Non-coding Circular RNAs Research Articles

Circular and long non-coding RNAs and their role in ophthalmologic diseases.

Long non-coding RNAs are 200 nucleotide long RNA molecules which lack or have limited protein-coding potential. They can regulate protein formation through several different mechanisms. Similarly, circular RNAs are reported to play a critical role in post-transcriptional gene regulation. Changes in the expression pattern of these molecules are established to underline various diseases, including cancer, cardiovascular, neurological and immunological disorders. Recent studies suggest that they are differentially expressed both in healthy ocular tissues as well as in eye pathologies, such as neovascularization, proliferative vitreoretinopathy, glaucoma, cataract, ocular malignancy or even strabismus. Aetiology of ocular diseases is multifactorial and combines genetic and environmental factors, including epigenetic and non-coding RNAs. In addition, disorders like diabetic retinopathy or age-related macular degeneration lack biomarkers for early detection as well as effective treatment methods that will allow controlling the disease progression at its early stages. The newly discovered non-coding RNAs seem to be the ideal candidate for novel molecular markers and therapeutic strategies. In this review, we summarize current knowledge about gene expression regulators - long non-coding and circular RNA molecules in eye diseases.

Long Noncoding RNA ANRIL: Lnc-ing Genetic Variation at the Chromosome 9p21 Locus to Molecular Mechanisms of Atherosclerosis.

Ever since the first genome-wide association studies (GWAS) on coronary artery disease (CAD), the Chr9p21 risk locus has emerged as a top signal in GWAS of atherosclerotic cardiovascular disease, including stroke and peripheral artery disease. The CAD risk SNPs on Chr9p21 lie within a stretch of 58 kilobases of non-protein-coding DNA, containing the gene body of the long noncoding RNA (lncRNA) antisense non coding RNA in the INK4 locus (ANRIL). How risk is affected by the Chr9p21 locus in molecular detail is a matter of ongoing research. Here we will review recent advances in the understanding that ANRIL serves as a key risk effector molecule of atherogenesis at the locus. One focus of this review is the shift in understanding that genetic variation at Chr9p21 not only affects the abundance of ANRIL, and in some cases expression of the adjacent CDKN2A/B tumor suppressors, but also impacts ANRIL splicing, such that 3′-5′-linked circular noncoding ANRIL RNA species are produced. We describe how the balance of linear and circular ANRIL RNA, determined by the Chr9p21 genotype, regulates molecular pathways and cellular functions involved in atherogenesis. We end with an outlook on how manipulating circular ANRIL abundance may be exploited for therapeutic purposes.

Potato Spindle Tuber Viroid Modulates Its Replication through a Direct Interaction with a Splicing Regulator.

Viroids are circular noncoding RNAs (ncRNAs) that infect plants. Despite differences in the genetic makeup and biogenesis, viroids and various long ncRNAs all rely on RNA structure-based interactions with cellular factors for function. Viroids replicating in the nucleus utilize DNA-dependent RNA polymerase II for transcription, a process that involves a unique splicing form of transcription factor IIIA (TFIIIA-7ZF). Here, we provide evidence showing that potato spindle tuber viroid (PSTVd) interacts with a TFIIIA splicing regulator (ribosomal protein L5 [RPL5]) in vitro and in vivo PSTVd infection compromises the regulatory role of RPL5 over splicing of TFIIIA transcripts, while ectopic expression of RPL5 reduces TFIIIA-7ZF expression and attenuates PSTVd accumulation. Furthermore, we illustrate that the RPL5 binding site on the PSTVd genome resides in the central conserved region critical for replication. Together, our data suggest that viroids can regulate their own replication and modulate specific regulatory factors leading to splicing changes in only one or a few genes. This study also has implications for understanding the functional mechanisms of ncRNAs and elucidating the global splicing changes in various host-pathogen interactions.IMPORTANCE Viroids are the smallest replicons among all living entities. As circular noncoding RNAs, viroids can replicate and spread in plants, often resulting in disease symptoms. Potato spindle tuber viroid (PSTVd), the type species of nuclear-replicating viroids, requires a unique splicing form of transcription factor IIIA (TFIIIA-7ZF) for its propagation. Here, we provide evidence showing that PSTVd directly interacts with a splicing regulator, RPL5, to favor the expression of TFIIIA-7ZF, thereby promoting viroid replication. This finding provides new insights to better understand viroid biology and sheds light on the noncoding RNA-based regulation of splicing. Our discovery also establishes RPL5 as a novel negative factor regulating viroid replication in the nucleus and highlights a potential means for viroid control.

