Somatic hypermutation of Ig genes is initiated by transcriptioncoupled cytidine deamination in Ig loci. Error-prone processing of the resultant DNA lesions is thought to cause extensive mutagenesis, but it is presently an enigma how and why error-prone rather than error-free repair pathways are recruited. During DNA replication, recruitment of error-prone translesion polymerases may be mediated by Rad6͞Rad18-mediated ubiquitination of proliferating cell nuclear antigen, a major switchboard controlling the fidelity of DNA lesion bypass in eukaryotes. By inactivation of Rad18 in the DT40 B cell line, we show that the Rad6 pathway is involved in somatic hypermutation in these cells. Our findings imply that targeted recruitment of mutagenic polymerases by the Rad6 pathway contributes to the complex process of somatic hypermutation and provide a framework for more detailed mechanistic studies of the mutagenesis phase of secondary Ig diversification.proliferating cell nuclear antigen ͉ ubiquitination ͉ Rad6 pathway G iven the many challenges that damage cellular DNA daily, the faithful maintenance of genetic information requires the interplay of multiple DNA repair pathways. In most cases, these mechanisms ensure restoration of the original DNA sequence, preventing mutations or aberrations that may lead to impairment of cellular function. In some instances, though, a certain imprecision may be tolerated or even favored by the cell to allow for survival in critical situations. DNA repair mechanisms that are inherently imprecise are the basis of the spontaneous mutability of all genomes and may be recruited and adapted for situations where high genetic variability is mandatory for survival.The adaptive immune system of vertebrates has been shaped in coevolution with pathogenic organisms of high genetic diversity and variability. The high diversity of the primary immune repertoire established during V(D)J recombination in B and T cells generates sufficient potential for recognition of any pathogen, but the affinity of binding is often not sufficient for effective neutralization. Therefore, a second wave of diversification during acute infections ensures that the binding affinity of the antibodies produced by B lymphocytes is fine-tuned to the task at hand. The underlying mechanism in humans is somatic hypermutation, which modifies the antigen binding region by targeted mutagenesis in the variable region of the Ig genes (1). An alternative diversification mechanism prevalent in chicken and some mammals, Ig gene conversion alters the same region by targeted homologous recombination with upstream Ig pseudogenes (2).Somatic hypermutation and Ig gene conversion are related processes (3) originating from the same initial DNA lesion. The transcription-coupled deamination of cytosines by activationinduced cytidine deaminase (AID) leads to uracil that may be processed to abasic sites or strand breaks by the excision repair pathway, i.e., uracil-N-glycosylase (4, 5). The resultant DNA lesions may be repaired by mutagenesis or reco...
Background. For many tumors, therapeutic options are sparse beyond the guidelines, especially for pancreatic cancer. At the same time, more and more biomarkers are known, informing about or supporting treatment decisions. Finally, tumor DNA analysis with next generation sequencing (NGS) is quickly becoming a routine test, at least for tumors. However, to analyse the vast amount of data and provide concrete, evidence-based treatment recommendations has been a challenge. Methods. Applying NGS in a quality controlled set-up together with the newly developed evidence-based software tool EngineusGUIDETM (CE-marked). Results. During the time from Oct 2013 until Oct 2015, 87 patients were analysed with EngineusGUIDE. In 7 cases, more than one tumor was investigated. NGS was performed (WXS = 48; panel/paired = 16, panel = 23). Sequencing could be performed in all but one patient (Whole Exome; bone metastasis). Sequencing quality was insufficient for analysis in 3 cases (paired panel), sequencing revealed insufficient tumor content in the sample for one patient (Whole Exome) leaving 82 patients. The indication was: Pancreatic Neoplasms = 21 cases; Colorectal Neoplasms = 12; Breast Neoplasms = 5; CUP = 6; NSCLC = 3; 2 cases each for Bronchial Neoplasms, Adenoid Cystic Carcinoma, Common Bile Duct Neoplasms, Glioblastoma, Multiple Myeloma, Prostatic Neoplasms and 1 case each for Adenocarcinoma, Duodenal Neoplasms, Endometrial Neoplasms, Hemangiosarcoma, Hypopharyngeal Neoplasms, Leukemia (Lymphocytic, Chronic, B-Cell), Liposarcoma, Liver Neoplasms, Lung Neoplasms, B-Cell Lymphoma, Mantle-Cell Lymphoma, Meningioma, Oropharyngeal Neoplasms, Ovarian Neoplasms, Paranasal Sinus Neoplasms, Parathyroid Neoplasms, Sarcoma, Sigmoid Neoplasms, Squamous Cell Neoplasms, Stomach Neoplasms, Thyroid Neoplasms, Urinary Bladder Neoplasms, Uveal melanoma. In 67/82 patients, druggable targets (response biomarkers) could be identified (range 0-8; median 2). In 45/82 patients (range 0-5; median 1) biomarkers indicated lack of efficacy (e.g. KRAS mutation in CRC). In 65/82 patients, biomarkers indicated increased toxicity (range 0-7; median 2), in 19/82 patients FDA-approved biomarkers for toxicity were detected (28 biomarkers). Of the positive biomarkers, 40 biomarkers in 26 patients indicated drugs approved in the indication, 75 biomarkers in 45 patients indicated approved drugs, and 58 biomarkers in 39 patients indicated experimental drugs (pre-clinical and phase I - III). Six patients have already received drugs recommended by EngineusGUIDE. In 11 patients, toxicity markers may explain observed toxicity during previous treatment. We are currently collecting the outcome parameters of EngineusGUIDE recommendations. Citation Format: Matthias Löhr, Katrin Stecker, Caroline Huelsewig, Sandra Morandell, Isin Ertongur, Sarah Luke-Glaser, Anna Laib, Linnéa Malgerud, Carlos Fernández Moro, Masoud Karimi, Johan Permert, Rainer Heuchel, Johan Lindberg, Valtteri Wirta, Alexander Picker, Marco Del Chiaro, Stephan L. Haas, Caroline S. Verbek, Lars Engstrand, Jens Siveke, David Jackson, Henrik Grönberg, Dirk Jäger, Stephan Brock. An evidence-based software tool for personalized cancer medicine to recommend therapeutic options and avoid toxicity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3165.
In contrast to lower eukaryotes, most vertebrate cells are characterized by a moderate efficiency of homologous recombination (HR) and limited feasibility of targeted genetic modifications. As a notable exception, the chicken DT40 B cell line is distinguished by efficient homology-mediated repair of DNA lesions during Ig gene conversion, and also shows exceptionally high gene-targeting efficiencies. The molecular basis of these phenomena is elusive. Here we show that the activity levels of Ubc13, the E2 enzyme responsible for non-canonical K63-linked polyubiquitination, are critical for high efficiency of Ig gene conversion and gene targeting in DT40. Ubc13+/− cells show substantially lower homology-mediated repair, yet do not display changes in somatic hypermutation, overall DNA repair or cell proliferation. Our results suggest that modulation of the activity of K63-linked polyubiquitination may be used to customize HR efficiencies in vertebrate cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.