Inactivation of the histone H3 K36 methyltransferase NSD1 confers resistance to EZH2 inhibition [RNA-Seq]
Ontology highlight
ABSTRACT: Disruption of antagonism between SWI/SNF chromatin remodelers and Polycomb repressor complexes drives the formation of numerous cancer types. Recently, an inhibitor of Polycomb protein EZH2 was approved for treatment of sarcomas mutant in SWI/SNF subunit SMARCB1, but resistance occurs. Here we sought to identify additional contributors to SWI/SNF-Polycomb antagonism and potential resistance mechanisms. We performed CRISPR screens and found that NSD1 loss caused resistance to EZH2 inhibition. NSD1 loss reduced H3K36me2 and impaired transcriptional activation of targets inhibited by EZH2 or activated by SMARCB1. Further, inhibiting the H3K36me2 demethylase KDM2A restored EZH2 inhibition in cells lacking NSD1. Our results expand the mechanistic understanding of SWI/SNF and Polycomb interplay and identify NSD1 as key for coordinating this transcriptional control.
Project description:Disruption of antagonism between SWI/SNF chromatin remodelers and Polycomb repressor complexes drives the formation of numerous cancer types. Recently, an inhibitor of Polycomb protein EZH2 was approved for treatment of sarcomas mutant in SWI/SNF subunit SMARCB1, but resistance occurs. Here we sought to identify additional contributors to SWI/SNF-Polycomb antagonism and potential resistance mechanisms. We performed CRISPR screens and found that NSD1 loss caused resistance to EZH2 inhibition. NSD1 loss reduced H3K36me2 and impaired transcriptional activation of targets inhibited by EZH2 or activated by SMARCB1. Further, inhibiting the H3K36me2 demethylase KDM2A restored EZH2 inhibition in cells lacking NSD1. Our results expand the mechanistic understanding of SWI/SNF and Polycomb interplay and identify NSD1 as key for coordinating this transcriptional control.
Project description:Epigenetic alterations have been increasingly implicated in oncogenesis. Analysis of Drosophila mutants suggests that Polycomb and SWI/SNF complexes can serve antagonistic developmental roles. However, the relevance of this relationship to human disease is unclear. Here we have investigated functional relationships between these epigenetic regulators in oncogenic transformation. Mechanistically, we show that loss of the SNF5 tumor suppressor leads to elevated expression of the Polycomb gene EZH2 and that Polycomb targets are broadly H3K27-trimethylated and repressed in SNF5-deficient fibroblasts and cancers. Further, we show antagonism between SNF5 and EZH2 in the regulation of stem cell-associated programs and that Snf5 loss activates those programs. Finally, using conditional mouse models, we show that inactivation of Ezh2 blocks tumor formation driven by Snf5 loss. Mouse Embryonic Fibroblasts (MEFs) conditionally inactivated for Ezh2, Snf5 and Ezh2, or from control WT MEFs were used to evaluated epigenetic antagonism between Snf5 and Ezh2 in the control of gene expression programs. Snf5-deficient lymphoma samples and control CD8+ WT T-cells were used to evaluate genetic programs misregulated by Snf5 inactivation during tumorigenesis. RNA was isolated from each of these samples and used for gene expression profiling on Affymetrix arrays.
Project description:Recent work has revealed essential epigenetic dependencies in many cancers. Based on the functional antagonism between BAF/SWI/SNF and Polycomb repressive complex 2 chromatin remodeling in SMARCB1-deficient sarcomas, we and colleagues recently completed the clinical trial of the EZH2 inhibitor tazemetostat, leading to its FDA approval. However, the principles of response and resistance to epigenetic therapy in general and tazemetostat in particular remain unknown. Using comparative functional genomics of clinical tumor specimens and diverse experimental model systems, we have now defined molecular mechanisms of resistance to tazemetostat in epithelioid sarcomas and rhabdoid tumors. We found distinct classes of acquired mutations that converge on the RB/E2F axis and decouple EZH2 inhibition-dependent tumor cell differentiation and cell cycle control. This allows tumor cells to escape tazemetostat-induced G1 arrest, despite an active transcriptional response, and provides a general mechanism for effective EZH2 inhibitor therapy. Thus, we develop combination strategies to circumvent tazemetostat resistance by using cell cycle bypass and synthetic lethal targeting, and provide prospective biomarkers for future therapy stratification. This offers a paradigm for rational epigenetic combination therapy suitable for immediate translation to clinical trials for patients.
