Prohibitin plays a critical role in Enterovirus 71 neuropathogenesis

Prohibitin 1 tethers lipid membranes and regulates OPA1-mediated membrane fusion

Prohibitins (PHBs) are ubiquitously expressed proteins in the mitochondrial inner membrane (MIM) that provide membrane scaffolds for both mitochondrial proteins and phospholipids. Eukaryotic PHB complexes contain two highly homologous PHB subunits, PHB1 and PHB2, which are involved in various cellular processes, including metabolic control through the regulation of mitochondrial dynamics and integrity. Their mechanistic actions at the molecular level, however, particularly those of PHB1, remain poorly understood. To gain insight into the mechanistic actions of PHB1, we established an overexpression system for the full-length recombinant protein using silkworm larvae and characterized its biophysical properties in vitro. Using recombinant PHB1 proteoliposomes reconstituted into MIM-mimicking phospholipids, we found that PHB1 forms an oligomer via its carboxy-terminal coiled-coil region. A proline substitution into the PHB1 coiled-coil collapsed its well-ordered oligomeric state, and its destabilization correlated with mitochondrial morphologic defects. Negative-staining electron microscopy revealed that homotypic PHB1-PHB1 interactions via the coiled-coil also induced liposome tethering with remodeling of the lipid membrane structure. We clarified that PHB1 promotes membrane fusion mediated by optic atrophy 1 (OPA1), a key regulator of MIM fusion. Additionally, the presence of PHB1 reduces the dependency of lipids and OPA1 for completing the fusion process. Our in vitro study provides structural insight into how the mitochondrial scaffold plays a crucial role in regulating mitochondrial dynamics. Modulating the structure and/or function of PHB1 may offer new therapeutic potential, not only for mitochondrial dysfunction but also for other cell-related disorders.

Enterovirus-A71 preferentially infects and replicates in human motor neurons, inducing neurodegeneration by ferroptosis

Enterovirus A71 (EV-A71) causes Hand, Foot, and Mouth Disease and has been clinically associated with neurological complications. However, there is a lack of relevant models to elucidate the neuropathology of EV-A71 and its mechanism, as the current models mainly utilize animal models or immortalized cell lines. In this study, we established a human motor neuron model for EV-A71 infection. Single cell transcriptomics of a mixed neuronal population reveal higher viral RNA load in motor neurons, suggesting higher infectivity and replication of EV-A71 in motor neurons. The elevated RNA load in motor neurons correlates with the downregulation of ferritin-encoding genes. Subsequent analysis confirms that neurons infected with EV-A71 undergo ferroptosis, as evidenced by increased levels of labile Fe2+ and peroxidated lipids. Notably, the Fe2+ chelator Deferoxamine improves mitochondrial function and promotes survival of motor neurons by 40% after EV-A71 infection. These findings deepen understanding of the molecular pathogenesis of EV-A71 infection, providing insights which suggest that improving mitochondrial respiration and inhibition of ferroptosis can mitigate the impact of EV-A71 infection in the central nervous system.

Enterovirus-A71 exploits RAB11 to recruit chaperones for virus morphogenesis

BACKGROUND

Enterovirus 71 (EV-A71) causes Hand, Foot and Mouth Disease (HFMD) in children and has been associated with neurological complications. The molecular mechanisms involved in EV-A71 pathogenesis have remained elusive.

METHODS

A siRNA screen in EV-A71 infected-motor neurons was performed targeting 112 genes involved in intracellular membrane trafficking, followed by validation of the top four hits using deconvoluted siRNA. Downstream approaches including viral entry by-pass, intracellular viral genome quantification by qPCR, Western blot analyses, and Luciferase reporter assays allowed determine the stage of the infection cycle the top candidate, RAB11A was involved in. Proximity ligation assay, co-immunoprecipitation and multiplex confocal imaging were employed to study interactions between viral components and RAB11A. Dominant negative and constitutively active RAB11A constructs were used to determine the importance of the protein's GTPase activity during EV-A71 infection. Mass spectrometry and protein interaction analyses were employed for the identification of RAB11A's host interacting partners during infection.

RESULTS

Small GTPase RAB11A was identified as a novel pro-viral host factor during EV-A71 infection. RAB11A and RAB11B isoforms were interchangeably exploited by strains from major EV-A71 genogroups and by Coxsackievirus A16, another major causative agent of HFMD. We showed that RAB11A was not involved in viral entry, IRES-mediated protein translation, viral genome replication, and virus exit. RAB11A co-localized with replication organelles where it interacted with structural and non-structural viral components. Over-expression of dominant negative (S25N; GDP-bound) and constitutively active (Q70L; GTP-bound) RAB11A mutants had no effect on EV-A71 infection outcome, ruling out RAB11A's involvement in intracellular trafficking of viral or host components. Instead, decreased ratio of intracellular mature viral particles to viral RNA copies and increased VP0:VP2 ratio in siRAB11-treated cells supported a role in provirion maturation hallmarked by VP0 cleavage into VP2 and VP4. Finally, chaperones, not trafficking and transporter proteins, were found to be RAB11A's top interacting partners during EV-A71 infection. Among which, CCT8 subunit from the chaperone complex TRiC/CCT was further validated and shown to interact with viral structural proteins specifically, representing yet another novel pro-viral host factor during EV-A71 infection.

CONCLUSIONS

This study describes a novel, unconventional role for RAB11A during viral infection where it participates in the complex process of virus morphogenesis by recruiting essential chaperone proteins.

Enterovirus A71 does not meet the uncoating receptor SCARB2 at the cell surface

Enterovirus A71 (EV-A71) infection involves a variety of receptors. Among them, two transmembrane protein receptors have been investigated in detail and shown to be critical for infection: P-selectin glycoprotein ligand-1 (PSGL-1) in lymphocytes (Jurkat cells), and scavenger receptor class B member 2 (SCARB2) in rhabdomyosarcoma (RD) cells. PSGL-1 and SCARB2 have been reported to be expressed on the surface of Jurkat and RD cells, respectively. In the work reported here, we investigated the roles of PSGL-1 and SCARB2 in the process of EV-A71 entry. We first examined the expression of SCARB2 in Jurkat cells, and detected it within the cytoplasm, but not on the cell surface. Further, using PSGL-1 and SCARB2 knockout cells, we found that although both PSGL-1 and SCARB2 are essential for virus infection of Jurkat cells, virus attachment to these cells requires only PSGL-1. These results led us to evaluate the cell surface expression and the roles of SCARB2 in other EV-A71-susceptible cell lines. Surprisingly, in contrast to the results of previous studies, we found that SCARB2 is absent from the surface of RD cells and other susceptible cell lines we examined, and that although SCARB2 is essential for infection of these cells, it is dispensable for virus attachment. These results indicate that a receptor other than SCARB2 is responsible for virus attachment to the cell and probably for internalization of virions, not only in Jurkat cells but also in RD cells and other EV-A71-susceptible cells. SCARB2 is highly concentrated in lysosomes and late endosomes, where it is likely to trigger acid-dependent uncoating of virions, the critical final step of the entry process. Our results suggest that the essential interactions between EV-A71 and SCARB2 occur, not at the cell surface, but within the cell.

Recent Advances in Enterovirus A71 Infection and Antiviral Agents

Enterovirus A71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease (HFMD) that majorly affects children. Most of the time, HFMD is a mild disease but can progress to severe complications, such as meningitis, brain stem encephalitis, acute flaccid paralysis, and even death. HFMD caused by EV-A71 has emerged as an acutely infectious disease of highly pathogenic potential in the Asia-Pacific region. In this review, we introduced the properties and life cycle of EV-A71, and the pathogenesis and the pathophysiology of EV-A71 infection, including tissue tropism and host range of virus infection, the diseases caused by the virus, as well as the genes and host cell immune mechanisms of major diseases caused by enterovirus 71 (EV-A71) infection, such as encephalitis and neurologic pulmonary edema. At the same time, clinicopathologic characteristics of EV-A71 infection were introduced. There is currently no specific medication for EV-A71 infection, highlighting the urgency and significance of developing suitable anti-EV-A71 agents. This overview also summarizes the targets of existing anti-EV-A71 agents, including virus entry, translation, polyprotein processing, replication, assembly and release; interferons; interleukins; the mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase B signaling pathways; the oxidative stress pathway; the ubiquitin-proteasome system; and so on. Furthermore, it overviews the effects of natural products, monoclonal antibodies, and RNA interference against EV-A71. It also discusses issues limiting the research of antiviral drugs. This review is a systematic and comprehensive summary of the mechanism and pathological characteristics of EV-A71 infection, the latest progress of existing anti-EV-A71 agents. It would provide better understanding and guidance for the research and application of EV-A71 infection and antiviral inhibitors.

