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A non-canonical GLTSCR1L-containing BAF complex mediates H3K27ac-dependent enhancer activities

ABSTRACT: H3K27ac is known to associate with regulatory active enhancers, but it’s exact role in enhancer function remains elusive. Using mass spectrometry-based interaction proteomics, we identified the Super Elongation Complex (SEC) and GBAF, a non-canonical GLTSCR1L- and BRD9-containing SWI/SNF chromatin remodeling complex, to be major interactors of H3K27ac. Our interaction proteomics analysis refined the composition of GBAF by adding BCL7A/B/C as a new subunit. We further characterized the conserved GLTSCR1/1L-contained “GiBAF”-domain, which we found to be responsible for GBAF complex formation and nuclear localization. Inhibition of the bromodomain of BRD9 revealed interaction between GLTSCR1L and BRD9 to be H3K27ac dependent and led to GLTSCR1L dislocation from its preferred binding sites at H3K27ac-associated enhancers. GLTSCR1L disassociation from chromatin resulted in a genome-wide downregulation of enhancer transcription. Our results indicate that GBAF is an enhancer-associated chromatin remodeller important for the correct transcriptional and regulatory activity of enhancers.

ORGANISM(S): Homo sapiens

PROVIDER: GSE121351 | GEO | 2018/10/17

REPOSITORIES: GEO

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Project description:The mammalian BRG1-associated factors (BAF) complex is a multi-subunit chromatin remodeling complex that is an important component of the embryonic stem cell (ESC) transcriptional regulatory network. However, the role of individual subunits in BAF complex targeting and function needs to be elucidated. Here, we find that the Bromodomain containing protein 9 (BRD9) and Glioma tumor suppressor candidate region gene 1 (GLTSCR1; also known as BICRA) or its paralog GLTSCR1-like (also known as BICRAL) define a smaller, non-canonical BAF complex (GBAF for GLTSCR1/1L-containing BAF complex) in mouse ESCs that is distinct from the canonical embryonic stem cell BAF (esBAF) and the polybromo-associated BAF (PBAF) complexes. GBAF lacks several esBAF subunits, including BAF47, BAF57 and ARID1A. We demonstrate that GBAF and esBAF complexes are targeted to different features of the genome and are co-bound with different sets of pluripotency transcription factors. Specifically, GBAF complexes co-localize with key regulators of naïve pluripotency, KLF4 and Sp5, on the genome. Consistent with this, we provide evidence that GBAF's specific function is to regulate the transcription of genes involved in the maintenance of naïve pluripotency, including Nanog and Prdm14. Additionally, we show that BRD9 is displaced from chromatin by the selective BRD9 bromodomain inhibitor, I-BRD9, and that this leads to changes in target gene expression. The function of the GBAF complex in ESCs is highly correlated with the function of BRD4, consistent with an association between GBAF complexes and BRD4. We find that GBAF complexes are directly recruited to chromatin by BRD4 in a bromodomain-dependent fashion and we identify a set of I-BRD9- and JQ1-sensitive BRD9 binding sites that determine the functional similarity between these epigenetic regulators. Together, our results demonstrate functionally specific roles for BAF complex assemblies in maintaining the transcriptional network of pluripotency, highlighting the biological importance of complex heterogeneity.

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A non-canonical GLTSCR1L-containing BAF complex mediates H3K27ac-dependent enhancer activities

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