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

WSSV early protein WSSV004 enhances viral replication by suppressing LDH activity

White spot syndrome virus (WSSV) is known to upregulate glycolysis to supply biomolecules and energy for the virus's replication. At the viral genome replication stage, lactate dehydrogenase (LDH), a glycolytic enzyme, shows increased activity without any increase in expression. In the present study, yeast 2-hybrid screening was used to identify WSSV proteins that interacted with LvLDH isoform 1 and 2, and these included the WSSV early protein WSSV004. The interaction between WSSV004 and LvLDH1/2 was confirmed by co-immunoprecipitation. Immunofluorescence showed that WSSV004 co-localized with LvLDH1/2 in the cytoplasm. dsRNA silencing experiments showed that WSSV004 was crucial for WSSV replication. However, although WSSV004 silencing led to the suppression of total LvLDH gene expression during the viral late stage, there was nevertheless a significant increase in LvLDH activity at this time. We also used affinity purification-mass spectrometry to identify cellular proteins that interact with WSSV004, and found a total of 108 host proteins and 3 WSSV proteins with which it potentially interacts. Bioinformatics analysis revealed that WSSV004 and its interacting proteins might be responsible for various biological pathways during infection, including vesicular transport machinery and RNA-related functions. Collectively, our study suggests that WSSV004 serves as a multifunctional modulator to facilitate WSSV replication.

Single-cell RNA-seq revealed heterogeneous responses and functional differentiation of hemocytes against white spot syndrome virus infection in Litopenaeus vannamei

Shrimp hemocytes are the vital immune cells participating in innate immune response to defend against viruses. However, the lack of specific molecular markers for shrimp hemocyte hindered the insightful understanding of their functional clusters and differential roles in combating microbial infections. In this study, we used single-cell RNA sequencing to map the transcriptomic landscape of hemocytes from the white spot syndrome virus (WSSV)-infected Litopenaeus vannamei and conjointly analyzed with our previous published single-cell RNA sequencing technology data from the healthy hemocytes. A total of 16 transcriptionally distinct cell clusters were identified, which occupied different proportions in healthy and WSSV-infected hemocytes and exerted differential roles in antiviral immune response. Following mapping of the sequencing data to the WSSV genome, we found that all types of hemocytes could be invaded by WSSV virions, especially the cluster 8, which showed the highest transcriptional levels of WSSV genes and exhibited a cell type-specific antiviral response to the viral infection. Further evaluation of the cell clusters revealed the delicate dynamic balance between hemocyte immune response and viral infestation. Unsupervised pseudo-time analysis of hemocytes showed that the hemocytes in immune-resting state could be significantly activated upon WSSV infection and then functionally differentiated to different hemocyte subsets. Collectively, our results revealed the differential responses of shrimp hemocytes and the process of immune-functional differentiation post-WSSV infection, providing essential resource for the systematic insight into the synergistic immune response mechanism against viral infection among hemocyte subtypes.

IMPORTANCE

Current knowledge of shrimp hemocyte classification mainly comes from morphology, which hinder in-depth characterization of cell lineage development, functional differentiation, and different immune response of hemocyte types during pathogenic infections. Here, single-cell RNA sequencing was used for mapping hemocytes during white spot syndrome virus (WSSV) infection in Litopenaeus vannamei, identifying 16 cell clusters and evaluating their potential antiviral functional characteristics. We have described the dynamic balance between viral infestation and hemocyte immunity. And the functional differentiation of hemocytes under WSSV stimulation was further characterized. Our results provided a comprehensive transcriptional landscape and revealed the heterogeneous immune response in shrimp hemocytes during WSSV infection.

