lncRNA TMPO antisense RNA 1 promotes the malignancy of cholangiocarcinoma cells by regulating let-7g-5p/ high-mobility group A1 axis.

Cholangiocarcinoma (CHOL) is often diagnosed at an advanced stage; therefore, exploring its key regulatory factors is important for earlier diagnosis and treatment. This study aimed to identify the mechanisms of long non-coding RNA (lncRNA) TMPO Antisense RNA 1 (TMPO-AS1), microRNA let-7 g-5p, and high-mobility group A1 (HMGA1) proteins in CHOL. Our results, through quantitative real-time PCR and Western blot detection, showed that TMPO-AS1 and HMGA1 were overexpressed while let-7 g-5p was underexpressed in CHOL. Cell function experiments in CHOL cells revealed that TMPO-AS1 knockdown inhibited cell proliferation, colony formation, and cell migration, but induced apoptosis. TMPO-AS1 knockdown also suppressed tumor growth in vivo. Together with luciferase assay and Western blotting, we found that TMPO-AS1 could sponge let-7 g-5p to promote HMGA1 expression. Moreover, HMGA1 overexpression attenuated the effect of TMPO-AS1 downregulation in CHOL cells. Overall, our findings identified the oncogenic effect of TMPO-AS1 on CHOL cells, which may put forward a novel methodology for CHOL diagnosis and therapy.

N6-methyladenosine-induced SVIL antisense RNA 1 restrains lung adenocarcinoma cell proliferation by destabilizing E2F1.

Accumulating evidence indicates that N6-methyladenosine (m6A) and long noncoding RNAs (lncRNAs) play crucial roles in cancer development. However, the biological roles of m6A and lncRNAs in lung cancer tumorigenesis are largely unknown. In this study, SVIL antisense RNA 1 (SVIL-AS1) was downregulated in lung adenocarcinoma (LUAD) tissues and was associated with a favorable prognosis in patients with LUAD. SVIL-AS1 overexpression suppressed LUAD cell proliferation and blocked cell cycle arrest. Mechanistically, METTL3 increased the m6A modification and transcript stability of SVIL-AS1. The enhanced SVIL-AS1 expression mediated by METTL3 suppressed E2F1 and E2F1-target genes. Moreover, SVIL-AS1 accelerated E2F1 degradation. The reduction in cell proliferation induced by SVIL-AS1 overexpression could be rescued by E2F1 overexpression or METTL3 knockdown. In conclusion, our work demonstrated the role and mechanism of METTL3-induced SVIL-AS1 in LUAD, which connects m6A and lncRNA in lung cancer carcinogenesis.

A review on the role of GAS6 and GAS6-AS1 in the carcinogenesis.

Growth arrest specific 6 (GAS6) encodes a protein that serves as a ligand for AXL receptor tyrosine kinase and stimulates cell proliferation. Notably, an antisense RNA, namely GAS6-AS1 is transcribed from chromosome 13q34, near GAS6 gene. In vitro functional experiments have demonstrated that GAS6-AS1 can promote proliferation, migration and invasive properties of transformed cells through enhancing entry into S-phase. Notably, mechanistic investigations have shown that GAS6-AS1 can regulate expression of GAS6 at the transcriptional or translational stages through constructing a RNA-RNA duplex, thus enhancing expression of AXL and inducing AXL signaling. Both GAS6 and its antisense transcript contribute in the pathogenesis of human malignancies. In the current review, we provide a summary of studies that appraised the role of these genes in the carcinogenesis.

BVES-AS1 inhibits the malignant behaviors of colon adenocarcinoma cells via regulating BVES.

