Influenza virus infection increases p53 activity: role of p53 in cell death and viral replication

In vitro antiviral activity of NanB bacterial sialidase against avian influenza H9N2 virus in MDCK cells

The avian influenza virus is an infectious agent that may cause global health problems in poultry and is potentially zoonotic. In the recent decades, bacterial-derived sialidases have been extensively studied for their ability to inhibit avian influenza virus infections. In this study, the antiviral activity of NanB sialidase from Pasteurella multocida was investigated through in vitro analysis using Madin-Darby canine kidney (MDCK) cells. NanB sialidase was purified from P. multocida to test its toxicity and its ability to hydrolyse its sialic acid receptors on MDCK cells. The H9N2 challenge virus was propagated in MDCK cells until cytopathic effects appeared. Antiviral activity of NanB sialidase was tested using MDCK cells, and then observed based on cell morphology, viral copy number, and expression of apoptosis-mediating genes. NanB sialidase effectively hydrolysed Neu5Acα(2,6)-Gal sialic acid at a dose of 129 mU/ml, while at 258 mU/ml, it caused toxicity to MDCK cells. Antiviral activity of sialidase was evident based on the significant decrease in viral copy number at all doses administered. The increase of p53 and caspase-3 expression was observed in infected cells without sialidase. Our study demonstrates the ability of NanB sialidase to inhibit H9N2 virus replication based on observations of sialic acid hydrolysis, reduction in viral copy number, and expression of apoptosis-related genes. The future application of sialidase may be considered as an antiviral strategy against avian influenza H9N2 virus infections. RESEARCH HIGHLIGHTSNanB sialidase effectively hydrolyses Neu5Acα(2,6)-Gal at a dose of 129 mU/ml.NanB sialidase from Pasteurella multocida can inhibit the entry of H9N2 virus into cells.NanB sialidase of Pasteurella multocida prevents infection-induced cell apoptosis.NanB sialidase reduces the H9N2 viral copy number in MDCK cells.

Systematic review and meta-analysis of genome-wide pooled CRISPR screens to identify host factors involved in influenza A virus infection

The host-virus interactome is increasingly recognized as an important research field to discover new therapeutic targets to treat influenza. Multiple pooled genome-wide CRISPR-Cas screens have been reported to identify new pro- and antiviral host factors of the influenza A virus. However, at present, a comprehensive summary of the results is lacking. We performed a systematic review of all reported CRISPR studies in this field in combination with a meta-analysis using the algorithm of meta-analysis by information content (MAIC). Two ranked gene lists were generated based on evidence in 15 proviral and 4 antiviral screens. Enriched pathways in the proviral MAIC results were compared to those of a prior array-based RNA interference (RNAi) meta-analysis. The top 50 proviral MAIC list contained genes whose role requires further elucidation, such as the endosomal ion channel TPCN1 and the kinase WEE1. Moreover, MAIC indicated that ALYREF, a component of the transcription export complex, has antiviral properties, whereas former knockdown experiments attributed a proviral role to this host factor. CRISPR-Cas-pooled screens displayed a bias toward early-replication events, whereas the prior RNAi meta-analysis covered early and late-stage events. RNAi screens led to the identification of a larger fraction of essential genes than CRISPR screens. In summary, the MAIC algorithm points toward the importance of several less well-known pathways in host-influenza virus interactions that merit further investigation. The results from this meta-analysis of CRISPR screens in influenza A virus infection may help guide future research efforts to develop host-directed anti-influenza drugs.

IMPORTANCE

Viruses rely on host factors for their replication, whereas the host cell has evolved virus restriction factors. These factors represent potential targets for host-oriented antiviral therapies. Multiple pooled genome-wide CRISPR-Cas screens have been reported to identify pro- and antiviral host factors in the context of influenza virus infection. We performed a comprehensive analysis of the outcome of these screens based on the publicly available gene lists, using the recently developed algorithm meta-analysis by information content (MAIC). MAIC allows the systematic integration of ranked and unranked gene lists into a final ranked gene list. This approach highlighted poorly characterized host factors and pathways with evidence from multiple screens, such as the vesicle docking and lipid metabolism pathways, which merit further exploration.

The nucleocapsid protein facilitates p53 ubiquitination-dependent proteasomal degradation via recruiting host ubiquitin ligase COP1 in PEDV infection

Porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric pathogen of the coronavirus family and caused severe economic losses to the global swine industry. Previous studies have established that p53 is a host restriction factor for PEDV infection, and p53 degradation occurs in PEDV-infected cells. However, the underlying molecular mechanisms through which PEDV viral proteins regulate p53 degradation remain unclear. In this study, we found that PEDV infection or expression of the nucleocapsid protein downregulates p53 through a post-translational mechanism: increasing the ubiquitination of p53 and preventing its nuclear translocation. We also show that the PEDV N protein functions by recruiting the E3 ubiquitin ligase COP1 and suppressing COP1 self-ubiquitination and protein degradation, thereby augmenting COP1-mediated degradation of p53. Additionally, COP1 knockdown compromises N-mediated p53 degradation. Functional mapping using truncation analysis showed that the N-terminal domains of N protein were responsible for interacting with COP1 and critical for COP1 stability and p53 degradation. The results presented here suggest the COP1-dependent mechanism for PEDV N protein to abolish p53 activity. This study significantly increases our understanding of PEDV in antagonizing the host antiviral factor p53 and will help initiate novel antiviral strategies against PEDV.

Role of Influenza A virus protein NS1 in regulating host nuclear body ND10 complex formation and its involvement in establishment of viral pathogenesis

Influenza viral infection is a seasonal infection which causes widespread acute respiratory issues among humans globally. This virus changes its surface receptor composition to escape the recognition process by the host's immune cells. Therefore, the present study focussed to identify some other important viral proteins which have a significant role in establishment of infection and having apparent conserved structural composition. This could facilitate the permanent vaccine development process or help in designing a drug against IAV (influenza A virus) infection which will eliminate the seasonal flu shot vaccination process. The NS1 (Non-structural protein 1) protein of IAV maintains a conserved structural motif. Earlier studies have shown its significant role in infection establishment. However, the mechanism by which viruses escape the host's ND10 antiviral action remains elusive. The present study clearly showed that IAV infection and NS1 transfection in A549 cells degraded the main component of the ND10 anti-viral complex, PML and therefore, inhibited the formation of Daxx-sp100-p53-PML complex (ND10) at the mid phase of infection/transfection. PML degradation activated the stress axis which increased cellular ROS (reactive oxygen species) levels as well as mitochondrial dysfunction. Additionally, IAV/NS1 increased cellular stress and p53 accumulation at the late phase of infection. These collectively activated apoptotic pathway in the host cells. Along with the inactivation of several interferon proteins, IAV was found to decrease p-IKKε. A549 cells transfected with pcDNA3.1-NS1 showed a similar effect in the interferon axis and IKKε. Moreover, NS1 induced the disintegration of the host's ND10 complex through the changes in the SUMOylation pattern of the PML nuclear body. These findings suggest the possible mechanism of how NS1 helps IAV to establish infection in the host cells. However, it demands further detailed study before targeting NS1 to develop permanent vaccines or novel drugs against IAV in future.

APOBEC3G Is a p53-Dependent Restriction Factor in Respiratory Syncytial Virus Infection of Human Cells Included in the p53/Immune Axis

Identifying and understanding genetic factors that influence the propagation of the human respiratory syncytial virus (RSV) can lead to health benefits and possibly augment recent vaccine approaches. We previously identified a p53/immune axis in which the tumor suppressor p53 directly regulates the expression of immune system genes, including the seven members of the APOBEC3 family of DNA cytidine deaminases (A3), which are innate immune sentinels against viral infections. Here, we examined the potential p53 and A3 influence in RSV infection, as well as the overall p53-dependent cellular and p53/immune axis responses to infection. Using a paired p53 model system of p53+ and p53- human lung tumor cells, we found that RSV infection activates p53, leading to the altered p53-dependent expression of A3D, A3F, and A3G, along with p53 site-specific binding. Focusing on A3G because of its 10-fold-greater p53 responsiveness to RSV, the overexpression of A3G can reduce RSV viral replication and syncytial formation. We also observed that RSV-infected cells undergo p53-dependent apoptosis. The study was expanded to globally address at the transcriptional level the p53/immune axis response to RSV. Nearly 100 genes can be directly targeted by the p53/immune axis during RSV infection based on our p53BAER analysis (Binding And Expression Resource). Overall, we identify A3G as a potential p53-responsive restriction factor in RSV infection. These findings have significant implications for RSV clinical and therapeutic studies and other p53-influenced viral infections, including using p53 adjuvants to boost the response of A3 genes.