Pan-cancer Analysis Combined with Experiments Deciphers PHB Regulation for Breast Cancer Cell Survival and Predicts Biomarker Function

BACKGROUND

Breast carcinoma has become the leading fatal disease among women. The location of prohibitin in the chromosome is close to the breast cancer susceptibility gene 1 (BRCA1). Accumulated research reported that prohibitin could interact with a variety of transcription factors and cell cycle-regulating proteins.

OBJECTIVE

This present study aims to comprehensively explore and reveal the biological functions of prohibitin on breast cancer via The Cancer Genome Atlas (TCGA) and validation experiment in vitro.

METHODS

Exploring the expression level of prohibitin across 27 tumors based on the TGGA database by bioinformatic methods and its relationship with tumor immune infiltration. Furthermore, we thus analyzed the biological roles of prohibitin on human breast cancer cell line MCF- 7 with pEGFP-prohibitin overexpression plasmid by western blotting and transwell-assay.

RESULTS

Firstly, we found prohibitin is overexpressed in most tumors based on The Cancer Genome Atlas database, and the negative relationships between prohibitin and tumors infiltrating lymphocytes including B lymphocyte, CD4 T lymphocyte, CD8 T lymphocyte, Neutrophil, Macrophage and Dendritic, and its significant correlation with the prognosis of human cancer. In vitro, expression not only inhibited cell viability and invasive abilities but also increased the apoptosis percentage of cells with a decreased percentage of the S phase and an increased G2 phase. The reduction of Bcl-2 was observed when prohibitin was upregulated, although the expression of E2F-1 did not change.

CONCLUSION

Although prohibitin is over-expressed in various cancer types, it functions as an important tumor suppressor that may suppress breast cancer cell proliferation and the invasive ability of MCF-7 by influencing its DNA synthesis and promoting cell apoptosis. All these may be likely associated with P53, erbB-2, and Bcl-2.

Mitochondrial Oxidative Phosphorylation in Viral Infections

Mitochondria have been identified as the "powerhouse" of the cell, generating the cellular energy, ATP, for almost seven decades. Research over time has uncovered a multifaceted role of the mitochondrion in processes such as cellular stress signaling, generating precursor molecules, immune response, and apoptosis to name a few. Dysfunctional mitochondria resulting from a departure in homeostasis results in cellular degeneration. Viruses hijack host cell machinery to facilitate their own replication in the absence of a bonafide replication machinery. Replication being an energy intensive process necessitates regulation of the host cell oxidative phosphorylation occurring at the electron transport chain in the mitochondria to generate energy. Mitochondria, therefore, can be an attractive therapeutic target by limiting energy for viral replication. In this review we focus on the physiology of oxidative phosphorylation and on the limited studies highlighting the regulatory effects viruses induce on the electron transport chain.

Interactome profiling of Crimean-Congo hemorrhagic fever virus glycoproteins

Crimean-Congo hemorrhagic fever virus (CCHFV) is a biosafety level-4 pathogen requiring urgent research and development efforts. The glycoproteins of CCHFV, Gn and Gc, are considered to play multiple roles in the viral life cycle by interactions with host cells; however, these interactions remain largely unclear to date. Here, we analyzed the cellular interactomes of CCHFV glycoproteins and identified 45 host proteins as high-confidence Gn/Gc interactors. These host molecules are involved in multiple cellular biological processes potentially associated with the physiological actions of the viral glycoproteins. Then, we elucidated the role of a representative cellular protein, HAX1. HAX1 interacts with Gn by its C-terminus, while its N-terminal region leads to mitochondrial localization. By the strong interaction, HAX1 sequestrates Gn to mitochondria, thus depriving Gn of its normal Golgi localization that is required for functional glycoprotein-mediated progeny virion packaging. Consistently, the inhibitory activity of HAX1 against viral packaging and hence propagation was further elucidated in the contexts of pseudotyped and authentic CCHFV infections in cellular and animal models. Together, the findings provide a systematic CCHFV Gn/Gc-cell protein-protein interaction map, but also unravel a HAX1/mitochondrion-associated host antiviral mechanism, which may facilitate further studies on CCHFV biology and therapeutic approaches.

Prohibitin1 facilitates viral replication by impairing the RIG-I-like receptor signaling pathway

IMPORTANCE

Type I interferon (IFN-I), produced by the innate immune system, plays an essential role in host antiviral responses. Proper regulation of IFN-I production is required for the host to balance immune responses and prevent superfluous inflammation. IFN regulatory factor 3 (IRF3) and subsequent sensors are activated by RNA virus infection to induce IFN-I production. Therefore, proper regulation of IRF3 serves as an important way to control innate immunity and viral replication. Here, we first identified Prohibitin1 (PHB1) as a negative regulator of host IFN-I innate immune responses. Mechanistically, PHB1 inhibited the nucleus import of IRF3 by impairing its binding with importin subunit alpha-1 and importin subunit alpha-5. Our study demonstrates the mechanism by which PHB1 facilitates the replication of multiple RNA viruses and provides insights into the negative regulation of host immune responses.

The many "Neurofaces" of Prohibitins 1 and 2: Crucial for the healthy brain, dysregulated in numerous brain disorders

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are nearly ubiquitously expressed. They are localized in mitochondria, cytosol and cell nuclei. In the healthy CNS, they occur in neurons and non-neuronal cells (oligodendrocytes, astrocytes, microglia, and endothelial cells) and fulfill pivotal functions in brain development and aging, the regulation of brain metabolism, maintenance of structural integrity, synapse formation, aminoacidergic neurotransmission and, probably, regulation of brain action of certain hypothalamic-pituitary hormones.With regard to the diseased brain there is increasing evidence that prohibitins are prominently involved in numerous major diseases of the CNS, which are summarized and discussed in the present review (brain tumors, neurotropic viruses, Alzheimer disease, Down syndrome, Fronto-temporal and vascular dementia, dementia with Lewy bodies, Parkinson disease, Huntington disease, Multiple sclerosis, Amyotrophic lateral sclerosis, stroke, alcohol use disorder, schizophrenia and autism). Unfortunately, there is no PHB-targeted therapy available for any of these diseases.

Variant enterovirus A71 found in immune-suppressed patient binds to heparan sulfate and exhibits neurotropism in B-cell-depleted mice

Enterovirus A71 (EV-A71) causes hand, foot, and mouth disease outbreaks with neurological complications and deaths. We previously isolated an EV-A71 variant in the stool, cerebrospinal fluid, and blood of an immunocompromised patient who had a leucine-to-arginine substitution on the VP1 capsid protein, resulting in increased heparin sulfate binding. We show here that this mutation increases the virus's pathogenicity in orally infected mice with depleted B cells, which mimics the patient's immune status, and increases susceptibility to neutralizing antibodies. However, a double mutant with even greater heparin sulfate affinity is not pathogenic, suggesting that increased heparin sulfate affinity may trap virions in peripheral tissues and reduce neurovirulence. This research sheds light on the increased pathogenicity of variant with heparin sulfate (HS)-binding ability in individuals with decreased B cell immunity.

Characterization of Plasmodium falciparum prohibitins as novel targets to block infection in humans by impairing the growth and transmission of the parasite

Prohibitins (PHBs) are highly conserved pleiotropic proteins as they have been shown to mediate key cellular functions. Here, we characterize PHBs encoding putative genes of Plasmodium falciparum by exploiting different orthologous models. We demonstrated that PfPHB1 (PF3D7_0829200) and PfPHB2 (PF3D7_1014700) are expressed in asexual and sexual blood stages of the parasite. Immunostaining indicated these proteins as mitochondrial residents as they were found to be localized as branched structures. We further validated PfPHBs as organellar proteins residing in Plasmodium mitochondria, where they interact with each other. Functional characterization was done in Saccharomyces cerevisiae orthologous model by expressing PfPHB1 and PfPHB2 in cells harboring respective mutants. The PfPHBs functionally complemented the yeast PHB1 and PHB2 mutants, where the proteins were found to be involved in stabilizing the mitochondrial DNA, retaining mitochondrial integrity and rescuing yeast cell growth. Further, Rocaglamide (Roc-A), a known inhibitor of PHBs and anti-cancerous agent, was tested against PfPHBs and as an antimalarial. Roc-A treatment retarded the growth of PHB1, PHB2, and ethidium bromide petite yeast mutants. Moreover, Roc-A inhibited growth of yeast PHBs mutants that were functionally complemented with PfPHBs, validating P. falciparum PHBs as one of the molecular targets for Roc-A. Roc-A treatment led to growth inhibition of artemisinin-sensitive (3D7), artemisinin-resistant (R539T) and chloroquine-resistant (RKL-9) parasites in nanomolar ranges. The compound was able to retard gametocyte and oocyst growth with significant morphological aberrations. Based on our findings, we propose the presence of functional mitochondrial PfPHB1 and PfPHB2 in P. falciparum and their druggability to block parasite growth.