Potato Spindle Tuber Viroid RNA-Templated Transcription: Factors and Regulation.

Viroids are circular noncoding RNAs that infect plants. Without encoding any protein, these noncoding RNAs contain the necessary genetic information for propagation in hosts. Nuclear-replicating viroids employ DNA-dependent RNA polymerase II (Pol II) for replication, a process that makes a DNA-dependent enzyme recognize RNA templates. Recently, a splicing variant of transcription factor IIIA (TFIIIA-7ZF) was identified as essential for Pol II to replicate potato spindle tuber viroid (PSTVd). The expression of TFIIIA-7ZF, particularly the splicing event, is regulated by a ribosomal protein (RPL5). PSTVd modulates its expression through a direct interaction with RPL5 resulting in optimized expression of TFIIIA-7ZF. This review summarizes the recent discoveries of host factors and regulatory mechanisms underlying PSTVd-templated transcription processes and raises new questions that may help future exploration in this direction. In addition, it briefly compares the machinery and the regulatory mechanism for PSTVd with the replication/transcription system of human hepatitis delta virus.

Prospect of Circular RNA in Hepatocellular Carcinoma: A Novel Potential Biomarker and Therapeutic Target.

CircRNA, a kind of tissue specific and covalently closed circular non-coding RNA is very abundant in eukaryocyte. Generally, circRNA is generated by back-splicing of protein-coding genes' pre-mRNA. Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. Due to the characteristics of poor prognosis and high recurrence, the pathogenesis of HCC is highly concerned by researchers worldwide. Recent studies demonstrated that numerous circRNAs were differentially expressed in HCC tissues and normal liver tissues, which is closely related with the development and prognosis of HCC. However, the mechanism of circRNA in HCC remains unclear. In this review, we summarized the abnormal expressions of circRNAs in HCC, discussed its role, and potential mechanisms, and tried to explore the prospective values of circRNA in the diagnosis, therapy, and prognosis of HCC.

Postsplicing-Derived Full-Length Intron Circles in the Protozoan Parasite Entamoeba histolytica.

Noncoding circular RNAs are widespread in the tree of life. Particularly, intron-containing circular RNAs which apparently upregulate their parental gene expression. Entamoeba histolytica, the causative agent of dysentery and liver abscesses in humans, codes for several noncoding RNAs, including circular ribosomal RNAs, but no intron containing circular RNAs have been described to date. Divergent RT-PCR and diverse molecular approaches, allowed us to detect bona fide full-length intronic circular RNA (flicRNA) molecules. Self-splicing reactions, RNA polymerase II inhibition with Actinomycin D, and second step of splicing-inhibition with boric acid showed that the production of flicRX13 (one of the flicRNAs found in this work, and our test model) depends on mRNA synthesis and pre-mRNA processing instead of self-splicing. To explore the cues and factors involved in flicRX13 biogenesis in vivo, splicing assays were carried out in amoeba transformants where splicing factors and Dbr1 (intron lariat debranching enzyme 1) were silenced or overexpressed, or where Rabx13 wild-type and mutant 5′ss (splice site) and branch site minigene constructs were overexpressed. Whereas SF1 (splicing factor 1) is not involved, the U2 auxiliary splicing factor, Dbr1, and the GU-rich 5′ss are involved in postsplicing flicRX13 biogenesis, probably by Dbr1 stalling, in a similar fashion to the formation of ciRNAs (circular intronic RNAs), but with distinctive 5′-3′ss ligation points. Different from the reported functions of ciRNAs, the 5′ss GU-rich element of flicRX13 possibly interacts with transcription machinery to silence its own gene in cis. Furthermore, introns of E. histolytica virulence-related genes are also processed as flicRNAs.