The underexpression of the long noncoding RNA blood vessel epicardial substance antisense RNA 1 (BVES-AS1) has been shown in colon adenocarcinoma (COAD) patients. However, its role in COAD remains to be explored. This study aimed to investigate the function and potential mechanism of BVES-AS1 in COAD. Colony formation, Cell Counting Kit-8, JC-1 mitochondrial membrane potential assay, wound healing, transwell, and western blot analyses were used to measure cell proliferation, apoptosis, migration, invasion, and epithelial-mesenchymal transition (EMT) in COAD cells. RNA pull-down, luciferase reporter, and RNA binding protein immunoprecipitation assays were used to detect the interaction of BVES-AS1 and downstream genes. BVES-AS1 was expressed at low levels in COAD cells. Overexpressed BVES-AS1 inhibited COAD cell proliferation, migration, invasion, and EMT while elevating cell apoptosis. Mechanistically, BVES-AS1 functioned as a competing endogenous RNA sponging miR-522-3p to regulate the expression of nearby gene blood vessel epicardial substance (BVES). Besides this, BVES-AS1 recruited TATA-box binding protein associated factor 15 (TAF15) to promote BVES messenger RNA stability. Taken together, our study confirmed that BVES-AS1 inhibited COAD progression via interacting with miR-522-3p and TAF15 to regulate BVES expression, which might offer a perspective for COAD treatment.

Potato CYCLING DOF FACTOR 1 and its lncRNA counterpart StFLORE link tuber development and drought response.

Plants regulate their reproductive cycles under the influence of environmental cues, such as day length, temperature and water availability. In Solanum tuberosum (potato), vegetative reproduction via tuberization is known to be regulated by photoperiod, in a very similar way to flowering. The central clock output transcription factor CYCLING DOF FACTOR 1 (StCDF1) was shown to regulate tuberization. We now show that StCDF1, together with a long non-coding RNA (lncRNA) counterpart, named StFLORE, also regulates water loss through affecting stomatal growth and diurnal opening. Both natural and CRISPR-Cas9 mutations in the StFLORE transcript produce plants with increased sensitivity to water-limiting conditions. Conversely, elevated expression of StFLORE, both by the overexpression of StFLORE or by the downregulation of StCDF1, results in an increased tolerance to drought through reducing water loss. Although StFLORE appears to act as a natural antisense transcript, it is in turn regulated by the StCDF1 transcription factor. We further show that StCDF1 is a non-redundant regulator of tuberization that affects the expression of two other members of the potato StCDF gene family, as well as StCO genes, through binding to a canonical sequence motif. Taken together, we demonstrate that the StCDF1-StFLORE locus is important for vegetative reproduction and water homeostasis, both of which are important traits for potato plant breeding.

Long Noncoding RNA EZR-AS1 Regulates the Proliferation, Migration, and Apoptosis of Human Venous Endothelial Cells via SMYD3.

Numerous studies have shown that long noncoding RNAs (lncRNAs) play essential roles in the development and progression of human cardiovascular diseases. However, whether lncRNA ezrin antisense RNA 1 (EZR-AS1) is associated with the progression of coronary heart disease (CHD) remains unclear. Accordingly, the aim of the present study was to evaluate the role of lncRNA EZR-AS1 in patients with CHD and in human venous endothelial cells (HUVECs). The findings revealed that lncRNA EZR-AS1 was highly expressed in the peripheral blood of patients with CHD. In vitro experiments showed that the overexpression of EZR-AS1 could enhance proliferation, migration, and apoptosis by upregulating the expression of EZR in HUVECs; downregulation of lncRNA EZR-AS1 resulted in the opposite effect. lncRNA EZR-AS1 was also found to regulate SET and MYND domain-containing protein 3 (SMYD3), a histone H3 lysine 4-specific methyltransferase, which subsequently mediated EZR transcription. Collectively, these results demonstrate that lncRNA EZR-AS1 plays an important role in HUVECs function via SMYD3 signaling.

[Non-coding Natural Antisense RNA: Mechanisms of Action in the Regulation of Target Gene Expression and Its Clinical Implications].

