PAXX and XLF DNA repair factors are functionally redundant in joining DNA breaks in a G1-arrested progenitor B-cell line.
Classical nonhomologous end joining (C-NHEJ) is a major mammalian DNA double-strand break (DSB) repair pathway. Core C-NHEJ factors, such as XRCC4, are required for joining DSB intermediates of the G1 phase-specific V(D)J recombination reaction in progenitor lymphocytes. Core factors also contribute to joining DSBs in cycling mature B-lineage cells, including DSBs generated during antibody class switch recombination (CSR) and DSBs generated by ionizing radiation. The XRCC4-like-factor (XLF) C-NHEJ protein is dispensable for V(D)J recombination in normal cells, but because of functional redundancy, it is absolutely required for this process in cells deficient for the ataxia telangiectasia-mutated (ATM) DSB response factor. The recently identified paralogue of XRCC4 and XLF (PAXX) factor has homology to these two proteins and variably contributes to ionizing radiation-induced DSB repair in human and chicken cells. We now report that PAXX is dispensable for joining V(D)J recombination DSBs in G1-arrested mouse pro-B-cell lines, dispensable for joining CSR-associated DSBs in a cycling mouse B-cell line, and dispensable for normal ionizing radiation resistance in both G1-arrested and cycling pro-B lines. However, we find that combined deficiency for PAXX and XLF in G1-arrested pro-B lines abrogates DSB joining during V(D)J recombination and sensitizes the cells to ionizing radiation exposure. Thus, PAXX provides core C-NHEJ factor-associated functions in the absence of XLF and vice versa in G1-arrested pro-B-cell lines. Finally, we also find that PAXX deficiency has no impact on V(D)J recombination DSB joining in ATM-deficient pro-B lines. We discuss implications of these findings with respect to potential PAXX and XLF functions in C-NHEJ.
Howard Hughes Medical Institute, Boston, MA 02115; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115; Department of Genetics, Harvard Medical School, Boston, MA 02115.
Vipul
V
Kumar
Howard Hughes Medical Institute, Boston, MA 02115; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115; Department of Genetics, Harvard Medical School, Boston, MA 02115 alt@enders.tch.harvard.edu.
Frederick W
FW
Alt
Howard Hughes Medical Institute, Boston, MA 02115; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115; Department of Genetics, Harvard Medical School, Boston, MA 02115.
Richard L
0000-0001-6963-4931
RL
Frock
D000818:Animals; D002645:Chickens / Q000235:genetics; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004249:DNA Damage / Q000528:radiation effects; D059766:DNA End-Joining Repair / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics* / Q000528:radiation effects; D045643:DNA Repair Enzymes / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D051379:Mice; D011839:Radiation, Ionizing; D060152:V(D)J Recombination / Q000235:genetics
D004268:DNA-Binding Proteins; C508551:NHEJ1 protein, human; C000595075:PAXX protein, human; C101467:XRCC4 protein, human; D045643:DNA Repair Enzymes
C-NHEJ; DNA repair; PAXX; V(D)J recombination; XLF