Abstract 2471: Clinical significance of noncoding circHIPK3 RNA in human hepatocellular carcinoma

Abstract Background and Aim: Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, with poor prognosis and high risk of recurrence. Previous studies have shown that various microRNAs (miRNAs) are frequently dysregulated in HCC, which contributes to cancer development and progression. Nonetheless, the regulation mechanism of miRNAs is still unclear. Circular noncoding RNA (circRNA) is highly conserved and stable covalently closed RNA circles with gene-regulatory potential. Recently, one abundant circRNA from HIPK3 gene, circHIPK3, has been identified, and its function has been elucidated as multiple miRNAs sponge. Thus, we aimed to investigate the clinical relevance of circHIPK3 in HCC. Materials and Methods: We analyzed clinical specimens from 152 pairs of HCC and corresponding normal liver (NL) tissues. Total RNAs were isolated from clinical tissues using Qiagen kit. CircHIPK3 expression levels were determined by quantitative real-time PCR (qRT-PCR), and its expression was normalized with GAPDH. In addition, we analyzed the correlation between circHIPK3 expression and various clinicopathologic features of HCC patients. Results: CircHIPK3 expression was significantly downregulated in HCC tissues compared to corresponding NL tissues (P=0.036). In HCC patients, circHIPK3 expression was strongly suppressed in more advanced tumors (P<0.001). Further correlation analysis showed that circHIPK3 expression was significantly associated with T stage (P<0.001), TNM stage (P<0.001), BCLC stage (P<0.001), and alpha-fetoprotein (AFP) expression (P=0.033). Conclusions: We have determined clinical significances of circHIPK3 expression in HCC, which may provide clinical evidence for the potential of circHIPK3 as novel markers for diagnosis and predicting prognosis in HCC patients. Citation Format: Gyeonghwa Kim, Jun Sik Yoon, Se Young Jang, Soo Young Park, Won Young Tak, Young-Oh Kweon, Keun Hur. Clinical significance of noncoding circHIPK3 RNA in human hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2471.

Association of microRNA-7 and its binding partner CDR1-AS with the prognosis and prediction of 1st-line tamoxifen therapy in breast cancer

The large number of non-coding RNAs (ncRNAs) and their breadth of functionalities has fuelled many studies on their roles in cancer. We previously linked four microRNAs to breast cancer prognosis. One of these microRNAs, hsa-miR-7, was found to be regulated by another type of ncRNA, the circular non-coding RNA (circRNA) CDR1-AS, which contains multiple hsa-miR-7 binding sites. Based on this finding, we studied the potential clinical value of this circRNA on breast cancer prognosis in a cohort based on a cohort that was previously analysed for hsa-miR-7 and in an adjuvant hormone-naïve cohort for 1st-line tamoxifen treatment outcomes, in which we also analysed hsa-miR-7. A negative correlation was observed between hsa-miR-7 and CDR1-AS in both cohorts. Despite associations with various clinical metrics (e.g., tumour grade, tumour size, and relapse location), CDR1-AS was neither prognostic nor predictive of relevant outcomes in our cohorts. However, we did observe stromal CDR1-AS expression, suggesting a possible cell-type specific interaction. Next to the known association of hsa-miR-7 expression with poor prognosis in primary breast cancer, we found that high hsa-miR-7 expression was predictive of an adverse response to tamoxifen therapy and poor progression-free and post-relapse overall survival in patients with recurrent disease.

CircRNA_0023642 promotes migration and invasion of gastric cancer cells by regulating EMT.