Recent advances in high-throughput technologies have revealed that 75% of the human genome is transcribed to RNA, whereas only 3% of transcripts are translated into proteins. Consequently, many long non-coding RNAs (lncRNAs) have been identified, which has improved our understanding of the complexity of biological processes. LncRNAs comprise multiple classes of RNA transcripts that regulate the transcription, stability and translation of protein-coding genes in a genome. Natural antisense transcripts (NATs) form one such class, and the GENCODE v30 catalog contains 16193 lncRNA loci, of which 5611 are antisense loci. This review outlines our emerging understanding of lncRNAs, with a particular focus on how lncRNAs regulate gene expression using interferon-α1 (IFN-α1) mRNA and its antisense partner IFN-α1 antisense (as)RNA as an example. We have identified and characterized the asRNA that determines post-transcriptional IFN-α1 mRNA levels. IFN-α1 asRNA stabilizes IFN-α1 mRNA by cytoplasmic sense-antisense duplex formation, which may enhance the accessibility of an RNA stabilizer protein or decrease the affinity of an RNA decay factor for the RNA. IFN-α1 asRNA can also act as competing molecules in the competing endogenous (ce)RNA network with other members of the IFNA multigene family mRNAs/asRNAs, and other cellular mRNA transcripts. Furthermore, antisense oligoribonucleotides representing functional domains of IFN-α1 asRNA inhibit influenza virus proliferation in the respiratory tract of virus-infected animals. Thus, these findings support, at least in part, the rationale that dissecting the activity of NAT on gene expression regulation promises to reveal previously unanticipated biology, with potential to provide new therapeutic approaches to diseases.

OTUD6B-AS1 Inhibits Viability, Migration, and Invasion of Thyroid Carcinoma by Targeting miR-183-5p and miR-21.

Background: The long noncoding RNA (lncRNA) functions as a regulator of initiation, progression, and metastasis of thyroid carcinomas. lncRNA OTUD6B antisense RNA 1 (OTUD6B-AS1) is a tumor-suppressive noncoding RNA in clear cell renal cell carcinoma. The role of OTUD6B-AS1 in thyroid carcinomas has not been reported yet. We aim to investigate the expression and biological functions of OTUD6B-AS1 in thyroid carcinomas. Methods: The expression level of OTUD6B-AS1 was measured in 60 paired human thyroid carcinoma tissues and corresponding adjacent normal thyroid tissues. The correlations between the OTUD6B-AS1 expression levels and clinicopathological features were evaluated using the Mann-Whitney test. The effects of OTUD6B-AS1 on thyroid carcinoma cells were determined via the MTT and transwell assays. The potential targets of OTUD6B-AS1 were screened using the online programs OncomiR and StarBase 3.0, and the LncBase Predicted v.2. Luciferase reporter assay was used to confirm the interactions between OTUD6B-AS1 and its potential targets. Results: OTUD6B-AS1 was downregulated in thyroid carcinoma tissue samples. The expression of OTUD6B-AS1 correlated with tumor size, clinical stage, and lymphatic metastasis of thyroid carcinoma. Overexpression of OTUD6B-AS1 significantly decreased the viability, migration, and invasion of thyroid carcinoma cells. Online programs predicted miR-183-5p and miR-21 as potential targets of OTUD6B-AS1. Luciferase reporter assays showed miR-183-5p and miR-21 bound to OTUD6B-AS1. Moreover, overexpression of miR-183-5p and miR-21 compromised the inhibitory effects of OTUD6B-AS1 on viability, migration, and invasion of thyroid carcinoma cells. Conclusions: Taken together, our findings present in vitro evidence of lncRNA OTUD6B-AS1 as a tumor suppressor in thyroid carcinomas. OTUD6B-AS1 inhibits viability, migration, and invasion of thyroid carcinoma by targeting miR-183-5p and miR-21.

Long non-coding RNA TP73-AS1 in cancers.

