Search Results (109)

Vairimorpha ceranae (formerly Nosema ceranae) is an obligate intracellular parasite that poses a major threat to the health of the honey bee. Circular RNAs (circRNAs) have been recognized as key regulators in gene expression and pathogen–host interactions. However, their expression patterns and regulatory roles in V. ceranae infection remain largely unexplored. In this study, we performed circRNA profiling in V. ceranae spores (NcCK) and the midguts of Apis mellifera ligustica workers at 7 d post inoculation (dpi) and 10 dpi (Nc7T and Nc10T) based on transcriptome sequencing, followed by in-depth investigation of the regulatory roles of differentially expressed circRNAs (DEcircRNAs). In total, 243 circRNAs were identified in V. ceranae, with lengths predominantly ranging from 201 to 400 nucleotides. Comparative analysis screened 70 and 192 DEcircRNAs in the NcCK vs. Nc7T and NcCK vs. Nc10T comparison groups, respectively, with a significant majority being downregulated. The parental genes of these DEcircRNAs were significantly enriched in fundamental cellular processes and critical pathways such as protein processing in the endoplasmic reticulum and ribosome biogenesis. Additionally, we constructed a competing endogenous RNA network, suggesting that DEcircRNAs could potentially interact with DEmiRNAs to modulate mRNAs associated with fungal proliferation-relevant signaling pathways like MAPK, PI3K–Akt, and cAMP. Moreover, numerous DEcircRNAs were predicted to contain internal ribosome entry site elements, indicative of their potential for protein coding. The back-splicing junctions and expression trends of selected DEcircRNAs were successfully validated by RT-PCR and qRT-PCR. Our data not only offer a valuable resource for future functional studies but also provide a basis for elucidating the circRNA-mediated mechanisms underlying microsporidian pathogenesis and host–pathogen interactions. Full article

RNA viruses encode multiple layers of regulatory information within their genomes, extending beyond their protein-coding sequences. Through local secondary structures and long-range RNA–RNA interactions, viral RNAs control essential steps of the viral life cycle, including translation, replication, genome cyclization, packaging, and evasion of host defenses. Over the last two decades, chemical probing approaches—particularly Selective 2′-Hydroxyl Acylation analyzed by a primer extension (SHAPE) and its high-throughput derivatives—have transformed our ability to investigate these structures at a single nucleotide resolution and on a genome-wide scale. These technologies have revealed that viral genomes are highly structured and contain numerous functional RNA elements within untranslated regions as well as coding sequences. In this review, we summarize the main experimental strategies used to profile viral RNA architecture, with a focus on SHAPE-based methodologies and complementary approaches. We then discuss the major classes of functional RNA structures identified across diverse viral families, focusing on elements involved in translation and replication, such as internal ribosome entry sites (IRES) and cyclization elements, as well as other functional structures, including XRN1-resistant and frameshifting elements. Finally, we examine how structure-guided analyses are opening new avenues for antiviral intervention, including antisense oligonucleotides, small molecules, and RNA-degrading chimeras. Together, these advances highlight the viral RNA structure as both a key determinant of virus biology and a promising target for therapeutic innovation. Full article

Programmed cell death 4 (PDCD4) protein is a tumour suppressor protein that inhibits mRNA translation by inhibiting RNA helicase, eukaryotic initiation factor 4A (eIF4A). We have previously reported that PDCD4 interacts with the internal ribosome entry site (IRES) element of B-cell lymphoma extra-large (Bcl-xL) mRNA and inhibits its IRES-mediated translation initiation. S6 kinase (S6K)-mediated phosphorylation of PDCD4 activates its degradation and derepresses IRES-mediated translation initiation of Bcl-xL mRNA. eIF3F (one of the subunits of eIF3 complex) was reported to recruit S6K to phosphorylate eIF3G. Therefore, we investigated the possibility of co-regulation of PDCD4 and eIF3F by S6K and the regulation of IRES-mediated translation initiation by PDCD4–eIF3F. Here, we demonstrated that PDCD4 interacts with several subunits of eIF3. Specifically, eIF3F directly interacts with PDCD4 in an RNA-independent manner. Depletion of PDCD4 in glioblastoma (GBM) cells resulted in decreased levels of certain eIF3 subunits, including eIF3F. Additionally, depletion of eIF3F from GBM cells decreased the levels of PDCD4 protein. We also showed that PDCD4 and eIF3F directly interact with Bcl-xL RNA independently of each other. By performing IRES reporter, polysome profiling assays and EMSA we have demonstrated that eIF3F regulates IRES-mediated translation of Bcl-xL mRNA, likely via its interaction with PDCD4. Full article