Targeting of Calbindin 1 rescues erythropoiesis in a human model of Diamond Blackfan anemia

Diamond Blackfan anemia (DBA) is an inherited bone marrow failure syndrome characterized by congenital anomalies, cancer predisposition and a severe hypo-proliferative anemia. It was the first disease linked to ribosomal dysfunction and >70 % of patients have been identified to have a haploinsufficiency of a ribosomal protein (RP) gene, with RPS19 being the most common mutation. There is significant variability within the disease in terms of phenotype as well as response to therapy suggesting that other genes contribute to the pathophysiology and potential management of this disease. To explore these questions, we performed a genome-wide CRISPR screen in a cellular model of DBA and identified Calbindin 1 (CALB1), a member of the calcium-binding superfamily, as a potential modifier of the disordered erythropoiesis in DBA. We used human derived CD34+ cells cultured in erythroid stimulating media with knockdown of RPS19 as a model for DBA to study the effects of CALB1. We found that knockdown of CALB1 in this DBA model promoted erythroid maturation. We also noted effects of CALB1 knockdown on cell cycle. Taken together, our results reveal CALB1 is a novel regulator of human erythropoiesis and has implications for using CALB1 as a novel therapeutic target in DBA.

The Wheel of p53 Helps to Drive the Immune System

The p53 tumor suppressor protein is best known as an inhibitor of the cell cycle and an inducer of apoptosis. Unexpectedly, these functions of p53 are not required for its tumor suppressive activity in animal models. High-throughput transcriptomic investigations as well as individual studies have demonstrated that p53 stimulates expression of many genes involved in immunity. Probably to interfere with its immunostimulatory role, many viruses code for proteins that inactivate p53. Judging by the activities of immunity-related p53-regulated genes it can be concluded that p53 is involved in detection of danger signals, inflammasome formation and activation, antigen presentation, activation of natural killer cells and other effectors of immunity, stimulation of interferon production, direct inhibition of virus replication, secretion of extracellular signaling molecules, production of antibacterial proteins, negative feedback loops in immunity-related signaling pathways, and immunologic tolerance. Many of these p53 functions have barely been studied and require further, more detailed investigations. Some of them appear to be cell-type specific. The results of transcriptomic studies have generated many new hypotheses on the mechanisms utilized by p53 to impact on the immune system. In the future, these mechanisms may be harnessed to fight cancer and infectious diseases.

Manganese Mediates Its Antiviral Functions in a cGAS-STING Pathway Independent Manner

The innate immune system is the first line of host defense sensing viral infection. Manganese (Mn) has recently been found to be involved in the activation of the innate immune DNA-sensing cGAS-STING pathway and subsequent anti-DNA virus function. However, it is still unclear whether Mn2+ mediates host defense against RNA viruses. In this study, we demonstrate that Mn2+ exhibited antiviral effects against various animal and human viruses, including RNA viruses such as PRRSVs and VSV, as well as DNA viruses such as HSV1, in a dose-dependent manner. Moreover, cGAS and STING were both investigated in the Mn2+ mediated antiviral roles using the knockout cells made by the CRISPR-Cas9 approach. Unexpectedly, the results revealed that neither cGAS knockout nor STING knockout had any effect on Mn2+-mediated antiviral functions. Nevertheless, we verified that Mn2+ promoted the activation of the cGAS-STING signaling pathway. These findings suggest that Mn2+ has broad-spectrum antiviral activities in a cGAS-STING pathway independent manner. This study also provides significant insights into redundant mechanisms participating in the Mn2+ antiviral functions, and also indicates a new target for Mn2+ antiviral therapeutics.

Exosomal microRNA expression profiles derived from A549 human lung cells in response to influenza A/H1N1pdm09 infection

Exosomes participate in intercellular communication by shuttling various small molecules from donor to recipient cells. We aimed to examine the role of exosomes and exosomal miRNAs in influenza virus infection. The results showed that influenza A/H1N1pdm09 infection could promote A549 cells to secrete exosomes, while blocking the generation of exosomes reduced viral RNA production. A total of 97 exosomal miRNAs with significantly altered expression were identified during influenza infection. Of 12 candidate miRNAs chosen for further validation, ten were confirmed by qRT-PCR. Among 5978 predicted target genes，we found 37 interferon pathway-related genes to be the potential targets of 29 differentially expressed miRNAs. Many target genes were annotated to various KEGG signaling pathways, some of which played important roles in influenza infection. These data will help to further understand the mechanism of influenza virus-host interactions, which is important for the development of preventative and therapeutic strategies against influenza virus.

TP53 Gene Therapy as a Potential Treatment for Patients with COVID-19

SGT-53 is a novel investigational agent that comprises an immunoliposome carrying a plasmid vector driving expression of the human TP53 gene that encodes wild-type human p53. SGT-53 is currently in phase II human trials for advanced pancreatic cancer. Although p53 is best known as a tumor suppressor, its participation in both innate and adaptive immune responses is well documented. It is now clear that p53 is an important component of the host response to various viral infections. To facilitate their viral life cycles, viruses have developed a diverse repertoire of strategies for counteracting the antiviral activities of host immune system by manipulating p53-dependent pathways in host cells. Coronaviruses reduce endogenous p53 levels in the cells they infect by enhancing the degradation of p53 in proteasomes. Thus, interference with p53 function is an important component in viral pathogenesis. Transfection of cells by SGT-53 has been shown to transiently produce exogenous p53 that is active as a pleiotropic transcription factor. We herein summarize the rationale for repurposing SGT-53 as a therapy for infection by SARS-CoV-2, the pathogen responsible for the COVID-19 pandemic. Because p53 regulation was found to play a crucial role in different infection stages of a wide variety of viruses, it is rational to believe that restoring p53 function based on SGT-53 treatment may lead to beneficial therapeutic outcomes for infectious disease at large including heretofore unknown viral pathogens that may emerge in the future.

Mandarin Fish (Siniperca chuatsi) p53 Regulates Glutaminolysis Induced by Virus via the p53/miR145-5p/c-Myc Pathway in Chinese Perch Brain Cells

p53, as an important tumor suppressor protein, has recently been implicated in host antiviral defense. The present study found that the expression of mandarin fish (Siniperca chuatsi) p53 (Sc-p53) was negatively associated with infectious spleen and kidney necrosis virus (ISKNV) and Siniperca chuatsi rhabdovirus (SCRV) proliferation as well as the expression of glutaminase 1 (GLS1) and glutaminolysis pathway-related enzymes glutamate dehydrogenase (GDH) and isocitrate dehydrogenase 2 (IDH2). This indicated that Sc-p53 inhibited the replication and proliferation of ISKNV and SCRV by negatively regulating the glutaminolysis pathway. Moreover, it was confirmed that miR145-5p could inhibit c-Myc expression by targeting the 3′ untranslated region (UTR). Sc-p53 could bind to the miR145-5p promoter region to promote its expression and to further inhibit the expression of c-Myc. The expression of c-Myc was proved to be positively correlated with the expression of GLS1 as well. All these suggested a negative relationship between the Sc-p53/miR145-5p/c-Myc pathway and GLS1 expression and glutaminolysis. However, it was found that after ISKNV and SCRV infection, the expressions of Sc-p53, miR145-5p, c-Myc, and GLS1 were all significantly upregulated, which did not match the pattern in normal cells. Based on the results, it was suggested that ISKNV and SCRV infection altered the Sc-p53/miR145-5p/c-Myc pathway. All of above results will provide potential targets for the development of new therapeutic strategies against ISKNV and SCRV.

