a proof-of-principle analysis, we demonstrate that ODMS can distinguish pathogenic and non-pathogenic MLH1 variants with a sensitivity of >95% and a specificity of >91%. We subsequently applied the screen to 51 MLH1 VUS and identified 31 pathogenic variants. CONCLUSION ODMS is a reliable tool to identify pathogenic MLH1 variants. Implementation in clinical diagnostics will improve clinical care of patients with suspected LS and their relatives.
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Affiliation(s)
- Hellen Houlleberghs
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Marleen Dekker
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jarnick Lusseveld
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Wietske Pieters
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Thomas van Ravesteyn
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Senno Verhoef
- Department of Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Robert M W Hofstra
- Department of Clinical Genetics, Erasmus MC, Erasmus University Rotterdam, Rotterdam, The Netherlands
| | - Hein Te Riele
- Division of Tumor Biology and Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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15
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Vermaut C, Leclerc J, Vasseur F, Wacrenier A, Lovecchio T, Boidin D, Rebergue MH, Cattan S, Manouvrier S, Lejeune S, Buisine MP. MSH2 c.1022T>C, p.Leu341Pro is a founder pathogenic variation and a major cause of Lynch syndrome in the North of France. Genes Chromosomes Cancer 2019; 59:111-118. [PMID: 31433521 DOI: 10.1002/gcc.22804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 08/16/2019] [Accepted: 08/16/2019] [Indexed: 11/10/2022] Open
Abstract
Interpretation of missense variants remains a major challenge for genetic diagnosis, even in well-known genes such as the DNA-mismatch repair (MMR) genes involved in Lynch syndrome. We report the characterization of a variant in MSH2: c.1022T>C, which was identified in 20 apparently unrelated families living in the North of France. A total of 150 patients from 20 families were included in this study. Family segregation studies, tumor analyses and functional analyses at both the RNA and protein levels were performed. Founder effect was evaluated by haplotype analysis.We show that MSH2 c.1022T>C is a missense variant (p.Leu341Pro) that affects protein stability. This variant is frequent in the North of France (7.7% of pathogenic variations identified in MMR genes), and is located on an ancestral haplotype. It is associated with a high risk of a broad tumor spectrum including brain and cutaneous cancers. The MSH2 c.1022T>C variant is a pathogenic founder variation associated with a high risk of cancer. These findings have important implications for genetic counseling and management of variant carriers.
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Affiliation(s)
- Catherine Vermaut
- Department of Biochemistry and Molecular Biology, Lille University Hospital, Lille, France
| | - Julie Leclerc
- Department of Biochemistry and Molecular Biology, Inserm UMR-S1172 - Jean-Pierre Aubert Research Center, Lille University, and Lille University Hospital, Lille, France
| | - Francis Vasseur
- Department of Biostatistics, Lille University and Lille University Hospital, Lille, France
| | - Agnes Wacrenier
- Department of Pathology, Lille University Hospital, Lille, France
| | - Tonio Lovecchio
- Department of Biochemistry and Molecular Biology, Lille University Hospital, Lille, France
| | - Denis Boidin
- Department of Biochemistry and Molecular Biology, Lille University Hospital, Lille, France
| | | | - Stephane Cattan
- Department of Gastroenterology, Lille University Hospital, Lille, France
| | - Sylvie Manouvrier
- Department of Clinical Genetics, Lille University Hospital, Lille, France.,Department of Clinical Genetics, Lille University EA 7364 - RADEME (Maladies RAres du Développement et du Métabolisme), and Lille University Hospital, Lille, France
| | - Sophie Lejeune
- Department of Clinical Genetics, Lille University Hospital, Lille, France
| | - Marie-Pierre Buisine
- Department of Biochemistry and Molecular Biology, Inserm UMR-S1172 - Jean-Pierre Aubert Research Center, Lille University, and Lille University Hospital, Lille, France
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16
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Rath A, Mishra A, Ferreira VD, Hu C, Omerza G, Kelly K, Hesse A, Reddi HV, Grady JP, Heinen CD. Functional interrogation of Lynch syndrome-associated MSH2 missense variants via CRISPR-Cas9 gene editing in human embryonic stem cells. Hum Mutat 2019; 40:2044-2056. [PMID: 31237724 DOI: 10.1002/humu.23848] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 05/08/2019] [Accepted: 06/19/2019] [Indexed: 12/18/2022]
Abstract
Lynch syndrome (LS) predisposes patients to cancer and is caused by germline mutations in the DNA mismatch repair (MMR) genes. Identifying the deleterious mutation, such as a frameshift or nonsense mutation, is important for confirming an LS diagnosis. However, discovery of a missense variant is often inconclusive. The effects of these variants of uncertain significance (VUS) on disease pathogenesis are unclear, though understanding their impact on protein function can help determine their significance. Laboratory functional studies performed to date have been limited by their artificial nature. We report here an in-cellulo functional assay in which we engineered site-specific MSH2 VUS using clustered regularly interspaced short palindromic repeats-Cas9 gene editing in human embryonic stem cells. This approach introduces the variant into the endogenous MSH2 loci, while simultaneously eliminating the wild-type gene. We characterized the impact of the variants on cellular MMR functions including DNA damage response signaling and the repair of DNA microsatellites. We classified the MMR functional capability of eight of 10 VUS providing valuable information for determining their likelihood of being bona fide pathogenic LS variants. This human cell-based assay system for functional testing of MMR gene VUS will facilitate the identification of high-risk LS patients.
