Penaeus monodon thioredoxin restores the DNA binding activity of oxidized white spot syndrome virus IE1

Proteomics analysis reveals a critical role for the WSSV immediate-early protein IE1 in modulating the host prophenoloxidase system

White spot syndrome virus (WSSV) is a large enveloped double-stranded DNA virus that is a major impediment for shrimp aquaculture worldwide. So far, the mechanisms of WSSV-host interactions are ill-defined. Recent studies have revealed that IE1, an immediate-early protein encoded by WSSV, is a multifunctional modulator implicated in virus-host interactions. In this study, the biological functions of IE1 were further explored by identifying its interacting proteins using GST-pull down and mass spectrometry analysis. A total of 361 host proteins that potentially bind to IE1 were identified. Bioinformatics analysis revealed that the identified IE1-interacting proteins were key molecules involved in various signaling pathways such as prophenoloxidase (proPO) system, PI3K-AKT, MAPK, Focal adhesion, and cell cycle. Among these, the regulatory role of IE1 in the shrimp proPO system was further studied. The Co-immunoprecipitation (Co-IP) results confirmed that IE1 interacted with the Ig-like domain of Penaeus vannamei proPO or proPO-like proteins (proPO1/2 and hemocyanin). In addition, we found that in vivo RNAi mediated knockdown of IE1 reduced the viral genes expression and viral loads, as well as caused an increase in the PO activity of hemocytes during infection, whereas recombinant IE1 protein could inhibit the PO activity in a dose-dependent manner. Finally, our result demonstrated that WSSV could suppress the PO activity of hemocytes at the early infection stage. Collectively, our current data indicate that IE1 is a novel viral regulator that negatively modulates the shrimp proPO system, which provide additional insights into the biological functions of IE1 during WSSV infection.

Infectious hypodermal and hematopoietic necrosis virus-like particle (IHHNV-VLP) induces peroxiredoxin expression and activity in Fenneropenaeus merguiensis

Virus like particles (VLPs) are non-infectious nanoparticles containing repetitive, high density viral epitopes on the surface and can prevent viral infections in aquatic animals. Here, we evaluated the immuno-stimulation effect of infectious hypodermal and hematopoietic necrosis virus like particle (IHHNV-VLP) using a next generation sequencing in Fenneropenaeus merguiensis to identify the important immune-related genes that may prevent viral infection. The in situ target of IHHNV was predominantly found in gill tissue following IHHNV-VLP administration in juvenile shrimp. Comparative transcriptome analysis in the injected gills showed that there were 326 unigenes expressed differently than the mock-injected samples. One of the most differential genes between the two animal groups was the antioxidative gene, peroxiredoxin (FmPrx), that was up-regulated after 6 h post-VLP injection. Phylogenetic tree analysis showed that this gene could be found among many shrimp species and was closely clustered among Prx families. The expression of FmPrx was also detected in all tissues examined, thus suggesting the multi-functional roles of this gene in many tissues. Administration of IHHNV-VLP in vivo led to a significant increase in peroxidase activity in gill tissue-approximately two-fold versus control animals; the WSSV copy number was significantly reduced. These data suggest that IHHNV-VLP exerts an immune-stimulating effect by enhancing the level of immune-related genes including FmPrx and its corresponding peroxidase activity, which are a well-known part of the shrimp innate immune system.

Litopenaeus vannamei Sma and Mad related protein 5 gene is involved in stress response and white spot syndrome virus infection

Cell survival is based on the stability of intracellular state. It was well known that biochemical reactions in cells require specific intracellular environments, such as pH and calcium concentration. While the mechanism of stabilizing the intracellular environment is complex and far from clear. In this study, a Sma and Mad related protein 5 gene (LvSmad5) of Litopenaeus vannamei was cloned. LvSmad5 was located to both cytoplasm and nucleus. And subcellular localization of LvSmad5 was responsed to the changing of cells internal and external environment. Besides, it was found that subcellular localization of LvSmad5 was also regulated by unfolded protein response. Moreover, it was proved that nucleic localization of LvSmad5 could significantly increase the white spot syndrome virus (WSSV) infection in shrimp, and knockdown expression of LvSmad5 decreased the cumulative mortality of WSSV infection shrimp. Further investigation revealed that cytoplasm LvSmad5 could interplay with shrimp hexokinase 1, and contribute to glycolysis. These results indicated that LvSmad5 played a role in L. vannamei environmental stress response, and was used by WSSV for its replication.

