bims-crepig Biomed News
on Chromatin regulation and epigenetics in cell fate and cancer
Issue of 2020‒05‒31
forty-three papers selected by
Connor Rogerson
University of Cambridge, MRC Cancer Unit


  1. Nat Commun. 2020 May 29. 11(1): 2680
    Ginno PA, Gaidatzis D, Feldmann A, Hoerner L, Imanci D, Burger L, Zilbermann F, Peters AHFM, Edenhofer F, Smallwood SA, Krebs AR, Schübeler D.
      DNA methylation is considered a stable epigenetic mark, yet methylation patterns can vary during differentiation and in diseases such as cancer. Local levels of DNA methylation result from opposing enzymatic activities, the rates of which remain largely unknown. Here we developed a theoretical and experimental framework enabling us to infer methylation and demethylation rates at 860,404 CpGs in mouse embryonic stem cells. We find that enzymatic rates can vary as much as two orders of magnitude between CpGs with identical steady-state DNA methylation. Unexpectedly, de novo and maintenance methylation activity is reduced at transcription factor binding sites, while methylation turnover is elevated in transcribed gene bodies. Furthermore, we show that TET activity contributes substantially more than passive demethylation to establishing low methylation levels at distal enhancers. Taken together, our work unveils a genome-scale map of methylation kinetics, revealing highly variable and context-specific activity for the DNA methylation machinery.
    DOI:  https://doi.org/10.1038/s41467-020-16354-x
  2. Nucleic Acids Res. 2020 May 27. pii: gkaa441. [Epub ahead of print]
    Zhu X, Lan B, Yi X, He C, Dang L, Zhou X, Lu Y, Sun Y, Liu Z, Bai X, Zhang K, Li B, Li MJ, Chen Y, Zhang L.
      Functional crosstalk between histone modifications and chromatin remodeling has emerged as a key regulatory mode of transcriptional control during cell fate decisions, but the underlying mechanisms are not fully understood. Here we discover an HRP2-DPF3a-BAF epigenetic pathway that coordinates methylated histone H3 lysine 36 (H3K36me) and ATP-dependent chromatin remodeling to regulate chromatin dynamics and gene transcription during myogenic differentiation. Using siRNA screening targeting epigenetic modifiers, we identify hepatoma-derived growth factor-related protein 2 (HRP2) as a key regulator of myogenesis. Knockout of HRP2 in mice leads to impaired muscle regeneration. Mechanistically, through its HIV integrase binding domain (IBD), HRP2 associates with the BRG1/BRM-associated factor (BAF) chromatin remodeling complex by interacting directly with the BAF45c (DPF3a) subunit. Through its Pro-Trp-Trp-Pro (PWWP) domain, HRP2 preferentially binds to H3K36me2. Consistent with the biochemical studies, ChIP-seq analyses show that HRP2 colocalizes with DPF3a across the genome and that the recruitment of HRP2/DPF3a to chromatin is dependent on H3K36me2. Integrative transcriptomic and cistromic analyses, coupled with ATAC-seq, reveal that HRP2 and DPF3a activate myogenic genes by increasing chromatin accessibility through recruitment of BRG1, the ATPase subunit of the BAF complex. Taken together, these results illuminate a key role for the HRP2-DPF3a-BAF complex in the epigenetic coordination of gene transcription during myogenic differentiation.
    DOI:  https://doi.org/10.1093/nar/gkaa441
  3. Cell. 2020 May 20. pii: S0092-8674(20)30553-5. [Epub ahead of print]
    Michealraj KA, Kumar SA, Kim LJY, Cavalli FMG, Przelicki D, Wojcik JB, Delaidelli A, Bajic A, Saulnier O, MacLeod G, Vellanki RN, Vladoiu MC, Guilhamon P, Ong W, Lee JJY, Jiang Y, Holgado BL, Rasnitsyn A, Malik AA, Tsai R, Richman CM, Juraschka K, Haapasalo J, Wang EY, De Antonellis P, Suzuki H, Farooq H, Balin P, Kharas K, Van Ommeren R, Sirbu O, Rastan A, Krumholtz SL, Ly M, Ahmadi M, Deblois G, Srikanthan D, Luu B, Loukides J, Wu X, Garzia L, Ramaswamy V, Kanshin E, Sánchez-Osuna M, El-Hamamy I, Coutinho FJ, Prinos P, Singh S, Donovan LK, Daniels C, Schramek D, Tyers M, Weiss S, Stein LD, Lupien M, Wouters BG, Garcia BA, Arrowsmith CH, Sorensen PH, Angers S, Jabado N, Dirks PB, Mack SC, Agnihotri S, Rich JN, Taylor MD.
      Posterior fossa A (PFA) ependymomas are lethal malignancies of the hindbrain in infants and toddlers. Lacking highly recurrent somatic mutations, PFA ependymomas are proposed to be epigenetically driven tumors for which model systems are lacking. Here we demonstrate that PFA ependymomas are maintained under hypoxia, associated with restricted availability of specific metabolites to diminish histone methylation, and increase histone demethylation and acetylation at histone 3 lysine 27 (H3K27). PFA ependymomas initiate from a cell lineage in the first trimester of human development that resides in restricted oxygen. Unlike other ependymomas, transient exposure of PFA cells to ambient oxygen induces irreversible cellular toxicity. PFA tumors exhibit a low basal level of H3K27me3, and, paradoxically, inhibition of H3K27 methylation specifically disrupts PFA tumor growth. Targeting metabolism and/or the epigenome presents a unique opportunity for rational therapy for infants with PFA ependymoma.
    Keywords:  cancer metabolism; ependymoma; epigenetics; hindbrain development; microenvironment; paediatric cancer
    DOI:  https://doi.org/10.1016/j.cell.2020.04.047
  4. Cell Rep. 2020 May 26. pii: S2211-1247(20)30629-X. [Epub ahead of print]31(8): 107676
    Lazar JE, Stehling-Sun S, Nandakumar V, Wang H, Chee DR, Howard NP, Acosta R, Dunn D, Diegel M, Neri F, Castillo A, Ibarrientos S, Lee K, Lescano N, Van Biber B, Nelson J, Halow J, Sandstrom R, Bates D, Urnov FD, Funnell APW, Stamatoyannopoulos JA.
      The human genome encodes millions of regulatory elements, of which only a small fraction are active within a given cell type. Little is known about the global impact of chromatin remodelers on regulatory DNA landscapes and how this translates to gene expression. We use precision genome engineering to reawaken homozygously inactivated SMARCA4, a central ATPase of the human SWI/SNF chromatin remodeling complex, in lung adenocarcinoma cells. Here, we combine DNase I hypersensitivity, histone modification, and transcriptional profiling to show that SMARCA4 dramatically increases both the number and magnitude of accessible chromatin sites genome-wide, chiefly by unmasking sites of low regulatory factor occupancy. By contrast, transcriptional changes are concentrated within well-demarcated remodeling domains wherein expression of specific genes is gated by both distal element activation and promoter chromatin configuration. Our results provide a perspective on how global chromatin remodeling activity is translated to gene expression via regulatory DNA.
    Keywords:  BAF complex; SMARCA4; cancer epigenetics; chromatin accessibility; chromatin domains; chromatin remodeling; gene regulation; lung adenocarcinoma; topologically associating domains
    DOI:  https://doi.org/10.1016/j.celrep.2020.107676
  5. BMC Bioinformatics. 2020 May 26. 21(1): 214
    Roth SJ, Heinz S, Benner C.
      BACKGROUND: Mounting evidence suggests several diseases and biological processes target transcription termination to misregulate gene expression. Disruption of transcription termination leads to readthrough transcription past the 3' end of genes, which can result in novel transcripts, changes in epigenetic states and altered 3D genome structure.RESULTS: We developed Automatic Readthrough Transcription Detection (ARTDeco), a tool to detect and analyze multiple features of readthrough transcription from RNA-seq and other next-generation sequencing (NGS) assays that profile transcriptional activity. ARTDeco robustly quantifies the global severity of readthrough phenotypes, and reliably identifies individual genes that fail to terminate (readthrough genes), are aberrantly transcribed due to upstream termination failure (read-in genes), and novel transcripts created as a result of readthrough (downstream of gene or DoG transcripts). We used ARTDeco to characterize readthrough transcription observed during influenza A virus (IAV) infection, validating its specificity and sensitivity by comparing its performance in samples infected with a mutant virus that fails to block transcription termination. We verify ARTDeco's ability to detect readthrough as well as identify read-in genes from different experimental assays across multiple experimental systems with known defects in transcriptional termination, and show how these results can be leveraged to improve the interpretation of gene expression and downstream analysis. Applying ARTDeco to a gene expression data set from IAV-infected monocytes from different donors, we find strong evidence that read-in gene-associated expression quantitative trait loci (eQTLs) likely regulate genes upstream of read-in genes. This indicates that taking readthrough transcription into account is important for the interpretation of eQTLs in systems where transcription termination is blocked.
