Super-enhancers delineate disease-associated regulatory nodes in T cells

The Elongation Factor Spt6 Maintains ESC Pluripotency by Controlling Super-Enhancers and Counteracting Polycomb Proteins

Spt6 coordinates nucleosome dis- and re-assembly, transcriptional elongation, and mRNA processing. Here, we report that depleting Spt6 in embryonic stem cells (ESCs) reduced expression of pluripotency factors, increased expression of cell-lineage-affiliated developmental regulators, and induced cell morphological and biochemical changes indicative of ESC differentiation. Selective downregulation of pluripotency factors upon Spt6 depletion may be mechanistically explained by its enrichment at ESC super-enhancers, where Spt6 controls histone H3K27 acetylation and methylation and super-enhancer RNA transcription. In ESCs, Spt6 interacted with the PRC2 core subunit Suz12 and prevented H3K27me3 accumulation at ESC super-enhancers and associated promoters. Biochemical as well as functional experiments revealed that Spt6 could compete for binding of the PRC2 methyltransferase Ezh2 to Suz12 and reduce PRC2 chromatin engagement. Thus, in addition to serving as a histone chaperone and transcription elongation factor, Spt6 counteracts repression by opposing H3K27me3 deposition at critical genomic regulatory regions.

Enhancer profiling identifies critical cancer genes and characterizes cell identity in adult T-cell leukemia

A number of studies have recently demonstrated that super-enhancers, which are large cluster of enhancers typically marked by a high level of acetylation of histone H3 lysine 27 and mediator bindings, are frequently associated with genes that control and define cell identity during normal development. Super-enhancers are also often enriched at cancer genes in various malignancies. The identification of such enhancers would pinpoint critical factors that directly contribute to pathogenesis. In this study, we performed enhancer profiling using primary leukemia samples from adult T-cell leukemia/lymphoma (ATL), which is a genetically heterogeneous intractable cancer. Super-enhancers were enriched at genes involved in the T-cell activation pathway, including IL2RA/CD25, CD30, and FYN, in both ATL and normal mature T cells, which reflected the origin of the leukemic cells. Super-enhancers were found at several known cancer gene loci, including CCR4, PIK3R1, and TP73, in multiple ATL samples, but not in normal mature T cells, which implicated those genes in ATL pathogenesis. A small-molecule CDK7 inhibitor, THZ1, efficiently inhibited cell growth, induced apoptosis, and downregulated the expression of super-enhancer-associated genes in ATL cells. Furthermore, enhancer profiling combined with gene expression analysis identified a previously uncharacterized gene, TIAM2, that was associated with super-enhancers in all ATL samples, but not in normal T cells. Knockdown of TIAM2 induced apoptosis in ATL cell lines, whereas overexpression of this gene promoted cell growth. Our study provides a novel strategy for identifying critical cancer genes.

Superenhancer Analysis Defines Novel Epigenomic Subtypes of Non-APL AML, Including an RARα Dependency Targetable by SY-1425, a Potent and Selective RARα Agonist

We characterized the enhancer landscape of 66 patients with acute myeloid leukemia (AML), identifying 6 novel subgroups and their associated regulatory loci. These subgroups are defined by their superenhancer (SE) maps, orthogonal to somatic mutations, and are associated with distinct leukemic cell states. Examination of transcriptional drivers for these epigenomic subtypes uncovers a subset of patients with a particularly strong SE at the retinoic acid receptor alpha (RARA) gene locus. The presence of a RARA SE and concomitant high levels of RARA mRNA predisposes cell lines and ex vivo models to exquisite sensitivity to a selective agonist of RARα, SY-1425 (tamibarotene). Furthermore, only AML patient-derived xenograft (PDX) models with high RARA mRNA were found to respond to SY-1425. Mechanistically, we show that the response to SY-1425 in RARA-high AML cells is similar to that of acute promyelocytic leukemia treated with retinoids, characterized by the induction of known retinoic acid response genes, increased differentiation, and loss of proliferation.Significance: We use the SE landscape of primary human AML to elucidate transcriptional circuitry and identify novel cancer vulnerabilities. A subset of patients were found to have an SE at RARA, which is predictive for response to SY-1425, a potent and selective RARα agonist, in preclinical models, forming the rationale for its clinical investigation in biomarker-selected patients. Cancer Discov; 7(10); 1136-53. ©2017 AACR.See related commentary by Wang and Aifantis, p. 1065.This article is highlighted in the In This Issue feature, p. 1047.

CCCTC-Binding Factor Translates Interleukin 2- and α-Ketoglutarate-Sensitive Metabolic Changes in T Cells into Context-Dependent Gene Programs

Despite considerable research connecting cellular metabolism with differentiation decisions, the underlying mechanisms that translate metabolite-sensitive activities into unique gene programs are still unclear. We found that aspects of the interleukin-2 (IL-2)-sensitive effector gene program in CD4⁺ and CD8⁺ T cells in type 1 conditions (Th1) were regulated by glutamine and alpha-ketoglutarate (αKG)-induced events, in part through changes in DNA and histone methylation states. We further identified a mechanism by which IL-2- and αKG-sensitive metabolic changes regulated the association of CCCTC-binding factor (CTCF) with select genomic sites. αKG-sensitive CTCF sites were often associated with loci containing IL-2- and αKG-sensitive genome organization patterns and gene expression in T cells. IL-2- and αKG-sensitive CTCF sites in T cells were also associated with genes from developmental pathways that had αKG-sensitive expression in embryonic stem cells. The data collectively support a mechanism wherein CTCF serves to translate αKG-sensitive metabolic changes into context-dependent differentiation gene programs.

