The co-chaperone Cdc37 regulates the rabies virus phosphoprotein stability by targeting to Hsp90AA1 machinery

Research Progress in RNA-Binding Proteins

RNA-binding proteins are everywhere and accompany RNA molecules at every stage of their molecular life, from "birth" (transcription) through "growing up" (maturation), "active life" (molecular function) until "death" (turnover) [...].

Structure and Dynamics of the Unassembled Nucleoprotein of Rabies Virus in Complex with Its Phosphoprotein Chaperone Module

As for all non-segmented negative RNA viruses, rabies virus has its genome packaged in a linear assembly of nucleoprotein (N), named nucleocapsid. The formation of new nucleocapsids during virus replication in cells requires the production of soluble N protein in complex with its phosphoprotein (P) chaperone. In this study, we reconstituted a soluble heterodimeric complex between an armless N protein of rabies virus (RABV), lacking its N-terminal subdomain (N_NT-ARM), and a peptide encompassing the N⁰ chaperon module of the P protein. We showed that the chaperone module undergoes a disordered-order transition when it assembles with N⁰ and measured an affinity in the low nanomolar range using a competition assay. We solved the crystal structure of the complex at a resolution of 2.3 Å, unveiling the details of the conserved interfaces. MD simulations showed that both the chaperon module of P and RNA-mediated polymerization reduced the ability of the RNA binding cavity to open and close. Finally, by reconstituting a complex with full-length P protein, we demonstrated that each P dimer could independently chaperon two N⁰ molecules.

HSP90AA1 interacts with CSFV NS5A protein and regulates CSFV replication via the JAK/STAT and NF-κB signaling pathway

Classical swine fever (CSF), caused by the classical swine fever virus (CSFV), is a highly contagious and fatal viral disease, posing a significant threat to the swine industry. Heat shock protein 90 kDa alpha class A member 1 (HSP90AA1) is a very conservative chaperone protein that plays an important role in signal transduction and viral proliferation. However, the role of HSP90AA1 in CSFV infection is unknown. In this study, we found that expression of HSP90AA1 could be promoted in PK-15 and 3D4/2 cells infected by CSFV. Over-expression of HSP90AA1 could inhibit CSFV replication and functional silencing of HSP90AA1 gene promotes CSFV replication. Further exploration revealed that HSP90AA1 interacted with CSFV NS5A protein and reduced the protein levels of NS5A. Since NS5A has an important role in CSFV replication and is closely related to type I IFN and NF-κB response, we further analyzed whether HSP90AA1 affects CSFV replication by regulating type I IFN and NF-κB pathway responses. Our research found HSP90AA1 positively regulated type I IFN response by promoting STAT1 phosphorylation and nuclear translocation processes and promoted the nuclear translocation processes of p-P65. However, CSFV infection antagonizes the activation of HSP90AA1 on JAK/STAT and NF-κB pathway. In conclusion, our study found that HSP90AA1 overexpression significantly inhibited CSFV replication and may inhibit CSFV replication by interacting with NS5A and activating JAK/STAT and NF-κB signaling pathways. These results provide new insights into the mechanism of action of HSP90AA1 in CSFV infection, which abundant the candidate library of anti-CSFV.

Hsp90 Activity Is Necessary for the Maturation of Rabies Virus Polymerase

Mononegavirales is an order of viruses with a genome in the form of a non-segmented negative-strand RNA that encodes several proteins. The functional polymerase complex of these viruses is composed of two proteins: a large protein (L) and a phosphoprotein (P). The replication of viruses from this order depends on Hsp90 chaperone activity. Previous studies have demonstrated that Hsp90 inhibition results in the degradation of mononegaviruses L protein, with exception of the rabies virus, for which the degradation of P protein was observed. Here, we demonstrated that Hsp90 inhibition does not affect the expression of rabies L and P proteins, but it inhibits binding of the P protein and L protein into functional viral polymerase. Rabies and the vesicular stomatitis virus, but not the measles virus, L proteins can be expressed independently of the presence of a P protein and in the presence of an Hsp90 inhibitor. Our results suggest that the interaction of L proteins with P proteins and Hsp90 in the process of polymerase maturation may be a process specific to particular viruses.

