Coronaviruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for the coronavirus disease 2019 (COVID-19) pandemic, present a significant threat to human health by inflicting a wide variety of health complications and even death. While conventional therapeutics often involve administering small molecules to fight viral infections, small non-coding RNA sequences, known as microRNAs (miRNAs/miR-), may present a novel antiviral strategy. We can take advantage of their ability to modulate host–virus interactions through mediating RNA degradation or translational inhibition. Investigations into miRNA and SARS-CoV-2 interactions can reveal novel therapeutic approaches against this virus. The viral genomes of SARS-CoV-2, severe acute respiratory syndrome coronavirus (SARS-CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV) were searched using the Nucleotide Basic Local Alignment Search Tool (BLASTn) for highly similar sequences, to identify potential binding sites for miRNAs hypothesized to play a role in SARS-CoV-2 infection. miRNAs that target angiotensin-converting enzyme 2 (ACE2), the receptor used by SARS-CoV-2 and SARS-CoV for host cell entry, were also predicted. Several relevant miRNAs were identified, and their potential roles in regulating SARS-CoV-2 infections were further assessed. Current treatment options for SARS-CoV-2 are limited and have not generated sufficient evidence on safety and efficacy for treating COVID-19. Therefore, by investigating the interactions between miRNAs and SARS-CoV-2, miRNA-based antiviral therapies, including miRNA mimics and inhibitors, may be developed as an alternative strategy to fight COVID-19.

Edited by Charles E. SamuelUpon immune recognition of viruses, the mammalian innate immune response activates a complex signal transduction network to combat infection. This activation requires phosphorylation of key transcription factors regulating IFN production and signaling, including IFN regulatory factor 3 (IRF3) and STAT1.ThemechanismsregulatingtheseSTAT1andIRF3phosphorylation events remain unclear. Here, using human and mouse cell lines along with gene microarrays, quantitative RT-PCR, viral infection and plaque assays, and reporter gene assays, we demonstrate that a microRNA cluster conserved among bilaterian animals, encoding miR-96, miR-182, and miR-183, regulates IFN signaling. In particular, we observed that the miR-183 cluster promotes IFN production and signaling, mediated by enhancing IRF3 and STAT1 phosphorylation. We also found that the miR-183 cluster activates the IFN pathway and inhibits vesicular stomatitis virus infection by directly targeting several negative regulators of IRF3 and STAT1 activities, including protein phosphatase 2A (PPP2CA) and tripartite motif-containing 27 (TRIM27). Overall, our work reveals an important role of the evolutionarily conserved miR-183 cluster in the regulation of mammalian innate immunity.

SummaryMicroRNAs (miRNAs) are part of a complex regulatory network that modulates cellular lipid metabolism. Here, we identify miR-124 as a regulator of triglyceride (TG) metabolism. This study advances our knowledge of the role of miR-124 in human hepatoma cells. Transcriptional profiling of Huh7.5 cells overexpressing miR-124 reveals enrichment for host factors involved in fatty acid oxidation among repressed miRNA targets. In addition, miR-124 down-regulates arylacetamide deacetylase (AADAC) and adipose triglyceride lipase, lipases proposed to mediate breakdown of hepatic TG stores for lipoprotein assembly and mitochondrial β-oxidation. Consistent with the inhibition of TG and fatty acid catabolism, miR-124 expression promotes cellular TG accumulation. Interestingly, miR-124 inhibits the production of hepatitis C virus, a virus that hijacks lipid pathways during its life cycle. Antiviral activity of miR-124 is consistent with repression of AADAC, a pro-viral host factor. Overall, our data highlight miR-124 as a novel regulator of TG metabolism in human hepatoma cells.

Endogenously expressed noncoding RNAs are regulators of mRNA translation and affect diverse biological pathways spanning embryogenesis to cholesterol and fatty acid metabolism. Recently, microRNAs have become an important therapeutic target with strategies that employ oligonucleotides as both mimics and inhibitors of target microRNAs, successfully altering gene expression and cellular pathways in relevant contexts. However, delivery of these exogenous effectors remains a major challenge. Here, we present a method for evaluating noncoding RNA delivery using the viral suppressor of RNA silencing (VSRS) protein p19, optimized for cellular delivery of small RNAs. Using genetic code expansion technology, p-azidophenylalanine (AzF) was incorporated into a recombinant p19 protein and used to develop a fluorescence resonance energy transfer (FRET) sensor. AzF was used to attach FRET acceptor moieties using bioorthogonal chemistry. We show that this strategy not only gives rise to FRET signals that report on small RNA binding, but also allows for fluorescence quenching as well, convenient for measuring RNA release. We demonstrate the successful use of a modified version of the probe to track the delivery and release of small RNAs into mammalian cells. The results provide a basis for a further development of vehicles for small RNA delivery and release for intervening in noncoding RNA biology.

Recently, microRNAs (miRNAs), as endogenous noncoding RNAs that inhibit mRNA translation, have been identified to broadly possess functional roles in regulating cellular signaling and metabolic processes due to their chemical and biological properties. In addition, they have emerged to be of critical importance in modulating host−virus interactions, especially for RNA viruses. Herein, we discovered that miR-383-5p targets certain lipid and cholesterol biosynthetic pathways and restricts Dengue virus (DENV) infection in hepatic cells. Global transcriptomics analysis of Huh7 human hepatoma cells overexpressing miR-383-5p revealed enrichment of lipid and cholesterol metabolic processes. Bioinformatics analysis of genes repressed in miR-383-5p overexpressing cells divulged the repression of a key target PLA2G4A, a pro-viral host factor essential for the production of infectious DENV particles. Our study demonstrated the effectiveness of miRNA mimics as tools to study cellular signaling pathways that contribute to viral pathogenesis. Overall, our study identifies miR-383-5p as an interesting host factor during DENV propagation and highlights a potential therapeutic role in the regulation of hepatic lipid metabolism and an antiviral response to DENV.