Enhancer-promoter Interactions Research Articles

TAD border deletion at the Kit locus causes tissue-specific ectopic activation of a neighboring gene

Topologically associated domains (TADs) restrict promoter-enhancer interactions, thereby maintaining the spatiotemporal pattern of gene activity. However, rearrangements of the TADs boundaries do not always lead to significant changes in the activity pattern. Here, we investigated the consequences of the TAD boundaries deletion on the expression of developmentally important genes encoding tyrosine kinase receptors: Kit, Kdr, Pdgfra. We used genome editing in mice to delete the TADs boundaries at the Kit locus and characterized chromatin folding and gene expression in pure cultures of fibroblasts, mast cells, and melanocytes. We found that although Kit is highly active in both mast cells and melanocytes, deletion of the TAD boundary between the Kit and Kdr genes results in ectopic activation only in melanocytes. Thus, the epigenetic landscape, namely the mutual arrangement of enhancers and actively transcribing genes, is important for predicting the consequences of the TAD boundaries removal. We also found that mice without a TAD border between the Kit and Kdr genes have a phenotypic manifestation of the mutation — a lighter coloration. Thus, the data obtained shed light on the principles of interaction between the 3D chromatin organization and epigenetic marks in the regulation of gene activity.

Enhancer selectivity across cell types delineates three functionally distinct enhancer-promoter regulation patterns

BackgroundMultiple enhancers co-regulating the same gene is prevalent and plays a crucial role during development and disease. However, how multiple enhancers coordinate the same gene expression across various cell types remains largely unexplored at genome scale.ResultsWe develop a computational approach that enables the quantitative assessment of enhancer specificity and selectivity across diverse cell types, leveraging enhancer-promoter (E-P) interactions data. We observe two well-known gene regulation patterns controlled by enhancer clusters, which regulate the same gene either in a limited number of cell types (Specific pattern, Spe) or in the majority of cell types (Conserved pattern, Con), both of which are enriched for super-enhancers (SEs). We identify a previously overlooked pattern (Variable pattern, Var) that multiple enhancers link to the same gene, but rarely coexist in the same cell type. These three patterns control the genes associating with distinct biological function and exhibit unique epigenetic features. Specifically, we discover a subset of Var patterns contains Shared enhancers with stable enhancer-promoter interactions in the majority of cell types, which might contribute to maintaining gene expression by recruiting abundant CTCF.ConclusionsTogether, our findings reveal three distinct E-P regulation patterns across different cell types, providing insights into deciphering the complexity of gene transcriptional regulation.

Impact of Interactions between Su(Hw)-Dependent Insulators on the Transvection Effect in Drosophila melanogaster.

Transvection is a phenomenon of interallelic communication in which enhancers can activate a specific promoter located on a homologous chromosome. Insulators play a significant role in ensuring functional interactions between enhancers and promoters. In the presented work, we created a model where two or three copies of the insulator are located next to enhancers and promoters localized on homologous chromosomes. Using the Su(Hw) insulator as a model, we showed that the functional interaction between a pair of insulators promotes enhancer-promoter trans-interactions. The interaction between the three insulators, on the contrary, can lead to the formation of chromatin loops that sterically hinder the full enhancer-promoter interaction. The results of the work suggest the participation of insulators in the regulation of homologous chromosome pairing and in communication between distant genomic loci.

Liver Sinusoidal Endothelial Cells Contribute to Portal Hypertension Through Collagen Type IV-Driven Sinusoidal Remodeling.

Portal hypertension (PHTN) is a severe complication of liver cirrhosis and is associated with intrahepatic sinusoidal remodeling induced by sinusoidal resistance and angiogenesis. Collagen type IV (COL4), a major component of basement membrane, forms in liver sinusoids upon chronic liver injury. However, the role, the cellular source and expression regulation of COL4 in liver diseases is unknown. Here, we examined how COL4 is produced and how it regulates sinusoidal remodeling in fibrosis and PHTN. Human cirrhotic liver sample RNA-sequencing showed increased COL4 expression, which was further confirmed via immunofluorescence staining. scRNA-sequencing identified liver sinusoidal endothelial cells (LSECs) as the predominant source of COL4 upregulation in mouse fibrotic liver. In addition, COL4 was upregulated in a tumor necrosis factor α-nuclear factor-κB dependent manner through an epigenetic mechanism in liver sinusoidal endothelial cells in vitro. Indeed, by utilizing a CRISPRi-dCas9-KRAB-mediated epigenome editing approach, epigenetic repression of the enhancer-promoter interaction showed silencing of COL4 gene expression. LSEC-specific COL4 gene mutation or repression in vivo abrogated sinusoidal resistance and angiogenesis, which thereby alleviated sinusoidal remodeling and PHTN. Our findings reveal that LSECs promote sinusoidal remodeling and PHTN during liver fibrosis through COL4 deposition.

