Robust chromosomal DNA repair via alternative end-joining in the absence of X-ray repair cross-complementing protein 1 (XRCC1).
Classical nonhomologous DNA end-joining (C-NHEJ), which is a major DNA double-strand break (DSB) repair pathway in mammalian cells, plays a dominant role in joining DSBs during Ig heavy chain (IgH) class switch recombination (CSR) in activated B lymphocytes. However, in B cells deficient for one or more requisite C-NHEJ factors, such as DNA ligase 4 (Lig4) or XRCC4, end-joining during CSR occurs by a distinct alternative end-joining (A-EJ) pathway. A-EJ also has been implicated in joining DSBs found in oncogenic chromosomal translocations. DNA ligase 3 (Lig3) and its cofactor XRCC1 are widely considered to be requisite A-EJ factors, based on biochemical studies or extrachromosomal substrate end-joining studies. However, potential roles for these factors in A-EJ of endogenous chromosomal DSBs have not been tested. Here, we report that Xrcc1 inactivation via conditional gene-targeted deletion in WT or XRCC4-deficient primary B cells does not have an impact on either CSR or IgH/c-myc translocations in activated B lymphocytes. Indeed, homozygous deletion of Xrcc1 does not impair A-EJ of I-SceI-induced DSBs in XRCC4-deficient pro-B-cell lines. Correspondingly, substantial depletion of Lig3 in Lig4-deficient primary B cells or B-cell lines does not impair A-EJ of CSR-mediated DSBs or formation of IgH/c-myc translocations. Our findings firmly demonstrate that XRCC1 is not a requisite factor for A-EJ of chromosomal DSBs and raise the possibility that DNA ligase 1 (Lig1) may contribute more to A-EJ than previously considered.
Program in Cellular and Molecular Medicine, Howard Hughes Medical Institute, Children's Hospital Boston and Department of Genetics, Immune Disease Institute, Harvard Medical School, Boston, MA 02115, USA.
Cristian
C
Boboila
Valentyn
V
Oksenych
Monica
M
Gostissa
Jing H
JH
Wang
Shan
S
Zha
Yu
Y
Zhang
Hua
H
Chai
Cheng-Sheng
CS
Lee
Mila
M
Jankovic
Liz-Marie Albertorio
LM
Saez
Michel C
MC
Nussenzweig
Peter J
PJ
McKinnon
Frederick W
FW
Alt
Bjoern
B
Schwer
D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology; D019070:Cell Lineage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D051379:Mice; D014178:Translocation, Genetic; D000076105:X-ray Repair Cross Complementing Protein 1
D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619352:Xrcc1 protein, mouse