Host Cell Vimentin Restrains Toxoplasma gondii Invasion and Phosphorylation of Vimentin is Partially Regulated by Interaction with TgROP18

Quantitative phosphoproteomic analysis of chicken DF-1 cells infected with Eimeria tenella, using tandem mass tag (TMT) and parallel reaction monitoring (PRM) mass spectrometry

Eimeria tenella is an obligate intracellular parasite which causes great harm to the poultry breeding industry. Protein phosphorylation plays a vital role in host cell-E. tenella interactions. However, no comprehensive phosphoproteomic analyses of host cells at various phases of E. tenella infection have been published. In this study, quantitative phosphoproteomic analysis of chicken embryo DF-1 fibroblasts that were uninfected (UI) or infected with E. tenella for 6 h (PI6, the early invasion phase) or 36 h (PI36, the trophozoite development phase) was conducted. A total of 10,122 phosphopeptides matched to 3,398 host cell phosphoproteins were identified and 13,437 phosphorylation sites were identified. Of these, 491, 1,253, and 275 differentially expressed phosphorylated proteins were identified in the PI6/UI, PI36/UI, and PI36/PI6 comparisons, respectively. KEGG pathway enrichment analysis showed that E. tenella modulated host cell processes through phosphorylation, including focal adhesion, regulation of the actin cytoskeleton, and FoxO signaling to support its early invasion phase, and modulating adherens junctions and the ErbB signaling pathway to favor its trophozoite development. These results enrich the data on the interaction between E. tenella and host cells and facilitate a better understanding of the molecular mechanisms underlying host-parasite relationships.

A candidate virulence factor of Eimeria tenella (EtROP30) predicted by virulence enhancement of transgenic Toxoplasma gondii

Difficulties of in vitro culture and genetic manipulation of Eimeria tenella have hindered the screening of virulence factors in this parasite. In this study, the E. tenella rhoptry protein 30 (EtROP30) was expressed in Toxoplasma gondii (RH∆Ku80-EtROP30), and its effect on the proliferation and virulence of parasites was investigated. The results revealed that the expression of EtROP30 had no impact on the invasion and egress processes. However, the RH∆Ku80-EtROP30 strain formed larger plaques compared to the RH∆Ku80, indicating that the EtROP30 expression promotes T. gondii proliferation. Furthermore, the RH∆Ku80-EtROP30 strain exhibited greater pathogenicity, resulting in earlier mortality and shorter overall survival time compared to RH∆Ku80. These results imply that EtROP30 expression facilitates parasite intracellular proliferation and virulence in mice, suggesting that EtROP30 might be a candidate virulence factor of E. tenella.

The molecular biophysics of extracellular vimentin and its role in pathogen-host interactions

Vimentin, an intermediate filament protein typically located in the cytoplasm of mesenchymal cells, can also be secreted as an extracellular protein. The organization of extracellular vimentin strongly determines its functions in physiological and pathological conditions, making it a promising target for future therapeutic interventions. The extracellular form of vimentin has been found to play a role in the interaction between host cells and pathogens. In this review, we first discuss the molecular biophysics of extracellular vimentin, including its structure, secretion, and adhesion properties. We then provide a general overview of the role of extracellular vimentin in mediating pathogen-host interactions, with a focus on its interactions with viruses and bacteria. We also discuss the implications of these findings for the development of new therapeutic strategies for combating infectious diseases.

Toxoplasma gondii rhoptry protein (TgROP18) enhances the expression of pro-inflammatory factor in LPS/IFN-γ-induced murine BV2 microglia cells via NF-κB signal pathway

Toxoplasma gondii, an opportunistic pathogenic protozoan, exhibits a strong predilection to infect the brain, causing severe neurological diseases, such as toxoplasmic encephalitis (TE), in immunocompromised patients. Microglia, the resident immune cells in the brain, is reported to play important roles in regulating the neuroinflammation mediated by T. gondii infection. Here we demonstrated that the tachyzoites of T. gondii RH strain could significantly upregulate the expression levels of microglial M1 phenotype markers including IL-1β, IL-6, TNF-α, iNOS and IL18 in activated murine BV2 microglia cells, which were regulated by T. gondii rhoptry protein 18 (TgROP18). Moreover, we found that TgROP18 could enhance the expression of M1 phenotype markers in activated murine BV2 microglia cells via activating NF-κB signal pathway. Additionally, TgROP18 was suggested to interact with the host p65 in activated murine BV2 microglia cells and induce the phosphorylation of p65 at S536. In summary, the present study demonstrated that TgROP18 could promote the activated microglia to polarize to M1 phenotype and enhanced the expression of pro-inflammatory factors via activating NF-κB signal pathway, which could contribute to elucidating the mechanism underlying the neuroinflammation mediated by activated microglia in the brain with T. gondii infection.