Inflammatory responses induce an identity crisis of alveolar macrophages, leading to pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a severe respiratory disease characterized by dyspnea caused by accumulation of surfactant protein. Dysfunction of alveolar macrophages (AMs), which regulate the homeostasis of surfactant protein, leads to the development of PAP; for example, in mice lacking BTB and CNC homology 2 (Bach2). However, how Bach2 helps prevent PAP is unknown, and the cell-specific effects of Bach2 are undefined. Using mice lacking Bach2 in specific cell types, we found that the PAP phenotype of Bach2-deficient mice is due to Bach2 deficiency in more than two types of immune cells. Depletion of hyperactivated T cells in Bach2-deficient mice restored normal function of AMs and ameliorated PAP. We also found that, in Bach2-deficient mice, hyperactivated T cells induced gene expression patterns that are specific to other tissue-resident macrophages and dendritic cells. Moreover, Bach2-deficient AMs exhibited a reduction in cell cycle progression. IFN-γ released from T cells induced Bach2 expression in AMs, in which Bach2 then bound to regulatory regions of inflammation-associated genes in myeloid cells. Of note, in AMs, Bach2 restricted aberrant responses to excessive T cell-induced inflammation, whereas, in T cells, Bach2 puts a brake on T cell activation. Moreover, Bach2 stimulated the expression of multiple histone genes in AMs, suggesting a role of Bach2 in proper histone expression. We conclude that Bach2 is critical for the maintenance of AM identity and self-renewal in inflammatory environments. Treatments targeting T cells may offer new therapeutic strategies for managing secondary PAP.

Linkage disequilibrium-dependent architecture of human complex traits shows action of negative selection

Recent work has hinted at the linkage disequilibrium (LD)-dependent architecture of human complex traits, where SNPs with low levels of LD (LLD) have larger per-SNP heritability. Here we analyzed summary statistics from 56 complex traits (average N = 101,401) by extending stratified LD score regression to continuous annotations. We determined that SNPs with low LLD have significantly larger per-SNP heritability and that roughly half of this effect can be explained by functional annotations negatively correlated with LLD, such as DNase I hypersensitivity sites (DHSs). The remaining signal is largely driven by our finding that more recent common variants tend to have lower LLD and to explain more heritability (P = 2.38 × 10^-104); the youngest 20% of common SNPs explain 3.9 times more heritability than the oldest 20%, consistent with the action of negative selection. We also inferred jointly significant effects of other LD-related annotations and confirmed via forward simulations that they jointly predict deleterious effects.

Chromosome contacts in activated T cells identify autoimmune disease candidate genes

Background

Autoimmune disease-associated variants are preferentially found in regulatory regions in immune cells, particularly CD4⁺ T cells. Linking such regulatory regions to gene promoters in disease-relevant cell contexts facilitates identification of candidate disease genes.

Results

Within 4 h, activation of CD4⁺ T cells invokes changes in histone modifications and enhancer RNA transcription that correspond to altered expression of the interacting genes identified by promoter capture Hi-C. By integrating promoter capture Hi-C data with genetic associations for five autoimmune diseases, we prioritised 245 candidate genes with a median distance from peak signal to prioritised gene of 153 kb. Just under half (108/245) prioritised genes related to activation-sensitive interactions. This included IL2RA, where allele-specific expression analyses were consistent with its interaction-mediated regulation, illustrating the utility of the approach.

Conclusions

Our systematic experimental framework offers an alternative approach to candidate causal gene identification for variants with cell state-specific functional effects, with achievable sample sizes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1285-0) contains supplementary material, which is available to authorized users.

T Cell Fates Zipped Up: How the Bach2 Basic Leucine Zipper Transcriptional Repressor Directs T Cell Differentiation and Function

Recent data illustrate a key role for the transcriptional regulator bric-a-brac, tramtrack, and broad complex and cap'n'collar homology (Bach)2 in orchestrating T cell differentiation and function. Although Bach2 has a well-described role in B cell differentiation, emerging data show that Bach2 is a prototypical member of a novel class of transcription factors that regulates transcriptional activity in T cells at super-enhancers, or regions of high transcriptional activity. Accumulating data demonstrate specific roles for Bach2 in favoring regulatory T cell generation, restraining effector T cell differentiation, and potentiating memory T cell development. Evidence suggests that Bach2 regulates various facets of T cell function by repressing other key transcriptional regulators such as B lymphocyte-induced maturation protein 1. In this review, we examine our present understanding of the role of Bach2 in T cell function and highlight the growing evidence that this transcriptional repressor functions as a key regulator involved in maintenance of T cell quiescence, T cell subset differentiation, and memory T cell generation.

Facultative CTCF sites moderate mammary super-enhancer activity and regulate juxtaposed gene in non-mammary cells

Precise spatiotemporal gene regulation is paramount for the establishment and maintenance of cell-specific programmes. Although there is evidence that chromatin neighbourhoods, formed by the zinc-finger protein CTCF, can sequester enhancers and their target genes, there is limited in vivo evidence for CTCF demarcating super-enhancers and preventing cross talk between distinct regulatory elements. Here, we address these questions in the Wap locus with its mammary-specific super-enhancer separated by CTCF sites from widely expressed genes. Mutational analysis demonstrates that the Wap super-enhancer controls Ramp3, despite three separating CTCF sites. Their deletion in mice results in elevated expression of Ramp3 in mammary tissue through augmented promoter–enhancer interactions. Deletion of the distal CTCF-binding site results in loss of Ramp3 expression in non-mammary tissues. This suggests that CTCF sites are porous borders, allowing a super-enhancer to activate a secondary target. Likewise, CTCF sites shield a widely expressed gene from suppressive influences of a silent locus.

Chromatin neighbourhoods, formed by CTCF, have been proposed to isolate enhancers and their target genes from other regulatory elements. Here, the authors provide evidence that while CTCF binding does regulates mammary-specific super-enhancers, CTCF sites are relatively porous borders.

Profiles of Long Noncoding RNAs in Human Naive and Memory T Cells

We employed whole-genome RNA-sequencing to profile mRNAs and both annotated and novel long noncoding RNAs (lncRNAs) in human naive, central memory, and effector memory CD4+ T cells. Loci transcribing both lineage-specific annotated and novel lncRNA are adjacent to lineage-specific protein-coding genes in the genome. Lineage-specific novel lncRNA loci are transcribed from lineage-specific typical- and supertranscriptional enhancers and are not multiexonic, thus are more similar to enhancer RNAs. Novel enhancer-associated lncRNAs transcribed from the IFNG locus bind the transcription factor NF-κB and enhance binding of NF-κB to the IFNG genomic locus. Depletion of the annotated lncRNA, IFNG-AS1, or one IFNG enhancer-associated lncRNA abrogates IFNG expression by memory T cells, indicating these lncRNAs have biologic function.