Hsp90 in Human Diseases: Molecular Mechanisms to Therapeutic Approaches

The maturation of hemeprotein dictates that they incorporate heme and become active, but knowledge of this essential cellular process remains incomplete. Studies on chaperon Hsp90 has revealed that it drives functional heme maturation of inducible nitric oxide synthase (iNOS), soluble guanylate cyclase (sGC) hemoglobin (Hb) and myoglobin (Mb) along with other proteins including GAPDH, while globin heme maturations also need an active sGC. In all these cases, Hsp90 interacts with the heme-free or apo-protein and then drives the heme maturation by an ATP dependent process before dissociating from the heme-replete proteins, suggesting that it is a key player in such heme-insertion processes. As the studies on globin maturation also need an active sGC, it connects the globin maturation to the NO-sGC (Nitric oxide-sGC) signal pathway, thereby constituting a novel NO-sGC-Globin axis. Since many aggressive cancer cells make Hbβ/Mb to survive, the dependence of the globin maturation of cancer cells places the NO-sGC signal pathway in a new light for therapeutic intervention. Given the ATPase function of Hsp90 in heme-maturation of client hemeproteins, Hsp90 inhibitors often cause serious side effects and this can encourage the alternate use of sGC activators/stimulators in combination with specific Hsp90 inhibitors for better therapeutic intervention.

Establishment of Human-Induced Pluripotent Stem Cell-Derived Neurons-A Promising In Vitro Model for a Molecular Study of Rabies Virus and Host Interaction

Rabies is a deadly viral disease caused by the rabies virus (RABV), transmitted through a bite of an infected host, resulting in irreversible neurological symptoms and a 100% fatality rate in humans. Despite many aspects describing rabies neuropathogenesis, numerous hypotheses remain unanswered and concealed. Observations obtained from infected primary neurons or mouse brain samples are more relevant to human clinical rabies than permissive cell lines; however, limitations regarding the ethical issue and sample accessibility become a hurdle for discovering new insights into virus-host interplays. To better understand RABV pathogenesis in humans, we generated human-induced pluripotent stem cell (hiPSC)-derived neurons to offer the opportunity for an inimitable study of RABV infection at a molecular level in a pathologically relevant cell type. This study describes the characteristics and detailed proteomic changes of hiPSC-derived neurons in response to RABV infection using LC-MS/MS quantitative analysis. Gene ontology (GO) enrichment of differentially expressed proteins (DEPs) reveals temporal changes of proteins related to metabolic process, immune response, neurotransmitter transport/synaptic vesicle cycle, cytoskeleton organization, and cell stress response, demonstrating fundamental underlying mechanisms of neuropathogenesis in a time-course dependence. Lastly, we highlighted plausible functions of heat shock cognate protein 70 (HSC70 or HSPA8) that might play a pivotal role in regulating RABV replication and pathogenesis. Our findings acquired from this hiPSC-derived neuron platform help to define novel cellular mechanisms during RABV infection, which could be applicable to further studies to widen views of RABV-host interaction.

Integrative Role of 14-3-3ε in Sleep Regulation

Sleep is a crucial factor for health and survival in all animals. In this study, we found by proteomic analysis that some cancer related proteins were impacted by the circadian clock. The 14-3-3ε protein, expression of which is activated by the circadian transcription factor Clock, regulates adult sleep of Drosophila independent of circadian rhythm. Detailed analysis of the sleep regulatory mechanism shows that 14-3-3ε directly targets the Ultrabithorax (Ubx) gene to activate transcription of the pigment dispersing factor (PDF). The dopamine receptor (Dop1R1) and the octopamine receptor (Oamb), are also involved in the 14-3-3ε pathway, which in 14-3-3ε mutant flies causes increases in the dopR1 and OAMB, while downregulation of the DopR1 and Oamb can restore the sleep phenotype caused by the 14-3-3ε mutation. In conclusion, 14-3-3ε is necessary for sleep regulation in Drosophila.

