DOCSLIB.ORG

Progress Toward Understanding Chromosome Silencing by Xist RNA

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Progress Toward Understanding Chromosome Silencing by Xist RNA Downloaded from genesdev.cshlp.org on September 27, 2021 - Published by Cold Spring Harbor Laboratory Press REVIEW Progress toward understanding chromosome silencing by Xist RNA Neil Brockdorff, Joseph S. Bowness, and Guifeng Wei Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom The X inactive-specific transcript (Xist) gene is the master mouse embryos and using mouse embryonic stem cell regulator of X chromosome inactivation in mammals. (mESC) models in vitro defined Xi features that are estab- Xist produces a long noncoding (lnc)RNA that accumu- lished early following the onset of Xist RNA expression, lates over the entire length of the chromosome from interpreted as indicating a role in establishment of X inac- which it is transcribed, recruiting factors to modify under- tivation. Important examples include exclusion of RNA lying chromatin and silence X-linked genes in cis. Recent Polymerase II (RNAPII), loss of histone modifications as- years have seen significant progress in identifying impor- sociated with gene activity, and acquisition of histone tant functional elements in Xist RNA, their associated modifications catalyzed by the Polycomb complexes RNA-binding proteins (RBPs), and the downstream path- PRC1 and PRC2. Conversely, Xi features that are estab- ways for chromatin modification and gene silencing. In lished after a delay following Xist RNA expression, for ex- this review, we summarize progress in understanding ample, CpG island DNA methylation and deposition of both how these pathways function in Xist-mediated si- the histone variant macroH2A, are thought to function lencing and the complex interplay between them. in maintenance rather than establishment of silencing. Significant progress toward defining the critical path- ways for establishment of gene silencing has come from X chromosome inactivation, the process that evolved in the identification of functional sequence elements in mammals to balance levels of X-linked gene expression in Xist RNA and the RNA-binding proteins (RBPs) that XX females relative to XY males, is controlled by a master they bind. Thus, deletion analysis defined the A repeat, regulator locus, Xist (X inactive-specific transcript), that is one of a number of conserved tandem repeat blocks (re- located on the X chromosome and functions in cis (for peated X7.5 in mice and X8 in humans) present in Xist review, see Heard et al. 1997). Xist produces a 15- to 17- RNA sequence (Fig. 2A), as being critical for silencing, kb-long noncoding RNA (lncRNA) that accumulates while multiple regions of the transcript were defined as over the chromosome from which it is transcribed, re- functioning redundantly to mediate local accumulation cruiting factors/complexes that act to modify the underly- of Xist RNA (Wutz et al. 2002). An important break- ing chromatin environment and repress X-linked gene through toward identifying the factors that interact with expression. Gene knockout and transgenic experiments the A repeat (and other regions of Xist RNA), came from demonstrated that Xist is both necessary and sufficient complementary studies that applied either proteomic or for chromosome inactivation (Penny et al. 1996; Lee and genetic screening strategies (Chu et al. 2015; McHugh Jaenisch 1997). et al. 2015; Minajigi et al. 2015; Moindrot et al. 2015; Studies over many years have defined chromatin fea- Monfort et al. 2015). Leading candidates that emerged tures, chromatin-associated factors, and higher-order from this work are summarized in Figure 2A,B. The RBP chromosome organization associated with the inactive SPEN, which functions through interaction with the his- X chromosome (Xi) (Fig. 1; Table 1). An important chal- tone deacetylase complex NCoR-HDAC3 (and possibly lenge for the field is to understand cause and effect. Which other factors), was shown to bind Xist A repeat directly features of Xi are required to establish gene silencing and (Monfort et al. 2015). The closely related RBP RBM15 depend on factors recruited directly by Xist RNA and also binds the A-repeat, and functions at least in part by which are secondary but possibly still important for recruiting the METTL3/14 complex responsible for cata- 6 6 long-term chromosome silencing