Multi-omics analysis of attenuated variant reveals potential evaluation marker of host damaging for SARS-CoV-2 variants

SARS-CoV-2 continues to threaten human society by generating novel variants via mutation and recombination. The high number of mutations that appeared in emerging variants not only enhanced their immune-escaping ability but also made it difficult to predict the pathogenicity and virulence based on viral nucleotide sequences. Molecular markers for evaluating the pathogenicity of new variants are therefore needed. By comparing host responses to wild-type and variants with attenuated pathogenicity at proteome and metabolome levels, six key molecules on the polyamine biosynthesis pathway including putrescine, SAM, dc-SAM, ODC1, SAMS, and SAMDC were found to be differentially upregulated and associated with pathogenicity of variants. To validate our discovery, human airway organoids were subsequently used which recapitulates SARS-CoV-2 replication in the airway epithelial cells of COVID-19 patients. Using ODC1 as a proof-of-concept, differential activation of polyamine biosynthesis was found to be modulated by the renin-angiotensin system (RAS) and positively associated with ACE2 activity. Further experiments demonstrated that ODC1 expression could be differentially activated upon a panel of SARS-CoV-2 variants of concern (VOCs) and was found to be correlated with each VOCs' pathogenic properties. Particularly, the presented study revealed the discriminative ability of key molecules on polyamine biosynthesis as a predictive marker for virulence evaluation and assessment of SARS-CoV-2 variants in cell or organoid models. Our work, therefore, presented a practical strategy that could be potentially applied as an evaluation tool for the pathogenicity of current and emerging SARS-CoV-2 variants.

An intranasal influenza virus-vectored vaccine prevents SARS-CoV-2 replication in respiratory tissues of mice and hamsters

Current available vaccines for COVID-19 are effective in reducing severe diseases and deaths caused by SARS-CoV-2 infection but less optimal in preventing infection. Next-generation vaccines which are able to induce mucosal immunity in the upper respiratory to prevent or reduce infections caused by highly transmissible variants of SARS-CoV-2 are urgently needed. We have developed an intranasal vaccine candidate based on a live attenuated influenza virus (LAIV) with a deleted NS1 gene that encodes cell surface expression of the receptor-binding-domain (RBD) of the SARS-CoV-2 spike protein, designated DelNS1-RBD4N-DAF. Immune responses and protection against virus challenge following intranasal administration of DelNS1-RBD4N-DAF vaccines were analyzed in mice and compared with intramuscular injection of the BioNTech BNT162b2 mRNA vaccine in hamsters. DelNS1-RBD4N-DAF LAIVs induced high levels of neutralizing antibodies against various SARS-CoV-2 variants in mice and hamsters and stimulated robust T cell responses in mice. Notably, vaccination with DelNS1-RBD4N-DAF LAIVs, but not BNT162b2 mRNA, prevented replication of SARS-CoV-2 variants, including Delta and Omicron BA.2, in the respiratory tissues of animals. The DelNS1-RBD4N-DAF LAIV system warrants further evaluation in humans for the control of SARS-CoV-2 transmission and, more significantly, for creating dual function vaccines against both influenza and COVID-19 for use in annual vaccination strategies.

Abstract 3749: Oncogenic role of Epstein-Barr virus lnc-BARTs in EBV associated tumors

