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Genetic screens reveal new targetable vulnerabilities in BAP1-deficient Mesothelioma

ABSTRACT: More than half of malignant mesothelioma patients show alterations in the BAP1 tumour suppressor gene. Being a member of the Polycomb repressive deubiquitinating (PR-DUB) complex, BAP1 loss results in an altered epigenome which may create new vulnerabilities that remain largely unknown. Here we performed a CRISPR/Cas9-kinome screen in mesothelioma cells that identified two kinases in the Mevalonate/Cholesterol biosynthesis pathway. Furthermore, our analysis of chromatin, expression and genetic perturbation data in mesothelioma cells suggests a dependency on Polycomb repressive complex 2 (PRC2) mediated silencing. Pharmacological inhibition of PRC2 elevates the expression of cholesterol biosynthesis genes only in BAP1-deficient mesothelioma, thereby sensitizing these cells to the combined targeting of PRC2 and the mevalonate pathway. Finally, by subjecting autochthonous Bap1-deficient mesothelioma mice or xenografts to mevalonate pathway inhibition (Zoledronic Acid) and PRC2 inhibition (Tazemetostat), we demonstrate a potent anti-tumour effect, suggesting a targeted combination therapy for Bap1-deficient mesothelioma

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE222376 | GEO | 2023/01/12

REPOSITORIES: GEO

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BAP1 activity regulates Polycomb occupancy and global chromatin condensation counteracting diffuse PCGF3/5-dependent H2AK119ub1 deposition

Project description:BAP1 is recurrently mutated or deleted in a large number of diverse cancer types, including mesothelioma, uveal melanoma and hepatocellular cholangiocarcinoma. BAP1 is the catalytic subunit of the Polycomb Repressive De-Ubiquitination complex (PR-DUB) which removes PRC1 mediated H2AK119ub1. We and others have shown that H2AK119ub1 is essential for maintaining transcriptional repression and contributes to PRC2 chromatin recruitment. However, the precise relationship between BAP1 and PRC1 remains mechanistically elusive. Using embryonic stem cells, we show that a major function of BAP1 is to restrict H2AK119ub1 deposition to target sites. This increases the stability of PcG complexes with their targets and prevents diffuse accumulation of H2AK119ub1 and H3K27me3 modifications. Loss of BAP1 results in a broad increase in H2AK119ub1 levels that are primarily dependent on PCGF3/5-PRC1 complexes with a mechanism that is reminiscent of X-chromosome inactivation. Increased genome-wide H2AK119ub1 levels titrates away PRC2 from its targets and stimulates diffuse H3K27me3 accumulation across the genome. This decreases the activity of PcG repressive machineries at physiological targets and induces a general compaction of the entire chromatin. Our findings provide evidences for a unifying model that resolves the apparent contradiction between BAP1 catalytic activity and its role in vivo, uncovering molecular vulnerabilities that could be useful for BAP1-related pathologies.

2021-06-27 | GSE162739 | GEO

Bap1 loss results in EZH2 dependent transformation

Project description:BAP1 and ASXL1 interact to form a polycomb deubiquitinase complex that removes monoubiquitin from histone H2A lysine 119 (H2AK119Ub). However, BAP1 and ASXL1 are mutated in distinct cancer types, consistent with independent roles in regulating epigenetic state and malignant transformation. Here we demonstrate that Bap1 loss results in increased trimethylated histone H3 lysine 27 (H3K27me3), elevated Ezh2 expression, and enhanced repression of Polycomb Repressive Complex 2 (PRC2) targets. These findings contrast with the reduction in H3K27me3 seen with Asxl1 loss. Conditional deletion of Bap1 and Ezh2 in vivo abrogates the myeloid progenitor expansion induced by Bap1 loss alone.

2015-10-05 | GSE61360 | GEO

A pan-cancer study to identify and characterize synthetic lethal drugs in BAP1-deficient cancers

Project description:BRCA-1 Associated Protein (BAP1) is a deubiquitinating enzyme that acts as a tumour suppressor. Inactivating mutations in the BAP1 gene have been identified in many cancers including cholangiocarcinoma, hepatocellular carcinoma, mesothelioma, uveal melanoma and renal cell carcinoma. Current standard therapeutic approaches for BAP1-deficient tumours are not particularly promising, contributing to poor overall survival and disease-free survival rates. Here, we found BAP1 to mediate the turnover of the key proteins in the DNA nucleotide excision repair (NER) pathway, and therefore promotes DNA repair. Importantly, we demonstrate that the loss of functional BAP1 sensitise tumour cells to LSD1 inhibitor, SP2509, in vitro and in vivo, through further impairment of NER efficiency. When used in combination with PARP1 inhibitor, Olaparib, we show that a synergistic drug combination response is achieved. Overall, our study identifies a drug combination approach that has the potential to be exploited clinically to target BAP1 deficient tumours.

2022-09-15 | PXD028470 | JPOST Repository

BAP1 complex promotes transcription by opposing PRC1-mediated H2A ubiquitylation

Project description:In Drosophila, a complex consisting of Calypso and ASX catalyzes H2A deubiquitination and has been reported to act as part of the Polycomb machinery in transcriptional silencing. The mammalian homologs of these proteins (BAP1 and ASXL1/2/3, respectively), are frequently mutated in various cancer types, yet their precise functions remain unclear. Using an integrative approach based on isogenic cell lines generated with CRISPR/Cas9, we uncover an unanticipated role for BAP1 in gene activation. This function requires the assembly of an enzymatically active BAP1-associated core complex (BAP1.com) containing one of the redundant ASXL proteins. We investigate the mechanism underlying BAP1.com-mediated transcriptional regulation and show that it does not participate in Polycomb-mediated silencing. Instead, our results establish that the function of BAP1.com is to safeguard transcriptionally active genes against silencing by the Polycomb Repressive Complex 1.

