Quantitative study of proteomic alterations in a Zebrafish (danio rerio) cell line infected with the Singapore Grouper Iridovirus (SGIV)

The interactome of Singapore grouper iridovirus protein ICP18 as revealed by proximity-dependent BioID approach

Singapore grouper iridovirus (SGIV) is a large double-stranded DNA virus that is a major threat to grouper aquaculture. The pathogenesis of SGIV is not well understood so far. Previous studies have revealed that ICP18, an immediate early protein encoded by SGIV ORF086R gene, promotes viral replication by regulating cell proliferation and virus assembly. In the present study, the potential functions of ICP18 were further explored by probing into its interactors using a proximity-dependent BioID method. Since our in-house grouper embryonic cells (a natural host cell of SGIV) could not be efficiently transfected with the plasmid DNA, and the grouper genome data for mass spectrometry-based protein identification is not currently available, we chosen a non-permissive cell (HEK293 T) as a substitute for this study. A total of 112 cellular proteins that potentially bind to ICP18 were identified by mass spectrometry analysis. Homology analysis showed that among these identified proteins, 110 candidate ICP18-interactors had homologous proteins in zebrafish (a host of SGIV), and shared high sequence identity. Further analysis revealed that the identified ICP18-interacting proteins modulate various cellular processes such as cell cycle and cell adhesion. In addition, the interaction between ICP18 and its candidate interactor, i.e., cyclin-dependent kinase1 (CDK1), was confirmed using Co-immunoprecipitation (Co-IP) and Pull-down assays. Collectively, our present data provides additional insight into the biological functions of ICP18 during viral infection, which could help in further unraveling the pathogenesis of SGIV.

Proteomic Profiling of Zebrafish Challenged by Spring Viremia of Carp Virus Provides Insight into Skin Antiviral Response

Spring viremia of carp virus (SVCV) causes the skin hemorrhagic disease in cyprinid species, but its molecular mechanism of skin immune response remains unclear at the protein level. In the present study, the differential proteomics of the zebrafish (Danio rerio) skin in response to SVCV infection were examined by isobaric tags for relative and absolute quantitation and quantitative polymerase chain reaction (qPCR) assays. A total of 3999 proteins were identified, of which 320 and 181 proteins were differentially expressed at 24 and 96 h postinfection, respectively. The expression levels of 16 selected immune-related differentially expressed proteins (DEPs) were confirmed by qPCR analysis. Furthermore, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that DEPs were significantly associated with complement, inflammation, and antiviral response. The protein-protein interaction network of cytoskeleton-associated proteins, ATPase-related proteins, and parvalbumins from DEPs was shown to be involved in skin immune response. This is first report on the skin proteome profiling of zebrafish against SVCV infection, which will contribute to understand the molecular mechanism of local mucosal immunity in fish.

iTRAQ analysis of liver immune-related proteins from darkbarbel catfish (Pelteobagrus vachelli) infected with Edwardsiella ictaluri

Edwardsiella ictaluri causes enteric septicemia of catfish (ESC), a major disease occurring in these siluriform fish. As the liver is an important organ for defending against bacterial pathogens in fish, this study aimed to determine the liver immune response at the protein level. The differential proteomes of the darkbarbel catfish liver in response to E. ictaluri infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using a 1.2-fold change in expression as a physiologically significant benchmark, a total of 819 differentially expressed proteins were reliably quantified using iTRAQ analysis, including 6 up-regulated proteins and 813 down-regulated proteins. GO enrichment analysis indicated that the "complement activation, alternative pathway" and "complement activation, classical pathway" were significantly enriched. KEGG enrichment analysis indicated the "antigen processing and presentation" and "bacterial secretion system" were significantly enriched. We selected the 6 up-regulated proteins and 10 immune-related down-regulated proteins for validation using real-time PCR. The 10 immune-related proteins included complement component C1r, C3, C5, C7, and C9 and plasma protease C1 inhibitor (C1-INH), signal recognition particle 54 kDa protein (SRP54), SRP receptor, proteasome activator complex subunit 1 (PSME1) and major histocompatibility complex class I (MHC class I) were selected from the GO clusters and KEGG pathways. The variations in mRNA expression for these genes were similar to the results of iTRAQ. This is the first report detailing the proteome response in the darkbarbel catfish liver during E. ictaluri infection and markedly contributes to our understanding of the defense mechanisms in the livers of darkbarbel catfish.

Plasma proteomic analysis of zebrafish following spring viremia of carp virus infection

To better understand spring viremia of carp virus (SVCV) pathogenesis in zebrafish proteomic analysis was used to examine the plasma protein profile in SVCV-infected zebrafish. A total of 3062 proteins were identified. Of those 137, 63 and 31 proteins were enriched in blood samples harvested at 1, 2 and 5 days post SVCV infection, respectively. These altered host proteins were classified based on their biological function: 23 proteins under the response to stimulus term were identified. Interestingly, at the top of the up-regulated proteins during SVCV infection were the proteins of the vitellogenin family (Vtg) and the grass carp reovirus-induced gene (Gig) proteins. Real-time RT-PCR evaluation of samples from internal organs verified that SVCV infection induced vtg and gig2 gene expression already at day 1 post-infection. Western blot analysis revealed the presence of Vtg protein only in blood of SVCV-infected fish. This is the first proteomic study to reveal the involvement of Vtg proteins in adult fish response to viral challenge. It also highlights the role of Gig proteins as important factors in antiviral response in fish. This work provides valuable relevant insight into virus-host interaction and the identification of molecular markers of fish response to virus.

Proteome profiling reveals immune responses in Japanese flounder (Paralichthys olivaceus) infected with Edwardsiella tarda by iTRAQ analysis

The liver is an important organ for bacterial pathogen attack in fish. The differential proteomic response of the Japanese flounder liver to Edwardsiella tarda infection was examined using isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 3290 proteins were identified and classified into categories related to biological process (51.4%), molecular function (63.6%), and cellular component (57.7%). KEGG enrichment analysis indicated the complement and coagulation cascade pathways and the mineral absorption pathway were significantly enriched. Among the differentially expressed proteins, those involved in mediating complement cascade (e.g. complement component C7, C8, C9, complement factor H, complement factor Bf/C2) and mineral absorption (e.g. ferritin, STEAP-4) were most significantly upregulated during infection. Subsequently, five significantly upregulated (C4, C8beta, ferritin middle subunit, PRDX4-like and KRT18) and one significantly downregulated (transferrin) candidate immune proteins were validated by multiple reaction monitoring (MRM) assays. Furthermore, changes in expression of 15 proteins in the complement cascade and mineral absorption pathways were validated at the transcriptional level using quantitative real-time PCR (qPCR). The transcriptional levels of four transcription factors (p21Ras, Rab-31-like, NF-κB, STAT3) were also investigated by qPCR following infection with E. tarda. This study contributes to understanding the defense mechanisms of the liver in fish.