through development lyzing N -methyladenosine (m A) on mRNA (Patil et al. and into adulthood? To address this issue, studies on early 2016). Additionally, the Lamin B receptor (LBR), was iden- tified as binding Xist RNA (McHugh et al. 2015). Al- though not a known RBP, subsequent work reported [Keywords: X chromosome inactivation; Xist; SPEN; NCoR–HDAC3; LBR; Polycomb; RBM15; m6A RNA methylation; chromatin] Corresponding authors: [email protected], neil.brockdorff@ bioch.ox.ac.uk © 2020 Brockdorff et al. This article, published in Genes & Development, Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.337196. is available under a Creative Commons License (Attribution-NonCom- 120. Freely available online through the Genes & Development Open Ac- mercial 4.0 International), as described at http://creativecommons.org/li- cess option. censes/by-nc/4.0/. GENES & DEVELOPMENT 34:733–744 Published by Cold Spring Harbor Laboratory Press; ISSN 0890-9369/20; www.genesdev.org 733 Downloaded from genesdev.cshlp.org on September 27, 2021 - Published by Cold Spring Harbor Laboratory Press Brockdorff et al. A Xi chromatin and in gene silencing by Xist RNA, includ- ing a summary of our understanding of their relative con- tribution and interplay. Assaying Xist-mediated chromosome silencing In considering recent advances in this field it is important to appreciate the varied models and assays that have been used in analyzing the contribution of different factors to Xist-mediated chromosome silencing, not least because reported findings may otherwise appear contradictory. As summarized in Figure 3A, the principal models that provide access to the developmental stage when X inacti- vation is established are early mouse embryos and plurip- B otent embryonic stem cells (mESCs). The latter include XX mESCs, which express Xist RNA from a single X chro- mosome when differentiated in vitro, XY mESCs with Xist expression driven by a doxycycline-activated promoter, ei- ther from the single X chromosome allele, or from an auto- somally integrated Xist transgene, and XX mESCs with a doxycycline inducible promoter engineered into one of the two Xist alleles. Models using inducible promoters of- fer the advantage of regulatable, synchronous, and homo- Figure 1. Features of the inactive X chromosome. (A) Compari- geneous Xist RNA expression within cell populations, son of chromatin features on the active X chromosome (Xa) and albeit at levels not necessarily equivalent to expression the inactive X chromosome (Xi) at the nucleosomal scale. Xi is Xist characterized by depletion of histone modifications associated from the physiological promoter. Analysis of X inacti- with gene activity, shown here histone acetylation, normally en- vation in embryos is important to verify observations in a riched at promoters and enhancers, H3K4me3, enriched at pro- physiological context. In addition to the aforementioned moters and H3K36me3, high levels of which occur within the models, some studies have analyzed XX somatic cells in bodies of active genes. Additionally, Xi chromatin has enhanced which X inactivation is already established. However, levels of histone modifications associated with gene repression; maintenance of X inactivation in somatic cells has been re- for example, H3K27me3, H2AK119ub1, H3K9me2/3, and high ported to be Xist-independent (Csankovszki et al. 1999), al- levels of the histone variant macroH2A. DNA methylation is ac- beit using relatively crude gene silencing assays, and as quired at CpG islands of Xi genes. RNA polymerase II (RNAPII) such these models may not be ideally suited to studying and associated general transcription factors (GTFs) are depleted the establishment of Xist-mediated silencing. from Xi, as are enhancer-bound transcription factors (TFs), as ev- idenced by reduced chromatin accessibility seen using ATAC- Assays for Xist-mediated silencing can be grouped into seq. Similarly, there are reduced levels of the insulator protein three categories; indirect phenotype/viability assays, di- CTCF and the cohesin complex at insulator/boundary elements. rect imaging based assays and direct molecular assays, (B) Changes in higher order structure of the Xi chromosome. Key for example, allelic RNA-seq, illustrated in Figure examples are an approximately twofold chromatin compaction 3B. Each of the approaches affords distinct advantages, relative to Xa, association of Xi with the nuclear and/or