IMPORTANCE Infectious spleen and kidney necrosis virus (ISKNV) and Siniperca chuatsi rhabdovirus (SCRV) as major causative agents have caused a serious threat to the mandarin fish farming industry (J.-J. Tao, J.-F. Gui, and Q.-Y. Zhang, Aquaculture 262:1–9, 2007, https://doi.org/10.1016/j.aquaculture.2006.09.030). Viruses have evolved the strategy to shape host-cell metabolism for their replication (S. K. Thaker, J. Ch’ng, and H. R. Christofk, BMC Biol 17:59, 2019, https://doi.org/10.1186/s12915-019-0678-9). Our previous studies showed that ISKNV replication induced glutamine metabolism reprogramming and that glutaminolysis was required for efficient replication of ISKNV and SCRV. In the present study, the mechanistic link between the p53/miR145-5p/c-Myc pathway and glutaminolysis in the Chinese perch brain (CPB) cells was provided, which will provide novel insights into ISKNV and SCRV pathogenesis and antiviral treatment strategies.

Differential miRNA expression profiling of Highly Pathogenic Avian Influenza Virus H5N1 infected chicken lungs reveals critical microRNAs, biological pathways and genes involved in the molecular pathogenesis

•

Highthrouput sequencing of small RNA of H5N1 infected and mock infected chicken lungs.

•

297 miRNAs identified in mock-infected and 201 miRNAs identified in AIV infected chicken lungs.

•

36 miRNAs were upregulated and 90 were downregulated during H5N1 infection.

•

Functional analysis and gene ontology of predicted target genes of expressed miRNAs.

•

MAPK pathway, NF-κB, IGF and gga-let-7b might play important role during H5N1 pathogenesis.

Novel Function of Avian p53 in Binding to ALV-J LTR Contributes to Its Antiviral Roles

Accumulating evidence suggests that p53 is involved in viral infection. However, it remains elusive whether avian p53 orchestrates avian leukosis virus (ALV) replication. We showed that p53 recruits the histone deacetylase 1 and 2 (HDAC1/2) complex to the ALV promoter to shut off ALV's promoter activity and viral replication. HDAC1/2 binding to the ALV promoter was abolished in the absence of p53. Moreover, we collected samples in ALV-infected chickens and found that the acetylation status of ALV-bound H3 and H4 histones correlated with ALV viremia. HDAC inhibitors (HDACi) potently increase ALV replication, but HDACi-promoted viral replication is dramatically reduced in cells with p53 depletion. These data demonstrate that p53 is critical for inhibition ALV replication and suggest that future studies of ALV replication need to account for the potential effects of p53 activity. IMPORTANCE Rous sarcoma virus (RSV)/ALV was the first retrovirus to be discovered, which was really the first hint that cancer, or a tumor, could be transmitted by a virus. The specific mechanisms that regulate ALV replication during infection remain poorly understood. Here, we show that avian p53 and HDAC complex inhibit ALV promoter activity and replication, and p53 inhibits ALV replication through binding to the ALV promoter. We demonstrated that the acetylation status of ALV-bound H3 and H4 histones correlates with ALV viremia level using clinical samples collected from commercial poultry. These findings identify both p53-mediated inhibition on ALV replication and a potential role for virus-induced tumorigenesis.

Identification of Nifurtimox and Chrysin as Anti-Influenza Virus Agents by Clinical Transcriptome Signature Reversion

The rapid development in the field of transcriptomics provides remarkable biomedical insights for drug discovery. In this study, a transcriptome signature reversal approach was conducted to identify the agents against influenza A virus (IAV) infection through dissecting gene expression changes in response to disease or compounds’ perturbations. Two compounds, nifurtimox and chrysin, were identified by a modified Kolmogorov–Smirnov test statistic based on the transcriptional signatures from 81 IAV-infected patients and the gene expression profiles of 1309 compounds. Their activities were verified in vitro with half maximal effective concentrations (EC₅₀s) from 9.1 to 19.1 μM against H1N1 or H3N2. It also suggested that the two compounds interfered with multiple sessions in IAV infection by reversing the expression of 28 IAV informative genes. Through network-based analysis of the 28 reversed IAV informative genes, a strong synergistic effect of the two compounds was revealed, which was confirmed in vitro. By using the transcriptome signature reversion (TSR) on clinical datasets, this study provides an efficient scheme for the discovery of drugs targeting multiple host factors regarding clinical signs and symptoms, which may also confer an opportunity for decelerating drug-resistant variant emergence.

How Influenza A Virus NS1 Deals with the Ubiquitin System to Evade Innate Immunity

Ubiquitination is a post-translational modification regulating critical cellular processes such as protein degradation, trafficking and signaling pathways, including activation of the innate immune response. Therefore, viruses, and particularly influenza A virus (IAV), have evolved different mechanisms to counteract this system to perform proper infection. Among IAV proteins, the non-structural protein NS1 is shown to be one of the main virulence factors involved in these viral hijackings. NS1 is notably able to inhibit the host's antiviral response through the perturbation of ubiquitination in different ways, as discussed in this review.

A blood RNA transcriptome signature for COVID-19

Background

COVID-19 is a respiratory viral infection with unique features including a more chronic course and systemic disease manifestations including multiple organ involvement; and there are differences in disease severity between ethnic groups. The immunological basis for disease has not been fully characterised. Analysis of whole-blood RNA expression may provide valuable information on disease pathogenesis.

Methods

We studied 45 patients with confirmed COVID-19 infection within 10 days from onset of illness and a control group of 19 asymptomatic healthy volunteers with no known exposure to COVID-19 in the previous 14 days. Relevant demographic and clinical information was collected and a blood sample was drawn from all participants for whole-blood RNA sequencing. We evaluated differentially-expressed genes in COVID-19 patients (log2 fold change ≥ 1 versus healthy controls; false-discovery rate < 0.05) and associated protein pathways and compared these to published whole-blood signatures for respiratory syncytial virus (RSV) and influenza. We developed a disease score reflecting the overall magnitude of expression of internally-validated genes and assessed the relationship between the disease score and clinical disease parameters.

Results

We found 135 differentially-expressed genes in the patients with COVID-19 (median age 35 years; 82% male; 36% Chinese, 53% South Asian ethnicity). Of the 117 induced genes, 14 were found in datasets from RSV and 40 from influenza; 95 genes were unique to COVID-19. Protein pathways were mostly generic responses to viral infections, including apoptosis by P53-associated pathway, but also included some unique pathways such as viral carcinogenesis. There were no major qualitative differences in pathways between ethnic groups. The composite gene-expression score was correlated with the time from onset of symptoms and nasal swab qPCR CT values (both p < 0.01) but was not related to participant age, gender, ethnicity or the presence or absence of chest X-ray abnormalities (all p > 0.05).

Conclusions

The whole-blood transcriptome of COVID-19 has overall similarity with other respiratory infections but there are some unique pathways that merit further exploration to determine clinical relevance. The approach to a disease score may be of value, but needs further validation in a population with a greater range of disease severity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01006-w.

The Crossroads between Host Copper Metabolism and Influenza Infection

Three main approaches are used to combat severe viral respiratory infections. The first is preemptive vaccination that blocks infection. Weakened or dead viral particles, as well as genetic constructs carrying viral proteins or information about them, are used as an antigen. However, the viral genome is very evolutionary labile and changes continuously. Second, chemical agents are used during infection and inhibit the function of a number of viral proteins. However, these drugs lose their effectiveness because the virus can rapidly acquire resistance to them. The third is the search for points in the host metabolism the effect on which would suppress the replication of the virus but would not have a significant effect on the metabolism of the host. Here, we consider the possibility of using the copper metabolic system as a target to reduce the severity of influenza infection. This is facilitated by the fact that, in mammals, copper status can be rapidly reduced by silver nanoparticles and restored after their cancellation.