Global quantitative proteomic analysis profiles of host protein expression in response to Enterovirus A71 infection in bronchial epithelial cells based on tandem mass tag (TMT) peptide labeling coupled with LC-MS/MS uncovers the key role of proteasome in virus replication

Enterovirus A71 (EV-A71) is a neurotropic human pathogen which mainly caused hand, foot and mouth disease (HFMD) mostly in children under 5 years-old. Generally, EV-A71-associated HFMD is a relatively self-limiting febrile disease, but there will still be a small percentage of patients with rapid disease progression and severe neurological complications. To date, the underlying mechanism of EV-A71 inducing pathological injury of central nervous system (CNS) remains largely unclear. It has been investigated and discussed the changes of mRNA, miRNA and circRNA expression profile during infection by EV-A71 in our previous studies. However, these studies were only analyzed at the RNA level, not at the protein level. It's the protein levels that ultimately do the work in the body. Here, to address this, we performed a tandem mass tag (TMT) peptide labeling coupled with LC-MS/MS approach to quantitatively identify cellular proteome changes at 24 h post-infection (hpi) in EV-A71-infected 16HBE cells. In total, 6615 proteins were identified by using TMT coupled with LC-MS/MS in this study. In the EV-A71- and mock-infected groups, 210 differentially expressed proteins were found, including 86 upregulated and 124 downregulated proteins, at 24 hpi. To ensure the validity and reliability of the proteomics data, 3 randomly selected proteins were verified by Western blot and Immunofluorescence analysis, and the results were consistent with the TMT results. Subsequently, functional enrichment analysis indicated that the up-regulated and down-regulated proteins were individually involved in various biological processes and signaling pathways, including metabolic process, AMPK signaling pathway, Neurotrophin signaling pathway, Viral myocarditis, GABAergic synapse, and so on. Moreover, among these enriched functional analysis, the "Proteasome" pathway was up-regulated, which has caught our attention. Inhibition of proteasome was found to obviously suppress the EV-A71 replication. Finally, further in-depth analysis revealed that these differentially expressed proteins contained distinct domains and localized in different subcellular components. Taken together, our data provided a comprehensive view of host cell response to EV-A71 and identified host proteins may lead to better understanding of the pathogenic mechanisms and host responses to EV-A71 infection, and also to the identification of new therapeutic targets for EV-A71 infection.

RNA interference of PHB1 enhances virulence of Vip3Aa to Sf9 cells and Spodoptera frugiperda larvae

BACKGROUND

In our previous work, we demonstrated that prohibitin 2 (PHB2) on the membrane of Sf9 cells was a receptor for Vip3Aa, and PHB2 in mitochondria contributed to the mitochondrial stability to reduce Vip3Aa toxicity. Prohibitin 1 (PHB1), another prohibitin family member, forms heterodimers with PHB2 to maintain the structure and stability of mitochondria. To explore whether PHB1 impacts the action process of Vip3Aa, we examined the correlation between PHB1 and Vip3Aa virulence.

RESULTS

We revealed that PHB1 did not colocalize with Vip3Aa in Sf9 cells. The pulldown and CoIP experiments confirmed that PHB1 interacted with neither Vip3Aa nor scavenger receptor-C (another Vip3Aa receptor). Downregulating phb1 expression in Sf9 cells did not affect the internalization of Vip3Aa but increased Vip3Aa toxicity. Further exploration revealed that the decrease of phb1 expression affected mitochondrial function, leading to increased ROS levels and mitochondrial membrane permeability and decreased mitochondrial membrane potential. The increase of mitochondrial cytochrome c release, caspase-3 activity and genomic DNA fragmentation implied that the apoptotic process was also affected. Finally, we applied RNAi to inhibit phb1 expression in Spodoptera frugiperda larvae. As a result, it significantly increased Vip3Aa virulence.

CONCLUSION

We found that PHB1 was not a receptor for Vip3Aa but played an essential role in mitochondria. The downregulation of phb1 expression in Sf9 cells caused instability of mitochondria, and the cells were more prone to apoptosis when challenged with Vip3Aa. The combined use of Vip3Aa and phb1 RNAi showed a synergistic effect against S. frugiperda larvae. © 2023 Society of Chemical Industry.

EV-A71 Mechanism of Entry: Receptors/Co-Receptors, Related Pathways and Inhibitors

Enterovirus A71, a non-enveloped single-stranded (+) RNA virus, enters host cells through three stages: attachment, endocytosis and uncoating. In recent years, receptors/co-receptors anchored on the host cell membrane and involved in this process have been continuously identified. Among these, hSCARB-2 was the first receptor revealed to specifically bind to a definite site of the EV-A71 viral capsid and plays an indispensable role during viral entry. It actually acts as the main receptor due to its ability to recognize all EV-A71 strains. In addition, PSGL-1 is the second EV-A71 receptor discovered. Unlike hSCARB-2, PSGL-1 binding is strain-specific; only 20% of EV-A71 strains isolated to date are able to recognize and bind it. Some other receptors, such as sialylated glycan, Anx 2, HS, HSP90, vimentin, nucleolin and fibronectin, were discovered successively and considered as "co-receptors" because, without hSCARB-2 or PSGL-1, they are not able to mediate entry. For cypA, prohibitin and hWARS, whether they belong to the category of receptors or of co-receptors still needs further investigation. In fact, they have shown to exhibit an hSCARB-2-independent entry. All this information has gradually enriched our knowledge of EV-A71's early stages of infection. In addition to the availability of receptors/co-receptors for EV-A71 on host cells, the complex interaction between the virus and host proteins and various intracellular signaling pathways that are intricately connected to each other is critical for a successful EV-A71 invasion and for escaping the attack of the immune system. However, a lot remains unknown about the EV-A71 entry process. Nevertheless, researchers have been continuously interested in developing EV-A71 entry inhibitors, as this study area offers a large number of targets. To date, important progress has been made toward the development of several inhibitors targeting: receptors/co-receptors, including their soluble forms and chemically designed compounds; virus capsids, such as capsid inhibitors designed on the VP1 capsid; compounds potentially interfering with related signaling pathways, such as MAPK-, IFN- and ATR-inhibitors; and other strategies, such as siRNA and monoclonal antibodies targeting entry. The present review summarizes these latest studies, which are undoubtedly of great significance in developing a novel therapeutic approach against EV-A71.

Proteomic and metabonomic analysis uncovering Enterovirus A71 reprogramming host cell metabolic pathway

Enterovirus A71 (EV71) infection can cause hand, foot, and mouth disease (HFMD) and severe neurological complications in children. However, the biological processes regulated by EV71 remain poorly understood. Herein, proteomics and metabonomics studies were conducted to uncover the mechanism of EV71 infection in rhabdomyosarcoma (RD) cells and identify potential drug targets. Differential expressed proteins from enriched membrane were analyzed by isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics technology. Twenty-six differential proteins with 1.5-fold (p < 0.05) change were detected, including 14 upregulated proteins and 12 downregulated proteins. The upregulated proteins are mainly involved in metabolic process, especially in the glycolysis pathway. Alpha-enolase (ENO1) protein was found to increase with temporal dependence following EV71 infection. The targeted metabolomics analysis revealed that glucose absorption and glycolysis metabolites were increased after EV71 infection. The glycolysis pathway was inhibited by knocking down ENO1 or the use of a glycolysis inhibitor (dichloroacetic acid [DCA]); and we found that EV71 infection was inhibited by depleting ENO1 or using DCA. Our study indicates that EV71 may reprogram glucose metabolism by activating glycolysis, and EV71 infection can be inhibited by interrupting the glycolysis pathway. ENO1 may be a potential target against EV71, and DCA could act as an inhibitor of EV71.

Recent advances in enterovirus A71 pathogenesis: a focus on fatal human enterovirus A71 infection

Enterovirus A71 (EV-A71) is one of the major pathogens responsible for hand, foot, and mouth disease (HFMD). Many HFMD outbreaks have been reported throughout the world in the past decades. Compared with other viruses, EV-A71 infection is more frequently associated with severe neurological complications and even death in children. EV-A71 can also infect adults and cause severe complications and death, although such cases are very uncommon. Although fatal cases of EV-A71 infection have been reported, the underlying mechanisms of EV-A71 infection, especially the mode of viral spread into the central nervous system (CNS) and mechanisms of pulmonary edema, which is considered to be the direct cause of death, have not yet been fully clarified, and more studies are needed. Here, we first summarize the pathological findings in various systems of patients with fatal EV-A71 infections, focussing in detail on gross changes, histopathological examination, tissue distribution of viral antigens and nucleic acids, systemic inflammatory cell infiltration, and tissue distribution of viral receptors and their co-localization with viral antigens. We then present our conclusions about viral dissemination, neuropathogenesis, and the mechanism of pulmonary edema in EV-A71 infection, based on pathological findings.

