Long antisense non-coding RNAs function to direct epigenetic complexes that regulate transcription in human cells

Long noncoding RNA: An emerging diagnostic and therapeutic target in kidney diseases

Long noncoding RNAs (lncRNAs) have critical roles in the development of many diseases including kidney disease. An increasing number of studies have shown that lncRNAs are involved in kidney development and that their dysregulation can result in distinct disease processes, including acute kidney injury, chronic kidney disease, and renal cell carcinoma. Understanding the roles of lncRNAs in kidney disease may provide new diagnostic and therapeutic opportunities in the clinic. This review provides an overview of lncRNA characteristics, and biological function and discusses specific studies that provide insight into the function and potential application of lncRNAs in kidney disease treatment.

Making Sense of Antisense lncRNAs in Hepatocellular Carcinoma

Transcriptome complexity is emerging as an unprecedented and fascinating domain, especially by high-throughput sequencing technologies that have unveiled a plethora of new non-coding RNA biotypes. This review covers antisense long non-coding RNAs, i.e., lncRNAs transcribed from the opposite strand of other known genes, and their role in hepatocellular carcinoma (HCC). Several sense-antisense transcript pairs have been recently annotated, especially from mammalian genomes, and an understanding of their evolutionary sense and functional role for human health and diseases is only beginning. Antisense lncRNAs dysregulation is significantly involved in hepatocarcinogenesis, where they can act as oncogenes or oncosuppressors, thus playing a key role in tumor onset, progression, and chemoradiotherapy response, as deduced from many studies discussed here. Mechanistically, antisense lncRNAs regulate gene expression by exploiting various molecular mechanisms shared with other ncRNA molecules, and exploit special mechanisms on their corresponding sense gene due to sequence complementarity, thus exerting epigenetic, transcriptional, post-transcriptional, and translational controls. The next challenges will be piecing together the complex RNA regulatory networks driven by antisense lncRNAs and, ultimately, assigning them a function in physiological and pathological contexts, in addition to defining prospective novel therapeutic targets and innovative diagnostic tools.

Crosstalk between non-coding RNAs expression profile, drug resistance and immune response in breast cancer

Drug resistance is one of the most critical challenges facing researchers in treating breast cancer. Despite numerous treatments for breast cancer, including conventional chemical drugs, monoclonal antibodies, and immunotherapeutic drugs known as immune checkpoint inhibitors (ICI), many patients resist various approaches. In recent years, the relationship between gene expression profiles and drug resistance phenotypes has attracted much attention. Non-coding RNAs (ncRNAs) are regulatory molecules that have been shown to regulate gene expression and cell transcriptome. Two categories, microRNAs and long non-coding RNAs have been more considered and studied among these ncRNAs. Studying the role of different ncRNAs in chemical drug resistance and ICI resistance together can be beneficial in selecting more effective treatments for breast cancer. Changing the expression and action mechanism of these regulatory molecules on drug resistance phenotypes is the main topic of this review article.

The regulatory role of antisense lncRNAs in cancer

Antisense long non-coding RNAs (antisense lncRNAs), transcribed from the opposite strand of genes with either protein coding or non-coding function, were reported recently to play a crucial role in the process of tumor onset and development. Functionally, antisense lncRNAs either promote or suppress cancer cell proliferation, migration, invasion, and chemoradiosensitivity. Mechanistically, they exert their regulatory functions through epigenetic, transcriptional, post-transcriptional, and translational modulations. Simultaneously, because of nucleotide sequence complementarity, antisense lncRNAs have a special role on its corresponding sense gene. We highlight the functions and molecular mechanisms of antisense lncRNAs in cancer tumorigenesis and progression. We also discuss the potential of antisense lncRNAs to become cancer diagnostic biomarkers and targets for tumor treatment.

MALAT1 rs619586 A/G polymorphisms are associated with decreased risk of lung cancer

Lung cancer is the leading cause of cancer-associated mortality worldwide. Genetic factors are reported to play important roles in lung carcinogenesis. To evaluate genetic susceptibility, we conducted a hospital-based case-control study on the effects of functional single nucleotide polymorphisms (SNPs) in long non-coding RNAs (lncRNAs) and microRNAs on lung cancer development. A total of 917 lung cancer cases and 925 control subjects were recruited. The MALAT1 rs619586 A/G genotype frequencies between patient and control groups were significantly different (P < .001), specifically, 83.85% vs 75.88% (AA), 15.60% vs 21.79% (AG), and 0.55% vs 2.32% (GG). When the homozygous genotype MALAT1 rs619586 AA was used as the reference group, AG (AG vs AA: adjusted odds ratio [OR] 0.65, 95% confidential interval [CI] 0.51-0.83, P = .001) and GG genotypes were associated with significantly decreased risk of lung cancer (GG vs AA: adjusted OR 0.22, 95% CI 0.08-0.59, P = .003). In the dominant model, MALAT1 rs619586 AG/GG variants were also associated with a significantly decreased risk of lung cancer (adjusted OR 0.61, 95% CI 0.48-0.78, P < .001). In the recessive model, when MALAT1 rs619586 AA/AG genotypes were used as the reference group, the GG homozygous genotype was also associated with significantly decreased risk for lung cancer (adjusted OR 0.24, 95% CI 0.09-0.64, P = .004). Hsa-miR-34b/c rs4938723 T > C, pri-miR-124-1 rs531564 C > G and hsa-miR-423 rs6505162 C > A SNPs were not associated with lung cancer risk. Our collective data indicated that MALAT1 rs619586 A/G SNPs significantly reduced the risk of lung cancer. Large-scale studies on different ethnic populations and tissue-specific biological characterization are required to validate the current findings.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.

Functions of histone modifications and histone modifiers in Schwann cells

Schwann cells (SCs) are the main glial cells present in the peripheral nervous system (PNS). Their primary functions are to insulate peripheral axons to protect them from the environment and to enable fast conduction of electric signals along big caliber axons by enwrapping them in a thick myelin sheath rich in lipids. In addition, SCs have the peculiar ability to foster axonal regrowth after a lesion by demyelinating and converting into repair cells that secrete neurotrophic factors and guide axons back to their former target to finally remyelinate regenerated axons. The different steps of SC development and their role in the maintenance of PNS integrity and regeneration after lesion are controlled by various factors among which transcription factors and chromatin-remodeling enzymes hold major functions. In this review, we discussed how histone modifications and histone-modifying enzymes control SC development, maintenance of PNS integrity and response to injury. The functions of histone modifiers as part of chromatin-remodeling complexes are discussed in another review published in the same issue of Glia.