Organic synthesis and anti-influenza A virus activity of cyclobakuchiols A, B, C, and D

Novel antiviral agents for influenza, which poses a substantial threat to humans, are required. Cyclobakuchiols A and B have been isolated from Psoralea glandulosa, and cyclobakuchiol C has been isolated from P. corylifolia. The structural differences between cyclobakuchiol A and C arise due to the oxidation state of isopropyl group, and these compounds can be derived from (+)-(S)-bakuchiol, a phenolic isoprenoid compound present in P. corylifolia seeds. We previously reported that bakuchiol induces enantiospecific anti-influenza A virus activity involving nuclear factor erythroid 2-related factor 2 (Nrf2) activation. However, it remains unclear whether cyclobakuchiols A–C induce anti-influenza A virus activity. In this study, cyclobakuchiols A, B, and C along with cyclobakuchiol D, a new artificial compound derived from cyclobakuchiol B, were synthesized and examined for their anti-influenza A virus activities using Madin-Darby canine kidney cells. As a result, cyclobakuchiols A–D were found to inhibit influenza A viral infection, growth, and the reduction of expression of viral mRNAs and proteins in influenza A virus-infected cells. Additionally, these compounds markedly reduced the mRNA expression of the host cell influenza A virus-induced immune response genes, interferon-β and myxovirus-resistant protein 1. In addition, cyclobakuchiols A–D upregulated the mRNA levels of NAD(P)H quinone oxidoreductase 1, an Nrf2-induced gene, in influenza A virus-infected cells. Notably, cyclobakuchiols A, B, and C, but not D, induced the Nrf2 activation pathway. These findings demonstrate that cyclobakuchiols have anti-influenza viral activity involving host cell oxidative stress response. In addition, our results suggest that the suitably spatial configuration between oxidized isopropyl group and phenol moiety in the structure of cyclobakuchiols is required for their effect.

TGF-β1 signaling inhibit the in vitro apoptotic, infection and stimulatory cell response induced by influenza H1N1 virus infection on A549 cells

Influenza A virus (IAV) infection induces host cell responses that could derive in inflammatory and apoptotic response. In this respect, in multiple pathological situations, TGF-β1 has shown anti-inflammatory effect, but its role during IAV infection is poorly understood. Interestingly, recent profiling expression studies have suggested that the TGF-β1 pathway could be functionally related to the IAV infection's host response. To gain an understanding of the involvement of TGF-β1's signaling pathway during IAV infection, we compared different apoptotic proteins such as TNFR1, Fas ligand, XIAP, cIAP, among others proteins, and pro-inflammatory elements like IL-1β in the A549 cells during IAV infection (H1N1/NC/99), with and without 1 h of pre-treatment with TGF-β1. Pre-incubation with TGF-β1 significantly inhibited apoptosis and the presence of pro-apoptotic factors. Moreover, the relative abundance of immunodetected IAV M1 protein along 24 -h post-infection period was abridged, which correlated with a disminished infectious viral progeny Additionally, caspase 1 activation and increase of IL-1β induced by IAV infection was also reduced by TGF-β1 signaling activation. Whereas IAV infection increase of Smad-7 and, as consequence, partially inhibiting Smad2/3 phosphorylation, pre-treatment with TGF-β1 blocked IAV-dependent Smad7 induction and prevented Smad2/3 signaling shutdown. All these data suggest the role of TGF-β1 signaling pathway in the control of host cell response induced by the IAV infection and identify a potential clinical target to modulate acute cell death.

Bluetongue Viruses Act as Novel Oncolytic Viruses to Effectively Inhibit Human Renal Cancer Cell Growth In Vitro and In Vivo

Background

The bluetongue virus (BTV) is the prototype virus in the genus Orbivirus within the family Reoviridae. Recent studies indicate that BTVs are capable of infecting and selectively lysing human hepatic carcinoma cells (Hep-3B) and prostate carcinoma cells (pc-3). This study was designed to evaluate the oncolytic potential of BTV in experimental models of human renal cancer in vitro and in vivo.

Material/Methods

Five human renal cancer cell lines, ACHN, CAKI-1, OS-RC-2, 786-O, and A498, were used in this study to analyze BTV replication. These cells were lysed by oncolysis compared to normal control. Xenograft models were used to assess the efficacy and toxicity of BTVs in vivo. Data were analyzed by one-way ANOVA or two-sided unpaired t tests.

Results

The results showed HPTEC cells to be relatively resistant to cytotoxic effects of BTVs and exhibited normal growth rate even at high dose of BTVs. Nonetheless, the renal cancer cells showed a remarkably higher sensitivity to BTVs. Moreover, the ultramicroscopic subcellular changes were also detected in the renal cells. The viral particles were observed in all the RCC cell lines, but not in HPTEC cells. Intratumoral injections of BTVs significantly decreased the tumor volume as compared to animals that received no virus treatment. Infection with BTVs significantly increased the percentage of apoptotic renal cancer cells but not the HPTEC cells. Moreover, BTV triggered apoptosis in renal cancer cells via a mitochondria-mediated pathway.

Conclusions

This study for the first time demonstrated the oncolytic potential of BTV in experimental models of human renal cancer. BTV exhibits the potential to inhibit human renal cancer cell growth in vitro and in vivo.

Role of p38 mitogen-activated protein kinase signalling in virus replication and potential for developing broad spectrum antiviral drugs

Mitogen-activated protein kinases (MAPKs) play a key role in complex cellular processes such as proliferation, development, differentiation, transformation and apoptosis. Mammals express at least four distinctly regulated groups of MAPKs which include extracellular signal-related kinases (ERK)-1/2, p38 proteins, Jun amino-terminal kinases (JNK1/2/3) and ERK5. p38 MAPK is activated by a wide range of cellular stresses and modulates activity of several downstream kinases and transcription factors which are involved in regulating cytoskeleton remodeling, cell cycle modulation, inflammation, antiviral response and apoptosis. In viral infections, activation of cell signalling pathways is part of the cellular defense mechanism with the basic aim of inducing an antiviral state. However, viruses can exploit enhanced cell signalling activities to support various stages of their replication cycles. Kinase activity can be inhibited by small molecule chemical inhibitors, so one strategy to develop antiviral drugs is to target these cellular signalling pathways. In this review, we provide an overview on the current understanding of various cellular and viral events regulated by the p38 signalling pathway, with a special emphasis on targeting these events for antiviral drug development which might identify candidates with broad spectrum activity.

The roles of signaling pathways in SARS-CoV-2 infection; lessons learned from SARS-CoV and MERS-CoV

The number of descriptions of emerging viruses has grown at an unprecedented rate since the beginning of the 21^st century. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is the third highly pathogenic coronavirus that has introduced itself into the human population in the current era, after SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Molecular and cellular studies of the pathogenesis of this novel coronavirus are still in the early stages of research; however, based on similarities of SARS-CoV-2 to other coronaviruses, it can be hypothesized that the NF-κB, cytokine regulation, ERK, and TNF-α signaling pathways are the likely causes of inflammation at the onset of COVID-19. Several drugs have been prescribed and used to alleviate the adverse effects of these inflammatory cellular signaling pathways, and these might be beneficial for developing novel therapeutic modalities against COVID-19. In this review, we briefly summarize alterations of cellular signaling pathways that are associated with coronavirus infection, particularly SARS-CoV and MERS-CoV, and tabulate the therapeutic agents that are currently approved for treating other human diseases.

M1 macrophage dependent-p53 regulates the intracellular survival of mycobacteria

Tumor suppressor p53 is not only affects immune responses but also contributes to antibacterial activity. However, its bactericidal function during mycobacterial infection remains unclear. In this study, we found that the p53-deficient macrophages failed to control Mycobacterium tuberculosis (Mtb), manifested as a lower apoptotic cell death rate and enhanced intracellular survival. The expression levels of p53 during Mtb infection were stronger in M1 macrophages than in M2 macrophages. The TLR2/JNK signaling pathway plays an essential role in the modulation of M1 macrophage polarization upon Mtb infection. It facilitates p53-mediated apoptosis through the production of reactive oxygen species, nitric oxide and inflammatory cytokines in Mtb-infected M1 macrophages. In addition, nutlin-3 effectively abrogated the intracellular survival of mycobacteria in both TB patients and healthy controls after H37Ra infection for 24 h, indicating that the enhancement of p53 production effectively suppressed the intracellular survival of Mtb in hosts. These results suggest that p53 can be a new therapeutic target for TB therapy.

Tetracycline and viruses: a possible treatment for COVID-19?