Prohibitins in neurodegeneration and mitochondrial homeostasis

The incidence of age-related neurodegenerative disorders has risen with the increase of life expectancy. Unfortunately, the diagnosis of such disorders is in most cases only possible when the neurodegeneration status is already advanced, and symptoms are evident. Although age-related neurodegeneration is a common phenomenon in living animals, the cellular and molecular mechanisms behind remain poorly understood. Pathways leading to neurodegeneration usually diverge from a common starting point, mitochondrial stress, which can serve as a potential target for early diagnosis and treatments. Interestingly, the evolutionarily conserved mitochondrial prohibitin (PHB) complex is a key regulator of ageing and metabolism that has been associated with neurodegenerative diseases. However, its role in neurodegeneration is still not well characterized. The PHB complex shows protective or toxic effects in different genetic and physiological contexts, while mitochondrial and cellular stress promote both up and downregulation of PHB expression. With this review we aim to shed light into the complex world of PHB’s function in neurodegeneration by putting together the latest advances in neurodegeneration and mitochondrial homeostasis associated with PHB. A better understanding of the role of PHB in neurodegeneration will add knowledge to neuron deterioration during ageing and help to identify early molecular markers of mitochondrial stress. This review will deepen our understanding of age-related neurodegeneration and provide questions to be addressed, relevant to human health and to improve the life quality of the elderly.

Transcriptome analysis of infected Crandell Rees Feline Kidney (CRFK) cells by canine parvovirus type 2c Laotian isolates

The advent of RNA sequencing technology provides insight into the dynamic nature of tremendous transcripts within Crandell-Reese feline kidney (CRFK) cells in response to canine parvovirus (CPV-2c) infection. A total of 1,603 genes displayed differentially expressed genes (DEGs), including 789 up-regulated genes and 814 downregulated genes in the infected cells. Gene expression profiles have shown a subtle pattern of defense mechanism and immune response to CPV through significant DEGs when extensively examined via Gene Ontology (GO) and pathway analysis. Prospective GO analysis was performed and identified several enriched GO biological process terms with significant participating roles in the immune system process and defense response to virus pathway. A Gene network was constructed using the 22 most significantly enriched genes of particular interests in defense response to virus pathways to illustrate the key pathways. Eleven genes (C1QBP, CD40, HYAL2, IFNB1, IFNG, IL12B, IL6, IRF3, LSM14A, MAVS, NLRC5) were identified, which are directly related to the defense response to the virus. Results of transcriptome profiling permit us to understand the heterogeneity of DEGs during in vitro experimental study of CPV infection, reflecting a unique transcriptome signature for the CPV virus. Our findings also demonstrate a distinct scenario of enhanced CPV responses in CRFK cells for viral clearance that involved multistep and perplexity of biological processes. Collectively, our data have given a fundamental role in anti-viral immunity as our highlights of this study, thus providing outlooks on future research priorities to be important in studying CPV.

SLC35B2 Acts in a Dual Role in the Host Sulfation Required for EV71 Infection

As an important neurotropic enterovirus, enterovirus 71 (EV71) is occasionally associated with severe neurological diseases and high mortality rates in infants and young children. Understanding the interaction between host factors and EV71 will play a vital role in developing antivirals and optimizing vaccines. Here, we performed a genome-wide CRISPR-Cas9 knockout screen and revealed that scavenger receptor class B member 2 (SCARB2), solute carrier family 35 member B2 (SLC35B2), and beta-1,3-glucuronyltransferase 3 (B3GAT3) are essential in facilitating EV71 replication. Subsequently, the exploration of molecular mechanisms suggested that the knockout of SLC35B2 or B3GAT3, not SCARB2, led to a remarkable decrease in the binding of EV71 to cells and internalization into cells. Furthermore, we found that the infection efficiency for EV71 was positively correlated with the level of host cell sulfation, not simply with the amount of heparan sulfate, suggesting that an unidentified sulfated protein(s) must contribute to EV71 infection. In support of this idea, we screened possible sulfated proteins among the proteinous receptors for EV71 and confirmed that SCARB2 could uniquely interact with both tyrosyl protein sulfotransferases in humans. We then performed mass spectrometric analysis of SCARB2, identifying five sites with tyrosine sulfation. The function verification test indicated that there were more than five tyrosine-sulfated sites on SCARB2. Finally, we constructed a model for EV71 entry in which both heparan sulfate and SCARB2 are regulated by SLC35B2 and act cooperatively to support viral binding, internalization, and uncoating. Taken together, this is the first time that we performed the pooled CRISPR-Cas9 genetic screening to investigate the interplay of host cells and EV71. Furthermore, we found that a novel host factor, SLC35B2, played a dual role in regulating the overall sulfation comprising heparan sulfate sulfation and protein tyrosine sulfation, which are critical for EV71 entry. IMPORTANCE As the most important nonpolio neurotropic enterovirus lacking specific treatments, EV71 can transmit to the central nervous system, leading to severe and fatal neurological complications in infants and young children. The identification of new factors that facilitate or inhibit EV71 replication is crucial to uncover the mechanisms of viral infection and pathogenesis. To date, only a few host factors involved in EV71 infection have been characterized. Herein, we conducted a genome-wide CRISPR-Cas9 functional knockout (GeCKO) screen for the first time to study EV71 in HeLa cells. The screening results are presented as a ranked list of candidates, including 518 hits in the positive selection that facilitate EV71 replication and 1,044 hits in the negative selection that may be essential for cell growth and survival or for suppressing EV71 infection. We subsequently concentrated on the top three hits in the positive selection: SCARB2, SLC35B2, and B3GAT3. The knockout of any of these three genes confers strong resistance against EV71 infection. We confirmed that EV71 infection is codependent on two receptors, heparan sulfate and SCARB2. We also identified a host entry factor, SLC35B2, indirectly facilitating EV71 infection through regulation of the host cell sulfation, and determined a novel posttranslational modification, protein tyrosine sulfation existing in SCARB2. This study revealed that EV71 infectivity exhibits a significant positive correlation with the level of cellular sulfation regulated by SLC35B2. Due to the sulfation pathway being required for many distinct viruses, including but not limited to EV71 and respiratory syncytial virus (RSV), which were tested in this study, SLC35B2 represents a target of broad-spectrum antiviral therapy.

Role of Non-Coding RNA in Neurological Complications Associated With Enterovirus 71

Enterovirus 71 (EV71) is the main pathogenic virus that causes hand, foot, and mouth disease (HFMD). Studies have reported that EV71-induced infections including aseptic meningitis, acute flaccid paralysis, and even neurogenic pulmonary edema, can progress to severe neurological complications in infants, young children, and the immunosuppressed population. However, the mechanisms through which EV71 causes neurological diseases have not been fully explored. Non-coding RNAs (ncRNAs), are RNAs that do not code for proteins, play a key role in biological processes and disease development associated with EV71. In this review, we summarized recent advances concerning the impacts of ncRNAs on neurological diseases caused by interaction between EV71 and host, revealing the potential role of ncRNAs in pathogenesis, diagnosis and treatment of EV71-induced neurological complications.

The Intricacy of the Viral-Human Protein Interaction Networks: Resources, Data, and Analyses

Viral infections are one of the major causes of human diseases that cause yearly millions of deaths and seriously threaten global health, as we have experienced with the COVID-19 pandemic. Numerous approaches have been adopted to understand viral diseases and develop pharmacological treatments. Among them, the study of virus-host protein-protein interactions is a powerful strategy to comprehend the molecular mechanisms employed by the virus to infect the host cells and to interact with their components. Experimental protein-protein interactions described in the scientific literature have been systematically captured into several molecular interaction databases. These data are organized in structured formats and can be easily downloaded by users to perform further bioinformatic and network studies. Network analysis of available virus-host interactomes allow us to understand how the host interactome is perturbed upon viral infection and what are the key host proteins targeted by the virus and the main cellular pathways that are subverted. In this review, we give an overview of publicly available viral-human protein-protein interactions resources and the community standards, curation rules and adopted ontologies. A description of the main virus-human interactome available is provided, together with the main network analyses that have been performed. We finally discuss the main limitations and future challenges to assess the quality and reliability of protein-protein interaction datasets and resources.