Overexpressed KCNK1 regulates potassium channels affecting molecular mechanisms and biological pathways in bladder cancer

BackgroundThis study aimed to explore the expression, molecular mechanism and its biological function of potassium two pore domain channel subfamily K member 1 (KCNK1) in bladder cancer (BC).MethodsWe integrated large numbers of external samples (n = 1486) to assess KCNK1 mRNA expression levels and collected in-house samples (n = 245) for immunohistochemistry (IHC) experiments to validate at the KCNK1 protein level. Single-cell RNA sequencing (scRNA-seq) analysis was performed to further assess KCNK1 expression and cellular communication. The transcriptional regulatory mechanisms of KCNK1 expression were explored by ChIP-seq, ATAC-seq and ChIA-PET data. Highly expressed co-expressed genes (HECEGs) of KCNK1 were used to explore potential signalling pathways. Furthermore, the immunoassay, clinical significance and molecular docking of KCNK1 were calculated.ResultsKCNK1 mRNA was significantly overexpressed in BC (SMD = 0.58, 95% CI [0.05; 1.11]), validated at the protein level (p < 0.0001). Upregulated KCNK1 mRNA exhibited highly distinguishing ability between BC and control samples (AUC = 0.82 [0.78–0.85]). Further, scRNA-seq analysis revealed that KCNK1 expression was predominantly clustered in BC epithelial cells and tended to increase with cellular differentiation. BC epithelial cells were involved in cellular communication mainly through the MK signalling pathway. Secondly, the KCNK1 transcription start site (TSS) showed promoter-enhancer interactions in three-dimensional space, while being transcriptionally regulated by GRHL2 and FOXA1. Most of the KCNK1 HECEGs were enriched in cell cycle–related signalling pathways. KCNK1 was mainly involved in cellular metabolism–related pathways and regulated cell membrane potassium channel activity. KCNK1 expression was associated with the level of infiltration of various immune cells. Immunotherapy and chemotherapy (docetaxel, paclitaxel and vinblastine) were more effective in BC patients in the high KCNK1 expression group. KCNK1 expression correlated with age, pathology grade and pathologic_M in BC patients.ConclusionsKCNK1 was significantly overexpressed in BC. A complex and sophisticated three-dimensional spatial transcriptional regulatory network existed in the KCNK1 TSS and promoted the upregulated of KCNK1 expression. The high expression of KCNK1 might be involved in the cell cycle, cellular metabolism, and tumour microenvironment through the regulation of potassium channels, and ultimately contributed to the deterioration of BC.

A Bidirectional Non-Coding RNA Promoter Mediates Long-Range Gene Expression Regulation.

Recent evidence suggests that human gene promoters display gene expression regulatory mechanisms beyond the typical single gene local transcription modulation. In mammalian genomes, genes with an associated bidirectional promoter are abundant; bidirectional promoter architecture serves as a regulatory hub for a gene pair expression. However, it has been suggested that its contribution to transcriptional regulation might exceed local transcription initiation modulation. Despite their abundance, the functional consequences of bidirectional promoter architecture remain largely unexplored. This work studies the long-range gene expression regulatory role of a long non-coding RNA gene promoter using chromosome conformation capture methods. We found that this particular bidirectional promoter contributes to distal gene expression regulation in a target-specific manner by establishing promoter-promoter interactions. In particular, we validated that the promoter-promoter interactions of this regulatory element with the promoter of distal gene BBX contribute to modulating the transcription rate of this gene; removing the bidirectional promoter from its genomic context leads to a rearrangement of BBX promoter-enhancer interactions and to increased gene expression. Moreover, long-range regulatory functionality is not directly dependent on its associated non-coding gene pair expression levels.

