Polycomb Repressive Complex Research Articles

H3K27 dimethylation dynamics reveal stepwise establishment of facultative heterochromatin in early mouse embryos.

Facultative heterochromatin is formed by Polycomb repressive complex 2 (PRC2)-deposited H3K27 trimethylation (H3K27me3) and PRC1-deposited H2AK119 mono-ubiquitylation (H2AK119ub1). How it is newly established after fertilization remains unclear. To delineate the establishment kinetics, here we profiled the temporal dynamics of H3K27 dimethylation (H3K27me2), which represents the de novo PRC2 catalysis, in mouse preimplantation embryos. H3K27me2 is newly deposited at CpG islands (CGIs), the paternal X chromosome (Xp) and putative enhancers during the eight-cell-to-morula transition, all of which follow H2AK119ub1 deposition. We found that JARID2, a PRC2.2-specific accessory protein possessing an H2AK119ub1-binding ability, colocalizes with SUZ12 at CGIs and Xp in morula embryos. Upon JARID2 depletion, SUZ12 chromatin binding and H3K27me2 deposition were attenuated and H3K27 acetylation at putative enhancers was increased in morulae and subsequently H3K27me3 failed to be deposited in blastocysts. These data reveal that facultative heterochromatin is established by PRC2.2-driven stepwise H3K27 methylation along pre-deposited H2AK119ub1 during early embryogenesis.

DNA methylation shapes the Polycomb landscape during the exit from naive pluripotency.

In mammals, 5-methylcytosine (5mC) and Polycomb repressive complex 2 (PRC2)-deposited histone 3 lysine 27 trimethylation (H3K27me3) are generally mutually exclusive at CpG-rich regions. As mouse embryonic stem cells exit the naive pluripotent state, there is massive gain of 5mC concomitantly with restriction of broad H3K27me3 to 5mC-free, CpG-rich regions. To formally assess how 5mC shapes the H3K27me3 landscape, we profiled the epigenome of naive and differentiated cells in the presence and absence of the DNA methylation machinery. Surprisingly, we found that 5mC accumulation is not required to restrict most H3K27me3 domains. Instead, this 5mC-independent H3K27me3 restriction is mediated by aberrant expression of the PRC2 antagonist Ezhip (encoding EZH inhibitory protein). At the subset of regions where 5mC appears to genuinely supplant H3K27me3, we identified 163 candidate genes that appeared to require 5mC deposition and/or H3K27me3 depletion for their activation in differentiated cells. Using site-directed epigenome editing to directly modulate 5mC levels, we demonstrated that 5mC deposition is sufficient to antagonize H3K27me3 deposition and confer gene activation at individual candidates. Altogether, we systematically measured the antagonistic interplay between 5mC and H3K27me3 in a system that recapitulates early embryonic dynamics. Our results suggest that H3K27me3 restraint depends on 5mC, both directly and indirectly. Our study also implies a noncanonical role of 5mC in gene activation, which may be important not only for normal development but also for cancer progression, as oncogenic cells frequently exhibit dynamic replacement of 5mC for H3K27me3 and vice versa.

GTSF1 is required for transposon silencing in the unicellular eukaryote Paramecium tetraurelia.

The PIWI-interacting RNA (piRNA) pathway is crucial for transposon repression and the maintenance of genomic integrity. Gametocyte-specific factor 1 (GTSF1), a PIWI-associated protein indispensable for transposon repression, has been recently shown to potentiate the catalytic activity of PIWI in many metazoans. Whether the requirement of GTSF1 extends to PIWI proteins beyond metazoans is unknown. In this study, we identified a homolog of GTSF1 in the unicellular eukaryote Paramecium tetraurelia (PtGtsf1) and found that its role as a PIWI-cofactor is conserved. PtGtsf1 interacts with PIWI (Ptiwi09) and Polycomb Repressive Complex 2 and is essential for PIWI-dependent DNA elimination of transposons during sexual development. PtGtsf1 is crucial for the degradation of PIWI-bound small RNAs that recognize the organism's own genomic sequences. Without PtGtsf1, self-matching small RNAs are not degraded and results in an accumulation of H3K9me3 and H3K27me3, which may disturb transposon recognition. Our results demonstrate that the PIWI-GTSF1 interaction also exists in unicellular eukaryotes with a role in transposon silencing.

