title: 53BP1 promotes microhomology-mediated end-joining in G1-phase cells.
abstract: Alternative non-homologous end joining (alt-NHEJ) was originally identified as a backup repair mechanism in the absence of classical NHEJ (c-NHEJ) factors but recent studies have demonstrated that alt-NHEJ is active even when c-NHEJ as well as homologous recombination is available. The functions of 53BP1 in NHEJ processes are not well understood. Here, we report that 53BP1 promotes DNA double-strand break (DSB) repair and genomic stability not only in c-NHEJ-proficient but also -deficient human G1-phase cells. Using an array of repair substrates we show that these effects of 53BP1 are correlated with a promotion of microhomology-mediated end-joining (MMEJ), a subtype of alt-NHEJ, in G1-phase. Consistent with a specific role in MMEJ we confirm that 53BP1 status does not affect c-NHEJ. 53BP1 supports sequence deletion during MMEJ consistent with a putative role in facilitating end-resection. Interestingly, promotion of MMEJ by 53BP1 in G1-phase cells is only observed in the presence of functional BRCA1. Depletion of both 53BP1 and BRCA1 increases repair needing microhomology usage and augments loss of DNA sequence, suggesting that MMEJ is a highly regulated DSB repair process. Together, these findings significantly expand our understanding of the cell-cycle-dependent roles of 53BP1 in DSB repair.
authors.affiliation: Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, BRB 323, Cleveland, OH 44106, USA.
authors.forename: Xiahui
authors.initials: X
authors.lastname: Xiong
authors.affiliation: Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, BRB 323, Cleveland, OH 44106, USA.
authors.forename: Zhanwen
authors.initials: Z
authors.lastname: Du
authors.affiliation: Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, BRB 323, Cleveland, OH 44106, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, BRB 323, Cleveland, OH 44106, USA.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Feng
authors.affiliation: Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine,1650 Orleans Street, Baltimore, MD 21231, USA.
authors.forename: Pan
authors.initials: P
authors.lastname: Fan
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, 1410 Laney Walker Blvd., CN-2134, Augusta, GA 30912, USA.
authors.forename: Chunhong
authors.initials: C
authors.lastname: Yan
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA.
authors.forename: Henning
authors.initials: H
authors.lastname: Willers
authors.affiliation: Department of Radiation Oncology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, BRB 323, Cleveland, OH 44106, USA jxz321@case.edu.
authors.forename: Junran
authors.initials: J
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D020552:Comet Assay; D059766:DNA End-Joining Repair; D017931:DNA Primers; D005455:Fluorescent Antibody Technique; D016193:G1 Phase; D042822:Genomic Instability; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D000071857:Tumor Suppressor p53-Binding Protein 1