OA30 Primary osteoarthritis chondrocyte map of chromatin conformation reveals novel effector genes

Abstract Background/Aims Osteoarthritis is a complex disease with a huge public health burden. Genome-wide association studies (GWAS) have identified hundreds of osteoarthritis-associated sequence variants, but the effector genes underpinning these signals remain largely elusive. Understanding chromosome organisation in 3D space is essential for identifying long-range contacts between distant genomic features (e.g., between genes and regulatory elements), in a tissue-specific manner. Here, we generate the first whole genome chromosome conformation analysis (Hi-C) map of primary osteoarthritis chondrocytes and identify novel effector genes for the disease. Methods Primary chondrocytes collected from eight knee osteoarthritis patients underwent Hi-C analysis to link chromosomal structure to genomic sequence. The identified loops were then combined with osteoarthritis GWAS results to identify variants involved in gene regulation via enhancer-promoter interactions. Results We identified 36 genetic variants residing within chromatin loop anchors that are associated with 13 osteoarthritis GWAS signals. Five of these variants reside directly in enhancer regions of 3 enhancer-promoter loops newly described in chondrocytes, pointing to high-confidence effector genes: PAPPA, NSD2 and NCOA6. PAPPA is directly associated with the turnover of IGF-1 transport proteins, and IGF-1 is an important factor in the repair of damaged chondrocytes. Conclusion We have constructed the first Hi-C map of primary human chondrocytes and have made it available as a resource for the scientific community. By integrating 3D-genomics with large-scale genetic association data, we identify high-confidence osteoarthritis effector genes which enhance our understanding of disease and can serve as putative high-value novel targets. Disclosure N. Bittner: None. C. Shi: None. D. Zhao: None. J. Ding: None. L. Southam: None. D. Swift: None. P. Kreitmaier: None. M. Tutino: None. J. Hankinson: None. M. Wilkinson: None. G. Orozco: None. E. Zeggini: None.

Development of a New Model System to Study Long-Distance Interactions Supported by Architectural Proteins.

Chromatin architecture is critical for the temporal and tissue-specific activation of genes that determine eukaryotic development. The functional interaction between enhancers and promoters is controlled by insulators and tethering elements that support specific long-distance interactions. However, the mechanisms of the formation and maintenance of long-range interactions between genome regulatory elements remain poorly understood, primarily due to the lack of convenient model systems. Drosophila became the first model organism in which architectural proteins that determine the activity of insulators were described. In Drosophila, one of the best-studied DNA-binding architectural proteins, Su(Hw), forms a complex with Mod(mdg4)-67.2 and CP190 proteins. Using a combination of CRISPR/Cas9 genome editing and attP-dependent integration technologies, we created a model system in which the promoters and enhancers of two reporter genes are separated by 28 kb. In this case, enhancers effectively stimulate reporter gene promoters in cis and trans only in the presence of artificial Su(Hw) binding sites (SBS), in both constructs. The expression of the mutant Su(Hw) protein, which cannot interact with CP190, and the mutation inactivating Mod(mdg4)-67.2, lead to the complete loss or significant weakening of enhancer-promoter interactions, respectively. The results indicate that the new model system effectively identifies the role of individual subunits of architectural protein complexes in forming and maintaining specific long-distance interactions in the D. melanogaster model.

TEAD2 initiates ground-state pluripotency by mediating chromatin looping

The transition of mouse embryonic stem cells (ESCs) between serum/LIF and 2i(MEK and GSK3 kinase inhibitor)/LIF culture conditions serves as a valuable model for exploring the mechanisms underlying ground and confused pluripotent states. Regulatory networks comprising core and ancillary pluripotency factors drive the gene expression programs defining stable naïve pluripotency. In our study, we systematically screened factors essential for ESC pluripotency, identifying TEAD2 as an ancillary factor maintaining ground-state pluripotency in 2i/LIF ESCs and facilitating the transition from serum/LIF to 2i/LIF ESCs. TEAD2 exhibits increased binding to chromatin in 2i/LIF ESCs, targeting active chromatin regions to regulate the expression of 2i-specific genes. In addition, TEAD2 facilitates the expression of 2i-specific genes by mediating enhancer-promoter interactions during the serum/LIF to 2i/LIF transition. Notably, deletion of Tead2 results in reduction of a specific set of enhancer-promoter interactions without significantly affecting binding of chromatin architecture proteins, CCCTC-binding factor (CTCF), and Yin Yang 1 (YY1). In summary, our findings highlight a novel prominent role of TEAD2 in orchestrating higher-order chromatin structures of 2i-specific genes to sustain ground-state pluripotency.