Diversity in heat shock protein families: functional implications in virus infection with a comprehensive insight of their role in the HIV-1 life cycle

Heat shock proteins (HSPs) are a group of cellular proteins that are induced during stress conditions such as heat stress, cold shock, UV irradiation and even pathogenic insult. They are classified into families based on molecular size like HSP27, 40, 70 and 90 etc, and many of them act as cellular chaperones that regulate protein folding and determine the fate of mis-folded or unfolded proteins. Studies have also shown multiple other functions of these proteins such as in cell signalling, transcription and immune response. Deregulation of these proteins leads to devastating consequences, such as cancer, Alzheimer's disease and other life threatening diseases suggesting their potential importance in life processes. HSPs exist in multiple isoforms, and their biochemical and functional characterization still remains a subject of active investigation. In case of viral infections, several HSP isoforms have been documented to play important roles with few showing pro-viral activity whereas others seem to have an anti-viral role. Earlier studies have demonstrated that HSP40 plays a pro-viral role whereas HSP70 inhibits HIV-1 replication; however, clear isoform-specific functional roles remain to be established. A detailed functional characterization of all the HSP isoforms will uncover their role in cellular homeostasis and also may highlight some of them as potential targets for therapeutic strategies against various viral infections. In this review, we have tried to comprehend the details about cellular HSPs and their isoforms, their role in cellular physiology and their isoform-specific functions in case of virus infection with a specific focus on HIV-1 biology.

AUY922 induces retinal toxicity through attenuating TRPM1

Background

Ocular adverse events are common dose-limiting toxicities in cancer patients treated with HSP90 inhibitors, such as AUY922; however, the pathology and molecular mechanisms that mediate AUY922-induced retinal toxicity remain undescribed.

Methods

The impact of AUY922 on mouse retinas and cell lines was comprehensively investigated using isobaric tags for relative and absolute quantitation (iTRAQ)‑based proteomic profiling and pathway enrichment analysis, immunohistochemistry and immunofluorescence staining, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, MTT assay, colony formation assay, and western blot analysis. The effect of AUY922 on the Transient Receptor Potential cation channel subfamily M member 1 (TRPM1)-HSP90 chaperone complex was characterized by coimmunoprecipitation. TRPM1-regulated gene expression was analyzed by RNAseq analysis and gene set enrichment analysis (GSEA). The role of TRPM1 was assessed using both loss-of-function and gain-of-function approaches.

Results

Here, we show that the treatment with AUY922 induced retinal damage and cell apoptosis, dysregulated the photoreceptor and retinal pigment epithelium (RPE) layers, and reduced TRPM1 expression. Proteomic profiling and functional annotation of differentially expressed proteins reveals that those related to stress responses, protein folding processes, regulation of apoptosis, cell cycle and growth, reactive oxygen species (ROS) response, cell junction assembly and adhesion regulation, and proton transmembrane transport were significantly enriched in AUY922-treated cells. We found that AUY922 triggered caspase-3-dependent cell apoptosis, increased ROS production and inhibited cell growth. We determined that TRPM1 is a bona fide HSP90 client and characterized that AUY922 may reduce TRPM1 expression by disrupting the CDC37-HSP90 chaperone complex. Additionally, GSEA revealed that TRPM1-regulated genes were associated with retinal morphogenesis in camera-type eyes and the JAK-STAT cascade. Finally, gain-of-function and loss-of-function analyses validated the finding that TRPM1 mediated the cell apoptosis, ROS production and growth inhibition induced by AUY922.

Conclusions

Our study demonstrates the pathology of AUY922-induced retinal toxicity in vivo. TRPM1 is an HSP90 client, regulates photoreceptor morphology and function, and mediates AUY922-induced cytotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00751-5.

Rabies Infection: An Overview of Lyssavirus-Host Protein Interactions

Viruses are obligatory intracellular parasites that use cell proteins to take the control of the cell functions in order to accomplish their life cycle. Studying the viral-host interactions would increase our knowledge of the viral biology and mechanisms of pathogenesis. Studies on pathogenesis mechanisms of lyssaviruses, which are the causative agents of rabies, have revealed some important host protein partners for viral proteins, especially for most studied species, i.e. RABV. In this review article, the key physical lyssavirus-host protein interactions, their contributions to rabies infection, and their exploitation are discussed to improve the knowledge about rabies pathogenesis.