PHB2 affects the virulence of Vip3Aa to Sf9 cells through internalization and mitochondrial stability

The vegetative insecticidal proteins (Vip3A) secreted by some Bacillus thuringiensis (Bt) strains during vegetative growth are regarded as a new generation of insecticidal toxins. Like insecticidal crystal proteins, they are also used in transgenic crops to control pests. However, their insecticidal mechanisms are far less defined than those of insecticidal crystal protein. Prohibitin 2 (PHB2) is a potential Vip3Aa binding receptor identified from the membrane of Sf9 cells in our previous work. In this paper, we demonstrated the interaction between Vip3Aa and PHB2 using pull-down, dot blotting, microscale thermophoresis, and co-immunoprecipitation assays. PHB2 is distributed on the cell membrane and in the cytoplasm, and the co-localization of PHB2 and Vip3Aa was observed in Sf9 cells using a confocal laser scanning microscope. Moreover, PHB2 could interact with scavenger receptor-C via its SPFH (stomatin, prohibitin, flotillin, and HflK/C) domain. Downregulation of phb2 expression reduced the degree of internalization of Vip3Aa, exacerbated Vip3Aa-mediated mitochondrial damage, and increased Vip3Aa toxicity to Sf9 cells. This suggested that PHB2 performs two different functions: Acting as an interacting partner to facilitate the internalization of Vip3Aa into Sf9 cells and maintaining the stability of mitochondria. The latter has a more important influence on the virulence of Vip3Aa.

Enterovirus A71 antivirals: Past, present, and future

Enterovirus A71 (EV-A71) is a significant human pathogen, especially in children. EV-A71 infection is one of the leading causes of hand, foot, and mouth diseases (HFMD), and can lead to neurological complications such as acute flaccid myelitis (AFM) in severe cases. Although three EV-A71 vaccines are available in China, they are not broadly protective and have reduced efficacy against emerging strains. There is currently no approved antiviral for EV-A71. Significant progress has been made in developing antivirals against EV-A71 by targeting both viral proteins and host factors. However, viral capsid inhibitors and protease inhibitors failed in clinical trials of human rhinovirus infection due to limited efficacy or side effects. This review discusses major discoveries in EV-A71 antiviral development, analyzes the advantages and limitations of each drug target, and highlights the knowledge gaps that need to be addressed to advance the field forward.

An auto-antibody identified from phenotypic directed screening platform shows host immunity against EV-A71 infection

Background

Enterovirus A71 (EV-A71) is a neurotropic virus which may cause severe neural complications, especially in infants and children. The clinical manifestations include hand-foot-and-mouth disease, herpangina, brainstem encephalitis, pulmonary edema, and other severe neurological diseases. Although there are some vaccines approved, the post-marketing surveillance is still unavailable. In addition, there is no antiviral drugs against EV-A71 available.

Methods

In this study, we identified a novel antibody that could inhibit viral growth through a human single chain variable fragment (scFv) library expressed in mammalian cells and panned by infection with lethal dose of EV-A71.

Results

We identified that the host protein α-enolase (ENO1) is the target of this scFv, and anti-ENO1 antibody was found to be more in mild cases than severe EV-A71 cases. Furthermore, we examined the antiviral activity in a mouse model. We found that the treatment of the identified 07-human IgG₁ antibody increased the survival rate after virus challenge, and significantly decreased the viral RNA and the level of neural pathology in brain tissue.

Conclusions

Collectively, through a promising intracellular scFv library expression and screening system, we found a potential scFv/antibody which targets host protein ENO1 and can interfere with the infection of EV-A71. The results indicate that the usage and application of this antibody may offer a potential treatment against EV-A71 infection.

Molecular Docking of SP40 Peptide towards Cellular Receptors for Enterovirus 71 (EV-A71)

Enterovirus 71 (EV-A71) is one of the predominant etiological agents of hand, foot and mouth disease (HMFD), which can cause severe central nervous system infections in young children. There is no clinically approved vaccine or antiviral agent against HFMD. The SP40 peptide, derived from the VP1 capsid of EV-A71, was reported to be a promising antiviral peptide that targeted the host receptor(s) involved in viral attachment or entry. So far, the mechanism of action of SP40 peptide is unknown. In this study, interactions between ten reported cell receptors of EV-A71 and the antiviral SP40 peptide were evaluated through molecular docking simulations, followed by in vitro receptor blocking with specific antibodies. The preferable binding region of each receptor to SP40 was predicted by global docking using HPEPDOCK and the cell receptor-SP40 peptide complexes were refined using FlexPepDock. Local molecular docking using GOLD (Genetic Optimization for Ligand Docking) showed that the SP40 peptide had the highest binding score to nucleolin followed by annexin A2, SCARB2 and human tryptophanyl-tRNA synthetase. The average GoldScore for 5 top-scoring models of human cyclophilin, fibronectin, human galectin, DC-SIGN and vimentin were almost similar. Analysis of the nucleolin-SP40 peptide complex showed that SP40 peptide binds to the RNA binding domains (RBDs) of nucleolin. Furthermore, receptor blocking by specific monoclonal antibody was performed for seven cell receptors of EV-A71 and the results showed that the blocking of nucleolin by anti-nucleolin alone conferred a 93% reduction in viral infectivity. Maximum viral inhibition (99.5%) occurred when SCARB2 was concurrently blocked with anti-SCARB2 and the SP40 peptide. This is the first report to reveal the mechanism of action of SP40 peptide in silico through molecular docking analysis. This study provides information on the possible binding site of SP40 peptide to EV-A71 cellular receptors. Such information could be useful to further validate the interaction of the SP40 peptide with nucleolin by site-directed mutagenesis of the nucleolin binding site.

Role of Prohibitins in Aging and Therapeutic Potential Against Age-Related Diseases

A decline in mitochondrial function has long been associated with age-related health decline. Several lines of evidence suggest that interventions that stimulate mitochondrial autophagy (mitophagy) can slow aging and prolong healthy lifespan. Prohibitins (PHB1 and PHB2) assemble at the mitochondrial inner membrane and are critical for mitochondrial homeostasis. In addition, prohibitins (PHBs) have diverse roles in cell and organismal biology. Here, we will discuss the role of PHBs in mitophagy, oxidative phosphorylation, cellular senescence, and apoptosis. We will also discuss the role of PHBs in modulating lifespan. In addition, we will review the links between PHBs and diseases of aging. Finally, we will discuss the emerging concept that PHBs may represent an attractive therapeutic target to counteract aging and age-onset disease.

Update on Phytochemical and Biological Studies on Rocaglate Derivatives from Aglaia Species

With about 120 species, Aglaia is one of the largest genera of the plant family Meliaceae (the mahogany plants). It is native to the tropical rainforests of the Indo-Australian region, ranging from India and Sri Lanka eastward to Polynesia and Micronesia. Various Aglaia species have been investigated since the 1960s for their phytochemical constituents and biological properties, with the cyclopenta[b]benzofurans (rocaglates or flavaglines) being of particular interest. Phytochemists, medicinal chemists, and biologists have conducted extensive research in establishing these secondary metabolites as potential lead compounds with antineoplastic and antiviral effects, among others. The varied biological properties of rocaglates can be attributed to their unusual structures and their ability to act as inhibitors of the eukaryotic translation initiation factor 4A (eIF4A), affecting protein translation. The present review provides an update on the recently reported phytochemical constituents of Aglaia species, focusing on rocaglate derivatives. Furthermore, laboratory work performed on investigating the biological activities of these chemical constituents is also covered.

Enterovirus-A71 exploits peripherin and Rac1 to invade the central nervous system

Enterovirus-A71 (EV-A71) has been associated with severe neurological forms of hand, foot, and mouth disease (HFMD). EV-A71 infects motor neurons at neuromuscular junctions (NMJs) to invade the central nervous system (CNS). Here, we investigate the role of peripherin (PRPH) during EV-A71 infection, a type III intermediate neurofilament involved in neurodegenerative conditions. In mice infected with EV-A71, PRPH co-localizes with viral particles in the muscles at NMJs and in the spinal cord. In motor neuron-like and neuroblastoma cell lines, surface-expressed PRPH facilitates viral entry, while intracellular PRPH influences viral genome replication through interactions with structural and non-structural viral components. Importantly, PRPH does not play a role during infection with coxsackievirus A16, another causative agent of HFMD rarely associated with neurological complications, suggesting that EV-A71 ability to exploit PRPH represents a unique attribute for successful CNS invasion. Finally, we show that EV-A71 also exploits some of the many PRPH-interacting partners. Of these, small GTP-binding protein Rac1 represents a potential druggable host target to limit neuroinvasion of EV-A71.