While majority of humans infected with Epstein-Barr virus (EBV) is asymptomatic for whole life, EBV is found to associate with several human cancers, including Burkitt’s lymphoma, Hodgkin’s diseases, post-transplant lymphoproliferative disorder (PTLD), nasopharyngeal carcinoma (NPC) and gastric carcinoma. Among these EBV associated tumors, EBV genome is found in 100% of NPC tumor cells. EBV establishes a latent infection in NPC cells, expressing few viral proteins, but elevated levels of non-coding RNAs transcribed from the BamHI-A region of the EBV genome, designated BamHI-A rightward transcripts (BARTs). The family of EBV BART RNAs comprises BART-microRNAs (miRNAs) and long non-coding RNAs (lnc-BARTs). While versatile functions of BART miRNAs have been revealed, little is known about the role of EBV lnc-BARTs. Here, we provided evidence to show that BARTs mRNA which derived from multiple exons of BART function as regulatory long non-coding RNA, namely lnc-BARTs, in modulating the core network for maintaining EBV latency and promoting NPC oncogenesis through epigenetic mechanisms. Our results showed that the apoptosis rate of NPC cell lines with knockdown of EBV lnc-BARTs was significantly increased, suggesting that lnc-BARTs have an anti-apoptotic effect in EBV associated tumors. MS analysis was performed to identify host factors which interact with EBV lnc-BARTs in NPC cells. Lnc-BARTs were shown to directly interact with several transcriptional regulators, including BRD4 and SC35. Notably, RNA-FISH assays demonstrated that lnc-BARTs co-localize with BRD4 and SC35 complexes in nuclear speckles, with these complexes being disrupted by treatment with JQ1, a BRD4 competitive inhibitor. RNA immunoprecipitation and RNA pulldown assays confirmed that lnc-BARTs bind to BRD4. ATAC sequencing analysis and transcriptome analysis further demonstrated that knockdown of BARTs in the EBV-harboring NPC cell line, C666-1, resulted in globally reduced chromatin accessibility downregulation of oncogenes like MYC and BCL2. In addition, ChIP sequencing analysis revealed that lnc-BARTs interfere PolII phosphorylation on promoters of genes. Our findings suggest that EBV lnc-BARTs are involved in epigenetic modulation of host gene expression through functional interaction with elongation regulatory machinery to maintain EBV latency and drive tumorigenesis in NPC.

Citation Format: LIU JIAYAN, Bobo Wing-Yee Mok, Songtao He, Honglin Chen. Oncogenic role of Epstein-Barr virus lnc-BARTs in EBV associated tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3749.

Abstract 3748: Epstein-Barr virus BART lncRNAs induce IKZF3/Aiolos to maintain EBV latency and promote tumorigenicity in nasopharyngeal carcinoma

Epstein-Barr virus (EBV) maintains latency in its associated tumors, including nasopharyngeal carcinoma (NPC), expressing very few viral proteins but abundant levels of noncoding RNAs (mainly EBERs and BARTs) in NPC cells. We found that IKZF3/Aiolos is a downstream target of BART lncRNAs in NPC cells. The functions of BART lncRNAs and IKZF3 in EBV latency and pathogenesis of NPC remain elusive. In this study, meta-analysis of eight EBV-associated studies showed that IKZF3/Aiolos was consistently upregulated in EBV-infected NPC cells. Our study further showed that transcription of IKZF3/Aiolos is highly upregulated in EBV-infected NPC cells and clinical tissue samples due to the action of EBV encoded BART lncRNAs, with IKZF3/Aiolos was expressed at higher levels in late stage (stage III & IV) NPC patients than in early stage (stage I & II) disease. Secondly, we found that IKZF3/Aiolos was upregulated in BART-activated NPC cells but downregulated in BART-knockdown NPC cells. In addition, this study further demonstrated that IKZF3/Aiolos modulates transcription of EBV BZLF1 and the cellular gene, LRIG1, to maintain EBV latency and promote NPC tumorigenesis in vitro and in vivo. Our results showed that the EBV lytic reactivator BZLF1 was upregulated in IKZF3/Aiolos knockout or Aiolos inhibitor-treated NPC cells. ChIP-qPCR, immunoprecipitation and immunofluorescence analyses further revealed that IKZF3/Aiolos induces H3K27 deacetylation to silence expression of BZLF1 and maintain EBV latency in NPC cells. Moreover, functional analyses and western blotting showed that IKZF3/Aiolos inhibited the tumor suppressor, LRIG1, to upregulate expression and phosphorylation of the cellular proto-oncogene Erb-B2 for NPC pathogenesis. Sphere- and colony-formation assays demonstrated that IKZF3/Aiolos enhances growth of NPC cells in vitro, and in vivo experiments further showed that IKZF3/Aiolos promotes tumorigenicity of NPC cells in NOD mice. Mechanically, we found that the expression of EBV lytic reactivator BZLF1 and cellular LRIG1 were negatively regulated by BART lncRNA/IKZF3/Aiolos regulatory machinery in NPC cells, while Erb-B2 was positively regulated, which indicated that IKZF3/Aiolos is a new biomarker for NPC and may lead to the development of novel diagnostic tests and treatments for NPC.

