DNA-PKcs and Artemis function in the end-joining phase of immunoglobulin heavy chain class switch recombination

• DOI: 10.1084/jem.20080044
• Publication Date: 2008-03-04T01:45:12Z
• Authors: Sonia Franco; Michael M. Murphy; Gang Li; Tiffany Borjeson; Cristian Boboila; Frederick W. Alt
• Keywords: Mice, Knockout; Recombination, Genetic; B-Lymphocytes; 0303 health sciences; Base Sequence; DNA Repair; Nuclear Proteins; Mice, Transgenic; Articles; DNA-Activated Protein Kinase; Endonucleases; Immunoglobulin Class Switching; Genomic Instability; Translocation, Genetic; 3. Good health; DNA-Binding Proteins; Mice; 03 medical and health sciences; Animals; DNA Probes; Immunoglobulin Heavy Chains; In Situ Hybridization, Fluorescence

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.