Artemis and Nonhomologous End Joining-Independent Influence of DNA-Dependent Protein Kinase Catalytic Subunit on Chromosome Stability

Abstract

Deficiency in both ATM and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is synthetically lethal in developing mouse embryos. Using mice that phenocopy diverse aspects of Atm deficiency, we have analyzed the genetic requirements for embryonic lethality in the absence of functional DNA-PKcs. Similar to the loss of ATM, hypomorphic mutations of Mre11 (Mre11^ATLD1) led to synthetic lethality when juxtaposed with DNA-PKcs deficiency (Prkdc^scid). In contrast, the more moderate DNA double-strand break response defects associated with the Nbs1^ΔB allele permitted viability of some Nbs1^ΔB/ΔBPrkdc^scid/scid embryos. Cell cultures from Nbs1^ΔB/ΔBPrkdc^scid/scid embryos displayed severe defects, including premature senescence, mitotic aberrations, sensitivity to ionizing radiation, altered checkpoint responses, and increased chromosome instability. The known functions of DNA-PKcs in the regulation of Artemis nuclease activity or nonhomologous end joining-mediated repair do not appear to underlie the severe genetic interaction. Our results reveal a role for DNA-PKcs in the maintenance of S/G₂-phase chromosome stability and in the induction of cell cycle checkpoint responses.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Annalee Baker and Hussein Hussein for diligent maintenance of our animal colony; Titia de Lange, Andy Koff, and members of the Petrini and de Lange labs for helpful advice and discussions; and Rob Fisher and Claire Attwooll for critical reading of the manuscript.

T.H.S. was supported by an NIH National Research Service Award and is a Leukemia and Lymphoma Society special fellow, L.D. is a Leukemia and Lymphoma Society fellow, D.B.R. is supported by grants from the NIH, and J.H.J.P. is supported by NIH grants and the Jean and Joel Smilow Initiative.