CtIP promotes microhomology-mediated alternative end joining during class-switch recombination.
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.
Immunology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.
Mieun
M
Lee-Theilen
Allysia J
AJ
Matthews
Dierdre
D
Kelly
Simin
S
Zheng
Jayanta
J
Chaudhuri
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004247:DNA / Q000737:chemistry; D053903:DNA Breaks, Double-Stranded; D055785:Gene Knockdown Techniques; D017578:Immunoglobulin Class Switching / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008957:Models, Genetic; D034741:RNA, Small Interfering / Q000502:physiology; D011995:Recombination, Genetic; D012689:Sequence Homology, Nucleic Acid
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004247:DNA; D034741:RNA, Small Interfering; C501070:RBBP8 protein, mouse