[Show abstract][Hide abstract] ABSTRACT: The Artemis gene encodes a DNA nuclease that plays important roles in non-homologous end-joining (NHEJ), a major double-strand break (DSB) repair pathway in mammalian cells. NHEJ factors repair general DSBs as well as programmed breaks generated during the lymphoid-specific DNA rearrangement, V(D)J recombination, which is required for lymphocyte development. Mutations that inactivate Artemis cause a human severe combined immunodeficiency syndrome associated with cellular radiosensitivity. In contrast, hypomorphic Artemis mutations result in combined immunodeficiency syndromes of varying severity, but, in addition, are hypothesized to predispose to lymphoid malignancy. To elucidate the distinct molecular defects caused by hypomorphic compared with inactivating Artemis mutations, we examined tumor predisposition in a mouse model harboring a targeted partial loss-of-function disease allele. We find that, in contrast to Artemis nullizygosity, the hypomorphic mutation leads to increased aberrant intra- and interchromosomal V(D)J joining events. We also observe that dysfunctional Artemis activity combined with p53 inactivation predominantly predisposes to thymic lymphomas harboring clonal translocations distinct from those observed in Artemis nullizygosity. Thus, the Artemis hypomorphic allele results in unique molecular defects, tumor spectrum and oncogenic chromosomal rearrangements. Our findings have significant implications for disease outcomes and treatment of patients with different Artemis mutations.
Human Molecular Genetics 02/2011; 20(4):806-19. DOI:10.1093/hmg/ddq524 · 6.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Artemis was initially discovered as the gene inactivated in human radiosensitive T(-)B(-) severe combined immunodeficiency, a syndrome characterized by the absence of B and T lymphocytes and cellular hypersensitivity to ionizing radiation. Hypomorphic Artemis alleles have also been identified in patients and are associated with combined immunodeficiencies of varying severity. We examine the molecular mechanisms underlying a syndrome of partial immunodeficiency caused by a hypomorphic Artemis allele using the mouse as a model system. This mutation, P70, leads to premature translation termination that deletes a large portion of a nonconserved C terminus. We find that homozygous Artemis-P70 mice exhibit reduced numbers of B and T lymphocytes, thereby recapitulating the patient phenotypes. The hypomorphic mutation results in impaired end processing during the lymphoid-specific DNA rearrangement known as V(D)J recombination, defective double-strand break repair, and increased chromosomal instability. Biochemical analyses reveal that the Artemis-P70 mutant protein interacts with the DNA-dependent protein kinase catalytic subunit and retains significant, albeit reduced, exo- and endonuclease activities but does not undergo phosphorylation. Together, our findings indicate that the Artemis C terminus has critical in vivo functions in ensuring efficient V(D)J rearrangements and maintaining genome integrity.
Journal of Experimental Medicine 05/2009; 206(4):893-908. DOI:10.1084/jem.20082396 · 12.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nonhomologous end-joining represents the major pathway used by human cells to repair DNA double-strand breaks. It relies on
the XRCC4/DNA ligase IV complex to reseal DNA strands. Here we report the high-resolution crystal structure of human XRCC4
bound to the carboxy-terminal tandem BRCT repeat of DNA ligase IV. The structure differs from the homologous Saccharomyces cerevisiae complex and reveals an extensive DNA ligase IV binding interface formed by a helix-loop-helix structure within the inter-BRCT
linker region, as well as significant interactions involving the second BRCT domain, which induces a kink in the tail region
of XRCC4. We further demonstrate that interaction with the second BRCT domain of DNA ligase IV is necessary for stable binding
to XRCC4 in cells, as well as to achieve efficient dominant-negative effects resulting in radiosensitization after ectopic
overexpression of DNA ligase IV fragments in human fibroblasts. Together our findings provide unanticipated insight for understanding
the physical and functional architecture of the nonhomologous end-joining ligation complex.