Shrimp SIRT1 activates of the WSSV IE1 promoter independently of the NF-κB binding site

Since the mechanisms by which cellular factors modulate replication of the shrimp viral pathogen white spot syndrome virus (WSSV) are still largely unknown, here we consider the sirtuins, a family of NAD⁺-dependent protein deacetylases that are known to function as regulatory factors that activate or suppress viral transcription and replication in mammals. In particular, we focus on SIRT1 by isolating and characterizing LvSIRT1 from white shrimp (Litopenaeus vannamei) and investigating its involvement in WSSV infection. DsRNA-mediated gene silencing led to the expression of WSSV genes and the replication of genomic DNAs being significantly decreased in LvSIRT1-silenced shrimp. The deacetylase activity of LvSIRT1 was significantly induced at the early stage (2 hpi) and the genome replication stage (12 hpi) of WSSV replication, but decreased at the late stage of WSSV replication (24 hpi). Treatment with the SIRT1 activator resveratrol further suggested that LvSIRT1 activation increased the expression of several WSSV genes (IE1, VP28 and ICP11). Lastly, we used transfection and dual luciferase assays in Sf9 insect cells to show that while the overexpression of LvSIRT1 facilitates the promoter activity of WSSV IE1, this enhancement of WSSV IE1 expression is achieved by a transactivation pathway that is NF-κB-independent.

A shrimp glycosylase protein, PmENGase, interacts with WSSV envelope protein VP41B and is involved in WSSV pathogenesis

Viral glycoproteins are expressed by many viruses, and during infection they usually play very important roles, such as receptor attachment or membrane fusion. The mature virion of the white spot syndrome virus (WSSV) is unusual in that it contains no glycosylated proteins, and there are currently no reports of any glycosylation mechanisms in the pathogenesis of this virus. In this study, we cloned a glycosylase, mannosyl-glycoprotein endo-β-N-acetylglucosaminidase (ENGase, EC 3.2.1.96), from Penaeus monodon and found that it was significantly up-regulated in WSSV-infected shrimp. A yeast two-hybrid assay showed that PmENGase interacted with both structural and non-structural proteins, and GST-pull down and co-immunoprecipitation (Co-IP) assays confirmed its interaction with the envelope protein VP41B. In the WSSV challenge tests, the cumulative mortality and viral copy number were significantly decreased in the PmEngase-silenced shrimp, from which we conclude that shrimp glycosylase interacts with WSSV in a way that benefits the virus. Lastly, we speculate that the deglycosylation activity of PmENGase might account for the absence of glycosylated proteins in the WSSV virion.

White Spot Syndrome Virus Establishes a Novel IE1/JNK/c-Jun Positive Feedback Loop to Drive Replication

Viruses need to hijack and manipulate host proteins to guarantee their replication. Herein, we uncovered that the DNA virus white spot syndrome virus (WSSV) established a novel positive feedback loop by hijacking the host JNK pathway via its immediate-early 1 (IE1) protein to drive replication. Specifically, the WSSV IE1 bound to host JNK, and enhanced JNK autoactivation by autophosphorylation, and in turn, elevated JNK kinase activity to its substrate c-Jun and induced IE1, which resulted in a viral gene-mediated positive feedback loop. Moreover, the activation of this loop is able to induce wsv056, wsv249, and wsv403, in addition to IE1 itself. Disruption of this loop during WSSV infection by knockdown of JNK, c-Jun or IE1 led to an increased survival rate and lower viral burdens in shrimp. Taken together, this loop may provide a potential target for the development of specific antiviral strategies or agents against WSSV infection.

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Lvc-Jun promotes WSSV IE1 induction via interacting with the promoter of IE1 gene

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The interaction of IE1-LvJNK enhances the autophosphorylation of LvJNK

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IE1 hijacks the JNK/c-Jun cascade to create a feedback loop to drive replication

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wsv056, wsv249, and wsv403 are also benefit from this positive feedback loop

Cloning and functional characterization of thioredoxin gene from kuruma shrimp Marsupenaeus japonicus