Comparative Transcriptome Analysis Reveals That WSSV IE1 Protein Plays a Crucial Role in DNA Replication Control

For DNA viruses, the immediate-early (IE) proteins are generally essential regulators that manipulate the host machinery to support viral replication. Recently, IE1, an IE protein encoded by white spot syndrome virus (WSSV), has been demonstrated to function as a transcription factor. However, the target genes of IE1 during viral infection remain poorly understood. Here, we explored the host target genes of IE1 using RNAi coupled with transcriptome sequencing analysis. A total of 429 differentially expressed genes (DEGs) were identified from penaeid shrimp, of which 284 genes were upregulated and 145 genes were downregulated after IE1 knockdown. GO and KEGG pathway enrichment analysis revealed the identified DEGs are significantly enriched in the minichromosome maintenance (MCM) complex and DNA replication, indicating that IE1 plays a critical role in DNA replication control. In addition, it was found that Penaeus vannamei MCM complex genes were remarkably upregulated after WSSV infection, while RNAi-mediated knockdown of PvMCM2 reduced the expression of viral genes and viral loads at the early infection stage. Finally, we demonstrated that overexpression of IE1 promoted the expression of MCM complex genes as well as cellular DNA synthesis in insect High-Five cells. Collectively, our current data suggest that the WSSV IE1 protein is a viral effector that modulates the host DNA replication machinery for viral replication.

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.

WSV056 Inhibits Shrimp Nitric Oxide Synthase Activity by Downregulating Litopenaeus vannamei Sepiapterin Reductase to Promote White Spot Syndrome Virus Replication

Sepiapterin reductase (Spr) plays an essential role in the biosynthesis of tetrahydrobiopterin (BH4), a key cofactor of multiple enzymes involved in various physiological and immune processes. Suppression of Spr could result in BH4 deficiency-caused diseases in human and murine models. However, information on the biological function of Spr in invertebrates is limited. In this study, two Sprs (CG12116 and Sptr) from Drosophila melanogaster were found to be downregulated in transgenic flies overexpressing white spot syndrome virus (WSSV) immediate-early protein WSV056. CG12116 and Sptr exerted an inhibitory effect on the replication of the Drosophila C virus. A Litopenaeus vannamei Spr (LvSpr) exhibiting similarity of 64.1–67.5% and 57.3–62.2% to that of invertebrate and vertebrate Sprs, respectively, were cloned. L. vannamei challenged with WSSV revealed a significant decrease in LvSpr transcription and Spr activity in hemocytes. In addition, the BH4 co-factored nitric oxide synthase (Nos) activity in shrimp hemocytes was reduced in WSSV-infected and LvSpr knockdown shrimp, suggesting WSSV probably inhibits the LvNos activity through LvSpr downregulation to limit the production of nitric oxide (NO). Knockdown of LvSpr and LvNos caused the reduction in NO level in hemocytes and the increase of viral copy numbers in WSSV-infected shrimp. Supplementation of NO donor DETA/NO or double gene knockdown of WSV056 + LvSpr and WSV056 + LvNos recovered the NO production, whereas the WSSV copy numbers were decreased. Altogether, the findings demonstrated that LvSpr and LvNos could potentially inhibit WSSV. In turn, the virus has evolved to attenuate NO production via LvSpr suppression by WSV056, allowing evasion of host antiviral response to ensure efficient replication.

Phosphorylation of Shrimp Tcf by a Viral Protein Kinase WSV083 Suppresses Its Antiviral Effect

Nuclear DNA-binding TCF proteins, which act as the main downstream effectors of Wnt signaling, are essential for the regulation of cell fate and innate immunity. However, their role during viral infection in shrimp remains unknown. Herein, we demonstrated that Litopenaeus vannamei TCF (LvTcf) acts independently of Lvβ-catenin to promote interferon-like protein LvVago1 production, thus mounting the response to WSSV infection. Further, we observed that WSV083, a WSSV serine/threonine protein kinase, bound to LvTcf and phosphorylated it. Phosphorylated LvTcf was then recognized and degraded via the ubiquitin-proteasome pathway. Moreover, mass spectrometry analyses indicated that the T39 and T104 residues of LvTcf were target sites phosphorylated by WSV083. Point mutation analyses suggested that additional sites of LvTcf may undergo phosphorylation via WSV083. Taken together, the current work provides valuable insights into host immunity and viral pathogenesis. LvTcf is not only a modulator of shrimp innate immunity but is also an important target for WSSV immune evasion. Thus, the current findings will help improve disease control in shrimps.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.