Tetracyclines have been used to treat many bacterial infections. The use of these antibiotics for the treatment of viral diseases dates to the 1960s to 1970s. Over the decades, the effect of tetracyclines on the pathogenesis of viral infections has been demonstrated both clinically and experimentally. Tetracyclines can act on viral infections either through their antibacterial properties or through direct antiviral action. This review focuses on clinical and experimental data that support the use of tetracycline in treating viral infections and highlights an important approach to slowing disease progression during viral infections. Tetracycline treatment might represent a strategy for eliminating the infection or inhibiting the progression of COVID-19.

p53 promotes ZDHHC1-mediated IFITM3 palmitoylation to inhibit Japanese encephalitis virus replication

The tumor suppressor p53 as an innate antiviral regulator contributes to restricting Japanese encephalitis virus (JEV) replication, but the mechanism is still unclear. The interferon-induced transmembrane protein 3 (IFITM3) is an intrinsic barrier to a range of virus infection, whether IFITM3 is responsible for the p53-mediated anti-JEV response remains elusive. Here, we found that IFITM3 significantly inhibited JEV replication in a protein-palmitoylation-dependent manner and incorporated into JEV virions to diminish the infectivity of progeny viruses. Palmitoylation was also indispensible for keeping IFITM3 from lysosomal degradation to maintain its protein stability. p53 up-regulated IFITM3 expression at the protein level via enhancing IFITM3 palmitoylation. Screening of palmitoyltransferases revealed that zinc finger DHHC domain-containing protein 1 (ZDHHC1) was transcriptionally up-regulated by p53, and consequently ZDHHC1 interacted with IFITM3 to promote its palmitoylation and stability. Knockdown of IFITM3 significantly impaired the inhibitory role of ZDHHC1 on JEV replication. Meanwhile, knockdown of either ZDHHC1 or IFITM3 expression also compromised the p53-mediated anti-JEV effect. Interestingly, JEV reduced p53 expression to impair ZDHHC1 mediated IFITM3 palmitoylation for viral evasion. Our data suggest the existence of a previously unrecognized p53-ZDHHC1-IFITM3 regulatory pathway with an essential role in restricting JEV infection and provide a novel insight into JEV-host interaction.

The tumor suppressor p53 contributes to the host antiviral response against Japanese encephalitis virus (JEV). We explored the downstream molecules responsible for the p53-mediated anti-JEV response. p53 transcriptionally up-regulated the expression of the palmitoyltransferase zinc finger DHHC domain-containing protein 1 (ZDHHC1) to enhance stability of the antiviral restriction factor interferon-induced transmembrane protein 3 (IFITM3) by regulating its palmitoylation. Knockdown of either ZDHHC1 or IFITM3 expression compromised the anti-JEV effect of p53. These observations suggest the existence of a previously unrecognized crosstalk between p53 and IFITM3, mediated by ZDHHC1, thus revealing a novel regulatory pathway p53-ZDHHC1-IFITM3 with an essential role in the p53-mediated anti-JEV response.

Host cell p53 associates with the feline calicivirus major viral capsid protein VP1, the protease-polymerase NS6/7, and the double-stranded RNA playing a role in virus replication

p53 is implicated in several cellular pathways such as induction of cell-cycle arrest, differentiation, senescence, and apoptosis. p53 is activated by a broad range of stress signals, including viral infections. While some viruses activate p53, others induce its inactivation, and occasionally p53 is differentially modulated during the replicative cycle. During calicivirus infections, apoptosis is required for virus exit and spread into the host; yet, the role of p53 during infection is unknown. By confocal microscopy, we found that p53 associates with FCV VP1, the protease-polymerase NS6/7, and the dsRNA. This interaction was further confirmed by proximity ligation assays, suggesting that p53 participates in the FCV replication. Knocked-down of p53 expression in CrFK cells before infection, resulted in a strong reduction of the non-structural protein levels and a decrease of the viral progeny production. These results indicate that p53 is associated with the viral replication complex and is required for an efficient FCV replication.

•

Host cell p53 protein levels and subcellular localization do not change during FCV infection.

•

Host cell p53 associates with FCV major viral capsid protein VP1, protease-polymerase NS6/7, and the dsRNA in FCV infected cells.

•

Host cell p53 is required for a FCV replication.

Ca2+ plays an antiviral role by increasing p53 expression to achieve protection against spring viraemia of carp virus infection

Calcium (Ca) is a messenger that regulates a multitude of physiological processes, but its functions in antiviral progress remain undefined. In this study, we found that Ca2+ enhances fish survival to defend against spring viraemia of carp virus (SVCV) infection by reversing the instability of p53 mediated by the viral protein. First, Ca2+ significantly protected cells and fish against SVCV infection by inducing early apoptosis. Additionally, p53 expression, which was inhibited by SVCV N protein, was upregulated by Ca2+ treatment. Then, the mechanism underlying the reduction of K63-linked p53 ubiquitination by SVCV N protein via the K358 site was completely prevented by Ca2+. These findings reveal the role of Ca2+ in lower vertebrates in the antiviral response, which is connected to and corresponds with viral immune evasion, providing a solution to fish diseases caused by pathogens.

Orf Virus VIR Antagonizes p53-Mediated Antiviral Effects to Facilitate Viral Replication

As a zoonotic disease, ovine contagious pustular dermatitis (Orf) is a serious threat to sheep as well as humans. Orf virus (ORFV) interferon resistance protein (VIR) is the principal virulence protein that encodes a dsRNA-binding protein to inhibit host antiviral response. p53 is one of the key proteins of the host antiviral innate immunity. It not only enhances type I interferon secretion but also induces apoptosis in infected cells, and plays a crucial role in the immune response against various viral infections. However, it remains to be elucidated what role p53 plays in ORFV replication and whether ORFV's own protein VIR regulates p53 expression to promote self-replication. In this study, we showed that p53 has an antiviral effect on ORFV and can inhibit ORFV replication. In addition, ORFV nonstructural protein VIR interacts with p53 and degrades p53, which inhibits p53-mediated positive regulation of downstream antiviral genes. This study provides new insight into the immune evasion mediated by ORFV and identifies VIR as an antagonistic factor for ORFV to evade the antiviral response.

A big data pipeline: Identifying dynamic gene regulatory networks from time-course Gene Expression Omnibus data with applications to influenza infection

A biological host response to an external stimulus or intervention such as a disease or infection is a dynamic process, which is regulated by an intricate network of many genes and their products. Understanding the dynamics of this gene regulatory network allows us to infer the mechanisms involved in a host response to an external stimulus, and hence aids the discovery of biomarkers of phenotype and biological function. In this article, we propose a modeling/analysis pipeline for dynamic gene expression data, called Pipeline4DGEData, which consists of a series of statistical modeling techniques to construct dynamic gene regulatory networks from the large volumes of high-dimensional time-course gene expression data that are freely available in the Gene Expression Omnibus repository. This pipeline has a consistent and scalable structure that allows it to simultaneously analyze a large number of time-course gene expression data sets, and then integrate the results across different studies. We apply the proposed pipeline to influenza infection data from nine studies and demonstrate that interesting biological findings can be discovered with its implementation.

Influenza virus and atherosclerosis

Influenza viruses infect the upper respiratory system, causing usually a self-limited disease with mild respiratory symptoms. Acute lung injury, pulmonary microvascular leakage and cardiovascular collapse may occur in severe cases, usually in the elderly or in immunocompromised patients. Acute lung injury is a syndrome associated with pulmonary oedema, hypoxaemia and respiratory failure. Influenza virus primarily binds to the epithelium, interfering with the epithelial sodium channel function. However, the main clinical devastating effects are caused by endothelial dysfunction, thought to be the main mechanism leading to pulmonary oedema, respiratory failure and cardiovascular collapse. A significant association was found between influenza infection and acute myocardial infarction (AMI). The incidence of admission due to AMI during an acute viral infection was six times as high during the 7 days after laboratory confirmation of influenza infection as during the control interval (10-fold in influenza B, 5-fold in influenza A, 3.5-fold in respiratory syncytial virus and 2.7-fold for all other viruses). Our review will focus on the mechanisms responsible for endothelial dysfunction during influenza infection leading to cardiovascular collapse and death.