As an important disulfide reductase of the intracellular antioxidant system, Thioredoxin (Trx) plays an important role in maintaining oxidative stress balance and protecting cells from oxidative damage. In recent years, there is increasing evidence that Trx is a key molecule in the pathogenesis of various diseases and a potential therapeutic target for major diseases including lung, colon, cervical, gastric and pancreatic cancer. However, few knowledge is known about the function of Trx in virus infection. In this study, we reported the cloning and functional investigation of a Trx homologue gene, named MjTrx, in shrimp Marsupenaeus japonicus suffered white spot syndrome virus (WSSV) infection. MjTrx is a 105-amino acid polypeptide with a conservative Cys-Gly-Pro-Cys motif in the catalytic center. Phylogenetic trees analysis showed that MjTrx has a higher relationship with Trx from other invertebrate and clustered with Trx1 from arthropod. MjTrx transcripts is abundant in the gill and intestine tissues and can be detected in the hemocytes, heart, stomach, and hepatopancreas tissues. The transcription levels of MjTrx in hemocytes, gills and intestine tissues of shrimp were significantly up-regulated after white spot syndrome virus infection. MjTrx was recombinant expressed in vitro and exhibited obvious disulfide reductase activity. In addition, overexpression MjTrx in shrimp resulted in the increase of hydrogen peroxide (H₂O₂) concentration in vivo. All these results strongly suggested that MjTrx functioned in redox homeostasis regulating and played an important role in shrimp antiviral immunity.

Effects of environmental stress on shrimp innate immunity and white spot syndrome virus infection

The shrimp aquaculture industry is plagued by disease. Due to the lack of deep understanding of the relationship between innate immune mechanism and environmental adaptation mechanism, it is difficult to prevent and control the diseases of shrimp. The shrimp innate immune system has received much recent attention, and the functions of the humoral immune response and the cellular immune response have been preliminarily characterized. The role of environmental stress in shrimp disease has also been investigated recently, attempting to clarify the interactions among the innate immune response, the environmental stress response, and disease. Both the innate immune response and the environmental stress response have a complex relationship with shrimp diseases. Although these systems are important safeguards, allowing shrimp to adapt to adverse environments and resist infection, some pathogens, such as white spot syndrome virus, hijack these host systems. As shrimp lack an adaptive immune system, immunization therapy cannot be used to prevent and control shrimp disease. However, shrimp diseases can be controlled using ecological techniques. These techniques, which are based on the innate immune response and the environmental stress response, significantly reduce the impact of shrimp diseases. The object of this review is to summarize the recent research on shrimp environmental adaptation mechanisms, innate immune response mechanisms, and the relationship between these systems. We also suggest some directions for future research.

Characterization and function of a β-catenin homolog from Litopenaeus vannamei in WSSV infection

As a conserved signaling pathway, Wnt/β-catenin signaling pathway participates in many physiological activities, including cell differentiation, apoptosis and so on. β-catenin is the key molecule of Wnt/β-catenin signaling pathway and plays a pivotal role. In this article, a β-catenin homolog from Litopenaeus vannamei (designed as Lv-β-catenin) was cloned and its role in WSSV infection was investigated. Sequence analysis suggested that Lv-β-catenin had characters of β-catenin family. Semi-quantitative RT-PCR showed that Lv-β-catenin transcripted in all detected tissues. In the subsequent WSSV infection experiments, it was found that the transcription levels of Lv-β-catenin were down-regulated, as well as the expression levels. Immunofluorescence assay further confirmed that WSSV could reduce the amount of Lv-β-catenin and promoted Lv-β-catenin to translocate into the nucleus. Moreover, we found that WSSV could influence the amount of Lv-β-catenin by ubiquitination. While Lv-β-catenin was up-regulated by a β-catenin activator GSK-3 Inhibitor IX, the transcription of virus immediate early gene WSSV069 was significantly inhibited. In addition, it was found that Lv-β-catenin could interact with WSSV069. Conclusively, our study provided evidences that β-catenin may participate in the WSSV infection, and Wnt/β-catenin signal pathway may play an important role in immune regulation.

Increased nucleoside diphosphate kinase activity induces white spot syndrome virus infection in Litopenaeus vannamei

Nucleoside diphosphate kinase (NDK), which has the same sequence as oncoprotein (OP) in humans, can induce nucleoside triphosphates in DNA replication by maintenance of the deoxynucleotide triphosphate (dNTP’s) and is known to be regulated by viral infection in the shrimp Litopenaeus vannamei. This paper describes the relationship between NDK and white spot syndrome virus (WSSV) infection. The recombinant NDK was produced by a prokaryotic expression system. WSSV copy numbers and mRNA levels of IE1 and VP28 were significantly increased in shrimp injected with recombinant NDK at 72 h after WSSV infection. After synthesizing dsRNA-NDK and confirming the efficacy of NDK silencing, we recorded the cumulative mortality of WSSV-infected shrimp injected with NDK and dsRNA-NDK. A comparison between the results demonstrated that silencing NDK delayed the death of shrimps. These findings indicate that NDK has an important role influencing the replication of WSSV replication in shrimp. Furthermore, NDK may have potential target as a new therapeutic strategy against WSSV infection in shrimp.