LncRNA AC093818.1 accelerates gastric cancer metastasis by epigenetically promoting PDK1 expression

Gastric cancer (GC) is a highly prevalent type of metastatic tumor. The mechanisms underlying GC metastasis are poorly understood. Some long noncoding RNAs (lncRNAs) reportedly play key roles in regulating metastasis of GC. However, the biological roles of five natural antisense lncRNAs (AC093818.1, CTD-2541M15.1, BC047644, RP11-597M12.1, and RP11-40A13.1) in GC metastasis remain unclear. In this study, the expression of these lncRNAs was measured by quantitative reverse transcription-polymerase chain reaction. Migration and invasion were evaluated by wound-healing and the Transwell assay, respectively. Stable cells were injected into the tail veins of nude mice. Sections of collected lung and liver tissues were stained using hematoxylin and eosin. Protein expression was analyzed by western blot. RNA immunoprecipitation (RIP) assay was used to verify whether the STAT3 and SP1 transcription factors bound to AC093818.1 in GC cells. Expression levels of the five lncRNAs, especially AC093818.1, were significantly upregulated in metastatic GC tissues relative to those in nonmetastatic GC tissues. AC093818.1 expression was correlated with invasion, lymphatic metastasis, distal metastasis, and tumor-node-metastasis stage. AC093818.1 expression was highly sensitive and specific in the diagnosis of metastatic or nonmetastatic GC. AC093818.1 overexpression promoted GC migration and invasion in vitro and in vivo. AC093818.1 overexpression increased PDK1, p-AKT1, and p-mTOR expression levels. AC093818.1 silencing decreased these expressions. AC093818.1 bound to transcription factors STAT3 and SP1, and SP1 or STAT3 silencing could alleviated the effect of AC093818.1 overexpression. The data demonstrate that lncRNA AC093818.1 accelerates gastric cancer metastasis by epigenetically promoting PDK1 expression. LncRNA AC093818.1 may be a potential therapeutic target for metastatic GC.

Antisense regulation of atrial natriuretic peptide expression

The cardiac hormone atrial natriuretic peptide (ANP) is a central regulator of blood volume and a therapeutic target in hypertension and heart failure. Enhanced ANP activity in such conditions through inhibition of the degradative enzyme neprilysin has shown clinical efficacy but is complicated by consequences of simultaneous accumulation of a heterogeneous array of other hormones. Targets for specific ANP enhancement have not been available. Here, we describe a cis-acting antisense transcript (NPPA-AS1), which negatively regulates ANP expression in human cardiomyocytes. We show that NPPA-AS1 regulates ANP expression via facilitating NPPA repressor RE1-silencing transcription factor (REST) binding to its promoter, rather than forming an RNA duplex with ANP mRNA. Expression of ANP mRNA and NPPA-AS1 was increased and correlated in isolated strained human cardiomyocytes and in hearts from patients with advanced heart failure. Further, inhibition of NPPA-AS1 in vitro and in vivo resulted in increased myocardial expression of ANP, increased circulating ANP, increased renal cGMP, and lower blood pressure. The effects of NPPA-AS1 inhibition on NPPA expression in human cardiomyocytes were further marked under cell-strain conditions. Collectively, these results implicate the antisense transcript NPPA-AS1 as part of a physiologic self-regulatory ANP circuit and a viable target for specific ANP augmentation.

Analysis of lncRNA-miRNA-mRNA Interactions in Hyper-proliferative Human Pulmonary Arterial Smooth Muscle Cells

We previously reported enhanced proliferation of smooth muscle cells on the combined exposure of HIV proteins and cocaine leading to the development of HIV-pulmonary arterial hypertension. Here, we attempt to comprehensively understand the interactions between long noncoding RNAs (lncRNAs), mRNAs and micro-RNAs (miRNAs) to determine their role in smooth muscle hyperplasia. Differential expression of lncRNAs, mRNAs and miRNAs were obtained by microarray and small-RNA sequencing from HPASMCs treated with and without cocaine and/or HIV-Tat. LncRNA to mRNA associations were conjectured by analyzing their genomic proximity and by interrogating their association to vascular diseases and cancer co-expression patterns reported in the relevant databases. Neuro-active ligand receptor signaling, Ras signaling and PI3-Akt pathway were among the top pathways enriched in either differentially expressed mRNAs or mRNAs associated to lncRNAs. HPASMC with combined exposure to cocaine and Tat (C + T) vs control identified the following top lncRNA-mRNA pairs, ENST00000495536-HOXB13, T216482-CBL, ENST00000602736-GDF7, and, TCONS_00020413-RND1. Many of the down-regulated miRNAs in the HPASMCs treated with C + T were found to be anti-proliferative and targets of up-regulated lncRNAs targeting up-regulated mRNAs, including down-regulation of miR-185, -491 and up-regulation of corresponding ENST00000585387. Specific knock down of the selected lncRNAs highlighted the importance of non-coding RNAs in smooth muscle hyperplasia.

Long non-coding RNAs: Functional regulatory players in breast cancer

Historically, the long-held protein-centered bias has denoted 98% of the human genome as 'Junk' DNA. However, the current work has shifted the perception of such 'junk' transcriptional products to functional regulatory molecules. The recent surveillance of the human transcriptome has highlighted the pivotal role of such non-coding RNA (ncRNA) molecules in diverse physiological and pathological conditions. Long non-coding RNA (lncRNA) is a recent class of ncRNA molecules that is still in its infancy stage. The main focus of this review is to unravel the importance of lncRNAs in the most prevalent malignancy among females which is Breast Cancer (BC). A specific focus on lncRNAs as prognostic markers among BC patients showing molecular subtype heterogeneity was also tackled in this review. Finally, the functional and the mechanistic roles of such booming ncRNA molecules in shaping the fate of the BC progression have been highlighted.

