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.

Role of Protein Kinase C in the Activation of Store-operated Ca^(2+) Entry in Airway Smooth Muscle Cells

Store-operated Ca2＋ channels （SOCs） are plasma membrane Ca2＋ permeable channels activated by depletion of intracellular Ca2＋ store. Ca2＋ entry through SOCs is known as store-operated Ca2＋ entry （SOCE）, which plays an important role in the functional regulation of airway smooth muscle cells （ASMCs）. Protein kinase C （PKC） has been shown to have an activating or inhibiting effect on SOCE, depending on cell types and PKC isoforms that are involved. In ASMCs, the effect of PKC on SOCE has not been elucidated so far. In this study, the role of PKC in the activation of SOCE in rat ASMCs was examined by using Ca2＋ fluorescence imaging technique. The results showed that acute application of PKC activators PMA and PDBu did not affect SOCE induced by the sarcoplasmic reticulum Ca2＋-ATPase （SERCA） inhibitor thapsigargin. The non-selective PKC inhibitor chelerythrine significantly inhibited thapsigargin- and bradykinin-induced SOCE. RT-PCR assay identified PKCα, δ and ε isoforms in rat ASMCs. PKCα-selective inhibitor G6976 and PKCε-inhibiting peptide Epsilon-V1-2 had no effect on SOCE; by contrast, PKCδ-selective inhibitor rottlerin attenuated SOCE dramatically, suggesting that PKCδ was the major PKC isoform involved in the activation of SOCE in ASMCs. Moreover, PKC down-regulation by extended exposure to high doses of PMA or PDBu also reduced SOCE, confirming the essential role of PKC in the activation of SOCE in ASMCs. In addition, PKC down-regulation did not influence the expression of stromal interaction molecule 1 （STIM1） and Orai1, two elementary molecules in the regulation and activation of SOCs. These results identified PKCδ as an essential PKC isoform involved in the activation of SOCE, and confirmed that PKC regulates the function of ASMCs in a SOCE-dependent manner.

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.

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.