Vimentin Inhibits Dengue Virus Type 2 Invasion of the Blood-Brain Barrier

Dengue virus (DENV) causes dengue fever, which is prevalent in the tropical and subtropical regions, and in recent years, has resulted in several major epidemics. Vimentin, a cytoskeletal component involved in DENV infection, is significantly reorganized during infection. However, the mechanism underlying the association between DENV infection and vimentin is still poorly understood. We generated vimentin-knockout (Vim-KO) human brain microvascular endothelial cells (HBMECs) and a Vim-KO SV129 suckling mouse model, combining the dynamic vimentin changes observed in vitro and differences in disease course in vivo, to clarify the role of vimentin in DENV-2 infection. We found that the phosphorylation and solubility of vimentin changed dynamically during DENV-2 infection of HBMECs, suggesting the regulation of vimentin by DENV-2 infection. The similar trends observed in the phosphorylation and solubility of vimentin showed that these characteristics are related. Compared with that in control cells, the DENV-2 viral load was significantly increased in Vim-KO HBMECs, and after DENV-2 infection, Vim-KO SV129 mice displayed more severe disease signs than wild-type SV129 mice, as well as higher viral loads in their serum and brain tissue, demonstrating that vimentin can inhibit DENV-2 infection. Moreover, Vim-KO SV129 mice had more disordered cerebral cortical nerve cells, confirming that Vim-KO mice were more susceptible to DENV-2 infection, which causes severe brain damage. The findings of our study help clarify the mechanism by which vimentin inhibits DENV-2 infection and provides guidance for antiviral treatment strategies for DENV infections.

Effects of host vimentin on Eimeria tenella sporozoite invasion

Background

Chicken coccidiosis is a parasitic disease caused by Eimeria of Apicomplexa, which has caused great economic loss to the poultry breeding industry. Host vimentin is a key protein in the process of infection of many pathogens. In an earlier phosphorylation proteomics study, we found that the phosphorylation level of host vimentin was significantly regulated after Eimeria tenella sporozoite infection. Therefore, we explored the role of host vimentin in the invasion of host cells by sporozoites.

Methods

Chicken vimentin protein was cloned and expressed. We used qPCR, western blotting, and indirect immunofluorescence to detect levels of mRNA transcription, translation, and phosphorylation, and changes in the distribution of vimentin after E. tenella sporozoite infection. The sporozoite invasion rate in DF-1 cells treated with vimentin polyclonal antibody or with small interfering RNA (siRNA), which downregulated vimentin expression, was assessed by an in vitro invasion test.

Results

The results showed that vimentin transcription and translation levels increased continually at 6–72 h after E. tenella sporozoite infection, and the total phosphorylation levels of vimentin also changed. About 24 h after sporozoite infection, vimentin accumulated around sporozoites in DF-1 cells. Treating DF-1 cells with vimentin polyclonal antibody or downregulating vimentin expression by siRNA significantly improved the invasion efficiency of sporozoites.

Conclusion

In this study, we showed that vimentin played an inhibitory role during the invasion of sporozoites. These data provided a foundation for clarifying the relationship between Eimeria and the host.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05107-4.

Toxoplasma gondii SAG1 targeting host cell S100A6 for parasite invasion and host immunity

Toxoplasma gondii surface antigen 1 (TgSAG1) is a surface protein of tachyzoites, which plays a crucial role in toxoplasma gondii infection and host cell immune regulation. However, how TgSAG1 regulates these processes remains elucidated. We utilized the biotin ligase -TurboID fusion with TgSAG1 to identify the host proteins interacting with TgSAG1, and identified that S100A6 was co-localized with TgSAG1 when T. gondii attached to the host cell. S100A6, either knocking down or blocking its functional epitopes resulted in inhibited parasites invasion. Meanwhile, S100A6 overexpression in host cells promoted T. gondii infection. We further verified that TgSAG1 could inhibit the interaction of host cell vimentin with S100A6 for cytoskeleton organization during T. gondii invasion. As an immunogen, TgSAG1 could promote the secretion of tumor necrosis factor alpha (TNF-α) through S100A6-Vimentin/PKCθ-NF-κB signaling pathway. In summary, our findings revealed a mechanism for how TgSAG1 functioned in parasitic invasion and host immune regulation.

