Broad genic repression domains signify enhanced silencing of oncogenes

TSCRE: a comprehensive database for tumor-specific cis-regulatory elements

Cis-regulatory elements (CREs) and super cis-regulatory elements (SCREs) are non-coding DNA regions which influence the transcription of nearby genes and play critical roles in development. Dysregulated CRE and SCRE activities have been reported to alter the expression of oncogenes and tumor suppressors, thereby regulating cancer hallmarks. To address the strong need for a comprehensive catalogue of dysregulated CREs and SCREs in human cancers, we present TSCRE (http://tscre.zsqylab.com/), an open resource providing tumor-specific and cell type-specific CREs and SCREs derived from the re-analysis of publicly available histone modification profiles. Currently, TSCRE contains 1 864 941 dysregulated CREs and 68 253 dysregulated SCREs identified from 1366 human patient samples spanning 17 different cancer types and 9 histone marks. Over 95% of these elements have been validated in public resources. TSCRE offers comprehensive annotations for each element, including associated genes, expression patterns, clinical prognosis, somatic mutations, transcript factor binding sites, cancer-type specificity, and drug response. Additionally, TSCRE integrates pathway and transcript factor enrichment analyses for each study, enabling in-depth functional and mechanistic investigations. Furthermore, TSCRE provides an interactive interface for users to explore any CRE and SCRE of interest. We believe TSCRE will be a highly valuable platform for the community to discover candidate cancer biomarkers.

Low RNA stability signifies strong expression regulatability of tumor suppressors

RNA expression of a gene is determined by not only transcriptional regulation, but also post-transcriptional regulation of RNA decay. The precise regulation of RNA stability in the cell plays an important role in normal development. Dysregulation of RNA stability can lead to diseases such as cancer. Here we found tumor suppressor RNAs tended to decay fast in normal cell types when compared with other RNAs. Consistent with a negative effect of m6A modification on RNA stability, we observed preferential deposition of m6A on tumor suppressor RNAs. Moreover, abundant m6A and fast decay of tumor suppressor RNAs both tended to be further enhanced in prostate cancer cells relative to normal prostate epithelial cells. Further, knockdown of m6A methyltransferase METTL3 and reader YTHDF2 in prostate cancer cells both posed stronger effect on tumor suppressor RNAs than on other RNAs. These results indicated a strong post transcriptional expression regulatability mediated by abundant m6A modification on tumor suppressor RNAs.

Low RNA stability signifies increased post-transcriptional regulation of cell identity genes

Cell identity genes are distinct from other genes with respect to the epigenetic mechanisms to activate their transcription, e.g. by super-enhancers and broad H3K4me3 domains. However, it remains unclear whether their post-transcriptional regulation is also unique. We performed a systematic analysis of transcriptome-wide RNA stability in nine cell types and found that unstable transcripts were enriched in cell identity-related pathways while stable transcripts were enriched in housekeeping pathways. Joint analyses of RNA stability and chromatin state revealed significant enrichment of super-enhancers and broad H3K4me3 domains at the gene loci of unstable transcripts. Intriguingly, the RNA m6A methyltransferase, METTL3, preferentially binds to chromatin at super-enhancers, broad H3K4me3 domains and their associated genes. METTL3 binding intensity is positively correlated with RNA m6A methylation and negatively correlated with RNA stability of cell identity genes, probably due to co-transcriptional m6A modifications promoting RNA decay. Nanopore direct RNA-sequencing showed that METTL3 knockdown has a stronger effect on RNA m6A and mRNA stability for cell identity genes. Our data suggest a run-and-brake model, where cell identity genes undergo both frequent transcription and fast RNA decay to achieve precise regulation of RNA expression.

Partial erosion on under-methylated regions and chromatin reprogramming contribute to oncogene activation in IDH mutant gliomas

BACKGROUND

IDH1/2 hotspot mutations are well known to drive oncogenic mutations in gliomas and are well-defined in the WHO 2021 classification of central nervous system tumors. Specifically, IDH mutations lead to aberrant hypermethylation of under-methylated regions (UMRs) in normal tissues through the disruption of TET enzymes. However, the chromatin reprogramming and transcriptional changes induced by IDH-related hypermethylation in gliomas remain unclear.

RESULTS

Here, we have developed a precise computational framework based on Hidden Markov Model to identify altered methylation states of UMRs at single-base resolution. By applying this framework to whole-genome bisulfite sequencing data from 75 normal brain tissues and 15 IDH mutant glioma tissues, we identified two distinct types of hypermethylated UMRs in IDH mutant gliomas. We named them partially hypermethylated UMRs (phUMRs) and fully hypermethylated UMRs (fhUMRs), respectively. We found that the phUMRs and fhUMRs exhibit distinct genomic features and chromatin states. Genes related to fhUMRs were more likely to be repressed in IDH mutant gliomas. In contrast, genes related to phUMRs were prone to be up-regulated in IDH mutant gliomas. Such activation of phUMR genes is associated with the accumulation of active H3K4me3 and the loss of H3K27me3, as well as H3K36me3 accumulation in gene bodies to maintain gene expression stability. In summary, partial erosion on UMRs was accompanied by locus-specific changes in key chromatin marks, which may contribute to oncogene activation.

CONCLUSIONS

Our study provides a computational strategy for precise decoding of methylation encroachment patterns in IDH mutant gliomas, revealing potential mechanistic insights into chromatin reprogramming that contribute to oncogenesis.

Deciphering a mitochondria-related signature to supervise prognosis and immunotherapy in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is a major public health problem in humans. The imbalance of mitochondrial function has been discovered to be closely related to the development of cancer recently. However, the role of mitochondrial-related genes in HCC remains unclear.

