Domain Ⅲ of Dengue Virus Serotype 2 Envelope: Expression at High Levels in Escherichia coli and Competitive Inhibition of Virus Entry

Obejective The domainⅢof dengue virus type 2 envelope was cloned and expressed in Escherichia coli and the inhibited effects of recombinant protein on virus was detected. Methods In this study, the domainⅢ(DⅢ) protein of the dengue virus type-2 (DENV-2) envelope (E) antigen was expressed in Escherichia coli by fusion with a carrier protein. The protein was puriifed using enzymatic cleavage and afifnity puriifcation. Rabbit immunization and antibody detection was carried out. Inhibition of DENV-2 infection was observed by DENV-2 EDⅢprotein and its immunity rabbits serum. Results The recombinant expression DENV-2 EDⅢ protein plasmid was constructed successfully. After isopropyl thiogalactoside induction, a speciifc soluble 29 kD protein was obtained, and the expression product accounted for 68.87%of the total protein of the cell lysate. Western blot demonstrated the reactivity of the recombinant protein with his-tag and DENV (Ⅰ-Ⅳ) monoclonal antibodies. The protein was puriifed using enzymatic cleavage and affinity purification. The purified recombinant EDⅢ protein inhibited the entry of DENV-2 into BHK-21 cells. DENV-2 plaque neutralization assays were carried out using serially diluted antibodies against EDⅢprotein. At a 1︰16 dilution, the antibodies produced at least 90%neutralization of the DENV-2 virus. Furthermore, the antibodies continued to exhibit high neutralization effects (approximately 80%) until the anti-EDⅢantibody titer reached 1︰1 024. Conclusions DENV-2 EDⅢwas cloned and expressed successfully. DENV-2 EDⅢprotein could be useful in the development of inexpensive dengue vaccine. The data also suggested that DENV-2 employed an attachment molecule or receptor for its entry into C6/36 mosquito cells.

How hepatitis C virus invades hepatocytes: The mystery of viral entry

Hepatitis C virus(HCV)infection is a global health problem,with an estimated 170 million people being chronically infected.HCV cell entry is a complex multi-step process,involving several cellular factors that trigger virus uptake into the hepatocytes.The high-density lipoprotein receptor scavenger receptor class B type I,tetraspanin CD81,tight junction protein claudin-1,and occludin are the main receptors that mediate the initial step of HCV infection.In addition,the virus uses cell receptor tyrosine kinases as entry regulators,such as epidermal growth factor receptor and ephrin receptor A2.This review summarizes the current understanding about how cell surface molecules are involved in HCV attachment,internalization,and membrane fusion,and how host cell kinases regulate virus entry.The advances of the potential antiviral agents targeting this process are introduced.

Cellular membrane cholesterol is required for porcine reproductive and respiratory syndrome virus entry and release in MARC-145 cells

Cholesterol represents one of the key constituents of small,dynamic,sterol-and sphingolipid-enriched domains on the plasma membrane.It has been reported that many viruses depend on plasma membrane cholesterol for efficient infection.In this study,the role of the plasma membrane cholesterol in porcine reproductive and respiratory syndrome virus(PRRSV) infection of MARC-145 cells was investigated.Pretreatment of MARC-145 cells with methyl-β-cyclodextrin(MβCD),a drug used to deplete cholesterol from cellular membrane,significantly reduced PRRSV infection in a dose-dependent manner.This inhibition was partially reversed by supplementing exogenous cholesterol following MβCD treatment,suggesting that the inhibition of PRRSV infection was specifically mediated by removal of cellular cholesterol.Further detailed studies showed that depletion of cellular membrane cholesterol significantly inhibited virus entry,especially virus attachment and release.These results indicate that the presence of cholesterol in the cellular membrane is a key component of PRRSV infection.

Entry of hepatitis C virus into the cell: A therapeutic target

Several receptors have been identified as implicated on viral entry into the hepatocyte; and, this interaction between the virus and potential receptors could modulate infection, spontaneous viral clearance, persistence of the infection and the widespread of the virus as outbreak. Nevertheless, the playing role of each of them remains controversial. The NiemannPick type C1 like 1 gene (NPC1L1) receptor has been recently implicated on hepatitis C virus (HCV) entry into the cell and ezetimibe, an anti-cholesterol drug seems to block that, emerging the idea to control hepatitis C outbreak modulating lipid-related receptors. Hepatitis C infection seems to modulate lipid metabolism according to host genetic background. Indeed, it circulates like a lipoviroparticle. The main aim of this field of vision would be to discuss the role of hepatocyte receptors implicated on virus entry, especially NPC1L1 and the therapeutic options derived from the better knowledge about HCV-lipidsreceptors interaction.