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Affiliation(s)
- Abhijit Rath
- Center for Molecular Oncology and Institute for Systems Genomics, UConn Health, Farmington, Connecticut
| | - Akriti Mishra
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut
| | | | - Chaoran Hu
- Department of Statistics, University of Connecticut, Storrs, Connecticut.,Connecticut Institute for Clinical and Translational Science, UConn Health, Farmington, Connecticut
| | - Gregory Omerza
- Clinical Genomics Laboratory, The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut
| | - Kevin Kelly
- Clinical Genomics Laboratory, The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut
| | - Andrew Hesse
- Clinical Genomics Laboratory, The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut
| | - Honey V Reddi
- Clinical Genomics Laboratory, The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut
| | - James P Grady
- Connecticut Institute for Clinical and Translational Science, UConn Health, Farmington, Connecticut
| | - Christopher D Heinen
- Center for Molecular Oncology and Institute for Systems Genomics, UConn Health, Farmington, Connecticut
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17
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Bouvet D, Bodo S, Munier A, Guillerm E, Bertrand R, Colas C, Duval A, Coulet F, Muleris M. Methylation Tolerance-Based Functional Assay to Assess Variants of Unknown Significance in the MLH1 and MSH2 Genes and Identify Patients With Lynch Syndrome. Gastroenterology 2019; 157:421-431. [PMID: 30998989 DOI: 10.1053/j.gastro.2019.03.071] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/07/2019] [Accepted: 03/29/2019] [Indexed: 12/12/2022]
Abstract
BACKGROUND & AIMS Approximately 75% of patients with suspected Lynch syndrome carry variants in MLH1 or MSH2, proteins encoded by these genes are required for DNA mismatch repair (MMR). However, 30% of these are variants of unknown significance (VUS). A assay that measures cell response to the cytotoxic effects of a methylating agent can determine the effects of VUS in MMR genes and identify patients with constitutional MMR-deficiency syndrome. We adapted this method to test the effects of VUS in MLH1 and MSH2 genes found in patients with suspected Lynch syndrome. METHODS We transiently expressed MLH1 or MSH2 variants in MLH1- or MSH2-null human colorectal cancer cell lines (HCT116 or LoVo), respectively. The MMR process causes death of cells with methylation-damaged DNA bases, so we measured proportions of cells that undergo death following exposure to the methylating agent; cells that escaped its toxicity were considered to have variants that affect function of the gene product. Using this assay, we analyzed 88 variants (mainly missense variants), comprising a validation set of 40 previously classified variants (19 in MLH1 and 21 in MSH2) and a prospective set of 48 VUS (25 in MLH1 and 23 in MSH2). Prediction scores were calculated for all VUS according to the recommendations of the American College of Medical Genetics and Genomics, based on clinical, somatic, in silico, population, and functional data. RESULTS The assay correctly classified 39 of 40 variants in the validation set. The assay identified 12 VUS that did alter function of the gene product and 28 VUS that did not; the remaining 8 VUS had intermediate effects on MMR capacity and could not be classified. Comparison of assay results with prediction scores confirmed the ability of the assay to discriminate VUS that affected the function of the gene products from those that did not. CONCLUSIONS Using an assay that measures the ability of the cells to undergo death following DNA damage induction by a methylating agent, we were able to assess whether variants in MLH1 and MSH2 cause defects in DNA MMR. This assay might be used to help assessing the pathogenicity of VUS in MLH1 and MSH2 found in patients with suspected Lynch syndrome.
