Alternative end-joining catalyzes robust IgH locus deletions and translocations in the combined absence of ligase 4 and Ku70.

Abstract

Class switch recombination (CSR) in B lymphocytes is initiated by introduction of multiple DNA double-strand breaks (DSBs) into switch (S) regions that flank immunoglobulin heavy chain (IgH) constant region exons. CSR is completed by joining a DSB in the donor S mu to a DSB in a downstream acceptor S region (e.g., S gamma1) by end-joining. In normal cells, many CSR junctions are mediated by classical nonhomologous end-joining (C-NHEJ), which employs the Ku70/80 complex for DSB recognition and XRCC4/DNA ligase 4 for ligation. Alternative end-joining (A-EJ) mediates CSR, at reduced levels, in the absence of C-NHEJ, even in combined absence of Ku70 and ligase 4, demonstrating an A-EJ pathway totally distinct from C-NHEJ. Multiple DSBs are introduced into S mu during CSR, with some being rejoined or joined to each other to generate internal switch deletions (ISDs). In addition, S-region DSBs can be joined to other chromosomes to generate translocations, the level of which is increased by absence of a single C-NHEJ component (e.g., XRCC4). We asked whether ISD and S-region translocations occur in the complete absence of C-NHEJ (e.g., in Ku70/ligase 4 double-deficient B cells). We found, unexpectedly, that B-cell activation for CSR generates substantial ISD in both S mu and S gamma1 and that ISD in both is greatly increased by the absence of C-NHEJ. IgH chromosomal translocations to the c-myc oncogene also are augmented in the combined absence of Ku70 and ligase 4. We discuss the implications of these findings for A-EJ in normal and abnormal DSB repair.

• Authors: Cristian Boboila, Mila Jankovic, Catherine T Yan, Jing H Wang, Duane R Wesemann, Tingting Zhang, Alex Fazeli, Lauren Feldman, Andre Nussenzweig, Michel Nussenzweig, Frederick W Alt
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 107 Issue 7 Pg. 3034-9 (Feb 16 2010) ISSN: 1091-6490 [Electronic] United States
• PMID: 20133803 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Antigens, Nuclear
• DNA Primers
• DNA-Binding Proteins
• Immunoglobulin Heavy Chains
• Xrcc6 protein, mouse
• Ku Autoantigen
• DNA Ligases
• DNA Ligase ATP

Topics

• Animals
• Antigens, Nuclear (genetics)
• B-Lymphocytes (immunology)
• Base Sequence
• Blotting, Southern
• DNA Breaks, Double-Stranded
• DNA Ligase ATP
• DNA Ligases (genetics)
• DNA Primers (genetics)
• DNA Repair (immunology)
• DNA-Binding Proteins (genetics)
• Genes, myc (genetics)
• Immunoglobulin Class Switching (genetics, immunology)
• Immunoglobulin Heavy Chains (genetics)
• Immunoglobulin Switch Region (genetics)
• In Situ Hybridization, Fluorescence
• Ku Autoantigen
• Mice
• Mice, Knockout
• Molecular Sequence Data
• Translocation, Genetic (genetics, immunology)