BACH transcription factors in innate and adaptive immunity

BTB and CNC homology (BACH) proteins are transcriptional repressors of the basic region leucine zipper (bZIP) transcription factor family. Recent studies indicate widespread roles of BACH proteins in controlling the development and function of the innate and adaptive immune systems, including the differentiation of effector and memory cells of the B and T cell lineages, CD4+ regulatory T cells and macrophages. Here, we emphasize similarities at a molecular level in the cell-type-specific activities of BACH factors, proposing that competitive interactions of BACH proteins with transcriptional activators of the bZIP family form a common mechanistic theme underlying their diverse actions. The findings contribute to a general understanding of how transcriptional repressors shape lineage commitment and cell-type-specific functions through repression of alternative lineage programmes.

BACH2 immunodeficiency illustrates an association between super-enhancers and haploinsufficiency

The transcriptional programs that guide lymphocyte differentiation depend on the precise expression and timing of transcription factors (TFs). The TF BACH2 is essential for T and B lymphocytes and is associated with an archetypal super-enhancer (SE). Single-nucleotide variants in the BACH2 locus are associated with several autoimmune diseases, but BACH2 mutations that cause Mendelian monogenic primary immunodeficiency have not previously been identified. Here we describe a syndrome of BACH2-related immunodeficiency and autoimmunity (BRIDA) that results from BACH2 haploinsufficiency. Affected subjects had lymphocyte-maturation defects that caused immunoglobulin deficiency and intestinal inflammation. The mutations disrupted protein stability by interfering with homodimerization or by causing aggregation. We observed analogous lymphocyte defects in Bach2-heterozygous mice. More generally, we observed that genes that cause monogenic haploinsufficient diseases were substantially enriched for TFs and SE architecture. These findings reveal a previously unrecognized feature of SE architecture in Mendelian diseases of immunity: heterozygous mutations in SE-regulated genes identified by whole-exome/genome sequencing may have greater significance than previously recognized.

Bach2 repression mediates Th17 cell induced inflammation and associates with clinical features of advanced disease in chronic pancreatitis

Objectives

Altered immune homeostasis and involvement of T cells has been reported in chronic pancreatitis (CP). We evaluated the role of Bach2 (BTB and CNC homology basic leucine zipper transcription factor 2), a key regulator of immune homeostasis in the chronicity of CP.

Methods

Expression of Bach2 and T-cell transcription factors, enumeration of BACH2+/CD4+ T-lymphocytes were performed by qRT-PCR and flow cytometry respectively. Bach2silenced human CD4+ T-lymphocytes were exposed to CP tissue extract to assess T-cell lineage commitment. Aryl hydrocarbon receptor (Ahr) and Deubiquitinase enzyme A (DUBA/OTUD5gene) were evaluated as markers of persistent Th17 cell differentiation. Bach2 gene (exons) was sequenced to identify risk variants and functionally validated.

Results

Decrease in Bach2 (p < 0.0001) and increase (p < 0.001) in TBX21, RORC, Ahr, PRDM1, IL23R mRNA were noted in pancreatic tissues, while BACH2+/CD4+ T-lymphocytes were decreased (p < 0.01) in circulation and tissues. Exposure of Bach2 silenced CD4+ T-lymphocytes to CP tissue extract showed increased Ahr, decreased OTUD5, and enhanced Th17 cell differentiation. Sequencing of Bach2 gene revealed association of novel variant (rs9111 in 5'-UTR) with advanced disease and luciferase assay confirmed its role in Bach2 repression.

Conclusion

Bach2 repression mediates Th17 cell induced inflammation and rs9111-TT in individuals with primary genetic susceptibility to CP is associated with clinical features of advanced disease.

Genetics of rheumatoid arthritis susceptibility, severity, and treatment response

A decade after the first genome-wide association study in rheumatoid arthritis (RA), a plethora of genetic association studies have been published on RA and its clinical or serological subtypes. We review the major milestones in the study of the genetic architecture of RA susceptibility, severity, and response to treatment. We set the scientific context necessary for non-geneticists to understand the potential clinical applications of human genetics and its significance for a stratified approach to the management of RA in the future.

Enhancers and chromatin structures: regulatory hubs in gene expression and diseases

Gene expression requires successful communication between enhancer and promoter regions, whose activities are regulated by a variety of factors and associated with distinct chromatin structures; in addition, functionally related genes and their regulatory repertoire tend to be arranged in the same subchromosomal regulatory domains. In this review, we discuss the importance of enhancers, especially clusters of enhancers (such as super-enhancers), as key regulatory hubs to integrate environmental cues and encode spatiotemporal instructions for genome expression, which are critical for a variety of biological processes governing mammalian development. Furthermore, we emphasize that the enhancer–promoter interaction landscape provides a critical context to understand the aetiologies and mechanisms behind numerous complex human diseases and provides new avenues for effective transcription-based interventions.

Expression of long non-coding RNAs in autoimmunity and linkage to enhancer function and autoimmune disease risk genetic variants

Genome-wide association studies have identified numerous genetic variants conferring autoimmune disease risk. Most of these genetic variants lie outside protein-coding genes hampering mechanistic explorations. Numerous mRNAs are also differentially expressed in autoimmune disease but their regulation is also unclear. The majority of the human genome is transcribed yet its biologic significance is incompletely understood. We performed whole genome RNA-sequencing [RNA-seq] to categorize expression of mRNAs, known and novel long non-coding RNAs [lncRNAs] in leukocytes from subjects with autoimmune disease and identified annotated and novel lncRNAs differentially expressed across multiple disorders. We found that loci transcribing novel lncRNAs were not randomly distributed across the genome but co-localized with leukocyte transcriptional enhancers, especially super-enhancers, and near genetic variants associated with autoimmune disease risk. We propose that alterations in enhancer function, including lncRNA expression, produced by genetics and environment, change cellular phenotypes contributing to disease risk and pathogenesis and represent attractive therapeutic targets.