Viral internal ribosome entry sites (IRESs) are specialized RNA structures that facilitate cap-independent translation as a strategy to usurp the host translational machinery. The Type 6 IRESs are the most streamlined mechanism to date, as they adopt a three pseudoknot RNA structure to initiate factorless translation initiation by directly recruiting the ribosome and drive translation. The Halastavi árva virus (HalV) IRES represents the most minimalistic subclass identified to date, whereby the IRES lacks specific pseudoknot domains that bind to the 40S subunit but instead recruits pre-assembled 80S ribosomes via a mechanism that is not fully understood. Here, we examined cellular conditions that can support HalV IRES translation. We demonstrated that the HalV IRES is translationally active in insect Sf21 lysates and Drosophila S2 cells, but inactive in mammalian RRL and wheat germ extract. Cells treated with heat shock or serum starvation suppressed HalV IRES activity, whereas virus infection robustly enhanced HalV IRES-mediated translation. Finally, the HalV IRES can support viral translation and replication using a heterologous viral replicon. These findings highlight the context-specific cellular conditions that allow ribosome assembly and translation by a factorless minimalist IRES. Full article

Hepatitis A virus (HAV) infection can occasionally cause acute severe hepatitis. Patients with this disease sometimes need to undergo liver transplantation with immunosuppressants. Although rare, breakthrough HAV infections, despite vaccination, appear to be more common among immunocompromised populations. The effect of immunosuppressants on HAV replication is unclear. In this study, we examined the effects of immunosuppressants on HAV HA11-1299 genotype IIIA replication in human hepatocytes, finding that azathioprine inhibited HAV replication with a half-maximal inhibitory concentration of 0.967 μmol/L. We further examined the effect of azathioprine on the replication of HAV HM175 18f genotype IB using replication-competent or replication-incompetent subgenomic replicon in HuhT7 cells. Azathioprine had significant inhibitory effects on the HAV replication-competent subgenomic replicon compared to the replication-incompetent subgenomic replicon. The effect of azathioprine on the activity of the HAV HM175 18f genotype IB-internal ribosomal entry site (IRES) was investigated in COS7-HAV-IRES cells using a reporter assay. Azathioprine at 1 μmol/L had a significant inhibitory effect on HAV IRES activity but at 0.5 μmol/L had no inhibitory effect. Azathioprine appears to inhibit HAV replication as well as HAV translation. In conclusion, we found that azathioprine inhibits HAV replication in human hepatocytes, meaning that it may be useful for patients with a HAV infection who need to use immunosuppressants. Full article

Circular RNA (circRNA) has emerged as a promising vector for drug delivery because, unlike linear mRNA, it does not require costly chemical modifications and offers greater stability and sustained expression in cells. Lacking the canonical 5′ cap structure, circRNA relies primarily on internal ribosome entry sites (IRES) to initiate translation, but IRES-mediated initiation is less efficient than cap-dependent translation. To overcome this limitation, we devised a dual-IRES strategy that introduces a second IRES to drive translation of the coding sequence (CDS). By testing several IRES elements known for high translational activity, this study shows that IRESs derived from the EMCV (Encephalomyocarditis virus) family can enhance expression when placed at the 3′ of the CDS, in coordination with the 5′ EMCV-derived IRES. The optimal dual-IRES combinations identified in this study display compatibility with two different coding sequences, offering a useful strategy to enhance circRNA translation. Full article