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Affiliation(s)
- Delphine Bouvet
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France
| | - Sahra Bodo
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France
| | - Annie Munier
- Sorbonne Université, Inserm, Centre de recherche Saint-Antoine, UMS30-LUMIC, Plateforme de Cytométrie en Flux CISA, site Saint-Antoine, Paris, France
| | - Erell Guillerm
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France; Genetics Department, AP-HP, Hôpital Universitaire Pitié-Salpétrière, Paris, France
| | - Romane Bertrand
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France
| | - Chrystelle Colas
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France; Institut Curie, Paris Sciences Lettres Research University, Department of Genetics, Paris, France
| | - Alex Duval
- Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France; Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, AP-HP, Biochimie, biologie moléculaire, Paris, France
| | - Florence Coulet
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France; Genetics Department, AP-HP, Hôpital Universitaire Pitié-Salpétrière, Paris, France
| | - Martine Muleris
- Sorbonne Université, Inserm, Centre de Recherche Saint-Antoine, CRSA, Paris, France; Equipe labellisée par la Ligue Nationale contre le Cancer, Paris, France.
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18
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Langers AMJ, Boonstra JJ, Hardwick JCH, van der Kraan J, Farina Sarasqueta A, Vasen HFA. Endoscopic full thickness resection for early colon cancer in Lynch syndrome. Fam Cancer 2019; 18:349-352. [PMID: 31111311 PMCID: PMC6559999 DOI: 10.1007/s10689-019-00132-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Subtotal colectomy is usually the therapy of choice in Lynch syndrome patients diagnosed with colon cancer. In patients who develop cancer after the age of 50-60 years, segmental colectomy is considered a good alternative. Although the endoscopic treatment of early colorectal cancer in non-Lynch patients has increased in the last decades, almost all patients with a Lynch syndrome-associated colorectal malignancy undergo surgery, even if the tumour is diagnosed in a (very) early stage. One of the endoscopic treatment options for early colorectal cancer is an endoscopic full thickness resection (eFTR). This treatment modality allows optimal pathological examination of the resection specimen, as a transmural resection is performed with optimal T-staging of the tumour. We report a case of a 62 year old man, diagnosed with MSH2-Lynch syndrome, who underwent successful eFTR treatment of an early (pT1) colon cancer located in the ascending colon, with no signs of recurrence 12 months after treatment. We discuss the pros and cons of endoscopic resection of early colorectal carcinoma in Lynch syndrome patients.
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Affiliation(s)
- Alexandra M J Langers
- Department of Gastroenterology and Hepatology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands.
| | - Jurjen J Boonstra
- Department of Gastroenterology and Hepatology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands
| | - James C H Hardwick
- Department of Gastroenterology and Hepatology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands
| | - Jolein van der Kraan
- Department of Gastroenterology and Hepatology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands
| | | | - Hans F A Vasen
- Department of Gastroenterology and Hepatology, Leiden University Medical Centre, PO Box 9600, 2300 RC, Leiden, The Netherlands
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19
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Rigter LS, Snaebjornsson P, Rosenberg EH, Atmodimedjo PN, Aleman BM, Ten Hoeve J, Geurts-Giele WR, van Ravesteyn TW, Hoeksel J, Meijer GA, Te Riele H, van Leeuwen FE, Dinjens WN, van Leerdam ME. Double somatic mutations in mismatch repair genes are frequent in colorectal cancer after Hodgkin's lymphoma treatment. Gut 2018; 67:447-455. [PMID: 29439113 DOI: 10.1136/gutjnl-2016-312608] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 10/07/2016] [Accepted: 10/18/2016] [Indexed: 12/12/2022]
Abstract
OBJECTIVE Hodgkin's lymphoma survivors who were treated with infradiaphragmatic radiotherapy or procarbazine-containing chemotherapy have a fivefold increased risk of developing colorectal cancer (CRC). This study aims to provide insight into the development of therapy-related CRC (t-CRC) by evaluating histopathological and molecular characteristics. DESIGN 54 t-CRCs diagnosed in a Hodgkin's lymphoma survivor cohort were analysed for mismatch repair (MMR) proteins by immunohistochemistry, microsatellite instability (MSI) and KRAS/BRAF mutations. MSI t-CRCs were evaluated for promoter methylation and mutations in MMR genes. Pathogenicity of MMR gene mutations was evaluated by in silico predictions and functional analyses. Frequencies were compared with a general population cohort of CRC (n=1111). RESULTS KRAS and BRAF mutations were