Comparative Epigenomics Reveals Host Diversity of the Trichinella Epigenomes and Their Effects on Differential Parasitism

Comparative epigenomics provides new insights on evolutionary biology in relation with complex interactions between species and their environments. In the present study, we focus on deciphering the conservation and divergence of DNA methylomes during Trichinella evolution. Whole-genome bisulfite sequencing and RNA-seq were performed on the two clades of Trichinella species, in addition to whole-genome sequencing. We demonstrate that methylation patterns of sing-copy orthologous genes (SCOs) of the 12 Trichinella species are host-related and can mirror known phylogenetic relationships. Among these SCOs, we identify a panel of genes exhibiting hyper-/hypo-methylated features in gene-bodies or respective promoters that play pivotal roles in transcriptome regulation. These hyper-/hypo-methylated SCOs are also of functional significance across developmental stages, as they are highly enriched species-specific and stage-specific expressed genes both in Ad and ML stages. We further identify a set of parasitism-related functional genes that exhibit host-related differential methylation and expression among those SCOs, including p53-like transcription factor and Cdc37 that are of functional significance for elucidating differential parasitology between the two clades of Trichinella. This comparative epigenome study can help to decipher the environmental effects on differential adaptation and parasitism of the genus Trichinella.

Heat Shock Protein 90 Chaperones E1A Early Protein of Adenovirus 5 and Is Essential for Replication of the Virus

Adenovirus infections tend to be mild, but they may pose a serious threat for young and immunocompromised individuals. The treatment is complicated because there are no approved safe and specific drugs for adenovirus infections. Here, we present evidence that 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG), an inhibitor of Hsp90 chaperone, decreases the rate of human adenovirus 5 (HAdV-5) replication in cell cultures by 95%. 17-AAG inhibited the transcription of early and late genes of HAdV-5, replication of viral DNA, and expression of viral proteins. 6 h after infection, Hsp90 inhibition results in a 6.3-fold reduction of the newly synthesized E1A protein level without a decrease in the E1A mRNA level. However, the Hsp90 inhibition does not increase the decay rate of the E1A protein that was constitutively expressed in the cell before exposure to the inhibitor. The co-immunoprecipitation proved that E1A protein interacted with Hsp90. Altogether, the presented results show, for the first time. that Hsp90 chaperones newly synthesized, but not mature, E1A protein. Because E1A serves as a transcriptional co-activator of adenovirus early genes, the anti-adenoviral activity of the Hsp90 inhibitor might be explained by the decreased E1A level.

Hsp90 is involved in pseudorabies virus virion assembly via stabilizing major capsid protein VP5

Many viruses utilize molecular chaperone heat shock protein 90 (Hsp90) for protein folding and stabilization, however, the role of Hsp90 in herpesvirus lifecycle is obscure. Here, we provide evidence that Hsp90 participates in pseudorabies virus (PRV) replication. Viral growth kinetics assays show that Hsp90 inhibitor geldanamycin (GA) abrogates PRV replication at the post-penetration step. Transmission electron microscopy demonstrates that dysfunction of Hsp90 diminishes the quantity of PRV nucleocapsids. Overexpression and knockdown of Hsp90 suggest that de novo Hsp90 is involved in PRV replication. Mechanismly, dysfunction of Hsp90 inhibits PRV major capsid protein VP5 expression. Co-immunoprecipitation and indirect immunofluorescence assays indicate that Hsp90 interacts with VP5. Interestingly, Hsp70, a collaborator of Hsp90, also interacts with VP5, but doesn't affect PRV growth. Finally, inhibition of Hsp90 results in PRV VP5 degradation in a proteasome-dependent manner. Collectively, our data suggest that Hsp90 contributes to PRV virion assembly and replication via stabilization of VP5.

Rabies virus phosphoprotein P5 binding to BECN1 regulates self-replication by BECN1-mediated autophagy signaling pathway

Background

Rabies virus (RABV) is reported to encode five phosphoproteins (P), which are involved in viral genomic replication, axonal transport, oxidative stress, interferon antagonism, and autophagy induction. However, the functions of the different P proteins are poorly understood.

Methods

Immunofluorescence staining and western blot were performed to detect the autophagy activity, the form of ring-like structure, and the colocalization of BECN1 and P. Co-immunoprecipitation was performed to detect the interaction between P and BECN1. QRT-PCR and TCID₅₀ assay were performed to detect the replication level of RABV. Small interfering RNA was used to detect the autophagy signaling pathway.