Background/Objectives: Coxsackievirus B4 (CVB4), a member of the Enterovirus genus and the Picornaviridae family, is a significant pathogen causing several human diseases such as pancreatitis, myocarditis, cardiomyopathy and type 1 diabetes. Despite its clinical impact, no vaccines or specific antiviral therapies are currently available. This study investigates the attenuation of CVB4 virulence through targeted mutations in the domain V of the IRES (Internal Ribosome Entry Segment) sequence present in the 5′ UTR (Untranslated Region) of the viral genome. Materials and Methods: We engineered six CVB4E2 mutants by introducing single nucleotide mutations in domain V of the IRES sequence using PCR-based site-directed mutagenesis assays. Mutants were rigorously evaluated in vitro for their replicative capacities on HeLa cell culture and for their in vitro translation efficiencies in standard rabbit reticulocyte lysates supplemented with HeLa cell S10 extracts. Using different strategies of immunization and lethal challenges in a Balb/c mice model, we evaluated the immune responses elicited by the most attenuated C488A mutant strain. Results: The obtained results demonstrated that the live-attenuated C488A mutant with the single mutation C to A at nucleotide position 488 of the viral IRES sequence exhibited a significant reduction in vitro of both viral productivity and translation efficiency. The oral immunization with the live-attenuated C488A mutant induced a potent immune response and protected Balb/c mice against lethal infection challenge with a pathogenic strain. Conclusions: These findings underscored the critical role of IRES in CVB4 virulence and highlighted the use of the live-attenuated C488A mutant strain as a promising candidate for developing a live-attenuated vaccine against CVB4 infections. Full article

Background: Survivin is an anti-apoptotic protein highly expressed during embryonic development and, in adults, mainly in the gastrointestinal epithelium. Its levels decrease in human gastric tissue and cultured cells upon exposure to Helicobacter pylori gamma-glutamyl transpeptidase (GGT), though the underlying mechanism remains unclear. Objective: We aimed to investigate the role of cap-independent translation driven by the Survivin 5′ untranslated region (5′UTR) in response to H. pylori infection in vitro. Methodology: Human cell lines (AGS, GES-1, HeLa, HEK293T) were used alongside bicistronic and monocistronic (Firefly/Renilla luciferases) reporter assays to assess short and long variants of the Survivin 5′UTR and HIV-1 internal ribosome entry site (IRES) sequences. Additional methods included in vitro transcription/translation, RT-qPCR, agarose gel electrophoresis, Western blotting, coupled/uncoupled translation assays, and siRNA silencing. Results: The short variant of the Survivin 5′ UTR supported cap-independent translation, like the HIV-1 IRES. Notably, H. pylori infection suppressed this translation in a GGT-dependent manner in gastric cells, and a similar reduction was observed following treatment with ATO, a known prooxidant. Conclusion: The Survivin 5′UTR exhibits cap-independent translation activity that is inhibited by H. pylori in a GGT-dependent manner, likely via oxidative stress. This mechanism helps to explain the downregulation of Survivin during gastric infection and indicates that oxidative stress can negatively affect both cellular and viral IRES-mediated translation. Full article

Background/Objectives: Selectively expressible RNA (seRNA) molecules represent a promising new platform for the induction of cell type-specific protein expression. Based on the sense–antisense interaction of the seRNA antisense domain with target cell-specific RNA molecules, the partial degradation of the seRNA molecule induces the activation of an internal ribosomal entry site to initiate translation. The selective expression of seRNA encoded proteins exclusively in target cells works both in vitro and in vivo but is associated with a lower expression intensity compared with classical mRNAs. Furthermore, seRNAs have so far been transfected into cells by plasmid-encoded seRNA expression systems, which is limiting their broad medical applicability. Here, we focus on the characterization of plasmid-based seRNA uptake and activation as well as on options to transfer the seRNA technology to additional vector systems to increase target cell-specific effector expression. Methods: seRNA constructs were generated as expression plasmids, AAV, DNA minicircles and IVT-RNA and delivered into different eukaryotic cell lines by transfection/transduction. Analyses were performed using fluorescence microscopy and, for quantitative analyses, flow cytometry. RNA stability and expression analyses were performed using qRT-PCR. Results: We show that seRNA-based plasmid systems are efficiently transfected into cells but that reduced RNA steady-state levels are present compared with control expression plasmids. This effect is most likely based on reduced transcription efficiency rather than seRNA stability. Furthermore, seRNA transcription from viral vectors or circular DNA significantly increased the effector expression of seRNAs and enabled linear expression regulation while maintaining target cell-specific activation and inactivation in non-target cells. Optimal results were achieved by adapting the technology to in vitro transcribed seRNA. Conclusions: Our data show that seRNA technology develops its full functionality regardless of the type of transfer vector used. Furthermore, expression strength can be regulated within a wide range while maintaining consistent functionality which will enable broad applicability in medicine in the future. Full article