Defining a TFAP2C-centered transcription factor network during murine peri-implantation

Transcription factors (TFs) play important roles in early embryonic development, but factors regulating TF action, relationships in signaling cascade, genome-wide localizations, and impacts on cell fate transitions during this process have not been clearly elucidated. In this study, we used uliCUT&RUN-seq to delineate a TFAP2C-centered regulatory network, showing that it involves promoter-enhancer interactions and regulates TEAD4 and KLF5 function to mediate cell polarization. Notably, we found that maternal retinoic acid metabolism regulates TFAP2C expression and function by inducing the active demethylation of SINEs, indicating that the RARG-TFAP2C-TEAD4/KLF5 axis connects the maternal-to-zygotic transition to polarization. Moreover, we found that both genomic imprinting and SNP-transferred genetic information can influence TF positioning to regulate parental gene expressions in a sophisticated manner. In summary, we propose a ternary model of TF regulation in murine embryonic development with TFAP2C as the core element and metabolic, epigenetic, and genetic information as nodes connecting the pathways.

The N-terminal dimerization domains of human and Drosophila CTCF have similar functionality

BackgroundCTCF is highly likely to be the ancestor of proteins that contain large clusters of C2H2 zinc finger domains, and its conservation is observed across most bilaterian organisms. In mammals, CTCF is the primary architectural protein involved in organizing chromosome topology and mediating enhancer–promoter interactions over long distances. In Drosophila, CTCF (dCTCF) cooperates with other architectural proteins to establish long-range interactions and chromatin boundaries. CTCFs of various organisms contain an unstructured N-terminal dimerization domain (DD) and clusters comprising eleven zinc-finger domains of the C2H2 type. The Drosophila (dCTCF) and human (hCTCF) CTCFs share sequence homology in only five C2H2 domains that specifically bind to a conserved 15 bp motif.ResultsPreviously, we demonstrated that CTCFs from different organisms carry unstructured N-terminal dimerization domains (DDs) that lack sequence homology. Here we used the CTCFattP(mCh) platform to introduce desired changes in the Drosophila CTCF gene and generated a series of transgenic lines expressing dCTCF with different variants of the N-terminal domain. Our findings revealed that the functionality of dCTCF is significantly affected by the deletion of the N-terminal DD. Additionally, we observed a strong impact on the binding of the dCTCF mutant to chromatin upon deletion of the DD. However, chromatin binding was restored in transgenic flies expressing a chimeric CTCF protein with the DD of hCTCF. Although the chimeric protein exhibited lower expression levels than those of the dCTCF variants, it efficiently bound to chromatin similarly to the wild type (wt) protein.ConclusionsOur findings suggest that one of the evolutionarily conserved functions of the unstructured N-terminal dimerization domain is to recruit dCTCF to its genomic sites in vivo.

Yin Yang 1 regulates cohesin complex protein SMC3 in mouse hematopoietic stem cells

AbstractYin Yang 1 (YY1) and structural maintenance of chromosomes 3 (SMC3) are 2 critical chromatin structural factors that mediate long-distance enhancer-promoter interactions and promote developmentally regulated changes in chromatin architecture in hematopoietic stem/progenitor cells (HSPCs). Although YY1 has critical functions in promoting hematopoietic stem cell (HSC) self-renewal and maintaining HSC quiescence, SMC3 is required for proper myeloid lineage differentiation. However, many questions remain unanswered regarding how YY1 and SMC3 interact with each other and affect hematopoiesis. We found that YY1 physically interacts with SMC3 and cooccupies with SMC3 at a large cohort of promoters genome wide, and YY1 deficiency deregulates the genetic network governing cell metabolism. YY1 occupies the Smc3 promoter and represses SMC3 expression in HSPCs. Although deletion of 1 Smc3 allele partially restores HSC numbers and quiescence in YY1 knockout mice, Yy1−/−Smc3+/− HSCs fail to reconstitute blood after bone marrow transplant. YY1 regulates HSC metabolic pathways and maintains proper intracellular reactive oxygen species levels in HSCs, and this regulation is independent of the YY1–SMC3 axis. Our results establish a distinct YY1–SMC3 axis and its impact on HSC quiescence and metabolism.

