Published online
doi:10.1084/jem.20080044
The Journal of Experimental Medicine, Vol. 205, No. 3, 557-564
The Rockefeller University Press, 0022-1007 $30.00
© Franco et al.
DNA-PKcs and Artemis function in the end-joining phase of immunoglobulin heavy chain class switch recombination
Sonia Franco,
Michael M. Murphy,
Gang Li,
Tiffany Borjeson,
Cristian Boboila, and
Frederick W. Alt
Howard Hughes Medical Institute, the Children's Hospital, Department of Genetics, Harvard Medical School, Boston, MA 02115
Immune Disease Institute, Boston, MA 02115
CORRESPONDENCE Frederick W. Alt: alt{at}enders.tch.harvard.edu
The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and Artemis are classical nonhomologous DNA end-joining (C-NHEJ) factors required for joining a subset of DNA double-strand breaks (DSB), particularly those requiring end processing. In mature B cells, activation-induced cytidine deaminase (AID) initiates class switch recombination (CSR) by introducing lesions into S regions upstream of two recombining CH exons, which are processed into DSBs and rejoined by C-NHEJ to complete CSR. The function of DNA-PKcs in CSR has been controversial with some reports but not others showing that DNA-PKcs–deficient mice are significantly impaired for CSR. Artemis-deficient B cells reportedly undergo CSR at normal levels. Overall, it is still not known whether there are any CSR-associated DSBs that require DNA-PKcs and/or Artemis to be joined. Here, we have used an immunoglobulin (Ig)H locus-specific fluorescent in situ hybridization assay to unequivocally demonstrate that both DNA-PKcs and, unexpectedly, Artemis are necessary for joining a subset of AID-dependent DSBs. In the absence of either factor, B cells activated for CSR frequently generate AID-dependent IgH locus chromosomal breaks and translocations. We also find that under specific activation conditions, DNA-PKcs–/– B cells with chromosomal breaks are eliminated or at least prevented from progressing to metaphase via a p53-dependent response.
Abbreviations used: AID, activation-induced cytidine deaminase; C-NHEJ, classical nonhomologous DNA end joining; CSR, class switch recombination; DDR, DNA damage response; DNA-PKcs, DNA–protein kinase catalytic subunit; DSB, double-strand break; Lig4, ligase IV; FISH, fluorescent in situ hybridization; HC, heavy chain; LC, light chain; PNA, peptide nucleic acid; RS, recombination signal sequence; T-FISH, telomere FISH.

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