    CONCLUSIONS: ARTDeco aids researchers investigating readthrough transcription in a variety of systems and contexts.
    Keywords:  Gene expression; Next-generation sequencing analysis; Readthrough transcription; Transcription termination; Transcriptomics
    DOI:  https://doi.org/10.1186/s12859-020-03551-0
  6. Cell Mol Life Sci. 2020 May 23.
    Yi M, Tan Y, Wang L, Cai J, Li X, Zeng Z, Xiong W, Li G, Li X, Tan P, Xiang B.
      Squamous cell carcinoma (SCC) is an aggressive malignancy that can originate from various organs. TP63 is a master regulator that plays an essential role in epidermal differentiation. It is also a lineage-dependent oncogene in SCC. ΔNp63α is the prominent isoform of TP63 expressed in epidermal cells and SCC, and overexpression promotes SCC development through a variety of mechanisms. Recently, ΔNp63α was highlighted to act as an epidermal-specific pioneer factor that binds closed chromatin and enhances chromatin accessibility at epidermal enhancers. ΔNp63α coordinates chromatin-remodeling enzymes to orchestrate the tissue-specific enhancer landscape and three-dimensional high-order architecture of chromatin. Moreover, ΔNp63α establishes squamous-like enhancer landscapes to drive oncogenic target expression during SCC development. Importantly, ΔNp63α acts as an upstream regulator of super enhancers to activate a number of oncogenic transcripts linked to poor prognosis in SCC. Mechanistically, ΔNp63α activates genes transcription through physically interacting with a number of epigenetic modulators to establish enhancers and enhance chromatin accessibility. In contrast, ΔNp63α also represses gene transcription via interacting with repressive epigenetic regulators. ΔNp63α expression is regulated at multiple levels, including transcriptional, post-transcriptional, and post-translational levels. In this review, we summarize recent advances of p63 in epigenomic and transcriptional control, as well as the mechanistic regulation of p63.
    Keywords:  Basal cell; Epigenetic reprogramming; Histone modification; Oncogene addiction; SWI/SNF complex; Ubiquitin–proteasome system
    DOI:  https://doi.org/10.1007/s00018-020-03539-2
  7. Am J Hum Genet. 2020 May 21. pii: S0002-9297(20)30125-7. [Epub ahead of print]
    Melo US, Schöpflin R, Acuna-Hidalgo R, Mensah MA, Fischer-Zirnsak B, Holtgrewe M, Klever MK, Türkmen S, Heinrich V, Pluym ID, Matoso E, Bernardo de Sousa S, Louro P, Hülsemann W, Cohen M, Dufke A, Latos-Bieleńska A, Vingron M, Kalscheuer V, Quintero-Rivera F, Spielmann M, Mundlos S.
      Genome-wide analysis methods, such as array comparative genomic hybridization (CGH) and whole-genome sequencing (WGS), have greatly advanced the identification of structural variants (SVs) in the human genome. However, even with standard high-throughput sequencing techniques, complex rearrangements with multiple breakpoints are often difficult to resolve, and predicting their effects on gene expression and phenotype remains a challenge. Here, we address these problems by using high-throughput chromosome conformation capture (Hi-C) generated from cultured cells of nine individuals with developmental disorders (DDs). Three individuals had previously been identified as harboring duplications at the SOX9 locus and six had been identified with translocations. Hi-C resolved the positions of the duplications and was instructive in interpreting their distinct pathogenic effects, including the formation of new topologically associating domains (neo-TADs). Hi-C was very sensitive in detecting translocations, and it revealed previously unrecognized complex rearrangements at the breakpoints. In several cases, we observed the formation of fused-TADs promoting ectopic enhancer-promoter interactions that were likely to be involved in the disease pathology. In summary, we show that Hi-C is a sensible method for the detection of complex SVs in a clinical setting. The results help interpret the possible pathogenic effects of the SVs in individuals with DDs.
    Keywords:  Hi-C; chromosome conformation capture; cytogenetics; developmental disorders; ectopic enhancer-promoter interactions; gene misregulation; neo-TAD; topologically associating domains
    DOI:  https://doi.org/10.1016/j.ajhg.2020.04.016
  8. Nucleic Acids Res. 2020 May 27. pii: gkaa382. [Epub ahead of print]
    Baumgarten N, Hecker D, Karunanithi S, Schmidt F, List M, Schulz MH.
      A current challenge in genomics is to interpret non-coding regions and their role in transcriptional regulation of possibly distant target genes. Genome-wide association studies show that a large part of genomic variants are found in those non-coding regions, but their mechanisms of gene regulation are often unknown. An additional challenge is to reliably identify the target genes of the regulatory regions, which is an essential step in understanding their impact on gene expression. Here we present the EpiRegio web server, a resource of regulatory elements (REMs). REMs are genomic regions that exhibit variations in their chromatin accessibility profile associated with changes in expression of their target genes. EpiRegio incorporates both epigenomic and gene expression data for various human primary cell types and tissues, providing an integrated view of REMs in the genome. Our web server allows the analysis of genes and their associated REMs, including the REM's activity and its estimated cell type-specific contribution to its target gene's expression. Further, it is possible to explore genomic regions for their regulatory potential, investigate overlapping REMs and by that the dissection of regions of large epigenomic complexity. EpiRegio allows programmatic access through a REST API and is freely available at https://epiregio.de/.
    DOI:  https://doi.org/10.1093/nar/gkaa382
  9. Mol Cell. 2020 May 16. pii: S1097-2765(20)30268-9. [Epub ahead of print]
    Kong M, Cutts EE, Pan D, Beuron F, Kaliyappan T, Xue C, Morris EP, Musacchio A, Vannini A, Greene EC.
      Structural maintenance of chromosomes (SMC) complexes are essential for genome organization from bacteria to humans, but their mechanisms of action remain poorly understood. Here, we characterize human SMC complexes condensin I and II and unveil the architecture of the human condensin II complex, revealing two putative DNA-entrapment sites. Using single-molecule imaging, we demonstrate that both condensin I and II exhibit ATP-dependent motor activity and promote extensive and reversible compaction of double-stranded DNA. Nucleosomes are incorporated into DNA loops during compaction without being displaced from the DNA, indicating that condensin complexes can readily act upon nucleosome-bound DNA molecules. These observations shed light on critical processes involved in genome organization in human cells.
    Keywords:  DNA curtain; SMC complexes; chromosome organization; condensin; crosslinking mass spectroscopy; electron microscopy; loop extrusion; single molecule
    DOI:  https://doi.org/10.1016/j.molcel.2020.04.026
  10. BMC Genomics. 2020 May 29. 21(1): 375
    Teng CS, Wu BH, Yen MR, Chen PY.
      BACKGROUND: DNA methylation is a major epigenetic modification involved in regulating gene expression. The effects of DNA methylation on gene expression differ by genomic location and vary across kingdoms, species and environmental conditions. To identify the functional regulatory roles of DNA methylation, the correlation between DNA methylation changes and alterations in gene expression is crucial. With the advance of next-generation sequencing, genome-wide methylation and gene expression profiling have become feasible. Current bioinformatics tools for investigating such correlation are designed to the assessment of DNA methylation at CG sites. The correlation of non-CG methylation and gene expression is very limited. Some bioinformatics databases allow correlation analysis, but they are limited to specific genomes such as that of humans and do not allow user-provided data.RESULTS: Here, we developed a bioinformatics web tool, MethGET (Methylation and Gene Expression Teller), that is specialized to analyse the association between genome-wide DNA methylation and gene expression. MethGET is the first web tool to which users can supply their own data from any genome. It is also the tool that correlates gene expression with CG, CHG, and CHH methylation based on whole-genome bisulfite sequencing data. MethGET not only reveals the correlation within an individual sample (single-methylome) but also performs comparisons between two groups of samples (multiple-methylomes). For single-methylome analyses, MethGET provides Pearson correlations and ordinal associations to investigate the relationship between DNA methylation and gene expression. It also groups genes with different gene expression levels to view the methylation distribution at specific genomic regions. Multiple-methylome analyses include comparative analyses and heatmap representations between two groups. These functions enable the detailed investigation of the role of DNA methylation in gene regulation. Additionally, we applied MethGET to rice regeneration data and discovered that CHH methylation in the gene body region may play a role in the tissue culture process, which demonstrates the capability of MethGET for use in epigenomic research.
    CONCLUSIONS: MethGET is a Python software that correlates DNA methylation and gene expression. Its web interface is publicly available at https://paoyang.ipmb.sinica.edu.tw/Software.html. The stand-alone version and source codes are available on GitHub at https://github.com/Jason-Teng/MethGET.
