Coronavirus replication is regulated by both host and viral RNA N6–methyladenosine modifications
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ABSTRACT: N6–methyladenosine (m6A) is the most abundant internal mRNA modification in eukaryotes, and it plays an important role in RNA metabolism and function. Recent studies have revealed that viral RNA m6A modification can play an anti-viral or pro-viral role depending on the virus. However, whether m6A methylation can modulate replication of coronaviruses, which cause some severe human and animal diseases such as Coronavirus Disease 2019 (COVID-19), remains unknown. Here, we determined that m6A modifications of porcine epidemic diarrhea coronavirus (PEDV) are exclusively located in the N gene at the 3’-end of the genome, and that PEDV infection alters the expression pattern of some host proteins involved in m6A modification. Depletion of m6A demethylases significantly increased PEDV replication and gene expression whereas knockdown of m6A methyltransferases slightly decreased PEDV infection. Interestingly, m6A binding proteins YTHDF 2 and 3 significantly inhibited PEDV replication whereas YTHDF1 has the opposite effect. When the major m6A sites in the N gene were mutated, the resultant recombinant PEDVs and PEDV replicons had a significant increase in replication and gene expression. This study illustrates that (i) addition of m6A to PEDV RNA inhibits viral replication, and (ii) both host and viral m6A machinery regulate coronavirus replication.
Project description:N6–methyladenosine (m6A) is the most abundant internal mRNA modification in eukaryotes, and it plays an important role in RNA metabolism and function. Recent studies have revealed that viral RNA m6A modification can play an anti-viral or pro-viral role in virus life cycle. However, whether m6A methylation can modulate replication of coronaviruses, which contain the largest known RNA genomes, remains elusive. Here, we determined that m6A modifications of porcine epidemic diarrhea coronavirus (PEDV) are exclusively located in the N gene at the 3’-end of genome, and that PEDV infection alters the expression pattern of host proteins involved in m6A modification. Depletion of m6A demethylases significantly increased PEDV replication and gene expression whereas knockdown of m6A methyltransferases slightly decreased PEDV infection. Interestingly, m6A binding proteins YTHDF 2 and 3 significantly inhibited PEDV replication whereas YTHDF1 has an opposite effect. When the major m6A sites in the N gene were mutated, the resultant recombinant PEDVs and PEDV replicons had a significant increase in replication and gene expression. This study illustrates that (i) addition of m6A to PEDV RNA inhibits viral replication, and (ii) both host and viral m6A machinery regulates coronavirus replication.
Project description:Swine coronavirus-porcine epidemic diarrhea virus (PEDV) with specific susceptibility to pigs has existed for decades, and recurrent epidemics caused by mutant strains have swept the world again since 2010. Here, single-cell RNA-sequencing was used to perform a systematic analysis of pig small intestines infected with PEDV for the first time. Multiple cell types were identified by representative markers, including the unique marker DNAH11 of tuft cells. Meanwhile, the goblet and tuft cells were also susceptible to PEDV except enterocytes. PEDV infection obviously upregulated REG3G, which significantly inhibited virus replication. Notably, IFN-DELTAs in goblet and enterocyte progenitor cells were increased in virus infected piglet, and IFN-DELTA5 could induce GBP1, ISG15, OAS2 and IFITM1 dramatically raised in IPEC-J2 cells and restricted PEDV replication. Complement molecules were mainly expressed in intestinal cells excepting tuft cells, but PEDV decreased C3, C4A, and C5 in enterocytes, thus escaping the antiviral effect of C3. Finally, enterocytes expressed almost all coronavirus entry factors, and PEDV infection caused significant upregulation of the coronavirus receptor ACE2 in porcine enterocyte cells. In summary, this study systematically studied the response of different cell types in small intestine of pigs after PEDV infection, which deepened the understanding of viral pathogenesis.
Project description:Porcine epidemic diarrhea virus (PEDV) is a deadly coronavirus for neonatal piglets and no effective vaccines are available. Transcriptional regulatory sequences (TRSs) are critical in regulating coronavirus discontinuous transcription. Also, TRSs contribute to a high recombination rate of coronaviruses, leading to difficulty in developing safe live vaccines. We hypothesize that recoding the TRS core sequences (TRS-CS) of PEDV can make the recombination impossible between the engineered vaccine virus and field strains or wildtype viruses. We used an infectious clone-derived reporter PEDV, dORF3-EGFP, as the backbone to generate a remodeled TRS (RMT) mutant that carries the recoded leader and body TRS-CSs. The RMT and dORF3-EGFP showed comparable replication efficiency in Vero cells. However, the incompatibility between the rewired and wildtype TRS-CSs led to few EGFP in RMT-infected cells. Furthermore, RMT and dORF3-EGFP had a similar attenuated phenotype, replication efficiency, and protective immunogenicity in neonatal pigs. RNA sequencing analysis indicated that EGFP transcription directed by the heterogenous TRS-CSs was significantly reduced to an extremely low level. Meanwhile, recombinant viruses were not detected in Vero cells and in pigs that were co-infected with RMT and a PEDV S-INDEL strain, Iowa106. In vitro and in vivo passaging of the RMT did not result in reversion mutations in the rewired TRS-CSs, introduced gaps, and disrupted wildtype TRSs. In summary, the RMT mutant was resistant to recombination and genetically stable and can be further optimized (e.g., deletion of the EGFP) to serve as a platform to develop safe PEDV live attenuated vaccines.