More and more evidence indicates that long non-coding RNAs (lncRNAs), as a kind of non-coding endogenous single-stranded RNA, play an essential role as oncogenes or tumour suppressors in the occurrence and development of human cancers. The tumour protein P73 antisense RNA 1 (TP73-AS1) was initially found to be down-regulated in oligodendroglioma and may act as a non-protein-encoding RNA. Since its discovery, TP73-AS1 has been identified as a carcinogenic regulator of many malignancies. At the same time, the high expression of TP73-AS1 is related to the clinicopathological features of patients with cancer. It also regulates cell proliferation, anti-apoptosis, invasion and metastasis through a variety of potential mechanisms, suggesting that it may be a promising biomarker and therapeutic target for cancer. In this review, we summarize the biological functions, mechanisms, and potential clinical implications of TP73-AS1 dysregulation in tumourigenesis and progression.

The world of asRNAs in Gram-negative and Gram-positive bacteria.

Bacteria exhibit an amazing diversity of mechanisms controlling gene expression to both maintain essential functions and modulate accessory functions in response to environmental cues. Over the years, it has become clear that bacterial regulation of gene expression is still far from fully understood. This review focuses on antisense RNAs (asRNAs), a class of RNA regulators defined by their location in cis and their perfect complementarity with their targets, as opposed to small RNAs (sRNAs) which act in trans with only short regions of complementarity. For a long time, only few functional asRNAs in bacteria were known and were almost exclusively found on mobile genetic elements (MGEs), thus, their importance among the other regulators was underestimated. However, the extensive application of transcriptomic approaches has revealed the ubiquity of asRNAs in bacteria. This review aims to present the landscape of studied asRNAs in bacteria by comparing 67 characterized asRNAs from both Gram-positive and Gram-negative bacteria. First we describe the inherent ambiguity in the existence of asRNAs in bacteria, second, we highlight their diversity and their involvement in all aspects of bacterial life. Finally we compare their location and potential mode of action toward their target between Gram-negative and Gram-positive bacteria and present tendencies and exceptions that could lead to a better understanding of asRNA functions.

Long Noncoding RNA GATA3-AS1 Promotes Cell Proliferation and Metastasis in Hepatocellular Carcinoma by Suppression of PTEN, CDKN1A, and TP53.

Background: Long noncoding RNAs (lncRNAs) have been known to play important roles in the progression of various types of human cancer. LncRNA GATA3 antisense RNA 1, GATA3-AS1, has been reported to be associated with T-cell development and differentiation. However, the expression pattern and function of GATA3-AS1 in hepatocellular carcinoma (HCC) remain unknown. Methods: Real-time quantitative PCR (RT-qPCR) assay was conducted to detect GATA3-AS1 expression levels in 80 cases of pairs HCC tissues and matched normal tissues. Chi-squared (χ 2) test was used to analyze the correlation between GATA3-AS1 expression and clinicopathologic variables. Survival curves were plotted using the Kaplan-Meier method and were compared via the log-rank test. The cell counting kit-8 (CCK-8) and wound scratch assays were applied to detect the effect of GATA3-AS1 knockdown and overexpression on cell growth and migration of HCC. RT-qPCR was performed for the detection of the phosphatase and tensin homolog (PTEN), cyclin-dependent kinase inhibitor 1A (CDKN1A), and tumor protein p53 (TP53) expression in HCC cells after GATA3-AS1 knockdown and overexpression. Results: GATA3-AS1 was significantly upregulated in HCC tissues compared with matched normal tissues. The high expression of GATA3-AS1 was significantly correlated with larger tumor size, advanced TNM stage, and more lymph node metastasis. High GATA3-AS1 expression was markedly correlated with shorter overall survival times of HCC patients. Furthermore, knockdown of GATA3-AS1 obviously inhibited Hep3B and HCCLM3 cell growth and migration, whereas overexpression of GATA3-AS1 had the opposite effects. In addition, GATA3-AS1 knockdown resulted in upregulated expression levels of tumor-suppressive genes, PTEN, CDKN1A, and TP53, in Hep3B and HCCLM3 cells, while restoration of GATA3-AS1 decreased PTEN, CDKN1A, and TP53 expression levels. Conclusion: Our data suggested that GATA3-AS1 promotes cell proliferation and metastasis of HCC by suppression of PTEN, CDKN1A, and TP53.