    Keywords:  Bioinformatics; Correlation; DNA methylation; Epigenome; Gene expression; Next-generation sequencing; Web server
    DOI:  https://doi.org/10.1186/s12864-020-6722-x
  11. Nat Commun. 2020 May 25. 11(1): 2606
    Kadota S, Ou J, Shi Y, Lee JT, Sun J, Yildirim E.
      Nucleoporin proteins (Nups) have been proposed to mediate spatial and temporal chromatin organization during gene regulation. Nevertheless, the molecular mechanisms in mammalian cells are not well understood. Here, we report that Nucleoporin 153 (NUP153) interacts with the chromatin architectural proteins, CTCF and cohesin, and mediates their binding across cis-regulatory elements and TAD boundaries in mouse embryonic stem (ES) cells. NUP153 depletion results in altered CTCF and cohesin binding and differential gene expression - specifically at the bivalent developmental genes. To investigate the molecular mechanism, we utilize epidermal growth factor (EGF)-inducible immediate early genes (IEGs). We find that NUP153 controls CTCF and cohesin binding at the cis-regulatory elements and POL II pausing during the basal state. Furthermore, efficient IEG transcription relies on NUP153. We propose that NUP153 links the nuclear pore complex (NPC) to chromatin architecture allowing genes that are poised to respond rapidly to developmental cues to be properly modulated.
    DOI:  https://doi.org/10.1038/s41467-020-16394-3
  12. Clin Epigenetics. 2020 May 24. 12(1): 72
    Zhang T, Gong Y, Meng H, Li C, Xue L.
      Increasing evidence has suggested that epigenetic and metabolic alterations in cancer cells are highly intertwined. As the master epigenetic regulator, enhancer of zeste homolog 2 (EZH2) suppresses gene transcription mainly by catalyzing the trimethylation of histone H3 at lysine 27 (H3K27me3) and exerts highly enzymatic activity in cancer cells. Cancer cells undergo the profound metabolic reprogramming and manifest the distinct metabolic profile. The emerging studies have explored that EZH2 is involved in altering the metabolic profiles of tumor cells by multiple pathways, which cover glucose, lipid, and amino acid metabolism. Meanwhile, the stability and methyltransferase activity of EZH2 can be also affected by the metabolic activity of tumor cells through various mechanisms, including post-translational modification. In this review, we have summarized the correlation between EZH2 and cellular metabolic activity during tumor progression and drug treatment. Finally, as a promising target, we proposed a novel strategy through a combination of EZH2 inhibitors with metabolic regulators for future cancer therapy.
    Keywords:  EZH2; Histone modification; Metabolism; Tumor therapy
    DOI:  https://doi.org/10.1186/s13148-020-00862-0
  13. Genes Dev. 2020 May 28.
    Szigety KM, Liu F, Yuan CY, Moran DJ, Horrell J, Gochnauer HR, Cohen RN, Katz JP, Kaestner KH, Seykora JT, Tobias JW, Lazar MA, Xu M, Millar SE.
      Chromatin modifiers play critical roles in epidermal development, but the functions of histone deacetylases in this context are poorly understood. The class I HDAC, HDAC3, is of particular interest because it plays divergent roles in different tissues by partnering with tissue-specific transcription factors. We found that HDAC3 is expressed broadly in embryonic epidermis and is required for its orderly stepwise stratification. HDAC3 protein stability in vivo relies on NCoR and SMRT, which function redundantly in epidermal development. However, point mutations in the NCoR and SMRT deacetylase-activating domains, which are required for HDAC3's enzymatic function, permit normal stratification, indicating that HDAC3's roles in this context are largely independent of its histone deacetylase activity. HDAC3-bound sites are significantly enriched for predicted binding motifs for critical epidermal transcription factors including AP1, GRHL, and KLF family members. Our results suggest that among these, HDAC3 operates in conjunction with KLF4 to repress inappropriate expression of Tgm1, Krt16, and Aqp3 In parallel, HDAC3 suppresses expression of inflammatory cytokines through a Rela-dependent mechanism. These data identify HDAC3 as a hub coordinating multiple aspects of epidermal barrier acquisition.
    Keywords:  HDAC3; KLF4; NCoR; SMRT; chromatin; epidermal barrier; epidermis; epigenetic; histone deacetylase; mouse
    DOI:  https://doi.org/10.1101/gad.333674.119
  14. EMBO J. 2020 May 25. e103786
    Ye B, Yang L, Qian G, Liu B, Zhu X, Zhu P, Ma J, Xie W, Li H, Lu T, Wang Y, Wang S, Du Y, Wang Z, Jiang J, Li J, Fan D, Meng S, Wu J, Tian Y, Fan Z.
      Lgr5+ intestinal stem cells (ISCs) exhibit self-renewal and differentiation features under homeostatic conditions, but the mechanisms controlling Lgr5 + ISC self-renewal remain elusive. Here, we show that the chromatin remodeler SRCAP is highly expressed in mouse intestinal epithelium and ISCs. Srcap deletion impairs both self-renewal of ISCs and intestinal epithelial regeneration. Mechanistically, SRCAP recruits the transcriptional regulator REST to the Prdm16 promoter and induces expression of this transcription factor. By activating PPARδ expression, Prdm16 in turn initiates PPARδ signaling, which sustains ISC stemness. Rest or Prdm16 deficiency abrogates the self-renewal capacity of ISCs as well as intestinal epithelial regeneration. Collectively, these data show that the SRCAP-REST-Prdm16-PPARδ axis is required for self-renewal maintenance of Lgr5 + ISCs.
    Keywords:   REST ; SRCAP ; PPARδ; intestinal stem cell; self-renewal
    DOI:  https://doi.org/10.15252/embj.2019103786
  15. Mol Cell. 2020 May 23. pii: S1097-2765(20)30276-8. [Epub ahead of print]
    Wu SY, Lee CF, Lai HT, Yu CT, Lee JE, Zuo H, Tsai SY, Tsai MJ, Ge K, Wan Y, Chiang CM.
      Bromodomain-containing protein 4 (BRD4) is a cancer therapeutic target in ongoing clinical trials disrupting primarily BRD4-regulated transcription programs. The role of BRD4 in cancer has been attributed mainly to the abundant long isoform (BRD4-L). Here we show, by isoform-specific knockdown and endogenous protein detection, along with transgene expression, the less abundant BRD4 short isoform (BRD4-S) is oncogenic while BRD4-L is tumor-suppressive in breast cancer cell proliferation and migration, as well as mammary tumor formation and metastasis. Through integrated RNA-seq, genome-wide ChIP-seq, and CUT&RUN association profiling, we identify the Engrailed-1 (EN1) homeobox transcription factor as a key BRD4-S coregulator, particularly in triple-negative breast cancer. BRD4-S and EN1 comodulate the extracellular matrix (ECM)-associated matrisome network, including type II cystatin gene cluster, mucin 5, and cathepsin loci, via enhancer regulation of cancer-associated genes and pathways. Our work highlights the importance of targeted therapies for the oncogenic, but not tumor-suppressive, activity of BRD4.
    Keywords:  BET inhibitor; BRD4; CUT&RUN; ECM; TNBC; bromodomain; drug resistance; enhancer; epigenetics; transcription factor
    DOI:  https://doi.org/10.1016/j.molcel.2020.04.034
  16. Proc Natl Acad Sci U S A. 2020 May 27. pii: 201913261. [Epub ahead of print]
    Dainese R, Gardeux V, Llimos G, Alpern D, Jiang JY, Meireles-Filho ACA, Deplancke B.
      Despite its popularity, chromatin immunoprecipitation followed by sequencing (ChIP-seq) remains a tedious (>2 d), manually intensive, low-sensitivity and low-throughput approach. Here, we combine principles of microengineering, surface chemistry, and molecular biology to address the major limitations of standard ChIP-seq. The resulting technology, FloChIP, automates and miniaturizes ChIP in a beadless fashion while facilitating the downstream library preparation process through on-chip chromatin tagmentation. FloChIP is fast (<2 h), has a wide dynamic range (from 106 to 500 cells), is scalable and parallelized, and supports antibody- or sample-multiplexed ChIP on both histone marks and transcription factors. In addition, FloChIP's interconnected design allows for straightforward chromatin reimmunoprecipitation, which allows this technology to also act as a microfluidic sequential ChIP-seq system. Finally, we ran FloChIP for the transcription factor MEF2A in 32 distinct human lymphoblastoid cell lines, providing insights into the main factors driving collaborative DNA binding of MEF2A and into its role in B cell-specific gene regulation. Together, our results validate FloChIP as a flexible and reproducible automated solution for individual or sequential ChIP-seq.