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TgSAG1 interacts with host protein S100A6 then regulates T. gondii infection

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TgSAG1 could regulate binding vimentin with S100A6 during T. gondii infection

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TgSAG1 regulate TNFα secretion through S100A6-vimentin/PKCθ-NF-κB signaling pathway

Toxoplasma gondii Type-I ROP18 Targeting Human E3 Ligase TRIM21 for Immune Escape

Toxoplasma gondii is an intracellular pathogen that exerts its virulence through inhibiting host’s innate immune responses, which is mainly related to the type II interferon (IFN-γ) response. IFN-γ inducible tripartite motif 21 (TRIM21), an E3 ligase, plays an important role in anti-infection responses against the intracellular pathogens including bacteria, virus, and parasite. We found that T. gondii virulence factor ROP18 of the type I RH strain (TgROP18_I) interacted with human TRIM21, and promoted the latter’s phosphorylation, which subsequently accelerated TRIM21 degradation through lysosomal pathway. Furthermore, TRIM21 protein level was found to be upregulated during RH and CEP strains of T. gondii infection. TRIM21 knocking down reduced the ubiquitin labeling on the parasitophorous vacuole membrane (PVM) [which led to parasitophorous vacuole (PV) acidification and death of CEP tachyzoites], and relieved the inhibition of CEP proliferation induced by IFN-γ in human foreskin fibroblast (HFF) cells which was consistent with the result of TRIM21 overexpression. On the other hand, TRIM21 overexpression enhanced the inhibition of CEP proliferation, and inhibited the binding of IκB-α with p65 to activate the IFN-γ-inducible NF-κB pathway, which might be resulted by TRIM21-IκB-α interaction. In brief, our research identified that in human cells, IFN-γ-inducible TRIM21 functioned in the innate immune responses against type III T. gondii infection; however, TgROP18_I promoted TRIM21 phosphorylation, leading to TRIM21 degradation for immune escape in type I strain infection.

iTRAQ-Based Phosphoproteomic Analysis of Toxoplasma gondii Tachyzoites Provides Insight Into the Role of Phosphorylation for its Invasion and Egress

The invasion and egress are two key steps in lytic cycle vital to the propagation of Toxoplasma gondii infection, and phosphorylation is believed to play important roles in these processes. However, the phosphoproteome of T. gondii at these two stages has not been characterized. In this study, we profiled the phosphoproteome of tachyzoites at the stages of “just invading” (JI) and “prior to egress” (PE) based on iTRAQ quantitative analysis, in which a total of 46 phosphopeptides, 42 phosphorylation sites, and 38 phosphoproteins were detected. In the comparison of PE vs. JI, 10 phosphoproteins were detected with their phosphorylation level significantly changed, and four of them were demonstrated to be significantly down-regulated at the transcriptional level. Bioinformatic analysis of these identified phosphoproteins suggested that phosphorylation-mediated modulation of protein function was employed to regulate the pathway of toxoplasmosis and metabolism and cellular processes correlated with tachyzoite’s binding, location, and metabolism, and thus play vital roles in the parasite lytic cycle. Moreover, cytoskeletal network (CN)-associated Inner Membrane Complex (IMC1, IMC4, IMC6 and IMC12), Intravascular Network (IVN)-related GRAs (GRA2, GRA3, GRA7 and GRA12), and Parasitophorous Vacuole Membrane (PVM)-localized ROP5 were shown to be enriched at the central nodes in the protein interaction network generated by bioinformatic analysis, in which the phosphorylation level of IMC4, GRA2, GRA3, and GRA12 were found to be significantly regulated. This study revealed the main cellular processes and key phosphoproteins crucial for the invasion and egress of T. gondii, which will provide new insights into the developmental biology of T. gondii in vitro and contribute to the understanding of pathogen-host interaction from the parasite perspective.

TgROP18 targets IL20RB for host-defense-related-STAT3 activation during Toxoplasma gondii infection

Background

Toxoplasma gondii is an opportunistic protozoan infecting almost one-third of the world’s population. Toxoplasma gondii rhoptry protein 18 (TgROP18) is a key virulence factor determining the parasite’s acute virulence and is secreted into host cells during infection. We previously identified the interaction of TgROP18 and host cell immune-related receptor protein IL20RB, and observed the activation of STAT3 in human keratinocytes (HaCaT) cells infected by the rop16 knockout RH strain, though TgROP16 is regarded as being responsible for host STAT3 activation during T. gondii invasion. Therefore, we hypothesize TgROP18 can activate host STAT3 through binding to IL20RB.

Methods

CRISPR-CAS9 technology was used to generate the ROP16 and ROP18 double knockout RH strain, RH-∆rop16∆rop18. SDS-PAGE and western blot were used to detect STAT3 activation in different HaCaT cells with high endogenous IL20RB expression treated with T. gondii tachyzoites infection, recombinant ROP18, or IL-20. FRET and co-immunoprecipitation (Co-IP) was used to detect the protein-protein interaction.