Project description:While oncogenes can potentially be inhibited with small molecules, the loss of tumor suppressors is more common and is problematic because the tumor suppressor proteins are no longer present to be targeted. Notable examples include SMARCB1-mutant cancers, which are highly lethal malignancies driven by the inactivation of a subunit of SWI/SNF chromatin remodeling complexes. To generate mechanistic insight into the consequences of SMARCB1 mutation and to identify vulnerabilities, we contributed 14 SMARCB1-mutant cell lines to a near genome-wide CRISPR screen as part of the Cancer Dependency Map Project1-3. Here, we report that the little-studied gene DDB1-CUL4 Associated Factor 5 (DCAF5) is required for the survival of SMARCB1-mutant cancers. We show that DCAF5 serves a quality control function for SWI/SNF complexes and promotes degradation of incompletely assembled SWI/SNF complexes in the absence of SMARCB1. Upon depletion of DCAF5, SMARCB1-deficient SWI/SNF complexes re-accumulate, bind to target loci, and restore SWI/SNF-mediated gene expression to levels sufficient to reverse the cancer state, including in vivo. Consequently, cancer results not from the loss of SMARCB1 function per se but rather from DCAF5-mediated degradation of SWI/SNF complexes. These data indicate that therapeutic targeting of ubiquitin-mediated quality control factors may effectively reverse the malignant state of some cancers driven by disruption of tumor suppressor complexes.
Project description:While oncogenes can potentially be inhibited with small molecules, the loss of tumor suppressors is more common and is problematic because the tumor suppressor proteins are no longer present to be targeted. Notable examples include SMARCB1-mutant cancers, which are highly lethal malignancies driven by the inactivation of a subunit of SWI/SNF chromatin remodeling complexes. To generate mechanistic insight into the consequences of SMARCB1 mutation and to identify vulnerabilities, we contributed 14 SMARCB1-mutant cell lines to a near genome-wide CRISPR screen as part of the Cancer Dependency Map Project1-3. Here, we report that the little-studied gene DDB1-CUL4 Associated Factor 5 (DCAF5) is required for the survival of SMARCB1-mutant cancers. We show that DCAF5 serves a quality control function for SWI/SNF complexes and promotes degradation of incompletely assembled SWI/SNF complexes in the absence of SMARCB1. Upon depletion of DCAF5, SMARCB1-deficient SWI/SNF complexes re-accumulate, bind to target loci, and restore SWI/SNF-mediated gene expression to levels sufficient to reverse the cancer state, including in vivo. Consequently, cancer results not from the loss of SMARCB1 function per se but rather from DCAF5-mediated degradation of SWI/SNF complexes. These data indicate that therapeutic targeting of ubiquitin-mediated quality control factors may effectively reverse the malignant state of some cancers driven by disruption of tumor suppressor complexes.
