title: Impact of DNA ligase IV on nonhomologous end joining pathways during class switch recombination in human cells.
abstract: Class switch recombination (CSR) is a region-specific, transcriptionally regulated, nonhomologous recombinational process that is initiated by activation-induced cytidine deaminase (AID). The initial lesions in the switch (S) regions are subsequently processed and resolved, leading to recombination of the two targeted S regions. The mechanisms by which repair and ligation of the broken DNA ends occurs is still elusive. Recently, a small number of patients lacking DNA ligase IV, a critical component of the nonhomologous end joining (NHEJ) machinery, have been identified. We show that these patients display a considerably increased donor/acceptor homology at Smu-Salpha junctions compared with healthy controls. In contrast, Smu-Sgamma junctions show an increased frequency of insertions but no increase in junctional homology. These altered patterns of junctional resolution may be related to differences in the homology between the Smu and the downstream isotype S regions, and could reflect different modes of switch junction resolution when NHEJ is impaired. These findings link DNA ligase IV, and thus NHEJ, to CSR.
authors.affiliation: Clinical Immunology, Department of Laboratory Medicine, Karolinska University Hospital Huddinge, SE-14186 Stockholm, Sweden.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Pan-Hammarström
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Jones
authors.forename: Aleksi
authors.initials: A
authors.lastname: Lähdesmäki
authors.forename: Wei
authors.initials: W
authors.lastname: Zhou
authors.forename: Richard A
authors.initials: RA
authors.lastname: Gatti
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarström
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Gennery
authors.forename: Michael R
authors.initials: MR
authors.lastname: Ehrenstein
mesh_terms: D001483:Base Sequence; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007070:Immunoglobulin A / Q000235:genetics / Q000276:immunology; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007074:Immunoglobulin G / Q000276:immunology; D008969:Molecular Sequence Data; D009154:Mutation; D011995:Recombination, Genetic; D017385:Sequence Homology
chemical_list: D007070:Immunoglobulin A; D007074:Immunoglobulin G; C000607893:LIG4 protein, human; D011088:DNA Ligases; D000072481:DNA Ligase ATP