Project description:Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic virus that causes severe gastrointestinal disease in neonatal piglets, often leading to high mortality. To advance the study of viral pathogenesis, it is essential to develop an in vitro model that accurately replicates swine enteric coronavirus infections. In this study, we designed a porcine intestinal apical-out organoid culture system that supports viral replication while allowing for long-term culture and experimental manipulation. Using apical-out organoids derived from the duodenum, jejunum, and ileum, we examined region-specific gene expression profiles in response to PEDV infection. Bulk RNA sequencing revealed distinct gene expression patterns, highlighting the regional differences in intestinal physiology during infection. Differential gene expression analysis indicated that each intestinal segment activates specific signaling pathways related to cell survival and antiviral responses following PEDV infection. Functional analyses identified key pathways involved in cell development, signaling, apoptosis, and survival. This study elucidates the mechanisms underlying the differential responses of specific intestinal regions to PEDV, which may inform the selection of optimal models for future PEDV research. In summary, our systematic investigation into the responses of various small intestine segments following PEDV infection provides deeper insights into viral pathogenesis.
Project description:Porcine epidemic diarrhea virus (PEDV) causes severe intestinal damage and high mortality in neonatal piglets. The continuous emergence of new strains has brought new challenges to prevention and control. In this study, we isolated and characterized a prevalent PEDV virulent strain, and analyzed 19,612 jejunal cells from PEDV-infected and control piglets using single-cell sequencing, revealing significant changes in cellular composition, gene expression, and intercellular communication. In response to PEDV infection, epithelial repair was enhanced through increased proliferation and differentiation of stem cells, transit-amplifying (TA) cells, and intestinal progenitor cells into enterocytes. Additionally, PEDV disrupted intercellular communication, compromising epithelial functionality while triggering immune responses, with IFN-II and IL-10 signaling activation acting as critical regulators of immune balance and tissue homeostasis. Beyond enterocytes, viral genes were detected in various other cell types. Further experiments confirmed that PEDV could initiate replication in B and T lymphocytes but was unable to produce infectious progeny, with T cells additionally undergoing virus-induced apoptosis. These findings provide new insights into PEDV tropism, immune evasion, and epithelial repair, revealing complex host-pathogen interactions that shape disease progression and tissue regeneration, thereby contributing to a better understanding of enteric coronavirus pathogenesis.
Project description:N6-methyladenosine (m6A) exerts many of its regulatory effects on eukaryotic mRNAs by recruiting cytoplasmic YT521-B homology domain family (YTHDF) proteins. Here, we show that in Arabidopsis, the interaction between m6A and the major YTHDF protein ECT2 also involves the mRNA-binding ALBA protein family. ALBA and YTHDF proteins physically associate via a deeply conserved short linear motif in the intrinsically disordered region of YTHDF proteins, their mRNA targets overlap, and ALBA4 binding sites are juxtaposed to m6A sites. These binding sites correspond to pyrimidine-rich elements previously found to be important for m6A binding of ECT2. Accordingly, both biological effects of ECT2 and its binding to m6A targets in vivo require ALBA association. Our results introduce the YTHDF-ALBA complex as the functional cytoplasmic m6A-reader in plants and define a molecular foundation for the concept of facilitated m6A reading that increases the potential for combinatorial control of biological m6A effects.