Citation Format: Songtao He, Jiayan Liu, Bobo Wing-Yee Mok, Sai Wah Tsao, Honglin Chen. Epstein-Barr virus BART lncRNAs induce IKZF3/Aiolos to maintain EBV latency and promote tumorigenicity in nasopharyngeal carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3748.

A broadly neutralizing antibody protects Syrian hamsters against SARS-CoV-2 Omicron challenge

The strikingly high transmissibility and antibody evasion of SARS-CoV-2 Omicron variants have posed great challenges to the efficacy of current vaccines and antibody immunotherapy. Here, we screen 34 BNT162b2-vaccinees and isolate a public broadly neutralizing antibody ZCB11 derived from the IGHV1-58 family. ZCB11 targets viral receptor-binding domain specifically and neutralizes all SARS-CoV-2 variants of concern, especially with great potency against authentic Omicron and Delta variants. Pseudovirus-based mapping of 57 naturally occurred spike mutations or deletions reveals that S371L results in 11-fold neutralization resistance, but it is rescued by compensating mutations in Omicron variants. Cryo-EM analysis demonstrates that ZCB11 heavy chain predominantly interacts with Omicron spike trimer with receptor-binding domain in up conformation blocking ACE2 binding. In addition, prophylactic or therapeutic ZCB11 administration protects lung infection against Omicron viral challenge in golden Syrian hamsters. These results suggest that vaccine-induced ZCB11 is a promising broadly neutralizing antibody for biomedical interventions against pandemic SARS-CoV-2.

SARS-CoV-2 variants of concern such as the Omicron variant pose a challenge for vaccination and antibody immunotherapy. Here, Zhou et al. isolate a broadly neutralizing antibody (bNAb), named ZCB11, that protects Golden Syrian hamsters against Omicron. Applying CryoEM the authors show that ZCB11 heavy chain predominantly interacts with RBD in up confirmation, which interferes with ACE2 receptor binding.

Pathogenicity, transmissibility, and fitness of SARS-CoV-2 Omicron in Syrian hamsters

The in vivo pathogenicity, transmissibility, and fitness of the SARS-CoV-2 Omicron (B.1.1.529) variant are unclear. We compared these virological attributes of this new variant of concern with those of the Delta (B.1.617.2) variant in a Syrian hamster model of COVID-19. Omicron-infected hamsters lost significantly less body weight and exhibited reduced clinical scores, respiratory tract viral burdens, cytokine/chemokine dysregulation, and lung damage than Delta-infected hamsters. Both variants were highly transmissible via contact transmission. In non-contact transmission studies, Omicron demonstrated similar or higher transmissibility than Delta. Delta outcompeted Omicron without selection pressure. This scenario drastically changed once immune selection pressure with neutralizing antibodies active against Delta but poorly active against Omicron was introduced. Next-generation vaccines and antivirals effective against this new VOC are urgently needed.

Differential effects of macrophage subtypes on SARS-CoV-2 infection in a human pluripotent stem cell-derived model

Dysfunctional immune responses contribute critically to the progression of Coronavirus Disease-2019 (COVID-19), with macrophages as one of the main cell types involved. It is urgent to understand the interactions among permissive cells, macrophages, and the SARS-CoV-2 virus, thereby offering important insights into effective therapeutic strategies. Here, we establish a lung and macrophage co-culture system derived from human pluripotent stem cells (hPSCs), modeling the host-pathogen interaction in SARS-CoV-2 infection. We find that both classically polarized macrophages (M1) and alternatively polarized macrophages (M2) have inhibitory effects on SARS-CoV-2 infection. However, M1 and non-activated (M0) macrophages, but not M2 macrophages, significantly up-regulate inflammatory factors upon viral infection. Moreover, M1 macrophages suppress the growth and enhance apoptosis of lung cells. Inhibition of viral entry using an ACE2 blocking antibody substantially enhances the activity of M2 macrophages. Our studies indicate differential immune response patterns in distinct macrophage phenotypes, which could lead to a range of COVID-19 disease severity.

