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Mapping of ISG15 interaction partners by Virotrap coupled to mass spectrometry

ABSTRACT: During infection, interferon production leads to upregulation of the interferon-stimulated gene 15 (ISG15) which encodes the ubiquitin-like protein ISG15. ISG15 has a profound role in restricting intracellular infection by viral and bacterial pathogens. It can exert its function either as a free intracellular or extracellular molecule, or as an ubiquitin-like conjugate to substrate proteins in a process called ISGylation. Here, we used a viral-like particle trapping (Virotrap) technology and GST pull down, both coupled to mass spectrometry, to screen for intracellular ISG15-binding proteins. As strongest hit, we identified RNF213, a very large interferon-induced protein targeted to lipid droplets and a genetic risk factor for Moyamoya disease, a rare cerebrovascular disorder. We verified binding of ISG15 and RNF213 with biochemical methods and imaging and found that interferon signaling induces ISGylation and oligomerization of RNF213 on the surface of lipid droplets, acting as a binding platform for ISGylated proteins. Moreover, we showed that knockdown of RNF213 promotes in vitro infection by Listeria monocytogenes, respiratory syncytial virus (RSV) and Coxsackie virus (CV) B3, suggesting a broad antimicrobial activity of RNF213. In contrast, overexpression of RNF213 restricted Listeria infection and was associated with a striking co-localization of RNF213 with intracellular bacteria. Infection experiments in RNF213 deficient mice corroborated these results in vivo, revealing a so far unknown function of RNF213 in the host defense against infection. Together, we report that RNF213 assembles into a binding platform for ISGylated proteins on the surface of lipid droplets, acting as a first step of an antimicrobial cellular pathway that processes ISGylated proteins. Our findings provide novel molecular insights into the ISGylation pathway and point towards an important role of the immune response to infection in the etiology of Moyamoya disease.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Fabien Thery

LAB HEAD: Francis Impens

PROVIDER: PXD018345 | Pride | 2021-08-16

REPOSITORIES: Pride

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Project description:Filamentous hemagglutinin (FHA), Bordetella pertussis' key adhesin, is both present at the cell surface and released in the extracellular milieu. To comprehend the role free FHA plays in the pathogenic process, we analyzed the global transcriptional changes in human peripheral blood mononuclear cells (PBMC) after exposure to that purified virulence factor. This analysis was undertaken with four different FHA preparations (FHA-1, FHA-2, FHA-3, and FHA-4), purified from four different B. pertussis strains. Cultures comprising 3x106 PBMC were stimulated for 0.5, 2, 4, and 6 hours with 5 ug/ml of each purified B. pertussis FHA. Control PBMC cultures were simultaneously treated with similar volumes of elution buffers (Mock-1 and Mock-2), and sampled at the same time points. The array experiment was composed of 27 samples. Most of the transcripts known to be part of the "common host-transcriptional response" that mediates inflammation were among the 1,235 array elements (representing 683 known unique genes) showing a greater than 3-fold change in transcript abundance between FHA-treated and untreated cells. We also identified an FHA-specific signature not observed in cells stimulated with B. pertussis LPS or heat-killed B. pertussis. This response, mounted by 13 genes, largely (69%, 9/13 genes) interferon (IFN)-regulated genes. Further analysis revealed that 18.3% (125 out of 683) of the FHA-responsive genes were in fact regulated by IFN. These included several major players of the antiviral IFN type I response, as well as three key components of the ISGylation pathway. Induction of the ubiquitin-like protein ISG15 and its specific protease USP18 was confirmed at the mRNA level by relative real-time polymerase chain reaction (RT-PCR). Western-blot analysis demonstrated the presence of both free ISG15 and several ISGylated conjugates in FHA-stimulated PBMC cell lysate. Intracellular FACS analysis provided further evidence that monocytes and a natural-killer (NK)-enriched cell population are the primary producers of ISG15 after FHA stimulation. Our results revealed new activities of free B. pertussis FHA: activation of the host IFN and ISGylation pathways. The consequences of such activation are yet to be resolved, but we hypothesize that FHA utilizes the ISGylation pathway or USP18 to regulate the IFN response, which in turn sensitizes the host to the infection and induces cell death. Groups of assays that are related as part of a time series. Infection: treatment with purified B. pertussis filamentous hemagglutinin (FHA) at 0.005 mg/mL Time: Samples were collected after various treatment time (hours) Keywords: time_series_design Computed

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Mapping of ISG15 interaction partners by Virotrap coupled to mass spectrometry

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