Structural and functional conservation of cis-acting RNA elements in coronavirus 5'-terminal genome regions

Structure predictions suggest a partial conservation of RNA structure elements in coronavirus terminal genome regions. Here, we determined the structures of stem-loops (SL) 1 and 2 of two alphacoronaviruses, human coronavirus (HCoV) 229E and NL63, by RNA structure probing and studied the functional relevance of these putative cis-acting elements. HCoV-229E SL1 and SL2 mutants generated by reverse genetics were used to study the effects on viral replication of single-nucleotide substitutions predicted to destabilize the SL1 and SL2 structures. The data provide conclusive evidence for the critical role of SL1 and SL2 in HCoV-229E replication and, in some cases, revealed parallels with previously characterized betacoronavirus SL1 and SL2 elements. Also, we were able to rescue viable HCoV-229E mutants carrying replacements of SL2 with equivalent betacoronavirus structural elements. The data obtained in this study reveal a remarkable degree of structural and functional conservation of 5′-terminal RNA structural elements across coronavirus genus boundaries.

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Conservation of 5'-terminal SL1 and SL2 elements in alpha- and betacoronaviruses.

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HCoV-229E reverse genetics data suggest critical role for SL1/2 in viral replication.

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Replacement of SL2 in HCoV-229E with betacoronavirus equivalents is tolerated.

Identification of new driver and passenger mutations within APOBEC-induced hotspot mutations in bladder cancer

BACKGROUND

APOBEC-driven mutagenesis and functional positive selection of mutated genes may synergistically drive the higher frequency of some hotspot driver mutations compared to other mutations within the same gene, as we reported for FGFR3 S249C. Only a few APOBEC-associated driver hotspot mutations have been identified in bladder cancer (BCa). Here, we systematically looked for and characterised APOBEC-associated hotspots in BCa.

METHODS

We analysed 602 published exome-sequenced BCas, for part of which gene expression data were also available. APOBEC-associated hotspots were identified by motif-mapping, mutation signature fitting and APOBEC-mediated mutagenesis comparison. Joint analysis of DNA hairpin stability and gene expression was performed to predict driver or passenger hotspots. Aryl hydrocarbon receptor (AhR) activity was calculated based on its target genes expression. Effects of AhR knockout/inhibition on BCa cell viability were analysed.

RESULTS

We established a panel of 44 APOBEC-associated hotspot mutations in BCa, which accounted for about half of the hotspot mutations. Fourteen of them overlapped with the hotspots found in other cancer types with high APOBEC activity. They mostly occurred in the DNA lagging-strand templates and the loop of DNA hairpins. APOBEC-associated hotspots presented systematically a higher prevalence than the other mutations within each APOBEC-target gene, independently of their functional impact. A combined analysis of DNA loop stability and gene expression allowed to distinguish known passenger from known driver hotspot mutations in BCa, including loss-of-function mutations affecting tumour suppressor genes, and to predict new candidate drivers, such as AHR Q383H. We further characterised AHR Q383H as an activating driver mutation associated with high AhR activity in luminal tumours. High AhR activity was also found in tumours presenting amplifications of AHR and its co-receptor ARNT. We finally showed that BCa cells presenting those different genetic alterations were sensitive to AhR inhibition.

CONCLUSIONS

Our study identified novel potential drivers within APOBEC-associated hotspot mutations in BCa reinforcing the importance of APOBEC mutagenesis in BCa. It could allow a better understanding of BCa biology and aetiology and have clinical implications such as AhR as a potential therapeutic target. Our results also challenge the dogma that all hotspot mutations are drivers and mostly gain-of-function mutations affecting oncogenes.