Nasal prevention of SARS-CoV-2 infection by intranasal influenza-based boost vaccination in mouse models

BACKGROUND

Vaccines in emergency use are efficacious against COVID-19, yet vaccine-induced prevention against nasal SARS-CoV-2 infection remains suboptimal.

METHODS

Since mucosal immunity is critical for nasal prevention, we investigated the efficacy of an intramuscular PD1-based receptor-binding domain (RBD) DNA vaccine (PD1-RBD-DNA) and intranasal live attenuated influenza-based vaccines (LAIV-CA4-RBD and LAIV-HK68-RBD) against SARS-CoV-2.

FINDINGS

Substantially higher systemic and mucosal immune responses, including bronchoalveolar lavage IgA/IgG and lung polyfunctional memory CD8 T cells, were induced by the heterologous PD1-RBD-DNA/LAIV-HK68-RBD as compared with other regimens. When vaccinated animals were challenged at the memory phase, prevention of robust SARS-CoV-2 infection in nasal turbinate was achieved primarily by the heterologous regimen besides consistent protection in lungs. The regimen-induced antibodies cross-neutralized variants of concerns. Furthermore, LAIV-CA4-RBD could boost the BioNTech vaccine for improved mucosal immunity.

INTERPRETATION

Our results demonstrated that intranasal influenza-based boost vaccination induces mucosal and systemic immunity for effective SARS-CoV-2 prevention in both upper and lower respiratory systems.

FUNDING

This study was supported by the Research Grants Council Collaborative Research Fund, General Research Fund and Health and Medical Research Fund in Hong Kong; Outbreak Response to Novel Coronavirus (COVID-19) by the Coalition for Epidemic Preparedness Innovations; Shenzhen Science and Technology Program and matching fund from Shenzhen Immuno Cure BioTech Limited; the Health@InnoHK, Innovation and Technology Commission of Hong Kong; National Program on Key Research Project of China; donations from the Friends of Hope Education Fund; the Theme-Based Research Scheme.

Neutralization of Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant by Sera From BNT162b2 or CoronaVac Vaccine Recipients

BACKGROUND

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant, designated as a variant of concern by the World Health Organization, carries numerous spike mutations that are known to evade neutralizing antibodies elicited by coronavirus disease 2019 (COVID-19) vaccines. A deeper understanding of the susceptibility of omicron variant to vaccine-induced neutralizing antibodies is urgently needed for risk assessment.

METHODS

Omicron variant strains HKU691 and HKU344-R346K were isolated from patients using TMPRSS2-overexpressing VeroE6 cells. Whole genome sequence was determined using nanopore sequencing. Neutralization susceptibility of ancestral lineage A virus and the omicron, delta and beta variants to sera from 25 BNT162b2 and 25 CoronaVac vaccine recipients was determined using a live virus microneutralization assay.

RESULTS

The omicron variant strain HKU344-R346K has an additional spike R346K mutation, which is present in 8.5% of strains deposited in the GISAID database. Only 20% and 24% of BNT162b2 recipients had detectable neutralizing antibody against the omicron variant HKU691 and HKU344-R346K, respectively, whereas none of the CoronaVac recipients had detectable neutralizing antibody titer against either omicron isolate. For BNT162b2 recipients, the geometric mean neutralization antibody titers (GMTs) of the omicron variant isolates (5.43 and 6.42) were 35.7-39.9-fold lower than that of the ancestral virus (229.4), and the GMTs of both omicron variant isolates were significantly lower than those of the beta and delta variants. There was no significant difference in the GMTs between HKU691 and HKU344-R346K.

CONCLUSIONS

Omicron variant escapes neutralizing antibodies elicited by BNT162b2 or CoronaVac. The additional R346K mutation did not affect the neutralization susceptibility. Our data suggest that the omicron variant may be associated with lower COVID-19 vaccine effectiveness.

