A SWI/SNF-dependent transcriptional repression mediated by POU2AF2/C11orf53 at enhancer.
Ontology highlight
ABSTRACT:
INSTRUMENT(S): LTQ Orbitrap Elite
ORGANISM(S): Homo Sapiens (human)
SUBMITTER: 
Lu Wang
LAB HEAD: Lu Wang
PROVIDER: PXD043238 | Pride | 2024-01-19
REPOSITORIES: Pride
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Project description:Recent studies have identified a previously uncharacterized protein C11orf53 (now named POU2AF2/OCA-T1), functions as a new co-activator of POU2F3, the master transcription factor which is critical for both normal and neoplastic tuft cell identity and viability. Here, we demonstrated that POU2AF2 functions as an “Yin-Yang” factor which mediates both transcriptional activation and repression at distal enhance elements. Loss of POU2AF2 led to an inhibition of active enhancer nearby genes, such as tuft cell identity genes, and a derepression of Polycomb-dependent poised enhancer nearby genes, which are critical for cell viability and differentiation. Mechanistically, depletion of POU2AF2 leads to a global redistribution of the chromatin occupancy of SWI/SNF complex, resulting in a significant 3D genome structure change and a subsequent transcriptional reprogramming. Genome wide CRISPR screen further demonstrated that POU2AF2 depletion or SWI/SNF inhibition led to a PTEN-dependent cell growth defect, which revealed a potential role of POU2AF2-SWI/SNF axis in small cell lung cancer pathogenesis. Finally, pharmacological inhibition of SWI/SNF phenocopied POU2AF2 depletion in terms of gene expression alteration and cell viability decease in SCLC-P subtype cells. Therefore, impeding POU2AF2 mediated SWI/SNF function represents a potential therapeutic approach for human SCLC therapy.
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Project description:Notch signaling plays a key role in many cell fate decisions during development by directing different gene expression programs via the transcription factor CSL, known as Su(H) in Drosophila Which target genes are responsive to Notch signaling is influenced by the chromatin state of enhancers, yet how this is regulated is not fully known. Detecting a specific increase in the histone variant H3.3 in response to Notch signaling, we tested which chromatin remodelers or histone chaperones are required for the changes in enhancer accessibility to Su(H) binding. We show a crucial role for the Brahma SWI/SNF chromatin remodeling complex, including the actin-related BAP55 subunit, in conferring enhancer accessibility and enabling the transcriptional response to Notch activity. The Notch-responsive regions have high levels of nucleosome turnover which depend on the Brahma complex, increase in magnitude with Notch signaling, and primarily involve histone H3.3. Together these results highlight the importance of SWI/SNF-mediated nucleosome turnover in rendering enhancers responsive to Notch.
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Project description:The switch/sucrose non-fermentable (SWI/SNF) complex has a crucial role in chromatin remodelling1 and is altered in over 20% of cancers2,3. Here we developed a proteolysis-targeting chimera (PROTAC) degrader of the SWI/SNF ATPase subunits, SMARCA2 and SMARCA4, called AU-15330. Androgen receptor (AR)+ forkhead box A1 (FOXA1)+ prostate cancer cells are exquisitely sensitive to dual SMARCA2 and SMARCA4 degradation relative to normal and other cancer cell lines. SWI/SNF ATPase degradation rapidly compacts cis-regulatory elements bound by transcription factors that drive prostate cancer cell proliferation, namely AR, FOXA1, ERG and MYC, which dislodges them from chromatin, disables their core enhancer circuitry, and abolishes the downstream oncogenic gene programs. SWI/SNF ATPase degradation also disrupts super-enhancer and promoter looping interactions that wire supra-physiologic expression of the AR, FOXA1 and MYC oncogenes themselves. AU-15330 induces potent inhibition of tumour growth in xenograft models of prostate cancer and synergizes with the AR antagonist enzalutamide, even inducing disease remission in castration-resistant prostate cancer (CRPC) models without toxicity. Thus, impeding SWI/SNF-mediated enhancer accessibility represents a promising therapeutic approach for enhancer-addicted cancers.
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Project description:SMARCB1 (also known as SNF5, INI1, and BAF47), a core subunit of the SWI/SNF (BAF) chromatin-remodeling complex, is inactivated in nearly all pediatric rhabdoid tumors. These aggressive cancers are among the most genomically stable, suggesting an epigenetic mechanism by which SMARCB1 loss drives transformation. Here we show that, despite having indistinguishable mutational landscapes, human rhabdoid tumors exhibit distinct enhancer H3K27ac signatures, which identify remnants of differentiation programs. We show that SMARCB1 is required for the integrity of SWI/SNF complexes and that its loss alters enhancer targeting-markedly impairing SWI/SNF binding to typical enhancers, particularly those required for differentiation, while maintaining SWI/SNF binding at super-enhancers. We show that these retained super-enhancers are essential for rhabdoid tumor survival, including some that are shared by all subtypes, such as SPRY1, and other lineage-specific super-enhancers, such as SOX2 in brain-derived rhabdoid tumors. Taken together, our findings identify a new chromatin-based epigenetic mechanism underlying the tumor-suppressive activity of SMARCB1.