    Keywords:  ChIP-seq; epigenetics; microfluidics; transcription factor
    DOI:  https://doi.org/10.1073/pnas.1913261117
  17. Oncogene. 2020 May 25.
    Richart L, Felipe I, Delgado P, Andrés MP, Prieto J, Pozo ND, García JF, Piris MA, Ramiro A, Real FX.
      Chromatin remodeling factors contribute to establish aberrant gene expression programs in cancer cells and therefore represent valuable targets for therapeutic intervention. BPTF (Bromodomain PhD Transcription Factor), a core subunit of the nucleosome remodeling factor (NURF), modulates c-MYC oncogenic activity in pancreatic cancer. Here, we analyze the role of BPTF in c-MYC-driven B-cell lymphomagenesis using the Eμ-Myc transgenic mouse model of aggressive B-cell lymphoma. We find that BPTF is required for normal B-cell differentiation without evidence of haploinsufficiency. In contrast, deletion of one Bptf allele is sufficient to delay lymphomagenesis in Eμ-Myc mice. Tumors arising in a Bptf heterozygous background display decreased c-MYC levels and pathway activity, together with increased activation of the NF-κB pathway, a molecular signature characteristic of human diffuse large B-cell lymphoma (DLBCL). In human B-cell lymphoma samples, we find a strong correlation between BPTF and c-MYC mRNA and protein levels, together with an anti-correlation between BPTF and NF-κB pathway activity. Our results indicate that BPTF is a relevant therapeutic target in B-cell lymphomas and that, upon its inhibition, cells acquire distinct oncogenic dependencies.
    DOI:  https://doi.org/10.1038/s41388-020-1331-3
  18. BMC Bioinformatics. 2020 May 29. 21(1): 222
    Ye C, Paccanaro A, Gerstein M, Yan KK.
      BACKGROUND: Genome-wide ligation-based assays such as Hi-C provide us with an unprecedented opportunity to investigate the spatial organization of the genome. Results of a typical Hi-C experiment are often summarized in a chromosomal contact map, a matrix whose elements reflect the co-location frequencies of genomic loci. To elucidate the complex structural and functional interactions between those genomic loci, networks offer a natural and powerful framework.RESULTS: We propose a novel graph-theoretical framework, the Corrected Gene Proximity (CGP) map to study the effect of the 3D spatial organization of genes in transcriptional regulation. The starting point of the CGP map is a weighted network, the gene proximity map, whose weights are based on the contact frequencies between genes extracted from genome-wide Hi-C data. We derive a null model for the network based on the signal contributed by the 1D genomic distance and use it to "correct" the gene proximity for cell type 3D specific arrangements. The CGP map, therefore, provides a network framework for the 3D structure of the genome on a global scale. On human cell lines, we show that the CGP map can detect and quantify gene co-regulation and co-localization more effectively than the map obtained by raw contact frequencies. Analyzing the expression pattern of metabolic pathways of two hematopoietic cell lines, we find that the relative positioning of the genes, as captured and quantified by the CGP, is highly correlated with their expression change. We further show that the CGP map can be used to form an inter-chromosomal proximity map that allows large-scale abnormalities, such as chromosomal translocations, to be identified.
    CONCLUSIONS: The Corrected Gene Proximity map is a map of the 3D structure of the genome on a global scale. It allows the simultaneous analysis of intra- and inter- chromosomal interactions and of gene co-regulation and co-localization more effectively than the map obtained by raw contact frequencies, thus revealing hidden associations between global spatial positioning and gene expression. The flexible graph-based formalism of the CGP map can be easily generalized to study any existing Hi-C datasets.
    Keywords:  3D genome; Hi-C data analysis; Network modularity; Network theory
    DOI:  https://doi.org/10.1186/s12859-020-03545-y
  19. Clin Epigenetics. 2020 May 29. 12(1): 74
    Larsson C, Cordeddu L, Siggens L, Pandzic T, Kundu S, He L, Ali MA, Pristovšek N, Hartman K, Ekwall K, Sjöblom T.
      BACKGROUND: The histone 3 lysine 4 (H3K4) monomethylase KMT2C is mutated across several cancer types; however, the effects of mutations on epigenome organization, gene expression, and cell growth are not clear. A frequently recurring mutation in colorectal cancer (CRC) with microsatellite instability is a single nucleotide deletion within the exon 38 poly-A(9) repeat (c.8390delA) which results in frameshift preceding the functional carboxy-terminal SET domain. To study effects of KMT2C expression in CRC cells, we restored one allele to wild type KMT2C in the two CRC cell lines RKO and HCT116, which both are homozygous c.8390delA mutant.RESULTS: Gene editing resulted in increased KMT2C expression, increased H3K4me1 levels, altered gene expression profiles, and subtle negative effects on cell growth, where higher dependence and stronger effects of KMT2C expression were observed in RKO compared to HCT116 cells. Surprisingly, we found that the two RKO and HCT116 CRC cell lines have distinct baseline H3K4me1 epigenomic profiles. In RKO cells, a flatter genome-wide H3K4me1 profile was associated with more increased H3K4me1 deposition at enhancers, reduced cell growth, and more differential gene expression relative to HCT116 cells when KMT2C was restored. Profiling of H3K4me1 did not indicate a highly specific regulation of gene expression as KMT2C-induced H3K4me1 deposition was found globally and not at a specific enhancer sub-set in the engineered cells. Although we observed variation in differentially regulated gene sets between cell lines and individual clones, differentially expressed genes in both cell lines included genes linked to known cancer signaling pathways, estrogen response, hypoxia response, and aspects of immune system regulation.
    CONCLUSIONS: Here, KMT2C restoration reduced CRC cell growth and reinforced genome-wide H3K4me1 deposition at enhancers; however, the effects varied depending upon the H3K4me1 status of KMT2C deficient cells. Results indicate that KMT2C inactivation may promote colorectal cancer development through transcriptional dysregulation in several pathways with known cancer relevance.
    Keywords:  Cancer; H3K4me1; KMT2C; MLL3
    DOI:  https://doi.org/10.1186/s13148-020-00863-z
  20. Cell Rep. 2020 May 26. pii: S2211-1247(20)30644-6. [Epub ahead of print]31(8): 107691
    Nafria M, Keane P, Ng ES, Stanley EG, Elefanty AG, Bonifer C.
      Acute myeloid leukemia (AML) is a hematopoietic malignancy caused by recurrent mutations in genes encoding transcriptional, chromatin, and/or signaling regulators. The t(8;21) translocation generates the aberrant transcription factor RUNX1-ETO (RUNX1-RUNX1T1), which by itself is insufficient to cause disease. t(8;21) AML patients show extensive chromatin reprogramming and have acquired additional mutations. Therefore, the genomic and developmental effects directly and solely attributable to RUNX1-ETO expression are unclear. To address this, we employ a human embryonic stem cell differentiation system capable of forming definitive myeloid progenitor cells to express RUNX1-ETO in an inducible fashion. Induction of RUNX1-ETO causes extensive chromatin reprogramming by interfering with RUNX1 binding, blocks differentiation, and arrests cellular growth, whereby growth arrest is reversible following RUNX1-ETO removal. Single-cell gene expression analyses show that RUNX1-ETO induction alters the differentiation of early myeloid progenitors, but not of other progenitor types, indicating that oncoprotein-mediated transcriptional reprogramming is highly target cell specific.
    Keywords:  Acute Myeloid Leukemia (AML); RUNX1-ETO; chromatin; human ES cell differentiation; myelopoiesis; single cell RNA-Seq
    DOI:  https://doi.org/10.1016/j.celrep.2020.107691
  21. BMC Bioinformatics. 2020 May 29. 21(1): 219
    Sauta E, Demartini A, Vitali F, Riva A, Bellazzi R.
      BACKGROUND: Reverse engineering of transcriptional regulatory networks (TRN) from genomics data has always represented a computational challenge in System Biology. The major issue is modeling the complex crosstalk among transcription factors (TFs) and their target genes, with a method able to handle both the high number of interacting variables and the noise in the available heterogeneous experimental sources of information.RESULTS: In this work, we propose a data fusion approach that exploits the integration of complementary omics-data as prior knowledge within a Bayesian framework, in order to learn and model large-scale transcriptional networks. We develop a hybrid structure-learning algorithm able to jointly combine TFs ChIP-Sequencing data and gene expression compendia to reconstruct TRNs in a genome-wide perspective. Applying our method to high-throughput data, we verified its ability to deal with the complexity of a genomic TRN, providing a snapshot of the synergistic TFs regulatory activity. Given the noisy nature of data-driven prior knowledge, which potentially contains incorrect information, we also tested the method's robustness to false priors on a benchmark dataset, comparing the proposed approach to other regulatory network reconstruction algorithms. We demonstrated the effectiveness of our framework by evaluating structural commonalities of our learned genomic network with other existing networks inferred by different DNA binding information-based methods.