Non-coding circular RNAs (circRNAs) have displayed dysregulated expression in various tumor tissues. However, their role in the progression of cancers remains largely unknown. We aimed at examining the expression, functions, and molecular mechanisms of a new circRNA (circRNA_0023642) in gastric cancer (GC). We evaluated the expression levels of circRNA_0023642 in GC tissues, adjacent normal tissues and cells lines using qRT-PCR. The functional roles of circRNA_0023642 in GC were determined by Cell Counting Kit-8 (CCK-8) assay, colony formation assay, transwell assay, and flow cytometric analysis. Western blot was used to analyze the effect of circRNA_0023642 on the expression of EMT-related proteins. We found that circRNA_0023642 was upregulated in GC tissues and cell lines. Functionally, down-regulation of circRNA_0023642 displayed the tumor-inhibitory effects by suppressing cell proliferation, migration, and invasion as well as inducing apoptosis. Mechanically, our results revealed that the abnormal expression of circRNA_0023642 could influence the EMT signaling pathway, which was demonstrated by measuring the expression levels of N-cadherin, vimentin snail, and E-cadherin. Our findings suggest that circRNA_0023642 serves as a metastasis activator by promoting EMT and may represent a novel molecular therapeutic target for GC.

Allelic RNA Motifs in Regulating Systemic Trafficking of Potato Spindle Tuber Viroid.

Intercellular RNA trafficking has been shown as a widely-existing phenomenon that has significant functions in many aspects of biology. Viroids, circular noncoding RNAs that cause plant diseases, have been a model to dissect the role of RNA structural motifs in regulating intercellular RNA trafficking in plants. Recent studies on potato spindle tuber viroid (PSTVd) showed that the RNA motif loop 19 is important for PSTVd to spread from palisade to spongy mesophyll in infected leaves. Here, we performed saturated mutational analysis to uncover all possible functional variants of loop 19 and exploit this data to pinpoint to a three-dimensional structural model of this motif. Interestingly, we found that two distinct structural motifs can replace loop 19 and retain the systemic trafficking capacity. One of the alternative structures rapidly emerged from the inoculation using a loop 19 abolished mutant that is not capable of systemic trafficking. Our observation indicates the flexibility of multiple structural arrangements interchangeably exerting similar function at a particular RNA locus. Taken together, this study deepens the understanding of RNA structural motifs-regulated viroid RNA trafficking, which has broad implications for studying RNA intercellular trafficking as well.

Circular noncoding RNAs as potential therapies and circulating biomarkers for cardiovascular diseases.

Recent advancements in genome-wide analyses and RNA-sequencing technologies led to the discovery of small noncoding RNAs, such as microRNAs (miRs), as well as both linear long noncoding RNAs (lncRNAs) and circular long noncoding RNAs (circRNAs). The importance of miRs and lncRNAs in the treatment, prognosis and diagnosis of cardiovascular diseases (CVDs) has been extensively reported. We also previously reviewed their implications in therapies and as biomarkers for CVDs. More recently, circRNAs have also emerged as important regulators in CVDs. CircRNAs are circular genome products that are generated by back splicing of specific regions of pre-messenger RNAs (pre-mRNAs). Growing interest in circRNAs led to the discovery of a wide array of their pathophysiological functions. CircRNAs have been shown to be key regulators of CVDs such as myocardial infarction, atherosclerosis, cardiomyopathy and cardiac fibrosis. Accordingly, circRNAs have been recently proposed as potential therapeutic targets and biomarkers for CVDs. In this review, we summarize the current state of the literature on circRNAs, starting with their biogenesis and global mechanisms of actions. We then provide a synopsis of their involvement in various CVDs. Lastly, we emphasize the great potential of circRNAs as biomarkers for the early detection of CVDs, and discuss several patents and recent papers that highlight the utilization of circRNAs as promising biomarkers.

RNA 3-dimensional structural motifs as a critical constraint of viroid RNA evolution.

