ATRX proximal protein associations boast roles beyond histone deposition.

William A Scott,Erum Z Dhanji,Grant S Stewart,Mila Mirceta,Boris J A Dyakov,Jonathon S Asa,Laura J Grange,Anne-Claude Gingras,Ema S Dreseris,Eric I Campos,Christopher E Pearson,John M Greally

doi:10.1371/journal.pgen.1009909

Abstract

The ATRX ATP-dependent chromatin remodelling/helicase protein associates with the DAXX histone chaperone to deposit histone H3.3 over repetitive DNA regions. Because ATRX-protein interactions impart functions, such as histone deposition, we used proximity-dependent biotinylation (BioID) to identify proximal associations for ATRX. The proteomic screen captured known interactors, such as DAXX, NBS1, and PML, but also identified a range of new associating proteins. To gauge the scope of their roles, we examined three novel ATRX-associating proteins that likely differed in function, and for which little data were available. We found CCDC71 to associate with ATRX, but also HP1 and NAP1, suggesting a role in chromatin maintenance. Contrastingly, FAM207A associated with proteins involved in ribosome biosynthesis and localized to the nucleolus. ATRX proximal associations with the SLF2 DNA damage response factor help inhibit telomere exchanges. We further screened for the proteomic changes at telomeres when ATRX, SLF2, or both proteins were deleted. The loss caused important changes in the abundance of chromatin remodelling, DNA replication, and DNA repair factors at telomeres. Interestingly, several of these have previously been implicated in alternative lengthening of telomeres. Altogether, this study expands the repertoire of ATRX-associating proteins and functions.

Highlights

The alpha thalassemia/intellectual disability, X-linked (ATRX) protein is an SNF2-type ATPdependent chromatin remodeller/helicase that maintains chromatin over repetitive DNA regions, such as pericentric heterochromatin and telomeres
ATRX is a protein that is needed to keep repetitive DNA regions organized. It does so in part by binding the DAXX histone chaperone to deposit histone proteins on DNA and assemble structures known as nucleosomes
ATRX-associating proteins were implicated in a range of functions, in addition to histone deposition

Summary

Introduction

The alpha thalassemia/intellectual disability, X-linked (ATRX) protein is an SNF2-type ATPdependent chromatin remodeller/helicase that maintains chromatin over repetitive DNA regions, such as pericentric heterochromatin and telomeres. The protein promotes chromatin compaction [1,2,3] and prompt DNA damage repair [4, 5]. ATRX deregulation is intimately linked to disease. Germline ATRX mutations cause ATR-X Syndrome, a rare X-linked disorder characterized by alpha thalassemia and intellectual disability [6]. Loss of functional ATRX is frequently observed in cancers that utilize alternative lengthening of telomeres (ALT) to extend telomeres and evade replicative senescence [7, 8]. Ectopic ATRX expression in ALT+, ATRX-null cells sharply suppresses ALT activity [9]

Methods

Results

Discussion

Conclusion