The MRVI1-AS1/ATF3 signaling loop sensitizes nasopharyngeal cancer cells to paclitaxel by regulating the Hippo-TAZ pathway.

Long non-coding RNA (lncRNA) plays an important role in malignant tumor occurrence, development, and chemoresistance, but the mechanism of how they affect nasopharyngeal cancer (NPC) paclitaxel chemosensitivity is unclear. In this study, lncRNA array of CNE-1 and HNE-2 paclitaxel-resistant cells and their parental strains revealed that the paclitaxel-resistant strains had significantly lower MRVI1-AS1 (murine retrovirus integration site 1 homolog antisense RNA 1) expression than the parental strains, and that MRVI1-AS1 overexpression in vitro and in vivo increased paclitaxel chemosensitivity. Further, MRVI1-AS1 upregulated ATF3 (activating transcription factor 3) by simultaneously inhibiting miR-513a-5p (microRNA-513a-5p) and miR-27b-3p expression levels to increase NPC paclitaxel chemosensitivity. Chromatin immunoprecipitation and quantitative real-time PCR showed that ATF3 could feed-back MRVI1-AS1 regulation positively. Furthermore, MRVI1-AS1 and ATF3 could form a positive feedback loop, which promoted the expression of RASSF1 (Ras association domain family member 1), a Hippo-TAZ (tafazzin) signaling pathway regulatory factor, thereby inhibiting TAZ expression. The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide) assay and flow cytometry showed that the decreased TAZ increased NPC cell paclitaxel chemosensitivity. Overall, the results indicate that the MRVI1-AS1/ATF3 signaling pathway can increase NPC paclitaxel chemosensitivity by modulating the Hippo-TAZ signaling pathway. Therefore, targeting the loop may be a new NPC treatment strategy.

Physiological roles of antisense RNAs in prokaryotes.

Prokaryotes encounter constant and often brutal modifications to their environment. In order to survive, they need to maintain fitness, which includes adapting their protein expression patterns. Many factors control gene expression but this review focuses on just one, namely antisense RNAs (asRNAs), a class of non-coding RNAs (ncRNAs) characterized by their location in cis and their perfect complementarity with their targets. asRNAs were considered for a long time to be trivial and only to be found on mobile genetic elements. However, recent advances in methodology have revealed that their abundance and potential activities have been underestimated. This review aims to illustrate the role of asRNA in various physiologically crucial functions in both archaea and bacteria, which can be regrouped in three categories: cell maintenance, horizontal gene transfer and virulence. A literature survey of asRNAs demonstrates the difficulties to characterize and assign a role to asRNAs. With the aim of facilitating this task, we describe recent technological advances that could be of interest to identify new asRNAs and to discover their function.

Long Non-Coding RNA ZEB1-Antisense 1 Affects Cell Migration and Invasion of Cervical Cancer by Regulating Epithelial-Mesenchymal Transition via the p38MAPK Signaling Pathway.

AIM: To investigate whether long non-coding RNA (lncRNA) ZEB1 antisense 1 (ZEB1-AS1) affects cell migration and invasion of cervical cancer by regulating epithelial-mesenchymal transition (EMT) via the p38MAPK pathway. METHODS: Human cervical cancer cell line Hela was classified into Control, NC siRNA, ZEB1-AS1 siRNA, SB203580 (p38MAPK pathway inhibitor) and ZEB1-AS1 siRNA + Anisomycin (p38MAPK pathway activator) groups. Quantitative real-time polymerase chain reaction was performed for ZEB1-AS1 expression, Western blotting to measure p38MAPK signaling pathway-/EMT-related proteins, and Wound-healing and Transwell assays to evaluate cell migration and invasion respectively. RESULTS: ZEB1-AS1 was upregulated in cancer tissues and related to major clinicopathological features of cervical cancer. Besides, patients with lower-ZEB1-AS1-expression had a higher 5-year survival rate than those patients with higher-ZEB1-AS1-expression. High ZEB1-AS1 expression and advanced Federation of Gynecology and Obstetrics stage were independent risk factors for patients' prognosis. Both ZEB1-AS1 siRNA and SB203580 effectively reduced p-p38 expression and the migration and invasion of Hela cells, with elevation of E-cadherin and reduction of Vimentin and N-cadherin. However, inhibitory effects of ZEB1-AS1 siRNA on EMT as well as cell migration and invasion of the Hela cell were reversed by Anisomycin. CONCLUSION: Inhibition of ZEB1-AS1 can block the p38MAPK signaling pathway, ultimately restricting the EMT and suppressing cell migration and invasion of cervical cancer cells.