Nucleic acid-based gene interfering and editing molecules, such as antisense oligonucleotides, ribozymes, small interfering RNAs (siRNAs), and CRISPR-Cas9-associated guide RNAs, are promising gene-targeting agents for therapeutic applications. Cancer’s heterogeneous and diverse nature demands gene-silencing technologies that are both specific and adaptable. RNase P ribozymes, called M1GS RNAs, are engineered constructs that link the catalytic M1 RNA from bacterial RNase P to a programmable guide sequence. This guide sequence directs the M1GS ribozyme to base-pair with a target RNA, inducing it to fold into a structure resembling pre-tRNA. Catalytic activity can be enhanced through in vitro selection strategies. In this review, we will discuss the application of M1GS ribozymes in targeting cancer-associated RNAs, focusing on the BCR-ABL transcript in leukemia, the internal ribosome entry site (IRES) of hepatitis C virus (HCV), and the replication and transcription activator (RTA) of Kaposi’s sarcoma-associated herpesvirus (KSHV). Together, these examples highlight the versatility of M1GS ribozymes across both viral and cellular oncogenic targets, underscoring their potential as a flexible synthetic biology platform for cancer therapy. Full article

Host factors play critical roles in viral IRES-mediated translation by modulating the efficiency and specificity of viral protein synthesis. In this study, we used small interfering RNA (siRNA) treatment to silence and plasmid-based expression to overexpress PKD1L3 and USP31. Silencing PKD1L3 and USP31 suppressed IRES activity in FMDV and CSFV RNAs, whereas the overexpression of PKD1L3 did not have a significant effect, and USP31 overexpression resulted in only a modest increase in CSFV-IRES activity. Silencing PKD1L3 significantly reduced EMCV-IRES activity but had no significant effect on HCV- or DENV-IRES activity, and silencing USP31 had no significant effect on the activities of these three IRESs. Notably, the combined overexpression of PKD1L3 and USP31 significantly suppressed HCV-IRES activity, suggesting potential context-dependent interactions. These findings indicated that PKD1L3 and USP31 contribute more prominently to CSFV-, FMDV-, and EMCV-IRES-mediated translation than to HCV- or DENV-IRES-driven translation. Collectively, our results provide new insights into the host factors involved in IRES-mediated viral translation, establish a foundation for future in vivo studies to elucidate the specific roles of PKD1L3 and USP31 during viral infection, and indicate potential strategies for mitigating these viruses. Full article

RNA therapy appears to be a promising strategy to treat various diseases. In recent years, mRNA vaccines have shown notable efficacy in preclinical studies for cancer vaccines, autoimmune disease, and pandemic intervention. Internal ribosome entry sites (IRESs) are structured RNA elements to initiate translation independent of 5-cap recognition of mRNA, particularly show efficient activity under disease stress that causes global canonical translation repression. Studies on distinct structural properties and interaction with translational factors have revealed the mechanisms and regulation of IRES-mediated translation. This allowed the application of IRES for cap-independent translation and dynamic modulation of protein expression in response to cell signals. In this review, we discuss the current platforms and emerging strategies for employing IRES-mediated translation towards novel RNA therapeutics. Full article