Essential role of long non-coding RNAs in de novo chromatin modifications: the genomic address code hypothesis

The epigenome, i.e., the whole of chromatin modifications, is transferred from mother to daughter cells during cell differentiation. When de novo chromatin modifications (establishment or erasure of, respectively, new or pre-existing DNA methylations and/or histone modifications) are made in a daughter cell, however, it has a different epigenome than its mother cell. Although de novo chromatin modification is an important event that comprises elementary processes of cell differentiation, its molecular mechanism remains poorly understood. We argue, in this letter, that a key to solving this problem lies in understanding the role of long non-coding RNAs (lncRNAs), a type of RNA that is becoming increasingly prominent in epigenetic studies. Many studies show that lncRNAs form ribonucleoprotein complexes in the nucleus and are involved in chromatin modifications. However, chromatin-modifying enzymes lack the information about genomic positions on which they act. It is known, on the other hand, that a single-stranded RNA in general can bind to a double-stranded DNA to form a triple helix. If each lncRNA forms a ribonucleoprotein complex with chromatin-modifying enzymes on one hand and, at the same time, a triple helix with a genomic region based on its specific nucleotide sequence on the other hand, it can induce de novo chromatin modifications at specific sites. Thus, the great variety of lncRNAs can be explained by the requirement for the diversity of "genomic address codes" specific to their cognate genomic regions where de novo chromatin modifications take place.

Synergistic roles for human U1 snRNA stem-loops in pre-mRNA splicing

During spliceosome assembly, interactions that bring the 5' and 3' ends of an intron in proximity are critical for the production of mature mRNA. Here, we report synergistic roles for the stem-loops 3 (SL3) and 4 (SL4) of the human U1 small nuclear RNA (snRNA) in maintaining the optimal U1 snRNP function, and formation of cross-intron contact with the U2 snRNP. We find that SL3 and SL4 bind distinct spliceosomal proteins and combining a U1 snRNA activity assay with siRNA-mediated knockdown, we demonstrate that SL3 and SL4 act through the RNA helicase UAP56 and the U2 protein SF3A1, respectively. In vitro analysis using UV crosslinking and splicing assays indicated that SL3 likely promotes the SL4-SF3A1 interaction leading to enhancement of A complex formation and pre-mRNA splicing. Overall, these results highlight the vital role of the distinct contacts of SL3 and SL4 in bridging the pre-mRNA bound U1 and U2 snRNPs during the early steps of human spliceosome assembly.

Conserved 3' UTR stem-loop structure in L1 and Alu transposons in human genome: possible role in retrotransposition

BACKGROUND

In the process of retrotransposition LINEs use their own machinery for copying and inserting themselves into new genomic locations, while SINEs are parasitic and require the machinery of LINEs. The exact mechanism of how a LINE-encoded reverse transcriptase (RT) recognizes its own and SINE RNA remains unclear. However it was shown for the stringent-type LINEs that recognition of a stem-loop at the 3'UTR by RT is essential for retrotransposition. For the relaxed-type LINEs it is believed that the poly-A tail is a common recognition element between LINE and SINE RNA. However polyadenylation is a property of any messenger RNA, and how the LINE RT recognizes transposon and non-transposon RNAs remains an open question. It is likely that RNA secondary structures play an important role in RNA recognition by LINE encoded proteins.

RESULTS

Here we selected a set of L1 and Alu elements from the human genome and investigated their sequences for the presence of position-specific stem-loop structures. We found highly conserved stem-loop positions at the 3'UTR. Comparative structural analyses of a human L1 3'UTR stem-loop showed a similarity to 3'UTR stem-loops of the stringent-type LINEs, which were experimentally shown to be recognized by LINE RT. The consensus stem-loop structure consists of 5-7 bp loop, 8-10 bp stem with a bulge at a distance of 4-6 bp from the loop. The results show that a stem loop with a bulge exists at the 3'-end of Alu. We also found conserved stem-loop positions at 5'UTR and at the end of ORF2 and discuss their possible role.

CONCLUSIONS

Here we presented an evidence for the presence of a highly conserved 3'UTR stem-loop structure in L1 and Alu retrotransposons in the human genome. Both stem-loops show structural similarity to the stem-loops of the stringent-type LINEs experimentally confirmed as essential for retrotransposition. Here we hypothesize that both L1 and Alu RNA are recognized by L1 RT via the 3'-end RNA stem-loop structure. Other conserved stem-loop positions in L1 suggest their possible functions in protein-RNA interactions but to date no experimental evidence has been reported.

