SRSF3 facilitates replication of influenza A virus via binding and promoting the transport of viral mRNA

Host-specific SRSF7 regulates polymerase activity and replication of influenza A virus

Avian influenza viruses crossing the host barrier to infect humans have caused great panic in human society and seriously threatened public health. Herein, we revealed that knockdown of SRSF7 significantly down-regulated influenza virus titers and viral protein expression. We further observed for the first time that human SRSF7, but not avian SRSF7, significantly inhibited polymerase activity (PB2627E). Molecular mapping demonstrated that amino acids 206 to 228 of human SRSF7 play a decisive role in regulating the polymerase activity, which contains the amino acid motif absent in avian SRSF7. Importantly, our results illustrated that the PB2627K-encoding influenza virus induces SRSF7 protein degradation more strongly via the lysosome pathway and not via the proteasome pathway. Functional enrichment analysis of SRSF7-related KEGG pathways indicated that SRSF7 is closely related to cell growth and death. Lastly, our results showed that knocking down SRSF7 interferes with normal polymerase activity. Taken together, our results advance our understanding of interspecies transmission and our findings point out new targets for the development of drugs preventing or treating influenza virus infection.

Illuminating the pathogenic role of SARS-CoV-2: Insights into competing endogenous RNAs (ceRNAs) regulatory networks

The appearance of SARS-CoV-2 in 2019 triggered a significant economic and health crisis worldwide, with heterogeneous molecular mechanisms that contribute to its development are not yet fully understood. Although substantial progress has been made in elucidating the mechanisms behind SARS-CoV-2 infection and therapy, it continues to rank among the top three global causes of mortality due to infectious illnesses. Non-coding RNAs (ncRNAs), being integral components across nearly all biological processes, demonstrate effective importance in viral pathogenesis. Regarding viral infections, ncRNAs have demonstrated their ability to modulate host reactions, viral replication, and host-pathogen interactions. However, the complex interactions of different types of ncRNAs in the progression of COVID-19 remains understudied. In recent years, a novel mechanism of post-transcriptional gene regulation known as "competing endogenous RNA (ceRNA)" has been proposed. Long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), and viral ncRNAs function as ceRNAs, influencing the expression of associated genes by sequestering shared microRNAs. Recent research on SARS-CoV-2 has revealed that disruptions in specific ceRNA regulatory networks (ceRNETs) contribute to the abnormal expression of key infection-related genes and the establishment of distinctive infection characteristics. These findings present new opportunities to delve deeper into the underlying mechanisms of SARS-CoV-2 pathogenesis, offering potential biomarkers and therapeutic targets. This progress paves the way for a more comprehensive understanding of ceRNETs, shedding light on the intricate mechanisms involved. Further exploration of these mechanisms holds promise for enhancing our ability to prevent viral infections and develop effective antiviral treatments.

Circular RNA hsa_circ_0050386 suppresses non-small cell lung cancer progression via regulating the SRSF3/FN1 axis

BACKGROUND

Lung cancer is the most prevalent cancer worldwide, with non-small cell lung cancer (NSCLC) accounting for 85% of all cases. Circular RNAs(circRNA) play crucial roles in regulating the progression of lung cancer. Despite the identification of a large number of circRNAs, their expression patterns, functions, and mechanisms of action in NSCLC development remain unclear.This study aims to investigate the transcriptional expressions, functions, and potential mechanisms of circRNA hsa_circ_0050386 in NSCLC.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was utilized for the analysis of hsa_circ_0050386 expression. Cell proliferation was detected using the IncuCyte Live Cell Analysis System and clone formation assays. Migration and invasion of NSCLC cells were evaluated through Transwell assays. Flow cytometry was performed to assay cell cycle and apoptosis. Western blot was used to investigate protein expression. Protein binding analysis was conducted by employing pull-down assays, RNA immunoprecipitation (RIP), and mass spectrometry. The role of hsa_circ_0050386 in vivo was evaluated through the use of a xenograft model.

