Targeting Dependency on a Paralog Pair of CBP/p300 against De-repression of KREMEN2 in SMARCB1-Deficient Cancers
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ABSTRACT: SMARCB1, a subunit of the SWI/SNF chromatin remodeling complex, is the causative gene of rhabdoid tumors and epithelioid sarcomas. Here, we identify a paralog pair of CBP and p300 as a synthetic lethal target in SMARCB1-deficient cancers by using a dual siRNA screening method based on the “simultaneous inhibition of a paralog pair” concept. Treatment with CBP/p300 dual inhibitors suppresses growth of cell lines and tumor xenografts derived from SMARCB1-deficient cells but not from SMARCB1-proficient cells. SMARCB1-containing SWI/SNF complexes localize with H3K27me3 and its methyltransferase EZH2 at the promotor region of the KREMEN2 locus, resulting in transcriptional downregulation of KREMEN2. By contrast, SMARCB1 deficiency leads to localization of H3K27ac, and recruitment of its acetyltransferases CBP and p300, at the KREMEN2 locus, resulting in transcriptional upregulation of KREMEN2, which cooperates with the SMARCA1 chromatin remodeling complex. Simultaneous inhibition of CBP/p300 leads to transcriptional downregulation of KREMEN2, followed by apoptosis induction via monomerization of KREMEN1 due to a failure to interact with KREMEN2, which suppresses anti-apoptotic signaling pathways. Taken together, our findings indicate that simultaneous inhibitors of CBP/p300 could be promising therapeutic agents for SMARCB1-deficient cancers.
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:Genes encoding subunits of SWI/SNF(BAF) chromatin remodeling complexes are collectively mutated in nearly 25% of all cancers. Utilizing a genome-wide CRISPR-Cas9 screen, we identify PHF6 as a specific vulnerability in pediatric malignant rhabdoid tumors (RTs), which are driven by inactivation of the SMARCB1 subunit of SWI/SNF. We establish that PHF6 co-localizes with residual SWI/SNF subcomplexes at promoters and enhancers. Here, PHF6 facilitates transcriptional activation by regulating deposition of H3K14ac downstream of active promoters and contributes to the establishment of H3K27ac at active promoters and enhancers. We show that PHF6 is essential for the maintenance of these marks in part via the regulation of their writers, HB01 and CBP/p300, respectively. As it directly regulates the H3K14ac mark, PHF6 may regulate pausing and serve as a mediator between chromatin regulatory function and RNA POL II pause release. Together, our results establish a mechanistic basis for dependence upon PHF6 in SMARCB1-mutant RTs.
Project description:Genes encoding subunits of SWI/SNF(BAF) chromatin remodeling complexes are collectively mutated in nearly 25% of all cancers. Utilizing a genome-wide CRISPR-Cas9 screen, we identify PHF6 as a specific vulnerability in pediatric malignant rhabdoid tumors (RTs), which are driven by inactivation of the SMARCB1 subunit of SWI/SNF. We establish that PHF6 co-localizes with residual SWI/SNF subcomplexes at promoters and enhancers. Here, PHF6 facilitates transcriptional activation by regulating deposition of H3K14ac downstream of active promoters and contributes to the establishment of H3K27ac at active promoters and enhancers. We show that PHF6 is essential for the maintenance of these marks in part via the regulation of their writers, HB01 and CBP/p300, respectively. As it directly regulates the H3K14ac mark, PHF6 may regulate pausing and serve as a mediator between chromatin regulatory function and RNA POL II pause release. Together, our results establish a mechanistic basis for dependence upon PHF6 in SMARCB1-mutant RTs.