nucleolar but equally has specific limitations. Phenotypic assays periphery, reduced TAD and compartment structure (related to provide evidence for the importance of a given factor in reduced CTCF/cohesin binding), with interactions instead occur- a physiological setting, but do not quantify the underlying ring within one of two large megadomains, and synchronous rep- deficiency in gene silencing. Imaging-based assays provide lication across most of the chromosome, usually in late S phase. a good basis for measuring silencing in individual cells, within a population, for example, in early embryos, but provide limited quantitation and throughput (the number that LBR has an unstructured SR domain that mediates in- of X-linked genes that is practical to assay). Molecular as- teraction with Xist RNA (Chen et al. 2016). Finally the
Load more

Recommended publications
  • Revealing the Mechanism of Xist-Mediated Silencing
    Revealing the Mechanism of Xist-mediated Silencing Thesis by Chun-Kan Chen In Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2018 Defended November 1, 2017 ii 2017 Chun-Kan Chen ORCID: 0000-0002-1194-9137 iii ACKNOWLEDGEMENTS First of all, I’d like to thank my great mentor, Dr. Mitch Guttman (California Institute of Technology, Pasadena, CA), who led me to become an independent researcher and gave me valuable advice that guided me to accomplish this thesis. He has always been supportive of my future plans and career goals. I really enjoyed every discussion we have had. We often generated some interesting ideas for projects during our discussions. I would also like to send my thanks to my lab mates, Amy Chow, Mario Blanco, and Erik Aznauryan, who helped me with many experiments to move the project forward. I’d like to acknowledge Dr. Kathrin Plath (University of California, Los Angeles, Los Angeles, CA) for the collaboration and his critical comments on this project. Also, I want to thank Jesse Engreitz and Patrick McDonel, who provided helpful comments and suggestions to the project. I want to thank my parents, brother, and parents-in-law who provided both instrumental and emotional support to assist me in completing my Ph.D. degree. I also want to thank my friends, Lily Chen, Pei-Ying Lin, Tzu-Yao Wang, and Wei Li, for giving me valuable social support during my years in graduate school. Last but not least, I would like to send my special thanks to my wife, Christine Juang, who has always been supportive.
    [Show full text]
  • Association of BRCA1 with the Inactive X Chromosome and XIST RNA
    FirstCite Published online e-publishing Association of BRCA1 with the inactive X chromosome and XIST RNA Shridar Ganesan1, Daniel P. Silver1, Ronny Drapkin1, Roger Greenberg1, Jean Feunteun2 and David M. Livingston1* 1The Dana-Farber Cancer Institute and Harvard Medical School, 1 Jimmy Fund Way, Boston, MA 02115, USA 2Laboratoire de Genetique et Transfert de Gene, Institut Gustav-Roussy, Villejuif 94805, France Breast cancer, early onset 1 (BRCA1) encodes a nuclear protein that participates in breast and ovarian cancer suppression. The molecular basis for the gender and tissue specificity of the BRCA1 cancer syn- drome is unknown. Recently, we observed that a fraction of BRCA1 in female cells is localized on the inactive X chromosome (Xi). Chromatin immunoprecipitation (ChIP) experiments have demonstrated that BRCA1 physically associates with Xi-specific transcript (XIST) RNA, a non-coding RNA known to coat Xi and to participate in the initiation of its inactivation during early embryogenesis. Cells lacking wild- type BRCA1 show abnormalities in Xi, including lack of proper XIST RNA localization. Reintroduction of wild-type, but not mutant, BRCA1 can correct this defect in XIST localization in these cells. Depletion of BRCA1 in female diploid cells led to a defect in proper XIST localization on Xi and in the development of normal Xi heterchromatic superstructure. Moreover, depletion of BRCA1 led to an increased likelihood of re-expression of a green fluorescent protein (GFP) reporter gene embedded on Xi. Taken together, these findings are consistent with a model in which BRCA1 function contributes to the maintenance of proper Xi heterochromatin superstructure. Although the data imply a novel gender-specific consequence of BRCA1 loss, the relevance of the BRCA1/Xi function to the tumour suppressor activity of BRCA1 remains unclear and needs to be tested.
