The protein encoded by this gene is an ATP-dependent DNA ligase that joins double-strand breaks during the non-homologous end joining pathway of double-strand break repair. It is also essential for V(D)J recombination. Lig4 forms a complex with XRCC4, and further interacts with the DNA-dependent protein kinase (DNA-PK) and XLF/Cernunnos, which are also required for NHEJ. The crystal structure of the Lig4/XRCC4 complex has been resolved.[2] Defects in this gene are the cause of LIG4 syndrome. The yeast homolog of Lig4 is Dnl4.
LIG4 Syndrome
In humans, deficiency of DNA ligase 4 results in a clinical condition known as LIG4 syndrome. This syndrome is characterized by cellular radiation sensitivity, growth retardation, developmental delay, microcephaly, facial dysmorphisms, increased disposition to leukemia, variable degrees of immunodeficiency and reduced number of blood cells.[3][4]
Haematopoietic stem cell aging
Accumulation of DNA damage leading to stem cell exhaustion is regarded as an important aspect of aging.[5][6] Deficiency of lig4 in pluripotent stem cells impairs Non-homologous end joining (NHEJ) and results in accumulation of DNA double-strand breaks and enhanced apoptosis.[4] Lig4 deficiency in the mouse causes a progressive loss of haematopoietic stem cells and bone marrow cellularity during aging.[7] The sensitivity of haematopoietic stem cells to lig4 deficiency suggests that lig4-mediated NHEJ is a key determinant of the ability of stem cells to maintain themselves against physiological stress over time.[4][7]
Interactions
LIG4 has been shown to interact with XRCC4 via its BRCT domain.[8][2] This interaction stabilizes LIG4 protein in cells; cells that are deficient for XRCC4, such as XR-1 cells, have reduced levels of LIG4.[9]
Mechanism
LIG4 is an ATP-dependent DNA ligase. LIG4 uses ATP to adenylate itself and then transfers the AMP group to the 5' phosphate of one DNA end. Nucleophilic attack by the 3' hydroxyl group of a second DNA end and release of AMP yield the ligation product. Adenylation of LIG4 is stimulated by XRCC4 and XLF.[10]
↑Rossi DJ, Bryder D, Seita J, Nussenzweig A, Hoeijmakers J, Weissman IL (June 2007). "Deficiencies in DNA damage repair limit the function of haematopoietic stem cells with age". Nature. 447 (7145): 725–9. doi:10.1038/nature05862. PMID17554309.
↑Bryans M, Valenzano MC, Stamato TD (January 1999). "Absence of DNA ligase IV protein in XR-1 cells: evidence for stabilization by XRCC4". Mutation Research. 433 (1): 53–8. doi:10.1016/s0921-8777(98)00063-9. PMID10047779.
Robins P, Lindahl T (September 1996). "DNA ligase IV from HeLa cell nuclei". The Journal of Biological Chemistry. 271 (39): 24257–61. doi:10.1074/jbc.271.39.24257. PMID8798671.
Grawunder U, Wilm M, Wu X, Kulesza P, Wilson TE, Mann M, Lieber MR (July 1997). "Activity of DNA ligase IV stimulated by complex formation with XRCC4 protein in mammalian cells". Nature. 388 (6641): 492–5. doi:10.1038/41358. PMID9242410.
Critchlow SE, Bowater RP, Jackson SP (August 1997). "Mammalian DNA double-strand break repair protein XRCC4 interacts with DNA ligase IV". Current Biology. 7 (8): 588–98. doi:10.1016/S0960-9822(06)00258-2. PMID9259561.
Grawunder U, Zimmer D, Lieber MR (July 1998). "DNA ligase IV binds to XRCC4 via a motif located between rather than within its BRCT domains". Current Biology. 8 (15): 873–6. doi:10.1016/S0960-9822(07)00349-1. PMID9705934.
Grawunder U, Zimmer D, Fugmann S, Schwarz K, Lieber MR (October 1998). "DNA ligase IV is essential for V(D)J recombination and DNA double-strand break repair in human precursor lymphocytes". Molecular Cell. 2 (4): 477–84. doi:10.1016/S1097-2765(00)80147-1. PMID9809069.
Riballo E, Critchlow SE, Teo SH, Doherty AJ, Priestley A, Broughton B, Kysela B, Beamish H, Plowman N, Arlett CF, Lehmann AR, Jackson SP, Jeggo PA (July 1999). "Identification of a defect in DNA ligase IV in a radiosensitive leukaemia patient". Current Biology. 9 (13): 699–702. doi:10.1016/S0960-9822(99)80311-X. PMID10395545.
Kim ST, Lim DS, Canman CE, Kastan MB (December 1999). "Substrate specificities and identification of putative substrates of ATM kinase family members". The Journal of Biological Chemistry. 274 (53): 37538–43. doi:10.1074/jbc.274.53.37538. PMID10608806.
Chen L, Trujillo K, Sung P, Tomkinson AE (August 2000). "Interactions of the DNA ligase IV-XRCC4 complex with DNA ends and the DNA-dependent protein kinase". The Journal of Biological Chemistry. 275 (34): 26196–205. doi:10.1074/jbc.M000491200. PMID10854421.
Lee KJ, Huang J, Takeda Y, Dynan WS (November 2000). "DNA ligase IV and XRCC4 form a stable mixed tetramer that functions synergistically with other repair factors in a cell-free end-joining system". The Journal of Biological Chemistry. 275 (44): 34787–96. doi:10.1074/jbc.M004011200. PMID10945980.
Riballo E, Doherty AJ, Dai Y, Stiff T, Oettinger MA, Jeggo PA, Kysela B (August 2001). "Cellular and biochemical impact of a mutation in DNA ligase IV conferring clinical radiosensitivity". The Journal of Biological Chemistry. 276 (33): 31124–32. doi:10.1074/jbc.M103866200. PMID11349135.
Sibanda BL, Critchlow SE, Begun J, Pei XY, Jackson SP, Blundell TL, Pellegrini L (December 2001). "Crystal structure of an Xrcc4-DNA ligase IV complex". Nature Structural Biology. 8 (12): 1015–9. doi:10.1038/nsb725. PMID11702069.
O'Driscoll M, Cerosaletti KM, Girard PM, Dai Y, Stumm M, Kysela B, Hirsch B, Gennery A, Palmer SE, Seidel J, Gatti RA, Varon R, Oettinger MA, Neitzel H, Jeggo PA, Concannon P (December 2001). "DNA ligase IV mutations identified in patients exhibiting developmental delay and immunodeficiency". Molecular Cell. 8 (6): 1175–85. doi:10.1016/S1097-2765(01)00408-7. PMID11779494.
Kuschel B, Auranen A, McBride S, Novik KL, Antoniou A, Lipscombe JM, Day NE, Easton DF, Ponder BA, Pharoah PD, Dunning A (June 2002). "Variants in DNA double-strand break repair genes and breast cancer susceptibility". Human Molecular Genetics. 11 (12): 1399–407. doi:10.1093/hmg/11.12.1399. PMID12023982.
Smogorzewska A, Karlseder J, Holtgreve-Grez H, Jauch A, de Lange T (October 2002). "DNA ligase IV-dependent NHEJ of deprotected mammalian telomeres in G1 and G2". Current Biology. 12 (19): 1635–44. doi:10.1016/S0960-9822(02)01179-X. PMID12361565.