present in 41% and 15% t-CRCs, respectively. Compared with CRCs in the general population, t-CRCs had a higher MSI frequency (24% vs 11%, p=0.003) and more frequent loss of MSH2/MSH6 staining (13% vs 1%, p<0.001). Loss of MLH1/PMS2 staining and MLH1 promoter methylation were equally common in t-CRCs and the general population. In MSI CRCs without MLH1 promoter methylation, double somatic MMR gene mutations (or loss of heterozygosity as second hit) were detected in 7/10 (70%) t-CRCs and 8/36 (22%) CRCs in the general population (p=0.008). These MMR gene mutations in t-CRCs were classified as pathogenic. MSI t-CRC cases could not be ascribed to Lynch syndrome. CONCLUSIONS We have demonstrated a higher frequency of MSI among t-CRCs, which results from somatic MMR gene mutations. This suggests a novel association of somatic MMR gene mutations with prior anticancer treatment.
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Affiliation(s)
- Lisanne S Rigter
- Department of Gastroenterology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Petur Snaebjornsson
- Department of Pathology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Efraim H Rosenberg
- Department of Pathology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Peggy N Atmodimedjo
- Department of Pathology, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, The Netherlands
| | - Berthe M Aleman
- Department of Radiation Oncology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jelle Ten Hoeve
- Division of Computational Biology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Willemina R Geurts-Giele
- Department of Pathology, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, The Netherlands
| | | | - Thomas W van Ravesteyn
- Division of Biological Stress Response, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Johan Hoeksel
- Division of Biological Stress Response, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Gerrit A Meijer
- Department of Pathology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Hein Te Riele
- Division of Biological Stress Response, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Flora E van Leeuwen
- Department of Epidemiology, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Winand N Dinjens
- Department of Pathology, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, The Netherlands
| | - Monique E van Leerdam
- Department of Gastroenterology, Netherlands Cancer Institute, Amsterdam, The Netherlands
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20
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Yuan LQ, Wang JH, Zhu K, Yang M, Gu WZ, Lai C, Li HM, Shu Q, Chen X. A highly malignant case of neuroblastoma with substantial increase of single-nucleotide variants and normal mismatch repair system: A case report. Medicine (Baltimore) 2017; 96:e8845. [PMID: 29390274 PMCID: PMC5815686 DOI: 10.1097/md.0000000000008845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
RATIONALE Neuroblastoma is a common abdominal malignancy in children. The chemoresistant and relapsed cases have poor prognosis. The genetic background and the mechanism of resistance remain unelucidated. Next-generation sequence (NGS) is becoming a popular tool to unravel the genetic background and to guide precision medicine in oncology studies as well as in clinical practice. PATIENT CONCERNS Here we report a neuroblastoma case of a boy aged 2 years and 8 months when first diagnosed, with multiple metastatic sites found in both lungs. The metastatic tumors were resistant to chemotherapy and the patient suffered from severe bone marrow suppression. NGS of the whole exon revealed somatic mutations including 9666 single-nucleotide variants (SNVs) from 5148 genes, 55 copy number variations (CNVs), and 140 insertion-deletion variations. The high frequency of SNVs makes it distinguished case. However, no mutation of key tumor driver genes with functional significance was identified. No abnormality was found in nucleic acid synthesis enzymes. No amplification of c-Myc and n-Myc was found by fluorescence in situ hybridization (FISH). Both NGS and immunohistochemistry (IHC) analysis indicated that DNA mismatch repair (MMR) system was intact. INTERVENTIONS After initial diagnosis, the patient received combinational chemotherapy, which includes vindesine, an analogue of adriamycin suggested by NGS data, for 4 months. Radical section of the tumor together with the left kidney and the left adrenal gland was performed 5 months after diagnosis. Postsurgical chemotherapy protocols was similar with the previous. OUTCOMES The patient died 2 years after initial diagnosis after 8 relapses following combinational chemotherapy. LESSONS This case of neuroblastoma is with pronounced somatic mutations but unidentified driver gene and therapeutic target. Although NGS is a potentially powerful tool to guide precision medicine, at current stage, its application in the clinic certainly has its limits. The underlying mechanism of the substantially increased SNV number, as well as the malignant behaviors of the tumor, is yet to be revealed.