    CONCLUSIONS: This Bayesian omics-data fusion based methodology allows to gain a genome-wide picture of the transcriptional interplay, helping to unravel key hierarchical transcriptional interactions, which could be subsequently investigated, and it represents a promising learning approach suitable for multi-layered genomic data integration, given its robustness to noisy sources and its tailored framework for handling high dimensional data.
    Keywords:  Bayesian networks; Genomic transcriptional networks; Hybrid structure learning algorithm; omics-data fusion
    DOI:  https://doi.org/10.1186/s12859-020-3510-1
  22. Nat Chem. 2020 May 29.
    Burton AJ, Haugbro M, Gates LA, Bagert JD, Allis CD, Muir TW.
      Elucidating the physiological binding partners of histone post-translational modifications (hPTMs) is key to understanding fundamental epigenetic regulatory pathways. Determining such interactomes will enable the study of how perturbations of these interactions affect disease. Here we use a synthetic biology approach to set a series of hPTM-controlled photo-affinity traps in native chromatin. Using quantitative proteomics, the local interactomes of these chemically customized chromatin landscapes are determined. We show that the approach captures transiently interacting factors such as methyltransferases and demethylases, as well as previously reported and novel hPTM reader proteins. We also apply this in situ proteomics approach to a recently disclosed cancer-associated histone mutation, H3K4M, revealing a number of perturbed interactions with the mutated tail. Collectively our studies demonstrate that modifying and interrogating native chromatin with chemical precision is a powerful tool for exploring epigenetic regulation and dysregulation at the molecular level.
    DOI:  https://doi.org/10.1038/s41557-020-0474-8
  23. Hepatology. 2020 May 26.
    Smith JL, Rodríguez TC, Mou H, Kwan SY, Pratt H, Zhang XO, Cao Y, Liang S, Ozata DM, Yu T, Yin Q, Hazeltine M, Weng Z, Sontheimer EJ, Xue W.
      BACKGROUND & AIMS: Despite surgical and chemotherapeutic advances, the five-year survival rate for Stage IV Hepatoblastoma (HB), the predominant pediatric liver tumor, remains at 27%. YAP1 and β-Catenin co-activation occurs in 80% of children's HB; however, a lack of conditional genetic models precludes tumor maintenance exploration. Thus, the need for a targeted therapy remains unmet. Given the predominance of YAP1 and β-Catenin activation in HB, we sought to evaluate YAP1 as a therapeutic target in HB.APPROACH & RESULTS: We engineered the first conditional HB murine model using hydrodynamic injection to deliver transposon plasmids encoding inducible YAP1S127A , constitutive β-CateninDelN90 , and a luciferase reporter to murine liver. Tumor regression was evaluated using bioluminescent imaging, and tumor landscape characterized using RNA and ATAC sequencing, and DNA foot-printing. Here we show that YAP1S127A withdrawal mediates >90% tumor regression with survival for 230+ days in mice. YAP1 S127A withdrawal promotes apoptosis in a subset of tumor cells and in remaining cells induces a cell fate switch driving therapeutic differentiation of HB tumors into Ki-67 negative "hbHep cells" with hepatocyte-like morphology and mature hepatocyte gene expression. YAP1 S127A withdrawal drives formation of hbHeps by modulating liver differentiation transcription factor (TF) occupancy. Indeed, tumor-derived hbHeps, consistent with their reprogrammed transcriptional landscape, regain partial hepatocyte function and rescue liver damage in mice.
    CONCLUSIONS: YAP1S127A withdrawal, without silencing oncogenic β-Catenin, significantly regresses hepatoblastoma, providing the first in vivo data to support YAP1 as a therapeutic target for HB. YAP1S127A withdrawal alone sufficiently drives long-term regression in hepatoblastoma because it promotes cell death in a subset of tumor cells and modulates transcription factor occupancy to reverse the fate of residual tumor cells to mimic functional hepatocytes.
    Keywords:  Liver cancer; Oncogene; Pediatric Cancer; Targeted Therapy; Therapeutic Differentiation
    DOI:  https://doi.org/10.1002/hep.31389
  24. Nat Commun. 2020 May 27. 11(1): 2658
    Zhao L, Xie L, Zhang Q, Ouyang W, Deng L, Guan P, Ma M, Li Y, Zhang Y, Xiao Q, Zhang J, Li H, Wang S, Man J, Cao Z, Zhang Q, Zhang Q, Li G, Li X.
      Epigenomic modifications are instrumental for transcriptional regulation, but comprehensive reference epigenomes remain unexplored in rice. Here, we develop an enhanced chromatin immunoprecipitation (eChIP) approach for plants, and generate genome-wide profiling of five histone modifications and RNA polymerase II occupancy with it. By integrating chromatin accessibility, DNA methylation, and transcriptome datasets, we construct comprehensive epigenome landscapes across various tissues in 20 representative rice varieties. Approximately 81.8% of rice genomes are annotated with different epigenomic properties. Refinement of promoter regions using open chromatin and H3K4me3-marked regions provides insight into transcriptional regulation. We identify extensive enhancer-like promoters with potential enhancer function on transcriptional regulation through chromatin interactions. Active and repressive histone modifications and the predicted enhancers vary largely across tissues, whereas inactive chromatin states are relatively stable. Together, these datasets constitute a valuable resource for functional element annotation in rice and indicate the central role of epigenomic information in understanding transcriptional regulation.
    DOI:  https://doi.org/10.1038/s41467-020-16457-5
  25. BMC Cancer. 2020 May 25. 20(1): 469
    Tran MGB, Bibby BAS, Yang L, Lo F, Warren AY, Shukla D, Osborne M, Hadfield J, Carroll T, Stark R, Scott H, Ramos-Montoya A, Massie C, Maxwell P, West CML, Mills IG, Neal DE.
      BACKGROUND: Therapeutic targeting of the androgen signaling pathway is a mainstay treatment for prostate cancer. Although initially effective, resistance to androgen targeted therapies develops followed by disease progression to castrate-resistant prostate cancer (CRPC). Hypoxia and HIF1a have been implicated in the development of resistance to androgen targeted therapies and progression to CRCP. The interplay between the androgen and hypoxia/HIF1a signaling axes was investigated.METHODS: In vitro stable expression of HIF1a was established in the LNCaP cell line by physiological induction or retroviral transduction. Tumor xenografts with stable expression of HIF1a were established in castrated and non-castrated mouse models. Gene expression analysis identified transcriptional changes in response to androgen treatment, hypoxia and HIF1a. The binding sites of the AR and HIF transcription factors were identified using ChIP-seq.
    RESULTS: Androgen and HIF1a signaling promoted proliferation in vitro and enhanced tumor growth in vivo. The stable expression of HIF1a in vivo restored tumor growth in the absence of endogenous androgens. Hypoxia reduced AR binding sites whereas HIF binding sites were increased with androgen treatment under hypoxia. Gene expression analysis identified seven genes that were upregulated both by AR and HIF1a, of which six were prognostic.
    CONCLUSIONS: The oncogenic AR, hypoxia and HIF1a pathways support prostate cancer development through independent signaling pathways and transcriptomic profiles. AR and hypoxia/HIF1a signaling pathways independently promote prostate cancer progression and therapeutic targeting of both pathways simultaneously is warranted.
    Keywords:  Androgen signaling; HIF1a signaling; Hypoxia; Prostate cancer
    DOI:  https://doi.org/10.1186/s12885-020-06890-6
  26. Oncogene. 2020 May 26.
    Koyen AE, Madden MZ, Park D, Minten EV, Kapoor-Vazirani P, Werner E, Pfister NT, Haji-Seyed-Javadi R, Zhang H, Xu J, Deng N, Duong DM, Pecen TJ, Frazier Z, Nagel ZD, Lazaro JB, Mouw KW, Seyfried NT, Moreno CS, Owonikoko TK, Deng X, Yu DS.
      Small cell lung cancer (SCLC) is a highly aggressive malignancy with poor outcomes associated with resistance to cisplatin-based chemotherapy. Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of polycomb repressive complex 2 (PRC2), which silences transcription through trimethylation of histone H3 lysine 27 (H3K27me3) and has emerged as an important therapeutic target with inhibitors targeting its methyltransferase activity under clinical investigation. Here, we show that EZH2 has a non-catalytic and PRC2-independent role in stabilizing DDB2 to promote nucleotide excision repair (NER) and govern cisplatin resistance in SCLC. Using a synthetic lethality screen, we identified important regulators of cisplatin resistance in SCLC cells, including EZH2. EZH2 depletion causes cellular cisplatin and UV hypersensitivity in an epistatic manner with DDB1-DDB2. EZH2 complexes with DDB1-DDB2 and promotes DDB2 stability by impairing its ubiquitination independent of methyltransferase activity or PRC2, thereby facilitating DDB2 localization to cyclobutane pyrimidine dimer crosslinks to govern their repair. Furthermore, targeting EZH2 for depletion with DZNep strongly sensitizes SCLC cells and tumors to cisplatin. Our findings reveal a non-catalytic and PRC2-independent function for EZH2 in promoting NER through DDB2 stabilization, suggesting a rationale for targeting EZH2 beyond its catalytic activity for overcoming cisplatin resistance in SCLC.