Abstract 1686: Dissecting the 3D enhancer-promoter hubs in prostate tumorigenesis

Abstract The transcription process is controlled by regulatory elements that are often located in non-coding regions. Among regulatory elements, activities of enhancers that are bound by cell-type specific transcription factors (TFs) are tightly linked to cell identity. Enhancers loop to interact with the promoters of target genes at a distance to drive different cell fates. Evidently, transcriptional dysregulation linked to enhancers that are differentially activated in cancer is an underlying factor in tumorigenesis. To identify enhancers linked to prostate tumorigenesis, we analyzed hundreds of in-house and public H3K27ac ChIP-seq data generated from normal prostate and prostate cancer cell lines and tissues. We identified thousands of prostate cancer-specific enhancers (PSEs) that were activated exclusively in cancer conditions. To further identify the target genes of PSEs, we performed 3C-derived assays, such as Hi-C and Micro-C, and mapped genome-wide interactions. However, they were limited by the resolution to detect enhancer-promoter interactions. The recent development of Region Capture Micro-C (RCMC), a hybridization-based capture Micro-C method, allowed us to deeply map the highly nested interactions between regulatory elements. By utilizing RCMC, we generated high-resolution, focal contact maps that revealed comprehensive enhancer-promoter interactions near PSEs in prostate cancer cells. Interestingly, we found that PSEs loop to other PSEs clustered in the proximal genomic region, in addition to promoters of significantly upregulated genes in cancer compared to normal cells. We termed these regions as multi-connected "3D enhancer-promoter hubs”. To mechanistically dissect these hubs, we deleted 5+ PSEs one by one using the CRISPR/Cas9 system and performed multi-omics analyses, including RNA-seq and ChIP-seq. We found that single deletions of a subset of PSEs led to the downregulation of multiple genes looped to the deleted PSE as well as to other PSEs. Moreover, we found that deletion reduced the activity of other connected PSEs. When we further evaluated the chromatin contacts of regulatory elements in the PSE-deleted cells, we observed that many chromatin contacts remained unaffected. Finally, we identified TFs that bind to PSEs, and we are currently in the process of investigating enhancer-promoter hub connectivity by performing knockdown experiments on these TFs. Furthermore, we are using molecular assays to identify PSEs that could exert a phenotypic shift in cancer cell identity to drive prostate tumorigenesis. Overall, our study not only provides mechanistic insights into the spatial regulation of 3D enhancer-promoter hubs but also identifies new non-coding drivers in prostate tumorigenesis. Citation Format: Huan Cao, Zexun Wu, Leonardo Gonzalez-Smith, Seolyn Yang, Suhn K. Rhie. Dissecting the 3D enhancer-promoter hubs in prostate tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1686.

Abstract 143: Molecular profiling of tumor-initiation events in rhabdomyosarcoma uncovers mitochondrial vulnerabilities