Recent advances in the understanding of enterovirus A71 infection: a focus on neuropathogenesis

Introduction: Hand, foot, and mouth disease caused by enterovirus A71 (EV-A71) is more frequently associated with neurological complications and deaths compared to other enteroviruses.Areas covered: The authors discuss current understanding of the neuropathogenesis of EV-A71 based on various clinical, human, and animal model studies. The authors discuss the important advancements in virus entry, virus dissemination, and neuroinvasion. The authors highlight the role of host immune system, host genetic factors, viral quasispecies, and heparan sulfate in EV-A71 neuropathogenesis.Expert opinion: Comparison of EV-A71 with EV-D68 and PV shows similarity in primary target sites and dissemination to the central nervous system. More research is needed to understand cellular tropisms, persistence of EV-A71, and other possible invasion routes. EV-A71 infection has varied clinical manifestations which may be attributed to multiple receptors usage. Future development of antivirals and vaccines should target neurotropic enteroviruses. Repurposing drug and immunomodulators used in combination could reduce the severity of EV-A71 infection. Only a few drugs have been tested in clinical trials, and in the absence of antiviral and vaccines (except China), active virus surveillance, good hand hygiene, and physical distancing should be advocated. A better understanding of EV-A71 neuropathogenesis is critical for antiviral and multivalent vaccines development.

Return of the Neurotropic Enteroviruses: Co-Opting Cellular Pathways for Infection

Enteroviruses are among the most common human infectious agents. While infections are often mild, the severe neuropathogenesis associated with recent outbreaks of emerging non-polio enteroviruses, such as EV-A71 and EV-D68, highlights their continuing threat to public health. In recent years, our understanding of how non-polio enteroviruses co-opt cellular pathways has greatly increased, revealing intricate host-virus relationships. In this review, we focus on newly identified mechanisms by which enteroviruses hijack the cellular machinery to promote their replication and spread, and address their potential for the development of host-directed therapeutics. Specifically, we discuss newly identified cellular receptors and their contribution to neurotropism and spread, host factors required for viral entry and replication, and recent insights into lipid acquisition and replication organelle biogenesis. The comprehensive knowledge of common cellular pathways required by enteroviruses could expose vulnerabilities amenable for host-directed therapeutics against a broad spectrum of enteroviruses. Since this will likely include newly arising strains, it will better prepare us for future epidemics. Moreover, identifying host proteins specific to neurovirulent strains may allow us to better understand factors contributing to the neurotropism of these viruses.

Prohibitin-1 Contributes to Cell-to-Cell Transmission of Herpes Simplex Virus 1 via the MAPK/ERK Signaling Pathway

Viral cell-to-cell spread, a method employed by several viral families for entrance via cell junctions, is highly relevant to the pathogenesis of various viral infections. Cell-to-cell spread of herpes simplex virus 1 (HSV-1) is known to depend greatly on envelope glycoprotein E (gE). However, the molecular mechanism by which gE acts in HSV-1 cell-to-cell spread and the mechanisms of cell-to-cell spread by other herpesviruses remain poorly understood. Here, we describe our identification of prohibitin-1 as a novel gE-interacting host cell protein. Ectopic expression of prohibitin-1 increased gE-dependent HSV-1 cell-to-cell spread. As observed with the gE-null mutation, decreased expression or pharmacological inhibition of prohibitin-1 reduced HSV-1 cell-to-cell spread without affecting the yield of virus progeny. Similar effects were produced by pharmacological inhibition of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway, wherein prohibitin-1 acts as a protein scaffold and is required for induction of this pathway. Furthermore, artificial activation of the MAPK/ERK pathway restored HSV-1 cell-to-cell spread impaired by the gE-null mutation. Notably, pharmacological inhibition of prohibitins or the MAPK/ERK pathway reduced viral cell-to-cell spread of representative members in all herpesvirus subfamilies. Our results suggest that prohibitin-1 contributes to gE-dependent HSV-1 cell-to-cell spread via the MAPK/ERK pathway and that this mechanism is conserved throughout the Herpesviridae, whereas gE is conserved only in the Alphaherpesvirinae subfamily.IMPORTANCE Herpesviruses are ubiquitous pathogens of various animals, including humans. These viruses primarily pass through cell junctions to spread to uninfected cells. This method of cell-to-cell spread is an important pathogenic characteristic of these viruses. Here, we show that the host cell protein prohibitin-1 contributes to HSV-1 cell-to-cell spread via a downstream intracellular signaling cascade, the MAPK/ERK pathway. We also demonstrate that the role of the prohibitin-1-mediated MAPK/ERK pathway in viral cell-to-cell spread is conserved in representative members of every herpesvirus subfamily. This study has revealed a common molecular mechanism of the cell-to-cell spread of herpesviruses.

Mapping the SARS-CoV-2-Host Protein-Protein Interactome by Affinity Purification Mass Spectrometry and Proximity-Dependent Biotin Labeling: A Rational and Straightforward Route to Discover Host-Directed Anti-SARS-CoV-2 Therapeutics

Protein-protein interactions (PPIs) are the vital engine of cellular machinery. After virus entry in host cells the global organization of the viral life cycle is strongly regulated by the formation of virus-host protein interactions. With the advent of high-throughput -omics platforms, the mirage to obtain a "high resolution" view of virus-host interactions has come true. In fact, the rapidly expanding approaches of mass spectrometry (MS)-based proteomics in the study of PPIs provide efficient tools to identify a significant number of potential drug targets. Generation of PPIs maps by affinity purification-MS and by the more recent proximity labeling-MS may help to uncover cellular processes hijacked and/or altered by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), providing promising therapeutic targets. The possibility to further validate putative key targets from high-confidence interactions between viral bait and host protein through follow-up MS-based multi-omics experiments offers an unprecedented opportunity in the drug discovery pipeline. In particular, drug repurposing, making use of already existing approved drugs directly targeting these identified and validated host interactors, might shorten the time and reduce the costs in comparison to the traditional drug discovery process. This route might be promising for finding effective antiviral therapeutic options providing a turning point in the fight against the coronavirus disease-2019 (COVID-19) outbreak.

Comparative Multiplexed Interactomics of SARS-CoV-2 and Homologous Coronavirus Nonstructural Proteins Identifies Unique and Shared Host-Cell Dependencies

Human coronaviruses (hCoVs) have become a threat to global health and society, as evident from the SARS outbreak in 2002 caused by SARS-CoV-1 and the most recent COVID-19 pandemic caused by SARS-CoV-2. Despite a high sequence similarity between SARS-CoV-1 and -2, each strain has a distinctive virulence. A better understanding of the basic molecular mechanisms mediating changes in virulence is needed. Here, we profile the virus-host protein-protein interactions of two hCoV nonstructural proteins (nsps) that are critical for virus replication. We use tandem mass tag-multiplexed quantitative proteomics to sensitively compare and contrast the interactomes of nsp2 and nsp4 from three betacoronavirus strains: SARS-CoV-1, SARS-CoV-2, and hCoV-OC43-an endemic strain associated with the common cold. This approach enables the identification of both unique and shared host cell protein binding partners and the ability to further compare the enrichment of common interactions across homologues from related strains. We identify common nsp2 interactors involved in endoplasmic reticulum (ER) Ca2+ signaling and mitochondria biogenesis. We also identify nsp4 interactors unique to each strain, such as E3 ubiquitin ligase complexes for SARS-CoV-1 and ER homeostasis factors for SARS-CoV-2. Common nsp4 interactors include N-linked glycosylation machinery, unfolded protein response associated proteins, and antiviral innate immune signaling factors. Both nsp2 and nsp4 interactors are strongly enriched in proteins localized at mitochondria-associated ER membranes suggesting a new functional role for modulating host processes, such as calcium homeostasis, at these organelle contact sites. Our results shed light on the role these hCoV proteins play in the infection cycle, as well as host factors that may mediate the divergent pathogenesis of OC43 from SARS strains. Our mass spectrometry workflow enables rapid and robust comparisons of multiple bait proteins, which can be applied to additional viral proteins. Furthermore, the identified common interactions may present new targets for exploration by host-directed antiviral therapeutics.

SFPH proteins as therapeutic targets for a myriad of diseases

The stomatin/prohibitin/flotillin/HflK/HflC (SPFH) domain is present in an evolutionarily conserved family of proteins that regulate a myriad of signaling pathways in archaea, bacteria and eukaryotes. The most studied SPFH proteins, prohibitins, have already been targeted by different families of small molecules to induce anticancer, cardioprotective, anti-inflammatory, antiviral, and antiosteoporotic activities. Ligands of other SPFH proteins have also been identified and shown to act as anesthetics, anti-allodynia, anticancer, and anti-inflammatory agents. These findings indicate that modulators of human or bacterial SPFH proteins can be developed to treat a wide variety of human disorders.

