TRF2-RAP1 is required to protect telomeres from engaging in homologous recombination-mediated deletions and fusions.

Rekha Rai,Yong Chen,Sandy Chang,Ming Lei

doi:10.1038/ncomms10881

Abstract

Repressor/activator protein 1 (RAP1) is a highly conserved telomere-interacting protein. Yeast Rap1 protects telomeres from non-homologous end joining (NHEJ), plays important roles in telomere length control and is involved in transcriptional gene regulation. However, a role for mammalian RAP1 in telomere end protection remains controversial. Here we present evidence that mammalian RAP1 is essential to protect telomere from homology directed repair (HDR) of telomeres. RAP1 cooperates with the basic domain of TRF2 (TRF2B) to repress PARP1 and SLX4 localization to telomeres. Without RAP1 and TRF2B, PARP1 and SLX4 HR factors promote rapid telomere resection, resulting in catastrophic telomere loss and the generation of telomere-free chromosome fusions in both mouse and human cells. The RAP1 Myb domain is required to repress both telomere loss and formation of telomere-free fusions. Our results highlight the importance of the RAP1-TRF2 heterodimer in protecting telomeres from inappropriate processing by the HDR pathway.

Highlights

Repressor/activator protein 1 (RAP1) is a highly conserved telomere-interacting protein
In contrast to chromosome fusions in cells devoid of TRF2, in which nearly 100% of chromosome fusion sites contain prominent telomeric signals, chromosome fusions in the absence of RAP1 do not possess any telomeric signal at fusion sites, suggesting that near complete telomere attrition occurred at chromosome ends before fusion[6]
Given the relative paucity of fused chromosomes observed in cells expressing TRF2L286R, we hypothesized that RAP1 co-operates with other Shelterin components to repress homology directed repair (HDR) at telomeres

Summary

Introduction

Repressor/activator protein 1 (RAP1) is a highly conserved telomere-interacting protein. The Saccharomyces cerevisiae Rap[1] (ScRap1) was originally discovered as a transcriptional regulator and later shown to be a multifunctional protein, with roles in subtelomeric silencing, telomere length regulation and telomere end protection against non-homologous end-joining (NHEJ)-mediated DNA repair[7,8,9,10,11]. In MEFs expressing mutant TRF2 that is unable to interact with endogenous RAP1, we observed increased loss of telomeric signals, elevated telomere sister chromatid exchanges (T-SCEs) and increased chromosome fusions due to increased homologous recombination (HR) at telomeres These results suggest that mouse RAP1 plays a role in protecting telomeres from initiating homology directed repair (HDR)[6]. In the absence of RAP1 and TRF2B, PARP1, SLX4 and proteins involved in HDR promote rapid telomere resection, catastrophic telomere loss and formation of telomere-free chromosome ends, culminating in massive telomere-free chromosome fusions in both mouse and human cells. Our results highlight the importance of the RAP1-TRF2 heterodimer in protecting telomeres from inappropriate processing by the HDR pathway

Methods

Results

Conclusion