Results

We observed that TgROP18 was involved in a synergic activation of the host JAK/STAT3 pathway together with TgROP16 in human HaCaT cells infected with T. gondii or treated with recombinant TgROP18 protein, stimulating host proinflammatory immune responses such as expression of TNF-α. The effect of recombinant ROP18 on STAT3 phosphorylation was presented in a dose-dependent manner. Additionally, TgROP18 was identified to target IL20RB on its extracellular domain. When we treated different cell lines with the recombinant ROP18, STAT3 phosphorylation could only be observed in the cells with endogenous IL20RB expression, such as HaCaT cells.

Conclusions

These findings indicate that TgROP18-IL20RB interaction upon T. gondii invasion was involved in STAT3 activation, which is associated with host cell defense.

Vimentin as a Multifaceted Player and Potential Therapeutic Target in Viral Infections

Vimentin is an intermediate filament protein that plays key roles in integration of cytoskeletal functions, and therefore in basic cellular processes such as cell division and migration. Consequently, vimentin has complex implications in pathophysiology. Vimentin is required for a proper immune response, but it can also act as an autoantigen in autoimmune diseases or as a damage signal. Although vimentin is a predominantly cytoplasmic protein, it can also appear at extracellular locations, either in a secreted form or at the surface of numerous cell types, often in relation to cell activation, inflammation, injury or senescence. Cell surface targeting of vimentin appears to associate with the occurrence of certain posttranslational modifications, such as phosphorylation and/or oxidative damage. At the cell surface, vimentin can act as a receptor for bacterial and viral pathogens. Indeed, vimentin has been shown to play important roles in virus attachment and entry of severe acute respiratory syndrome-related coronavirus (SARS-CoV), dengue and encephalitis viruses, among others. Moreover, the presence of vimentin in specific virus-targeted cells and its induction by proinflammatory cytokines and tissue damage contribute to its implication in viral infection. Here, we recapitulate some of the pathophysiological implications of vimentin, including the involvement of cell surface vimentin in interaction with pathogens, with a special focus on its role as a cellular receptor or co-receptor for viruses. In addition, we provide a perspective on approaches to target vimentin, including antibodies or chemical agents that could modulate these interactions to potentially interfere with viral pathogenesis, which could be useful when multi-target antiviral strategies are needed.

Toxoplasma gondii ROP18 inhibits human glioblastoma cell apoptosis through a mitochondrial pathway by targeting host cell P2X1

Background

Apoptosis plays a critical role in the embryonic development, homeostasis of immune system and host defense against intracellular microbial pathogens. Infection by the obligate intracellular pathogen Toxoplasma gondii can both inhibit and induce host cell apoptosis; however, the parasitic factors involved remain unclear. The T. gondii virulence factor ROP18 (TgROP18) has been reported to regulate host cell apoptosis; nevertheless, results for this regulation have been rarely reported or have provided contradictory findings. Human purinergic receptor 1 (P2X1) is an ATP-gated ion channel that responds to ATP stimulation and functions in cell apoptosis mediation. The precise roles of TgROP18 in T. gondii pathogenesis, and the relationship between TgROP18 and host P2X1 in host cell apoptosis are yet to be revealed.

Methods

Apoptosis rates were determined by flow cytometry (FCM) and TUNEL assay. The interaction between TgROP18 and the host P2X1 was measured by fluorescence resonance energy transfer (FRET) and co-immunoprecipitation (co-IP) assay. Calcium influx and mitochondrial membrane depolarization were determined by FCM after JC-1 staining. The translocation of cytochrome C (Cyt C), Bax and Bcl2 proteins, expression of the apoptotic proteins PARP and caspase activation were detected by western blotting.

Results

The apoptosis rates of glial or immune cells (human SF268, mouse RAW264.7 and human THP-1 cells) infected by any T. gondii strain (RH-type I, ME49-type II and VEG-type III) were significantly inhibited compared with their uninfected controls. TgROP18 inhibited ATP-induced apoptosis of SF268 with P2X1 expression, but had no effect on RAW264.7 or THP-1 cells without detectable P2X1 expression. It was further identified that TgROP18 interacted with P2X1, and overexpression of ROP18 in COS7 cells significantly inhibited cell apoptosis mediated by P2X1. Moreover, TgROP18 also inhibited P2X1-mediated Ca²⁺ influx, translocation of cytochrome C from the mitochondria to the cytosol, and ATP-triggered caspase activation.

