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: 33.12). 02/2006; 124(2):287-99. DOI: 10.1016/j.cell.2005.12.030
Source: PubMed

ABSTRACT 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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    • "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 · 4.52 Impact Factor
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    • "These processes are essential for adaptive immunity and are defective in LIG4 patients, resulting in SCID in some cases [Buck et al., 2006b; Pan- Hammarstrom et al., 2005; van der Burg et al., 2006]. SCID is also a feature of infants with mutations in three other components of the NHEJ machinery; DCLRE1C, encoding Artemis [Moshous et al., 2001], PRKDC, encoding the catalytic subunit of DNA-PK (DNAdependent protein kinase) [van der Burg et al., 2009], and NHEJ1, encoding Cernunnos-XLF [Buck et al., 2006a]. Microcephalic primordial dwarfism (MPD) is defined by the presence of both prenatal and postnatal growth restriction resulting in extreme reduction in both head circumference (OFC) and height (more than 4 s.d. "
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    ABSTRACT: Ligase IV syndrome is a rare differential diagnosis for Nijmegen Breakage syndrome owing to a shared predisposition to lympho-reticular malignancies, significant microcephaly and radiation hypersensitivity. Only 16 cases with mutations in LIG4 have been described to date with phenotypes varying from malignancy in developmentally normal individuals, to severe combined immunodeficiency and early mortality. Here we report the identification of biallelic truncating LIG4 mutations in 11 patients with microcephalic primordial dwarfism presenting with restricted prenatal growth and extreme postnatal global growth failure (average OFC -10.1 s.d., height -5.1 s.d.). Subsequently most patients developed thrombocytopenia and leucopenia later in childhood and many were found to have previously unrecognised immunodeficiency following molecular diagnosis. None have yet developed malignancy, though all patients tested had cellular radiosensitivity. A genotype:phenotype correlation was also noted with position of truncating mutations corresponding to disease severity. This work extends the phenotypic spectrum associated with LIG4 mutations, establishing that extreme growth retardation with microcephaly is a common presentation of bilallelic truncating mutations. Such growth failure is therefore sufficient to consider a diagnosis of LIG4 deficiency and early recognition of such cases is important as bone marrow failure, immunodeficiency and sometimes malignancy are long term sequelae of this disorder. This article is protected by copyright. All rights reserved.
    Human Mutation 01/2014; 35(1). DOI:10.1002/humu.22461 · 5.05 Impact Factor
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    • "Thus, for NHEJ it is possible that XRCC4–XLF filaments do not form until DNA-PKcs has been released and, at this point, the filaments function to restrict DNA end resection. This would be consistent with reports that end resection during V(D)J recombination may be restricted by XLF (Buck et al. 2006; Dai et al. 2003). As a general theme, stable binding at damaged DNA sites can not only protect damage but also control pathway choice as seen for Atl1 taking base damage into the nucleotide excision repair (NER) pathway (Tubbs et al. 2009) by recruiting TFIIH and initiating removal of a 27 nucleotide patch (Fuss and Tainer 2011). "
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    ABSTRACT: DNA double strand breaks (DSBs), induced by ionizing radiation (IR) and endogenous stress including replication failure, are the most cytotoxic form of DNA damage. In human cells, most IR-induced DSBs are repaired by the nonhomologous end joining (NHEJ) pathway. One of the most critical steps in NHEJ is ligation of DNA ends by DNA ligase IV (LIG4), which interacts with, and is stabilized by, the scaffolding protein X-ray cross-complementing gene 4 (XRCC4). XRCC4 also interacts with XRCC4-like factor (XLF, also called Cernunnos); yet, XLF has been one of the least mechanistically understood proteins and precisely how XLF functions in NHEJ has been enigmatic. Here, we examine current combined structural and mutational findings that uncover integrated functions of XRCC4 and XLF and reveal their interactions to form long, helical protein filaments suitable to protect and align DSB ends. XLF-XRCC4 provides a global structural scaffold for ligating DSBs without requiring long DNA ends, thus ensuring accurate and efficient ligation and repair. The assembly of these XRCC4-XLF filaments, providing both DNA end protection and alignment, may commit cells to NHEJ with general biological implications for NHEJ and DSB repair processes and their links to cancer predispositions and interventions.
    Biochemistry and Cell Biology 02/2013; 91(1):31-41. DOI:10.1139/bcb-2012-0058 · 2.35 Impact Factor
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