    [Show full text]
  • Genetic and Epigenetic Mechanisms of the Regulation of Mouse Embryonic Stem Cells Self-Renewal by the Pluripotency Transcription Factor Nanog
    Genetic and epigenetic mechanisms of the regulation of mouse embryonic stem cells self-renewal by the pluripotency transcription factor Nanog Victor HEURTIER Thèse de doctorat de Biologie Dirigée par Pablo NAVARRO GIL Laboratoire Epigénétique des cellules souches – Institut Pasteur Sorbonne Université Ecole doctorale Complexité du Vivant (ED 515) Présentée et soutenue publiquement le 18/09/2018 Devant un jury composé de : Président : Pr MOUCHEL-VIELH Emmanuèle, Professeur Rapporteur : Dr SAVATIER Pierre, Directeur de Recherche Rapporteur : Dr RADA-IGLESIAS Alvaro, Chef d’équipe Examinateur : Dr AZUARA Veronique, Maître de conférences Examinateur : Dr PINSKAYA Marina, Maître de conférences Directeur de thèse : Dr NAVARRO GIL Pablo, Chef d’équipe Abstract Mouse embryonic stem (ES) cells are derived from the pre-implantation blastocyst and are able to maintain their pluripotent state through virtually limitless cell divisions in vitro. The study of the mechanisms regulating the specific features of ES cells led to the discovery of the transcription factors (TFs) governing their unique transcriptome. Among those TFs, Nanog plays a central role in the gene regulatory network that supports ES cells self-renewal. However, the molecular mechanisms by which Nanog exerts its functions are not fully elucidated. We adapted an inducible CRISPR activation (CRISPRa) system in mouse ES cells and demonstrated its functionality to stimulate transcription at endogenous loci. We then accurately determined the list of Nanog responsive genes using gain (CRISPRa cell line) and loss of function experiments and total RNA sequencing. Moreover, the DNA binding profiles of distinct pluripotency TFs were assessed genome-wide by chromatin immunoprecipitation (ChIP) and sequencing upon Nanog depletion and revealed the importance of the latter in the regulation of the pluripotency network activity at thousands of loci.
    [Show full text]
  • SPEN Induces Mir-4652-3P to Target HIPK2 in Nasopharyngeal Carcinoma
    Li et al. Cell Death and Disease (2020) 11:509 https://doi.org/10.1038/s41419-020-2699-2 Cell Death & Disease ARTICLE Open Access SPEN induces miR-4652-3p to target HIPK2 in nasopharyngeal carcinoma Yang Li1,YuminLv1, Chao Cheng2,YanHuang3,LiuYang1, Jingjing He1,XingyuTao1, Yingying Hu1,YutingMa1, Yun Su1,LiyangWu1,GuifangYu4, Qingping Jiang5,ShuLiu6,XiongLiu7 and Zhen Liu1 Abstract SPEN family transcriptional repressor (SPEN), also known as the SMART/HDAC1-associated repressor protein (SHARP), has been reported to modulate the malignant phenotypes of breast cancer, colon cancer, and ovarian cancer. However, its role and the detail molecular basis in nasopharyngeal carcinoma (NPC) remain elusive. In this study, the SPEN mRNA and protein expression was found to be increased in NPC cells and tissues compared with nonmalignant nasopharyngeal epithelial cells and tissues. Elevated SPEN protein expression was found to promote the pathogenesis of NPC and lead to poor prognosis. Knockdown of SPEN expression resulted in inactivation ofPI3K/AKT and c-JUN signaling, thereby suppressing NPC migration and invasion. In addition, miR-4652-3p was found to be a downstream inducer of SPEN by targeting the homeodomain interacting protein kinase 2 (HIPK2) gene, a potential tumor suppressor that reduces the activation of epithelial–mesenchymal transition (EMT) signaling, thereby reducing its expression and leading to increased NPC migration, invasion, and metastasis. In addition, SPEN was found to induce miR-4652-3p expression by activating PI3K/AKT/c-JUN signaling to target HIPK2. Our data provided a new molecular mechanism for SPEN as a metastasis promoter through activation of PI3K/AKT signaling, thereby stimulating the c-JUN/miR-4652-3p axis to target HIPK2 in NPC.
