MicroRNA-21-3p modulates FGF2 to facilitate influenza A virus H5N1 replication by refraining type I interferon response

Virus versus host: influenza A virus circumvents the immune responses

Influenza A virus (IAV) is a highly contagious pathogen causing dreadful losses to humans and animals around the globe. As is known, immune escape is a strategy that benefits the proliferation of IAVs by antagonizing, blocking, and suppressing immune surveillance. The HA protein binds to the sialic acid (SA) receptor to enter the cytoplasm and initiate viral infection. The conserved components of the viral genome produced during replication, known as the pathogen-associated molecular patterns (PAMPs), are thought to be critical factors for the activation of effective innate immunity by triggering dependent signaling pathways after recognition by pattern recognition receptors (PRRs), followed by a cascade of adaptive immunity. Viral infection-induced immune responses establish an antiviral state in the host to effectively inhibit virus replication and enhance viral clearance. However, IAV has evolved multiple mechanisms that allow it to synthesize and transport viral components by "playing games" with the host. At its heart, this review will describe how host and viral factors interact to facilitate the viral evasion of host immune responses.

Micro-Players of Great Significance-Host microRNA Signature in Viral Infections in Humans and Animals

Over time, more and more is becoming known about micro-players of great significance. This is particularly the case for microRNAs (miRNAs; miR), which have been found to participate in the regulation of many physiological and pathological processes in both humans and animals. One such process is viral infection in humans and animals, in which the host miRNAs—alone or in conjunction with the virus—interact on two levels: viruses may regulate the host’s miRNAs to evade its immune system, while the host miRNAs can play anti- or pro-viral roles. The purpose of this comprehensive review is to present the key miRNAs involved in viral infections in humans and animals. We summarize the data in the available literature, indicating that the signature miRNAs in human viral infections mainly include 12 miRNAs (i.e., miR-155, miR-223, miR-146a, miR-122, miR-125b, miR-132, miR-34a, miR -21, miR-16, miR-181 family, let-7 family, and miR-10a), while 10 miRNAs are commonly found in animals (i.e., miR-155, miR-223, miR-146a, miR-145, miR-21, miR-15a/miR-16 cluster, miR-181 family, let-7 family, and miR-122) in this context. Knowledge of which miRNAs are involved in different viral infections and the biological functions that they play can help in understanding the pathogenesis of viral diseases, facilitating the future development of therapeutic agents for both humans and animals.

Host Non-Coding RNA Regulates Influenza A Virus Replication

Outbreaks of influenza, caused by the influenza A virus (IAV), occur almost every year in various regions worldwide, seriously endangering human health. Studies have shown that host non-coding RNA is an important regulator of host-virus interactions in the process of IAV infection. In this paper, we comprehensively analyzed the research progress on host non-coding RNAs with regard to the regulation of IAV replication. According to the regulation mode of host non-coding RNAs, the signal pathways involved, and the specific target genes, we found that a large number of host non-coding RNAs directly targeted the PB1 and PB2 proteins of IAV. Nonstructural protein 1 and other key genes regulate the replication of IAV and indirectly participate in the regulation of the retinoic acid-induced gene I-like receptor signaling pathway, toll-like receptor signaling pathway, Janus kinase signal transducer and activator of transcription signaling pathway, and other major intracellular viral response signaling pathways to regulate the replication of IAV. Based on the above findings, we mapped the regulatory network of host non-coding RNAs in the innate immune response to the influenza virus. These findings will provide a more comprehensive understanding of the function and mechanism of host non-coding RNAs in the cellular anti-virus response as well as clues to the mechanism of cell-virus interactions and the discovery of antiviral drug targets.

Functional Roles of Non-coding RNAs in the Interaction Between Host and Influenza A Virus

Non-coding RNAs (ncRNAs) are extensively expressed in various cells and tissues, and studies have shown that ncRNAs play significant roles in cell regulation. However, in the past few decades, the knowledge of ncRNAs has been increased dramatically due to their transcriptional ability and multiple regulatory functions. Typically, regulatory ncRNAs include long ncRNAs (lncRNAs), miRNAs, piRNAs, Y RNAs, vault RNAs, and circular RNAs (circRNAs), etc. Previous studies have revealed that various ncRNAs are involved in the host responses to virus infection and play critical roles in the regulation of host-virus interactions. In this review, we discuss the conceptual framework and biological regulations of ncRNAs to elucidate their functions in response to viral infection, especially influenza A virus (IAV) infection. In addition, we summarize the ncRNAs that are associated with innate immunity and involvement of interferons and their stimulated genes (ISGs) during IAV infection.