RESULTS

The study discovered that hsa_circ_0050386 displayed lower expression levels in NSCLC tissues when compared to adjacent normal tissues. Patients exhibiting lower levels of hsa_circ_0050386 expression exhibited an inverse correlation with the Clinical Stage, T-stage, and M-stage of NSCLC. Functionally, hsa_circ_0050386 suppressed the proliferation and invasion of NSCLC cells both in vitro and in vivo. A comprehensive examination exposed the interaction between hsa_circ_0050386 and RNA binding protein Serine and arginine-rich splicing factor 3 (SRSF3), resulting in the down-regulation of Fibronectin 1 (FN1) expression, which inhibits the progression of NSCLC.

CONCLUSIONS

Our study shows that hsa_circ_0050386 suppresses the malignant biological behavior of NSCLC cells by down-regulating the expression of FN1, and may serve as a potential biomarker and therapeutic target for NSCLC treatment.

Serine-arginine protein kinases and their targets in viral infection and their inhibition

Accumulating evidence has consolidated the interaction between viral infection and host alternative splicing. Serine-arginine (SR) proteins are a class of highly conserved splicing factors critical for the spliceosome maturation, alternative splicing and RNA metabolism. Serine-arginine protein kinases (SRPKs) are important kinases that specifically phosphorylate SR proteins to regulate their distribution and activities in the central pre-mRNA splicing and other cellular processes. In addition to the predominant SR proteins, other cytoplasmic proteins containing a serine-arginine repeat domain, including viral proteins, have been identified as substrates of SRPKs. Viral infection triggers a myriad of cellular events in the host and it is therefore not surprising that viruses explore SRPKs-mediated phosphorylation as an important regulatory node in virus-host interactions. In this review, we briefly summarize the regulation and biological function of SRPKs, highlighting their involvement in the infection process of several viruses, such as viral replication, transcription and capsid assembly. In addition, we review the structure-function relationships of currently available inhibitors of SRPKs and discuss their putative use as antivirals against well-characterized viruses or newly emerging viruses. We also highlight the viral proteins and cellular substrates targeted by SRPKs as potential antiviral therapeutic candidates.

Nonmuscle myosin IIA promotes the internalization of influenza A virus and regulates viral polymerase activity through interacting with nucleoprotein in human pulmonary cells

Influenza A virus (IAV), responsible for seasonal epidemics and recurring pandemics, represents a global threat to public health. Given the risk of a potential IAV pandemic, it is increasingly important to better understand virus-host interactions and develop new anti-viral strategies. Here, we reported nonmuscle myosin IIA (MYH9)-mediated regulation of IAV infection. MYH9 depletion caused a profound inhibition of IAV infection by reducing viral attachment and internalization in human lung epithelial cells. Surprisingly, overexpression of MYH9 also led to a significant reduction in viral productive infection. Interestingly, overexpression of MYH9 retained viral attachment, internalization, or uncoating, but suppressed the viral ribonucleoprotein (vRNP) activity in a minigenome system. Further analyses found that excess MYH9 might interrupt the formation of vRNP by interacting with the viral nucleoprotein (NP) and result in the reduction of the completed vRNP in the nucleus, thereby inhibiting subsequent viral RNA transcription and replication. Together, we discovered that MYH9 can interact with IAV NP protein and engage in the regulation of vRNP complexes, thereby involving viral replication. These findings enlighten new mechanistic insights into the complicated interface of host-IAV interactions, ultimately making it an attractive target for the generation of antiviral drugs.

TREX (transcription/export)-NP complex exerts a dual effect on regulating polymerase activity and replication of influenza A virus

Influenza A viruses effectively hijack the intracellular "resources" to complete transcription and replication, which involve extensive interactions between the viral and host proteins. Herein, we screened the host factors, which belong to DExD/H-box protein family members, RNA-binding proteins or mitochondrial anchoring proteins, to investigate their effects on polymerase activity. We observed DDX39B and DDX39A, DEAD-box RNA-Helicases, exert a dual effect on regulating polymerase activity and replication of influenza A viruses. We further revealed that DDX39B and DDX39A interact with viral NP and NS1 proteins. Interestingly, the viral NP proteins could reverse the inhibitory effect of excess DDX39B or DDX39A on polymerase activity. Mechanistically, the TREX complex subunits, THOC1, THOC4 and CIP29, were recruited to DDX39B-DDX39A-NP complex in an ATP-dependent manner, via the interaction with DDX39B or DDX39A, followed by excess TREX-NP complexes interfere with the normal oligomerization state of NP depending on the ratio between the viral and host proteins. On the other hand, the TREX complex, an evolutionarily conserved protein complex, is responsible for the integration of several mRNA processing steps to export viral mRNA. Knockdown of TREX complex subunits significantly down-regulated viral titers and protein levels, accompanied by retention of viral mRNA in the nucleus. Taken together, screening the host factors that regulate the replication of influenza virus advances our understanding of viral pathogenesis and our findings point out a previously unclear mechanism of TREX complex function.

