Identification of human autoantibodies to the DNA ligase IV/XRCC4 complex and mapping of an autoimmune epitope to a potential regulatory region.
The nonhomologous end-joining pathway is the principal mechanism for repair of ionizing radiation-induced, double-strand breaks in mammalian cells. Three polypeptides in this pathway, including the two subunits of Ku protein and the catalytic subunit of the DNA-dependent protein kinase, are known targets of autoantibodies in systemic rheumatic diseases. Here we show that two additional polypeptides in the pathway, DNA ligase IV and XRCC4, are also targets of autoantibodies. These Abs were present in 20% of patients with systemic lupus erythematosus and overlap syndrome. Previous work has shown that XRCC4 is subject to radiation-induced post-translational modification, including phosphorylation by DNA-dependent protein kinase and cleavage by caspase 3. We mapped a major autoimmune epitope in XRCC4 and found that it encompassed a DNA-dependent protein kinase phosphorylation site, which is located at serine 260; that it was adjacent to a site for caspase 3, which cleaves after residue 265; and that it also spanned a site for the inflammatory protease, granzyme B, which cleaves after residue 254. The finding that five different polypeptides in the nonhomologous end-joining pathway are potential targets of autoantibodies together with the observation that one of the autoimmune epitopes in XRCC4 coincides with a sequence that is a nexus for radiation-induced regulatory events suggest that exposure to agents that introduce DNA double-strand breaks may be one of the factors that influences the development of an autoimmune response in susceptible individuals.
Lee
Kyung-Jong
KJ
Program in Gene Regulation, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912, USA.
Dong
Xingwen
X
Wang
Jingsong
J
Takeda
Yoshihiko
Y
Dynan
William S
WS
D000595:Amino Acid Sequence; D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D001323:Autoantibodies / Q000097:blood*; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000276:immunology*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007106:Immune Sera / Q000378:metabolism; D015151:Immunoblotting; D016056:Immunodominant Epitopes / Q000032:analysis* / Q000276:immunology; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000201:enzymology; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010446:Peptide Fragments / Q000276:immunology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D021122:Protein Subunits
D001323:Autoantibodies; D004268:DNA-Binding Proteins; D007106:Immune Sera; D016056:Immunodominant Epitopes; C000607893:LIG4 protein, human; D009687:Nuclear Proteins; D010446:Peptide Fragments; D021122:Protein Subunits; C101467:XRCC4 protein, human; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D011088:DNA Ligases; D000072481:DNA Ligase ATP