Downregulation of microRNA‑221 facilitates H1N1 influenza A virus replication through suppression of type‑IFN response by targeting the SOCS1/NF‑κB pathway

Accumulating data has indicated that host microRNAs (miRNAs/miRs) play essential roles in innate immune responses to viral infection; however, the roles and the underlying mechanisms of miRNAs in influenza A virus (IAV) replication remain unclear. The present study examined on the effects of miRNAs on hemagglutinin (H)1 neuraminidase (N)1 replication and antiviral innate immunity. Using a microarray assay, the expression profiles of miRNA molecules in IAV-infected A549 cells were analyzed. The results indicated that miR-221 was significantly downregulated in IAV-infected A549 cells. It was also observed that IAV infection decreased the expression levels of miR-221 in A549 cells in a dose- and time-dependent manner. Functionally, upregulation of miR-221 repressed IAV replication, whereas knockdown of miR-221 had an opposite effect. Subsequently, it was demonstrated that miR-221 overexpression could enhance IAV-triggered IFN-α and IFN-β production and IFN-stimulated gene expression levels, while miR-221-knockdown had the opposite effect. Target prediction and dual luciferase assays indicated that suppressor of cytokine signaling 1 (SOCS1) was a direct target of miR-221 in A549 cells. Furthermore, knockdown of SOCS1 efficiently abrogated the influences caused by miR-221 inhibition on IAV replication and the type-I IFN response. It was also found that the miR-221 positively regulated NF-κB activation in IAV-infected A549 cells. Taken together, these data suggested that miR-221-downregulation promotes IAV replication by suppressing type-I IFN response through targeting SOCS1/NF-κB pathway. These findings suggest that miR-221 may serve as a novel potential therapeutic target for IAV treatment.

Circular RNA circPIKfyve acts as a sponge of miR-21-3p to enhance antiviral immunity through regulating MAVS in teleost fish

Circular RNAs (circRNAs) are a class of widespread and diverse covalently closed circular endogenous RNAs that exert crucial functions in regulating gene expression in mammals. However, the function and regulation mechanism of circRNAs in lower vertebrates are still unknown. Here, we discovered a novel circRNA derived from PIKfyve, named circPIKfyve, that is related to the antiviral responses in teleost fish. The results showed that circPIKfyve plays essential roles in host antiviral immunity and inhibition of SCRV replication. Moreover, we also found that the antiviral effect inhibited by miR-21-3p could be reversed with the addition of circPIKfyve. In mechanism, our data revealed that circPIKfyve is a competitive endogenous RNA (ceRNA) of MAVS by sponging miR-21-3p, leading to activation of NF-κB/IRF3 pathway, which then enhance the innate antiviral responses. In addition, we firstly found that RNA binding protein QKI is involved in the formation and regulation of circPIKfyve. Our results provided a strong basis that circRNAs to play a regulatory role in antiviral immune responses in teleost fish.Importance: Here, we identified a novel circRNA, namely, circPIKfyve, that can act as a key regulator of the innate immune response in teleost fish. circPIKfyve acts as a molecular sponge by competitive adsorbing of miR-21-3p, thereby increasing the abundance of MAVS and activating the downstream NF-κB/IRF3 pathway to enhance the antiviral response. In addition, this study was the first to find that QKI protein is involved in regulating the formation of circPIKfyve in fish. The overall results of this study suggest that circPIKfyve plays an active regulatory role in the antiviral immune response of teleost fish.

The Importance of miRNA Identification During Respiratory Viral Infections

The expression of small non-coding RNA MicroRNAs (miRNAs) during respiratory viral infections is of critical importance as they are implicated in the viral replication, immune responses and severity of disease pathogenesis. Respiratory viral infections have an extensive impact on human health across the globe. For that is essential to understand the factors that regulate the host response against infections. The differential miRNA pattern induced by respiratory viruses has been reported, including include influenza A virus (IAV), human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), adenovirus (AdV), and more recently, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. In this commentary, we highlight the importance of miRNAs identification and the contribution of these molecules in the modulation of the immune response through the upregulation and downregulation of miRNAs expression in different immune and non-immune cells.

MiR-4334-5p Facilitates Foot and Mouth Disease Virus Propagation by Suppressing Interferon Pathways via Direct Targeting ID1

Emerging evidence indicates that the host microRNAs (miRNAs) are important intracellular regulators and play pivotal roles in intricate host-pathogen interaction networks. In our previous studies, ssc-microRNA-4334-5p (miR-4334-5p) was identified as a differentially expressed miRNA in microarray-based miRNAs profiling experiment, but whether miR-4334-5p regulates foot and mouth disease virus (FMDV) propagation is less understood. Here, we demonstrated that miR-4334-5p expression level was up-regulated shortly after FMDV infection, transfection of miR-4334-5p mimics promoted, while inhibitor transfection suppressed FMDV replication correspondingly. Further bioinformatic analysis and experimental study suggested ID1 was the direct target of miR-4334-5p, suppressing FMDV replication by regulating interferon (IFN) pathways. These findings shed light on microRNAs-ID1-interferon axis in regulating FMDV replication.