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Affiliation(s)
- Lin-Qing Yuan
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
| | - Jin-Hu Wang
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
| | - Kun Zhu
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
| | - Min Yang
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
| | - Wei-Zhong Gu
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
- The Key Laboratory of Diagnosis and Treatment of Neonatal Diseases of Zhejiang Province, Hangzhou, Zhejiang, China
| | - Can Lai
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
| | - Hao-Min Li
- Institute of Translational Medicine, Zhejiang University
- The Key Laboratory of Diagnosis and Treatment of Neonatal Diseases of Zhejiang Province, Hangzhou, Zhejiang, China
| | - Qiang Shu
- The Key Laboratory of Diagnosis and Treatment of Neonatal Diseases of Zhejiang Province, Hangzhou, Zhejiang, China
| | - Xi Chen
- Departments of Central Laboratory, Pathology, Oncology and Radiology, The Children's Hospital of Zhejiang University School of Medicine
- The Key Laboratory of Diagnosis and Treatment of Neonatal Diseases of Zhejiang Province, Hangzhou, Zhejiang, China
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21
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Moore EA, Xu YZ. The effect of S-substitution at the O6-guanine site on the structure and dynamics of a DNA oligomer containing a G:T mismatch. PLoS One 2017; 12:e0184801. [PMID: 28910418 PMCID: PMC5599020 DOI: 10.1371/journal.pone.0184801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 08/31/2017] [Indexed: 11/21/2022] Open
Abstract
The effect of S-substitution on the O6 guanine site of a 13-mer DNA duplex containing a G:T mismatch is studied using molecular dynamics. The structure, dynamic evolution and hydration of the S-substituted duplex are compared with those of a normal duplex, a duplex with S-substitution on guanine, but no mismatch and a duplex with just a G:T mismatch. The S-substituted mismatch leads to cell death rather than repair. One suggestion is that the G:T mismatch recognition protein recognises the S-substituted mismatch (GS:T) as G:T. This leads to a cycle of futile repair ending in DNA breakage and cell death. We find that some structural features of the helix are similar for the duplex with the G:T mismatch and that with the S-substituted mismatch, but differ from the normal duplex, notably the helical twist. These differences arise from the change in the hydrogen-bonding pattern of the base pair. However a marked feature of the S-substituted G:T mismatch duplex is a very large opening. This showed considerable variability. It is suggested that this enlarged opening would lend support to an alternative model of cell death in which the mismatch protein attaches to thioguanine and activates downstream damage-response pathways. Attack on the sulphur by reactive oxygen species, also leading to cell death, would also be aided by the large, variable opening.