    [Show full text]
  • O-Glcnacylation Regulates the Stability and Enzymatic Activity of the Histone Methyltransferase EZH2
    O-GlcNAcylation regulates the stability and enzymatic activity of the histone methyltransferase EZH2 Pei-Wen Loa, Jiun-Jie Shieb, Chein-Hung Chena, Chung-Yi Wua, Tsui-Ling Hsua, and Chi-Huey Wonga,1 aGenomics Research Center, Academia Sinica, Taipei 115, Taiwan; and bInstitute of Chemistry, Academia Sinica, Taipei 115, Taiwan Contributed by Chi-Huey Wong, May 16, 2018 (sent for review February 1, 2018; reviewed by Michael D. Burkart, Benjamin G. Davis, and Gerald W. Hart) Protein O-glycosylation by attachment of β-N-acetylglucosamine maintenance and differentiation in embryonic stem cells (14, 15). (GlcNAc) to the Ser or Thr residue is a major posttranslational It was suggested that O-GlcNAcylation might play an important glycosylation event and is often associated with protein folding, role in the regulation of PRC1-mediated gene expression, and stability, and activity. The methylation of histone H3 at Lys-27 along this line the O-GlcNAcylation of EZH2 at S76 in the PRC2 catalyzed by the methyltransferase EZH2 was known to suppress complex was reported to stablize EZH2 in our previous study (16). gene expression and cancer development, and we previously The PRC2 complex is composed of Enhancer of zeste 2 (EZH2), reported that the O-GlcNAcylation of EZH2 at S76 stabilized Suppressor of Zeste 12 (Suz12), Extraembryonic endoderm (EED), EZH2 and facilitated the formation of H3K27me3 to inhibit tumor AE binding protein 2 (AEBP2), and retinoblastoma binding protein suppression. In this study, we employed a fluorescence-based method 4/7 (RBBP4/7) (17, 18). Within the PRC2 complex, EZH2 catalyzes the di- and trimethylation of histone H3 at lysine 27 (K27) to form of sugar labeling combined with mass spectrometry to investigate H3K27me2/3 to regulate embryonic and cancer development EZH2 glycosylation and identified five O-GlcNAcylation sites.
    [Show full text]
  • The Mutational Landscape of Myeloid Leukaemia in Down Syndrome
    cancers Review The Mutational Landscape of Myeloid Leukaemia in Down Syndrome Carini Picardi Morais de Castro 1, Maria Cadefau 1,2 and Sergi Cuartero 1,2,* 1 Josep Carreras Leukaemia Research Institute (IJC), Campus Can Ruti, 08916 Badalona, Spain; [email protected] (C.P.M.d.C); [email protected] (M.C.) 2 Germans Trias i Pujol Research Institute (IGTP), Campus Can Ruti, 08916 Badalona, Spain * Correspondence: [email protected] Simple Summary: Leukaemia occurs when specific mutations promote aberrant transcriptional and proliferation programs, which drive uncontrolled cell division and inhibit the cell’s capacity to differentiate. In this review, we summarize the most frequent genetic lesions found in myeloid leukaemia of Down syndrome, a rare paediatric leukaemia specific to individuals with trisomy 21. The evolution of this disease follows a well-defined sequence of events and represents a unique model to understand how the ordered acquisition of mutations drives malignancy. Abstract: Children with Down syndrome (DS) are particularly prone to haematopoietic disorders. Paediatric myeloid malignancies in DS occur at an unusually high frequency and generally follow a well-defined stepwise clinical evolution. First, the acquisition of mutations in the GATA1 transcription factor gives rise to a transient myeloproliferative disorder (TMD) in DS newborns. While this condition spontaneously resolves in most cases, some clones can acquire additional mutations, which trigger myeloid leukaemia of Down syndrome (ML-DS). These secondary mutations are predominantly found in chromatin and epigenetic regulators—such as cohesin, CTCF or EZH2—and Citation: de Castro, C.P.M.; Cadefau, in signalling mediators of the JAK/STAT and RAS pathways.