Roles of host proteases in the entry of SARS-CoV-2

The spike protein(S)of SARS-CoV-2 is responsible for viral attachment and entry,thus a major factor for host suscep-tibility,tissue tropism,virulence and pathogenicity.The S is divided with S1 and S2 region,and the S1 contains the receptor-binding domain(RBD),while the S2 contains the hydrophobic fusion domain for the entry into the host cell.Numerous host proteases have been implicated in the activation of SARS-CoV-2 S through various c leavage sites.In this article,we review host proteases including furin,trypsin,transmembrane protease serine 2(TMPRSS2)and cathepsins in the activation of SARS-CoV-2 S.Many betacoronaviruses including SARS-CoV-2 have polybasic residues at the S1/S2 site which is subjected to the cleavage by furin.The S1/S2 cleavage facilitates more assessable RBD to the receptor ACE2,and the binding triggers further conformational changes and exposure of the S2'site to proteases such as type Il transmembrane serine proteases(TTPRs)including TMPRSS2.In the presence of TMPRSS2 on the target cells,SARS-CoV-2 can utilize a direct entry route by fusion of the viral envelope to the cellular membrane.In the absence of TMPRSS2,SARS-CoV-2 enter target cells via endosomes where multiple cathepsins cleave the S for the successful entry.Additional host proteases involved in the cleavage of the S were discussed.This article also includes roles of 3C-like protease inhibitors which have inhibitory activity against cathepsin L in the entry of SARS-CoV-2,and discussed the dual roles of such inhibitors in virus replication.

Artificial intelligence and machine learning could support drug development for hepatitis A virus internal ribosomal entry sites

Hepatitis A virus(HAV)infection is still an important health issue worldwide.Although several effective HAV vaccines are available,it is difficult to perform universal vaccination in certain countries.Therefore,it may be better to develop antivirals against HAV for the prevention of severe hepatitis A.We found that several drugs potentially inhibit HAV internal ribosomal entry site-dependent translation and HAV replication.Artificial intelligence and machine learning could also support screening of anti-HAV drugs,using drug repositioning and drug rescue approaches.

Cautious optimism in anticipation of hepatitis B curative therapies

Despite relative effectiveness of current hepatitis B therapies,there is still no curative agents available.The new emerging approaches hold promise to achieve cure and loss of hepatitis B surface antigen.Studies or clinical trials investigating new therapies remain small and either focus on patients with low viral load and without hepatotoxic injury or patients with hepatitis D co-infection,which makes it challenging to assess their effectiveness and side effect profile in hepatitis B population.

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

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

Identification of niclosamide as a novel antiviral agent against porcine epidemic diarrhea virus infection by targeting viral internalization

Porcine epidemic diarrhea virus(PEDV),an enteropathogenic coronavirus,has catastrophic impacts on the global pig industry.However,there remain no effective drugs against PEDV infection.In this study,we utilized a recombinant PEDV expressing renilla luciferase(PEDV-Rluc)to screen potential anti-PEDV agents from an FDAapproved drug library in Vero cells.Four compounds were identified that significantly decreased luciferase activity of PEDV-Rluc.Among them,niclosamide was further characterized because it exhibited the most potent antiviral activity with the highest selectivity index.It can efficiently inhibit viral RNA synthesis,protein expression and viral progeny production of classical and variant PEDV strains in a dose-dependent manner.Time of addition assay showed that niclosamide exhibited potent anti-PEDV activity when added simultaneously with or after virus infection.Furthermore,niclosamide significantly inhibited the entry stage of PEDV infection by affecting viral internalization rather than viral attachment to cells.In addition,a combination with other small molecule inhibitors of endosomal acidification enhanced the anti-PEDV effect of niclosamide in vitro.Taken together,these findings suggested that niclosamide is a novel antiviral agent that might provide a basis for the development of novel drug therapies against PEDV and other related pathogenic coronavirus infections.

Comparison of lentiviruses pseudotyped with S proteins from coronaviruses and cell tropisms of porcine coronaviruses

The surface glycoproteins of coronaviruses play an important role in receptor binding and cell entry. Different coronaviruses interact with their specific receptors to enter host cells. Lentiviruses pseudotyped with their spike proteins(S) were compared to analyze the entry efficiency of various coronaviruses. Our results indicated that S proteins from different coronaviruses displayed varied abilities to mediate pseudotyped virus infection. Furthermore, the cell tropisms of porcine epidemic diarrhea virus(PEDV) and transmissible gastroenteritis virus(TGEV) have been characterized by live and pseudotyped viruses. Both live and pseudoviruses could infected VeroCCL-81(monkey kidney), Huh-7(human liver), and PK-15(pig kidney) cells efficiently. CCL94(cat kidney) cells could be infected efficiently by TGEV but not PEDV. Overall, our study provides new insights into the mechanisms of viral entry and forms a basis for antiviral drug screening.

Discovery and development of antiviral drugs

In this short review we summarize the different strategies for discovery and development of antiviral agents, including targeting virus entry into host, virus replication within cells, infant virus assembly and release from the infected cells. The progress on development of various classes of antivirus agents and their potential in virus therapy, mainly targeting human immunodeficiency virus （HIV）, was also discussed.