DNA mismatch repair is required for the host innate response and controls cellular fate after influenza virus infection

Despite the cytopathic nature of influenza A virus (IAV) replication, we recently reported that a subset of lung epithelial club cells is able to intrinsically clear virus and survive infection. However, the mechanisms that drive cell survival during a normally lytic infection remained unclear. Using a loss-of-function screening approach, we discovered that the DNA mismatch repair (MMR) pathway is essential for club cell survival of IAV infection. Repair of virally-induced oxidative damage by the DNA MMR pathway not only allowed cell survival of infection but also facilitated host gene transcription, including the expression of antiviral and stress response genes. Enhanced viral suppression of the DNA MMR pathway prevented club cell survival and increased the severity of viral disease in vivo. Altogether, these results identify previously unappreciated roles for DNA MMR as a central modulator of cellular fate and a contributor to the innate antiviral response, which together, control influenza viral disease severity.

Lysine-specific post-translational modifications of proteins in the life cycle of viruses

The process of protein post-translational modifications (PTM) is one of the critical mechanisms of regulation of many cellular processes, which makes it an attractive target for various viruses. Since viruses cannot replicate on their own, they have developed unique abilities to alter metabolic and signaling cell pathways, including protein PTMs, to ensure faithful replication of their genomes. This review describes several ways of how lysine-specific PTMs are used by various viruses to ensure its successful invasion and replication. Covalent modifications like acetylation, ubiquitination, and methylation form a complex system of reversible and often competing modifications, which adds an additional level of complexity to the system of regulation of the activity of host proteins involved in viral replication and propagation. In furthering these, we also describe the manner in which PTM pathways can also be accosted by various types of viruses to neutralize the host's cellular mechanisms for anti-viral protection and highlight key areas for future therapeutic targeting and design.

Activation of innate immunity by mitochondrial dsRNA in mouse cells lacking p53 protein

Viral and cellular double-stranded RNA (dsRNA) is recognized by cytosolic innate immune sensors, including RIG-I-like receptors. Some cytoplasmic dsRNA is commonly present in cells, and one source is mitochondrial dsRNA, which results from bidirectional transcription of mitochondrial DNA (mtDNA). Here we demonstrate that Trp53 mutant mouse embryonic fibroblasts contain immune-stimulating endogenous dsRNA of mitochondrial origin. We show that the immune response induced by this dsRNA is mediated via RIG-I-like receptors and leads to the expression of type I interferon and proinflammatory cytokine genes. The mitochondrial dsRNA is cleaved by RNase L, which cleaves all cellular RNA including mitochondrial mRNAs, increasing activation of RIG-I-like receptors. When mitochondrial transcription is interrupted there is a subsequent decrease in this immune-stimulatory dsRNA. Our results reveal that the role of p53 in innate immunity is even more versatile and complex than previously anticipated. Our study, therefore, sheds new light on the role of endogenous RNA in diseases featuring aberrant immune responses.

Comparative transcriptome analysis reveals the role of p53 signalling pathway during red-spotted grouper nervous necrosis virus infection in Lateolabrax japonicus brain cells

Nervous necrosis virus (NNV) is one of the fish pathogens that have caused mass mortalities of many marine and freshwater fishes in the world. To better comprehend the molecular immune mechanism of sea perch (Lateolabrax japonicus) against NNV infection, the comparative transcriptome analysis of red-spotted grouper nervous necrosis virus (RGNNV)-infected or mock-infected L. japonicus brain (LJB) cells was performed via RNA sequencing technology. Here, 1,969 up-regulated genes and 9,858 down-regulated genes, which were widely implicated in immune response pathways, were identified. Furthermore, we confirmed that p53 signalling pathway was repressed at 48 hr post-RGNNV infection, as indicated by up-regulation of Mdm2 and down-regulation of p53 and its downstream target genes, including Bax, Casp8 and CytC. Overexpression of L. japonicus p53 (Ljp53) significantly inhibited RGNNV replication and up-regulated the expression of apoptosis-related genes, whereas the down-regulation caused by pifithrin-α led to the opposite effect, suggesting Ljp53 might promote cell apoptosis to repress virus replication. Luciferase assay indicated that Ljp53 could enhance the promoter activities of zebrafish interferon (IFN)1, indicating that Ljp53 could exert its anti-RGNNV activities by enforcing the type I IFN response. This study revealed the potential antiviral role of p53 during NNV infection.

Spring viraemia of carp virus modulates p53 expression using two distinct mechanisms

p53, which regulates cell-cycle arrest and apoptosis, is a crucial target for viruses to release cells from cell-cycle checkpoints or to protect cells from apoptosis for their own benefit. Viral evasion mechanisms of aquatic viruses remain mysterious. Here, we report the spring viremia of carp virus (SVCV) degrading and stabilizing p53 in the ubiquitin-proteasome pathway by the N and P proteins, respectively. Early in an SVCV infection, significant induction was observed in the S phase and p53 was decreased in the protein level. Further experiments demonstrated that p53 interacted with SVCV N protein and was degraded by suppressing the K63-linked ubiquitination. However, the increase of p53 was observed late in the infection and experiments suggested that p53 was bound to SVCV P protein and stabilized by enhancing the K63-linked ubiquitination. Finally, lysine residue 358 was the key site for p53 K63-linked ubiquitination by the N and P proteins. Thus, our findings suggest that fish p53 is modulated by SVCV N and P protein in two distinct mechanisms, which uncovers the strategy for the subversion of p53-mediated host innate immune responses by aquatic viruses.

The Nonstructural NS1 Protein of Influenza Viruses Modulates TP53 Splicing through Host Factor CPSF4

Influenza A viruses (IAV) are known to modulate and "hijack" several cellular host mechanisms, including gene splicing and RNA maturation machineries. These modulations alter host cellular responses and enable an optimal expression of viral products throughout infection. The interplay between the host protein p53 and IAV, in particular through the viral nonstructural protein NS1, has been shown to be supportive for IAV replication. However, it remains unknown whether alternatively spliced isoforms of p53, known to modulate p53 transcriptional activity, are affected by IAV infection and contribute to IAV replication. Using a TP53 minigene, which mimics intron 9 alternative splicing, we have shown here that the NS1 protein of IAV changes the expression pattern of p53 isoforms. Our results demonstrate that CPSF4 (cellular protein cleavage and polyadenylation specificity factor 4) independently and the interaction between NS1 and CPSF4 modulate the alternative splicing of TP53 transcripts, which may result in the differential activation of p53-responsive genes. Finally, we report that CPSF4 and most likely beta and gamma spliced p53 isoforms affect both viral replication and IAV-associated type I interferon secretion. All together, our data show that cellular p53 and CPSF4 factors, both interacting with viral NS1, have a crucial role during IAV replication that allows IAV to interact with and alter the expression of alternatively spliced p53 isoforms in order to regulate the cellular innate response, especially via type I interferon secretion, and perform efficient viral replication.IMPORTANCE Influenza A viruses (IAV) constitute a major public health issue, causing illness and death in high-risk populations during seasonal epidemics or pandemics. IAV are known to modulate cellular pathways to promote their replication and avoid immune restriction via the targeting of several cellular proteins. One of these proteins, p53, is a master regulator involved in a large panel of biological processes, including cell cycle arrest, apoptosis, or senescence. This "cellular gatekeeper" is also involved in the control of viral infections, and viruses have developed a wide diversity of mechanisms to modulate/hijack p53 functions to achieve an optimal replication in their hosts. Our group and others have previously shown that p53 activity is finely modulated by different multilevel mechanisms during IAV infection. Here, we characterized IAV nonstructural protein NS1 and the cellular factor CPSF4 as major partners involved in the IAV-induced modulation of the TP53 alternative splicing that was associated with a strong modulation of p53 activity and notably the p53-mediated antiviral response.