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Affiliation(s)
- Elaine Ann Moore
- School of Life, Health and Chemical Sciences, STEM Faculty, The Open University, Milton Keynes, Buckinghamshire, United Kingdom
- * E-mail:
| | - Yao-Zhong Xu
- School of Life, Health and Chemical Sciences, STEM Faculty, The Open University, Milton Keynes, Buckinghamshire, United Kingdom
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22
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Houlleberghs H, Goverde A, Lusseveld J, Dekker M, Bruno MJ, Menko FH, Mensenkamp AR, Spaander MCW, Wagner A, Hofstra RMW, te Riele H. Suspected Lynch syndrome associated MSH6 variants: A functional assay to determine their pathogenicity. PLoS Genet 2017; 13:e1006765. [PMID: 28531214 PMCID: PMC5460888 DOI: 10.1371/journal.pgen.1006765] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 06/06/2017] [Accepted: 04/18/2017] [Indexed: 12/14/2022] Open
Abstract
Lynch syndrome (LS) is a hereditary cancer predisposition caused by inactivating mutations in DNA mismatch repair (MMR) genes. Mutations in the MSH6 DNA MMR gene account for approximately 18% of LS cases. Many LS-associated sequence variants are nonsense and frameshift mutations that clearly abrogate MMR activity. However, missense mutations whose functional implications are unclear are also frequently seen in suspected-LS patients. To conclusively diagnose LS and enroll patients in appropriate surveillance programs to reduce morbidity as well as mortality, the functional consequences of these variants of uncertain clinical significance (VUS) must be defined. We present an oligonucleotide-directed mutagenesis screen for the identification of pathogenic MSH6 VUS. In the screen, the MSH6 variant of interest is introduced into mouse embryonic stem cells by site-directed mutagenesis. Subsequent selection for MMR-deficient cells using the DNA damaging agent 6-thioguanine (6TG) allows the identification of MMR abrogating VUS because solely MMR-deficient cells survive 6TG exposure. We demonstrate the efficacy of the genetic screen, investigate the phenotype of 26 MSH6 VUS and compare our screening results to clinical data from suspected-LS patients carrying these variant alleles. The colorectal and endometrial cancer predisposition Lynch syndrome (LS) is caused by an inherited heterozygous defect in one of four DNA mismatch repair (MMR) genes. Deleterious mutations (e.g., protein-deleting or -truncating) in DNA MMR genes unambiguously allow for the clinical diagnosis LS and hence enable appropriate surveillance measures to be taken to reduce cancer risk and ensure early detection of tumors. However, currently about one-third of detected MMR gene variants are subtle with less clear functional consequences: missense mutations affecting a single amino acid may be innocuous, hence not causing LS, or partially or fully destroy protein function. As long as uncertainty exists about their pathogenicity, such mutations are labeled ‘variants of uncertain (clinical) significance’ (VUS). VUS hamper genetic counseling and therefore the need for functional testing of VUS is widely recognized. To functionally annotate MMR gene VUS, we have developed a high content cellular assay in which the VUS is introduced in a cell culture by oligonucleotide-directed gene modification. Should the VUS be deleterious for MMR, the modified cells survive exposure to the guanine analog 6-thioguanine (6TG) and 6TG-resistant colonies appear. Should the mutation not affect MMR, no colonies appear. Here we present the adaptation and application of this protocol to the functional annotation of variants of the MMR gene MSH6. Implementation of our assay in clinical genetics laboratories will provide clinicians with information for proper counseling of mutation carriers and treatment of their of tumors.
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Affiliation(s)
- Hellen Houlleberghs
- Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Anne Goverde
- Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Jarnick Lusseveld
- Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Marleen Dekker
- Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Marco J. Bruno
- Department of Gastroenterology and Hepatology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Fred H. Menko
- Family Cancer Clinic, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Arjen R. Mensenkamp
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Manon C. W. Spaander
- Department of Gastroenterology and Hepatology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Anja Wagner
- Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Robert M. W. Hofstra
- Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Hein te Riele
- Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, The Netherlands
- * E-mail:
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23
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Predicting the impact of Lynch syndrome-causing missense mutations from structural calculations. PLoS Genet 2017; 13:e1006739. [PMID: 28422960 PMCID: PMC5415204 DOI: 10.1371/journal.pgen.1006739] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 05/03/2017] [Accepted: 04/05/2017] [Indexed: 12/02/2022] Open
Abstract
Accurate methods to assess the pathogenicity of mutations are needed to fully leverage the possibilities of genome sequencing in diagnosis. Current data-driven and bioinformatics approaches are, however, limited by the large number of new variations found in each newly sequenced genome, and often do not provide direct mechanistic insight. Here we demonstrate, for the first time, that saturation mutagenesis, biophysical modeling and co-variation analysis, performed in silico, can predict the abundance, metabolic stability, and function of proteins inside living cells. As a model system, we selected the human mismatch repair protein, MSH2, where missense variants are known to cause the hereditary cancer predisposition disease, known as Lynch syndrome. We show that the majority of disease-causing MSH2 mutations give rise to folding defects and proteasome-dependent degradation rather than inherent loss of function, and accordingly our in silico modeling data accurately identifies disease-causing mutations and outperforms the traditionally used genetic disease predictors. Thus, in conclusion, in silico biophysical modeling should be considered for making genotype-phenotype predictions and for diagnosis of Lynch syndrome, and perhaps other hereditary diseases. The protein quality control system targets misfolded proteins for degradation. So far it has not been possible from sequence or structural data to predict the biological stability of a misfolded protein, or the effect of mutations on intracellular protein levels. Here we demonstrate that in silico saturation mutagenesis and biophysical calculations of the structural stability of the human mismatch repair protein MSH2 correlate with cellular protein levels, turnover and function. Of 24 different MSH2 variants, some of which are linked to Lynch syndrome, a destabilization of as little as 3 kcal/mol is sufficient to cause rapid degradation via the ubiquitin-proteasome pathway. Thus, biophysical modeling can, to a large extent, predict the metabolic stability of proteins. We also show that the same biophysical calculations can be used to distinguish with high accuracy neutral sequence variation from pathogenic variants, and that the calculations outperform several traditionally used disease predictors. We therefore suggest the method to be of potential value for patient stratification in Lynch syndrome, and perhaps other hereditary diseases.