Results

We found that P5 attaches to N-terminal residues 1–139 of BECN1 (beclin1) on the BECN1 ring-like structure through amino acid residues 173–222 of P5. Subsequently, we found that P5-induced autophagosomes did not fuse with lysosomes. Becn1 silencing did not recover P5 overexpression-induced promotion of RABV replication. Mechanistically, RABV protein PΔN82 (P5) induced incomplete autophagy via the BECN1-mediated signaling pathway.

Conclusions

Our data indicate that P5 binding to the BECN1 ring benefits RABV replication by inducing BECN1 signaling pathway-dependent incomplete autophagy, which provides a potential target for antiviral drugs against RABV.

Proteostasis in Viral Infection: Unfolding the Complex Virus-Chaperone Interplay

Viruses are obligate intracellular parasites that rely on their hosts for protein synthesis, genome replication, and viral particle production. As such, they have evolved mechanisms to divert host resources, including molecular chaperones, facilitate folding and assembly of viral proteins, stabilize complex structures under constant mutational pressure, and modulate signaling pathways to dampen antiviral responses and prevent premature host death. Biogenesis of viral proteins often presents unique challenges to the proteostasis network, as it requires the rapid and orchestrated production of high levels of a limited number of multifunctional, multidomain, and aggregation-prone proteins. To overcome such challenges, viruses interact with the folding machinery not only as clients but also as regulators of chaperone expression, function, and subcellular localization. In this review, we summarize the main types of interactions between viral proteins and chaperones during infection, examine evolutionary aspects of this relationship, and discuss the potential of using chaperone inhibitors as broad-spectrum antivirals.

The LC8-RavP ensemble Structure Evinces A Role for LC8 in Regulating Lyssavirus Polymerase Functionality

The rabies and Ebola viruses recruit the highly conserved host protein LC8 for their own reproductive success. In vivo knockouts of the LC8 recognition motif within the rabies virus phosphoprotein (RavP) result in completely nonlethal viral infections. In this work, we examine the molecular role LC8 plays in viral lethality. We show that RavP and LC8 colocalize in rabies infected cells, and that LC8 interactions are essential for efficient viral polymerase functionality. NMR, SAXS, and molecular modeling demonstrate that LC8 binding to a disordered linker adjacent to an endogenous dimerization domain results in restrictions in RavP domain orientations. The resulting ensemble structure of RavP-LC8 tetrameric complex is similar to that of a related virus phosphoprotein that does not bind LC8, suggesting that with RavP, LC8 binding acts as a switch to induce a more active conformation. The high conservation of the LC8 motif in Lyssavirus phosphoproteins and its presence in other analogous proteins such as the Ebola virus VP35 evinces a broader purpose for LC8 in regulating downstream phosphoprotein functions vital for viral replication.

Molecular detection of Hsp90 inhibitor suppressing PCV2 replication in host cells

Porcine Circovirus Type 2 (PCV2) is a pathogen that has the ability to cause devastating disease manifestations in pig populations with major economic implications. Our previous research found that Hsp90 is required for PCV2 production in PK-15 and 3D4/31 cells. The aim of this study was to evaluate the effect of Hsp90 inhibitor regulating PCV2 replication and to explore its underlying mechanism. In PK-15 and 3D4/31 cells treated with 17-AAG after viral adsorption, replication of PCV2 was attenuated as assessed by quantitating the expression of viral protein. Following NF-κB activation it was observed that 24hpi with PCV2 was significantly inhibited in the presence of 17-AAG. The expression of Hsp90 associated client proteins in PCV2-infected cells were also reduced in the presence of 17-AAG. However, treatment with MG-132 failed to rescue 17-AAG mediated reduction of PCV2 production in host cells. Thus, Hsp90 regulates PCV2 by modulating cellular signaling proteins. These results highlight the importance of cellular proteins during PCV2 infection and the possibility of targeting cellular chaperones for developing new anti-rotaviral strategies.