Project description:Viruses employ various strategies to evade innate immunity. Despite many studies on host or viral gene expression, how the cellular proteome responds to internal or external cues, has not been fully investigated. Using a Hepatitis B Virus (HBV) replication model, we performed proteomic analyses of HBV-replicating cells in G1/S and G2/M phases, as a function of IFN-alpha, providing specific information of how HBV infection, in combination with IFN-alpha, alters the hepatocyte proteome. We identified the conserved LSm (Like-Sm1-8) proteins were differentially expressed as a function of HBV replication and IFN-alpha. Specifically, in G2/M, IFN-alpha increased protein level of LSm1, the unique subunit of cytoplasmic LSm1-7 complex involved in mRNA decay. By contrast, IFN-alpha decreased LSm8, the unique subunit of nuclear LSm2-8 complex, a chaperone of U6 spliceosomal RNA. These results suggest cytoplasmic LSm1-7 has antiviral role, whereas nuclear LSm2-8 complex is pro-viral. Employing HBV replication and infection models, siRNA-mediated knockdown of LSm1 increased the level of all viral RNAs. Conversely, knockdown of LSm8 reduced viral RNA levels, dependent on N6-adenosine methylation (m6A) of the epsilon stem-loop at the 5 end of pre-Core/pregenomic (preC/pg) RNA. Methylated RNA immunoprecipitation (MeRIP) assays demonstrated reduced viral RNA methylation upon LSm8 knockdown, dependent on the m6A modification, suggesting the LSm2-8 complex has a role in mediating this modification. Interestingly, splicing inhibitor Cp028 acting upstream of LSm2-8 complex, suppressed levels of viral RNAs without reducing the m6A modification. This observation suggests Cp028 has novel antiviral effects, likely potentiating IFN-alpha -mediated suppression of HBV biosynthesis.
Project description:N6-methyladenosine (m6A) is the most prevalent internal modification of mRNAs in most eukaryotes. Likewise, viral RNAs may acquire m6A methylation during replication within these cells. Here we show that RNAs of human respiratory syncytial virus (RSV), a medically important non-segmented negative-sense (NNS) RNA virus, are modified by m6A within discreet regions and that these modifications enhance viral replication and pathogenesis. Overexpression of m6A binding proteins significantly enhanced RSV replication and gene expression. Knockdown of m6A methyltransferases decreased viral replication and gene expression whereas knockdown of m6A demethylases had the opposite effect. The G gene contained the most abundant m6A modifications. Recombinant RSV expressing a G gene lacking different m6A sites, resulted in RSVs with various degrees of defects in replication in A549 cells, primary well differentiated human airway epithelial (HAE) cultures, upper and lower respiratory tract of cotton rats, and were also less pathogenic to the lungs of cotton rats. One of the m6A-deficient rgRSVs, rgRSV-G12, was completely attenuated yet retained high immunogenicity in cotton rats. Moreover, a small molecule that inhibits S-adenosyl-L-homocysteine (SAH) hydrolase, thereby reducing the cellular SAH pool and viral RNA m6A, also inhibited RSV replication in HAE cells. Collectively, our results demonstrate viral m6A methylation upregulates RSV replication and pathogenesis and identify viral m6A methylation as a target for rational design of live attenuated vaccine candidates and for novel antiviral therapeutic agents for RSV.
Project description:N6-methyladenosine (m6A) is the most abundant internal mRNA nucleotide modification in mammals, regulating critical aspects of cell physiology and differentiation. The YTHDF proteins are the primary readers of m6A modifications and exert physiological functions of m6A in the cytosol. Elucidating the regulatory mechanisms of YTHDF proteins is critical to understanding m6A biology. Here, we report a mechanism that protein post-translational modifications control the biological functions of the YTHDF proteins. We find that YTHDF1 and YTHDF3, but not YTHDF2, carry high levels of nutrient-sensing O-GlcNAc modifications. O-GlcNAc modification attenuates the translation promoting function of YTHDF1 and YTHDF3 by blocking their interactions with proteins associated with mRNA translation. We further demonstrate that O-GlcNAc modifications on YTHDF1 and YTHDF2 regulate the assembly, stability, and disassembly of stress granule, facilitating rapid exchange of m6A-modified mRNAs in stress granules for recovery from stress. Therefore, our results discover an important regulatory pathway of YTHDF functions, adding an additional layer of complexity to the post-transcriptional regulation function of mRNA m6A.
Project description:To deal with the broad spectrum of coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), that threatens human health, it is essential to develop not only drugs that target viral proteins but also consider drugs that target host proteins/cellular processes to protect them from being hijacked for viral infection and replication. To this end, it has been reported that autophagy is deeply involved in coronavirus infection. In this study, we used airway organoids to screen a chemical library of autophagic modulators to identify compounds that could potentially be used to fight against infections by a broad range of coronaviruses. Among the 80 autophagy-related compounds tested, cycloheximide and thapsigargin reduced SARS-CoV-2 infection efficiency in a dose-dependent manner. Cycloheximide treatment reduced the infection efficiency of not only six SARS-CoV-2 variants but also human coronavirus (HCoV)-229E and HCoV-OC43. Cycloheximide treatment also reversed viral infection-induced innate immune responses. However, even low dose (1 μM) cycloheximide treatment altered the expression profile of ribosomal RNAs, thus side effects such as inhibition of protein synthesis in host cells must be considered. These results suggest that cycloheximide has broad-spectrum anti-coronavirus activity in vitro and warrants further investigation.