Pseudogenes in gastric cancer pathogenesis: a review article

Cancer burden rises globally at an alarming pace. According to GLOBOCAN 2012, gastric cancer (GC) is regarded as the fifth most common malignancy in the world. Being twice as high in men as in women, GC is the third leading cause of cancer mortality in both sexes globally. Being labeled as 'junk DNA', pseudogenes were considered as nonfunctional 'trash', which contribute nothing to survival of the organism; therefore, a number of strategies have been developed to circumvent their accidental detection. Recent progresses have confirmed that pseudogenes can have broad and multifaceted spectrum of activities in human cancers in general and GC in particular. Furthermore, the mentioned functions are parental gene-dependent and/or -independent. Therefore, pseudogenes can be regarded as the emerging class of elaborate modulators of gene expression involved in pathogenesis of human cancers including gastric adenocarcinoma.

Long non-coding RNA H19 promotes the migration and invasion of colon cancer cells via MAPK signaling pathway

Long non-coding RNA H19 has been identified to be dysregulated in a number of tumor types, and is closely associated with cancer progression. RAS/mitogen-activated protein kinase (MAPK) is an important intracellular signaling transduction pathway. Activation of the RAS-MAPK signaling pathway is one of the most frequent carcinogenic events in human cancer. However, the mechanism of H19 in promoting the migration and invasion of colorectal cancer (CRC) cells, and the association between H19 and RAS-MAPK signaling pathway is not well understood. The aim of the present study was to investigate the function of H19 on CRC metastasis and invasion, and assess the association between H19 and the RAS-MAPK signaling pathway. The migration and invasion of CRC cells were analyzed using Transwell migration and invasion assays. To elucidate the association between H19 and the RAS-MAPK signaling pathway and determine the expression level of active RAS in CRC cells, Ras activity assay and Western blotting were performed. It was indicated that the overexpression of H19 was able to increase the migration and invasion of CRC cells and this may be mediated by the regulation of RAS activation. Therefore, H19 may promote metastasis and invasion in colorectal cancer by activating the RAS-MAPK signaling pathway.

Sheep skeletal muscle transcriptome analysis reveals muscle growth regulatory lncRNAs

As widely distributed domestic animals, sheep are an important species and the source of mutton. In this study, we aimed to evaluate the regulatory lncRNAs associated with muscle growth and development between high production mutton sheep (Dorper sheep and Qianhua Mutton Merino sheep) and low production mutton sheep (Small-tailed Han sheep). In total, 39 lncRNAs were found to be differentially expressed. Using co-expression analysis and functional annotation, 1,206 co-expression interactions were found between 32 lncRNAs and 369 genes, and 29 of these lncRNAs were found to be associated with muscle development, metabolism, cell proliferation and apoptosis. lncRNA–mRNA interactions revealed 6 lncRNAs as hub lncRNAs. Moreover, three lncRNAs and their associated co-expressed genes were demonstrated by cis-regulatory gene analyses, and we also found a potential regulatory relationship between the pseudogene lncRNA LOC101121401 and its parent gene FTH1. This study provides a genome-wide resolution of lncRNA and mRNA regulation in muscles from mutton sheep.

linc00673 (ERRLR01) is a prognostic indicator of overall survival in breast cancer

LncRNAs are novel noncoding RNAs involved in the epigenetic regulation of gene expression by recruiting ribonucleoprotein complexes to specific genomic loci to initiate histone methylation and/or other chromatin modifications. LncRNAs themselves function as tumor suppressors or oncogenes, depending on the gene regulatory networks they govern. We identified lnc00673 (ERRLR01) as a marker of overall survival (OS) in breast cancer patients. Specifically, ERRLR01 levels were elevated in triple-negative breast cancer (TNBC) as compared with Luminal-A, Luminal-B, and HER2 breast cancer subtypes. ERRLR01 levels were also inversely correlated with breast cancer survival across all breast cancer patients. Upon stratification, OS in ERα^- tumors correlated with negative overall survival, while in ERα⁺ tumors, ERRLR01 correlated with positive outcomes. This suggests ERRLR01 is modulated by hormone signaling in breast cancer. Gene-network analysis revealed ERRLR01 correlated with distinct pathways including "epithelial development" and "cellular differentiation." These data suggest ERRLR01 operates as an oncogene in TNBC, as well as a biomarker in breast cancer patients.

The molecular dynamics of long noncoding RNA control of transcription in PTEN and its pseudogene

RNA has been found to interact with chromatin and modulate gene transcription. In human cells, little is known about how long noncoding RNAs (lncRNAs) interact with target loci in the context of chromatin. We find here, using the phosphatase and tensin homolog (PTEN) pseudogene as a model system, that antisense lncRNAs interact first with a 5' UTR-containing promoter-spanning transcript, which is then followed by the recruitment of DNA methyltransferase 3a (DNMT3a), ultimately resulting in the transcriptional and epigenetic control of gene expression. Moreover, we find that the lncRNA and promoter-spanning transcript interaction are based on a combination of structural and sequence components of the antisense lncRNA. These observations suggest, on the basis of this one example, that evolutionary pressures may be placed on RNA structure more so than sequence conservation. Collectively, the observations presented here suggest a much more complex and vibrant RNA regulatory world may be operative in the regulation of gene expression.

Unraveling long non-coding RNAs through analysis of high-throughput RNA-sequencing data

Extensive genome-wide transcriptome study mediated by high throughput sequencing technique has revolutionized the study of genetics and epigenetic at unprecedented resolution. The research has revealed that besides protein-coding RNAs, large proportions of mammalian transcriptome includes a heap of regulatory non protein-coding RNAs, the number encoded within human genome is enigmatic. Many taboos developed in the past categorized these non-coding RNAs as ''dark matter" and "junks". Breaking the myth, RNA-seq-- a recently developed experimental technique is widely being used for studying non-coding RNAs which has acquired the limelight due to their physiological and pathological significance. The longest member of the ncRNA family-- long non-coding RNAs, acts as stable and functional part of a genome, guiding towards the important clues about the varied biological events like cellular-, structural- processes governing the complexity of an organism. Here, we review the most recent and influential computational approach developed to identify and quantify the long non-coding RNAs serving as an assistant for the users to choose appropriate tools for their specific research.