Conclusions

Toxoplasma gondii infection inhibits ATP-induced host cell apoptosis, regardless of strain virulence and host cell lines. TgROP18 targets the purinergic receptor P2X1 of the SF268 human neural cells and inhibits ATP-induced apoptosis through the mitochondrial pathway, suggesting a sensor role for the host proapoptotic protein P2X1 in this process.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3529-1) contains supplementary material, which is available to authorized users.

iTRAQ-based phosphoproteomic analysis reveals host cell's specific responses to Toxoplasma gondii at the phases of invasion and prior to egress

Protein phosphorylation plays a key role in host cell-T. gondii interaction. However, the phosphoproteome data of host cell at various phases of T. gondii infection has not been thoroughly described. In this study, we assessed the host phosphoproteome data with isobaric tags for relative and absolute quantification (iTRAQ) method during the phases of T. gondii invasion (30 min post infection, PI) and prior to egress (28 h PI). Our iTRAQ analysis revealed a total of 665 phosphoproteins, among which the significantly regulated phosphoproteins in different between-group comparisons were further analyzed. Functional analysis of these significantly regulated phosphoproteins suggested that T. gondii modulated host cell processes through phosphorylation including cell cycle regulation, inducing apoptosis, blocking the synthesis of some inflammatory factors, mediating metabolism to support its proliferation at the infection phase prior to egress, and utilizing membrane and energy from host cell, reorganizing cytoskeleton to favor its invasion and PV formation at the phase of invasion. The phosphorylation level of Smad2, CTNNA1, and HSPB1 identified with western blot revealed a consistent trend of change with iTRAQ result. These newly identified and significantly regulated phosphoproteins from our phosphoproteome data may provide new clues to unravel the host cell's complex reaction against T. gondii infection and the interaction between the host cell and T. gondii.

[Effect of vimentin on activation of NLRP3 inflammasome in the brain of mice with EV71 infection]

OBJECTIVE

To explore whether vimentin (VIM) mediates the activation of inflammasome in mice with EV71 infection in the central nervous system.

METHODS

Forty VIM knockout mice (VIM^-/-, 3 to 5 days old) were randomly divided into control group and infection group. The infection group was intraperitoneally injected with EV71 (10⁸ TCID₅₀), while the control group was injected with PBS (10 µL); another 40 wild-type mice (WT, 3 to 5 days old) were grouped in the same manner. The general conditions of mice were observed each day. Western blotting, ELISA, and RT-PCR were used to measure the levels of IL-1β and casepase-1 in the brain or cerebrospinal fluid. The pathological changes in the cerebella and brain were observed using immunohistochemistry.

RESULTS

Compared with the control group, the VIM^-/- mice infected with EV71 showed no significant changes in NLRP3, IL-1β or caspase-1 expression. The WT mice infected with EV71 showed obviously increased NLRP3, IL-1β, and caspase-1 expressions in the central nervous system. The neurons of infected VIM^-/- mice exhibited milder cell damage than the those in WT mice.

CONCLUSION

VIM mediates the activation of inflammasome and promotes brain inflammation and neuronal damage in mice with EV71 infection in the central nervous system.

Genome-Wide Bimolecular Fluorescence Complementation-Based Proteomic Analysis of Toxoplasma gondii ROP18's Human Interactome Shows Its Key Role in Regulation of Cell Immunity and Apoptosis

Toxoplasma gondii rhoptry protein ROP18 (TgROP18) is a key virulence factor secreted into the host cell during invasion, where it modulates the host cell response by interacting with its host targets. However, only a few TgROP18 targets have been identified. In this study, we applied a high-throughput protein-protein interaction (PPI) screening in human cells using bimolecular fluorescence complementation (BiFC) to identify the targets of Type I strain ROP18 (ROP18_I) and Type II strain ROP18 (ROP18_II). From a pool of more than 18,000 human proteins, 492 and 141 proteins were identified as the targets of ROP18_I and ROP18_II, respectively. Gene ontology, search tool for the retrieval of interacting genes/proteins PPI network, and Ingenuity pathway analyses revealed that the majority of these proteins were associated with immune response and apoptosis. This indicates a key role of TgROP18 in manipulating host's immunity and cell apoptosis, which might contribute to the immune escape and successful parasitism of the parasite. Among the proteins identified, the immunity-related proteins N-myc and STAT interactor, IL20RB, IL21, ubiquitin C, and vimentin and the apoptosis-related protein P2RX1 were further verified as ROP18_I targets by sensitized emission-fluorescence resonance energy transfer (SE-FRET) and co-immunoprecipitation. Our study substantially contributes to the current limited knowledge on human targets of TgROP18 and provides a novel tool to investigate the function of parasite effectors in human cells.