RASSF1-AS1, an antisense lncRNA of RASSF1A, inhibits the translation of RASSF1A to exacerbate cardiac fibrosis in mice.

Cardiac fibrosis is associated with various cardiovascular diseases and can eventually lead to heart failure. Dysregulation of long non-coding RNAs (lncRNAs) are recognized as one of the key mechanisms of cardiac diseases. However, the roles and underlying mechanisms of lncRNAs in cardiac fibrosis have not been explicitly defined. Here, we investigated the role of an antisense (AS) lncRNA from the Ras association domain-containing protein 1 isoform A (RASSF1A) gene locus, named RASSF1-AS1, in the development of cardiac fibrosis. Cardiac fibrosis mouse model was established by isoproterenol injection. We found that RASSF1A protein was downregulated, whereas RASSF1-AS1 was markedly upregulated during cardiac fibrosis. Overexpression and knockdown of mouse primary cardiac fibroblasts showed that RASSF1-AS1 negatively regulated RASSF1A expression at the post-transcriptional level. According to the landscape analysis and sense-AS binding evaluation, RASSF1-AS1 partially overlaps with RASSF1A messenger RNA (mRNA) at the exon2 region. RNA pull-down and luciferase activity assays confirmed that RASSF1-AS1 directly bound to RASSF1A mRNA and suppressed its translation. Furthermore, wild-type RASSF1-AS1 had a promoting effect on nuclear factor-κB activation and cardiac fibrosis, but mutated RASSF1-AS1, in which the binding region was deleted, had no effect. In conclusion, RASSF1-AS1 inhibits the translation of RASSF1A to exacerbate cardiac fibrosis in mice, indicating a potential application of RASSF1-AS1 as a therapy target for cardiac fibrosis.

Antisense RNA: the new favorite in genetic research.

Antisense RNA molecule represents a unique type of DNA transcript that comprises 19-23 nucleotides and is complementary to mRNA. Antisense RNAs play the crucial role in regulating gene expression at multiple levels, such as at replication, transcription, and translation. In addition, artificial antisense RNAs can effectively regulate the expression of related genes in host cells. With the development of antisense RNA, investigating the functions of antisense RNAs has emerged as a hot research field. This review summarizes our current understanding of antisense RNAs, particularly of the formation of antisense RNAs and their mechanism of regulating the expression of their target genes. In addition, we detail the effects and applications of antisense RNAs in antivirus and anticancer treatments and in regulating the expression of related genes in plants and microorganisms. This review is intended to highlight the key role of antisense RNA in genetic research and guide new investigators to the study of antisense RNAs.

Activity of Streptococcus mutans VicR Is Modulated by Antisense RNA.