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Project description:Small cell lung cancers (SCLC) are comprised of heterogeneous subtypes marked by lineage-specific transcription factors, including ASCL1, NEUROD1, and POU2F3. POU2F3-positive SCLC, ~12% of all cases, are uniquely dependent on POU2F3 itself; as such, approaches to attenuate POU2F3 expression may represent new therapeutic opportunities for this subtype. Here using genome-scale CRISPR/Cas9-based screens reporting on POU2F3 expression in SCLC cell lines, we define mSWI/SNF complexes, including non-canonical BAF complexes (ncBAF), as top regulators of POU2F3 and dependencies specific to the POU2F3-positive subtype. Notably, clinical-grade pharmacologic mSWI/SNF complex inhibition attenuates proliferation of all POU2F3-positive SCLCs, while disruption of ncBAF via BRD9 degradation is uniquely effective in pure non-neuroendocrine POU2F3-SCLCs. mSWI/SNF complexes maintain accessibility over gene loci central to POU2F3-mediated gene regulatory networks. Finally, chemical targeting of SMARCA4/2 mSWI/SNF ATPases and BRD9 decrease POU2F3-SCLC tumor growth and increase survival in vivo. Taken together, these results define mSWI/SNF-mediated global governance of the POU2F3 oncogenic program and suggest mSWI/SNF inhibition as a therapeutic strategy in SCLC.
2024-06-14 | GSE249258 | GEO
Project description:Cancer cells frequently depend on chromatin regulatory activities to maintain a malignant phenotype. Here, we show that leukemia cells require the mammalian SWI/SNF chromatin remodeling complex for their survival and aberrant self-renewal potential. While Brg1, an ATPase subunit of SWI/SNF, is known to suppress tumor formation in several cell types, we found that leukemia cells instead rely on Brg1 to support their oncogenic transcriptional program, which includes Myc as one of its key targets. To account for this context-specific function, we identify a cluster of lineage-specific enhancers located 1.7 Mb downstream from Myc that are occupied by SWI/SNF as well as the BET protein Brd4. Brg1 is required at these distal elements to maintain transcription factor occupancy and for long-range chromatin looping interactions with the Myc promoter. Notably, these distal Myc enhancers coincide with a region that is focally amplified in ?3% of acute myeloid leukemias. Together, these findings define a leukemia maintenance function for SWI/SNF that is linked to enhancer-mediated gene regulation, providing general insights into how cancer cells exploit transcriptional coactivators to maintain oncogenic gene expression programs.
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Project description:Several cancer core regulatory circuitries (CRCs) depend on the sustained generation of DNA accessibility by SWI/SNF chromatin remodelers. However, the window when SWI/SNF is acutely essential in these settings has not been identified. Here we used neuroblastoma (NB) cells to model and dissect the relationship between cell-cycle progression and SWI/SNF ATPase activity. We find that SWI/SNF inactivation impairs coordinated occupancy of non-pioneer CRC members at enhancers within 1 hour, rapidly breaking their autoregulation. By precisely timing inhibitor treatment following synchronization, we show that SWI/SNF is dispensable for survival in S and G2/M, but becomes acutely essential only during G1 phase. We furthermore developed a new approach to analyze the oscillating patterns of genome-wide DNA accessibility across the cell cycle, which revealed that SWI/SNF-dependent CRC binding sites are enriched at enhancers with peak accessibility during G1 phase, where they activate genes involved in cell-cycle progression. SWI/SNF inhibition strongly impairs G1-S transition and potentiates the ability of retinoids used clinically to induce cell-cycle exit. Similar cell-cycle effects in diverse SWI/SNF-addicted settings highlight G1-S transition as a common cause of SWI/SNF dependency. Our results illustrate that deeper knowledge of the temporal patterns of enhancer-related dependencies may aid the rational targeting of addicted cancers.
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Project description:The Brg1/Brm-associated factor (BAF) chromatin remodeling complex directly binds the CD4 silencer and is essential for CD4 repression during T-cell development, because deletion of the ATPase subunit Brg1 or a dominant negative mutant of BAF57 each impairs CD4 repression in early thymocytes. Paradoxically, BAF57 is dispensable for remodeling nucleosomes in vitro or for binding of the BAF complex to the CD4 silencer in vivo. Thus, it is unclear whether BAF57-dependent CD4 repression involves chromatin remodeling and, if so, how the remodeling translates into CD4 repression. Here we show that nucleosomes at the CD4 silencer occupy multiple translational frames. BAF57 dominant negative mutant does not alter these frames, but reduces the accessibility of the entire silencer without affecting the flanking regions, concomitant with localized accumulation of linker histone H1 and eviction of Runx1, a key repressor of CD4 transcription that directly binds the CD4 silencer. Our data indicate that precise nucleosome positioning is not critical for the CD4 silencer function and that BAF57 participates in remodeling H1-containing chromatin at the CD4 silencer, which enables Runx1 to access the silencer and repress CD4. In addition to BAF57, multiple other subunits in the BAF complex are also dispensable for chromatin remodelling in vitro. Our data suggest that these subunits could also help remodel chromatin at a step after the recruitment of the BAF complex to target genes.
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Project description:The SWI/SNF chromatin-remodeling complex, pivotal in transcriptional regulation, has emerged as a significant player in tumorigenesis, unveiling therapeutic targeting prospects in specific malignancies. This investigation accentuates the potential of targeting the SWI/SNF complex in POU2F3-driven Small Cell Lung Cancer (SCLC) and POU2AF1-dependent multiple myelomas. Employing functional CRISPR screening and pharmacological validation, we identified a distinct and biased dependency of POU2F3-driven SCLC cells on the SWI/SNF complex. In vivo studies exhibited significant tumor growth inhibition in POU2F3-driven SCLC xenografts with an orally administered SMARCA2/4 PROTAC degrader. Furthermore, the exploration extended to POU2AF1 complex-dependent B-cell malignancies, revealing similar sensitivity to the SWI/SNF ATPase PROTAC degrader, suggesting a shared therapeutic potential in POU2F complex-driven malignancies. These collective findings highlight the SWI/SNF complex as a promising therapeutic target, catalyzing the advancement of innovative and efficacious treatment approaches to address these transcription factor-driven malignancies, addressing a critical medical challenge.
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