Abstract Background: Alveolar Rhabdomyosarcoma (ARMS) is a very aggressive soft tissue tumor affecting children and adolescents. It is found that pediatric patients with RMS harboring chimeric PAX fusion transcription factors (TFs) exhibit a greater incidence of tumor relapse, metastasis, and poor survival outcome, thereby underscoring the urgent need to develop effective therapies to treat this subtype of childhood cancer. Methods: We generated a novel ARMS model by stable transduction of myogenic progenitor cells with a cassette encoding the exact PAX3/7-FOXO1 fusion protein found in ARMS tumors. We analyzed genome-wide expression levels with RNA-seq and utilized Cut&amp;Run to map the binding sites of PAX3/7-FOXO1, active histone marks, enhancers, and super-enhancers in our novel model. Hi-C and promoter capture HiC (pCHiC) were also performed to generate 3D chromatin conformation maps in cells expressing the oncogenic TFs. We compared these data with analogous datasets from orthotopic patient-derived xenografts (O-PDXs) of PAX3/7-FOXO1 fusion-positive ARMS tumors from St. Jude and established ARMS cell lines to validate whether our model system recapitulates ARMS tumors. CRISPRi was performed to silence key targets in two representative ARMS cell lines and proliferation was scored after silencing. Next, we found that ARMS tumors displayed anomalies in mitochondrial mass and numbers, metabolic parameters, and membrane potential by performing TEM, Seahorse assays, and FACS-based TMRM and mitotracker Red dye uptake in a panel of ARMS cells and PDX samples. We performed cell viability and colony forming assays in ARMS cells treated with single drugs and combinations of drugs targeting FGFR4 and mitochondrial metabolism. Results: Our data provide evidence to support muscle progenitors as potential cells-of-origin for ARMS. We showed that rewiring of chromatin architecture mediated by PAX3/7-FOXO1 TFs is evident across established cell lines, primary tumors as well as O-PDXs. By integrating PAX3/7-FOXO1 binding, RNA-seq, and pCHiC data, we identified key promoter-enhancer (P-En) interactions that are erased or established de novo at multiple loci of master TFs like MYOD, MYOG and MYCN. We also identified key regulators of proliferation, including FGFR4, and mitochondrial function that are essential for tumor growth and invasiveness. Our data indicated aberrant and enhanced mitochondrial metabolism in ARMS as well as selective sensitivity to mitochondrial inhibitors in RMS cells. Administration of these inhibitors preferentially inhibited cell viability and clonogenicity in ARMS, and prompted a pre-clinical phase II study to test these inhibitors at St. Jude Research Hospital. Conclusion: We present a novel treatment strategy leveraging the mitochondrial dependencies of fusion positive PAX-driven tumors which can be exploited for precision therapy in high-risk ARMS. Citation Format: Bhargab Kalita, Gerard Martinez-Cebrian, Justina McEvoy, Brittney Gordon, Kaley Blankenship, Asa Karlstorm, Elizabeth Stewart, Michael Dyer, Brian Dynlacht. Molecular profiling of tumor-initiation events in rhabdomyosarcoma uncovers mitochondrial vulnerabilities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 143.

H3K4me1 facilitates promoter-enhancer interactions and gene activation during embryonic stem cell differentiation

Histone H3 lysine 4 mono-methylation (H3K4me1) marks poised or active enhancers. KMT2C (MLL3) and KMT2D (MLL4) catalyze H3K4me1, but their histone methyltransferase activities are largely dispensable for transcription during early embryogenesis in mammals. To better understand the role of H3K4me1 in enhancer function, we analyze dynamic enhancer-promoter (E-P) interactions and gene expression during neural differentiation of the mouse embryonic stem cells. We found that KMT2C/D catalytic activities were only required for H3K4me1 and E-P contacts at a subset of candidate enhancers, induced upon neural differentiation.By contrast, a majority of enhancers retained H3K4me1 in KMT2C/D catalytic mutant cells. Surprisingly, H3K4me1 signals at these KMT2C/D-independent sites were reduced after acute depletion ofKMT2B, resulting in aggravated transcriptional defects. Our observations therefore implicate KMT2B in the catalysis of H3K4me1 at enhancers and provide additional support for an active role of H3K4me1 in enhancer-promoter interactions and transcription in mammalian cells.

Increased enhancer-promoter interactions during developmental enhancer activation in mammals.

Remote enhancers are thought to interact with their target promoters via physical proximity, yet the importance of this proximity for enhancer function remains unclear. Here we investigate the three-dimensional (3D) conformation of enhancers during mammalian development by generating high-resolution tissue-resolved contact maps for nearly a thousand enhancers with characterized in vivo activities in ten murine embryonic tissues. Sixty-one percent of developmental enhancers bypass their neighboring genes, which are often marked by promoter CpG methylation. The majority of enhancers display tissue-specific 3D conformations, and both enhancer-promoter and enhancer-enhancer interactions are moderately but consistently increased upon enhancer activation in vivo. Less than 14% of enhancer-promoter interactions form stably across tissues; however, these invariant interactions form in the absence of the enhancer and are likely mediated by adjacent CTCF binding. Our results highlight the general importance of enhancer-promoter physical proximity for developmental gene activation in mammals.

Multi-omics analysis reveals epigenetically regulated processes and patient classification in lung adenocarcinoma.