Tumor suppressor p53 inhibits porcine epidemic diarrhea virus infection via interferon-mediated antiviral immunity

p53 is a tumor suppressor gene that can be activated in many contexts, such as DNA damage or stressful conditions. p53 has also been shown to be important for responses to certain viral infections. Porcine epidemic diarrhea virus (PEDV) is a major enteric pathogen of the coronavirus family that causes extensive mortality among piglets. The involvement of p53 during PEDV infection has not previously been investigated. In this study, we detected p53 upregulation in response to PEDV infection. Treatment with a p53 specific activator or p53 overexpression markedly decreased viral replication, and we showed that there was more viral progeny produced in p53 knock-out cells than in p53 wild-type cells. Finally, we demonstrated that inhibition of viral infection by p53 was mediated via p53-dependent IFN signaling, leading to IFN-stimulated response element (ISRE) activation, as well as the upregulation of IFN-stimulated genes (ISGs) and IFN-β released from infected cells. These findings demonstrate that p53 suppresses PEDV infection, offering a novel therapeutic strategy for combatting this deadly disease in piglets.

miR-193b represses influenza A virus infection by inhibiting Wnt/β-catenin signalling

Due to an increasing emergence of new and drug‐resistant strains of the influenza A virus (IAV), developing novel measures to combat influenza is necessary. We have previously shown that inhibiting Wnt/β‐catenin pathway reduces IAV infection. In this study, we aimed to identify antiviral human microRNAs (miRNAs) that target the Wnt/β‐catenin signalling pathway. Using a miRNA expression library, we identified 85 miRNAs that up‐regulated and 20 miRNAs that down‐regulated the Wnt/β‐catenin signalling pathway. Fifteen miRNAs were validated to up‐regulate and five miRNAs to down‐regulate the pathway. Overexpression of four selected miRNAs (miR‐193b, miR‐548f‐1, miR‐1‐1, and miR‐509‐1) that down‐regulated the Wnt/β‐catenin signalling pathway reduced viral mRNA, protein levels in A/PR/8/34‐infected HEK293 cells, and progeny virus production. Overexpression of miR‐193b in lung epithelial A549 cells also resulted in decreases of A/PR/8/34 infection. Furthermore, miR‐193b inhibited the replication of various strains, including H1N1 (A/PR/8/34, A/WSN/33, A/Oklahoma/3052/09) and H3N2 (A/Oklahoma/309/2006), as determined by a viral reporter luciferase assay. Further studies revealed that β‐catenin was a target of miR‐193b, and β‐catenin rescued miR‐193b‐mediated suppression of IAV infection. miR‐193b induced G0/G1 cell cycle arrest and delayed vRNP nuclear import. Finally, adenovirus‐mediated gene transfer of miR‐193b to the lung reduced viral load in mice challenged by a sublethal dose of A/PR/8/34. Collectively, our findings suggest that miR‐193b represses IAV infection by inhibiting Wnt/β‐catenin signalling.

MicroRNA-34/449 family and viral infections

MicroRNAs are short, endogenous, nonprotein-coding RNAs that are essential for regulation of cellular processes through gene silencing. The miR-34/449 family is conserved in mammalian organisms and generally comprises six homologous genes: miR-34a, miR-34b, miR-34c, miR-449a, miR-449b and miR-449c, at three genomic loci. Strong similarity in the sequence of these miRNAs, particularly at the seed region, predicts robust functional redundancy. A large proportion of the literature on the miR-34/449 family focuses on its role in regulating cell cycle arrest and apoptosis by modulating E2F- and p53-related signaling pathways. A growing subset of the literature reports that the miR-34/449 family is involved in the regulation of immune responses and viral infections, and data suggest the potential for miR-34/446 as a diagnostic and therapeutic target. In this review, we discuss our current understanding of the conservation and transcriptional regulation of the miR-34/449 family and review the literature on its functions in viral infections.

Utilization of Dianthus superbus L and its bioactive compounds for antioxidant, anti-influenza and toxicological effects

Dianthus superbus (DS) is a traditional medicinal herb well known for its medicinal and therapeutic potential and widely distributed in various Asian countries. The ethyl acetate (EA), butanol (Bu) and distilled water (DW) extracts of DS assessed for extraction of bioactive compounds and their biological activities. The chemical analysis was done using LC-MS/MS and antioxidant, anticancer and antiviral activities were determined. EA extracts showed strong anticancer activity with IC₅₀ of 9.5, 13.8 and 69.9 μg/mL on SKOV, NCL-H1299 and Caski cancer cell lines, respectively. The Bu extracts exhibited strongest antiviral activity with respect to both influenza A and B viruses with IC₅₀ values of 4.97 and 3.9 μg/mL, respectively. Also the metabolic profile for EA, Bu and DW extracts shows high variations and influence precisely the antioxidant, anticancer and antiviral properties. The quercetin 3- rutinoside and isorhamnetin 3- glucoside showed higher neuraminidase inhibition activity in dose dependent manner. Molecular docking study revealed that flavonol glycosides have higher binding activities towards influenza polymerase membrane glycoprotein. Correlation study showed that flavonol glycosides were linked to anti-influenza activity and cyclic peptides with anticancer activities. This study provides vital information for effective utilization of DS for medicinal, food and therapeutic purposes.

p53 mediated IFN-β signaling to affect viral replication upon TGEV infection

TGEV can induce IFN-β production, which in turn plays a vital role in host antiviral immune responses. Our previous studies showed that TGEV infection activated p53 signaling to induce host cell apoptosis, which might influence virus replication. However, whether there be an interaction between p53 and IFN-β signaling in the process of TGEV infection is unknown. In the present study, we used low dose of TGEV to infect p53 wild-type PK-15 cells (WT PK-15 cells) and p53 deficient cells (p53-/- PK-15 cells), to investigate the modulation of IFN signaling and virus replication by p53. The results showed that the IFN-β expression and production were notably inhibited in p53-/- PK-15 cells compared with that in WT PK-15 cells at early stage of TGEV infection. In addition, TGEV-induced the changes in mRNA levels of TRIF, TRAM, MDA5, RIG-I, IPS-1, IRF9, IRF3, ISG15 and ISG20 were notably hindered in p53-/- PK-15 cells before 36 h post infection (p.i.). Moreover, TGEV genomic RNA and sub genomic mRNA (N gene and ORF7) levels showed significant increase in p53-/- PK-15 cells compared with WT PK-15 cells after TGEV infection. And viral titers were observably enhanced in p53-/- PK-15 cells. Furthermore, exogenous IFN-β and polyinosinic-polycytidylic acid (poly (I:C)) treatment markedly inhibited the mRNA levels of TGEV gRNA, N and ORF7 in WT PK-15 cells and p53-/- PK-15 cells compared to control. Taken together, these results demonstrated that p53 may mediate IFN-β signaling to inhibit viral replication early after TGEV infection.

p53 and the Viral Connection: Back into the Future ‡

The discovery of the tumor suppressor p53, through its interactions with proteins of tumor-promoting viruses, paved the way to the understanding of p53 roles in tumor virology. Over the years, accumulating data suggest that WTp53 is involved in the viral life cycle of non-tumor-promoting viruses as well. These include the influenza virus, smallpox and vaccinia viruses, the Zika virus, West Nile virus, Japanese encephalitis virus, Human Immunodeficiency Virus Type 1, Human herpes simplex virus-1, and more. Viruses have learned to manipulate WTp53 through different strategies to improve their replication and spreading in a stage-specific, bidirectional way. While some viruses require active WTp53 for efficient viral replication, others require reduction/inhibition of WTp53 activity. A better understanding of WTp53 functionality in viral life may offer new future clinical approaches, based on WTp53 manipulation, for viral infections.

Influenza A Virus Facilitates Its Infectivity by Activating p53 to Inhibit the Expression of Interferon-Induced Transmembrane Proteins

Human influenza virus (IAV) are among the most common pathogens to cause human respiratory infections. A better understanding on interplay between IAV and host factors may provide clues for disease prevention and control. While many viruses are known to downregulate p53 upon entering the cell to reduce the innate host antiviral response, IAV infection is unusual in that it activates p53. However, it has not been clear whether this process has proviral or antiviral effects. In this study, using human isogenic p53 wild-type and p53null A549 cells generated from the CRISPR/Cas9 technology, we observed that p53null cells exhibit significantly reduced viral propagation when infected with influenza A virus (strain A/Puerto Rico/8/1934 H1N1). Genome-wide microarray analysis revealed that p53 regulates the expression of a large set of interferon-inducible genes, among which the interferon-induced transmembrane family members IFITM1, IFITM2, and IFITM3 were most significantly downregulated by the expression of p53. Knockdown of interferon-induced transmembrane proteins (IFITMs) by short interfering RNAs enhanced influenza virus infectivity in p53null A549 cells, while overexpressed IFITMs in A549 cells blocked virus entry. Intriguingly, regulation of IFITMs by p53 is independent of its transcriptional activity, as the p53 short isoform Δ40p53 recapitulates IFITM regulation. Taken together, these data reveal that p53 activation by IAV is an essential step in maintaining its infectivity. This novel association between human p53 and the broad spectrum antiviral proteins, the IFITMs, demonstrates a previous mechanism employed by influenza virus to enhance its propagation via p53 inhibition of IFITMs.

