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Enhancer architecture-dependent multilayered transcriptional regulation orchestrates RA signal-induced early differentiation of ESC

ABSTRACT: Signaling pathway driven target gene transcriptions are critical for fate determination of embryonic stem cells (ESC), but enhancer architecture-dependent transcriptional regulation remains largely unclear in this process. Here, we described a complex enhancer architecture-dependent multilayered transcriptional regulation that orchestrates retinoic acid (RA) signal-induced early differentiation of ESC. Specifically, we identified Hoxa1 and lncRNA Halr1 as the direct downstream target genes of RA signal. Chromosome conformation capture based screens show that increased enhancer interactions promoted by RA signal are essential for Hoxa1 and Halr1 expressions during early ESC differentiation. Furthermore, we find that HOXA1 promotes Halr1 expression through direct binding to enhancers; conversely, absence of Halr1 RNA enhances interaction between Hoxa1 chromatin and multiple enhancers, but weakens interaction with HoxA cluster internal chromatin, thereby promoting RA signal-induced Hoxa1 overactivation and early differentiation of ESC. These results indicate that Halr1 binds to chromatin not only acts as a brake to orchestrate interaction between enhancers and Hoxa1 chromatin, but also acts as a binder to maintain chromatin interaction within HoxA cluster. In summary, these findings reveal a complex multilayered transcriptional regulation involving the synergistic regulation of enhancer, transcription factor and lncRNA, and that increases our understanding of the intrinsic molecular mechanisms of RA signal-induced ESC differentiation.

ORGANISM(S): Mus musculus

PROVIDER: GSE169058 | GEO | 2021/04/16

REPOSITORIES: GEO

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Project description:FOXA1 is a pioneer factor that is important in hormone dependent cancer cells to stabilise nuclear receptors, such as estrogen receptor (ER) to chromatin. FOXA1 binds to enhancers regions that are enriched in H3K4mono- and dimethylation (H3K4me1, H3K4me2) histone marks and evidence suggests that these marks are requisite events for FOXA1 to associate with enhancers to initate subsequent gene expression events. However, exogenous expression of FOXA1 has been shown to induce H3K4me1 and H3K4me2 signal at enhancer elements and the order of events and the functional importance of these events is not clear. We performed a FOXA1 Rapid Immunoprecipitation Mass Spectrometry of Endogenous Proteins (RIME) screen in ERα-positive MCF-7 breast cancer cells in order to identify FOXA1 interacting partners and we found histone-lysine N-methyltransferase (MLL3) as the top FOXA1 interacting protein. MLL3 is typically thought to induce H3K4me3 at promoter regions, but recent findings suggest it may contribute to H3K4me1 deposition, in line with our observation that MLL3 associates with an enhancer specific protein. We performed MLL3 ChIP-seq in breast cancer cells and unexpectedly found that MLL3 binds mostly at non-promoter regions enhancers, in contrast to the prevailing hypothesis. MLL3 was shown to occupy regions marked by FOXA1 occupancy and as expected, H3K4me1 and H3K4me2. MLL3 binding was dependent on FOXA1, indicating that FOXA1 recruits MLL3 to chromatin. Motif analysis and subsequent genomic mapping revealed a role for Grainy head like protein-2 (GRHL2) which was shown to co-occupy regions of the chromatin with MLL3. Regions occupied by all three factors, namely FOXA1, MLL3 and GRHL2, were most enriched in H3K4me1. MLL3 silencing decreased H3K4me1 at enhancer elements, but had no appreciable impact on H3K4me3 at enhancer elements. We identify a complex relationship between FOXA1, MLL3 and H3K4me1 at enhancers in breast cancer and propose a mechanism whereby the pioneer factor FOXA1 can interact with a chromatin modifier MLL3, recruiting it to chromatin to facilitate the deposition of H3K4me1 histone marks, subsequently demarcating active enhancer elements.

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Enhancer architecture-dependent multilayered transcriptional regulation orchestrates RA signal-induced early differentiation of ESC

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