CtIP promotes microhomology-mediated alternative end joining during class-switch recombination

Nat Struct Mol Biol. 2011 Jan;18(1):75-9. doi: 10.1038/nsmb.1942. Epub 2010 Dec 5.

Abstract

Immunoglobulin heavy chain (Igh locus) class-switch recombination (CSR) requires targeted introduction of DNA double strand breaks (DSBs) into repetitive 'switch'-region DNA elements in the Igh locus and subsequent ligation between distal DSBs. Both canonical nonhomologous end joining (C-NHEJ) that seals DNA ends with little or no homology and a poorly defined alternative end joining (A-NHEJ, also known as alt-NHEJ) process that requires microhomology ends for ligation have been implicated in CSR. Here, we show that the DNA end-processing factor CtIP is required for microhomology-directed A-NHEJ during CSR. Additionally, we demonstrate that microhomology joins that are enriched upon depletion of the C-NHEJ component Ku70 require CtIP. Finally, we show that CtIP binds to switch-region DNA in a fashion dependent on activation-induced cytidine deaminase. Our results establish CtIP as a bona fide component of microhomology-dependent A-NHEJ and unmask a hitherto unrecognized physiological role of microhomology-mediated end joining in a C-NHEJ-proficient environment.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / physiology*
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / physiology*
  • Cell Line
  • DNA / chemistry
  • DNA Breaks, Double-Stranded
  • Gene Knockdown Techniques
  • Immunoglobulin Class Switching / genetics
  • Immunoglobulin Class Switching / physiology*
  • Mice
  • Models, Genetic
  • RNA, Small Interfering / physiology
  • Recombination, Genetic*
  • Sequence Homology, Nucleic Acid

Substances

  • Carrier Proteins
  • Cell Cycle Proteins
  • CtIP protein, mouse
  • RNA, Small Interfering
  • DNA