The VicRK 2-component system of Streptococcus mutans regulates genes associated with cell wall biogenesis and biofilm formation. A putative RNase III-encoding gene ( rnc) is located downstream from the vicRKX operon. The goals of this study were to investigate the potential role of VicR in the regulation of adjacent downstream genes and evaluate transcription levels of vicR during planktonic and biofilm growth. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to investigate whether vicRKX and adjacent downstream genes were cotranscribed. Binding of purified recombinant VicR protein to promoter regions of vicR, rnc, and syfA genes was confirmed by electrophoretic mobility shift assay and by chromatin immunoprecipitation analyses. VicR antisense (AS vicR) RNA was detected by Northern blotting and qRT-PCR assays. AS vicR overexpression mutants were constructed, and the biofilm biomass was determined by crystal violet microtiter assay. Adjacent downstream genes rnc, smc, syfA, smu.1511, and syfB were cotranscribed with vicRKX. The predicted promoter regions of vicR, rnc, and syfA genes were directly regulated by VicR. An AS vicR RNA transcript was detected upstream of the rnc gene. Expression of the AS vicR RNA transcript was elevated in planktonic cultures and repressed during biofilm growth. In addition, Western blot data showed that expression of the VicR protein decreased by 35% in planktonic as compared with biofilm cultures. Furthermore, we show that overexpression of AS vicR led to a reduction in biofilm formation. The downstream genes rnc, smc, syfA, smu.1511, and syfB are cotranscribed with vicRKX. VicR is autophosphorylated, and rnc and syfA are directly regulated by VicR. Expression of VicR protein correlated inversely with different levels of AS vicR RNA transcript and growth conditions. The biofilm biomass decreased in the AS vicR overexpression mutant. These data suggest a role for the AS vicR RNA transcript in posttranscriptional regulation of VicR protein production in S. mutans.

Type I Toxin-Antitoxin Systems: Regulating Toxin Expression via Shine-Dalgarno Sequence Sequestration and Small RNA Binding.

Toxin-antitoxin (TA) systems are small genetic loci composed of two adjacent genes: a toxin and an antitoxin that prevents toxin action. Despite their wide distribution in bacterial genomes, the reasons for TA systems being on chromosomes remain enigmatic. In this review, we focus on type I TA systems, composed of a small antisense RNA that plays the role of an antitoxin to control the expression of its toxin counterpart. It does so by direct base-pairing to the toxin-encoding mRNA, thereby inhibiting its translation and/or promoting its degradation. However, in many cases, antitoxin binding is not sufficient to avoid toxicity. Several cis-encoded mRNA elements are also required for repression, acting to uncouple transcription and translation via the sequestration of the ribosome binding site. Therefore, both antisense RNA binding and compact mRNA folding are necessary to tightly control toxin synthesis and allow the presence of these toxin-encoding systems on bacterial chromosomes.

Widespread Antisense Transcription in Prokaryotes.

Although bacterial genomes are usually densely protein-coding, genome-wide mapping approaches of transcriptional start sites revealed that a significant fraction of the identified promoters drive the transcription of noncoding RNAs. These can be trans-acting RNAs, mainly originating from intergenic regions and, in many studied examples, possessing regulatory functions. However, a significant fraction of these noncoding RNAs consist of natural antisense transcripts (asRNAs), which overlap other transcriptional units. Naturally occurring asRNAs were first observed to play a role in bacterial plasmid replication and in bacteriophage λ more than 30 years ago. Today's view is that asRNAs abound in all three domains of life. There are several examples of asRNAs in bacteria with clearly defined functions. Nevertheless, many asRNAs appear to result from pervasive initiation of transcription, and some data point toward global functions of such widespread transcriptional activity, explaining why the search for a specific regulatory role is sometimes futile. In this review, we give an overview about the occurrence of antisense transcription in bacteria, highlight particular examples of functionally characterized asRNAs, and discuss recent evidence pointing at global relevance in RNA processing and transcription-coupled DNA repair.

An antisense RNA capable of modulating the expression of the tumor suppressor microRNA-34a.

The microRNA-34a is a well-studied tumor suppressor microRNA (miRNA) and a direct downstream target of TP53 with roles in several pathways associated with oncogenesis, such as proliferation, cellular growth, and differentiation. Due to its broad tumor suppressive activity, it is not surprising that miR34a expression is altered in a wide variety of solid tumors and hematological malignancies. However, the mechanisms by which miR34a is regulated in these cancers is largely unknown. In this study, we find that a long noncoding RNA transcribed antisense to the miR34a host gene, is critical for miR34a expression and mediation of its cellular functions in multiple types of human cancer. We name this long noncoding RNA lncTAM34a, and characterize its ability to facilitate miR34a expression under different types of cellular stress in both TP53-deficient and wild-type settings.