Viroids are circular noncoding RNAs infecting plants [1, 2]. During infection, viroids, like RNA viruses, generate swarms of sequence variants called quasispecies [3, 4]. Viroids in Avsunviroidae family replicate in chloroplasts and display the highest mutation rates among all living entities [5]. Viroids in Pospiviroidae family replicate in the nucleus with a relatively lower mutation rate resembling some RNA viruses [6]. Those sequence variants generated during replication are described by the concept of sequence space, which harnesses a geometric representation to illustrate genetic similarities via physical distances. Given the high mutation rate and fast propagation, viroid RNAs have a potentially large sequence space for the evolution of new variants. However, in reality, they use only a small fraction of this space. Constraints of viral sequence space may include genome size, replication fidelity, error thresholds, host or tissue tropism, etc. These factors have been nicely reviewed elsewhere [3, 7, 8] and are not the focus of this Pearl. In addition, RNA secondary structures have been considered, though not adequately, as a constraint factor [8]. Viroids, in contrast to viruses, entirely rely on their RNA structural motifs for function due to their noncoding nature, which offers insights into their capacity to explore regions of sequence space influenced by RNA structures. Here, we describe that 3-dimensional (3D) structural motifs formed by non–Watson-Crick (non-WC) base pairs in viroid RNAs act as a critical constraint for the sequence space of viroid genome evolution. This constraint operates because RNA 3D motifs can play crucial roles by mediating (1) RNA–RNA interactions for the folding of a part or a whole of RNA into a distinct tertiary conformation and (2) RNA–protein interactions. Therefore, mutations in a 3D motif that do not disrupt the structure and function will be retained in the population, whereas mutations that disrupt the 3D structures of motifs, and consequently the function, will be lost.

The Potential Role of circRNA in Tumor Immunity Regulation and Immunotherapy.

Non-coding RNAs (ncRNAs) can be divided into circular non-coding RNAs (circRNAs) and linear ncRNAs. ncRNAs exist in different cell types, including normal cells, tumor cells and immunocytes. Linear ncRNAs, such as long ncRNAs and microRNAs, have been found to play important roles in the regulation of tumor immunity and immunotherapy; however, the functions of circRNAs in tumor immunity and immunotherapy are less known. Here, we review the current status of ncRNAs in the regulation of tumor immunity and immunotherapy and emphatically discuss the potential roles of circRNAs as tumor antigens in the regulation of tumor immunity and immunotherapy.

Inhibitory effects of novel isothiocyanate derivative on proliferation and invasion of glioma U251 cells and regulation of circRNAs and lncRNAs

// Yu Zhu 1 and Ping Yang 1 1 Department of Clinical Laboratory, Tianjin Huanhu Hospital, Tianjin Key Laboratory of Cerebral Vessels and Neural Degeneration, Tianjin 300350, P.R. China Correspondence to: Yu Zhu, email: zhuyutj@126.com Ping Yang, email: tjhhhospitallab@126.com Keywords: glioma; isothiocyanate; lncRNAs; circRNAs; proliferation Received: November 08, 2017 Accepted: December 26, 2017 Published: January 02, 2018 ABSTRACT Gliomas proliferation and invasion plays the critical roles in the tumor progression. Isothiocyanate is the hydrolysis products of Brassica vegetables and suppress many types of tumor including gliomas. We design and synthesized an isothiocyanate derivative by computer-aided drug design base on alkylglycerone phosphate synthase (AGPS) to improve targeting and explore its effect on the proliferation, invasion, apoptosis, cell cycle, and the expression of circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs) in U251 cell line. The isothiocyanate derivative suppressed proliferation and invasion by inducing apoptosis with improving the activity of caspase-3/8 and blocked the cell cycle at G2/M phase and regulating the expression of circRNAs and lncRNAs involved in the above biological behavior in human glioma U251 cells. Our results showed the effect of isothiocyanate derivative on the anti-tumor activity, which shows potential for application as a anti-glioma drug.

Circular RNA Expression Profile and Analysis of Their Potential Function in Psoriasis