    [Show full text]
  • Automethylation of PRC2 Promotes H3K27 Methylation and Is Impaired in H3K27M Pediatric Glioma
    Downloaded from genesdev.cshlp.org on October 5, 2021 - Published by Cold Spring Harbor Laboratory Press Automethylation of PRC2 promotes H3K27 methylation and is impaired in H3K27M pediatric glioma Chul-Hwan Lee,1,2,7 Jia-Ray Yu,1,2,7 Jeffrey Granat,1,2,7 Ricardo Saldaña-Meyer,1,2 Joshua Andrade,3 Gary LeRoy,1,2 Ying Jin,4 Peder Lund,5 James M. Stafford,1,2,6 Benjamin A. Garcia,5 Beatrix Ueberheide,3 and Danny Reinberg1,2 1Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York 10016, USA; 2Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA; 3Proteomics Laboratory, New York University School of Medicine, New York, New York 10016, USA; 4Shared Bioinformatics Core, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA; 5Department of Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA The histone methyltransferase activity of PRC2 is central to the formation of H3K27me3-decorated facultative heterochromatin and gene silencing. In addition, PRC2 has been shown to automethylate its core subunits, EZH1/ EZH2 and SUZ12. Here, we identify the lysine residues at which EZH1/EZH2 are automethylated with EZH2-K510 and EZH2-K514 being the major such sites in vivo. Automethylated EZH2/PRC2 exhibits a higher level of histone methyltransferase activity and is required for attaining proper cellular levels of H3K27me3. While occurring inde- pendently of PRC2 recruitment to chromatin, automethylation promotes PRC2 accessibility to the histone H3 tail. Intriguingly, EZH2 automethylation is significantly reduced in diffuse intrinsic pontine glioma (DIPG) cells that carry a lysine-to-methionine substitution in histone H3 (H3K27M), but not in cells that carry either EZH2 or EED mutants that abrogate PRC2 allosteric activation, indicating that H3K27M impairs the intrinsic activity of PRC2.
    [Show full text]
  • Osrrm, a Spen-Like Rice Gene Expressed Specifically in the Endosperm
    Shi-Yan Chen et al. npg Cell Research (2007) 17:713-721. npg713 © 2007 IBCB, SIBS, CAS All rights reserved 1001-0602/07 $ 30.00 ORIGINAL ARTICLE www.nature.com/cr OsRRM, a Spen-like rice gene expressed specifically in the endosperm Shi-Yan Chen1, 2, Zong-Yang Wang1, Xiu-Ling Cai1 1National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai 200032, China; 2Graduate School of the Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100039, China We used the promoter trap technique to identify a rice plant, named 107#, in which the β-glucuronidase (GUS) reporter gene was expressed specifically in the endosperm. A single copy of the T-DNA was inserted into the plant genome, and a candidate gene OsRRM was identified by the insertion. The OsRRM promoter directed GUS expression specifically in rice endosperm, analogous to the GUS expression pattern observed in 107#. OsRRM is a single-copy gene in rice and encodes a nuclear protein containing 1 005 amino-acid residues with two RNA recognition motifs and one Spen paralog and ortholog C-terminal domain. Western blot analysis confirmed that the OsRRM protein was specifically expressed in rice endosperm. Ectopic expression of OsRRM in transgenic plants led to abnormalities, such as short stature, retarded growth and low fructification rates. Our data, in conjunction with the reported function ofSpen genes, implicated OsRRM in the regulation of cell development in rice endosperm. Keywords: RRM, Spen, promoter trap, GUS, rice Cell Research (2007) 17:713-721.