    DOI:  https://doi.org/10.1038/s41388-020-1332-2
  27. PLoS Genet. 2020 May 28. 16(5): e1008832
    Li X, Liu M, Ren X, Loncle N, Wang Q, Hemba-Waduge RU, Yu SH, Boube M, Bourbon HG, Ni JQ, Ji JY.
      Dysregulation of CDK8 (Cyclin-Dependent Kinase 8) and its regulatory partner CycC (Cyclin C), two subunits of the conserved Mediator (MED) complex, have been linked to diverse human diseases such as cancer. Thus, it is essential to understand the regulatory network modulating the CDK8-CycC complex in both normal development and tumorigenesis. To identify upstream regulators or downstream effectors of CDK8, we performed a dominant modifier genetic screen in Drosophila based on the defects in vein patterning caused by specific depletion or overexpression of CDK8 or CycC in developing wing imaginal discs. We identified 26 genomic loci whose haploinsufficiency can modify these CDK8- or CycC-specific phenotypes. Further analysis of two overlapping deficiency lines and mutant alleles led us to identify genetic interactions between the CDK8-CycC pair and the components of the Decapentaplegic (Dpp, the Drosophila homolog of TGFβ) signaling pathway. We observed that CDK8-CycC positively regulates transcription activated by Mad (Mothers against dpp), the primary transcription factor downstream of the Dpp/TGFβ signaling pathway. CDK8 can directly interact with Mad in vitro through the linker region between the DNA-binding MH1 (Mad homology 1) domain and the carboxy terminal MH2 (Mad homology 2) transactivation domain. Besides CDK8 and CycC, further analyses of other subunits of the MED complex have revealed six additional subunits that are required for Mad-dependent transcription in the wing discs: Med12, Med13, Med15, Med23, Med24, and Med31. Furthermore, our analyses confirmed the positive roles of CDK9 and Yorkie in regulating Mad-dependent gene expression in vivo. These results suggest that CDK8 and CycC, together with a few other subunits of the MED complex, may coordinate with other transcription cofactors in regulating Mad-dependent transcription during wing development in Drosophila.
    DOI:  https://doi.org/10.1371/journal.pgen.1008832
  28. Commun Biol. 2020 May 25. 3(1): 262
    Fatima A, Irmak D, Noormohammadi A, Rinschen MM, Das A, Leidecker O, Schindler C, Sánchez-Gaya V, Wagle P, Pokrzywa W, Hoppe T, Rada-Iglesias A, Vilchez D.
      Histones modulate gene expression by chromatin compaction, regulating numerous processes such as differentiation. However, the mechanisms underlying histone degradation remain elusive. Human embryonic stem cells (hESCs) have a unique chromatin architecture characterized by low levels of trimethylated histone H3 at lysine 9 (H3K9me3), a heterochromatin-associated modification. Here we assess the link between the intrinsic epigenetic landscape and ubiquitin-proteasome system of hESCs. We find that hESCs exhibit high expression of the ubiquitin-conjugating enzyme UBE2K. Loss of UBE2K upregulates the trimethyltransferase SETDB1, resulting in H3K9 trimethylation and repression of neurogenic genes during differentiation. Besides H3K9 trimethylation, UBE2K binds histone H3 to induce its polyubiquitination and degradation by the proteasome. Notably, ubc-20, the worm orthologue of UBE2K, also regulates histone H3 levels and H3K9 trimethylation in Caenorhabditis elegans germ cells. Thus, our results indicate that UBE2K crosses evolutionary boundaries to promote histone H3 degradation and reduce H3K9me3 repressive marks in immortal cells.
    DOI:  https://doi.org/10.1038/s42003-020-0984-3
  29. PLoS Genet. 2020 May 26. 16(5): e1008770
    Præstholm SM, Siersbæk MS, Nielsen R, Zhu X, Hollenberg A, Cheng SY, Grøntved L.
      Hormone-dependent activation of enhancers includes histone hyperacetylation and mediator recruitment. Histone hyperacetylation is mostly explained by a bimodal switch model, where histone deacetylases (HDACs) disassociate from chromatin, and histone acetyl transferases (HATs) are recruited. This model builds on decades of research on steroid receptor regulation of transcription. Yet, the general concept of the bimodal switch model has not been rigorously tested genome wide. We have used a genomics approach to study enhancer hyperacetylation by the thyroid hormone receptor (TR), described to operate as a bimodal switch. H3 acetylation, HAT and HDAC ChIP-seq analyses of livers from hypo- and hyperthyroid wildtype, TR deficient and NCOR1 disrupted mice reveal three types of thyroid hormone (T3)-regulated enhancers. One subset of enhancers is bound by HDAC3-NCOR in the absence of hormone and constitutively occupy TR and HATs irrespective of T3 levels, suggesting a poised enhancer state in absence of hormone. In presence of T3, HDAC3-NCOR1 dissociates from these enhancers leading to histone hyperacetylation, suggesting a histone acetylation rheostat function of HDACs at poised enhancers. Another subset of enhancers, not occupied by HDACs, is hyperacetylated in a T3-dependent manner, where TR is recruited to chromatin together with HATs. Lastly, a subset of enhancers, is not occupied directly by TR yet require TR for histone hyperacetylation. This indirect enhancer activation involves co-association with TR bound enhancers within super-enhancers or topological associated domains. Collectively, this demonstrates various mechanisms controlling hormone-dependent transcription and adds significant details to the otherwise simple bimodal switch model.
    DOI:  https://doi.org/10.1371/journal.pgen.1008770
  30. Nucleic Acids Res. 2020 May 25. pii: gkaa412. [Epub ahead of print]
    David FPA, Litovchenko M, Deplancke B, Gardeux V.
      Single-cell omics enables researchers to dissect biological systems at a resolution that was unthinkable just 10 years ago. However, this analytical revolution also triggered new demands in 'big data' management, forcing researchers to stay up to speed with increasingly complex analytical processes and rapidly evolving methods. To render these processes and approaches more accessible, we developed the web-based, collaborative portal ASAP (Automated Single-cell Analysis Portal). Our primary goal is thereby to democratize single-cell omics data analyses (scRNA-seq and more recently scATAC-seq). By taking advantage of a Docker system to enhance reproducibility, and novel bioinformatics approaches that were recently developed for improving scalability, ASAP meets challenging requirements set by recent cell atlasing efforts such as the Human (HCA) and Fly (FCA) Cell Atlas Projects. Specifically, ASAP can now handle datasets containing millions of cells, integrating intuitive tools that allow researchers to collaborate on the same project synchronously. ASAP tools are versioned, and researchers can create unique access IDs for storing complete analyses that can be reproduced or completed by others. Finally, ASAP does not require any installation and provides a full and modular single-cell RNA-seq analysis pipeline. ASAP is freely available at https://asap.epfl.ch.
    DOI:  https://doi.org/10.1093/nar/gkaa412
  31. PLoS One. 2020 ;15(5): e0233191
    Alomairi J, Molitor AM, Sadouni N, Hussain S, Torres M, Saadi W, Dao LTM, Charbonnier G, Santiago-Algarra D, Andrau JC, Puthier D, Sexton T, Spicuglia S.
      The Ikzf1 locus encodes the lymphoid specific transcription factor Ikaros, which plays an essential role in both T and B cell differentiation, while deregulation or mutation of IKZF1/Ikzf1 is involved in leukemia. Tissue-specific and cell identity genes are usually associated with clusters of enhancers, also called super-enhancers, which are believed to ensure proper regulation of gene expression throughout cell development and differentiation. Several potential regulatory regions have been identified in close proximity of Ikzf1, however, the full extent of the regulatory landscape of the Ikzf1 locus is not yet established. In this study, we combined epigenomics and transcription factor binding along with high-throughput enhancer assay and 4C-seq to prioritize an enhancer element located 120 kb upstream of the Ikzf1 gene. We found that deletion of the E120 enhancer resulted in a significant reduction of Ikzf1 mRNA. However, the epigenetic landscape and 3D topology of the locus were only slightly affected, highlighting the complexity of the regulatory landscape regulating the Ikzf1 locus.
