Leaky Scid Phenotype Associated with Defective V(D)J Coding End Processing in Artemis-Deficient Mice

Abstract

Radiosensitive severe combined immune deficiency in humans results from mutations in Artemis, a protein which, when coupled with DNA-dependent protein kinase catalytic subunit (DNA-PKcs), possesses DNA hairpin-opening activity in vitro. Here, we report that Artemis-deficient mice have an overall phenotype similar to that of DNA-PKcs-deficient mice-including severe combined immunodeficiency associated with defects in opening and joining V(D)J coding hairpin ends and increased cellular ionizing radiation sensitivity. While these findings strongly support the notion that Artemis functions with DNA-PKcs in a subset of NHEJ functions, differences between Artemis- and DNA-PKcs-deficient phenotypes, most notably decreased fidelity of V(D)J signal sequence joining in DNA-PKcs-deficient but not Artemis-deficient fibroblasts, suggest additional functions for DNA-PKcs. Finally, Artemis deficiency leads to chromosomal instability in fibroblasts, demonstrating that Artemis functions as a genomic caretaker.

Human SNM1B is required for normal cellular response to both DNA interstrand crosslink-inducing agents and ionizing radiation

“…In contrast, hSNM1C/ARTEMIS functions in the pathway for DSB repair. Inactivating mutations in human and mouse SNM1C/ARTEMIS result in hypersensitivity to IR but not to ICL-inducing agents (Callebaut et al, 2002;Rooney et al, 2002). Our studies of hSNM1B suggest a more general role for its gene product.…”

Regulation and mechanisms of mammalian double-strand break repair

“…Artemis has intrinsic 5 0 -3 0 exonuclease activity, and upon phosphorylation by DNA-PK acquires an endonuclease activity that opens hairpin loops, removes 5 0 overhangs and shortens 3 0 overhangs . Despite clear evidence that deficiency in Artemis nearly ablates V(D)J recombination, this same deficiency is associated with only mild (Btwofold) radiosensitivity, no apparent change in the proportions of accurate vs resection-based end-joining of transfected substrates (Noordzij et al, 2003), and no gross defect in DSB repair as measured by PFGE (Nicolas et al, 1996;Rooney et al, 2002;SM Yannone and DJ Chen, personal communication). Inasmuch as complementation of this radiosensitivity by ectopic Artemis expression has yet to be demonstrated, a direct role for Artemis in NHEJ (except in the specific case of V(D)J recombination) is still in doubt.…”

DNA double-strand break repair and development

“…DNA-PK-deficient mice, while viable, show impaired lymphocyte development and V(D)J recombination, increased cellular sensitivity to ionizing radiation (IR) and spontaneous chromosomal instability (Rooney et al, 2002). The differential phenotypic severity between NHEJ-deficient mice reflects the relative repair ability in a V(D)J end-joining assay (Gu et al, 2000).…”