Shrimp STAT was hijacked by white spot syndrome virus immediate-early protein IE1 involved in modulation of viral genes

STATs are a family of transcription factors that regulate a cascade of cellular processes including cell growth, differentiation, apoptosis and immune responses. However, they are usually targeted by viruses to assist infection. In this study, we identified that white spot syndrome virus (WSSV) immediate-early protein IE1 interacted with Litopenaeus vannamei STAT (LvSTAT) and thereby led to its phosphorylation activation. In addition, we demonstrated that LvSTAT could bind to the promoters of the viral immediate-early genes wsv051 and ie1 through STAT-binding motifs in vitro and vivo, allowing the enhancement of their promoters' activities. Moreover, IE1 could promote the transcriptional activation activity of LvSTAT to augment the transcription of wsv051 and ie1. In conclusion, our findings revealed a novel linkage between WSSV IE1 and shrimp STAT, which was a clue to well understand how WSSV adopted the active strategies to modulate the shrimp signaling pathway.

Six Hours after Infection, the Metabolic Changes Induced by WSSV Neutralize the Host's Oxidative Stress Defenses

Levels of intracellular ROS (reactive oxygen species) were significantly increased in hemocytes collected from WSSV-infected shrimp within the first 30–120 min after infection. Measurement of the NADPH/NADP⁺ and GSH/GSSG ratios revealed that after a significant imbalance toward the oxidized forms at 2 hpi, redox equilibrium was subsequently restored. Meanwhile, high levels of lactic acid production, elevated NADH/NAD⁺ ratios, and metabolic changes in the glycolysis pathway show that the Warburg effect was triggered by the virus. The timing of these changes suggests that WSSV uses this metabolic shift into aerobic glycolysis to counteract the high levels of ROS produced in response to viral infection. We further show that if the Warburg effect is inhibited by chemical inhibition of the PI3K-Akt-mTOR signaling pathway, or if the pentose phosphate pathway is chemically inhibited, then in both cases, the production of intracellular ROS is sustained. We conclude that WSSV uses the PI3K-Akt-mTOR-regulated Warburg effect to restore host redox balance and to counter the ROS produced by the host in response to WSSV infection. We also found that pyruvate kinase activity was inhibited by WSSV. This inhibition is likely to increase the availability of the raw materials essential for WSSV gene expression and replication.

Regulation of the immediate-early genes of white spot syndrome virus by Litopenaeus vannamei kruppel-like factor (LvKLF)

Kruppel-like factors (KLFs) belong to a subclass of Cys2/His2 zinc-finger DNA-binding proteins, and act as important regulators with diverse roles in cell growth, proliferation, differentiation, apoptosis and tumorigenesis. Our previous research showed that PmKLF from Penaeus monodon is crucial for white spot syndrome virus (WSSV) infection, yet the mechanisms by which PmKLF influences WSSV infection remain unclear. This study cloned KLF from Litopenaeus vannamei (LvKLF), which had 93% similarity with PmKLF. LvKLF formed a dimer via the C-terminal zinc-finger motif. Knockdown of LvKLF expression by dsRNA injection in WSSV-challenged shrimps was found to significantly inhibit the transcription of two important immediate-early (IE) genes, IE1 and WSSV304, and also reduced WSSV copy numbers. Moreover, reporter assays revealed that the promoter activities of these two WSSV IE genes were substantially enhanced by LvKLF. Mutations introduced in the promoter sequences of IE1 and WSSV304 were shown to abolish LvKLF activation of promoter activities; and an electrophoretic mobility shift assay demonstrated that LvKLF binds to putative KLF-response elements (KRE) in the promoters. Taken together, these results indicate that LvKLF transcriptional regulation of key IE genes is critical to WSSV replication.