Low dose inocula of SARS-CoV-2 Alpha variant transmits more efficiently than earlier variants in hamsters

Emerging variants of SARS-CoV-2 have been shown to rapidly replace original circulating strains in humans soon after they emerged. There is a lack of experimental evidence to explain how these natural occurring variants spread more efficiently than existing strains of SARS-CoV-2 in transmission. We found that the Alpha variant (B.1.1.7) increased competitive fitness over earlier parental D614G lineages in in-vitro and in-vivo systems. Using hamster transmission model, we further demonstrated that the Alpha variant is able to replicate and shed more efficiently in the nasal cavity of hamsters than other variants with low dose and short duration of exposure. The capability to initiate effective infection with low inocula may be one of the key factors leading to the rapid transmission of emerging variants of SARS-CoV-2.

Viral MicroRNAs Encoded by Nucleocapsid Gene of SARS-CoV-2 Are Detected during Infection, and Targeting Metabolic Pathways in Host Cells

MicroRNAs (miRNAs) are critical regulators of gene expression that may be used to identify the pathological pathways influenced by disease and cellular interactions. Viral miRNAs (v-miRNAs) encoded by both DNA and RNA viruses induce immune dysregulation, virus production, and disease pathogenesis. Given the absence of effective treatment and the prevalence of highly infective SARS-CoV-2 strains, improved understanding of viral-associated miRNAs could provide novel mechanistic insights into the pathogenesis of COVID-19. In this study, SARS-CoV-2 v-miRNAs were identified by deep sequencing in infected Calu-3 and Vero E6 cell lines. Among the ~0.1% small RNA sequences mapped to the SARS-CoV-2 genome, the top ten SARS-CoV-2 v-miRNAs (including three encoded by the N gene; v-miRNA-N) were selected. After initial screening of conserved v-miRNA-N-28612, which was identified in both SARS-CoV and SARS-CoV-2, its expression was shown to be positively associated with viral load in COVID-19 patients. Further in silico analysis and synthetic-mimic transfection of validated SARS-CoV-2 v-miRNAs revealed novel functional targets and associations with mechanisms of cellular metabolism and biosynthesis. Our findings support the development of v-miRNA-based biomarkers and therapeutic strategies based on improved understanding of the pathophysiology of COVID-19.

TOP1 inhibition therapy protects against SARS-CoV-2-induced lethal inflammation

The ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently affecting millions of lives worldwide. Large retrospective studies indicate that an elevated level of inflammatory cytokines and pro-inflammatory factors are associated with both increased disease severity and mortality. Here, using multidimensional epigenetic, transcriptional, in vitro, and in vivo analyses, we report that topoisomerase 1 (TOP1) inhibition suppresses lethal inflammation induced by SARS-CoV-2. Therapeutic treatment with two doses of topotecan (TPT), an FDA-approved TOP1 inhibitor, suppresses infection-induced inflammation in hamsters. TPT treatment as late as 4 days post-infection reduces morbidity and rescues mortality in a transgenic mouse model. These results support the potential of TOP1 inhibition as an effective host-directed therapy against severe SARS-CoV-2 infection. TPT and its derivatives are inexpensive clinical-grade inhibitors available in most countries. Clinical trials are needed to evaluate the efficacy of repurposing TOP1 inhibitors for severe coronavirus disease 2019 (COVID-19) in humans.

Characterization of an attenuated SARS-CoV-2 variant with a deletion at the S1/S2 junction of the spike protein

SARS-CoV-2 is of zoonotic origin and contains a PRRA polybasic cleavage motif which is considered critical for efficient infection and transmission in humans. We previously reported on a panel of attenuated SARS-CoV-2 variants with deletions at the S1/S2 junction of the spike protein. Here, we characterize pathogenicity, immunogenicity, and protective ability of a further cell-adapted SARS-CoV-2 variant, Ca-DelMut, in in vitro and in vivo systems. Ca-DelMut replicates more efficiently than wild type or parental virus in Vero E6 cells, but causes no apparent disease in hamsters, despite replicating in respiratory tissues. Unlike wild type virus, Ca-DelMut causes no obvious pathological changes and does not induce elevation of proinflammatory cytokines, but still triggers a strong neutralizing antibody and T cell response in hamsters and mice. Ca-DelMut immunized hamsters challenged with wild type SARS-CoV-2 are fully protected, with little sign of virus replication in the upper or lower respiratory tract, demonstrating sterilizing immunity.