AS-IL6 promotes glioma cell invasion by inducing H3K27Ac enrichment at the IL6 promoter and activating IL6 transcription

Interleukin-6 (IL-6) is widely expressed in a variety of malignant tumors; thus, targeting the IL-6/STAT3 pathway represents a promising therapeutic strategy for malignant cancers. In this study, we identified a noncoding RNA, AS-IL6, which is transcribed antisense to IL6 and induces IL6 expression in glioma cells. Knockdown of AS-IL6 attenuates LPS-induced IL6 transcription. Interestingly, AS-IL6 does not change IL6 mRNA stability, but induces the enrichment of histone H3 acetylated at lysine 27 (H3K27Ac) at the IL6 promoter. In addition, we found that depletion of AS-IL6 inhibits the invasive ability of glioblastoma cells, while treatment of cells with recombinant IL6 reverses this effect. Our results reveal a novel mechanism of IL6 regulation and demonstrate an oncogenic role for AS-IL6 in glioma cells.

Long non-coding RNAs: Mechanism of action and functional utility

Recent RNA sequencing studies have revealed that most of the human genome is transcribed, but very little of the total transcriptomes has the ability to encode proteins. Long non-coding RNAs (lncRNAs) are non-coding transcripts longer than 200 nucleotides. Members of the non-coding genome include microRNA (miRNA), small regulatory RNAs and other short RNAs. Most of long non-coding RNA (lncRNAs) are poorly annotated. Recent recognition about lncRNAs highlights their effects in many biological and pathological processes. LncRNAs are dysfunctional in a variety of human diseases varying from cancerous to non-cancerous diseases. Characterization of these lncRNA genes and their modes of action may allow their use for diagnosis, monitoring of progression and targeted therapies in various diseases. In this review, we summarize the functional perspectives as well as the mechanism of action of lncRNAs.

Association of lnc-LAMC2-1:1 rs2147578 and CASC8 rs10505477 Polymorphisms with Risk of Childhood Acute Lymphoblastic Leukemia

Long non-coding RNAs (lncRNAs) are a novel class of non-protein coding RNAs that are involved in a wide variety of biological processes. There are limited data regarding the impact of lnc-LAMC2-1:1 rs2147578 as well as CASC8 rs10505477 T>C polymorphisms on cancer development. Here we examined for the first time whether rs2147578 and rs10505477 polymorphisms are associated with childhood acute lymphoblastic leukemia (ALL) in a total of 110 cases and 120 healthy controls. Genotyping was achieved by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The rs2147578 variant increased the risk of ALL in codominant (OR=4.33, 95%CI=2.00-9.37, p<0.0001, CG vs CC, and OR=5.81, 95%CI=2.30-14.69, p=0.0002, GG vs CC), dominant (OR=4.63, 95%CI=2.18-9.86, p<0.0001, CG+GG vs CC), overdominant (OR=1.74, 95%CI=1.02-2.97, p=0.0444, CG vs CC+GG) and allele (OR=1.91, 95%CI=1.32-2.77, p=0.0008, G vs C) inheritance models tested. No significant association was found between the CASC8 rs10505477 T>C variant and risk of childhood ALL. In conclusion, the present study revealed that the lnc-LAMC2-1:1 rs2147578 polymorphism may be a risk factor for developing childhood ALL. Further studies with larger sample sizes with different ethnicities are now required to confirm our findings.

Long non-coding RNA DBCCR1-003 regulate the expression of DBCCR1 via DNMT1 in bladder cancer

Background

Many long non coding RNAs have been identified as key modulators in cancer development. A lncRNA, DBCCR1-003, derived from the locus of tumor suppressor gene DBCCR1 (deleted in bladder cancer chromosome region 1), has unknown function. In the present study, we explored function and molecular mechanism of DBCCR1-003 in bladder cancer (BC) development.

Methods

We evaluated the expression levels of DBCCR1-003 in tissues and cells with western blot and quantitative real-time polymerase chain reaction. Multiple approaches including chromatin immunoprecipitation assay and RNA immunoprecipitation were used to confirm the direct binding of DBCCR1-003 to DNMT1. The recombinant vector overexpressing DBCCR1-003 was constructed. Cell proliferation assay, colony formation assay and flow cytometric analysis were employed to measure the role of DBCCR1-003 in regulation of cell proliferation, cycle and apoptosis.

Results

Firstly we detected the expression of DBCCR1-003, DBCCR1, DNMT1 (DNA methyltransferase 1) and DNA methylation in the promoter of DBCCR1. We found low expression of DBCCR1-003, same as DBCCR1, while high expression of DNMT1 and hypermethylation of DBCCR1 gene promoter in BC tissues and T24 cells line. Further studies revealed that treatment of DNMT inhibitor, 5-aza-2-deoxycytidine(DAC), or overexpression of DBCCR1-003 led to increased DBCCR1 expression by reversion of promoter hypermethylation and DNMT1 binding to DBCCR1 promoter in T24 cells. Importantly, RNA immunoprecipitation (RIP) showed that DBCCR1-003 physically associates with DNMT1. The binding of them was increased with the inhibition of DBCCR1 promoter methylation, indicating that DBCCR1-003 may bind to DNMT1 and prevent DNMT1-mediated the methylation of DBCCR1. Furthermore, overexpression of DBCCR1-003 resulted in significant inhibition of T24 cells growth through the inducing G0/G1 arrest and apoptosis.

Conclusions

Taken together, these findings demonstrated that a novel tumor suppressor DBCCR1-003 regulates the expression of DBCCR1 via binding to DNMT1 and preventing DNMT1-mediated the methylation of DBCCR1 in BC. LncRNA DBCCR1-003 may serve as a novel biomarker and therapeutic target for BC in future cancer clinic.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-016-0356-8) contains supplementary material, which is available to authorized users.