Flavaglines as natural products targeting eIF4A and prohibitins: From traditional Chinese medicine to antiviral activity against coronaviruses

Flavaglines are cyclopenta[b]benzofurans found in plants of the genus Aglaia, several species of which are used in traditional Chinese medicine. These compounds target the initiation factor of translation eIF4A and the scaffold proteins prohibitins-1 and 2 (PHB1/2) to exert various pharmacological activities, including antiviral effects against several types of viruses, including coronaviruses. This review is focused on the antiviral effects of flavaglines and their therapeutic potential against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Prohibitin ligands: a growing armamentarium to tackle cancers, osteoporosis, inflammatory, cardiac and neurological diseases

Over the last three decades, the scaffold proteins prohibitins-1 and -2 (PHB1/2) have emerged as key signaling proteins regulating a myriad of signaling pathways in health and diseases. Small molecules targeting PHBs display promising effects against cancers, osteoporosis, inflammatory, cardiac and neurodegenerative diseases. This review provides an updated overview of the various classes of PHB ligands, with an emphasis on their mechanism of action and therapeutic potential. We also describe how these ligands have been used to explore PHB signaling in different physiological and pathological settings.

Mitochondria Targeted Viral Replication and Survival Strategies-Prospective on SARS-CoV-2

SARS-CoV-2 is a positive sense RNA coronavirus that constitutes a new threat for the global community and economy. While vaccines against SARS-CoV-2 are being developed, the mechanisms through which this virus takes control of an infected cell to replicate remains poorly understood. Upon infection, viruses completely rely on host cell molecular machinery to survive and replicate. To escape from the immune response and proliferate, viruses strategically modulate cellular metabolism and alter subcellular organelle architecture and functions. One way they do this is by modulating the structure and function of mitochondria, a critical cellular metabolic hub but also a key platform for the regulation of cellular immunity. This versatile nature of mitochondria defends host cells from viruses through several mechanisms including cellular apoptosis, ROS signaling, MAVS activation and mitochondrial DNA-dependent immune activation. These events are regulated by mitochondrial dynamics, a process by which mitochondria alter their structure (including their length and connectivity) in response to stress or other cues. It is therefore not surprising that viruses, including coronaviruses hijack these processes for their survival. In this review, we highlight how positive sense RNA viruses modulate mitochondrial dynamics and metabolism to evade mitochondrial mediated immune response in order to proliferate.

Comparative multiplexed interactomics of SARS-CoV-2 and homologous coronavirus non-structural proteins identifies unique and shared host-cell dependencies

Human coronaviruses (hCoV) have become a threat to global health and society, as evident from the SARS outbreak in 2002 caused by SARS-CoV-1 and the most recent COVID-19 pandemic caused by SARS-CoV-2. Despite high sequence similarity between SARS-CoV-1 and -2, each strain has distinctive virulence. A better understanding of the basic molecular mechanisms mediating changes in virulence is needed. Here, we profile the virus-host protein-protein interactions of two hCoV non-structural proteins (nsps) that are critical for virus replication. We use tandem mass tag-multiplexed quantitative proteomics to sensitively compare and contrast the interactomes of nsp2 and nsp4 from three betacoronavirus strains: SARS-CoV-1, SARS-CoV-2, and hCoV-OC43 - an endemic strain associated with the common cold. This approach enables the identification of both unique and shared host cell protein binding partners and the ability to further compare the enrichment of common interactions across homologs from related strains. We identify common nsp2 interactors involved in endoplasmic reticulum (ER) Ca 2+ signaling and mitochondria biogenesis. We also identifiy nsp4 interactors unique to each strain, such as E3 ubiquitin ligase complexes for SARS-CoV-1 and ER homeostasis factors for SARS-CoV-2. Common nsp4 interactors include N -linked glycosylation machinery, unfolded protein response (UPR) associated proteins, and anti-viral innate immune signaling factors. Both nsp2 and nsp4 interactors are strongly enriched in proteins localized at mitochondrial-associated ER membranes suggesting a new functional role for modulating host processes, such as calcium homeostasis, at these organelle contact sites. Our results shed light on the role these hCoV proteins play in the infection cycle, as well as host factors that may mediate the divergent pathogenesis of OC43 from SARS strains. Our mass spectrometry workflow enables rapid and robust comparisons of multiple bait proteins, which can be applied to additional viral proteins. Furthermore, the identified common interactions may present new targets for exploration by host-directed anti-viral therapeutics.

Prohibitin 1/2 mediates Dengue-3 entry into human neuroblastoma (SH-SY5Y) and microglia (CHME-3) cells

Background

Very few studies have identified receptor molecules for dengue virus (DENV) on neural cells. This study was designed to identify putative receptor/(s) involved in entry of DENV-3 in human neural cells of various lineages; neuronal-SH-SY5Y, astroglial-U-87 MG and microglial-CHME-3 cells.

Result

Virus overlay protein binding assay, LC-MS/MS and SEQUEST identified prohibitin1/2 (PHB1/2) as interacting proteins on SH-SY5Y, CHME-3, and U-87 MG cells. Infection inhibition and siRNA assays confirmed the role of PHB1/2 in the entry of DENV-3 into SH-SY5Y and CHME-3 cells but not in U-87 MG cells. Indirect immunofluorescence and flow-cytometry demonstrated the presence of PHB1/2 on the surface of SH-SY5Y and CHME-3 cells. Co-immunoprecipitation and Western blot, as well as double labelling, reconfirmed the interaction between PHB1/2 and DENV-3 EDIII protein.

Conclusion

These observations together for the first time indicate that PHB1/2 may serve as a putative receptor for DENV-3 in SH-SY5Y and CHME-3 cells. The study provided insights into DENV-3 and neural cell interactions.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

Interaction between PHB2 and Enterovirus A71 VP1 Induces Autophagy and Affects EV-A71 Infection

Enterovirus A71 (EV-A71) is a major pathogen that causes severe and fatal cases of hand-foot-and-mouth disease (HFMD). HFMD caused by EV-A71 seriously endangers children’s health. Although autophagy is an important antiviral defense mechanism, some viruses have evolved strategies to utilize autophagy to promote self-replication. EV-A71 can utilize autophagy vesicles as replication scaffolds, indicating that EV-A71 infection is closely related to its autophagy induction mechanism. VP1, a structural protein of EV-A71, has been reported to induce autophagy, but the underlying mechanism is still unclear. In this study, we found that the C-terminus (aa 251–297) of VP1 induces autophagy. Mass spectrometry analysis suggested that prohibitin 2 (PHB2) interacts with the C-terminus of the EV-A71 VP1 protein, and this was further verified by coimmunoprecipitation assays. After PHB2 knockdown, EV-A71 replication, viral particle release, and viral protein synthesis were reduced, and autophagy was inhibited. The results suggest that PHB2 interaction with VP1 is essential for induction of autophagy and the infectivity of EV-A71. Furthermore, we confirmed that EV-A71 induced complete autophagy that required autolysosomal acidification, thus affecting EV-A71 infection. In summary, this study revealed that the host protein PHB2 is involved in an autophagy mechanism during EV-A71 infection.

Aglaia odorata Lour. extract inhibit ischemic neuronal injury potentially via suppressing p53/Puma-mediated mitochondrial apoptosis pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Aglaia odorata Lour. is a traditional Chinese medicinal plant possessing properties of improving blood circulation, and it is widely used in the treatment of dizziness, traumatic injuries and bruises.

AIM OF STUDY

In this study, we are aimed to investigate the cerebral protection effect of the extracts from leaves of Aglaia odorata Lour. (ELA) and the potential mechanism in vivo and in vitro.

MATERIALS AND METHODS

The therapeutic effect of ELA on ischemic cerebral stroke was measured on a middle cerebral artery occlusion (MCAO) rat model. Protective effect of ELA on oxygen-glucose deprivation/reperfusion (OGD/R)-induced PC12 cells was measured by MTT assay. The apoptotic cells were observed by Hoechst 33258 staining and acridine orange/ethidium bromide double staining assay. Mitochondria were observed by Mitotracker staining assay. The mitochondrial membrane potential was determined by JC-1 staining assay. Western blot was used to investigate the effects of ELA on apoptosis-related proteins.