Topoisomerase 1 inhibition therapy protects against SARS-CoV-2-induced inflammation and death in animal models

The ongoing pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is currently affecting millions of lives worldwide. Large retrospective studies indicate that an elevated level of inflammatory cytokines and pro-inflammatory factors are associated with both increased disease severity and mortality. Here, using multidimensional epigenetic, transcriptional, in vitro and in vivo analyses, we report that Topoisomerase 1 (Top1) inhibition suppresses lethal inflammation induced by SARS-CoV-2. Therapeutic treatment with two doses of Topotecan (TPT), a FDA-approved Top1 inhibitor, suppresses infection-induced inflammation in hamsters. TPT treatment as late as four days post-infection reduces morbidity and rescues mortality in a transgenic mouse model. These results support the potential of Top1 inhibition as an effective host-directed therapy against severe SARS-CoV-2 infection. TPT and its derivatives are inexpensive clinical-grade inhibitors available in most countries. Clinical trials are needed to evaluate the efficacy of repurposing Top1 inhibitors for COVID-19 in humans.

Abstract 272: Oncogenic role of epstein-barr virus lnc-BARTs in nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV) is associated with several human cancers, including Burkitt's lymphoma, Hodgkin's diseases, post-transplant lymphoproliferative disorder (PTLD), nasopharyngeal carcinoma (NPC) and gastric carcinoma. Among these EBV associated tumors, EBV genome is found in 100% of NPC tumor cells. EBV establishes a latent infection in NPC cells, expressing few viral proteins, but elevated levels of non-coding RNAs transcribed from the BamHI-A region of the EBV genome, designated BamHI-A rightward transcripts (BARTs). The family of BART RNAs comprises BART-microRNAs (miRNAs) and long non-coding RNAs (lnc-BARTs). While versatile functions of BART miRNAs continue to be revealed, little is known about EBV lnc-BARTs. Here, we provide evidence to show that lnc-BARTs derived from multiple exons of BART RNA function as nuclear long non-coding RNAs in modulating host gene expression in NPC cells. We found that lnc-BARTs upregulate transcription of SEPT9, matrix metalloproteinase (MMP) genes and IKZF3 (Aiolos) and accelerate N-cadherin cleavage. As a member of the Septin family, SEPT9 (cytoskeletal interacting protein, Septin 9) is involved in cytokinesis and cell cycle control. Aiolos can negatively regulate expression of p66Shc, which is associated with the oxidative stress response and apoptosis, and our data also showed that knockout of IKZF3 in NPC cells enhanced transcription of p66Shc protein. Our results indicated that the apoptosis rate of NPC cell lines with knockdown of lnc-BARTs was significantly increased, suggesting that lnc-BARTs have an anti-apoptotic effect in EBV associated tumors. To understand the molecular basis of gene regulation by EBV BART-lncRNAs, ChIRP-MS analysis was performed: lnc-BARTs were shown to directly interact with several transcriptional regulators, including BRD4 and KDM1B. Notably, RNA FISH assays demonstrated that lnc-BARTs co-localize with BRD4 and P-TEFb complexes in nuclear speckles, with these complexes being disrupted by treatment with JQ1, a BRD4 competitive inhibitor. RNA immunoprecipitation and RNA pulldown assays confirmed that lnc-BARTs bind directly to BRD4. In addition, transcriptome analysis revealed that knockdown of BARTs in the EBV-harboring NPC cell line, C666-1, resulted in downregulation of MYC and BCL2, genes downstream of BRD4. BRD4-ChIP and ATAC sequencing analysis further demonstrated that knockdown of lnc-BARTs reduced both BRD4-mediated epigenetic modulation of host gene expression and chromatin accessibility. We suggest that EBV lnc-BARTs are involved in epigenetic modulation of host gene expression through functional interaction with BRD4 regulatory machinery to maintain EBV latency in NPC cells, and that lnc-BARTs modulate host gene expression to drive tumorigenesis in NPC.

Citation Format: Jiayan Liu, Bobo Wing-Yee Mok, Songtao He, Honglin Chen. Oncogenic role of epstein-barr virus lnc-BARTs in nasopharyngeal carcinoma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 272.