Chaperoning the Mononegavirales: Current Knowledge and Future Directions

The order Mononegavirales harbors numerous viruses of significant relevance to human health, including both established and emerging infections. Currently, vaccines are only available for a small subset of these viruses, and antiviral therapies remain limited. Being obligate cellular parasites, viruses must utilize the cellular machinery for their replication and spread. Therefore, targeting cellular pathways used by viruses can provide novel therapeutic approaches. One of the key challenges confronted by both hosts and viruses alike is the successful folding and maturation of proteins. In cells, this task is faced by cellular molecular chaperones, a group of conserved and abundant proteins that oversee protein folding and help maintain protein homeostasis. In this review, we summarize the current knowledge of how the Mononegavirales interact with cellular chaperones, highlight key gaps in our knowledge, and discuss the potential of chaperone inhibitors as antivirals.

Hsp90 interacts with multiple dengue virus 2 proteins

Infections with the mosquito-borne dengue virus (DENV) remain a significant public health challenge. In the absence of a commercial therapeutic to treat DENV infection, a greater understanding of the processes of cellular replication is required. The abundant cellular chaperone protein heat shock protein 90 (Hsp90) has been shown to play a proviral role in the replication cycle of several viruses, predominantly through the stabilization of specific viral proteins. To investigate any potential role of Hsp90 in DENV infection the interaction between Hsp90 and DENV proteins was determined through co-immunoprecipitation experiments. Six DENV proteins namely envelope (E) and nonstructural (NS) proteins NS1, NS2B, NS3, NS4B and NS5 were shown to interact with Hsp90, and four of these proteins (E, NS1, NS3 and NS5) were shown to colocalize to a variable extent with Hsp90. Despite the extensive interactions between Hsp90 and DENV proteins, inhibition of the activity of Hsp90 had a relatively minor effect on DENV replication, with inhibition of Hsp90 resulting in a decrease of cellular E protein (but not nonstructural proteins) coupled with an increase of E protein in the medium and an increased virus titer. Collectively these results indicate that Hsp90 has a slight anti-viral effect in DENV infection.

Rabies Virus Infection Induces Microtubule Depolymerization to Facilitate Viral RNA Synthesis by Upregulating HDAC6

Rabies virus (RABV) is the cause of rabies, and is associated with severe neurological symptoms, high mortality rate, and a serious threat to human health. Although cellular tubulin has recently been identified to be incorporated into RABV particles, the effects of RABV infection on the microtubule cytoskeleton remain poorly understood. In this study, we show that RABV infection induces microtubule depolymerization as observed by confocal microscopy, which is closely associated with the formation of the filamentous network of the RABV M protein. Depolymerization of microtubules significantly increases viral RNA synthesis, while the polymerization of microtubules notably inhibits viral RNA synthesis and prevents the viral M protein from inducing the formation of the filamentous network. Furthermore, the histone deacetylase 6 (HDAC6) expression level progressively increases during RABV infection, and the inhibition of HDAC6 deacetylase activity significantly decreases viral RNA synthesis. In addition, the expression of viral M protein alone was found to significantly upregulate HDAC6 expression, leading to a substantial reduction in its substrate, acetylated α-tubulin, eventually resulting in microtubule depolymerization. These results demonstrate that HDAC6 plays a positive role in viral transcription and replication by inducing microtubule depolymerization during RABV infection.

Identification and characterization of host cell proteins interacting with Scylla serrata reovirus non-structural protein p35

We have previously shown that non-structural protein p35, encoded by Scylla serrata reovirus (SsRV) S10, may act as a viroporin. To characterize the role of p35 protein in the modulation of cellular function, a yeast two-hybrid system was used to screen a cDNA library derived from S. serrata to find its interacting partner. Protein interactions were confirmed in vitro by GST pull-down. Full cDNAs of p35 interactors were cloned by the rapid amplification of cDNA ends. After two-hybrid library screening, we isolated partial cDNAs encoding hemocyanin, cryptocyanin, and TAX1BP1. Interaction of p35 with each of hemocyanin, cryptocyanin, and TAX1BP1 was confirmed by GST pull-down. The full-length cDNA fragments of hemocyanin, cryptocyanin, and TAX1BP1 were 2287, 2422, and 3437 bp, respectively, and they encoded three putative proteins with molecular masses of ~76.9, ~79.2, and ~107.2 kDa, respectively. This study casts new light on the function and physiological significance of p35 during the SsRV replication cycle.