Transcriptional gene silencing in humans

It has been over a decade since the first observation that small non-coding RNAs can functionally modulate epigenetic states in human cells to achieve functional transcriptional gene silencing (TGS). TGS is mechanistically distinct from the RNA interference (RNAi) gene-silencing pathway. TGS can result in long-term stable epigenetic modifications to gene expression that can be passed on to daughter cells during cell division, whereas RNAi does not. Early studies of TGS have been largely overlooked, overshadowed by subsequent discoveries of small RNA-directed post-TGS and RNAi. A reappraisal of early work has been brought about by recent findings in human cells where endogenous long non-coding RNAs function to regulate the epigenome. There are distinct and common overlaps between the proteins involved in small and long non-coding RNA transcriptional regulatory mechanisms, suggesting that the early studies using small non-coding RNAs to modulate transcription were making use of a previously unrecognized endogenous mechanism of RNA-directed gene regulation. Here we review how non-coding RNA plays a role in regulation of transcription and epigenetic gene silencing in human cells by revisiting these earlier studies and the mechanistic insights gained to date. We also provide a list of mammalian genes that have been shown to be transcriptionally regulated by non-coding RNAs. Lastly, we explore how TGS may serve as the basis for development of future therapeutic agents.

RNA-seq analysis identifies key long non-coding RNAs connected to the pathogenesis of alcohol-associated head and neck squamous cell carcinoma

Alcohol consumption has been implicated in the pathogenesis of head and neck squamous cell carcinoma (HNSCC), although its mechanism is poorly understood. Recent advances in the identification and understanding of long non-coding RNAs (lncRNAs) have indicated that these molecules have a profound effect on numerous biological processes, including tumorigenesis and oncogenesis. The present authors hypothesize that alcohol-mediated dysregulation of lncRNAs is a key event in HNSCC pathogenesis. An in silico differential expression analysis utilizing RNA sequencing (RNA-seq) data from 34 HNSCC patients, which included alcohol drinkers and non-alcohol drinkers, identified a panel of lncRNAs that were dysregulated due to alcohol consumption. Normal oral keratinocytes were then exposed to ethanol and acetaldehyde to validate the RNA-seq results. Two lncRNAs that were differentially expressed due to alcohol consumption were identified from RNA-seq analysis of the clinical data: lnc-PSD4-1 and lnc-NETO-1. Oral keratinocytes exposed to alcohol and acetaldehyde demonstrated dysregulation of these two lncRNAs, thus validating the results of RNA-seq analysis. In addition, low expression of the lnc-PSD4-1 isoform, lnc-PSD4-1:14, exhibited a strong correlation with high survival rates in a Cox proportional hazards regression model. Therefore, these lncRNAs may play a key role in the early pathogenesis of HNSCC, since they are dysregulated in both clinical data and in vitro experiments mimicking the effects of alcohol use.

Aberrant methylation-mediated downregulation of long noncoding RNA LOC100130476 correlates with malignant progression of esophageal squamous cell carcinoma

BACKGROUND

Dysregulated long non-coding RNAs (lncRNAs) are involved in many complicated human diseases including cancer.

AIMS

To determine the role and methylation status of a new lncRNA LOC100130476 in the pathogenesis of esophageal squamous cell carcinoma (ESCC).

METHODS

One hundred and twenty three ESCC patients with tumor tissues and corresponding adjacent normal tissues were enrolled. The expression level and methylation status of LOC100130476 in esophageal cancer cell lines and primary ESCC samples were respectively detected.

RESULTS

Significant downregulation of LOC100130476 was detected in esophageal cancer cell lines and primary ESCC tumor tissues. Up-regulation of LOC100130476 led to the inhibition of proliferation and invasiveness of the cancer cells. Aberrant hypermethylation of the CpG sites in exon 1 closing to the transcription start site was found to be more tumor-specific and to be more critical for gene silencing. Hypermethylation of these CpG sites was associated with TNM stage and pathological differentiation. ESCC patients in stage III and IV, with low expression or hypermethylation of the CpG sites in exon 1 demonstrated poor patient survival.

CONCLUSIONS

LOC100130476 is down-regulated in ESCC at least partly by hypermethylation of CpG sites in exon 1 and its hypermethylation may have prognostic implications for ESCC patients.

Clinical Significance of Long Non-Coding RNA CASC8 rs10505477 Polymorphism in Lung Cancer Susceptibility, Platinum-Based Chemotherapy Response, and Toxicity

Long non-coding RNA (lncRNA) CASC8 rs10505477 polymorphism has been identified to be related to risk of many kinds of cancers, such as colorectal cancer, gastric cancer, and invasive ovarian cancer, and it may be involved in the prognosis of gastric cancer patients who have received platinum-based chemotherapy after surgical treatment. So far, there is no study investigating the clinical significance of lncRNA CASC8 rs10505477 in lung cancer susceptibility and treatment. In this study, we genotyped 498 lung cancer patients and 213 healthy control subjects to explore the correlation between the rs10505477 polymorphism and lung cancer risk in a Chinese population. Among the 498 patients, 467 were selected for the chemotherapy response and toxicity study. We found that the single nucleotide polymorphisms (SNP) rs10505477 was greatly related to lung cancer risk in male and adenocarcinoma subgroups in recessive model (adjusted OR = 0.51, 95%CI = 0.29–0.90, p = 0.02; adjusted OR = 0.52, 95%CI = 0.30–0.89, p = 0.02, respectively). It was also closely correlated with platinum-based chemotherapy response in dominant model (adjusted OR = 1.58, 95%CI = 1.05–2.39, p = 0.03). Additionally, we observed that CASC8 rs10505477 polymorphism was significantly relevant to severe hematologic toxicity in non-small-cell lung cancer (NSCLC) subgroup in dominant model (adjusted OR = 0.59, 95%CI = 0.35–0.98, p = 0.04) and in additive model (adjusted OR = 0.62, 95%CI = 0.43–0.90, p = 0.01). Furthermore, it was found that rs10505477 polymorphism was greatly associated with gastrointestinal toxicity in SCLC and cisplatin subgroups in dominant model (adjusted OR = 7.82, 95%CI = 1.36–45.07, p = 0.02; adjusted OR = 1.94, 95%CI = 1.07–3.53, p = 0.03, respectively). Thus, lncRNA CASC8 rs10505477 could serve as a possible risk marker for diagnosing lung cancer, and could be used to forecast the response and toxicity of platinum-based treatment in lung cancer patients.

The Impact of External Factors on the Epigenome: In Utero and over Lifetime

Epigenetic marks change during fetal development, adult life, and aging. Some changes play an important role in the establishment and regulation of gene programs, but others seem to occur without any apparent physiological role. An important future challenge in the field of epigenetics will be to describe how the environment affects both of these types of epigenetic change and to learn if interaction between them can determine healthy and disease phenotypes during lifetime. Here we discuss how chemical and physical environmental stressors, diet, life habits, and pharmacological treatments can affect the epigenome during lifetime and the possible impact of these epigenetic changes on pathophysiological processes.

