Disease relevance of XRCC4

• Protein mapping studies revealed that XRCC4 interacted with ligase IV via the unique carboxy-terminal ligase IV extension that comprises two tandem BRCT (BRCA1 carboxyl terminus) homology motifs, which are also found in other DNA repair-associated factors and in the breast cancer susceptibility protein BRCA1 [1].
• Mice doubly deficient for either XRCC4 or DNA ligase IV and p53 invariably develop lymphomas bearing characteristic chromosome translocations with gene amplification [2].
• XRCC4 suppresses medulloblastomas with recurrent translocations in p53-deficient mice [3].
• Clonogenic survival assays showed that the adenovirus expressing the truncated XRCC4 protein sensitizes MDA-MB-231 breast tumor cells to ionizing radiation, presumably through interference with the functional activity of ligase IV, leading to inhibition of the final ligation step in end joining [4].

High impact information on XRCC4

• XLF interacts with the XRCC4-DNA ligase IV complex to promote DNA nonhomologous end-joining [5].
• XRCC4 was identified via a complementation cloning method that employed an ionizing radiation (IR)-sensitive hamster cell line [6].
• Our findings demonstrate that differentiating lymphocytes and neurons strictly require the XRCC4 and DNA ligase IV end-joining proteins and point to the general stage of neuronal development in which these proteins are necessary [6].
• By gene-targeted mutation, we show that XRCC4 deficiency in primary murine cells causes growth defects, premature senescence, IR sensitivity, and inability to support V(D)J recombination [6].
• The XRCC4 gene maps to the previously identified locus on human chromosome 5, is deleted in XR-1 cells, and encodes a ubiquitously expressed product unrelated to any described protein [7].

Biological context of XRCC4

• XRCC4 recruitment was accompanied by its DNA-PK-dependent phosphorylation [8].
• BACKGROUND: Mammalian cells deficient in the XRCC4 DNA repair protein are impaired in DNA double-strand break repair and are consequently hypersensitive to ionising radiation [1].
• We also observe higher genomic instability in Ku-deficient cells than in XRCC4-null cells [9].
• In addition, our data implicate mammalian ligase IV in V(D)J recombination and the repair of radiation-induced DNA damage, and provide a model for the potentiation of these processes by XRCC4 [1].
• By contrast, telomere length is not altered in cells impaired in XRCC4 or DNA ligase IV, two other NHEJ components [9].

Anatomical context of XRCC4

• The levels of expression of the different proteins were similar in all the cell lines, but the activities of the DNA-PK and XRCC4/ligaseIV complexes showed some differences [10].
• In eukaryotic cells, DNA double-strand breaks can be repaired by non-homologous end-joining, a process dependent upon Ku70/80, XRCC4 and DNA ligase IV [11].
• FISH analysis of normal human lymphocytes using DNA from the two resistant hybrids as probes produced a common region of hybridization at 5q13-q14, suggesting that the XRCC4 gene is in this region of chromosome 5 [12].
• To map the XRCC4 human DNA repair gene subchromosomally, a gamma-ray-resistant human:XR-1 hamster hybrid cell containing fragments of human chromosome 5 and the pSV2neo plasmid was lethally irradiated and fused with the gamma-ray-sensitive XR-1 mutant cell [12].
• Identification of DNA-PKcs phosphorylation sites in XRCC4 and effects of mutations at these sites on DNA end joining in a cell-free system [13].

Associations of XRCC4 with chemical compounds

• 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 [14].
• Substitution of each of these sites to alanine (in combination) reduced the ability of DNA-PK to phosphorylate XRCC4 in vitro by at least two orders of magnitude [15].
• We report that XRCC4 is an efficient in vitro substrate of DNA-PK and another unidentified serine/ threonine protein kinase(s) [16].

Physical interactions of XRCC4

• Mammalian DNA double-strand break repair protein XRCC4 interacts with DNA ligase IV [1].

Regulatory relationships of XRCC4

• Activity of DNA ligase IV stimulated by complex formation with XRCC4 protein in mammalian cells [17].

Other interactions of XRCC4

• Central to NHEJ is the protein complex containing DNA Ligase IV and XRCC4 [5].
• In addition, under p460 kinase permissive conditions, XRCC4 is detected at DNA ends in a phosphorylated form [18].
• The mutagen sensitivity values correlated with the NER capacity (P = .05) and the expression of XRCC4 (P = .01) and RAD51 (P = .06) genes [19].
• Aprataxin possesses a divergent forkhead associated (FHA) domain that closely resembles the FHA domain present in polynucleotide kinase, and appears to mediate the interactions with CK2-phosphorylated XRCC1 and XRCC4 through this domain [20].
• Furthermore, AHNAK and the DNA ligase IV-XRCC4 complex co-immunoprecipitate demonstrating an in vivo interaction [21].

Analytical, diagnostic and therapeutic context of XRCC4

• A core protein complex comprising the Ku70/80 heterodimer together with a complex between DNA ligase IV and XRCC4 is conserved throughout eukaryotes and assembles at double-strand breaks to mediate ligation of broken DNA ends [22].
• Moreover, a combination of sensitive methods of sequence analysis revealed that Cernunnos can be associated with the XRCC4 family of proteins and that it corresponds to the genuine homolog of the yeast Nej1 protein [23].
• Western blot analysis indicates that levels of DNA ligase IV protein are almost undetectable in these cells, however, introduction of the XRCC4 cDNA into XR-1 resulted in a return to wild type levels of the protein [24].
• Gene expression of HIF-1alpha and XRCC4 measured in human samples by real-time RT-PCR using the sigmoidal curve-fitting method [25].
• Binding of the XRCC4 fragment to ligase IV in vivo was confirmed by immunoprecipitation [4].

References