EMBRYONIC FLOWER 1 regulates male reproduction by repressing the jasmonate pathway downstream transcription factor MYB26.

The evolutionarily conserved Polycomb repressive complexes (PRC) mediate genome-wide transcriptional silencing and regulate a plethora of development, as well as environmental responses in multicellular organisms. The PRC2-catalyzed trimethylation of lysine 27 on histone H3 (H3K27me3) is recognized by reader-effector modules of PRC1 to implement gene repression. Here, we report that the Arabidopsis (Arabidopsis thaliana) H3K27me3 effector EMBRYONIC FLOWER 1 (EMF1) interacts with and constrains the R2R3 DNA binding transcription factor MYB26 by a eudicot-conserved motif in the stamen. MYB26 activates the transcription of two NAC domain genes, NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) and NST2, whose encoded proteins mediate anther secondary cell thickening in jasmonate (JA)-regulated stamen maturation. In this process, the transcriptional activity of MYB26 is negatively modulated by the JAZ-PRC repressive complex to precisely regulate the expression of NST1 and NST2. Disruption of EMF1 repression stimulates MYB26, leading to the excessive transcription of the two NAC genes and male sterility. Our results reveal a novel mechanism in polycomb-mediated gene silencing and illustrate that the plant Polycomb complex regulates stamen development by preventing the hypersensitivity of JA responses in male reproduction.

THE EPIGENETIC REGULATORY PROTEIN CBX2 AS A NOVEL THERAPEUTIC TARGET FOR GLIOBLASTOMA

Abstract AIMS Glioblastoma (GBM) is the deadliest and most common form of brain tumour. The average length of survival for GBM patients remains low, in part, due to a lack of targeted therapeutics. Identification and validation of novel therapeutic targets is therefore crucial. Chomobox 2 (CBX2; a component of polycomb repressive complex 1 (PRC1)), represses gene expression and has a pro-oncogenic role in several aggressive cancer subtypes. CBX2 expression is elevated in GBM, however, very little is known about its role in this deadly disease. We aim to assess the phenotypic and gene expression effects of preventing CBX2-chromatin interaction in patient-derived GBM cell models, and to determine the functional mechanisms by which CBX2 promotes GBM progression; thereby determining its potential as a novel therapeutic target. METHOD Crucial to impactful target validation is the use of translationally relevant models, this study utilises a 3D spheroid model, using patient-derived cells, which more closely recapitulates the in vivo tumour microenvironment. GBM cell monolayers and spheroids were treated with SW2_152F, a selective CBX2 inhibitor. The phenotypic effects of CBX2 inhibition were assessed by cell count, CellTiter-Glo viability assays, fluorescence microscopy, and flow cytometry. Genes and biological pathways differentially regulated following CBX2 inhibition were assessed by RNA-sequencing and Gene Set Enrichment Analysis (GSEA). RESULTS Inhibition of CBX2 induced cell death and reduced cell viability in both 2D and 3D GBM cultures. RNA-seq and GSEA of SW2_152F-treated cells identified dysregulation of gene signatures involved in pro-oncogenic MYC and E2F signalling pathways, and dysregulation of genes associated with G2/M cell cycle progression. CONCLUSION Preventing CBX2-chromatin interaction induces GBM cell death. Further research will identify CBX2- chromatin binding sites to characterise the activity and direct regulatory role of CBX2 in GBM. Furthermore, we will assess the phenotypic and gene expression effects of CBX2 inhibition and depletion on ex vivo maintained GBM tissue biopsies.

BMI-1 in Breast Cancer - Biological Role and Clinical Implications.

Breast cancer is the most frequent cancer among women. Despite extensive research in recent years the molecular basis of breast cancer development, growth and metastasis remains unclear. Numerous studies highlight the involvement of BMI-1 in tumorigenesis. BMI-1 protein is a key component of Polycomb Repressive Complex 1, which by ubiquitinylation of histone H2A, regulates expression of genes involved in various cellular processes including cell cycle, proliferation and programmed cell death. Overexpression of BMI-1 has been often associated with breast cancer development and progression. This review summarizes the current state of knowledge of BMI-1's role in breast cancer biology and its potential significance as prognostic marker and potential target of new anticancer therapy.

Lockd Enhances Mandibular Mesenchymal Stem Cell Proliferation While Inhibiting Osteogenic Capability via Binding With SUZ12 in the Inflammatory Microenvironment.