Methods

The RNA-sequencing profiles and patient information of 365 samples were derived from the Cancer Genome Atlas (TCGA) dataset. The mitochondria-related prognostic model was established by univariate Cox regression analysis and LASSO Cox regression analysis. We further determined the differences in immunity and drug sensitivity between low- and high-risk groups. Validation data were obtained from the International Cancer Genome Consortium (ICGC) dataset of patients with HCC. The protein and mRNA expression of six mitochondria-related genes in tissues and cell lines was verified by immunohistochemistry and qRT-PCR.

Results

The six mitochondria-related gene signature was constructed for better prognosis forecasting and immunity, based on which patients were divided into high-risk and low-risk groups. The ROC curve, nomogram, and calibration curve exhibited admirable clinical predictive performance of the model. The risk score was associated with clinicopathological characteristics and proved to be an independent prognostic factor in patients with HCC. The above results were verified in the ICGC validation cohort. Compared with normal tissues and cell lines, the protein and mRNA expression of six mitochondria-related genes was upregulated in HCC tissues and cell lines.

Conclusion

The signature could be an independent factor that supervises the immunotherapy response of HCC patients and possess vital guidance value for clinical diagnosis and treatment.

MAFB promotes the malignant phenotypes by IGFBP6 in esophageal squamous cell carcinomas

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignant diseases in the world. Although the somatic alterations have been fully identified, there are still no targeted drugs at present. Our previous studies revealed that loss of grand H3K27me3 domains mediated transcriptional activation of a series of genes in ESCC. Among them, we focus on the investigation of MAFB, as its high expression is associated with a poor prognosis in ESCC. Functional assays show that knockdown of MAFB significantly suppresses cell growth, migration and invasion. Mechanistic investigation demonstrates that MAFB exerts its function by upregulating IGFBP6. Our findings suggest that MAFB may play a tumor-promoting role and may act as a potential therapeutic target for ESCC.

Methylation-dependent and -independent roles of EZH2 synergize in CDCA8 activation in prostate cancer

Cell division cycle-associated 8 (CDCA8) is a component of chromosomal passenger complex (CPC) that participates in mitotic regulation. Although cancer-related CDCA8 hyperactivation has been widely observed, its molecular mechanism remains elusive. Here, we report that CDCA8 overexpression maintains tumorigenicity and is associated with poor clinical outcome in patients with prostate cancer (PCa). Notably, enhancer of zeste homolog 2 (EZH2) is identified to be responsible for CDCA8 activation in PCa. Genome-wide assays revealed that EZH2-induced H3K27 trimethylation represses let-7b expression and thus protects the let-7b-targeting CDCA8 transcripts. More importantly, EZH2 facilitates the self-activation of E2F1 by recruiting E2F1 to its own promoter region in a methylation-independent manner. The high level of E2F1 further promotes transcription of CDCA8 along with the other CPC subunits. Taken together, our study suggests that EZH2-mediated cell cycle regulation in PCa relies on both its methyltransferase and non-methyltransferase activities.

A minimal standardized human bone marrow microphysiological system to assess resident cell behavior during normal and pathological processes

Bone marrow is a complex and dynamic microenvironment that provides essential cues to resident cells. We developed a standardized three-dimensional (3D) model to decipher mechanisms that control human cells during hematological and non-hematological processes. Our simple 3D-model is constituted of a biphasic calcium phosphate-based scaffold and human cell lines to ensure a high reproducibility. We obtained a minimal well-organized bone marrow-like structure in which various cell types and secreted extracellular matrix can be observed and characterized by in situ imaging or following viable cell retrieval. The complexity of the system can be increased and customized, with each cellular component being independently modulated according to the issue investigated. Introduction of pathological elements in this 3D-system accurately reproduced changes observed in patient bone marrow. Hence, we have developed a handy and flexible standardized microphysiological system that mimics human bone marrow, allowing histological analysis and functional assays on collected cells.

Loss of grand histone H3 lysine 27 trimethylation domains mediated transcriptional activation in esophageal squamous cell carcinoma

Trimethylation of histone H3 lysine 27 trimethylation (H3K27me3) may be recruited by repressive Polycomb complexes to mediate gene silencing, which is critical for maintaining embryonic stem cell pluripotency and differentiation. However, the roles of aberrant H3K27me3 patterns in tumorigenesis are not fully understood. Here, we discovered that grand silencer domains (breadth > 50 kb) for H3K27me3 were significantly associated with epithelial cell differentiation and exhibited high gene essentiality and conservation in human esophageal epithelial cells. These grand H3K27me3 domains exhibited high modification signals involved in gene silencing, and preferentially occupied the entirety of topologically associating domains and interact with each other. We found that widespread loss of the grand H3K27me3 domains in of esophageal squamous cell carcinomas (ESCCs) were enriched in genes involved in epithelium and endothelium differentiation, which were significantly associated with overexpression with increase of active modifications of H3K4me3, H3K4me1, and H3K27ac marks, as well as DNA hypermethylation in the gene bodies. A total of 208 activated genes with loss of grand H3K27me3 domains in ESCC were identified, where the higher expression and mutation of T-box transcription factor 20 (TBX20) were associated with worse patients’ outcomes. Our results showed that knockdown of TBX20 may have led to a striking defect in esophageal cancer cell growth and carcinogenesis-related pathway, including cell cycle and homologous recombination. Together, our results reveal that loss of grand H3K27me3 domains represent a catalog of remarkable activating regulators involved in carcinogenesis.