Spatially restricted loading of BRD2 at DNA double-strand breaks protects H4 acetylation domains and promotes DNA repair

Ozge Gursoy-Yuzugullu,Brendan D Price,Chelsea Carman

doi:10.1038/s41598-017-13036-5

Ozge Gursoy-Yuzugullu, Brendan D Price + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-13036-5

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Abstract

The n-terminal tail of histone H4 recruits repair proteins, including 53BP1, to DNA double-strand breaks (DSB) and undergoes dynamic acetylation during DSB repair. However, how H4 acetylation (H4Ac) recruits repair proteins and reorganizes chromatin during DNA repair is unclear. Here, we show that the bromodomain protein BRD2 is recruited to DSBs. This recruitment requires binding of BRD2’s tandem bromodomains to H4Ac, which is generated at DSBs by the Tip60/KAT5 acetyltransferase. Binding of BRD2 to H4Ac protects the underlying acetylated chromatin from attack by histone deacetylases and allows acetylation to spread along the flanking chromatin. However, BRD2 recruitment is spatially restricted to a chromatin domain extending only 2 kb either side of the DSB, and BRD2 does not spread into the chromatin domains flanking the break. Instead, BRD2 facilitates recruitment of a second bromodomain protein, ZMYND8, which spreads along the flanking chromatin, but is excluded from the DSB region. This creates a spatially restricted H4Ac/BRD2 domain which reorganizes chromatin at DSBs, limits binding of the L3MBTL1 repressor and promotes 53BP1 binding, while limiting end-resection of DSBs. BRD2 therefore creates a restricted chromatin environment surrounding DSBs which facilitates DSB repair and which is framed by extensive ZMYND8 domains on the flanking chromatin.

Highlights

The repair of DNA double-strand breaks (DSBs) requires recruitment of DNA repair proteins to the site of damage and is linked to changes in nucleosome dynamics and histone modification[1,2]
BRD2 was reduced on the chromatin flanking the p84-Zinc Finger Nucleases (ZFNs) DSB (Fig. 1a) and this loss extended at least 50 kb from the DSB (Supplementary Figure 1b)
BRD2 and ZMYND8 were recruited to a specialized, bipartite chromatin domain in which BRD2 occupies a spatially restricted region at the DSB while ZMYND8 spreads along the flanking chromatin

Summary

Introduction

The repair of DNA double-strand breaks (DSBs) requires recruitment of DNA repair proteins to the site of damage and is linked to changes in nucleosome dynamics and histone modification[1,2]. The unacetylated H4 tail binds to the acidic patch[8,9], promoting nucleosome interaction and formation of compact chromatin at the DSB9–11 This repressive chromatin may restrict local nucleosome motion, limit transcription and erase local epigenetic modifications which may inhibit repair[12]. Studies have shown that the acetylated H4 tail provides a binding surface for a number of bromodomain proteins[28,29] This includes ZMYND8, which recruits the repressive NuRD complex to DSBs and promotes transcriptional silencing during repair[29,30] and BRD4, which may limit spreading of DNA damage signals along the chromatin[31]. BRD2 defines a novel, spatially restricted chromatin domain which surrounds the DSB and is essential for DSB repair

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