Aberrant DNA methylation is a hallmark of many cancer types. Despite our knowledge of epigenetic and transcriptomic alterations in lung adenocarcinoma (LUAD), we lack robust multi-modal molecular classifications for patient stratification. This is partly because the impact of epigenetic alterations on lung cancer development and progression is still not fully understood. To that end, we identified disease-associated processes under epigenetic regulation in LUAD. We performed a genome-wide expression-methylation Quantitative Trait Loci (emQTL) analysis by integrating DNA methylation and gene expression data from 453 patients in the TCGA cohort. Using a community detection algorithm, we identified distinct communities of CpG-gene associations with diverse biological processes. Interestingly, we identified a community linked to hormone response and lipid metabolism; the identified CpGs in this community were enriched in enhancer regions and binding regions of transcription factors such as FOXA1/2, GRHL2, HNF1B, AR, and ESR1. Furthermore, the CpGs were connected to their associated genes through chromatin interaction loops. These findings suggest that the expression of genes involved in hormone response and lipid metabolism in LUAD is epigenetically regulated through DNA methylation and enhancer-promoter interactions. By applying consensus clustering on the integrated expression-methylation pattern of the emQTL-genes and CpGs linked to hormone response and lipid metabolism, we further identified subclasses of patients with distinct prognoses. This novel patient stratification was validated in an independent patient cohort of 135 patients and showed increased prognostic significance compared to previously defined molecular subtypes.

Enhancer-promoter interactions are reconfigured through the formation of long-range multiway hubs as mouse ES cells exit pluripotency

Enhancers bind transcription factors, chromatin regulators, and non-coding transcripts to modulate the expression of target genes. Here, we report 3D genome structures of single mouse ES cells as they are induced to exit pluripotency and transition through a formative stage prior to undergoing neuroectodermal differentiation. We find that there is a remarkable reorganization of 3D genome structure where inter-chromosomal intermingling increases dramatically in the formative state. This intermingling is associated with the formation of a large number of multiway hubs that bring together enhancers and promoters with similar chromatin states from typically 5-8 distant chromosomal sites that are often separated by many Mb from each other. In the formative state, genes important for pluripotency exit establish contacts with emerging enhancers within these multiway hubs, suggesting that the structural changes we have observed may play an important role in modulating transcription and establishing new cell identities.

Enhancer–promoter interactions become more instructive in the transition from cell-fate specification to tissue differentiation

To regulate expression, enhancers must come in proximity to their target gene. However, the relationship between the timing of enhancer–promoter (E–P) proximity and activity remains unclear, with examples of uncoupled, anticorrelated and correlated interactions. To assess this, we selected 600 characterized enhancers or promoters with tissue-specific activity in Drosophila embryos and performed Capture-C in FACS-purified myogenic or neurogenic cells during specification and tissue differentiation. This enabled direct comparison between E–P proximity and activity transitioning from OFF-to-ON and ON-to-OFF states across developmental conditions. This showed remarkably similar E–P topologies between specified muscle and neuronal cells, which are uncoupled from activity. During tissue differentiation, many new distal interactions emerge where changes in E–P proximity reflect changes in activity. The mode of E–P regulation therefore appears to change as embryogenesis proceeds, from largely permissive topologies during cell-fate specification to more instructive regulation during terminal tissue differentiation, when E–P proximity is coupled to activation.

Unveiling Alterations of Epigenetic Modifications and Chromatin Architecture Leading to Lipid Metabolic Reprogramming during the Evolutionary Trastuzumab Adaptation of HER2-Positive Breast Cancer.

Secondary trastuzumab resistance represents an evolutionary adaptation of HER2-positive breast cancer during anti-HER2 treatment. Most current studies have tended to prioritize HER2 and its associated signaling pathways, often overlooking broader but seemingly less relevant cellular processes, along with their associated genetic and epigenetic mechanisms. Here, transcriptome data is not only characterized but also examined epigenomic and 3D genome architecture information in both trastuzumab-sensitive and secondary-resistant breast cancer cells. The findings reveal that the global metabolic reprogramming associated with trastuzumab resistance may stem from genome-wide alterations in both histone modifications and chromatin structure. Specifically, the transcriptional activities of key genes involved in lipid metabolism appear to be regulated by variant promoter H3K27me3 and H3K4me3 modifications, as well as promoter-enhancer interactions. These discoveries offer valuable insights into how cancer cells adapt to anti-tumor drugs and have the potential to impact future diagnostic and treatment strategies.