Beacons Contribute Valuable Empirical Information to Theoretical 3-D Aptamer-Peptide Binding

DNA aptamers were developed against five different peptides from the known binding regions of anti-Cytomegalovirus and anti-Herpes Simplex Virus-2 antibodies and the aptamers were ranked by relative affinity based on an ELISA-like (ELASA) microplate assay. The secondary structures of the top five highest affinity aptamers were studied for stem-loop commonalities and the most probable peptide binding sites. Two of these stem-loop structures were converted into beacons by addition of TYE 665 dye on the 5' end and Iowa Black quencher on the 3' end. When competed against increasing concentrations of each of the five peptides, only three of the possible ten interactions demonstrated "lights on" fluorescence beacon responses. When modeled by generation of PDB files, after passage through PATCHDOCK and YASARA, two of the aptamer beacon-peptide interactions showed no theoretical evidence of separating the G-C stem-loop region, despite clear empirical evidence of separation of the fluorophore and quencher beyond the Förster distance leading to abundant fluorescence. And in the second beacon's case, YASARA modeling suggested that the beacon was always open despite clear empirical evidence that it was not (no fluorescence response) and only opened in the presence of one of the five peptides. These results are interpreted as a demonstration that 3-dimensional docking software such as PATCHDOCK and YASARA, which are based on rigid receptor-ligand shape complementarity may not reflect the "induced-fit" interactions between aptamers and their cognate targets. Therefore, for the most complete and accurate picture of aptamer-peptide binding, several theoretical and empirical (e.g., beacon fluorescence) analysis methods may be needed.

Circulating miRNAs can serve as potential diagnostic biomarkers in chronic myelogenous leukemia patients

Introduction

Chronic Myelogenous Leukemia (CML) is a myeloproliferative disorder described as a malignant blood disorder by accounts for 15–20% of all adult leukemia. MicroRNAs (miRNAs) play an important role in post-transcriptional regulation of gene expressions. Expression level of tumor suppressor-miRNAs, described as miRNAs that target the oncogens, can contribute to diagnosis and prognosis of some malignant disorders including CML. We theorized that according to the excessive proliferation and alteration in miRNA expressions, there could be a change in the expression of miRNAs in plasma carried by exosomes.

Methods

We consequently decided to detect the differences between normal and aberrant miRNA expression in human plasma sample to find out the possibility of diagnosis by these alterations. The expression of candidate miRNAs were compared using RNA extracted from the plasma of 50 patients, as well as 30 healthy individuals. We analysed the plasma miR-16-1, miR-20, miR-106, miR-126, miR-155, miR-222, and miR-451 expression levels in CML patients by individual real-time quantitative RT-PCR.

Results

All selected miRNAs were found to be upregulated in newly diagnosed CML patients compared to the control, while upregulation of only three (miR-20, 106 and 222) were significant (17.4, 19 and 74.95 fold change, respectively; p<0.0001).

In conclusion

microRNAs have a potential use in treatment of CML, as they can target the genes involved in cell cycle, MAPK, growth inhibition, TGF beta, and p53 signaling pathways. Therefore, these miRNA signatures provide the basis for their utilization as biomarkers in CML.

Translation initiation factor 3 families: what are their roles in regulating cyanobacterial and chloroplast gene expression?

Initiation is a key control point for the regulation of translation in prokaryotes and prokaryotic-like translation systems such as those in plant chloroplasts. Genome sequencing and biochemical studies are increasingly demonstrating differences in many aspects of translation between well-studied microbes such as Escherichia coli and lesser studied groups such as cyanobacteria. Analyses of chloroplast translation have revealed its prokaryotic origin but also uncovered many unique aspects that do not exist in E. coli. Recently, a novel form of posttranscriptional regulation by light color was discovered in the filamentous cyanobacterium Fremyella diplosiphon that requires a putative stem-loop and involves the use of two different prokaryotic translation initiation factor 3s (IF3s). Multiple (up to five) putative IF3s have now been found to be encoded in 22 % of sequenced cyanobacterial genomes and 26 % of plant nuclear genomes. The lack of similar light-color regulation of gene expression in most of these species suggests that IF3s play roles in regulating gene expression in response to other environmental and developmental cues. In the plant Arabidopsis, two nuclear-encoded IF3s have been shown to localize to the chloroplasts, and the mRNA levels encoding these vary significantly in certain organ and tissue types and during several phases of development. Collectively, the accumulated data suggest that in about one quarter of photosynthetic prokaryotes and eukaryotes, IF3 gene families are used to regulate gene expression in addition to their traditional roles in translation initiation. Models for how this might be accomplished in prokaryotes versus eukaryotic plastids are presented.