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:Dysfunction of epigenetic modulators such as the SWI/SNF complex is involved in a wide spectrum of cancer entities, yet their precise role in carcinogenesis is not clear to date Among SWI/SNF-mutant entities, SMARCB1-deficient cancers such as Epithelioid Sarcoma (EpS) are characterized by this genetic event in an otherwise rather silent mutational landscape. However, its oncogenic role remains unclear. Here, we generate a panel of SMARCB1 re-expressing Epithelioid Sarcoma (EpS) cell lines and employ a functional multi-omics approach to characterize and compare the function of the residual SMARCB1-deficient and the physiological SWI/SNF complex in EpS. We show that SWI/SNF holds canonical characteristics of both tumor-suppressors and proto-oncogenes due to its multi-faceted role in the regulation of the epigenome. Our data indicates that the loss of SMARCB1 causes an overall loss of SWI/SNF chromatin affinity at cis-regulatory enhancer elements, inducing a preference for uncontrolled proliferation and cell cycle progression as opposed to development and differentiation. As epigenetic regulation is a dynamic complex, we further demonstrate that EpS cell lines depend on continuous residual SWI/SNF action to maintain clonogenicity and proliferation. Consequently, our models exhibit markedly increased sensitivity to pharmacological inhibition of the residual SWI/SNF when compared with SWI/SNF-proficient cancer entities. Collectively, our results shed new light on the pleiotropic, deregulated pathways upon SWI/SNF dysfunction in EpS and provide inroads for further therapeutic approaches.
Project description:Dysfunction of epigenetic modulators such as the SWI/SNF complex is involved in a wide spectrum of cancer entities, yet their precise role in carcinogenesis is not clear to date Among SWI/SNF-mutant entities, SMARCB1-deficient cancers such as Epithelioid Sarcoma (EpS) are characterized by this genetic event in an otherwise rather silent mutational landscape. However, its oncogenic role remains unclear. Here, we generate a panel of SMARCB1 re-expressing Epithelioid Sarcoma (EpS) cell lines and employ a functional multi-omics approach to characterize and compare the function of the residual SMARCB1-deficient and the physiological SWI/SNF complex in EpS. We show that SWI/SNF holds canonical characteristics of both tumor-suppressors and proto-oncogenes due to its multi-faceted role in the regulation of the epigenome. Our data indicates that the loss of SMARCB1 causes an overall loss of SWI/SNF chromatin affinity at cis-regulatory enhancer elements, inducing a preference for uncontrolled proliferation and cell cycle progression as opposed to development and differentiation. As epigenetic regulation is a dynamic complex, we further demonstrate that EpS cell lines depend on continuous residual SWI/SNF action to maintain clonogenicity and proliferation. Consequently, our models exhibit markedly increased sensitivity to pharmacological inhibition of the residual SWI/SNF when compared with SWI/SNF-proficient cancer entities. Collectively, our results shed new light on the pleiotropic, deregulated pathways upon SWI/SNF dysfunction in EpS and provide inroads for further therapeutic approaches.
Project description:While oncogenes can potentially be inhibited with small molecules, the loss of tumor suppressors is more common and presents a conundrum for precision therapy because the proteins are no longer present. SMARCB1-mutant cancers epitomize this challenge because these highly lethal cancers are driven by inactivation of a single gene, a subunit of SWI/SNF chromatin remodeling complexes. To generate mechanistic insight into the consequences of SMARCB1 mutation and to seek vulnerabilities, we contributed 16 SMARCB1-mutant cell lines to a near-genomewide CRISPR screen as part of the Cancer Dependency Map1-3. Here we report that the little-studied gene DCAF5 (DDB1-CUL4 Associated Factor 5) is a specific dependency in SMARCB1-mutant cancers. We show that DCAF5 serves a quality control function for SWI/SNF complexes and in the absence of SMARCB1 DCAF5 causes degradation of incompletely assembled SWI/SNF complexes. Upon inhibition of DCAF5 SMARCB1-deficient SWI/SNF complexes re-accumulate, bind to target loci, and restore gene expression to levels sufficient to fully reverse the cancer state, including in a xenograft mouse model. 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 DCAF5 may be sufficient to restore substantial SWI/SNF function and reverse cancer phenotypes caused by SMARCB1 loss.