RNA Directed Modulation of Phenotypic Plasticity in Human Cells

Natural selective processes have been known to drive phenotypic plasticity, which is the emergence of different phenotypes from one genome following environmental stimulation. Long non-coding RNAs (lncRNAs) have been observed to modulate transcriptional and epigenetic states of genes in human cells. We surmised that lncRNAs are governors of phenotypic plasticity and drive natural selective processes through epigenetic modulation of gene expression. Using heat shocked human cells as a model we find several differentially expressed transcripts with the top candidates being lncRNAs derived from retro-elements. One particular retro-element derived transcripts, Retro-EIF2S2, was found to be abundantly over-expressed in heat shocked cells. Over-expression of Retro-EIF2S2 significantly enhanced cell viability and modulated a predisposition for an adherent cellular phenotype upon heat shock. Mechanistically, we find that this retro-element derived transcript interacts directly with a network of proteins including 40S ribosomal protein S30 (FAU), Eukaryotic translation initiation factor 5A (EIF5A), and Ubiquitin-60S ribosomal protein L40 (UBA52) to affect protein modulated cell adhesion pathways. We find one motif in Retro-EIF2S2 that exhibits binding to FAU and modulates phenotypic cell transitions from adherent to suspension states. The observations presented here suggest that retroviral derived transcripts actively modulate phenotypic plasticity in human cells in response to environmental selective pressures and suggest that natural selection may play out through the action of retro-elements in human cells.

Investigation of long noncoding RNAs expression profile as potential serum biomarkers in patients with hepatocellular carcinoma

There is an increasing interest in using long noncoding RNAs (lncRNAs) as biomarkers in cancer. Predictive biomarkers in hepatocellular carcinoma (HCC) have great benefit in the choice of therapeutic modality for HCC. The aim of this study is to assess lncRNA-urothelial carcinoma associated-1 (lncRNA-UCA1) and WD repeat containing, antisense to TP53 (WRAP53) expression as novel noninvasive biomarkers for diagnosis of HCC in sera of HCC patients compared with chronic hepatitis C virus (HCV) patients and healthy volunteers and to analyze their relationship with respect to the clinicopathologic features. We retrieved HCC characteristic lncRNAs, lncRNA-UCA1 and lncRNA-WRAP53, based on the microarray signature profiling (released by LncRNADisease database). Quantitative reverse-transcriptase polymerase chain reaction assay (RT-qPCR) was then used to evaluate the expression of selected lncRNAs in the serum of 160 participants. Furthermore, in 20 of 82 HCC cases involved in the study, we examined the expression of lncRNA-UCA1 and lncRNA-WRAP53 in 20 HCC tissues and adjacent nontumor tissues and analyzed its correlation with the serum level of these lncRNAs. The prognostic significance of the investigated parameters in HCC patients was explored. We found that lncRNA-UCA1 and lncRNA-WRAP53 were significantly higher in sera of HCC than those with chronic HCV infection or healthy volunteers. Our data suggested that the increased expression of UCA1 and WRAP53 was associated with advanced clinical parameters in HCC. Of note, tissue levels of the chosen lncRNAs strongly correlate with their sera level. The combination of both lncRNAs with serum alpha fetoprotein resulted in improved sensitivity to 100%. The median follow-up period was 21.5 months. LncRNA-WRAP53 was significant independent prognostic markers in relapse-free survival. LncRNA-UCA1 and lncRNA-WRAP53 upregulation may serve as novel serum biomarkers for HCC diagnosis and prognosis.

PARTICLE, a Triplex-Forming Long ncRNA, Regulates Locus-Specific Methylation in Response to Low-Dose Irradiation

Exposure to low-dose irradiation causes transiently elevated expression of the long ncRNA PARTICLE (gene PARTICLE, promoter of MAT2A-antisense radiation-induced circulating lncRNA). PARTICLE affords both a cytosolic scaffold for the tumor suppressor methionine adenosyltransferase (MAT2A) and a nuclear genetic platform for transcriptional repression. In situ hybridization discloses that PARTICLE and MAT2A associate together following irradiation. Bromouridine tracing and presence in exosomes indicate intercellular transport, and this is supported by ex vivo data from radiotherapy-treated patients. Surface plasmon resonance indicates that PARTICLE forms a DNA-lncRNA triplex upstream of a MAT2A promoter CpG island. We show that PARTICLE represses MAT2A via methylation and demonstrate that the radiation-induced PARTICLE interacts with the transcription-repressive complex proteins G9a and SUZ12 (subunit of PRC2). The interplay of PARTICLE with MAT2A implicates this lncRNA in intercellular communication and as a recruitment platform for gene-silencing machineries through triplex formation in response to irradiation.

A novel antisense long noncoding RNA regulates the expression of MDC1 in bladder cancer

Antisense long noncoding RNAs (lncRNAs) play important roles in regulating the expression of coding genes in post-transcriptional level. However, detailed expression profile of lncRNAs and functions of antisense lncRNAs in bladder cancer remains unclear. To investigate regulation of lncRNAs in bladder cancer and demonstrate their functions, we performed lncRNAs microarray analysis in 3 paired bladder cancer tissues. Further molecular assays were conducted to determine the potential role of identified antisense lncRNA MDC1-AS. As a result, a series of lncRNAs were differentially expressed in bladder cancer tissues in microarray screen. In a larger size of samples validation, we found that the expression levels of MDC1-AS and MDC1 was down-regulated in bladder cancer. After over-expression of MDC1-AS, increased levels of MDC1 were observed in bladder cancer cells. We also found a remarkably inhibitory role of antisense lncRNA MDC1-AS on malignant cell behaviors in bladder cancer cells EJ and T24. Subsequently, knockdown of MDC1 revealed that suppressing role of MDC1-AS was attributed to up-regulation of MDC1. In summary, we have identified a novel antisense lncRNA MDC1-AS, which may participate in bladder cancer through up-regulation of its antisense tumor-suppressing gene MDC1. Further studies should be conducted to demonstrate detailed mechanism of our findings.