    DOI:  https://doi.org/10.1371/journal.pone.0233191
  32. Development. 2020 May 28. pii: dev.178582. [Epub ahead of print]
    Liu D, Kousa AI, O'Neill KE, Rouse P, Popis M, Farley AM, Tomlinson SR, Ulyanchenko S, Guillemot F, Seymour PA, Jørgensen MC, Serup P, Koch U, Radtke F, Blackburn CC.
      Thymus function depends on the epithelial compartment of the thymic stroma. Cortical thymic epithelial cells (cTECs) regulate T cell lineage commitment and positive selection, while medullary (m) TECs impose central tolerance on the T cell repertoire. During thymus organogenesis, these functionally distinct sub-lineages are thought to arise from a common thymic epithelial progenitor cell (TEPC). The mechanisms controlling cTEC and mTEC production from the common TEPC are not however understood. Here, we show that emergence of the earliest mTEC lineage-restricted progenitors requires active NOTCH signaling in progenitor TEC and that, once specified, further mTEC development is NOTCH-independent. In addition, we demonstrate that persistent NOTCH activity favors maintenance of undifferentiated TEPC at the expense of cTEC differentiation. Finally, we uncover a cross-regulatory relationship between NOTCH and FOXN1, a master regulator of TEC differentiation. These data establish NOTCH as a potent regulator of TEPC and mTEC fate during fetal thymus development and are thus of high relevance to strategies aimed at generating/regenerating functional thymic tissue in vitro and in vivo.
    Keywords:  Cell fate regulation; Differentiation; Lineage divergence; Notch signaling; Progenitor cell; Stem cell; Thymic epithelial cell; Thymus
    DOI:  https://doi.org/10.1242/dev.178582
  33. Nat Commun. 2020 May 27. 11(1): 2649
    Feigman MJ, Moss MA, Chen C, Cyrill SL, Ciccone MF, Trousdell MC, Yang ST, Frey WD, Wilkinson JE, Dos Santos CO.
      Pregnancy causes a series of cellular and molecular changes in mammary epithelial cells (MECs) of female adults. In addition, pregnancy can also modify the predisposition of rodent and human MECs to initiate oncogenesis. Here, we investigate how pregnancy reprograms enhancer chromatin in the mammary epithelium of mice and influences the transcriptional output of the oncogenic transcription factor cMYC. We find that pregnancy induces an expansion of the active cis-regulatory landscape of MECs, which influences the activation of pregnancy-related programs during re-exposure to pregnancy hormones in vivo and in vitro. Using inducible cMYC overexpression, we demonstrate that post-pregnancy MECs are resistant to the downstream molecular programs induced by cMYC, a response that blunts carcinoma initiation, but does not perturb the normal pregnancy-induced epigenomic landscape. cMYC overexpression drives post-pregnancy MECs into a senescence-like state, and perturbations of this state increase malignant phenotypic changes. Taken together, our findings provide further insight into the cell-autonomous signals in post-pregnancy MECs that underpin the regulation of gene expression, cellular activation, and resistance to malignant development.
    DOI:  https://doi.org/10.1038/s41467-020-16479-z
  34. Cell Rep. 2020 May 26. pii: S2211-1247(20)30636-7. [Epub ahead of print]31(8): 107683
    Jin Z, Chen J, Huang H, Wang J, Lv J, Yu M, Guo X, Zhang Y, Cai T, Xi R.
      Balanced stem cell self-renewal and differentiation is essential for maintaining tissue homeostasis, but the underlying mechanisms are poorly understood. Here, we identified the transcription factor SRY-related HMG-box (Sox) 100B, which is orthologous to mammalian Sox8/9/10, as a common target and central mediator of the EGFR/Ras and JAK/STAT signaling pathways that coordinates intestinal stem cell (ISC) proliferation and differentiation during both normal epithelial homeostasis and stress-induced intestinal repair in Drosophila. The two stress-responsive pathways directly regulate Sox100B transcription via two separate enhancers. Interestingly, an appropriate level of Sox100B is critical for its function, as its depletion inhibits ISC proliferation via cell cycle arrest, while its overexpression also inhibits ISC proliferation by directly suppressing EGFR expression and additionally promotes ISC differentiation by activating a differentiation-promoting regulatory circuitry composed of Sox100B, Sox21a, and Pdm1. Thus, our study reveals a Sox family transcription factor that functions as a stress-responsive signaling nexus that ultimately controls tissue homeostasis and regeneration.
    Keywords:  cell division; cell fate determination; dSox9; dosage effect; dosage-dependent; intestinal epithelium; recovery; tissue-damage; tumorigenesis
    DOI:  https://doi.org/10.1016/j.celrep.2020.107683
  35. Mol Cell Proteomics. 2020 May 28. pii: mcp.RA120.002078. [Epub ahead of print]
    Adams MK, Banks CAS, Thornton JL, Kempf C, Zhang Y, Miah S, Hao Y, Sardiu ME, Killer M, Hattem G, Murray A, Katt M, Florens LA, Washburn MP.
      Despite the continued analysis of HDAC inhibitors in clinical trials, the heterogeneous nature of the protein complexes they target limits our understanding of the beneficial and off-target effects associated with their application. Among the many HDAC protein complexes found within the cell, Sin3 complexes are conserved from yeast to humans and likely play important roles as regulators of transcriptional activity. The presence of two Sin3 paralogs in humans, SIN3A and SIN3B, may result in a heterogeneous population of Sin3 complexes and contributes to our poor understanding of the functional attributes of these complexes. Here, we profile the interaction networks of SIN3A and SIN3B to gain insight into complex composition and organization. In accordance with existing data, we show that Sin3 paralog identity influences complex composition. Additionally, chemical crosslinking mass spectrometry identifies domains that mediate interactions between Sin3 proteins and binding partners. The characterization of rare SIN3B proteoforms provides additional evidence for the existence of conserved and divergent elements within human Sin3 proteins. Together, these findings shed light on both the shared and divergent properties of human Sin3 proteins and highlight the heterogeneous nature of the complexes they organize.
    Keywords:  Chromatin function or biology; Cross linking; DSSO; Epigenetics; Histone deacetylase; Nuclear Translocation; Pathway Analysis; Protein complex analysis; Protein-Protein Interactions*; SIN3; Subcellular analysis; Systems biology*
    DOI:  https://doi.org/10.1074/mcp.RA120.002078
  36. Cells. 2020 May 24. pii: E1304. [Epub ahead of print]9(5):
    Gaggi G, Di Credico A, Izzicupo P, Antonucci I, Crescioli C, Di Giacomo V, Di Ruscio A, Amabile G, Alviano F, Di Baldassarre A, Ghinassi B.
      Human perinatal stem cells (SCs) can be isolated from fetal annexes without ethical or safety limitations. They are generally considered multipotent; nevertheless, their biological characteristics are still not fully understood. The aim of this study was to investigate the pluripotency potential of human perinatal SCs as compared to human induced pluripotent stem cells (hiPSCs). Despite the low expression of the pluripotent factors NANOG, OCT4, SOX2, and C-KIT in perinatal SC, we observed minor differences in the promoters DNA-methylation profile of these genes with respect to hiPSCs; we also demonstrated that in perinatal SCs miR-145-5p had an inverse trend in comparison to these stemness markers, suggesting that NANOG, OCT4, and SOX2 were regulated at the post-transcriptional level. The reduced expression of stemness markers was also associated with shorter telomere lengths and shift of the oxidative metabolism between hiPSCs and fetal annex-derived cells. Our findings indicate the differentiation ability of perinatal SCs might not be restricted to the mesenchymal lineage due to an epigenetic barrier, but other regulatory mechanisms such as telomere shortening or metabolic changes might impair their differentiation potential and challenge their clinical application.
    Keywords:  DNA methylation; NANOG; OCT4; SOX2; amniotic epithelial cells; amniotic fluid stem cells; fetal membrane mesenchymal stromal cells; miRNAs expression; perinatal stem cells; telomere length
    DOI:  https://doi.org/10.3390/cells9051304
  37. Genome Biol. 2020 May 28. 21(1): 126
    Tian L, Li Y, Edmonson MN, Zhou X, Newman S, McLeod C, Thrasher A, Liu Y, Tang B, Rusch MC, Easton J, Ma J, Davis E, Trull A, Michael JR, Szlachta K, Mullighan C, Baker SJ, Downing JR, Ellison DW, Zhang J.
      To discover driver fusions beyond canonical exon-to-exon chimeric transcripts, we develop CICERO, a local assembly-based algorithm that integrates RNA-seq read support with extensive annotation for candidate ranking. CICERO outperforms commonly used methods, achieving a 95% detection rate for 184 independently validated driver fusions including internal tandem duplications and other non-canonical events in 170 pediatric cancer transcriptomes. Re-analysis of TCGA glioblastoma RNA-seq unveils previously unreported kinase fusions (KLHL7-BRAF) and a 13% prevalence of EGFR C-terminal truncation. Accessible via standard or cloud-based implementation, CICERO enhances driver fusion detection for research and precision oncology. The CICERO source code is available at https://github.com/stjude/Cicero.