2019-01-28 | PXD011808 | Pride

aCGH data for mesothelioma cell lines

Project description:Malignant pleural mesotheliomas (MPMs) often show CDKN2A and NF2 inactivation but other highly recurrent mutations have not been described. To identify additional driver genes, we used an integrated genomic analysis of 53 MPM tumor samples to guide a focused sequencing effort that uncovered somatic inactivating mutations in BAP1 in 23% of MPM. The BAP1 nuclear deubiquitinase is known to target histones (together with ASXL1 as a Polycomb repressor subunit) and the HCF1 transcriptional co-factor, and we show that BAP1 knockdown in MPM cell lines affects E2F and Polycomb target genes. These findings implicate transcriptional deregulation in the pathogenesis of MPM. Genomic DNA was harvested from untreated malignant pleural mesothelioma (MPM) cell lines and used to generate gain/loss profiles for each line using aCGH.

2011-05-19 | E-GEOD-29383 | biostudies-arrayexpress

Mesothelioma tumor gene expression profiles

Project description:Malignant pleural mesotheliomas (MPMs) often show CDKN2A and NF2 inactivation but other highly recurrent mutations have not been described. To identify additional driver genes, we used an integrated genomic analysis of 53 MPM tumor samples to guide a focused sequencing effort that uncovered somatic inactivating mutations in BAP1 in 23% of MPM. The BAP1 nuclear deubiquitinase is known to target histones (together with ASXL1 as a Polycomb repressor subunit) and the HCF1 transcriptional co-factor, and we show that BAP1 knockdown in MPM cell lines affects E2F and Polycomb target genes. These findings implicate transcriptional deregulation in the pathogenesis of MPM. Total RNA from 53 pleural mesothelioma tumors was extracted and hybridized to Affymetrix gene expression arrays to compile a set of gene expression profiling data for this disease.

2011-05-19 | E-GEOD-29354 | biostudies-arrayexpress

Mesothelioma tumor aCGH profiles

Project description:Malignant pleural mesotheliomas (MPMs) often show CDKN2A and NF2 inactivation but other highly recurrent mutations have not been described. To identify additional driver genes, we used an integrated genomic analysis of 53 MPM tumor samples to guide a focused sequencing effort that uncovered somatic inactivating mutations in BAP1 in 23% of MPM. The BAP1 nuclear deubiquitinase is known to target histones (together with ASXL1 as a Polycomb repressor subunit) and the HCF1 transcriptional co-factor, and we show that BAP1 knockdown in MPM cell lines affects E2F and Polycomb target genes. These findings implicate transcriptional deregulation in the pathogenesis of MPM. DNA from 53 malignant pleural mesothelioma tumors was collected and hybridized to aCGH arrays. Data were analyzed to create gain and loss profiles for each tumor. This submission includes gcNormalized-data.

2011-09-25 | E-GEOD-29902 | biostudies-arrayexpress

Two distinct functional axes of positive feedback-enforced PRC2 recruitment in mouse embryonic stem cells

Project description:Polycomb Repressive Complex 2 (PRC2) plays an essential role in development by catalysing trimethylation of histone H3 lysine 27 (H3K27me3), resulting in gene repression. PRC2 consists of two sub-complexes, PRC2.1 and PRC2.2, in which the PRC2 core associates with distinct ancillary subunits such as MTF2 and JARID2, respectively. Both MTF2, present in PRC2.1, and JARID2, present in PRC2.2, play a role in core PRC2 recruitment to target genes in mouse embryonic stem cells (mESCs). However, it remains unclear how these distinct sub-complexes cooperate to establish H3K27me3 domains. Here, we combine a range of Polycomb mutant mESCs with chemical inhibition of PRC2 catalytic activity, to systematically dissect their relative contributions to PRC2 binding to target loci. We find that PRC2.1 and PRC2.2 mediate two distinct paths for recruitment, with mutually reinforced binding. Part of the cross-talk between PRC2.1 and PRC2.2 occurs via their catalytic product H3K27me3, which is bound by the PRC2 core-subunit EED, thereby mediating a positive feedback. Strikingly, removal of either JARID2 or H3K27me3 only has a minor effect on PRC2 recruitment, whereas their combined ablation largely attenuates PRC2 recruitment. This strongly suggests an unexpected redundancy between JARID2 and EED-H3K27me3-mediated recruitment of PRC2. Furthermore, we demonstrate that all core PRC2 recruitment occurs through the combined action of MTF2-mediated recruitment of PRC2.1 to DNA and PRC1-mediated recruitment of JARID2-containing PRC2.2. Both axes of binding are supported by EED-H3K27me3 positive feedback, but to a different degree. Finally, we provide evidence that PRC1 and PRC2 mutually reinforce reciprocal binding. Together, these data disentangle the interdependent and cooperative interactions between Polycomb complexes that are important to establish Polycomb repression at target sites.

2020-08-07 | PXD014290 | Pride

Two distinct functional axes of positive feedback-enforced PRC2 recruitment in mouse embryonic stem cells

2021-09-22 | PXD020684 | Pride

Expression data of vrn2/- emf2/+ and wild-type ovules and seeds

Project description:Polycomb Group proteins belonging to the Polycomb Repressive Complex 2 (PRC2) repress seed coat development before fertilization. Removal of PRC2 function in the integuments initiates autonomous seed coat development. We used microarrays to identify those genes that are under PRC2 control and become derepressed in mutants deficient for the PRC2 genes VRN2 and EMF2. Since vrn2 emf2 double mutants have strong developmental aberrations, we used the mutant combination vrn2/- emf2/+ .

2016-11-15 | GSE85751 | GEO

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