Higher-Order Chromatin Regulation of Inflammatory Gene Expression

Whether it is caused by viruses and bacteria infection, or low-grade chronic inflammation of atherosclerosis and cellular senescence, the transcription factor (TF) NF-κB plays a central role in the inducible expression of inflammatory genes. Accumulated evidence has indicated that the chromatin environment is the main determinant of TF binding in gene expression regulation, including the stimulus-responsive NF-κB. Dynamic changes in intra- and interchromosomes are the key regulatory mechanisms promoting the binding of TFs. When an inflammatory process is triggered, NF-κB binds to enhancers or superenhancers, triggering the transcription of enhancer RNA (eRNA), driving the chromatin of the NF-κB-binding gene locus to construct transcriptional factories, and forming intra- or interchromosomal contacts. These processes reveal a mechanism in which intrachromosomal contacts appear to be cis-control enhancer-promoter communications, whereas interchromosomal regulatory elements construct trans-form relationships with genes on other chromosomes. This article will review emerging evidence on the genome organization hierarchy underlying the inflammatory response.

Functional Architectures of Local and Distal Regulation of Gene Expression in Multiple Human Tissues

Genetic variants that modulate gene expression levels play an important role in the etiology of human diseases and complex traits. Although large-scale eQTL mapping studies routinely identify many local eQTLs, the molecular mechanisms by which genetic variants regulate expression remain unclear, particularly for distal eQTLs, which these studies are not well powered to detect. Here, we leveraged all variants (not just those that pass stringent significance thresholds) to analyze the functional architecture of local and distal regulation of gene expression in 15 human tissues by employing an extension of stratified LD-score regression that produces robust results in simulations. The top enriched functional categories in local regulation of peripheral-blood gene expression included coding regions (11.41×), conserved regions (4.67×), and four histone marks (p < 5 × 10^-5 for all enrichments); local enrichments were similar across the 15 tissues. We also observed substantial enrichments for distal regulation of peripheral-blood gene expression: coding regions (4.47×), conserved regions (4.51×), and two histone marks (p < 3 × 10^-7 for all enrichments). Analyses of the genetic correlation of gene expression across tissues confirmed that local regulation of gene expression is largely shared across tissues but that distal regulation is highly tissue specific. Our results elucidate the functional components of the genetic architecture of local and distal regulation of gene expression.

Antagonism of B cell enhancer networks by STAT5 drives leukemia and poor patient survival

The transcription factor STAT5 has a critical role in B cell acute lymphoblastic leukemia (B-ALL). How STAT5 mediates this effect is unclear. Here we found that activation of STAT5 worked together with defects in signaling components of the precursor to the B cell antigen receptor (pre-BCR), including defects in BLNK, BTK, PKCβ, NF-κB1 and IKAROS, to initiate B-ALL. STAT5 antagonized the transcription factors NF-κB and IKAROS by opposing regulation of shared target genes. Super-enhancers showed enrichment for STAT5 binding and were associated with an opposing network of transcription factors, including PAX5, EBF1, PU.1, IRF4 and IKAROS. Patients with a high ratio of active STAT5 to NF-κB or IKAROS had more-aggressive disease. Our studies indicate that an imbalance of two opposing transcriptional programs drives B-ALL and suggest that restoring the balance of these pathways might inhibit B-ALL.

Mechanisms and consequences of Jak-STAT signaling in the immune system

Kinases of the Jak ('Janus kinase') family and transcription factors (TFs) of the STAT ('signal transducer and activator of transcription') family constitute a rapid membrane-to-nucleus signaling module that affects every aspect of the mammalian immune system. Research on this paradigmatic pathway has experienced breakneck growth in the quarter century since its discovery and has yielded a stream of basic and clinical insights that have profoundly influenced modern understanding of human health and disease, exemplified by the bench-to-bedside success of Jak inhibitors ('jakinibs') and pathway-targeting drugs. Here we review recent advances in Jak-STAT biology, focusing on immune cell function, disease etiology and therapeutic intervention, as well as broader principles of gene regulation and signal-dependent TFs.

Functional Enhancers As Master Regulators of Tissue-Specific Gene Regulation and Cancer Development

Tissue-specific transcription is critical for normal development, and abnormalities causing undesirable gene expression may lead to diseases such as cancer. Such highly organized transcription is controlled by enhancers with specific DNA sequences recognized by transcription factors. Enhancers are associated with chromatin modifications that are distinct epigenetic features in a tissue-specific manner. Recently, super-enhancers comprising enhancer clusters co-occupied by lineage-specific factors have been identified in diverse cell types such as adipocytes, hair follicle stem cells, and mammary epithelial cells. In addition, noncoding RNAs, named eRNAs, are synthesized at super-enhancer regions before their target genes are transcribed. Many functional studies revealed that super-enhancers and eRNAs are essential for the regulation of tissue-specific gene expression. In this review, we summarize recent findings concerning enhancer function in tissue-specific gene regulation and cancer development.

Guidance of regulatory T cell development by Satb1-dependent super-enhancer establishment

Most Foxp3+ regulatory T (Treg) cells develop in the thymus as a functionally mature T cell subpopulation specialized for immune suppression. Their cell fate appears to be determined before Foxp3 expression; yet molecular events that prime Foxp3- Treg precursor cells are largely obscure. We found that Treg cell-specific super-enhancers (Treg-SEs), which were associated with Foxp3 and other Treg cell signature genes, began to be activated in Treg precursor cells. T cell-specific deficiency of the genome organizer Satb1 impaired Treg-SE activation and the subsequent expression of Treg signature genes, causing severe autoimmunity due to Treg cell deficiency. These results suggest that Satb1-dependent Treg-SE activation is crucial for Treg cell lineage specification in the thymus and that its perturbation is causative of autoimmune and other immunological diseases.

