SARS-CoV-2 cell entry and targeted antiviral development

Severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)is the causative agent of the pandemic coronavirus disease 2019(COVID-19),which threatens human health and public safety.In the urgent campaign to develop anti-S ARS-CoV-2 therapies,the initial entry step is one of the most appealing targets.In this review,we summarize the current understanding of SARS-CoV-2 cell entry,and the development of targeted antiviral strategies.Moreover,we speculate upon future directions toward nextgeneration of SARS-CoV-2 entry inhibitors during the upcoming post-pandemic era.

No evidence for increased cell entry or antibody evasion by Delta sublineage AY.4.2

Since the beginning of the COVID-19 pandemic,multiple SARS-CoV-2 variants have emerged.While some variants spread only locally,others,referred to as variants of concern,disseminated globally and became drivers of the pandemic.All SARS-CoV-2 variants harbor mutations relative to the virus circulating early in the pandemic,and mutations in the viral spike(S)protein are considered of particular relevance since the S protein mediates host cell entry and constitutes the key target of the neutralizing antibody response.As a consequence,mutations in the S protein may increase SARS-CoV-2 infectivity and enable its evasion of neutralizing antibodies.Furthermore,mutations in the S protein can modulate viral transmissibility and pathogenicity.

Targeting host factors:A novel rationale for the management of hepatitis C virus

Hepatitis C is recognized as a major threat to global public health. The current treatment of patients with chronic hepatitis C is the addition of ribavirin to interferon-based therapy which has limited efficacy, poor tolerability, and significant expense. New treatment options that are more potent and less toxic are much needed. Moreover, more effective treatment is an urgent priority for those who relapse or do not respond to current regimens. A major obstacle in combating hepatitis C virus （HCV） infection is that the fidelity of the viral replication machinery is notoriously low, thus enabling the virus to quickly develop mutations that resist compounds targeting viral enzymes. Therefore, an approach targeting the host cofactors, which are indispensable for the propagation of viruses, may be an ideal target for the development of antiviral agents because they have a lower rate of mutation than that of the viral genome, as long as they have no side effects to patients. Drugs targeting, for example, receptors of viral entry, host metabolism or nuclear receptors, which are factors required to complete the HCV life cycle, may be more effective in combating the viral infection. Targeting host cofactors of the HCV life cycle is an attractive concept because it imposes a higher genetic barrier for resistance than direct antiviral compounds. However the principle drawback of this strategy is the greater potential for cellular toxicity.

High-resolution 3D Structures Reveal the Biological Functions of Reoviruses

Viruses in the family Reoviridae are non-enveloped particles comprising a segmented double-stranded RNA genome surrounded by a two-layered or multi-layered icosahedral protein capsid.These viruses are classified into two sub-families based on their particle structural organization.Recent studies have focused on high-resolution three-dimensional structures of reovirus particles by using cryo-electron microscopy (cryo-EM) to approach the resolutions seen in X-ray crystallographic structures.The results of cryo-EM image reconstructions allow tracing of most of the protein side chains,and thus permit integration of structural and functional information into a coherent mechanism for reovirus assembly and entry.

Single virus tracking of Ebola virus entry through lipid rafts in living host cells

Ebola virus(EBOV)is one of the most pathogenic viruses in humans which can cause a lethal hemorrhagic fever.Understanding the cellular entry mechanisms of EBOV can promote the development of new therapeutic strategies to control virus replication and spread.It has been known that EBOV virions bind to factors expressed at the host cell surface.Subsequently,the virions are internalized by a macropinocytosis-like process,followed by being trafficked through early and late endosomes.Recent researches indicate that the entry of EBOV into cells requires integrated and functional lipid rafts.Whilst lipid rafts have been hypothesized to play a role in virus entry,there is a current lack of supporting data.One major technical hurdle is the lack of effective approaches for observing viral entry.To provide evidence on the involvement of lipid rafts in the entry process of EBOV,we generated the fluorescently labeled Ebola virus like particles(VLPs),and utilized single-particle tracking(SPT)to visualize the entry of fluorescent Ebola VLPs in live cells and the interaction of Ebola VLPs with lipid rafts.In this study,we demonstrate the compartmentalization of Ebola VLPs in lipid rafts during entry process,and inform the essential function of lipid rafts for the entry of Ebola virus.As such,our study provides evidence to show that the raft integrity is critical for Ebola virus pathogenesis and that lipid rafts can serve as potential targets for the development of novel therapeutic strategies.

COVID-19 and Chronic Viral Liver Diseases

Coronavirus causes an outbreak of viral pneumonia that spread throughout the world. Liver injury is becoming more widely recognized as a component of the clinical picture of COVID-19 infection. We aimed to review this relation in a concise way. This review article includes a large number of patients from both western and eastern countries with no clear difference of liver affection. The more severe and frequent liver injury, the more severe COVID-19 infection. Up to half of patients developed hepatitis with serum ALT elevation. Both hepatocellular and/or ductular injury were observed as evidenced by alkaline phosphatase elevation. Increase incidence of morbidity and mortality had been recorded in patients with CLD. Cirrhosis mortality extended in line with the Child-Turcotte-Pugh class. The incidence of ACLF in CLD patients with COVID 19 is not clear. There are no significant associations with the etiology of liver disease and death in cirrhosis. COVID-19 hinders HCV elimination by 2030. Patients should continue their medications if already receiving treatment. Patients with occult or resolved HBV and COVID-19 who are receiving immunosuppressive agents should use antiviral therapy to prevent viral flare-ups.

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.

Endosomes and Microtubles are Required for Productive Infection in Aquareovirus

Grass carp reovirus(GCRV),the genus Aquareovirus in family Reoviridae,is viewed as the most pathogenic aquareovirus.To understand the molecular mechanism of how aquareovirus initiates productive infection,the roles of endosome and microtubule in cell entry of GCRV are investigated by using quantum dots(QDs)-tracking in combination with biochemical approaches.We found that GCRV infection and viral protein synthesis were significantly inhibited by pretreating host cells with endosome acidification inhibitors NH4Cl,chloroquine and bafilomycin A1(Bafi).Confocal images indicated that GCRV particles could colocalize with Rab5,Rab7 and lysosomes in host cells.Further ultrastructural examination validated that viral particle was found in late endosomes.Moreover,disruption of microtubules with nocodazole clearly blocked GCRV entry,while no inhibitory effects were observed with cytochalasin D treated cells in viral infection,hinting that intracellular transportation of endocytic uptake in GCRV infected cells is via microtubules but not actin filament.Notably,viral particles were observed to transport along microtubules by using QD-labeled GCRV.Altogether,our results suggest that GCRV can use endosomes and microtubules to initiate productive infection.