To investigate the role of lncRNA Lockd in mandibular mesenchymal stem cell (M-MSC) proliferation and osteogenic capability in the inflammatory microenvironment, focusing on its interaction with SUZ12. Using lncR Lockd knockdown/overexpression cell models and a murine periodontitis model, we explored Lockd's effects on M-MSC proliferation and osteogenic capability in the inflammatory microenvironment. Predictions from multiple databases and a series of rescue experiments revealed the regulatory role of the Lockd/SUZ12 signalling axis of M-MSC in the inflammatory microenvironment. Lockd was found to stimulate M-MSC proliferation but impair osteogenic differentiation. The in vitro studies suggested that the activation of Lockd negatively inhibited the osteogenic differentiation process and may ultimately impact bone formation in periodontitis. Mechanistically, it was elucidated that Lockd interacts with SUZ12, a core component of the polycomb repressive complex 2 (PRC2), and may affect the PRC2 complex's role in osteogenic gene expression. Lockd boosts the proliferation of M-MSCs but inhibits their osteogenic differentiation by interacting with SUZ12, potentially inhibiting osteogenic capability in the inflammatory microenvironment.

Epigenetic regulation by polycomb repressive complex 1 promotes cerebral cavernous malformations.

Cerebral cavernous malformations (CCMs) are anomalies of the cerebral vasculature. Loss of the CCM proteins CCM1/KRIT1, CCM2, or CCM3/PDCD10 trigger a MAPK-Krüppel-like factor 2 (KLF2) signaling cascade, which induces a pathophysiological pattern of gene expression. The downstream target genes that are activated by KLF2 are mostly unknown. Here we show that Chromobox Protein Homolog 7 (CBX7), component of the Polycomb Repressive Complex 1, contributes to pathophysiological KLF2 signaling during zebrafish cardiovascular development. CBX7/cbx7a mRNA is strongly upregulated in lesions of CCM patients, and in human, mouse, and zebrafish CCM-deficient endothelial cells. The silencing or pharmacological inhibition of CBX7/Cbx7a suppresses pathological CCM phenotypes in ccm2 zebrafish, CCM2-deficient HUVECs, and in a pre-clinical murine CCM3 disease model. Whole-transcriptome datasets from zebrafish cardiovascular tissues and human endothelial cells reveal a role of CBX7/Cbx7a in the activation of KLF2 target genes including TEK, ANGPT1, WNT9, and endoMT-associated genes. Our findings uncover an intricate interplay in the regulation of Klf2-dependent biomechanical signaling by CBX7 in CCM. This work also provides insights for therapeutic strategies in the pathogenesis of CCM.

Species-specific satellite DNA composition dictates de novo formation of PRC1-mediated pericentric heterochromatin.

Pericentromeres are heterochromatic regions adjacent to centromeres that ensure accurate chromosome segregation. Despite their conserved function, they are composed of rapidly evolving A/T-rich satellite DNA. This paradoxical observation is partially resolved by epigenetic mechanisms that maintain heterochromatin, independent of specific DNA sequences. However, it is unclear how satellite DNA sequence variation impacts de novo formation of pericentric heterochromatin, which is initially absent from paternal chromosomes in the zygote. Here we show that satellite variation has functional consequences for zygotic heterochromatin formation, recruitment of the Chromosome Passenger Complex (CPC), and interactions with spindle microtubules. In M. musculus zygotes, Polycomb Repressive Complex 1 (PRC1) is recruited to pericentric satellites by its AT-hook domain, which binds runs of A/T nucleotides, to generate H2AK119ub1 (H2Aub) heterochromatin. By fertilizing M. musculus eggs with sperm from other mouse species, we show that species-specific satellite sequences differ in their ability to recruit PRC1 and form H2Aub. This satellite-DNA mediated increase in PRC1 heterochromatin leads to reduced CPC recruitment and increased microtubule forces on kinetochores. Our results provide a direct link between satellite DNA composition and pericentromere function in the zygote, when epigenetic pathways maintaining pericentromere heterochromatin are absent.