The histone demethylase UTX regulates the lineage-specific epigenetic program of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are innate-like lymphocytes that protect against infection, autoimmune disease and cancer. However, little is known about the epigenetic regulation of iNKT cell development. Here we found that the H3K27me3 histone demethylase UTX was an essential cell-intrinsic factor that controlled an iNKT-cell lineage-specific gene-expression program and epigenetic landscape in a demethylase-activity-dependent manner. UTX-deficient iNKT cells exhibited impaired expression of iNKT cell signature genes due to a decrease in activation-associated H3K4me3 marks and an increase in repressive H3K27me3 marks within the promoters occupied by UTX. We found that JunB regulated iNKT cell development and that the expression of genes that were targets of both JunB and the iNKT cell master transcription factor PLZF was UTX dependent. We identified iNKT cell super-enhancers and demonstrated that UTX-mediated regulation of super-enhancer accessibility was a key mechanism for commitment to the iNKT cell lineage. Our findings reveal how UTX regulates the development of iNKT cells through multiple epigenetic mechanisms.

Lingering Questions about Enhancer RNA and Enhancer Transcription-Coupled Genomic Instability

Intergenic and intragenic enhancers found inside topologically associated regulatory domains (TADs) express noncoding RNAs, known as enhancer RNAs (eRNAs). Recent studies have indicated these eRNAs play a role in gene regulatory networks by controlling promoter and enhancer interactions and topology of higher-order chromatin structure. Misregulation of enhancer and promoter associated noncoding RNAs (ncRNAs) could stabilize deleterious secondary DNA structures, noncoding RNA associated DNA/RNA hybrid formation, and promote collisions of transcription complexes with replisomes. It is revealing that many chromosomal aberrations, some associated with malignancies, are present inside enhancer and/or promoter sequences. Here, we expand on current concepts to discuss enhancer RNAs and enhancer transcription, and how enhancer transcription influences genomic organization and integrity.

Biogenesis and Transcriptional Regulation of Long Noncoding RNAs in the Human Immune System

The central dogma of molecular biology states that DNA makes RNA makes protein. Discoveries over the last quarter of a century found that the process of DNA transcription into RNA gives rise to a diverse array of functional RNA species, including genes that code for protein and noncoding RNAs. For decades, the focus has been on understanding how protein-coding genes are regulated to influence protein expression. However, with the completion of the Human Genome Project and follow-up ENCODE data, it is now appreciated that only 2-3% of the genome codes for protein-coding gene exons and that the bulk of the transcribed genome, apart from ribosomal RNAs, is at the level of noncoding RNA genes. In this article, we focus on the biogenesis and regulation of a distinct class of noncoding RNA molecules termed long, noncoding RNAs in the context of the immune system.

CD8+ T Cells Utilize Highly Dynamic Enhancer Repertoires and Regulatory Circuitry in Response to Infections

Differentiation of effector and memory CD8⁺ T cells is accompanied by extensive changes in the transcriptome and histone modifications at gene promoters; however, the enhancer repertoire and associated gene regulatory networks are poorly defined. Using histone mark chromatin immunoprecipitation coupled with deep sequencing, we mapped the enhancer and super-enhancer landscapes in antigen-specific naive, differentiated effector, and central memory CD8⁺ T cells during LCMV infection. Epigenomics-based annotation revealed a highly dynamic repertoire of enhancers, which were inherited, de novo activated, decommissioned and re-activated during CD8⁺ T cell responses. We employed a computational algorithm to pair enhancers with target gene promoters. On average, each enhancer targeted three promoters and each promoter was regulated by two enhancers. By identifying enriched transcription factor motifs in enhancers, we defined transcriptional regulatory circuitry at each CD8⁺ T cell response stage. These multi-dimensional datasets provide a blueprint for delineating molecular mechanisms underlying functional differentiation of CD8⁺ T cells.

Comparative analyses of super-enhancers reveal conserved elements in vertebrate genomes

Super-enhancers (SEs) are key transcriptional drivers of cellular, developmental, and disease states in mammals, yet the conservational and regulatory features of these enhancer elements in nonmammalian vertebrates are unknown. To define SEs in zebrafish and enable sequence and functional comparisons to mouse and human SEs, we used genome-wide histone H3 lysine 27 acetylation (H3K27ac) occupancy as a primary SE delineator. Our study determined the set of SEs in pluripotent state cells and adult zebrafish tissues and revealed both similarities and differences between zebrafish and mammalian SEs. Although the total number of SEs was proportional to the genome size, the genomic distribution of zebrafish SEs differed from that of the mammalian SEs. Despite the evolutionary distance separating zebrafish and mammals and the low overall SE sequence conservation, ∼42% of zebrafish SEs were located in close proximity to orthologs that also were associated with SEs in mouse and human. Compared to their nonassociated counterparts, higher sequence conservation was revealed for those SEs that have maintained orthologous gene associations. Functional dissection of two of these SEs identified conserved sequence elements and tissue-specific expression patterns, while chromatin accessibility analyses predicted transcription factors governing the function of pluripotent state zebrafish SEs. Our zebrafish annotations and comparative studies show the extent of SE usage and their conservation across vertebrates, permitting future gene regulatory studies in several tissues.

Immune disease-associated variants in gene enhancers point to BET epigenetic mechanisms for therapeutic intervention

Genome-wide association studies have identified thousands of single nucleotide polymorphisms in the human genome that are statistically associated with particular disease traits. In this Perspective, we review emerging data suggesting that most single nucleotide polymorphisms associated with immune-mediated diseases are found in regulatory regions of the DNA - parts of the genome that control expression of the protein encoding genes - rather than causing mutations in proteins. We discuss how the emerging understanding of particular gene regulatory regions, gene enhancers and the epigenetic mechanisms by which they are regulated is opening up new opportunities for the treatment of immune-mediated diseases, focusing particularly on the BET family of epigenetic reader proteins as potential therapeutic targets.