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Mcilhatton MA, Boivin GP, Groden J. Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer. BIOMED RESEARCH INTERNATIONAL 2016; 2016:1414383. [PMID: 27413734 PMCID: PMC4931062 DOI: 10.1155/2016/1414383] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 05/09/2016] [Indexed: 12/20/2022]
Abstract
Technical and biological innovations have enabled the development of more sophisticated and focused murine models that increasingly recapitulate the complex pathologies of human diseases, in particular cancer. Mouse models provide excellent in vivo systems for deciphering the intricacies of cancer biology within the context of precise experimental settings. They present biologically relevant, adaptable platforms that are amenable to continual improvement and refinement. We discuss how recent advances in our understanding of tumorigenesis and the underlying deficiencies of DNA repair mechanisms that drive it have been informed by using genetically engineered mice to create defined, well-characterized models of human colorectal cancer. In particular, we focus on how mechanisms of DNA repair can be manipulated precisely to create in vivo models whereby the underlying processes of tumorigenesis are accelerated or attenuated, dependent on the composite alleles carried by the mouse model. Such models have evolved to the stage where they now reflect the initiation and progression of sporadic cancers. The review is focused on mouse models of colorectal cancer and how insights from these models have been instrumental in shaping our understanding of the processes and potential therapies for this disease.
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Affiliation(s)
- Michael A. Mcilhatton
- Department of Cancer Biology and Genetics, The Ohio State University, 460 West 12th Avenue, Columbus, OH 43210, USA
| | - Gregory P. Boivin
- Department of Pathology, Boonshoft School of Medicine, Wright State University, Health Sciences Building 053, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Joanna Groden
- Department of Cancer Biology and Genetics, The Ohio State University, 460 West 12th Avenue, Columbus, OH 43210, USA
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25
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Enhanced gene targeting to evaluate Lynch syndrome alterations. Proc Natl Acad Sci U S A 2016; 113:3918-20. [PMID: 27035997 DOI: 10.1073/pnas.1602650113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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26
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LNA modification of single-stranded DNA oligonucleotides allows subtle gene modification in mismatch-repair-proficient cells. Proc Natl Acad Sci U S A 2016; 113:4122-7. [PMID: 26951689 DOI: 10.1073/pnas.1513315113] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Synthetic single-stranded DNA oligonucleotides (ssODNs) can be used to generate subtle genetic modifications in eukaryotic and prokaryotic cells without the requirement for prior generation of DNA double-stranded breaks. However, DNA mismatch repair (MMR) suppresses the efficiency of gene modification by >100-fold. Here we present a commercially available ssODN design that evades MMR and enables subtle gene modification in MMR-proficient cells. The presence of locked nucleic acids (LNAs) in the ssODNs at mismatching bases, or also at directly adjacent bases, allowed 1-, 2-, or 3-bp substitutions in MMR-proficient mouse embryonic stem cells as effectively as in MMR-deficient cells. Additionally, in MMR-proficient Escherichia coli, LNA modification of the ssODNs enabled effective single-base-pair substitution. In vitro, LNA modification of mismatches precluded binding of purified E. coli MMR protein MutS. These findings make ssODN-directed gene modification particularly well suited for applications that require the evaluation of a large number of sequence variants with an easy selectable phenotype.
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