Consequence of a Hypomorphic Artemis Mutation on V(D)J Recombination and Proper Immune Function.

Abstract

The generation of antigen receptors requires a gene rearrangement process known as V(D)J recombination. Double stranded breaks produced during recombination must be repaired by the nonhomologous end joining pathway. One critical factor important for this recombination event is the Artemis nuclease, which processes the DNA ends before ligation. Patients with mutations affecting the catalytic N-terminal domain of Artemis are radiosensitive and do not produce B and T cells. Hypomorphic Artemis mutations involving the nonconserved C-terminus have also been described. These patients have a partial B and T cell deficiency but exhibit a predisposition to lymphoid malignancies.

Here, I study the regulation of the Artemis nuclease during V(D)J recombination and the genetic interactions between the Artemis C-terminal domain and DNA damage inducible protein kinase, ATM. I define a region in the C-terminus that is required for endonucleolytic activity and preventing aberrant V(D)J recombination. The findings presented here also suggest that there may be previously undescribed regulatory features located in the Artemis N-terminus that are separate from catalytic activity. To analyze the in vivo consequences resulting from the loss of the Artemis C-terminus, I utilized a hypomorphic Artemis mouse model harboring an allele that results in C-terminal truncation, Artemis-P70. Cellular and in vivo assays suggest that the Artemis C-terminus and the ATM kinase cooperate to facilitate V(D)J recombination and loss of both factors can result in a lymphocyte deficiency that is more severe than in mice deficient for one factor. Although ATM deficient mice succumb to thymic lymphoma, mice harboring homozygous mutations in both Artemis-P70 and ATM are surprisingly tumor-free. These mice, however, had inflamed colons with T cell and neutrophil infiltration.

These findings together emphasize the importance of the regulatory domains of Artemis. A disregulated nuclease can facilitate aberrant recombination and that can disrupt proper lymphocyte development. A lymphocyte defect may operate in concert with other factors such as DNA repair deficiency and cytokine imbalance which together could promote chronic inflammation. Finally, results presented here suggest that there may be other means of Artemis regulation that are dependent on features located in the conserved N-terminal domain.