A tissue checkpoint regulates type 2 immunity

Group 2 innate lymphoid cells (ILC2s) and CD4+ type 2 helper T cells (TH2 cells) are defined by their similar effector cytokines, which together mediate the features of allergic immunity. We found that tissue ILC2s and TH2 cells differentiated independently but shared overlapping effector function programs that were mediated by exposure to the tissue-derived cytokines interleukin 25 (IL-25), IL-33 and thymic stromal lymphopoietin (TSLP). Loss of these three tissue signals did not affect lymph node priming, but abrogated the terminal differentiation of effector TH2 cells and adaptive lung inflammation in a T cell-intrinsic manner. Our findings suggest a mechanism by which diverse perturbations can activate type 2 immunity and reveal a shared local-tissue-elicited checkpoint that can be exploited to control both innate and adaptive allergic inflammation.

Impact of the gut microbiota on enhancer accessibility in gut intraepithelial lymphocytes

The gut microbiota impacts many aspects of host biology including immune function. One hypothesis is that microbial communities induce epigenetic changes with accompanying alterations in chromatin accessibility, providing a mechanism that allows a community to have sustained host effects even in the face of its structural or functional variation. We used Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq) to define chromatin accessibility in predicted enhancer regions of intestinal αβ⁺ and γδ⁺ intraepithelial lymphocytes purified from germ-free mice, their conventionally raised (CONV-R) counterparts, and mice reared germ free and then colonized with CONV-R gut microbiota at the end of the suckling-weaning transition. Characterizing genes adjacent to traditional enhancers and super-enhancers revealed signaling networks, metabolic pathways, and enhancer-associated transcription factors affected by the microbiota. Our results support the notion that epigenetic modifications help define microbial community-affiliated functional features of host immune cell lineages.

Update on the genetic architecture of rheumatoid arthritis

Human genetic studies into rheumatoid arthritis (RA) have uncovered more than 100 genetic loci associated with susceptibility to RA and have refined the RA-association model for HLA variants. The majority of RA-risk variants are highly shared across multiple ancestral populations and are located in noncoding elements that might have allele-specific regulatory effects in relevant tissues. Emerging multi-omics data, high-density genotype data and bioinformatic approaches are enabling researchers to use RA-risk variants to identify functionally relevant cell types and biological pathways that are involved in impaired immune processes and disease phenotypes. This Review summarizes reported RA-risk loci and the latest insights from human genetic studies into RA pathogenesis, including how genetic data has helped to identify currently available drugs that could be repurposed for patients with RA and the role of genetics in guiding the development of new drugs.

Targeting cytokine signaling in autoimmunity: back to the future and beyond

Cytokines represent structurally diverse soluble factors with critical roles in normal immune function and the pathogenesis of autoimmunity. The emergence of many successful biological therapies targeting cytokines and cytokine receptors exemplifies the importance of cytokines in driving human autoimmune disease; unsurprisingly, there is no paucity of reviews on this subject. Nonetheless, many patients with autoimmune disease do not respond to biologicals, and cure remains an unmet goal. Thus, targeting the intracellular pathways employed by cytokines provides new therapeutic opportunities. A subset of cytokines utilizes the Janus kinase-signal transducer of activators of transcription (JAK-STAT) pathway as a mode of signal transduction. First generation JAK inhibitors (jakinibs) are used to treat rheumatologic disease, and second-generation jakinibs are being developed. Simultaneously, rapid advances are being made in our understanding of the genomic and epigenomic impact of cytokines. In this review, we will briefly review the role of JAK-STAT-dependent cytokines in immune-mediated disease, the current status of Jakinibs, and future possibilities for therapeutic intervention using genomic insights.

Nucleoporin-mediated regulation of cell identity genes

Here, Ibarra et al. investigate the contribution of nuclear envelope components to the regulation of cell type-specific gene expression and show a role for NPC components in the regulation of cell type-specific gene expression The authors found that nucleoporin-associated superenhancers localize preferentially to the nuclear periphery, and, in the absence of nucleoporins, transcriptional changes of SE-associated genes were observed.

The organization of the genome in the three-dimensional space of the nucleus is coupled with cell type-specific gene expression. However, how nuclear architecture influences transcription that governs cell identity remains unknown. Here, we show that nuclear pore complex (NPC) components Nup93 and Nup153 bind superenhancers (SE), regulatory structures that drive the expression of key genes that specify cell identity. We found that nucleoporin-associated SEs localize preferentially to the nuclear periphery, and absence of Nup153 and Nup93 results in dramatic transcriptional changes of SE-associated genes. Our results reveal a crucial role of NPC components in the regulation of cell type-specifying genes and highlight nuclear architecture as a regulatory layer of genome functions in cell fate.

The Functionality and Evolution of Eukaryotic Transcriptional Enhancers

Enhancers regulate precise spatial and temporal patterns of gene expression in eukaryotes and, moreover, evolutionary changes in these modular cis-regulatory elements may represent the predominant genetic basis for phenotypic evolution. Here, we review approaches to identify and functionally analyze enhancers and their transcription factor binding sites, including assay for transposable-accessible chromatin-sequencing (ATAC-Seq) and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9, respectively. We also explore enhancer functionality, including how transcription factor binding sites combine to regulate transcription, as well as research on shadow and super enhancers, and how enhancers can act over great distances and even in trans. Finally, we discuss recent theoretical and empirical data on how transcription factor binding sites and enhancers evolve. This includes how the function of enhancers is maintained despite the turnover of transcription factor binding sites as well as reviewing studies where mutations in enhancers have been shown to underlie morphological change.

Chemical JAK inhibitors for the treatment of rheumatoid arthritis

INTRODUCTION

Considerable advances in the treatment of rheumatoid arthritis (RA) have been made following the advent of biological disease-modifying anti-rheumatic drugs (DMARDs). However, biological DMARDs require intravenous or subcutaneous injection and some patients fail to respond to these drugs or lose their primary response. Currently, Janus kinase (JAK) inhibitors have been developed as a new class of DMARD that inhibits the non-receptor tyrosine kinase family JAK involved in intracellular signaling of various cytokines and growth factors. Areas covered: Several JAK inhibitors such as tofacitinib and baricitinib are oral synthetic DMARD that inhibit JAK1, 2 and 3. Both drugs have shown feasible efficacy and tolerable safety. In this article, efficacy and adverse events from the phase III trials of JAK inhibitors are overviewed. In addition, pharmacokinetics and mechanism of action of JAK inhibitors in relevance to efficacy and adverse events are covered. Expert opinion: JAK inhibitors are novel therapies for RA that inhibit multiple cytokines and signaling pathways. Further studies are needed to determine their risk-benefit ratio and selection of the most appropriate patients for such therapy.

