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Inhibiting EZH2 Targets Atypical Teratoid Rhabdoid Tumor by Triggering Viral Mimicry via Both RNA and DNA Sensing Pathways [CUT&RUN]

ABSTRACT: Loss of function mutations in SMARCB1 are prevalent in pediatric atypical teratoid rhabdoid tumors (ATRTs) and confer an oncogenic dependency on EZH2, providing a compelling rationale for treating these genetically defined cancers via EZH2 inhibition (EZH2i). EZH2i results in tumor regression in SMARCB1-deficient tumors in preclinical studies, but the molecular mechanism has not been fully elucidated. Here we found that the sensitivity of SMARCB1-deficient tumors to EZH2i is associated with the viral mimicry response that depends on both double-stranded RNA (dsRNA) and cytoplasmic DNA sensing pathways. Unlike other epigenetic therapies targeting transcriptional repressors, viral mimicry by EZH2i in SMARCB1-deficient tumors is not triggered by crypt initiation of endogenous retroelements, but rather mediated by increased expression of genes enriched for intronic inverted-repeat Alu (IR-Alu) elements. Interestingly, we found that interferon-stimulated genes (ISGs) are highly enriched for dsRNA-forming intronic IR-Alu elements, suggesting a positive feedback loop whereby interferon response leads to dsRNA formation from intronic ISGs and activation of viral mimicry. Moreover, EZH2i in ATRT cells also enhances the expression of full-length LINE-1 elements, leading to genomic instability and cGAS/STING response in a process dependent on reverse transcriptase activity. Supporting this mechanism, co-depletion of dsRNA sensing and cytoplasmic DNA sensing completely rescues the viral mimicry response to EZH2i in SMARCB1-deficient tumors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE213248 | GEO | 2024/09/05

REPOSITORIES: GEO

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Inhibiting EZH2 Targets Atypical Teratoid Rhabdoid Tumor by Triggering Viral Mimicry via Both RNA and DNA Sensing Pathways [RNA-Seq]

Project description:Loss of function mutations in SMARCB1 are prevalent in pediatric atypical teratoid rhabdoid tumors (ATRTs) and confer an oncogenic dependency on EZH2, providing a compelling rationale for treating these genetically defined cancers via EZH2 inhibition (EZH2i). EZH2i results in tumor regression in SMARCB1-deficient tumors in preclinical studies, but the molecular mechanism has not been fully elucidated. Here we found that the sensitivity of SMARCB1-deficient tumors to EZH2i is associated with the viral mimicry response that depends on both double-stranded RNA (dsRNA) and cytoplasmic DNA sensing pathways. Unlike other epigenetic therapies targeting transcriptional repressors, viral mimicry by EZH2i in SMARCB1-deficient tumors is not triggered by crypt initiation of endogenous retroelements, but rather mediated by increased expression of genes enriched for intronic inverted-repeat Alu (IR-Alu) elements. Interestingly, we found that interferon-stimulated genes (ISGs) are highly enriched for dsRNA-forming intronic IR-Alu elements, suggesting a positive feedback loop whereby interferon response leads to dsRNA formation from intronic ISGs and activation of viral mimicry. Moreover, EZH2i in ATRT cells also enhances the expression of full-length LINE-1 elements, leading to genomic instability and cGAS/STING response in a process dependent on reverse transcriptase activity. Supporting this mechanism, co-depletion of dsRNA sensing and cytoplasmic DNA sensing completely rescues the viral mimicry response to EZH2i in SMARCB1-deficient tumors.

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Targeting DHX9 triggers interferon response and replication stress in Small Cell Lung Cancer [RIP-Seq II]

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Targeting DHX9 triggers interferon response and replication stress in Small Cell Lung Cancer [RIP-seq I]

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Project description:Aberrant activation of innate immune receptors can cause a spectrum of immune disorders, such as Aicardi-Goutières syndrome (AGS). One such receptor is MDA5, a viral double-stranded RNA (dsRNA) sensor that induces antiviral immune response. We here demonstrate that constitutive activation of MDA5 in AGS results from the loss of tolerance to cellular dsRNAs formed by Alu retroelements. While wild-type MDA5 cannot efficiently recognize Alu-dsRNA because its filament formation on dsRNA is impaired by the imperfect duplex structure, AGS-variants of MDA5 display reduced sensitivity to duplex structural irregularities, assembling signaling-competent filaments on Alu-dsRNA. Moreover, we identified an unexpected role of RNA-rich cellular environment in suppressing aberrant MDA5 oligomerization, highlighting context-dependence of self vs. non-self discrimination. Overall, our work demonstrates that the increased efficiency of MDA5 to recognize dsRNA comes at a cost of self-recognition, and implicates a unique role of Alu RNAs as virus-like elements that shape the primate immune system.

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Select EZH2 inhibitors enhance the viral mimicry effects of DNMT inhibition through a mechanism involving Calcium-Calcineurin-NFAT signaling [EM-seq]

Project description:DNA methyltransferase inhibitors (DNMTi) are FDA-approved for various hematological malignancies but have limited efficacy in solid tumors. DNA hypomethylation with these drugs is associated with elevated lysine 27 tri-methylation on histone H3 (H3K27me3). We hypothesized that this EZH2-dependent repressive mark limits the full potential of DNMTi. Here, we show in cell line and tumoroid models of colorectal cancer, that low-dose DNMTi sensitizes cells to selective EZH2 inhibitors (EZH2i) that have limited single agent toxicity, and that EZH2i enhances DNMTi-driven molecular and therapeutic effects. Through integrative epigenomic analyses, we reveal that DNMTi induces H3K27me3 accumulation at genomic regions poised with EZH2. Unexpectedly, combined treatment alters the epigenome landscape to promote transcriptional upregulation of the Calcium-Calcineurin-NFAT signaling pathway. Blocking this pathway limits the transcriptional activating effects of the drug combination, including expression of transposable elements and innate immune response genes within a viral defense pathway. Consistently, we demonstrate positive correlations between DNMTi- and viral infection-associated transcription profiles and Calcium signal activation in colon cancer patient samples. Collectively, our study demonstrates that compensatory EZH2 activity following DNA hypomethylation presents a barrier to the therapeutic action of DNMTi in colon cancer, reveals a new application of EZH2i beyond cancers associated with PRC2 hyperactivity, and links Calcium-Calcineurin-NFAT signaling to epigenetic therapy-induced viral mimicry.

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