Homeobox B9 promotes the invasion and metastasis of hepatocellular carcinoma cells via the EZH2–MIR203A–SNAI2 axis

BackgroundResearch has elucidated that homeobox B9 (HOXB9), an important transcriptional activator, plays a pivotal role in promoting the invasion and metastasis of hepatocellular carcinoma (HCC) cells. However, the mechanism by which HOXB9 promotes the invasion and metastasis of HCC cells is incompletely understood and needs further exploration.MethodsHOXB9 and snail family transcriptional repressor 2 (SNAI2) expression were analyzed using qRT-PCR and western blotting. The invasion and metastasis of hepatocellular carcinoma (HCC) cells were investigated using in vitro and in vivo assays. The H3K27me3 enrichment and HOXB9 interaction with microRNA 203a (MIR203A) or SNAI2 were detected using ChIP-qPCR. Transcriptional activities of SNAI2 and MIR203A promoter were detected using dual-luciferase reporter assays. Co-IP and GST pull-down assays were performed to confirm the binding between HOXB9 and EZH2.ResultsHOXB9 and SNAI2 were highly expressed in HCC tissues and their expression was positively intercorrelated and associated with poor prognosis in patients with HCC. In vitro and in vivo experiments confirmed that HOXB9 can upregulate the expression of SNAI2 to promote the invasion and metastasis of HCC cells. Furthermore, HOXB9 elevated SNAI2 expression by inhibiting MIR203A expression, a tumor suppressor gene, in HCC cells. Mechanistically, HOXB9 recruited enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) through interaction with its WD-binding domain, which increased EZH2-mediated histone H3 lysine 27 trimethylation (H3K27me3) at the MIR203A promoter region, in turn repressing the transcriptional activity and expression of MIR203A and consequently increasing the SNAI2 level in HCC cells. Finally, empirical evidence from in vitro and in vivo studies confirmed that mitigation of the HOXB9-mediated enhancement of epigenetic silencing of MIR203A inhibited SNAI2 expression, impeding the invasion and metastasis of HCC cells.ConclusionsOur study reveals a novel mechanism by which HOXB9 promotes the invasion and metastasis of HCC cells and expands the understanding of the function of HOXB9 in tumor progression and provides a novel therapeutic strategy for curtailing HCC invasion and metastasis.

Importin α4 deficiency induces psychiatric disorder-related behavioral deficits and neuroinflammation in mice

Importin α4, which is encoded by the Kpna4 gene, is a well-characterized nuclear-cytoplasmic transport factor known to mediate transport of transcription factors including NF-κB. Here, we report that Kpna4 knock-out (KO) mice exhibit psychiatric disorder-related behavioral abnormalities such as anxiety-related behaviors, decreased social interaction, and sensorimotor gating deficits. Contrary to a previous study predicting attenuated NF-κB activity as a result of Kpna4 deficiency, we observed a significant increase in expression levels of NF-κB genes and proinflammatory cytokines such as TNFα, Il-1β or Il-6 in the prefrontal cortex or basolateral amygdala of the KO mice. Moreover, examination of inflammatory responses in primary cells revealed that Kpna4 deficient cells have an increased inflammatory response, which was rescued by addition of not only full length, but also a nuclear transport-deficient truncation mutant of importin α4, suggesting contribution of its non-transport functions. Furthermore, RNAseq of sorted adult microglia and astrocytes and subsequent transcription factor analysis suggested increases in polycomb repressor complex 2 (PRC2) activity in Kpna4 KO cells. Taken together, importin α4 deficiency induces psychiatric disorder-related behavioral deficits in mice, along with an increased inflammatory response and possible alteration of PRC2 activity in glial cells.

MIR164B ensures robust Arabidopsis leaf development by compensating for compromised POLYCOMB REPRESSIVE COMPLEX2 function.

Robustness is pervasive throughout biological systems, enabling them to maintain persistent outputs despite perturbations in their components. Here, we reveal a mechanism contributing to leaf morphology robustness in the face of genetic perturbations. In Arabidopsis (Arabidopsis thaliana), leaf shape is established during early development through the quantitative action of the CUP-SHAPED COTYLEDON2 (CUC2) protein, whose encoding gene is negatively regulated by the co-expressed MICRORNA164A (MIR164A) gene. Compromised epigenetic regulation due to defective Polycomb Repressive Complex 2 (PRC2) function results in the transcriptional derepression of CUC2 but has no impact on CUC2 protein dynamics or early morphogenesis. We solve this apparent paradox by showing that compromised PRC2 function simultaneously derepresses the expression of another member of the MIR164 gene family, MIR164B. This mechanism dampens CUC2 protein levels, thereby compensating for compromised PRC2 function and canalizing early leaf morphogenesis. Furthermore, we show that this compensation mechanism is active under different environmental conditions. Our findings shed light on how the interplay between different steps of gene expression regulation can contribute to developmental robustness.