Epigenomic Consequences of Coding and Noncoding Driver Mutations

Chromatin alterations are integral to the pathogenic process of cancer, as demonstrated by recent discoveries of frequent mutations in chromatin-modifier genes and aberrant DNA methylation states in different cancer types. Progress is being made on elucidating how chromatin alterations, and how proteins catalyzing these alterations, mechanistically contribute to tissue-specific tumorigenesis. In parallel, technologies enabling the genome-wide profiling of histone modifications have revealed the existence of noncoding driver genetic alterations in cancer. In this review, we survey the current knowledge of coding and noncoding cancer drivers, and discuss their impact on the chromatin landscape. Translational implications of these findings for novel cancer therapies are also presented.

RNA Sequencing of Formalin-Fixed, Paraffin-Embedded Specimens for Gene Expression Quantification and Data Mining

Background. Proper rRNA depletion is crucial for the successful utilization of FFPE specimens when studying gene expression. We performed a study to evaluate two major rRNA depletion methods: Ribo-Zero and RNase H. RNAs extracted from 4 samples were treated with the two rRNA depletion methods in duplicate and sequenced (N = 16). We evaluated their reducibility, ability to detect RNA, and ability to molecularly subtype these triple negative breast cancer specimens. Results. Both rRNA depletion methods produced consistent data between the technical replicates. We found that the RNase H method produced higher quality RNAseq data as compared to the Ribo-Zero method. In addition, we evaluated the RNAseq data generated from the FFPE tissue samples for noncoding RNA, including lncRNA, enhancer/super enhancer RNA, and single nucleotide variation (SNV). We found that the RNase H is more suitable for detecting high-quality, noncoding RNAs as compared to the Ribo-Zero and provided more consistent molecular subtype identification between replicates. Unfortunately, neither method produced reliable SNV data. Conclusions. In conclusion, for FFPE specimens, the RNase H rRNA depletion method performed better than the Ribo-Zero. Neither method generates data sufficient for SNV detection.

Shrinking the Psoriasis Assessment Gap: Early Gene-Expression Profiling Accurately Predicts Response to Long-Term Treatment

There is an "assessment gap" between the moment a patient's response to treatment is biologically determined and when a response can actually be determined clinically. Patients' biochemical profiles are a major determinant of clinical outcome for a given treatment. It is therefore feasible that molecular-level patient information could be used to decrease the assessment gap. Thanks to clinically accessible biopsy samples, high-quality molecular data for psoriasis patients are widely available. Psoriasis is therefore an excellent disease for testing the prospect of predicting treatment outcome from molecular data. Our study shows that gene-expression profiles of psoriasis skin lesions, taken in the first 4 weeks of treatment, can be used to accurately predict (>80% area under the receiver operating characteristic curve) the clinical endpoint at 12 weeks. This could decrease the psoriasis assessment gap by 2 months. We present two distinct prediction modes: a universal predictor, aimed at forecasting the efficacy of untested drugs, and specific predictors aimed at forecasting clinical response to treatment with four specific drugs: etanercept, ustekinumab, adalimumab, and methotrexate. We also develop two forms of prediction: one from detailed, platform-specific data and one from platform-independent, pathway-based data. We show that key biomarkers are associated with responses to drugs and doses and thus provide insight into the biology of pathogenesis reversion.

Genetic dissection of the α-globin super-enhancer in vivo

Many genes determining cell identity are regulated by clusters of Mediator-bound enhancer elements collectively referred to as super-enhancers. These super-enhancers have been proposed to manifest higher-order properties important in development and disease. Here we report a comprehensive functional dissection of one of the strongest putative super-enhancers in erythroid cells. By generating a series of mouse models, deleting each of the five regulatory elements of the α-globin super-enhancer individually and in informative combinations, we demonstrate that each constituent enhancer seems to act independently and in an additive fashion with respect to hematological phenotype, gene expression, chromatin structure and chromosome conformation, without clear evidence of synergistic or higher-order effects. Our study highlights the importance of functional genetic analyses for the identification of new concepts in transcriptional regulation.

Base-pair-resolution genome-wide mapping of active RNA polymerases using precision nuclear run-on (PRO-seq)

We provide a protocol for precision nuclear run-on sequencing (PRO-seq) and its variant, PRO-cap, which map the location of active RNA polymerases (PRO-seq) or transcription start sites (TSSs) (PRO-cap) genome-wide at high resolution. The density of RNA polymerases at a particular genomic locus directly reflects the level of nascent transcription at that region. Nuclei are isolated from cells and, under nuclear run-on conditions, transcriptionally engaged RNA polymerases incorporate one or, at most, a few biotin-labeled nucleotide triphosphates (biotin-NTPs) into the 3' end of nascent RNA. The biotin-labeled nascent RNA is used to prepare sequencing libraries, which are sequenced from the 3' end to provide high-resolution positional information for the RNA polymerases. PRO-seq provides much higher sensitivity than ChIP-seq, and it generates a much larger fraction of usable sequence reads than ChIP-seq or NET-seq (native elongating transcript sequencing). Similarly to NET-seq, PRO-seq maps the RNA polymerase at up to base-pair resolution with strand specificity, but unlike NET-seq it does not require immunoprecipitation. With the protocol provided here, PRO-seq (or PRO-cap) libraries for high-throughput sequencing can be generated in 4-5 working days. The method has been applied to human, mouse, Drosophila melanogaster and Caenorhabditis elegans cells and, with slight modifications, to yeast.

