DNA ligase III and DNA ligase IV carry out genetically distinct forms of end joining in human somatic cells.
Ku-dependent C-NHEJ (classic non-homologous end joining) is the primary DNA EJing (end joining) repair pathway in mammals. Recently, an additional EJing repair pathway (A-NHEJ; alternative-NHEJ) has been described. Currently, the mechanism of A-NHEJ is obscure although a dependency on LIGIII (DNA ligase III) is often implicated. To test the requirement for LIGIII in A-NHEJ we constructed a LIGIII conditionally-null human cell line using gene targeting. Nuclear EJing activity appeared unaffected by a deficiency in LIGIII as, surprisingly, so were random gene targeting integration events. In contrast, LIGIII was required for mitochondrial function and this defined the gene's essential activity. Human Ku:LIGIII and Ku:LIGIV (DNA ligase IV) double knockout cell lines, however, demonstrated that LIGIII is required for the enhanced A-NHEJ activity that is observed in Ku-deficient cells. Most unexpectedly, however, the majority of EJing events remained LIGIV-dependent. In conclusion, although human LIGIII has an essential function in mitochondrial maintenance, it is dispensable for most types of nuclear DSB repair, except for the A-NHEJ events that are normally suppressed by Ku. Moreover, we describe that a robust Ku-independent, LIGIV-dependent repair pathway exists in human somatic cells.
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States. Electronic address: so2411@columbia.edu.
Sehyun
S
Oh
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States.
Adam
A
Harvey
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States. Electronic address: jzimbric@gmail.com.
Jacob
J
Zimbric
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States. Electronic address: yongbao.x.wang@questdiagnostics.com.
Yongbao
Y
Wang
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States.
Thanh
T
Nguyen
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States.
Pauline J
PJ
Jackson
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, United States. Electronic address: hendr064@umn.edu.
Eric A
EA
Hendrickson
D034961:Antigens, Nuclear / Q000235:genetics; D002460:Cell Line; D059766:DNA End-Joining Repair; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D045325:HCT116 Cells; D006801:Humans; D000072200:Ku Autoantigen; D000075223:Poly-ADP-Ribose Binding Proteins; D029867:Xenopus Proteins
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; C000607893:LIG4 protein, human; D000075223:Poly-ADP-Ribose Binding Proteins; D029867:Xenopus Proteins; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D011088:DNA Ligases; D000072481:DNA Ligase ATP; C000618816:DNA ligase III alpha protein, Xenopus; C000618817:LIG3 protein, human
A-NHEJ; C-NHEJ; Double-strand break repair; Gene targeting; Homologous recombination; Ku; Ligase III; Ligase IV; Non-homologous end joining