Cut-and-Run: A Distinct Mechanism by which V(D)J Recombination Causes Genome Instability.

Christopher M Kirkham,Alastair L Smith,Anthony M Ford,Roman Tuma,Adam P Kupinski,Joan Boyes,James N.F Scott,Peter G Stockley,Xiaoling Wang,David R Westhead

doi:10.1016/j.molcel.2019.02.025

Christopher M Kirkham, Alastair L Smith + Show 8 more

Open Access

https://doi.org/10.1016/j.molcel.2019.02.025

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Abstract

SummaryV(D)J recombination is essential to generate antigen receptor diversity but is also a potent cause of genome instability. Many chromosome alterations that result from aberrant V(D)J recombination involve breaks at single recombination signal sequences (RSSs). A long-standing question, however, is how such breaks occur. Here, we show that the genomic DNA that is excised during recombination, the excised signal circle (ESC), forms a complex with the recombinase proteins to efficiently catalyze breaks at single RSSs both in vitro and in vivo. Following cutting, the RSS is released while the ESC-recombinase complex remains intact to potentially trigger breaks at further RSSs. Consistent with this, chromosome breaks at RSSs increase markedly in the presence of the ESC. Notably, these breaks co-localize with those found in acute lymphoblastic leukemia patients and occur at key cancer driver genes. We have named this reaction “cut-and-run” and suggest that it could be a significant cause of lymphocyte genome instability.

Highlights

V(D)J recombination stochastically joins individual V, D, and J gene segments, to generate vast arrays of immunoglobulin and T cell receptor genes that enable vertebrates to combat almost infinite numbers of potential pathogens
We have named this reaction ‘‘cut-and-run’’ and propose that the excised signal circle (ESC) triggers a double strand break (DSB) at one recombination signal sequences (RSSs) and ‘‘runs,’’ to potentially trigger breaks at additional RSSs. Consistent with this idea, we find that the frequency of broken RSSs increases significantly in the presence of the ESC and that these breaks mirror those associated with chromosome translocations or interstitial deletions in lymphoid cancers
The unique arrangement of two head-to-head RSSs in the signal joint (SJ) (Figure 1A) could potentially form a distinct complex with RAG proteins to influence ESC activity. To test if this is the case, RAG interactions with the SJ were examined in vitro, and we first asked if our RAG cutting conditions obey the 12/23 rule that ensures that efficient RAG cleavage occurs only between RSSs with different spacer lengths

Summary

Introduction

V(D)J recombination stochastically joins individual V, D, and J gene segments, to generate vast arrays of immunoglobulin and T cell receptor genes that enable vertebrates to combat almost infinite numbers of potential pathogens. One of the most common recombination errors is end donation (Roth, 2003), which occurs when a broken recombination signal sequence (RSS) is joined with a broken DNA end that was formed independently, for example, via ionizing radiation If this brings an oncogene under the control of the strong transcriptional elements of the antigen receptor loci, malignant transformation can result. This process is thought to underpin 30%–40% of the chromosome translocations found in follicular and mantle cell lymphomas (Ja€ger et al, 2000; Welzel et al, 2001)

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