RESULTS

We showed that ELA was an effective neuroprotective agent. In vivo experiments, ELA exerted significant protective effect on MCAO model. TTC staining showed that ELA could reduce cerebral infarction area against MCAO insult. HE and Nissl's staining indicated that ELA could reverse the damage of cortex and hippocampus caused by MCAO. In vitro experiments, ELA showed significant protective effect on OGD/R-induced PC12 cells by reducing the number of apoptotic cells, increasing mitochondrial membrane potential, and reducing superoxide aggregation, further suppressing mitochondrial caspase-9/3 apoptosis pathway. Moreover, protective effect of ELA on mitochondrial function may be exerted by inhibiting p53/Puma signal pathway.

CONCLUSION

Our results suggest that ELA exerts a marked neuroprotective effect against cerebral ischemia potentially via suppressing p53/Puma-mediated mitochondrial caspase-9/3 apoptosis pathway.

Comparison of broad-spectrum antiviral activities of the synthetic rocaglate CR-31-B (-) and the eIF4A-inhibitor Silvestrol

Rocaglates, a class of natural compounds isolated from plants of the genus Aglaia, are potent inhibitors of translation initiation. They are proposed to form stacking interactions with polypurine sequences in the 5′-untranslated region (UTR) of selected mRNAs, thereby clamping the RNA substrate onto eIF4A and causing inhibition of the translation initiation complex. Since virus replication relies on the host translation machinery, it is not surprising that the rocaglate Silvestrol has broad-spectrum antiviral activity. Unfortunately, synthesis of Silvestrol is sophisticated and time-consuming, thus hampering the prospects for further antiviral drug development. Here, we present the less complex structured synthetic rocaglate CR-31-B (−) as a novel compound with potent broad-spectrum antiviral activity in primary cells and in an ex vivo bronchial epithelial cell system. CR-31-B (−) inhibited the replication of corona-, Zika-, Lassa-, Crimean Congo hemorrhagic fever viruses and, to a lesser extent, hepatitis E virus (HEV) at non-cytotoxic low nanomolar concentrations. Since HEV has a polypurine-free 5′-UTR that folds into a stable hairpin structure, we hypothesized that RNA clamping by Silvestrol and its derivatives may also occur in a polypurine-independent but structure-dependent manner. Interestingly, the HEV 5′-UTR conferred sensitivity towards Silvestrol but not to CR-31-B (−). However, if an exposed polypurine stretch was introduced into the HEV 5′-UTR, CR-31-B (−) became an active inhibitor comparable to Silvestrol. Moreover, thermodynamic destabilization of the HEV 5′-UTR led to reduced translational inhibition by Silvestrol, suggesting differences between rocaglates in their mode of action, most probably by engaging Silvestrol's additional dioxane moiety.

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The synthetic rocaglate CR-31-B (−) has broad-spectrum antiviral activity comparable to that of Silvestrol.

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Both compounds show remarkably low cytotoxicity in primary cells.

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Silvestrol and CR-31-B (−) are highly efficient against HCoV-229E in a primary human bronchial epithelial cell system.

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Both compounds reduce LASV and CCHFV titers by about 3–4 logs in primary murine hepatocytes.

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Only Silvestrol with its characteristic dioxane moiety can clamp polypurine-free structured RNAs onto the eIF4A helicase.

Cellular receptors for enterovirus A71

Enterovirus 71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease. EV-A71 infection is sometimes associated with severe neurological diseases such as acute encephalitis, acute flaccid paralysis, and cardiopulmonary failure. Therefore, EV-A71 is a serious public health concern. Scavenger receptor class B, member 2 (SCARB2) is a type III transmembrane protein that belongs to the CD36 family and is a major receptor for EV-A71. SCARB2 supports attachment and internalization of the virus and initiates conformational changes that lead to uncoating of viral RNA in the cytoplasm. The three-dimensional structure of the virus-receptor complex was elucidated by cryo-electron microscopy. Two α-helices in the head domain of SCARB2 bind to the G-H loop of VP1 and the E-F loop of VP2 capsid proteins of EV-A71. Uncoating takes place in a SCARB2- and low pH-dependent manner. In addition to SCARB2, other molecules support cell surface binding of EV-A71. Heparan sulfate proteoglycans, P-selectin glycoprotein ligand-1, sialylated glycan, annexin II, vimentin, fibronectin, and prohibitin enhance viral infection by retaining the virus on the cell surface. These molecules are known as “attachment receptors” because they cannot initiate uncoating. In vivo, SCARB2 expression was observed in EV-A71 antigen-positive neurons and epithelial cells in the crypts of the palatine tonsils in patients that died of EV-A71 infection. Adult mice are not susceptible to infection by EV-A71, but transgenic mice that express human SCARB2 become susceptible to EV-A71 infection and develop neurological diseases similar to those observed in humans. Attachment receptors may also be involved in EV-A71 infection in vivo. Although heparan sulfate proteoglycans are expressed by many cultured cell lines and enhance infection by a subset of EV-A71 strains, they are not expressed by cells that express SCARB2 at high levels in vivo. Thus, heparan sulfate-positive cells merely adsorb the virus and do not contribute to replication or dissemination of the virus in vivo. In addition to these attachment receptors, cyclophilin A and human tryptophanyl aminoacyl-tRNA synthetase act as an uncoating regulator and an entry mediator that can confer susceptibility to non-susceptibile cells in the absence of SCARB2, respectively. The roles of attachment receptors and other molecules in EV-A71 pathogenesis remain to be elucidated.

STAT3 Regulates the Type I IFN-Mediated Antiviral Response by Interfering with the Nuclear Entry of STAT1

Signal transducer and activator of transcription 3 (STAT3) is a multifunctional factor that regulates inflammation and immunity. Knowledge of its regulatory mechanisms is very limited. Here, we showed that enterovirus 71 (EV71) infection induced the phosphorylation of STAT3 and the expression of its downstream inflammatory regulators. Knockdown of STAT3 with siRNAs significantly restricted viral RNA and protein levels, and also reduced viral titers. With further investigation, we found that importin α family member Karyopherin-α1 (KPNA1) was employed by both STAT1 and STAT3 for their nuclear import. The phosphorylated and un-phosphorylated STAT3 competed with STAT1 for binding to the decreased KPNA1 post infection and repressed downstream ISG expression. STAT3 knockdown alleviated the repressed type I IFN-mediated antiviral response upon infection and led to decreased viral replication. Taken together, our data suggested the role of STAT3 in maintaining the balance of inflammation and antiviral responses in the central nervous system (CNS) upon infection.

Multifunctionality of structural proteins in the enterovirus life cycle

Members of the genus Enterovirus have a significant effect on human health, especially in infants and children. Since the viral genome has limited coding capacity, Enteroviruses subvert a range of cellular processes for viral infection via the interaction of viral proteins and numerous cellular factors. Intriguingly, the capsid-receptor interaction plays a crucial role in viral entry and has significant implications in viral pathogenesis. Moreover, interactions between structural proteins and host factors occur directly or indirectly in multiple steps of viral replication. In this review, we focus on the current understanding of the multifunctionality of structural proteins in the viral life cycle, which may constitute valuable targets for antiviral and therapeutic interventions.

Cholix toxin, an eukaryotic elongation factor 2 ADP-ribosyltransferase, interacts with Prohibitins and induces apoptosis with mitochondrial dysfunction in human hepatocytes

Vibrio cholerae produced-Cholix toxin (Cholix) is a cytotoxin that ADP-ribosylates eukaryotic elongation factor 2, inhibiting protein synthesis, and inducing apoptosis. Here, we identified prohibitin (PHB) 1 and 2 as novel Cholix-interacting membrane proteins in immortalised human hepatocytes and HepG2 cells by Cholix immunoprecipitation assays. The expression level of PHB1 was decreased by Cholix after a 12hr incubation. Cholix-induced poly (ADP-ribose) polymerase (PARP) cleavage was significantly enhanced in PHB (PHB1 or PHB2) knockdown cells. In contrast, transiently overexpressed PHB in hepatocytes attenuated Cholix-induced Bax/Bak conformational changes and PARP cleavage. In addition, Cholix-induced reactive oxygen species production and accumulation of fragmented mitochondria were enhanced in PHB-knockdown cells. Furthermore, Cholix induced activation of Rho-associated coiled coil-containing protein kinase 1 (ROCK1), which was enhanced in PHB-knockdown cells, followed by actin filament depolymerisation and accumulation of tubulin in the blebbing cells. Inhibition of ROCK1 by siRNA or its inhibitor suppressed Cholix-induced PARP cleavage and reactive oxygen species generation. Our findings identify PHB as a new protein that interacts with Cholix and is involved in Cholix-induced mitochondrial dysfunction and cytoskeletal rearrangement by ROCK1 activation during apoptosis.