Regulatory RNAs and control of epigenetic mechanisms: expectations for cognition and cognitive dysfunction

The diverse functions of noncoding RNAs (ncRNAs) can influence virtually every aspect of the transcriptional process including epigenetic regulation of genes. In the CNS, regulatory RNA networks and epigenetic mechanisms have broad relevance to gene transcription changes involved in long-term memory formation and cognition. Thus, it is becoming increasingly clear that multiple classes of ncRNAs impact neuronal development, neuroplasticity, and cognition. Currently, a large gap exists in our knowledge of how ncRNAs facilitate epigenetic processes, and how this phenomenon affects cognitive function. In this review, we discuss recent findings highlighting a provocative role for ncRNAs including lncRNAs and piRNAs in the control of epigenetic mechanisms involved in cognitive function. Furthermore, we discuss the putative roles for these ncRNAs in cognitive disorders such as schizophrenia and Alzheimer's disease.

RNA-directed epigenetic silencing of Periostin inhibits cell motility

The over-expression of Periostin, a member of the fasciclin family of proteins, has been reported in a number of cancers and, in particular, in metastatic tumours. These include breast, ovarian, lung, colon, head and neck, pancreatic, prostate, neuroblastoma and thyroid cancers. It is thought that Periostin plays a major role in the development of metastases owing to its apparent involvement in restructuring of the extracellular matrix to create a microenvironment favouring invasion and metastases, angiogenesis, independent proliferation, avoidance of apoptosis and the ability for cells to re-enter the cell cycle. As such we reasoned that targeted suppression of Periostin at the promoter and epigenetic level could result in the stable inhibition of cell motility. We find here that promoter-directed small antisense non-coding RNAs can induce transcriptional gene silencing of Periostin that results ultimately in a loss of cellular motility. The observations presented here suggest that cell motility and possibly metastasis can be controlled by transcriptional and epigenetic regulation of Periostin, offering a potentially new and novel manner to control the spread of cancerous cells.

Prognostic significance of long non-coding RNA PCAT-1 expression in human hepatocellular carcinoma

BACKGROUND

Long non-coding RNAs (lncRNAs) play widespread roles in gene regulation and cellular processes. However, the functional roles of lncRNAs in hepatocellular carcinoma (HCC) are not yet well elucidated. The aim of the present study was to measure the levels of lncRNA PCAT-1 expression in HCC and evaluate its clinical significance in the development and progression of HCC.

METHODS

We examined the expression of PCAT-1 in 117 HCC tissues and adjacent non-tumor tissues using quantitative real-time-PCR and analyzed its correlation with the clinical parameters.

RESULTS

Our data showed that PCAT-1 expression in HCC tissues was significantly increased compared with adjacent non-tumor tissues (P<0.05). Up-regulated expression of PCAT-1 was significantly associated with TNM stage and metastasis (P<0.05), but not other clinical parameters. Moreover, Kaplan-Meier survival analysis showed that a high expression level of PCAT-1 resulted in a significantly poor overall survival of HCC patients. The multivariate Cox regression analysis demonstrated that PCAT-1 expression level was an independent prognostic factor for the overall survival rate of HCC patients.

CONCLUSIONS

Our data suggested that the increased expression of PCAT-1 was associated with advanced clinical parameters and poor overall survival of HCC patients, indicating that PCAT-1 up-regulation may serve as a novel biomarker of poor prognosis in HCC patients.

Long noncoding RNAs POLR2E rs3787016 C/T and HULC rs7763881 A/C polymorphisms are associated with decreased risk of esophageal cancer

Worldwide, rates of esophageal cancer have been keeping highly in recent decades. Genetic variants in multiple cellular pathways might play an important role in altering risk of esophageal carcinoma. In this study, long noncoding RNAs (lncRNAs) functional single nucleotide polymorphisms (SNPs) were investigated in Chinese Han populations. We have genotyped the ANRIL rs2151280 T/C, POLR2E rs3787016 C/T, and HULC rs7763881 A/C SNPs in 380 esophageal squamous cell carcinoma (ESCC) cases and 380 cancer-free controls. POLR2E rs3787016 C/T was associated with a significantly decreased risk for ESCC (CT vs. CC: OR 0.62, 95 % CI 0.44-0.87, P = 0.005; adjusted OR 0.62, 95 % CI 0.44-0.87, P = 0.005). The other SNP, HULC rs7763881, also showed a suggestive association (AC vs. AA: OR 0.70, 95 % CI 0.50-0.98, P = 0.037; adjusted OR 0.69, 95 % CI 0.49-0.97, P = 0.031). ANRIL rs2151280 T/C SNP was not associated with risk of ESCC. In the future, larger studies with other ethnic populations, tissue-specific biological characterization, and detailed individual information should be undertaken to validate current findings.

The theory of RNA-mediated gene evolution

Observations over the last decade suggest that some RNA transcripts, such as non-coding RNAs, function in regulating the transcriptional and epigenetic state of gene expression. DNA methylation appears to be operative in non-coding RNA regulation of gene expression. Interestingly, methylated cytosines undergo deamination to remove the methylation, which if not properly repaired results in the methylated cytosine being recognized by the cell as a thymine. This observation suggests that the process of non-coding RNA-directed epigenetic targeting also has the potential to alter the genomic landscape of the cell by changing cytosines to thymines and ultimately influence the evolution of the cell. This proposed theory of "RNA-mediated gene evolution" might be one possible mechanism of action whereby RNA participates in the natural selective process to drive cellular and possibly organismal evolution.