Lirex: A Package for Identification of Long Inverted Repeats in Genomes

Long inverted repeats (LIRs) are evolutionarily and functionally important structures in genomes because of their involvement in RNA interference, DNA recombination, and gene duplication. Identification of LIRs is highly complicated when mismatches and indels between the repeats are permitted. Long inverted repeat explorer (Lirex) was developed and introduced in this report. Written in Java, Lirex provides a user-friendly interface and allows users to specify LIR searching criteria, such as length of the region, as well as pattern and size of the repeats. Recombinogenic LIRs can be selected on the basis of mismatch rate and internal spacer size from identified LIRs. Lirex, as a cross-platform tool to identify LIRs in a genome, may assist in designing following experiments to explore the function of LIRs. Our tool can identify more LIRs than other LIR searching tools. Lirex is publicly available at http://124.16.219.129/Lirex.

Identification of a novel circovirus in blood sample of giant pandas (Ailuropoda melanoleuca)

The members of the family Circoviridae are considered to be one of the smallest autonomously replicating viruses that are classified into two genera, Circovirus and Cyclovirus. Circoviruses have been found in a variety of vertebrates, but whether they infect endangered protected animals has not been studied in much detail. Here, viral metagenomics and PCR methods were used to detect and verify viral nucleic acid in the blood sample from giant pandas. According to these methods, the complete genome sequence of a novel circovirus, the giant panda associated circovirus (GPCV) from the blood sample of three giant pandas was identified. The GPCV genome is 2090 bp in size and reveals two putative ambisense open-reading frames, encoding the major structural capsid protein and the replication associated protein, respectively, the latter having two predicted introns. Pairwise sequence comparison and phylogenetic analyses indicated GPCV was a putative new species within genus Circovirus based on the species demarcation criteria of the International Committee on the Taxonomy of Viruses. It is the first time that circovirus has been identified from blood sample of giant pandas. These efforts will contribute to future analyses to illuminate the evolutionary relationships between classified and newly identified members of the family Circoviridae.

Distinct cis elements in the 3' UTR of the C. elegans cebp-1 mRNA mediate its regulation in neuronal development

The 3' untranslated regions (3' UTRs) of mRNAs mediate post-transcriptional regulation of genes in many biological processes. Cis elements in 3' UTRs can interact with RNA-binding factors in sequence-specific or structure-dependent manners, enabling regulation of mRNA stability, translation, and localization. Caenorhabditis elegans CEBP-1 is a conserved transcription factor of the C/EBP family, and functions in diverse contexts, from neuronal development and axon regeneration to organismal growth. Previous studies revealed that the levels of cebp-1 mRNA in neurons depend on its 3' UTR and are also negatively regulated by the E3 ubiquitin ligase RPM-1. Here, by systematically dissecting cebp-1's 3' UTR, we test the roles of specific cis elements in cebp-1 expression and function in neurons. We present evidence for a putative stem-loop in the cebp-1 3' UTR that contributes to basal expression levels of mRNA and to negative regulation by rpm-1. Mutant animals lacking the endogenous cebp-1 3' UTR showed a noticeable increased expression of cebp-1 mRNA and enhanced the neuronal developmental phenotypes of rpm-1 mutants. Our data reveal multiple cis elements within cebp-1's 3' UTR that help to optimize CEBP-1 expression levels in neuronal development.