    [Show full text]
  • Long Non‑Coding Rnas XIST and MALAT1 Hijack the PD‑L1 Regulatory Signaling Pathway in Breast Cancer Subtypes
    ONCOLOGY LETTERS 22: 593, 2021 Long non‑coding RNAs XIST and MALAT1 hijack the PD‑L1 regulatory signaling pathway in breast cancer subtypes AMANY SAMIR1, REDA ABDEL TAWAB2 and HEND M. EL TAYEBI1 1Molecular Pharmacology Research Group, Department of Pharmacology and Toxicology, German University in Cairo, Cairo 11835; 2Department of General Surgery, Ain Shams University, Cairo 11772, Egypt Received July 18, 2020; Accepted January 14, 2021 DOI: 10.3892/ol.2021.12854 Abstract. Long non‑coding RNAs (lncRNAs) have attracted presence of lncRNAs. Therefore, the results of the present widespread attention as potential biological and patho‑ study indicated that although miR‑182‑5p exhibited an onco‑ logical regulators. lncRNAs are involved in several biological genic effect, XIST exerted a dominant effect on the regulation processes in cancer. Triple negative breast cancer (TNBC) is of the PD‑L1 signaling pathway via the inhibition of the onco‑ characterized by strong heterogeneity and aggressiveness. At genic function of MALAT1. present, the implication of microRNAs (miRs) and lncRNAs in immunotherapy has been poorly studied. Nevertheless, Introduction the blockade of immune checkpoints, particularly that of the programmed cell‑death protein‑1/programmed cell‑death In the context of tumor biology, the six hallmarks of cancer ligand‑1 (PD‑L1) axis, is considered as a principle approach in have been proposed to be associated with progressively breast cancer (BC) therapy. The present study aimed to inves‑ growing tumors and to be responsible for the complexity of tigate the interaction between immune‑modulatory upstream neoplastic diseases, and these are limitless replicative poten‑ signaling pathways of the PD‑L1 transcript that could enhance tial, evading apoptosis, self‑sufficiency in growth signals, personalized targeted therapy.
    [Show full text]
  • Non-Coding RNA: X-Chromosome Inactivation Unravelled
    RESEARCH HIGHLIGHTS Nature Reviews Molecular Cell Biology | AOP, published online 8 May 2015; doi:10.1038/nrm3998 NON-CODING RNA X-chromosome inactivation unravelled The long non-coding RNA (lncRNA) specific and reproducible set of ten suggesting that SAFA acts to localize Xist (X inactive-specific transcript) is proteins that directly interact with Xist to genomic DNA. Depleting required for the transcriptional silenc- Xist. Of these proteins, knocking Xist binds to SHARP led to the retention of Pol II ing of one X chromosome in each cell, down the genes encoding scaffold SHARP to at Xist-coated X chromosomes, in a process known as X-chromosome attachment factor A (SAFA; also recruit SMRT indicating that SHARP might be inactivation (XCI) that occurs during known as HNRNPU), SMRT- and required for initiating transcriptional mammalian female development. HDAC1-associated repressor protein and activate silencing following Xist localization, Owing to technical limitations, little (SHARP; also known as SPEN or HDAC3 … possibly by recruiting the transcrip- is known about the mechanism of MSX2-interacting protein) and resulting in tional co-repressors SMRT and transcriptional silencing during XCI. lamin-B receptor (LBR) largely abol- HDAC3. Indeed, depleting SMRT McHugh et al. now describe using ished the silencing of XCI‑affected gene silencing or HDAC3 (but not other HDACs) RNA antisense purification followed genes in the male ES cells as well as in abrogated Xist-dependent gene by quantitative mass spectrometry differentiating female ES cells. These silencing. Another feature of XCI (RAP–MS) — a novel approach for three proteins are therefore required is the recruitment of the Polycomb identifying proteins that directly for Xist-mediated gene silencing.
