Impact of a Hypomorphic Artemis disease allele on lymphocyte development, DNA end processing, and genome stability

Abstract

Artemis was initially discovered as the gene inactivated in human radiosensitive T -B - severe combined immunodefciency, a syndrome characterized by the absence of B and T lymphocytes and cellular hypersensitivity to ionizing radiation. Hypomorphic Artemis alleles have also been identifed in patients and are associated with combined immunodefciencies of varying severity. We examine the molecular mechanisms underlying a syndrome of partial immunodefciency 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 fnd 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-specifc 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 signifcant, albeit reduced, exo- and endonuclease activities but does not undergo phosphorylation. Together, our fndings indicate that the Artemis C terminus has critical in vivo functions in ensuring effcient V(D)J rearrangements and maintaining genome integrity. © 2009 Huang et al.