Background/Aims: Circular RNAs (circRNAs) are evolutionary conserved circular non-coding RNAs that play a role in several diseases by sequestering (sponging) microRNAs (miRNAs). However, their role in psoriasis remains unclear. In the present study, we investigated the expression of circRNAs and analyzed their potential functions in psoriasis. Methods: The SBC human ceRNA array V1.0 was used to analyze circRNA expression in psoriatic lesions and normal healthy skin tissues. Functional analyses were performed using Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Putative miRNA response elements (MREs) were identified using miRNA target prediction software. Six upregulated circRNAs were verified by quantitative real-time reverse transcription polymerase chain reaction in psoriatic lesions and healthy skin tissues. Results: A total of 4956 circRNAs (3016 upregulated and 1940 downregulated; fold change ≥2 and p< 0.05) were identified as differentially expressed in psoriasis. Furthermore, 4405 MREs were identified among the differentially expressed circRNAs. hsa_circ_0061012 was upregulated in psoriatic lesions compared with normal healthy skin tissues. The top five MREs of hsa_circ_0061012 were hsa-miR-7157-5p, hsa-miR-4769-3p, hsa-miR-6817-5p, hsa-miR-4310, and hsa-miR-6882-3p. GO analysis was carried out to investigate the biological functions enriched among the upregulated targets of five miRNAs in psoriasis. The GO analysis identified that most of top 30 of GO enrichment are related to psoriasis. Conclusion: hsa_circ_0061012 might be a candidate biomarker for psoriasis. The results provide a new perspective for a better understanding of ceRNA-mediated gene regulation in psoriasis, and provide a novel theoretical basis for further studies on the function of circRNA in psoriasis.

Circular siRNAs for Reducing Off-Target Effects and Enhancing Long-Term Gene Silencing in Cells and Mice.

Circular non-coding RNAs are found to play important roles in biology but are still relatively unexplored as a structural motif for chemically regulating gene function. Here, we investigated whether small interfering RNA (siRNA) with a circular structure can circumvent off-target gene silencing, a problem often observed with standard linear duplex siRNA. In the present work, we, for the first time, synthesized a series of circular siRNAs by cyclizing two ends of a single-stranded RNA (sense or antisense strand) to construct circular siRNAs that were more resistant to enzymatic degradation. Gene silencing of GFP and luciferase was successfully achieved using these circular siRNAs with circular sense strand RNAs and their complementary linear antisense strand RNAs. The off-target effect of sense strand RNAs was evaluated and no cross off-target effects were observed. In addition, we successfully achieved longer gene-silencing efficiency in mice with circular siRNAs than with linear siRNAs. These results indicate the promise of circular siRNAs for overcoming off-target effects of siRNAs and enhancing the possible long-term effect of siRNA gene silencing in basic research and drug development.

Different rates of spontaneous mutation of chloroplastic and nuclear viroids as determined by high-fidelity ultra-deep sequencing.

Mutation rates vary by orders of magnitude across biological systems, being higher for simpler genomes. The simplest known genomes correspond to viroids, subviral plant replicons constituted by circular non-coding RNAs of few hundred bases. Previous work has revealed an extremely high mutation rate for chrysanthemum chlorotic mottle viroid, a chloroplast-replicating viroid. However, whether this is a general feature of viroids remains unclear. Here, we have used high-fidelity ultra-deep sequencing to determine the mutation rate in a common host (eggplant) of two viroids, each representative of one family: the chloroplastic eggplant latent viroid (ELVd, Avsunviroidae) and the nuclear potato spindle tuber viroid (PSTVd, Pospiviroidae). This revealed higher mutation frequencies in ELVd than in PSTVd, as well as marked differences in the types of mutations produced. Rates of spontaneous mutation, quantified in vivo using the lethal mutation method, ranged from 1/1000 to 1/800 for ELVd and from 1/7000 to 1/3800 for PSTVd depending on sequencing run. These results suggest that extremely high mutability is a common feature of chloroplastic viroids, whereas the mutation rates of PSTVd and potentially other nuclear viroids appear significantly lower and closer to those of some RNA viruses.

Circular non-coding RNAs in diabetic retinopathy

Diabetes mellitus is a pandemic disease currently affecting more than 400 million people worldwide (1). The common symptom of Diabetes is hyperglycemia. Chronically elevated blood glucose concentrations result in severe morbidities such as cardiac infarction, stroke, nephropathy, neuropathy and retinopathy primarily caused by micro- and macrovascular dysfunctions (1). Diabetic retinopathy (DR) is a multi-stage disease with a complex pathogenesis comprising changes in function and/or viability of several cell types such as pericytes, vascular endothelial cells, glial cells, neuronal cells and immune cells (2,3). Clinically the first symptoms of a beginning DR are presented as microaneurysms of the retinal vasculature and neuronal dysfunctions with not yet detectable neurodegeneration (2,3). The underlying cause of this disease is still subject of research and involves, amongst other reasons, formation of reactive oxygen species (ROS), reactive metabolites, activation of protein kinase C and the hexosamine pathway (3,4). However, given the complexity of retinal retinopathy, which currently affects ~one-third of people with type 2 diabetes and its temporal disease stages other players, such as non-coding RNAs (ncRNAs) might also play a role.