    Keywords:  Cloud computing; Fusion visualization; Gene fusion; Precision oncology; RNA-seq
    DOI:  https://doi.org/10.1186/s13059-020-02043-x
  38. Nat Genet. 2020 May 25.
    Lee HO, Hong Y, Etlioglu HE, Cho YB, Pomella V, Van den Bosch B, Vanhecke J, Verbandt S, Hong H, Min JW, Kim N, Eum HH, Qian J, Boeckx B, Lambrechts D, Tsantoulis P, De Hertogh G, Chung W, Lee T, An M, Shin HT, Joung JG, Jung MH, Ko G, Wirapati P, Kim SH, Kim HC, Yun SH, Tan IBH, Ranjan B, Lee WY, Kim TY, Choi JK, Kim YJ, Prabhakar S, Tejpar S, Park WY.
      Immunotherapy for metastatic colorectal cancer is effective only for mismatch repair-deficient tumors with high microsatellite instability that demonstrate immune infiltration, suggesting that tumor cells can determine their immune microenvironment. To understand this cross-talk, we analyzed the transcriptome of 91,103 unsorted single cells from 23 Korean and 6 Belgian patients. Cancer cells displayed transcriptional features reminiscent of normal differentiation programs, and genetic alterations that apparently fostered immunosuppressive microenvironments directed by regulatory T cells, myofibroblasts and myeloid cells. Intercellular network reconstruction supported the association between cancer cell signatures and specific stromal or immune cell populations. Our collective view of the cellular landscape and intercellular interactions in colorectal cancer provide mechanistic information for the design of efficient immuno-oncology treatment strategies.
    DOI:  https://doi.org/10.1038/s41588-020-0636-z
  39. Cell Oncol (Dordr). 2020 May 28.
    Esopi D, Graham MK, Brosnan-Cashman JA, Meyers J, Vaghasia A, Gupta A, Kumar B, Haffner MC, Heaphy CM, De Marzo AM, Meeker AK, Nelson WG, Wheelan SJ, Yegnasubramanian S.
      BACKGROUND: In cancers, maintenance of telomeres often occurs through activation of the catalytic subunit of telomerase, encoded by TERT. Yet, most cancers show only modest levels of TERT gene expression, even in the context of activating hotspot promoter mutations (C228T and C250T). The role of epigenetic mechanisms, including DNA methylation, in regulating TERT gene expression in cancer cells is as yet not fully understood.METHODS: Here, we have carried out the most comprehensive characterization to date of TERT promoter methylation using ultra-deep bisulfite sequencing spanning the CpG island surrounding the core TERT promoter in 96 different human cell lines, including primary, immortalized and cancer cell types, as well as in control and reference samples.
    RESULTS: In general, we observed that immortalized and cancer cell lines were hypermethylated in a region upstream of the recurrent C228T and C250T TERT promoter mutations, while non-malignant primary cells were comparatively hypomethylated in this region. However, at the allele-level, we generally found that hypermethylation of promoter sequences in cancer cells is associated with repressed expression, and the remaining unmethylated alleles marked with open chromatin are largely responsible for the observed TERT expression in cancer cells.
    CONCLUSIONS: Our findings suggest that hypermethylation of the TERT promoter alleles signals transcriptional repression of those alleles, leading to attenuation of TERT activation in cancer cells. This type of fine tuning of TERT expression may account for the modest activation of TERT expression in most cancers.
    Keywords:  Cancer; DNA methylation; Epigenetics; High-throughput sequencing; TERT promoter mutation; Telomerase regulation; Telomeres and telomerase
    DOI:  https://doi.org/10.1007/s13402-020-00531-7
  40. Genome Res. 2020 May 27. pii: gr.261248.120. [Epub ahead of print]
    Godfrey AK, Naqvi S, Chmatal L, Chick JM, Mitchell RN, Gygi SP, Skaletsky H, Page DC.
      Little is known about how human Y-Chromosome gene expression directly contributes to differences between XX (female) and XY (male) individuals in nonreproductive tissues. Here, we analyzed quantitative profiles of Y-Chromosome gene expression across 36 human tissues from hundreds of individuals. Although it is often said that Y-Chromosome genes are lowly expressed outside the testis, we report many instances of elevated Y-Chromosome gene expression in a nonreproductive tissue. A notable example is EIF1AY, which encodes eukaryotic translation initiation factor 1A (eIF-1A), together with its X-linked homolog EIF1AX Evolutionary loss of a Y-linked microRNA target site enabled upregulation of EIF1AY, but not EIF1AX, in the heart. Consequently, this essential translation initiation factor is nearly twice as abundant in male as in female heart tissue at the protein level. Divergence between the X and Y Chromosomes in regulatory sequence can therefore lead to tissue-specific, Y-Chromosome-driven sex biases in expression of critical, dosage-sensitive regulatory genes.
    DOI:  https://doi.org/10.1101/gr.261248.120
  41. Nat Biotechnol. 2020 May 25.
    Girelli G, Custodio J, Kallas T, Agostini F, Wernersson E, Spanjaard B, Mota A, Kolbeinsdottir S, Gelali E, Crosetto N, Bienko M.
      With the exception of lamina-associated domains, the radial organization of chromatin in mammalian cells remains largely unexplored. Here we describe genomic loci positioning by sequencing (GPSeq), a genome-wide method for inferring distances to the nuclear lamina all along the nuclear radius. GPSeq relies on gradual restriction digestion of chromatin from the nuclear lamina toward the nucleus center, followed by sequencing of the generated cut sites. Using GPSeq, we mapped the radial organization of the human genome at 100-kb resolution, which revealed radial patterns of genomic and epigenomic features and gene expression, as well as A and B subcompartments. By combining radial information with chromosome contact frequencies measured by Hi-C, we substantially improved the accuracy of whole-genome structure modeling. Finally, we charted the radial topography of DNA double-strand breaks, germline variants and cancer mutations and found that they have distinctive radial arrangements in A and B subcompartments. We conclude that GPSeq can reveal fundamental aspects of genome architecture.
    DOI:  https://doi.org/10.1038/s41587-020-0519-y
  42. Development. 2020 May 28. pii: dev.178988. [Epub ahead of print]
    Li J, Gordon J, Chen ELY, Xiao S, Wu L, Zúñiga-Pflücker JC, Manley NR.
      The cortical and medullary thymic epithelial cell (cTEC and mTEC) lineages are essential for inducing T cell lineage commitment, T cell positive selection and the establishment of self-tolerance, but the mechanisms controlling their fetal specification and differentiation are poorly understood. Here, we show that Notch signaling is required to specify and expand the mTEC lineage. Notch1 is expressed by and active in TEC progenitors. Deletion of Notch1 in TECs resulted in depletion of mTEC progenitors and dramatic reductions in mTECs during fetal stages, consistent with defects in mTEC specification and progenitor expansion. Conversely, forced Notch signaling in all TEC resulted in widespread expression of mTEC progenitor markers and profound defects in TEC differentiation. In addition, lineage-tracing analysis indicated that all mTECs have a history of receiving a Notch signal, consistent with Notch signaling occurring in mTEC progenitors. These data provide strong evidence for a requirement for Notch signaling in specification of the mTEC lineage.
    Keywords:  Foxn1; Notch; Thymus; lineage; mTEC
    DOI:  https://doi.org/10.1242/dev.178988
  43. PLoS One. 2020 ;15(5): e0233630
    Kim M, Lin S.
      Characterization of distinct histone methylation and acetylation binding patterns in promoters and prediction of novel regulatory regions remains an important area of genomic research, as it is hypothesized that distinct chromatin signatures may specify unique genomic functions. However, methods that have been proposed in the literature are either descriptive in nature or are fully parametric and hence more restrictive in pattern discovery. In this article, we propose a two-step non-parametric statistical inference procedure to characterize unique histone modification patterns and apply it to analyzing the binding patterns of four histone marks, H3K4me2, H3K4me3, H3K9ac, and H4K20me1, in human B-lymphoblastoid cells. In the first step, we used a functional principal component analysis method to represent the concatenated binding patterns of these four histone marks around the transcription start sites as smooth curves. In the second step, we clustered these curves to reveal several unique classes of binding patterns. These uncovered patterns were used in turn to scan the whole-genome to predict novel and alternative promoters. Our analyses show that there are three distinct promoter binding patterns of active genes. Further, 19654 regions not within known gene promoters were found to overlap with human ESTs, CpG islands, or common SNPs, indicative of their potential role in gene regulation, including being potential novel promoter regions.
    DOI:  https://doi.org/10.1371/journal.pone.0233630