Project description:While oncogenes can potentially be inhibited with small molecules, the loss of tumor suppressors is more common and is problematic because the tumor suppressor proteins are no longer present to be targeted. Notable examples include SMARCB1-mutant cancers, which are highly lethal malignancies driven by the inactivation of a subunit of SWI/SNF chromatin remodeling complexes. To generate mechanistic insight into the consequences of SMARCB1 mutation and to identify vulnerabilities, we contributed 14 SMARCB1-mutant cell lines to a near genome-wide CRISPR screen as part of the Cancer Dependency Map Project1-3. Here, we report that the little-studied gene DDB1-CUL4 Associated Factor 5 (DCAF5) is required for the survival of SMARCB1-mutant cancers. We show that DCAF5 serves a quality control function for SWI/SNF complexes and promotes degradation of incompletely assembled SWI/SNF complexes in the absence of SMARCB1. Upon depletion of DCAF5, SMARCB1-deficient SWI/SNF complexes re-accumulate, bind to target loci, and restore SWI/SNF-mediated gene expression to levels sufficient to reverse the cancer state, including in vivo. Consequently, cancer results not from the loss of SMARCB1 function per se but rather from DCAF5-mediated degradation of SWI/SNF complexes. These data indicate that therapeutic targeting of ubiquitin-mediated quality control factors may effectively reverse the malignant state of some cancers driven by disruption of tumor suppressor complexes.
Project description:Here we performed transcriptional profiling of the prostate cancer cell lines LNCaP and 22Rv1 comparing non-targeting siRNA treatment versus siRNAs targeting SWI/SNF complex proteins (SMARCA2, SMARCA4, and SMARCB1). Goal was to determine the effect of SWI/SNF knockdown on gene expression in prostate cancer. Two-condition experiment: non-targeting siRNA versus SWI/SNF-siRNA treated cells. Three SWI/SNF proteins were targeted: SMARCA2, SMARCA4, and SMARB1. Biological replicates: 1 control replicate, 2 treatment replicates per SWI/SNF protein. Technical replicates: 1 replicate per SWI/SNF protein. Cell lines: 22Rv1 and LNCaP.
Project description:The SWI/SNF chromatin remodeling complex is altered in ~20% of human cancers. ARID1A, a component of the SWI/SNF chromatin-remodeling complex, is the most frequently mutated epigenetic regulator in human cancers. Inactivation of the SWI/SNF complex is synthetically lethal with inhibition of EZH2 activity. EZH2 inhibitors are entering clinical trials for specific tumor types with SWI/SNF mutations. However, mechanisms of de novo or acquired resistance to EZH2 inhibitors in cancers with inactivating SWI/SNF mutations are unknown. Here we show that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 drives resistance to EZH2 inhibitors in ARID1A-mutated ovarian cancer cells.
Project description:The SWI/SNF chromatin remodeling complex is altered in ~20% of human cancers. ARID1A, a component of the SWI/SNF chromatin-remodeling complex, is the most frequently mutated epigenetic regulator in human cancers. Inactivation of the SWI/SNF complex is synthetically lethal with inhibition of EZH2 activity. EZH2 inhibitors are entering clinical trials for specific tumor types with SWI/SNF mutations. However, mechanisms of de novo or acquired resistance to EZH2 inhibitors in cancers with inactivating SWI/SNF mutations are unknown. Here we show that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 drives resistance to EZH2 inhibitors in ARID1A-mutated ovarian cancer cells.
Project description:We executed CUT&RUN-seq for SWI/SNF components ARID1A, BRD9, SMARCA4, SMARCB1, SMARCE1, as well as ESRRB, SOX2, and EZH2 in asynchronous and mitotic cells and reported that, in asynchronous cells, ARID1A localized primarily at enhancer regions and EZH2 preferentially deposited at bivalent promoters and silent enhancer domains. The remaining factors were enriched at both TSS/promoters and to varying degrees at active enhancers. Unexpectedly, in mitosis, the chromatin regulatory factors almost all tethered at proximal gene regions with very little binding at enhancers. While the SWI/SNF subunits were bound principally at promoters, EZH2, the catalytic subunit of Polycomb Repressive Complex 2 was bound at both promoters and silent enhancers in mitotic cells. Moreover, we reported that upon the degradation of SMARCE1 in mitosis, the occupancy of SOX2, ESRRB, and EZH2 on mitotic chromatin was disrupted.