In this study, we investigated the regulation of polymerase activity by host factors associated with vRNPs (PB2₆₂₇E, PB2₆₂₇K, PB2₆₂₇ domain del, PB2₆₂₇ CON) and provided novel insights into regulatory mechanisms of DDX39B and DDX39A during viral replication. Our results demonstrated that DDX39B and its paralog DDX39A inhibited polymerase activity via forming TREX-NP complex with concomitant effects on the oligomeric state of NP proteins. Moreover, TREX complex is necessary for expression of viral proteins. Our findings provided potential therapeutic targets for dealing with IAV infection.

DDX5/METTL3-METTL14/YTHDF2 Axis Regulates Replication of Influenza A Virus

DEAD-box helicase 5 (DDX5), a member of the DEAD/H-box helicases, is known to participate in all aspects of RNA metabolism. However, its regulatory effect in antiviral innate immunity during replication of influenza virus remains unclear. Herein, we found that human DDX5 promotes replication of influenza virus in A549 cells. Moreover, our results further revealed that DDX5 relies on its N terminus to interact with the nucleoprotein (NP) of influenza virus, which is independent of RNA. Of course, we also observed colocalization of DDX5 with NP in the context of transfection or infection. However, influenza virus infection had no significant effect on the protein expression and nucleocytoplasmic distribution of DDX5. Importantly, we found that DDX5 suppresses antiviral innate immunity induced by influenza virus infection. Mechanistically, DDX5 downregulated the mRNA levels of interferon beta (IFN-β), interleukin 6 (IL-6), and DHX58 via the METTL3-METTL14/YTHDF2 axis. We revealed that DDX5 bound antiviral transcripts and regulated immune responses through YTHDF2-dependent mRNA decay. Taken together, our data demonstrate that the DDX5/METTL3-METTL14/YTHDF2 axis regulates the replication of influenza A virus. IMPORTANCE The replication and transcription of influenza virus depends on the participation of many host factors in cells. Exploring the relationship between viruses and host factors will help us fully understand the characteristics and pathogenic mechanisms of influenza viruses. In this study, we showed that DDX5 interacted with the NP of influenza virus. We demonstrated that DDX5 downregulated the expression of IFN-β and IL-6 and the transcription of antiviral genes downstream from IFN-β in influenza virus-infected A549 cells. Additionally, DDX5 downregulated the mRNA levels of antiviral transcripts via the METTL3-METTL14/YTHDF2 axis. Our findings provide a novel perspective to understand the mechanism by which DDX5 regulates antiviral immunity.

ARNT Inhibits H5N1 Influenza A Virus Replication by Interacting with the PA Protein

Increasing evidence suggests that the polymerase acidic (PA) protein of influenza A viruses plays an important role in viral replication and pathogenicity. However, information regarding the interaction(s) of host factors with PA is scarce. By using a yeast two-hybrid screen, we identified a novel host factor, aryl hydrocarbon receptor nuclear translocator (ARNT), that interacts with the PA protein of the H5N1 virus. The interaction between PA and human ARNT was confirmed by co-immunoprecipitation and immunofluorescence microscopy. Moreover, overexpression of ARNT downregulated the polymerase activity and inhibited virus propagation, whereas knockdown of ARNT significantly increased the polymerase activity and virus replication. Mechanistically, overexpression of ARNT resulted in the accumulation of PA protein in the nucleus and inhibited both the replication and transcription of the viral genome. Interaction domain mapping revealed that the bHLH/PAS domain of ARNT mainly interacted with the C-terminal domain of PA. Together, our results demonstrate that ARNT inhibits the replication of the H5N1 virus and could be a target for the development of therapeutic strategies against H5N1 influenza viruses.