    [Show full text]
  • Polycomb Repressor Complex 2 Function in Breast Cancer (Review)
    INTERNATIONAL JOURNAL OF ONCOLOGY 57: 1085-1094, 2020 Polycomb repressor complex 2 function in breast cancer (Review) COURTNEY J. MARTIN and ROGER A. MOOREHEAD Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON N1G2W1, Canada Received July 10, 2020; Accepted September 7, 2020 DOI: 10.3892/ijo.2020.5122 Abstract. Epigenetic modifications are important contributors 1. Introduction to the regulation of genes within the chromatin. The poly- comb repressive complex 2 (PRC2) is a multi‑subunit protein Epigenetic modifications, including DNA methylation complex that is involved in silencing gene expression through and histone modifications, play an important role in gene the trimethylation of lysine 27 at histone 3 (H3K27me3). The regulation. The dysregulation of these modifications can dysregulation of this modification has been associated with result in pathogenicity, including tumorigenicity. Research tumorigenicity through the increased repression of tumour has indicated an important influence of the trimethylation suppressor genes via condensing DNA to reduce access to the modification at lysine 27 on histone H3 (H3K27me3) within transcription start site (TSS) within tumor suppressor gene chromatin. This methylation is involved in the repression promoters. In the present review, the core proteins of PRC2, as of multiple genes within the genome by condensing DNA well as key accessory proteins, will be described. In addition, to reduce access to the transcription start site (TSS) within mechanisms controlling the recruitment of the PRC2 complex gene promoter sequences (1). The recruitment of H1.2, an H1 to H3K27 will be outlined. Finally, literature identifying the histone subtype, by the H3K27me3 modification has been a role of PRC2 in breast cancer proliferation, apoptosis and suggested as a mechanism for mediating this compaction (1).
    [Show full text]
  • The Estrogen Receptor Cofactor SPEN Functions As a Tumor Suppressor and Candidate Biomarker of Drug Responsiveness in Hormone-Dependent Breast Cancers
    Author Manuscript Published OnlineFirst on August 21, 2015; DOI: 10.1158/0008-5472.CAN-14-3475 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. SPEN is a tumor suppressor in ERα positive breast cancers Title The estrogen receptor cofactor SPEN functions as a tumor suppressor and candidate biomarker of drug responsiveness in hormone-dependent breast cancers. Running Title SPEN is a tumor suppressor in ERα positive breast cancers Authors and affiliations: Légaré, Stéphanie1,2, Cavallone, Luca2, Mamo, Aline2, Chabot, Catherine2, Sirois, Isabelle1,2, Magliocco, Anthony3, Klimowicz, Alexander3, Tonin, Patricia N.4, Buchanan, Marguerite2, Keilty, Dana1,2, Hassan, Saima1,2, Laperrière, David5, Mader, Sylvie5,6, Aleynikova, Olga2, Basik Mark1,2 Keywords - Transcriptional corepressor - Tumor suppressor gene - Estrogen receptor positive breast cancers - Endocrine resistance Financial support • Stéphanie Légaré • Supported by a McGill Integrated Cancer Research Training Program studentship (FRN53888) and a doctoral award from the Fonds de recherche du Québec – Santé. • Isabelle Sirois • Recipient of the Eileen Iwanicki postdoctoral fellowship in Breast Cancer Research from the Canadian Institutes of Health Research in partnership with the Breast Cancer Society of Canada. 1 Dept of Surgery and Oncology, McGill University, Montréal, Québec, Canada. 2 Dept of Oncology and Surgery, Lady Davis Institute for Medical Research, Montréal, Québec, Canada. 3 Dept of Pathology, University of Calgary, Calgary, Alberta, Canada. 4 Depts of Human Genetics and Medicine, McGill University and The Research Institute of the McGill University Health Centre, Montréal, Québec, Canada. 5 Institut de recherche en immunologie et cancérologie, IRIC, Montréal, Québec, Canada. 6 Dept de Biochimie, Université de Montréal, Montréal, Québec, Canada.
    [Show full text]