PRC2-RNA interactions: Viewpoint from Tom Cech, Chen Davidovich, and Richard Jenner

Diverse biochemical, structural, and invivo data support models for the regulation of polycomb repressive complex 2 (PRC2) activity by RNAs, which may contribute to the maintenance of epigenetic states. Here, we summarize this research and also suggest why it can be difficult to capture biologically relevant PRC2-RNA interactions in living cells.

PRC2-RNA interactions: Viewpoint from YongWoo Lee and Jeannie T. Lee

Here, we expound on the view that Xist RNA directly controls Polycomb repressive complex 2 (PRC2) recruitment, off-loading to chromatin, catalytic activity, and eviction from chromatin. RNA-PRC2 interactions also control RNA polymerase II transcription pausing. Dynamic RNA folding determines PRC2 activity. Disparate studies and interpretations abound but can be reconciled.

The expression and role of SUZ12 in lung adenocarcinoma.

SUZ12 is one of the core members of the polycomb repressive complex 2 (PRC2), but its expression and role in lung adenocarcinoma (LUAD) are unclear. We aimed to explore the expression, prognosis, biological functions and roles of SUZ12 in LUAD. The expression of SUZ12 was detected by immunohistochemical staining, qRT-PCR, and western blotting in LUAD tissues and cells. The biological functions and molecular mechanisms of SUZ12 were characterized by a range of invitro and invivo experiments. SUZ12 was overexpressed in LUAD tissues, and high SUZ12 expression was correlated with worse clinicopathological features and a poorer prognosis. Knockdown of SUZ12 significantly inhibited cell growth, colony formation, invasion, and migration, and induced apoptosis and G1/S phase arrest, while overexpression of SUZ12 had the opposite effects. Knockdown of SUZ12 decreased the tumorigenic capacity of A549 cells invivo. The expression of key signaling molecules related to the cell cycle, apoptosis, migration, and immunity were altered by the knockdown or overexpression of SUZ12. SUZ12 can directly bind to the Bax promoter region, EZH2 and H3K27me3 levels dependents on SUZ12. The expression levels of SUZ12 and Bax were negatively correlated in LUAD tissues. SUZ12 is a new oncogene related to the poor prognosis of LUAD. SUZ12 regulates LUAD progression by regulating the expression of related signaling molecules, and as a part of the PRC2 complex, it may bind to the Bax promoter to silence Bax expression.

Resectable Non-Small Cell Lung Cancer Heterogeneity and Recurrence Assessed by Tissue Next-Generation Sequencing Genotyping and Circulating Tumor Cell EZH2 Characterization

IntroductionNon-small cell lung cancer (NSCLC) is the most common type of lung neoplasm. Despite surgical resection, it has a high relapse rate, accounting for 30–55% of all cases. Next-generation sequencing (NGS) based on a customized gene panel and the analysis of circulating tumor cells (CTCs) can help identify heterogeneity, stratify high-risk patients, and guide treatment decisions. In this descriptive study involving a small prospective cohort, we focus on the phenotypic characterization of CTCs, particularly concerning EZH2 expression (a member of the Polycomb Repression Complex 2), as well as on the mutation profiles of the tissue using a customized gene panel and their association with poor outcomes in NSCLC. MethodsIsolation and characterization of EZH2 on CTCs were evaluated before surgical resection (CTC1) and one month after surgery (CTC2) in resectable NSCLC patients. Targeted NGS was performed using a customized 50-gene panel on tissue samples from a subset of patients. Results76 patients with resectable NSCLC were recruited. The top mutated genes in the cohort included TP53, FLT1, MUC5AC, EGFR, and NLRP3. Pair of genes that had mutually exclusive mutations was TP53-RIN3, and pairs of genes with co-occurring mutations were CD163-TLR4, FGF10-FOXP2, ADAMTSL3-FLT1, ADAMTSL3-MUC5AC and MUC5AC-NLRP3. CTCs decreased significantly between the two time points CTC1 and CTC2 (p<0.0001), and CTCs+ patients with high EZH2 expression had an 87% increased risk of death (p=0.018). ConclusionsIntegrating molecular profiling of tumors and CTC characterization can provide valuable insights into tumor heterogeneity and improve patient stratification for resectable NSCLC.