A novel p53 paralogue mediates antioxidant defense of mosquito cells to survive dengue virus replication

Mosquito cells allow dengue viruses (DENVs) to undergo replication without causing serious deleterious effects on the cells, leading to advantages for dissemination to other cells. Despite this, increased accumulation of reactive oxygen species (ROS) is usually detected in C6/36 cells with DENV2 infection as shown in mammalian cells. Uniquely, oxidative stress caused by the ROS is alleviated by eliciting antioxidant defense which leads to protection of mosquito cells from the infection. In the present study, a novel p53 paralogue (p53-2) was identified and proved to be regulated in C6/36 cells with DENV2 infection. With a gene-knockdown technique, p53-2 was demonstrated to transcribe catalase which plays a critical role in reducing ROS accumulation and the death rate of infected cells. Ecologically, a higher survival rate of mosquito cells is a prerequisite for prosperous production of viral progeny, allowing infected mosquitoes to remain healthy and active for virus transmission.

Influenza A viruses alter the stability and antiviral contribution of host E3-ubiquitin ligase Mdm2 during the time-course of infection

The interplay between influenza A viruses (IAV) and the p53 pathway has been reported in several studies, highlighting the antiviral contribution of p53. Here, we investigated the impact of IAV on the E3-ubiquitin ligase Mdm2, a major regulator of p53, and observed that IAV targets Mdm2, notably via its non-structural protein (NS1), therefore altering Mdm2 stability, p53/Mdm2 interaction and regulatory loop during the time-course of infection. This study also highlights a new antiviral facet of Mdm2 possibly increasing the list of its many p53-independent functions. Altogether, our work contributes to better understand the mechanisms underlining the complex interactions between IAV and the p53 pathway, for which both NS1 and Mdm2 arise as key players.

cfa-miR-143 Promotes Apoptosis via the p53 Pathway in Canine Influenza Virus H3N2-Infected Cells

MicroRNAs regulate multiple aspects of the host response to viral infection. This study verified that the expression of cfa-miR-143 was upregulated in vivo and in vitro by canine influenza virus (CIV) H3N2 infection. To understand the role of cfa-miR-143 in CIV-infected cells, the target gene of cfa-miR-143 was identified and assessed for correlations with proteins involved in the apoptosis pathway. A dual luciferase reporter assay showed that cfa-miR-143 targets insulin-like growth factor binding protein 5 (Igfbp5). Furthermore, a miRNA agomir and antagomir of cfa-miR-143 caused the downregulation and upregulation of Igfbp5, respectively, in CIV-infected madin-darby canine kidney (MDCK) cells. This study demonstrated that cfa-miR-143 stimulated p53 and caspase3 activation and induced apoptosis via the p53 pathway in CIV H3N2-infected cells. In conclusion, CIV H3N2 induced the upregulation of cfa-miR-143, which contributes to apoptosis via indirectly activating the p53-caspase3 pathway.

Autophagy activation is required for influenza A virus-induced apoptosis and replication

Autophagy and apoptosis are two major interconnected host cell responses to viral infection, including influenza A virus (IAV). Thus, delineating these events could facilitate the development of better treatment options and provide an effective anti-viral strategy for controlling IAV infection. We used A549 cells and mouse embryonic fibroblasts (MEF) to study the role of virus-induced autophagy and apoptosis, the cross-talk between both pathways, and their relation to IAV infection [ATCC strain A/Puerto Rico/8/34(H1N1) (hereafter; PR8)]. PR8-infected and mock-infected cells were analyzed by immunoblotting, immunofluorescence confocal microscopy, electron microscopy and flow cytometry (FACS). We found that PR8 infection simultaneously induced autophagy and apoptosis in A549 cells. Autophagy was associated with Bax and Bak activation, intrinsic caspase cleavage and subsequent PARP-1 and BID cleavage. Both Bax knockout (KO) and Bax/Bak double knockout MEFs displayed inhibition of virus-induced cytopathology and cell death and diminished virus-mediated caspase activation, suggesting that virus-induced apoptosis is Bax/Bak-dependent. Biochemical inhibition of autophagy induction with 3-methyladenine blocked both virus replication and apoptosis pathways. These effects were replicated using autophagy-refractory Atg3 KO and Atg5 KO cells. Taken together, our data indicate that PR8 infection simultaneously induces autophagy and Bax/caspase-dependent apoptosis, with autophagy playing a role to support PR8 replication, in part, by modulating virus-induced apoptosis.

Mandarin fish p53: Genomic structure, alternatively spliced variant and its mRNA expression after virus challenge

A number of size variants of the p53 protein have been described in mammal, but little is known about alternative splicing of p53 expression and function in the fish. In our previous study, the immune defense and antiviral responses of p53 had been determined in mandarin fish (Siniperca chuatsi). However, the role of its splicing variants remains unknown. In the present study, the organization of mandarin fish p53 (Sc-p53) genome sequence was determined and a novel splice variant was characterized. The Sc-p53 genomic sequence was composed of 5543 bp, containing 11 exons and 10 introns, which was similar to other species. Then, a 1106 bp full-length cDNA of a novel splice variant p53 from mandarin fish (designed as Sc-p53I6) was cloned and characterized. Quantitative real-time PCR assays revealed that Sc-p53I6 was expressed in all tissues examined, and it was most abundant in the gill, hemocyte and hind kidney. Western blotting analysis revealed that Sc-p53I6 protein was abundant in liver, trunk kidney, hind kidney, stomach and heart. In addition, the regulation of Sc-p53I6 gene expression after virus infection was determined and characterized. The results showed twice rise expression pattern of Sc-p53I6 in CPB cells and spleen of mandarin fish in response to infectious kidney and spleen necrosis virus (ISKNV). However, a different expression pattern, once rise, of Sc-p53I6 in response to Siniperca chuatsi rhabdovirus (SCRV) infection was found. The mRNA expression of Sc-p53I6 was significantly up-regulated in CPB at 4 h and spleen of mandarin fish at 12 h post-infection. These results will shed a new light on antiviral response mechanisms of p53 in mandarin fish.

Identification of two p53 isoforms from Litopenaeus vannamei and their interaction with NF-κB to induce distinct immune response

p53 is a transcription factor with capability of regulating diverse NF-κB dependent biological progresses such as inflammation and host defense, but the actual mechanism remains unrevealed. Herein, we firstly identified two novel alternatively spliced isoforms of p53 from Litopenaeus vannamei (LvΔNp53 and the full-length of p53, LvFLp53). We then established that the two p53 isoforms exerted opposite effects on regulating NF-κB induced antimicrobial peptides (AMPs) and white spot syndrome virus (WSSV) immediate-early (IE) genes expression, suggesting there could be a crosstalk between p53 and NF-κB pathways. Of note, both of the two p53 isoforms could interact directly with LvDorsal, a shrimp homolog of NF-κB. In addition, the activation of NF-κB mediated by LvDorsal was provoked by LvΔNp53 but suppressed by LvFLp53, and the increased NF-κB activity conferred by LvΔNp53 can be attenuated by LvFLp53. Furthermore, silencing of LvFLp53 in shrimp caused higher mortalities and virus loads under WSSV infection, whereas LvΔNp53-knockdown shrimps exhibited an opposed RNAi phenotype. Taken together, these findings present here provided some novel insight into different roles of shrimp p53 isoforms in immune response, and some information for us to understand the regulatory crosstalk between p53 pathway and NF-κB pathway in invertebrates.