Effect of Circular ANRIL on the Inflammatory Response of Vascular Endothelial Cells in a Rat Model of Coronary Atherosclerosis

Background/Aims: This study aims to investigate the role of circular antisense non-coding RNA at the INK4 locus (cANRIL) in the inflammatory response of vascular endothelial cells (ECs) in a rat model of coronary atherosclerosis (AS). A rat model of AS was established with rats that were injected with a large dose of vitamin D₃ and fed a high-fat diet. Methods: Sixty Wistar rats were randomly assigned into control, model, empty vector, over-expressed cANRIL and low-expressed cANRIL groups (12 rats in each group). Sixteen weeks later, the ultrastructure of their coronary arteries was observed via transmission electron microscopy. Rat serum lipid levels were analyzed using an automatic biochemical analyzer, and their atherogenic index (AI) values were calculated. Hematoxylin and eosin staining was used to observe the endothelial morphology of rats. Additionally, rat EC apoptosis was tested via a TUNEL assay. Enzyme-linked immunosorbent assays (ELISAs) were applied to measure serum levels of interleukin-1 (IL-1), IL-6, matrix metalloproteinase-9 (MMP-9) and C-reactive protein (CRP). The cANRIL, Bax, bcl-2 and caspase-3 mRNA expression levels were measured with a quantitative real-time polymerase chain reaction (qRT-PCR). The protein expression levels of Bax, bcl-2 and caspase-3 were detected using immunohistochemistry. Results: In the control group, ECs were closely arranged with normal structures, and there was no proliferation. In the model, empty vector and over-expressed cANRIL groups, some cells were not present, and atherosclerotic plaques and thrombi appeared. However, in the under-expressed cANRIL group, the cells had a normal structure. Compared with the model and empty vector groups, the levels of total cholesterol (CHOL), triglycerides (TGs), low density lipoprotein (LDL), IL-1, IL-6, MMP-9, CRP, cANRIL, Bax, and caspase-3, AI values, and rates of EC apoptosis decreased in the low-expressed cANRIL group, while HDL (high density lipoprotein) levels and mRNA and protein expression levels of bcl-2 were increased. The changes in expression levels in the over-expressed cANRIL group were the opposite of those in the low-expressed cANRIL group. Conclusions: Our study provides evidence that reduced cANRIL expression could prevent coronary AS by reducing vascular EC apoptosis and inflammatory factor expression.

Replication of a pathogenic non-coding RNA increases DNA methylation in plants associated with a bromodomain-containing viroid-binding protein.

Viroids are plant-pathogenic molecules made up of single-stranded circular non-coding RNAs. How replicating viroids interfere with host silencing remains largely unknown. In this study, we investigated the effects of a nuclear-replicating Potato spindle tuber viroid (PSTVd) on interference with plant RNA silencing. Using transient induction of silencing in GFP transgenic Nicotiana benthamiana plants (line 16c), we found that PSTVd replication accelerated GFP silencing and increased Virp1 mRNA, which encodes bromodomain-containing viroid-binding protein 1 and is required for PSTVd replication. DNA methylation was increased in the GFP transgene promoter of PSTVd-replicating plants, indicating involvement of transcriptional gene silencing. Consistently, accelerated GFP silencing and increased DNA methylation in the of GFP transgene promoter were detected in plants transiently expressing Virp1. Virp1 mRNA was also increased upon PSTVd infection in natural host potato plants. Reduced transcript levels of certain endogenous genes were also consistent with increases in DNA methylation in related gene promoters in PSTVd-infected potato plants. Together, our data demonstrate that PSTVd replication interferes with the nuclear silencing pathway in that host plant, and this is at least partially attributable to Virp1. This study provides new insights into the plant-viroid interaction on viroid pathogenicity by subverting the plant cell silencing machinery.