Attenuated SARS-CoV-2 variants with deletions at the S1/S2 junction

The emergence of SARS-CoV-2 has led to the current global coronavirus pandemic and more than one million infections since December 2019. The exact origin of SARS-CoV-2 remains elusive, but the presence of a distinct motif in the S1/S2 junction region suggests the possible acquisition of cleavage site(s) in the spike protein that promoted cross-species transmission. Through plaque purification of Vero-E6 cultured SARS-CoV-2, we found a series of variants which contain 15-30-bp deletions (Del-mut) or point mutations respectively at the S1/S2 junction. Examination of the original clinical specimen from which the isolate was derived, and 26 additional SARS-CoV-2 positive clinical specimens, failed to detect these variants. Infection of hamsters shows that one of the variants (Del-mut-1) which carries deletion of 10 amino acids (30bp) does not cause the body weight loss or more severe pathological changes in the lungs that is associated with wild type virus infection. We suggest that the unique cleavage motif promoting SARS-CoV-2 infection in humans may be under strong selective pressure, given that replication in permissive Vero-E6 cells leads to the loss of this adaptive function. It would be important to screen the prevalence of these variants in asymptomatic infected cases. The potential of the Del-mut variants as an attenuated vaccine or laboratory tool should be evaluated.

Epstein-Barr Virus BART Long Non-coding RNAs Function as Epigenetic Modulators in Nasopharyngeal Carcinoma

Epstein-Barr virus (EBV) establishes lifelong latent infection in humans and is associated with several lymphoid and epithelial cancers. In nasopharyngeal carcinoma (NPC), EBV expresses few viral proteins but elevated levels of Bam-HI A rightward transcripts (BARTs) RNA, which includes viral microRNAs and long non-coding RNAs (lncRNAs). BART lncRNAs localize within the nucleus of EBV-infected cells and knockdown of BART lncRNAs significantly affects the expression of genes associated with cell adhesion, oxidoreductase activity, inflammation, and immunity. Notably, downregulation of IKAROS family zinc finger 3 (IKZF3/Aiolos), which plays a role in lymphocyte development and cell attachment, occurred in NPC C666-1 cells following BART lncRNA-knockdown. Since Aiolos expression is normally restricted to lymphoid cells and rarely observed in epithelial cells, induction of Aiolos by BART lncRNA was confirmed by expressing the major BART lncRNA isoform, RPMS1, in EBV-positive and -negative cells. BART lncRNA associated with the CBP/p300 complex and RNA polymerase II (Pol II) in the nucleus, suggesting that BART lncRNAs may mediate epigenetic regulation of gene expression through interaction with the chromatin remodeling machinery. This contention is further supported by evidence that BART lncRNA appears to stall Pol II at the promoter region and may regulate IFNB1 and CXCL8 expression by inhibiting transcription by Pol II in NPC. We hypothesize that EBV BART lncRNA expression modulates host gene expression and maintains EBV latency by interfering with histone methylation and acetylation processes. Aberrant expression of affected host genes mediated by BART lncRNA may lead to immune evasion, progression, and metastasis of NPC.

The role of nuclear NS1 protein in highly pathogenic H5N1 influenza viruses

The non-structural protein (NS1) of influenza A viruses (IAV) performs multiple functions during viral infection. NS1 contains two nuclear localization signals (NLS): NLS1 and NLS2. The NS1 protein is located predominantly in the nucleus during the early stages of infection and subsequently exported to the cytoplasm. A nonsense mutation that results in a large deletion in the carboxy-terminal region of the NS1 protein that contains the NLS2 domain was found in some IAV subtypes, including highly pathogenic avian influenza (HPAI) H7N9 and H5N1 viruses. We introduced different mutations into the NLS domains of NS1 proteins in various strains of IAV, and demonstrated that mutation of the NLS2 region in the NS1 protein of HPAI H5N1 viruses severely affects its nuclear localization pattern. H5N1 viruses expressing NS1 protein that is unable to localize to the nucleus are less potent in antagonizing cellular antiviral responses than viruses expressing wild-type NS1. However, no significant difference was observed with respect to viral replication and pathogenesis. In contrast, the replication and antiviral defenses of H1N1 viruses are greatly attenuated when nuclear localization of the NS1 protein is blocked. Our data reveals a novel functional plasticity for NS1 proteins among different IAV subtypes.

Abstract 3500: Epstein-Barr virus BART noncoding RNAs modulate host gene expression for virus latency leading to oncogenesis in epithelial cells

Epstein-Barr virus (EBV) efficiently establishes and maintains a state of latency in resting B cells, with persistent asymptomatic infections occurring in more than 95% of the human population worldwide. Besides causing lifelong infections in resting B cells in the majority of people, EBV has been found to associate with several human cancers occurring in immune competent individuals, in which the virus expresses very few viral proteins in EBV infected cancer cells through a distinct viral latency program. It is believed that this type of mechanism has been adopted by EBV to allow the virus to evade host immune surveillance. Nasopharyngeal carcinoma (NPC) is prevalent in southern China, Southeast Asian countries and some African countries but uncommon in rest of the world. In NPC 100% of cancer cells are infected with EBV, and EBV is recognized one of the major etiological factors. However, the details of how EBV maintains latency and contributes to the oncogenesis of NPC remain mostly elusive. Notably, EBV abundantly expresses a family of non-coding RNAs derived from the BamHI A region of the viral genome (BARTs). It is hypothesized that this family of viral non-coding RNAs is key to maintaining viral latency, evading immune surveillance and triggering oncogenesis in EBV associated tumors. We have shown a mechanism for the regulation of the abundant expression of BARTs in NPC which involves the constitutive activation of NF-κB signaling typically observed in NPC cells and have also identified a regulatory loop through which BARTs support EBV latency in NPC. Using high throughput RNA-seq analysis we further demonstrated that BART RNAs modulate expression of cellular genes associated with anti-inflammatory and immune-modulating properties, oxidoreductase activity, and cell migration and invasion in NPC cells. BART non-coding RNAs are predominantly localized in the nucleus and associate with the CBP/p300 complex. Our data showed that EBV BARTs modulate genes responsive to the mitochondria-associated adapter molecule (MAVS) through halting cellular Pol II in the promoter region and downregulating gene expression. In the nucleus, BART non-coding RNAs modulate chromatin acetylation through interaction with CBP/p300. We have generated a working model with evidence showing that Epstein-Barr virus shuts off most of the viral proteins to evade immune surveillance, but through expression of high levels of BART non-coding RNAs can modulate cellular gene expression to provide an optimal environment for maintenance of viral latency in cancer cells. Alteration of cellular gene expression by EBV BART non-coding RNAs for establishment and maintenance of EBV latency in epithelial cells can therefore lead to the oncogenic process for EBV associated tumors.

Citation Format: Rob Verhoeven, Bobo Wing-Yee Mok, Shuang Tong, Honglin Chen. Epstein-Barr virus BART noncoding RNAs modulate host gene expression for virus latency leading to oncogenesis in epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3500. doi:10.1158/1538-7445.AM2017-3500

An NS-segment exonic splicing enhancer regulates influenza A virus replication in mammalian cells

Influenza virus utilizes host splicing machinery to process viral mRNAs expressed from both M and NS segments. Through genetic analysis and functional characterization, we here show that the NS segment of H7N9 virus contains a unique G540A substitution, located within a previously undefined exonic splicing enhancer (ESE) motif present in the NEP mRNA of influenza A viruses. G540A supports virus replication in mammalian cells while retaining replication ability in avian cells. Host splicing regulator, SF2, interacts with this ESE to regulate splicing of NEP/NS1 mRNA and G540A substitution affects SF2–ESE interaction. The NS1 protein directly interacts with SF2 in the nucleus and modulates splicing of NS mRNAs during virus replication. We demonstrate that splicing of NEP/NS1 mRNA is regulated through a cis NEP-ESE motif and suggest a unique NEP-ESE may contribute to provide H7N9 virus with the ability to both circulate efficiently in avian hosts and replicate in mammalian cells.

Some circulating avian influenza A viruses can infect humans, but the mechanism enabling species jump is poorly understood. Here, Huang et al. identify a nucleotide in NEP of avian H7N9 viruses that affects splicing efficiency of the NS segment and supports virus replication in avian and mammalian cells.