title: Positive Cofactor 4 (PC4) is critical for DNA repair pathway re-routing in DT40 cells.
abstract: PC4 is an abundant single-strand DNA binding protein that has been implicated in transcription and DNA repair. Here, we show that PC4 is involved in the cellular DNA damage response. To elucidate the role, we used the DT40 chicken B cell model, which produces clustered DNA lesions at Ig loci via the action of activation-induced deaminase. Our results help resolve key aspects of immunoglobulin diversification and suggest an essential role of PC4 in repair pathway choice. We show that PC4 ablation in gene conversion (GC)-active cells significantly disrupts GC but has little to no effect on targeted homologous recombination. In agreement, the global double-strand break repair response, as measured by γH2AX foci analysis, is unperturbed 16 hours post irradiation. In cells with the pseudo-genes removed (GC inactive), PC4 ablation reduced the overall mutation rate while simultaneously increasing the transversion mutation ratio. By tagging the N-terminus of PC4, gene conversion and somatic hypermutation are all but abolished even when native non-tagged PC4 is present, indicating a dominant negative effect. Our data point to a very early and deterministic role for PC4 in DNA repair pathway re-routing.
authors.affiliation: Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH). Department of Radiation Sciences - Research Unit Radiation Cytogenetics, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
authors.forename: Randolph B
authors.initials: RB
authors.lastname: Caldwell
authors.affiliation: Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH). Department of Radiation Sciences - Research Unit Radiation Cytogenetics, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Braselmann
authors.affiliation: Clinical Cooperation Group 'Personalized Radiotherapy of Head and Neck Cancer', Helmholtz Zentrum München, Ingolstaedter Landstr 1, 85764, Neuherberg, Germany.|Department of Radiotherapy and Radiation Oncology, Ludwig-Maximilians-University Munich, Marchioninistr 15, 81377, Munich, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Schoetz
authors.affiliation: Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH). Department of Radiation Sciences - Research Unit Radiation Cytogenetics, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Heuer
authors.affiliation: Bundeswehr Institute of Radiobiology affiliated to the University of Ulm. Neuherbergstr. 11, 80937 Muenchen, Germany.
authors.forename: Harry
authors.initials: H
authors.lastname: Scherthan
authors.affiliation: Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH). Department of Radiation Sciences - Research Unit Radiation Cytogenetics, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.|Clinical Cooperation Group 'Personalized Radiotherapy of Head and Neck Cancer', Helmholtz Zentrum München, Ingolstaedter Landstr 1, 85764, Neuherberg, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Zitzelsberger
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000502:physiology*; D001402:B-Lymphocytes / Q000378:metabolism*; D002460:Cell Line; D002645:Chickens; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000737:chemistry*; D007136:Immunoglobulins / Q000737:chemistry; D009154:Mutation; D010641:Phenotype; D010865:Pilot Projects; D000072417:Protein Domains; D012333:RNA, Messenger / Q000378:metabolism; D011995:Recombination, Genetic; D019076:Transgenes
chemical_list: D030161:Avian Proteins; D004268:DNA-Binding Proteins; D006657:Histones; D007136:Immunoglobulins; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins