H3K27 Trimethylation Research Articles

The SET domain protein PsKMT3 regulates histone H3K36 trimethylation and modulates effector gene expression in the soybean pathogen Phytophthora sojae.

Plant pathogens secrete effector proteins to overcome host immunity and promote colonization. In oomycete plant pathogens, the expression of many effector genes is altered upon infection; however, the regulatory mechanisms are unclear. In this study, we identified a su(var)3-9, enhancer of zeste, and trithorax (SET) domain protein-encoding gene, PsKMT3, that was highly induced at early infection stages in Phytophthora sojae. Deletion of PsKMT3 led to asexual development and pathogenicity defects. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and western blot analyses demonstrated that histone H3K36 trimethylation (H3K36me3) was significantly reduced genome-wide in mutants. RNA-seq analysis identified 374 genes encoding secreted proteins that were differentially expressed in pskmt3 at the mycelium stage. The significantly altered genes encompassed the RxLR (Arg-x-Lys-Arg) effector gene family, including the essential effector genes Avh23, Avh181, Avh240, and Avh241. Transcriptome analysis at early infection stages showed misregulation of effector gene expression waves in pskmt3. H3K36me3 was directly and indirectly associated with RxLR effector gene activation. Our results reveal a role of a SET domain protein in regulating effector gene expression and modulating histone methylation in P. sojae.

Optical nanoscopy approach to unveil chromatin alterations implicated in neuroblastoma transformation.

Chromatin organization is a well-orchestrated mechanism regulating cellular physiology and its changes are associated with the onset of many diseases, including cancer. Neuroblastoma (NB) is the most common extracranial tumor in childhood, and it shows remarkable heterogeneity in the phenotypes and evolutionary patterns. Although the molecular mechanisms of this heterogeneity are still unclear, the impairment of the “epigenetic machinery” and the consequent chromatin reorganization might play an important role. We aim to assess the possible alterations in chromatin nanoscale architecture correlated with NB transformation using NB cells genetically engineered to overexpress the non-coding RNA NDM29, which promotes differentiation of tumor cells into a neuronal lineage. In both malignant NB cells (Mock) and neuron-like cells (S1.1), we explored chromatin organization and nuclear architecture by optical nanoscale microscopy using both confocal and stimulation emission depletion (STED) imaging methods, in parallel with molecular biology analyses. We characterized the nuclear 3D morphology of Mock vs. S1.1 cells by measuring volume, shape, and circularity of the nuclei as well as chromatin compaction and distribution. We imaged the immunolabeled histone H3 modifications (H3K9 trimethylation and H3K9 acetylation) to characterize chromatin regions typically associated with highly and poorly condensed chromatin, respectively. In parallel, we quantified the global DNA methylation status by measuring the levels of 5-methylcytosine (5-mC) using the enzyme-linked immunosorbent assay (ELISA) MethylFlash Global DNA. Comparing Mock vs. S1.1 cells, we observed (i) significant remodeling of nuclear morphometry; (ii) marked rearrangement of chromatin domains rich in highly-acetylated and -methylated H3K9; (iii) changes in average chromatin compaction and DNA methylation. Altogether, the results point to an involvement of epigenetic mechanisms which may sustain the chromatin remodeling during NB malignant transformation, paving the way towards new prognostic and therapeutic approaches and understanding chromatin remodeling in physiological/pathological processes.

Genistein induces endocrine resistance in human breast cancer by suppressing H3K27 trimethylation.

Genistein (GE), the most important phytoestrogen in diet, is known to behave as a partial agonist of estrogen receptor α and shows a proliferative effect on the growth of breast cancer cell lines. Recent research has reported that long-term consumption of low doses of GE results in hormone-independent growth phenotypes of MCF-7 tumors, with increased HER2. Overexpression of HER2 has been associated with endocrine resistance in human breast cancer, but whether long-term low-level GE-induced HER2 expression is the cause of endocrine resistance remains to be determined. Short-term and long-term treatments with GE may have different effects on HER2 expression. We found that low doses of GE had estrogen-like effects and inhibited HER2 expression after short-term exposure in estrogen receptor-positive breast cancers cells. However, in contrast to short-term exposure, long-term exposure induced an increase in HER2 expression, which led to endocrine resistance. During long-term low-level exposure, the continuous activation of ERK1/2-phosphorylated EZH2 at Ser21 resulted in a decrease of lysine 27 trimethylation. As H3K27me3 levels decreased, the expression of interleukin-6 (IL-6) and IL-8 increased, and HER2 levels gradually increased, forming a feedback loop of ERK1/2/EZH2/IL-6 and IL-8/HER2. We identified a novel pathway by which EZH2 phosphorylation contributed to long-term low-level GE-induced HER2 overexpression and provided new insight for long-term low-level GE-induced acquired endocrine resistance. For breast cancer patients, long-term low-level use of soy supplements has potential health risks, and monitoring dietary exposure to GE is advisable when patients are treated with tamoxifen.

WDR5 represents a therapeutically exploitable target for cancer stem cells in glioblastoma.

Glioblastomas (GBMs) are heterogeneous, treatment-resistant tumors driven by populations of cancer stem cells (CSCs). However, few molecular mechanisms critical for CSC population maintenance have been exploited for therapeutic development. We developed a spatially resolved loss-of-function screen in GBM patient-derived organoids to identify essential epigenetic regulators in the SOX2-enriched, therapy-resistant niche and identified WDR5 as indispensable for this population. WDR5 is a component of the WRAD complex, which promotes SET1 family-mediated Lys4 methylation of histone H3 (H3K4me), associated with positive regulation of transcription. In GBM CSCs, WDR5 inhibitors blocked WRAD complex assembly and reduced H3K4 trimethylation and expression of genes involved in CSC-relevant oncogenic pathways. H3K4me3 peaks lost with WDR5 inhibitor treatment occurred disproportionally on POU transcription factor motifs, including the POU5F1(OCT4)::SOX2 motif. Use of a SOX2/OCT4 reporter demonstrated that WDR5 inhibitor treatment diminished cells with high reporter activity. Furthermore, WDR5 inhibitor treatment and WDR5 knockdown altered the stem cell state, disrupting CSC in vitro growth and self-renewal, as well as in vivo tumor growth. These findings highlight the role of WDR5 and the WRAD complex in maintaining the CSC state and provide a rationale for therapeutic development of WDR5 inhibitors for GBM and other advanced cancers.

Epigenetic modification of CSDE1 locus dictates immune recognition of nascent tumorigenic cells.

Weak immunogenicity of tumor cells is a root cause for the ultimate failure of immunosurveillance and immunotherapy. Although tumor evolution can be shaped by immunoediting toward a less immunogenic phenotype, mechanisms governing the initial immunogenicity of primordial tumor cells or original cancer stem cells remain obscure. Here, using a single tumor-repopulating cell (TRC) to form tumors in immunodeficient or immunocompetent mice, we demonstrated that immunogenic heterogeneity is an inherent trait of tumorigenic cells defined by the activation status of signal transducer and activator of transcription 1 (STAT1) protein in the absence of immune pressure. Subsequent investigation identified that the RNA binding protein cold shock domain-containing protein E1 (CSDE1) can promote STAT1 dephosphorylation by stabilizing T cell protein tyrosine phosphatase (TCPTP). A methyltransferase SET and MYN domain-containing 3 (SMYD3) was further identified to mediate H3K4 trimethylation of CSDE1 locus, which was under the regulation of mechanotransduction by cell-matrix and cell-cell contacts. Thus, owing to the differential epigenetic modification and subsequent differential expression of CSDE1, nascent tumorigenic cells may exhibit either a high or low immunogenicity. This identified SMYD3-CSDE1 pathway represents a potential prognostic marker for cancer immunotherapy effectiveness that requires further investigation.

A truncated and catalytically inactive isoform of KDM5B histone demethylase accumulates in breast cancer cells and regulates H3K4 tri-methylation and gene expression

KDM5B histone demethylase is overexpressed in many cancers and plays an ambivalent role in oncogenesis, depending on the specific context. This ambivalence could be explained by the expression of KDM5B protein isoforms with diverse functional roles, which could be present at different levels in various cancer cell lines. We show here that one of these isoforms, namely KDM5B-NTT, accumulates in breast cancer cell lines due to remarkable protein stability relative to the canonical PLU-1 isoform, which shows a much faster turnover. This isoform is the truncated and catalytically inactive product of an mRNA with a transcription start site downstream of the PLU-1 isoform, and the consequent usage of an alternative ATG for translation initiation. It also differs from the PLU-1 transcript in the inclusion of an additional exon (exon-6), previously attributed to other putative isoforms. Overexpression of this isoform in MCF7 cells leads to an increase in bulk H3K4 methylation and induces derepression of a gene cluster, including the tumor suppressor Cav1 and several genes involved in the interferon-alpha and -gamma response. We discuss the relevance of this finding considering the hypothesis that KDM5B may possess regulatory roles independent of its catalytic activity.

Inhibition of EZH2 Causes Retrotransposon Derepression and Immune Activation in Porcine Lung Alveolar Macrophages.

Alveolar macrophages (AMs) form the first defense line against various respiratory pathogens, and their immune response has a profound impact on the outcome of respiratory infection. Enhancer of zeste homolog 2 (EZH2), which catalyzes the trimethylation of H3K27 for epigenetic repression, has gained increasing attention for its immune regulation function, yet its exact function in AMs remains largely obscure. Using porcine 3D4/21 AM cells as a model, we characterized the transcriptomic and epigenomic alterations after the inhibition of EZH2. We found that the inhibition of EZH2 causes transcriptional activation of numerous immune genes and inhibits the subsequent infection by influenza A virus. Interestingly, specific families of transposable elements, particularly endogenous retrovirus elements (ERVs) and LINEs which belong to retrotransposons, also become derepressed. While some of the derepressed ERV families are pig-specific, a few ancestral families are known to be under EZH2-mediated repression in humans. Given that derepression of ERVs can promote innate immune activation through "viral mimicry", we speculate that ERVs may also contribute to the coinciding immune activation in AMs after the inhibition of EZH2. Overall, this study improves the understanding of the EZH2-related immune regulation in AMs and provides novel insights into the epigenetic regulation of retrotransposons in pigs.

Combination Treatment of a Phytochemical and a Histone Demethylase Inhibitor-A Novel Approach towards Targeting TGFβ-Induced EMT, Invasion, and Migration in Prostate Cancer.

Minimizing side effects, overcoming cancer drug resistance, and preventing metastasis of cancer cells are of growing interest in current cancer therapeutics. Phytochemicals are being researched in depth as they are protective to normal cells and have fewer side effects. Hesperetin is a citrus bioflavonoid known to inhibit TGFβ-induced epithelial-to-mesenchymal transition (EMT), migration, and invasion of prostate cancer cells. Targeting epigenetic modifications that cause cancer is another class of upcoming therapeutics, as these changes are reversible. Global H3K27me3 levels have been found to be reduced in invasive prostate adenocarcinomas. Combining a demethylase inhibitor and a known anti-cancer phytochemical is a unique approach to targeting cancer to attain the aforementioned objectives. In the current study, we used an H3K27 demethylase (JMJD3/KDM6B) inhibitor to study its effects on TGFβ-induced EMT in prostate cancer cells. We then gave a combined hesperetin and GSK-J4 treatment to the PC-3 and LNCaP cells. There was a dose-dependent increase in cytotoxicity and inhibition of TGFβ-induced migration and invasion of prostate cancer cells after GSK-J4 treatment. GSK-J4 not only induced trimethylation of H3K27 but also induced the trimethylation of H3K4. Surprisingly, there was a reduction in the H3K9me3 levels. GSK-J4 alone and a combination of hesperetin and GSK-J4 treatment effectively inhibit the important hallmarks of cancer, such as cell proliferation, migration, and invasion, by altering the epigenetic landscape of cancer cells.

Montelukast Increased IL-25, IL-33, and TSLP via Epigenetic Regulation in Airway Epithelial Cells.

The epithelium-derived cytokines interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP) are important mediators that initiate innate type 2 immune responses in asthma. Leukotriene receptor antagonists (LTRAs) are commonly used to prevent asthma exacerbations. However, the effects of LTRAs on epithelium-derived cytokines expression in airway epithelial cells are unclear. This study aimed to investigate the effects of LTRAs on the expression of epithelium-derived cytokines in human airway epithelial cells and to explore possible underlying intracellular processes, including epigenetic regulation. A549 or HBE cells in air-liquid interface conditions were pretreated with different concentrations of LTRAs. The expression of epithelium-derived cytokines and intracellular signaling were investigated by real-time PCR, enzyme-linked immunosorbent assay, and Western blot. In addition, epigenetic regulation was investigated using chromatin immunoprecipitation analysis. The expression of IL-25, IL-33, and TSLP was increased under LTRAs treatment and suppressed by inhaled corticosteroid cotreatment. Montelukast-induced IL-25, IL-33, and TSLP expression were mediated by the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways and regulated by histone H3 acetylation and H3K36 and H3K79 trimethylation. LTRAs alone might increase inflammation and exacerbate asthma by inducing the production of IL-25, IL-33, and TSLP; therefore, LTRA monotherapy may not be an appropriate therapeutic option for asthma.

An antisteatosis response regulated by oleic acid through lipid droplet-mediated ERAD enhancement.

Although excessive lipid accumulation is a hallmark of obesity-related pathologies, some lipids are beneficial. Oleic acid (OA), the most abundant monounsaturated fatty acid (FA), promotes health and longevity. Here, we show that OA benefits Caenorhabditis elegans by activating the endoplasmic reticulum (ER)-resident transcription factor SKN-1A (Nrf1/NFE2L1) in a lipid homeostasis response. SKN-1A/Nrf1 is cleared from the ER by the ER-associated degradation (ERAD) machinery and stabilized when proteasome activity is low and canonically maintains proteasome homeostasis. Unexpectedly, OA increases nuclear SKN-1A levels independently of proteasome activity, through lipid droplet-dependent enhancement of ERAD. In turn, SKN-1A reduces steatosis by reshaping the lipid metabolism transcriptome and mediates longevity from OA provided through endogenous accumulation, reduced H3K4 trimethylation, or dietary supplementation. Our findings reveal an unexpected mechanism of FA signal transduction, as well as a lipid homeostasis pathway that provides strategies for opposing steatosis and aging, and may mediate some benefits of the OA-rich Mediterranean diet.

Genomic Patterns of Malignant Peripheral Nerve Sheath Tumor (MPNST) Evolution Correlate with Clinical Outcome and Are Detectable in Cell-Free DNA.

MPNST is the most common cause of death and morbidity for individuals with NF1, a relatively common tumor predisposition syndrome. Our results suggest that somatic copy-number and methylation profiling of tumor or cfDNA could serve as a biomarker for early diagnosis and to stratify patients into prognostic and treatment-related subgroups. This article is highlighted in the In This Issue feature, p. 517.

Expression of EZH2 and H3K27me3 predicts tumor biology of urothelial carcinoma.

Enhancer of zeste homolog 2 (EZH2) is one of the major epigenetic modifiers involved in the transcriptional repression of target genes through trimethylation of H3K27 (lysine 27 residue of histone H3). Deregulated expression of both EZH2 and H3K27me3 has been implicated in the biological behavior and prognostic outcome of various malignancies. To assess the role of EZH2 and H3K27me3 in the carcinogenesis of urothelial carcinoma of urinary bladder. One hundred fifty consecutive urothelial carcinoma cases of urinary bladder (54.7% high-grade) were included in this study. Immunohistochemical analysis for EZH2 and H3K27me3 was performed on whole tissue sections. A multiplication score obtained by multiplying staining intensity and proportion of positively stained neoplastic cells was used for assessment. EZH2 showed a significant correlation with the tumor grade and lamina propria invasion (p < 0.001). The cases with high EZH2 expression showed a significantly high proliferative index (Mean- 32.7%; p < 0.001). In contrast, negative and low expression of H3K27me3 was significantly more common in high-grade cases (p = 0.006). The expression of H3K27me3 was significantly associated with lamina propria (p = 0.01) and deep muscle invasion (p = 0.007). EZH2 showed a significantly higher expression in the high-grade invasive areas as compared to the high-grade non-invasive areas of the same tumor (p = 0.03). This study establishes an important role of the key epigenetic regulators EZH2 and H3K27me3 in the pathobiology of urothelial carcinomas. Strong expression of EZH2 and weak expression of H3K27me3 are associated with higher grade, proliferative index and invasive behavior.

Genomic markers of recurrence risk in atypical meningioma following gross total resection.

Meningiomas are the most common primary central nervous system (CNS) tumor in adults and CNS World Health Organization grade 2 (atypical) meningiomas show an intermediate risk of recurrence/progression. Molecular parameters are needed to better inform management following gross total resection (GTR). We performed comprehensive genomic analysis of tumor tissue from 63 patients who underwent radiologically confirmed GTR of a primary grade 2 meningioma, including a CLIA-certified target next-generation sequencing panel (n = 61), chromosomal microarray (n = 63), genome-wide methylation profiling (n = 62), H3K27me3 immunohistochemistry (n = 62), and RNA-sequencing (n = 19). Genomic features were correlated with long-term clinical outcomes (median follow-up: 10 years) using Cox proportional hazards regression modeling and published molecular prognostic signatures were evaluated. The presence of specific copy number variants (CNVs), including -1p, -10q, -7p, and -4p, was the strongest predictor of decreased recurrence-free survival (RFS) within our cohort (P < .05). NF2 mutations were frequent (51%) but did not show a significant association with RFS. DNA methylation-based classification assigned tumors to DKFZ Heidelberg benign (52%) or intermediate (47%) meningioma subclasses and was not associated with RFS. H3K27 trimethylation (H3K27me3) was unequivocally lost in 4 tumors, insufficient for RFS analysis. Application of published integrated histologic/molecular grading systems did not improve prediction of recurrence risk over the presence of -1p or -10q alone. CNVs are strong predictors of RFS in grade 2 meningiomas following GTR. Our study supports incorporation of CNV profiling into clinical evaluation to better guide postoperative patient management, which can be readily implemented using existing, clinically validated technologies.

EZH inhibitors in lymphoma therapy

Enhancer of zeste homolog (EZH), a subunit of polycomb repressive complex 2 (PRC2), suppresses gene expression by methylation of H3K27. EZH is closely associated with B-cell development and pathogenesis of certain malignant lymphomas. In follicular lymphoma (FL), gain-of-function mutation and upregulation of EZH2 are observed in approximately 30% and 15% of cases, respectively. Moreover, one-third of diffuse large B-cell lymphomas carry an EZH2 mutation, mostly co-existing with translocation involving Bcl-2. Genome-wide trimethylation of H3K27 is a unique characteristic induced by upregulation of both EZH2 and EZH1, and is responsible for more than half of the gene suppression that occurs in adult T-cell leukemia/lymphoma (ATL). Inhibition of EZH can reduce H3K27 methylation and subsequently restore epigenetically suppressed genes. Currently, an EZH2 inhibitor and dual EZH1/2 inhibitor have been clinically used to treat relapsed/refractory FL and ATL, respectively. EZH-targeted treatment for lymphoma has only just begun, and further development of these drugs for various other malignancies, both alone and in combination with other therapeutics, is ongoing.

DPY30 Promotes Proliferation and Cell Cycle Progression of Colorectal Cancer Cells via Mediating H3K4 Trimethylation.

DPY30, a core subunit of the SET1/MLL histone H3K4 methyltransferase complexes, plays an important role in diverse biological functions through the epigenetic regulation of gene transcription, especially in cancer development. However, its involvement in human colorectal carcinoma (CRC) has not been elucidated yet. Here we demonstrated that DPY30 was overexpressed in CRC tissues, and significantly associated with pathological grading, tumor size, TNM stage, and tumor location. Furthermore, DPY30 knockdown remarkably suppressed the CRC cell proliferation through downregulation of PCNA and Ki67 in vitro and in vivo, simultaneously induced cell cycle arrest at S phase by downregulating Cyclin A2. In the mechanistic study, RNA-Seq analysis revealed that enriched gene ontology of cell proliferation and cell growth was significantly affected. And ChIP result indicated that DPY30 knockdown inhibited H3 lysine 4 trimethylation (H3K4me3) and attenuated interactions between H3K4me3 with PCNA, Ki67 and cyclin A2 respectively, which led to the decrease of H3K4me3 establishment on their promoter regions. Taken together, our results demonstrate overexpression of DPY30 promotes CRC cell proliferation and cell cycle progression by facilitating the transcription of PCNA, Ki67 and cyclin A2 via mediating H3K4me3. It suggests that DPY30 may serve as a potential therapeutic molecular target for CRC.

TRIM28 secures skeletal stem cell fate during skeletogenesis by silencing neural gene expression and repressing GREM1/AKT/mTOR signaling axis

Long bones are generated by mesoderm-derived skeletal progenitor/stem cells (SSCs) through endochondral ossification, a process of sequential chondrogenic and osteogenic differentiation tightly controlled by the synergy between intrinsic and microenvironment cues. Here, we report that loss of TRIM28, a transcriptional corepressor, in mesoderm-derived cells expands the SSC pool, weakens SSC osteochondrogenic potential, and endows SSCs with properties of ectoderm-derived neural crest cells (NCCs), leading to severe defects of skeletogenesis. TRIM28 preferentially enhances H3K9 trimethylation and DNA methylation on chromatin regions more accessible in NCCs; loss of this silencing upregulates neural gene expression and enhances neurogenic potential. Moreover, TRIM28 loss causes hyperexpression of GREM1, which is an extracellular signaling factor promoting SSC self-renewal and SSC neurogenic potential by activating AKT/mTORC1 signaling. Our results suggest that TRIM28-mediated chromatin silencing establishes a barrier for maintaining the SSC lineage trajectory and preventing a transition to ectodermal fate by regulating both intrinsic and microenvironment cues.

Regulation of telomere silencing by the core histones-autophagy-Sir2 axis.

Telomeres contain compacted heterochromatin, and genes adjacent to telomeres are subjected to transcription silencing. Maintaining telomere structure integrity and transcription silencing is important to prevent the occurrence of premature aging and aging-related diseases. How telomere silencing is regulated during aging is not well understood. Here, we find that the four core histones are reduced during yeast chronological aging, leading to compromised telomere silencing. Mechanistically, histone loss promotes the nuclear export of Sir2 and its degradation by autophagy. Meanwhile, reducing core histones enhances the autophagy pathway, which further accelerates autophagy-mediated Sir2 degradation. By screening the histone mutant library, we identify eight histone mutants and one histone modification (histone methyltransferase Set1-catalyzed H3K4 trimethylation) that regulate telomere silencing by modulating the core histones-autophagy-Sir2 axis. Overall, our findings reveal core histones and autophagy as causes of aging-coupled loss of telomere silencing and shed light on dynamic regulation of telomere structure during aging.

Structure-Based Design of the Indole-Substituted Triazolopyrimidines as New EED-H3K27me3 Inhibitors for the Treatment of Lymphoma.

Interrupting the embryonic ectoderm development (EED)-H3K27me3 interaction represents a promising strategy to allosterically inhibit polycomb repressive complex 2 (PRC2) for cancer therapy. In this work, we report the structure-based design of new triazolopyrimidine-based EED inhibitors, which structurally feature the electron-rich indole ring at the C8 position. Particularly, ZJH-16 directly binds to EED (HTRF IC50 = 2.72 nM, BLI KD = 4.4 nM) and potently inhibits the growth of KARPAS422 and Pfeiffer cells. In both cells, ZJH-16 is selectively engaged with EED and reduces H3K27 trimethylation levels. ZJH-16 inhibits the gene silencing function of PRC2 in KARPAS422 cells. ZJH-16 possesses favorable pharmacokinetic (PK) profiles with an excellent oral bioavailability (F = 94.7%). More importantly, ZJH-16 shows robust tumor regression in the KARPAS422 xenograft model after oral administration with the tumor growth inhibition reaching nearly 100%. The robust antitumor efficacy and favorable PK profiles of ZJH-16 warrant further advanced preclinical development for lymphoma treatment.

HP1 proteins regulate nucleolar structure and function by secluding pericentromeric constitutive heterochromatin.

Nucleoli are nuclear compartments regulating ribosome biogenesis and cell growth. In embryonic stem cells (ESCs), nucleoli containing transcriptionally active ribosomal genes are spatially separated from pericentromeric satellite repeat sequences packaged in largely repressed constitutive heterochromatin (PCH). To date, mechanisms underlying such nuclear partitioning and the physiological relevance thereof are unknown. Here we show that repressive chromatin at PCH ensures structural integrity and function of nucleoli during cell cycle progression. Loss of heterochromatin proteins HP1α and HP1β causes deformation of PCH, with reduced H3K9 trimethylation (H3K9me3) and HP1γ levels, absence of H4K20me3 and upregulated major satellites expression. Spatially, derepressed PCH aberrantly associates with nucleoli accumulating severe morphological defects during S/G2 cell cycle progression. Hp1α/β deficiency reduces cell proliferation, ribosomal RNA biosynthesis and mobility of Nucleophosmin, a major nucleolar component. Nucleolar integrity and function require HP1α/β proteins to be recruited to H3K9me3-marked PCH and their ability to dimerize. Correspondingly, ESCs deficient for both Suv39h1/2 H3K9 HMTs display similar nucleolar defects. In contrast, Suv4-20h1/2 mutant ESCs lacking H4K20me3 at PCH do not. Suv39h1/2 and Hp1α/β deficiency-induced nucleolar defects are reminiscent of those defining human ribosomopathy disorders. Our results reveal a novel role for SUV39H/HP1-marked repressive constitutive heterochromatin in regulating integrity, function and physiology of nucleoli.

Long noncoding RNA MEG3 inhibits oral squamous cell carcinoma progression via GATA3.

Oral squamous cell carcinoma (OSCC) accounts for about 90% of oral cancers. Expression of the long noncoding RNA (lncRNA) maternally expressed 3 (MEG3) has previously been reported to be downregulated in OSCC, and its overexpression can inhibit proliferation, migration, and invasion and promote apoptosis of OSCC cells. However, the mechanism underlying MEG3 downregulation in OSCC has not been well characterized. Here we report that low expression of MEG3 is caused by H3K27me3 modification of the MEG3 gene locus, and this is associated with the poor prognosis of OSCC. Overexpression of MEG3 inhibited the proliferation and invasion of OSCC cells. We observed that MEG3 was modified by m6A and bound to YTHDC1. Enhancer-controlled genes positively regulated by MEG3 were functionally enriched for the 'negative regulation of Wnt signaling pathway' term, as determined using metascape. GATA3 was predicted to be a transcription factor for these genes, and was demonstrated to bind to MEG3. Knockdown of GATA3 countered the effects on proliferation, invasion, and increased transcription of HIC1 and PRICKLE1 induced by MEG3 overexpression. In conclusion, our data suggest that MEG3 is downregulated in OSCC due to trimethylation of H3K27 at the MEG3 gene locus. The inhibitory effect of MEG3 on proliferation and invasion of OSCC cells was dependent on the binding of GATA3.