Potential roles of noncoding RNAs in environmental epigenetic transgenerational inheritance

"Epigenetic transgenerational inheritance" (ETI) has been defined as germline (sperm or egg) transmission of epigenetic information between generations in the absence of direct exposures or genetic manipulations. Among reported cases of ETI in mammals, the majority are induced by environmental factors, including environmental toxicants [e.g. agricultural fungicide vinclozolin, plastic additive bisphenol A, pesticide methoxychlor, dioxin, di-(2-ethylhexyl) phthalate, dichlorodiphenyltrichloroethane, and hydrocarbons] and poor nutritional conditions. Although the ETI phenomenon is well established, the underlying mechanism remains elusive. Putative epimutations, including changes in DNA methylation and histone modification patterns, have been reported, but it remains unclear how these epimutations are formed in the first place, and how they are memorized in the germline and then get transmitted to subsequent generations. Based on recent advances in our understanding of regulatory noncoding RNAs (ncRNAs), I propose that ncRNAs are involved in ETI, during both the initial epimutation formation and the subsequent germline transmission of epimutations. ncRNAs can function at epigenetic levels by affecting DNA methylation and histone modifications, thereby changing gene transcriptional activities, which can lead to an altered mRNA transcriptome associated with a disease phenotype. Alternatively, novel or altered ncRNA expression can cause dysregulated post-transcriptional regulation, thus directly affecting the mRNA transcriptome and inducing a disease phenotype. Sperm-borne ncRNAs are potential mediators for epigenetic memory across generations, but they alone may not be sufficient for stable transmission of epimutations across generations. Overall, research on ncRNAs in the context of ETI is urgently needed to shed light on the underlying mechanism of ETI.

Combination of hepatocyte specific delivery and transformation dependent expression of shRNA inducing transcriptional gene silencing of c-Myc promoter in hepatocellular carcinoma cells

Background

A specific targeting modality for hepatocellular carcinoma (HCC) could ideally encompass a liver cell specific delivery system of a transcriptional unit that is active only in neoplastic cells. Sendai virosomes, derived from Sendai viral envelopes, home to hepatocytes based on the liver specific expression of asialoglycoprotein receptors (ASGPRs) which are recognized by the Sendai virosomal fusion (F) proteins. As reported earlier by us and other groups, transcriptional gene silencing (TGS) does not require continuous presence of the effector siRNA/shRNA molecule and is heritable, involving epigenetic modifications, leading to long term transcriptional repression. This could be advantageous over conventional gene therapy approaches, since continuous c-Myc inactivation is required to suppress hepatocarcinoma cells.

Methods

Exploiting such virosomal delivery, the alpha-fetoprotein (AFP) promoter, in combination with various tumour specific enhancers, was used to drive the expression of shRNA directed against ME1a1 binding site of the proto-oncogene c-Myc P2 promoter, in order to induce TGS in neoplastic liver cells.

Results

The dual specificity achieved by the Sendai virosomal delivery system and the promoter/enhancer guided expression ensured that the shRNA inducing TGS was active only in liver cells that had undergone malignant transformation. Our results indicate that such a bimodal therapeutic system induced specific activation of apoptosis in hepatocarcinoma cells due to heterochromatization and increased DNA methylation of the CpG islands around the target loci.

Conclusions

The Sendai virosomal delivery system, combined with AFP promoter/enhancer expression machinery, could serve as a generalized mechanism for the expression of genes deleterious to transformed hepatocarcinoma cells. In this system, the epigenetic suppression of c-Myc could have an added advantage for inducing cell death in the targeted cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-582) contains supplementary material, which is available to authorized users.

Natural antisense transcripts

Recent years have seen the increasing understanding of the crucial role of RNA in the functioning of the eukaryotic genome. These discoveries, fueled by the achievements of the FANTOM, and later GENCODE and ENCODE consortia, led to the recognition of the important regulatory roles of natural antisense transcripts (NATs) arising from what was previously thought to be 'junk DNA'. Roughly defined as non-coding regulatory RNA transcribed from the opposite strand of a coding gene locus, NATs are proving to be a heterogeneous group with high potential for therapeutic application. Here, we attempt to summarize the rapidly growing knowledge about this important non-coding RNA subclass.

Evolutionary conservation of long non-coding RNAs; sequence, structure, function

BACKGROUND

Recent advances in genomewide studies have revealed the abundance of long non-coding RNAs (lncRNAs) in mammalian transcriptomes. The ENCODE Consortium has elucidated the prevalence of human lncRNA genes, which are as numerous as protein-coding genes. Surprisingly, many lncRNAs do not show the same pattern of high interspecies conservation as protein-coding genes. The absence of functional studies and the frequent lack of sequence conservation therefore make functional interpretation of these newly discovered transcripts challenging. Many investigators have suggested the presence and importance of secondary structural elements within lncRNAs, but mammalian lncRNA secondary structure remains poorly understood. It is intriguing to speculate that in this group of genes, RNA secondary structures might be preserved throughout evolution and that this might explain the lack of sequence conservation among many lncRNAs.

SCOPE OF REVIEW

Here, we review the extent of interspecies conservation among different lncRNAs, with a focus on a subset of lncRNAs that have been functionally investigated. The function of lncRNAs is widespread and we investigate whether different forms of functionalities may be conserved.

MAJOR CONCLUSIONS

Lack of conservation does not imbue a lack of function. We highlight several examples of lncRNAs where RNA structure appears to be the main functional unit and evolutionary constraint. We survey existing genomewide studies of mammalian lncRNA conservation and summarize their limitations. We further review specific human lncRNAs which lack evolutionary conservation beyond primates but have proven to be both functional and therapeutically relevant.

GENERAL SIGNIFICANCE

Pioneering studies highlight a role in lncRNAs for secondary structures, and possibly the presence of functional "modules", which are interspersed with longer and less conserved stretches of nucleotide sequences. Taken together, high-throughput analysis of conservation and functional composition of the still-mysterious lncRNA genes is only now becoming feasible.

An HIV-encoded antisense long noncoding RNA epigenetically regulates viral transcription

The abundance of long noncoding RNAs (lncRNAs) and their wide range of functional roles in human cells are fast becoming realized. Importantly, lncRNAs have been identified as epigenetic modulators and consequently play a pivotal role in the regulation of gene expression. A human immunodeficiency virus-encoded antisense RNA transcript has recently been reported and we sought to characterize this RNA and determine its potential role in viral transcription regulation. The intrinsic properties of this human immunodeficiency virus-expressed lncRNA were characterized and the data presented here suggest that it functions as an epigenetic brake to modulate viral transcription. Suppression of this long antisense transcript with small single-stranded antisense RNAs resulted in the activation of viral gene expression. This lncRNA was found to localize to the 5' long-term repeats (LTR) and to usurp components of endogenous cellular pathways that are involved in lncRNA directed epigenetic gene silencing. Collectively, we find that this viral expressed antisense lncRNA is involved in modulating human immunodeficiency virus gene expression and that this regulatory effect is due to an alteration in the epigenetic landscape at the viral promoter.