Targeting EZH2 attenuates the ferroptosis-mediated osteoblast–osteoclast imbalance in rheumatoid arthritis

ObjectiveThe enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) can regulate osteogenesis and osteoclastogenesis. This study aimed to further explore the effects of EZH2 modification on ferroptosis and the osteoblast–osteoclast balance in rheumatoid arthritis (RA) in vitro and in vivo. MethodsBone marrow mesenchymal stromal cells were transfected with EZH2 overexpression (oeEZH2) and EZH2 shRNA (shEZH2) plasmids with or without ferrostatin-1 (Fer-1) treatment and subjected to an osteoblast differentiation assay. The cells were then cocultured with bone marrow-derived macrophages and subjected to an osteoclast differentiation assay. Collagen-induced arthritis (CIA) mice were generated and injected with shEZH2 adeno-associated virus (AAV). ResultsOeEZH2 repressed osteoblast differentiation, as reflected by decreased ALP and Alizarin Red S staining and increased OPN, RUNX2, OPG and RANKL; however, shEZH2 had the opposite effects. Besides, oeEZH2 promoted osteoblast ferroptosis, as suggested by increased MDA, Fe2+, ROS, and PTGS2 but decreased GPX4 and SLC7A11; these effects could be attenuated by Fer-1 treatment. In contrast, shEZH2 ameliorated osteoblast ferroptosis. OeEZH2 subsequently increased osteoclast differentiation, as indicated by increased TRAP+ multinucleated cells, NFATC1, CTSK, and c-FOS; however, shEZH2 had the opposite effect, except that it did not regulate CTSK. In CIA mice, shEZH2 AAV decreased the clinical symptom score, histological score of cartilage, and systemic inflammation (TNF-α and IL-6) and repressed bone ferroptosis and restored the osteoblast–osteoclast balance to some extent, as reflected by immunohistochemical staining of related markers. ConclusionTargeting EZH2 attenuates the ferroptosis-mediated osteoblast–osteoclast imbalance in RA, revealing its potential as a treatment target.

Characterisation and evolution of the PRC2 complex and its functional analysis under various stress conditions in rice

The polycomb repressive complex 2 (PRC2) is a chromatin-associated methyltransferase responsible for catalysing the trimethylation of H3K27, an inhibitory chromatin marker associated with gene silencing. This enzymatic activity is crucial for normal organismal development and the maintenance of gene expression patterns that preserve cellular identity, subsequently influencing plant growth and abiotic stress responses. Therefore, in this study, we investigated the evolutionary characteristics and functional roles of PRC2 in plants. We identified 209 PRC2 genes, including E(z), Su(z), Esc, and Nurf55 families, using 18 representative plant species and revealed that recent gene replication events have led to an expansion in the Nurf55 family, resulting in a greater number of members compared to the E(z), Su(z), and Esc families. Furthermore, protein structure and motif composition analyses highlighted the potential functional site regions within PRC2 members. In addition, we selected rice, a representative monocotyledonous plant, as the model species for food crops. Our findings revealed that SDG711, SDG718, and MSI1-5 genes were induced by abscisic acid (ABA) and/or methyl jasmonate (MeJA) hormones, suggesting that these genes play an important role in abiotic stress and disease resistance. Further experiments involving rice blast fungus treatments confirmed that the expression of SDG711 and MSI1-5 was induced by Magnaporthe oryzae strain GUY11. Multiple protein interaction assays revealed that the M. oryzae effector AvrPiz-t interacts with PRC2 core member SDG711 to increase H3K27me3 levels. Notably, inhibition of PRC2 or mutation of SDG711 enhanced rice resistance to M. oryzae. Collectively, these results provide new insights into PRC2 evolution in plants and its significant functions in rice.