Relative Quantification of siRNA Strand Loading into Ago2 for Design of Highly Active siRNAs

In RNA interference (RNAi), silencing is achieved through the interaction of double-stranded small interfering RNAs (siRNAs) with essential RNAi pathway proteins, including Argonaute 2 (Ago2). Based on these interactions, one strand of the siRNA is loaded into Ago2 forming the active RNA-induced silencing complex (RISC). Optimal siRNAs maximize RISC activity against the intended target and minimize off-target silencing. To achieve the desired activity and specificity, selection of the appropriate siRNA strand for loading into Ago2 is essential. Here, we provide a protocol to quantify the relative loading of individual siRNA strands into Ago2, one factor in determining the capacity of a siRNA to achieve silencing activity and target specificity.

Conjunction of G-quadruplex and stem-loop in the 5' untranslated region of mouse hepatocyte nuclear factor 4-alpha1 mediates strong inhibition of protein expression

Hepatocyte nuclear factor 4-alpha (HNF4α) is a well-established master regulator of liver development and function. Restoration of HNF4α can treat multiple liver disorders and liver cancers. To date, HNF4α is still "undruggable" due to lack of known activating ligands. Thus, understanding the regulatory mechanism of HNF4α expression may help develop an alternative approach to modulate HNF4α protein levels. G-quadruplexes (G4) are non-canonical stable secondary structures discovered mostly in the promoters of oncogenes. Recent genome-wide studies demonstrate the enrichment of G4s in the 5' untranslated region (UTR). By protoporphyrin IX-binding assay and circular dichroism spectrum, we validated the presence of a chemically highly stable 4-ring G4 within the 5' UTR of mouse Hnf4a1. Our real-time PCR and Western blot data showed that the Hnf4a1 5' UTR caused a remarkable translational suppression regardless of a moderate effect on Hnf4a1 mRNA levels. The subsequent deletion/mutation analysis of Hnf4a1 5' UTR using dual-luciferase reporter assays further demonstrated that although the disruption of the chemically highly stable 4-ring G4 resulted in a marked attenuation of inhibition, the G4 alone only weakly inhibited translation. Likewise, disruption of a long stem-loop adjacent to the 4-ring G4 markedly attenuated translational inhibition, although the stem-loop alone only exerted a weak inhibitory effect. Thus, the tight conjunction of G4s and an adjacent stem-loop within the Hnf4a1 5' UTR was both necessary and sufficient to mediate the very strong translational repression. Our results establish a novel working model that a chemically stable G4 may require co-factors to be bio-stable for exerting biological functions.

Dual dye-labeled aptamers for detection of dichlorvos using ratiometric fluorescence resonance energy transfer

BACKGROUND

Dichlorvos (DDVP) is an efficient and highly toxic organophosphorus pesticide. Considering its effects on human health and ecosystems, pesticide residue and pollution monitoring is of great significance. Traditional methods like chromatography with mass spectrometry are not portable or rapid because they use large instruments and complex pre-processing methods. Compared with other optional on-site detection technologies, like enzymatic and antibody methods, aptamers are advantageous because they are stable, readily modified, and inexpensive. Therefore, screening and developing a specific adapter for DDVP detection is necessary and will be of practical value.

RESULTS

We screened, modified, and compared two dual-labeled aptamer probes (Cy3-DV55-Cy5 and Cy3-DV65-Cy5). The kinetics studied showed that 5 min was sufficient for the detection reaction. Both aptamers showed selectivity for DDVP but DV55 was superior to DV65. To research the binding stabilities and the mechanism between the aptamers and DDVP, the secondary structures, melting temperatures, fluorescence quenching types, and constants were investigated. Which showed that DV55 was specific for DDVP and showed better binding than DV65. Comparison of the UV absorption and FRET for DV55 and the truncated structures suggested that loop 3 in DV55 might play an important role in the binding of DV55 to DDVP. The Cy3-DV55-Cy5 aptamer had a linear range of 0-100 μM for DDVP detection and the limit of detection was 150 nM. Simulated pesticide residue detection experiments showed that the method was simple, fast, and had acceptable recovery (89.8%-105.2 %).

SIGNIFICANCE

Pesticide detection is important but on-site detection methods are usually not portable or rapid. We developed two dual-labeled aptamer probes that could feasibly be practically applied to rapid on-site DDVP detection of pesticide residues and pollutants. This research provides experimental and theoretical data for the development and design of similar pesticide probes.