Genetics and immunity in the era of single-cell genomics

Recent developments in the field of single-cell genomics (SCG) are changing our understanding of how functional phenotypes of cell populations emerge from the behaviour of individual cells. Some of the applications of SCG include the discovery of new gene networks and novel cell subpopulations, fine mapping of transcription kinetics, and the relationships between cell clonality and their functional phenotypes. Immunology is one of the fields that is benefiting the most from such advancements, providing us with completely new insights into mammalian immunity. In this review, we start by covering new immunological insights originating from the use of single-cell genomic tools, specifically single-cell RNA-sequencing. Furthermore, we discuss how new genetic study designs are starting to explain inter-individual variation in the immune response. We conclude with a perspective on new multi-omics technologies capable of integrating several readouts from the same single cell and how such techniques might push our biological understanding of mammalian immunity to a new level.

Multiple layers of transcriptional regulation by PLZF in NKT-cell development

The transcription factor PLZF [promyelocytic leukemia zinc finger, encoded by zinc finger BTB domain containing 16 (Zbtb16)] is induced during the development of innate and innate-like lymphocytes to direct their acquisition of a T-helper effector program, but the molecular mechanisms involved are poorly understood. Using biotinylation-based ChIP-seq and microarray analysis of both natural killer T (NKT) cells and PLZF-transgenic thymocytes, we identified several layers of regulation of the innate-like NKT effector program. First, PLZF bound and regulated genes encoding cytokine receptors as well as homing and adhesion receptors; second, PLZF bound and activated T-helper-specific transcription factor genes that in turn control T-helper-specific programs; finally, PLZF bound and suppressed the transcription of Bach2, a potent general repressor of effector differentiation in naive T cells. These findings reveal the multilayered architecture of the transcriptional program recruited by PLZF and elucidate how a single transcription factor can drive the developmental acquisition of a broad effector program.

Hierarchy within the mammary STAT5-driven Wap super-enhancer

Super-enhancers comprise of dense transcription factor platforms highly enriched for active chromatin marks. A paucity of functional data led us to investigate their role in the mammary gland, an organ characterized by exceptional gene regulatory dynamics during pregnancy. ChIP-Seq for the master regulator STAT5, the glucocorticoid receptor, H3K27ac and MED1, identified 440 mammary-specific super-enhancers, half of which were associated with genes activated during pregnancy. We interrogated the Wap super-enhancer, generating mice carrying mutations in STAT5 binding sites within its three constituent enhancers. Individually, only the most distal site displayed significant enhancer activity. However, combinatorial mutations showed that the 1,000-fold gene induction relied on all enhancers. Disabling the binding sites of STAT5, NFIB and ELF5 in the proximal enhancer incapacitated the entire super-enhancer, suggesting an enhancer hierarchy. The identification of mammary-specific super-enhancers and the mechanistic exploration of the Wap locus provide insight into the complexity of cell-specific and hormone-regulated genes.

Epigenetic mechanisms involved in modulation of inflammatory diseases

PURPOSE OF REVIEW

The activation of inflammatory response is dependent upon genetic factors and epigenetic control mechanisms. This overview will highlight recent advances in the understanding of epigenetic dynamics during cellular inflammation.

RECENT FINDINGS

There is a growing body of evidence indicating that alterations of the chromatin state associate with an increased risk of chronic disease development and inflammation. Epigenetic alterations respond rapidly to environmental changes and have a profound effect on gene regulatory cross-wirings and transcriptional regulation.

SUMMARY

Systematic dissection of the mechanisms underlying epigenetic effects during inflammatory response is a critical step toward elucidation of the cell's molecular processes and holds potential for the development of novel therapies for the treatment of chronic diseases.

Dysregulation of Th1, Th2, Th17, and T regulatory cell-related transcription factor signaling in children with autism

Autism is a neurodevelopmental disorder characterized by stereotypic repetitive behaviors, impaired social interactions, and communication deficits. Numerous immune system abnormalities have been described in individuals with autism including abnormalities in the ratio of Th1/Th2/Th17 cells; however, the expression of the transcription factors responsible for the regulation and differentiation of Th1/Th2/Th17/Treg cells has not previously been evaluated. Peripheral blood mononuclear cells (PBMCs) from children with autism (AU) or typically developing (TD) control children were stimulated with phorbol-12-myristate 13-acetate (PMA) and ionomycin in the presence of brefeldin A. The expressions of Foxp3, RORγt, STAT-3, T-bet, and GATA-3 mRNAs and proteins were then assessed. Our study shows that children with AU displayed altered immune profiles and function, characterized by a systemic deficit of Foxp3⁺ T regulatory (Treg) cells and increased RORγt⁺, T-bet⁺, GATA-3⁺, and production by CD4⁺ T cells as compared to TD. This was confirmed by real-time PCR (RT-PCR) and western blot analyses. Our results suggest that autism impacts transcription factor signaling, which results in an immunological imbalance. Therefore, the restoration of transcription factor signaling may have a great therapeutic potential in the treatment of autistic disorders.

T-bet Activates Th1 Genes through Mediator and the Super Elongation Complex

The transcription factor T-bet directs Th1 cell differentiation, but the molecular mechanisms that underlie this lineage-specific gene regulation are not completely understood. Here, we show that T-bet acts through enhancers to allow the recruitment of Mediator and P-TEFb in the form of the super elongation complex (SEC). Th1 genes are occupied by H3K4me3 and RNA polymerase II in Th2 cells, while T-bet-mediated recruitment of P-TEFb in Th1 cells activates transcriptional elongation. P-TEFb is recruited to both genes and enhancers, where it activates enhancer RNA transcription. P-TEFb inhibition and Mediator and SEC knockdown selectively block activation of T-bet target genes, and P-TEFb inhibition abrogates Th1-associated experimental autoimmune uveitis. T-bet activity is independent of changes in NF-κB RelA and Brd4 binding, with T-bet- and NF-κB-mediated pathways instead converging to allow P-TEFb recruitment. These data provide insight into the mechanism through which lineage-specifying factors promote differentiation of alternative T cell fates.