Positive (+) sense RNA viruses include many important pathogens that exploit noncanonical translation mechanisms to express their genomes within the host cells. Unlike DNA or negative (−) sense RNA viruses, (+) sense RNA viruses can directly function as mRNAs, even though they lack typical features of host mRNAs, such as the 5′ cap structure required for canonical translation initiation. Instead, they exploit structured RNA elements to recruit host translational machinery without the 5′ cap, bypassing the canonical translation initiation mechanism. Prominent examples include internal ribosome entry sites (IRESs) and 3′ cap-independent translation enhancers (3′ CITEs). These RNA modules facilitate translation initiation by recruiting the ribosomal subunits, either directly or through initiation factors, and mediating long-range RNA-RNA interactions. Other regulatory motifs, such as frameshifting signals, allow the ribosome to shift reading frames to regulate protein output. All these RNA elements function through RNA-protein interactions and often utilize host and virus-encoded proteins to hijack the host’s translational apparatus. Over the past several years, various structural biology approaches, including biochemical and enzymatic probing, X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and cryogenic electron microscopy (cryo-EM), have revealed the unique structural roles of these viral RNA elements and their protein complexes. Although a few structures of IRES and CITE domains have been solved through these methods, the structures of these RNA elements and their structure-function relationship have remained largely unknown. This review discusses the current understanding of translation-related RNA structures in (+) sense RNA viruses, the critical RNA-protein interactions they mediate, and various structural biology approaches used to study them. Since the genome of these viruses serves as a template for two mutually exclusive virological processes, namely genome translation and replication, the review also discusses how viruses can utilize RNA structure-based strategies to regulate the switch between genome translation and replication, highlighting future directions for exploring these fundamental virological processes to develop antiviral therapeutics able to combat diseases caused by these pathogens. Full article

Porcine Reproductive and Respiratory Syndrome (PRRS) causes significant economic losses in the swine industry. Circular RNAs (circRNAs), a class of stable non-coding RNAs, are increasingly recognized as regulators in immune responses and host–virus interactions. This study investigated the genome-wide circRNA responses in porcine alveolar macrophages (PAMs), key cell targets of PRRSV, following treatment with a modified live virus (MLV) vaccine or two interferon (IFN) subtypes (IFN-α1, IFN-ω5). Using RNA sequencing, we identified over 1000 differentially expressed circRNAs across treatment groups, revealing both conserved and distinct expression profiles. Gene Ontology and KEGG pathway analyses indicated that circRNA-associated genes are significantly enriched in immune-related processes and pathways, including cytokine signaling and antiviral defense. Notably, IFN-ω5 treatment induced a pronounced circRNA response, aligning with its potent antiviral activity. We further explored the regulatory potential of these circRNAs by predicting miRNA binding sites, revealing complex circRNA-miRNA interaction networks. Additionally, we assessed the coding potential of differentially expressed circRNAs by identifying open reading frames (ORFs), internal ribosome entry sites (IRESs), and N6-methyladenosine (m⁶A) modification sites, suggesting a subset may undergo non-canonical translation. These findings provide a comprehensive landscape of circRNA expression in PAMs under different antiviral conditions, highlighting their potential roles as immune regulators and novel players in interferon-mediated antiviral responses, particularly downstream of IFN-ω5. This work contributes to understanding the non-coding RNA landscape in the PRRSV-swine model and suggests circRNAs as potential targets for future antiviral strategies. Full article

The tumor microenvironment creates strong stress conditions, including hypoxia and nutrient depletion, which cause the blocking of cap-dependent translation. Under stressful conditions, cancer cells exploit the cap-independent translation mechanism mediated by internal ribosome entry site (IRES), which ensures continued protein synthesis. IRES elements located in the 5′ untranslated regions of specific mRNAs allow selective translation of key anti-apoptotic and adaptive proteins. These proteins promote cellular processes that sustain cell survival, among them metabolic reprogramming, redox balance, and epithelial-to-mesenchymal transition, thus facilitating tumor progression and therapy resistance. IRES activity is dynamically regulated by IRES trans-acting factors, such as YB-1, PTB, and hnRNPA1, which respond to cellular stress by enhancing translation of crucial mRNAs. Emerging therapeutic strategies include pharmacological IRES inhibitors, RNA-based approaches targeting ITAF interactions, and IRES-containing vectors for controlled therapeutic gene expression. A deeper understanding of translational reprogramming, IRES structural diversity, and ITAF function is essential to develop targeted interventions to overcome therapeutic resistance and eliminate persistent tumor cell populations. Full article