Cernunnos, a Novel Nonhomologous End-Joining Factor, Is Mutated in Human Immunodeficiency with Microcephaly

INSERM, Hôpital Necker-Enfants Malades, U768 Unité Développement Normal et Pathologique du Système Immunitaire, Paris, France.
Cell (Impact Factor: 32.24). 02/2006; 124(2):287-99. DOI: 10.1016/j.cell.2005.12.030
Source: PubMed


DNA double-strand breaks (DSBs) occur at random upon genotoxic stresses and represent obligatory intermediates during physiological DNA rearrangement events such as the V(D)J recombination in the immune system. DSBs, which are among the most toxic DNA lesions, are preferentially repaired by the nonhomologous end-joining (NHEJ) pathway in higher eukaryotes. Failure to properly repair DSBs results in genetic instability, developmental delay, and various forms of immunodeficiency. Here we describe five patients with growth retardation, microcephaly, and immunodeficiency characterized by a profound T+B lymphocytopenia. An increased cellular sensitivity to ionizing radiation, a defective V(D)J recombination, and an impaired DNA-end ligation process both in vivo and in vitro are indicative of a general DNA repair defect in these patients. All five patients carry mutations in the Cernunnos gene, which was identified through cDNA functional complementation cloning. Cernunnos/XLF represents a novel DNA repair factor essential for the NHEJ pathway.

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Available from: Alessandro Plebani, Oct 09, 2015
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    • "For these specific disorders, causative defects have been identified in central components of the atr-dependent Dna damage response (DDr), in a centrosome-associated protein and in components of the Dna replication licensing machinery, respectively (Bicknell et al. 2011a, b; Griffith et al. 2008; Guernsey et al. 2011; O'Driscoll et al. 2003; Ogi et al. 2012; Qvist et al. 2011; rauch et al. 2008). Defects in Dna double strand break repair and other genome stability pathways can also cause MPD (Buck et al. 2006; Ijspeert et al. 2013; Murray et al. 2014; O'Driscoll et al. 2001; shaheen et al. 2014; shamseldin et al. 2012). Primary microcephaly (PM) with and without overt short stature is commonly caused by defects in centrosome and spindle pole-associated proteins (Mahmood et al. 2011; Poirier et al. 2013; thornton and Woods 2009). "
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    ABSTRACT: Defects in centrosome, centrosomal-associated and spindle-associated proteins are the most frequent cause of primary microcephaly (PM) and microcephalic primordial dwarfism (MPD) syndromes in humans. Mitotic progression and segregation defects, microtubule spindle abnormalities and impaired DNA damage-induced G2-M cell cycle checkpoint proficiency have been documented in cell lines from these patients. This suggests that impaired mitotic entry, progression and exit strongly contribute to PM and MPD. Considering the vast protein networks involved in coordinating this cell cycle stage, the list of potential target genes that could underlie novel developmental disorders is large. One such complex network, with a direct microtubule-mediated physical connection to the centrosome, is the kinetochore. This centromeric-associated structure nucleates microtubule attachments onto mitotic chromosomes. Here, we described novel compound heterozygous variants in CENPE in two siblings who exhibit a profound MPD associated with developmental delay, simplified gyri and other isolated abnormalities. CENPE encodes centromere-associated protein E (CENP-E), a core kinetochore component functioning to mediate chromosome congression initially of misaligned chromosomes and in subsequent spindle microtubule capture during mitosis. Firstly, we present a comprehensive clinical description of these patients. Then, using patient cells we document abnormalities in spindle microtubule organization, mitotic progression and segregation, before modeling the cellular pathogenicity of these variants in an independent cell system. Our cellular analysis shows that a pathogenic defect in CENP-E, a kinetochore-core protein, largely phenocopies PCNT-mutated microcephalic osteodysplastic primordial dwarfism-type II patient cells. PCNT encodes a centrosome-associated protein. These results highlight a common underlying pathomechanism. Our findings provide the first evidence for a kinetochore-based route to MPD in humans.
    Human Genetics 04/2014; 133(8). DOI:10.1007/s00439-014-1443-3 · 4.82 Impact Factor
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    • "Ku70/Ku80 then recruits the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) to form a DNA-PK complex (5). This kinase complex phosphorylates the nuclease Artemis to facilitate the initial processing of ends, and provides protection of the ends required for the following DNA ligation by another complex containing DNA ligase IV, XRCC4 and XRCC4-like factor (XLF; also called Cernunnos or NHEJ1) (2,6,7). XLF is structurally similar to XRCC4 and physically interacts with XRCC4. "
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    ABSTRACT: XRCC4-like factor (XLF) is involved in non-homologous end joining-mediated repair of DNA double-strand breaks (DSBs). Mutations in the WRN gene results in the development of Werner syndrome (WS), a rare autosomal recessive disorder characterized by premature ageing and genome instability. In the present study, it was identified that XLF protein levels were lower in WRN-deficient fibroblasts, compared with normal fibroblasts. Depletion of WRN in HeLa cells led to a decrease of XLF mRNA and its promoter activity. Chromatin immunoprecipitation assays demonstrated that WRN was associated with the XLF promoter. Depletion of XLF in normal human fibroblasts increased the percentage of β-galactosidase (β-gal) staining-positive cells, indicating acceleration in cellular senescence. Taken together, the results suggest that XLF is a transcriptional target of WRN and may be involved in the regulation of cellular senescence.
    Molecular Medicine Reports 03/2014; 9(5). DOI:10.3892/mmr.2014.2030 · 1.55 Impact Factor
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    • "Cernunnos deficiency, causing SCID, was first described in 2006 [5, 6]. In the literature, 13 cases were reported (Turkish, Italian, and French); all had similarly low T cells and absent or very low B cell numbers with normal NK cells. "
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    ABSTRACT: Artemis, DNA ligase IV, DNA protein kinase catalytic subunit, and Cernunnos/XLF genes in nonhomologous end joining pathways of DNA repair mechanisms have been identified as responsible for radiosensitive SCID. Here, we present a 3-year-old girl patient with severe growth retardation, bird-like face, recurrent perianal abscess, pancytopenia, and polydactyly. Firstly, she was thought as Fanconi anemia and spontaneous DNA breaks were seen on chromosomal analysis. After that DEB test was found to be normal and Fanconi anemia was excluded. Because of that she had low IgG and IgA levels, normal IgM level, and absence of B cells in peripheral blood; she was considered as primary immunodeficiency, Nijmegen breakage syndrome. A mutation in NBS1 gene was not found; then Cernunnos/XLF deficiency was investigated due to clinical similarities with previously reported cases. Homozygous mutation in Cernunnos/XLF gene (NHEJ1) was identified. She is now on regular IVIG prophylaxis and has no new infection. Fully matched donor screening is in progress for bone marrow transplantation which is curative treatment of the disease. In conclusion, the patients with microcephaly, bird-like face, and severe growth retardation should be evaluated for hypogammaglobulinemia and primary immunodeficiency diseases.
    01/2014; 2014:614238. DOI:10.1155/2014/614238
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