White spot syndrome virus strains of different virulence induce distinct immune response in Cherax quadricarinatus

In this study, we identified three white spot syndrome virus (WSSV) strains (WSSV-CN01, WSSV-CN02 and WSSV-CN03) with significant differences in virulence. Among them, WSSV-CN01 caused significant higher and earlier mortality in redclaw crayfish Cherax quadricarinatus, thus was determined as high-virulent, while WSSV-CN02 and WSSV-CN03 were moderate-virulent and low-virulent. By investigating the total number of the circulating haemocytes and the activity of immune relative enzymes, we demonstrated that the different virulent WSSV strains induced distinct immune response in the host. Notably, a dramatic reduction of circulating haemocytes was observed in the crayfish infected with WSSV-CN01 and WSSV-CN02 but not WSSV-CN03. Further analysis revealed that cell death induced by WSSV-CN01 and WSSV-CN02 might be responsible for the decrease of circulating haemocytes.

Molecular characterization, immune response against white spot syndrome virus infection of peroxiredoxin 4 in Fenneropenaeus chinensis and its antioxidant activity

Peroxiredoxins (Prx) are a family of antioxidant proteins and perform important functions in intracellular signal transduction. Here, we report a Prx gene from Chinese shrimp Fenneropenaeus chinensis. The full-length cDNA of FcPrx gene contained an open reading frame of 735 bp encoding a polypeptide of 275 amino acids. The molecular mass of the deduced amino acid of FcPrx is 27445.43 Da with an estimated pI of 5.71. Sequence comparison showed that the FcPrx shares high identities with Prx IVs and it was named FcPrx4. A real-Time PCR (qRT-PCR) assay was developed to assess the mRNA expression of FcPrx4 in different tissues and temporal expression in hemocytes and hepatopancreas of F. chinensis challenged by white spot syndrome virus (WSSV). Transcripts of FcPrx4 can be detected in all tissues examined. The expression of FcPrx4 showed significant up-regulation in shrimp hemocytes and hepatopancreas after artificial infection with WSSV. A fusion protein containing FcPrx4 was produced in vitro and was confirmed by Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) assay. And activity analysis indicated that the recombinant FcPrx4 proteins can reduce H2O2 in the presence of dithiothreitol.

Characterization of a 2-Cys peroxiredoxin IV in Marsupenaeus japonicus (kuruma shrimp) and its role in the anti-viral immunity

Accumulating evidence suggests that peroxiredoxins (Prx) are key molecules in the pathogenesis of various infectious diseases and are potential therapeutic targets for major diseases such as cancers. In this study, we report a peroxiredoxin IV (Prx IV) in Marsupenaeus japonicus, designated as MjPrx IV, which exhibited peroxidase activity and participated in the anti-white spot syndrome virus (WSSV) immune response. MjPrx IV is a 245-amino acid polypeptide with a predicted 19-amino acid signal peptide, an Ahpc-TSA domain, and a 1-Cys PrxC domain. Phylogenetic analysis revealed that the protein belongs to the Prx IV subfamily. MjPrx IV transcripts were detected in the gills, hepatopancreas, heart, stomach, ovaries, spermary, and intestine tissues, and are upregulated in the gonads, gills and hemocytes of shrimp after WSSV challenge. The mature MjPrx IV peptide was recombinantly expressed in an Escherichia coli system. The protein exhibited peroxidase activity. Furthermore, dsRNA suppression of MjPrx IV increased WSSV replication in shrimp, whereas rMjPrx IV injection into shrimp decreased WSSV replication. These data suggest that MjPrx IV has an important role in shrimp antiviral immunity. To our knowledge, this study is the first to report a shrimp Prx IV that has anti-WSSV activity.

White spot syndrome virus IE1 and WSV056 modulate the G1/S transition by binding to the host retinoblastoma protein

DNA viruses often target cellular proteins to modulate host cell cycles and facilitate viral genome replication. However, whether proliferation of white spot syndrome virus (WSSV) requires regulation of the host cell cycle remains unclear. In the present study, we show that two WSSV paralogs, IE1 and WSV056, can interact with Litopenaeus vannamei retinoblastoma (Rb)-like protein (lv-RBL) through the conserved LxCxE motif. Further investigation revealed that IE1 and WSV056 could also bind to Drosophila retinoblastoma family protein 1 (RBF1) in a manner similar to how they bind to lv-RBL. Using the Drosophila RBF-E2F pathway as a model system, we demonstrated that both IE1 and WSV056 could sequester RBF1 from Drosophila E2F transcription factor 1 (E2F1) and subsequently activate E2F1 to stimulate the G1/S transition. Our findings provide the first evidence that WSSV may regulate cell cycle progression by targeting the Rb-E2F pathway.