Relationship between EZH2 expression and prognosis of patients with hepatocellular carcinoma using a pathomics predictive model

BackgroundEnhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) is overexpressed in hepatocellular carcinoma, promoting tumorigenesis and correlating with poor prognosis. Traditional histopathological examinations are insufficient to accurately predict hepatocellular carcinoma (HCC) survival; however, pathomics models can predict EZH2 expression and HCC prognosis. This study aimed to investigate the relationship between pathomics features and EZH2 expression for predicting overall survival of patients with HCC. MethodsWe analyzed 267 patients with HCC from the Cancer Genome Atlas database, with available pathological images and gene expression data. RNA sequencing data were divided into high and low EZH2 expression groups for prognosis and survival analysis. Pathological image features were screened using mRMR_RFE. A pathological model was constructed using a gradient boosting machine (GBM) algorithm, and efficiency evaluation and survival analysis of the model were performed. The R package “survminer” took the pathomics score (PS) cutoff value of 0.4628 to divide the patients into two groups: high and low PS expression. Survival analyses included Kaplan–Meier curve analysis, univariate and multivariate Cox regression analyses, and interaction tests. Potential pathomechanisms were explored through enrichment, differential, immune cell infiltration abundance, and gene mutation analyses. ResultEZH2 was highly expressed in tumor samples but poorly expressed in normal tissue samples. Univariate and multivariate Cox regression analyses revealed that EZH2 was an independent risk factor for HCC (hazard ratio [HR], 2.792 and 3.042, respectively). Seven imaging features were selected to construct a pathomics model to predict EZH2. Decision curve analysis showed that the model had high clinical utility. Multivariate Cox regression analysis showed that high PS expression was an independent risk factor for HCC prognosis (HR, 2.446). The Kaplan–Meier curve showed that high PS expression was a risk factor for overall survival. ConclusionEZH2 expression can affect the prognosis of patients with liver cancer. Our pathological model could predict EZH2 expression and prognosis of patients with HCC with high accuracy and robustness, making it a new and potentially valuable tool.

HCV infection activates the proteasome via PA28γ acetylation and heptamerization to facilitate the degradation of RNF2, a catalytic component of polycomb repressive complex 1.

We previously reported that hepatitis C virus (HCV) infection or HCV core protein expression induces HOX gene expression by impairing histone H2A monoubiquitination via a proteasome-dependent reduction in the level of RNF2, a key catalytic component of polycomb repressive complex 1 (H. Kasai, K. Mochizuki, T. Tanaka, A. Yamashita, et al., J Virol 95:e01784-20, 2021, https://doi.org/10.1128/jvi.01784-20). In this study, we aimed to investigate the mechanism by which HCV infection accelerates RNF2 degradation. Yeast two-hybrid screening and an immunoprecipitation assay revealed that RNF2 is a PA28γ-binding protein. The proteasome activator PA28γ destabilized the RNF2 protein in a proteasome-dependent manner, since RNF2 degradation was impaired by PA28γ knockout or MG132 treatment. HCV infection or core protein expression reduced the levels of RNF2 and histone H2A K119 monoubiquitination and induced the expression of HOX genes in the presence of PA28γ, while PA28γ knockout reversed these changes. Treatment with a lysine acetyltransferase inhibitor inhibited the acetylation of PA28γ at K195 and the degradation of the RNF2 protein, while treatment with a lysine deacetylase inhibitor accelerated these events in a PA28γ-dependent manner. RNF2 protein degradation was increased by expression of the acetylation mimetic PA28γ mutant but not by expression of the acetylation-defective mutant or the proteasome activation-defective mutant. Furthermore, HCV infection or core protein expression facilitated the interaction between PA28γ and the lysine acetyltransferase CBP/p300 and then accelerated PA28γ acetylation and heptazmerization to promote RNF2 degradation. These data suggest that HCV infection accelerates the acetylation-dependent heptamerization of PA28γ to increase the proteasomal targeting of RNF2.IMPORTANCEHCV is a causative agent of HCV-related liver diseases, including hepatic steatosis, cirrhosis, and hepatocellular carcinoma. PA28γ, which, in heptameric form, activates the 20S core proteasome for the degradation of PA28γ-binding proteins, is responsible for HCV-related liver diseases. HCV core protein expression or HCV infection accelerates RNF2 degradation, leading to the induction of HOX gene expression via a decrease in the level of H2Aub on HOX gene promoters. However, the mechanism of RNF2 degradation in HCV-infected cells has not been clarified. The data presented in this study suggest that PA28γ acetylation and heptamerization are promoted by HCV infection or by core protein expression to activate the proteasome for the degradation of RNF2 and are responsible for HCV propagation. This study provides novel insights valuable for the development of therapies targeting both HCV propagation and HCV-related diseases.