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.

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

Aquatic animal viruses mediated immune evasion in their host

Viruses are important and lethal pathogens that hamper aquatic animals. The result of the battle between host and virus would determine the occurrence of diseases. The host will fight against virus infection with various responses such as innate immunity, adaptive immunity, apoptosis, and so on. On the other hand, the virus also develops numerous strategies such as immune evasion to antagonize host antiviral responses. Here, We review the research advances on virus mediated immune evasions to host responses containing interferon response, NF-κB signaling, apoptosis, and adaptive response, which are executed by viral genes, proteins, and miRNAs from different aquatic animal viruses including Alloherpesviridae, Iridoviridae, Nimaviridae, Birnaviridae, Reoviridae, and Rhabdoviridae. Thus, it will facilitate the understanding of aquatic animal virus mediated immune evasion and potentially benefit the development of novel antiviral applications.

Cloning, identification and function analysis of a Chibby homolog from Litopenaeus vannamei

Chibby, a vital inhibitor molecule of Wnt/β-catenin signaling pathway, participates in development and stem cell differentiation through the regulation of β-catenin. Our previous studies have demonstrated that Litopenaeus vannamei β-catenin (Lv-β-catenin) was involved in WSSV infection and could inhibit virus replication by modulating the host immune system. In the study, a Chibby homolog from L. vannamei (designed as Lv-Chibby) was isolated and its role in WSSV infection was investigated. Sequence analysis suggested that Lv-Chibby was a novel homolog of Chibby family. It could transcript in all examined tissues, including hemocyte, gill, intestine, hepatopancreas, muscle and heart. Real-time quantitative PCR demonstrated that Lv-Chibby could take part in WSSV infection and be down-regulated by WSSV. Further studies confirmed that Lv-Chibby was able to interact with Lv-β-catenin. Moreover, the relationship of Lv-β-catenin, Lv-Chibby and WSSV069 was investigated. It was shown that Lv-Chibby enhanced the interaction between Lv-β-catenin and WSSV069. Interestingly, WSSV069 promoted the interaction between Lv-β-catenin and Lv-Chibby under high concentration, while low concentration of WSSV069 inhibited their interaction. A subsequent immunofluorescence assay revealed that WSSV069 appeared to reduce the nuclear entry of Lv-β-catenin. In sum, these results implied that Wnt/β-catenin signal pathway plays an important role in the defense against virus, and Chibby could be modulated by WSSV to regulate the signal pathway.

The immediate early protein WSV187 can influence viral replication via regulation of JAK/STAT pathway in Drosophila

The world production of shrimp is seriously affected by the white spot syndrome virus (WSSV). Viral immediate-early (IE) genes encode regulatory proteins critical for the viral lifecycle. In spite of their importance, only five out of the 21 identified WSSV IE genes are functionally characterized. Here, we report the use of Drosophila melanogaster as a model to explore the role of WSSV IE gene wsv187. In vivo expression of WSV187 in transgenic flies show WSV187 localized in the cytoplasm. Overexpression of wsv187 results wing defects consistent with phenotypes observed in JAK/STAT exacerbated flies. After artificial infection of the DCV virus, the flies expressing wsv187 showed a lower viral load, a higher survival rate and an up-regulated STAT92E expression. These data demonstrate wsv187 plays a role in the controlling of virus replication by activating host JAK/STAT pathway.

Role of Litopenaeus vannamei Yin Yang 1 in the Regulation of the White Spot Syndrome Virus Immediate Early Gene ie1

Yin Yang 1 (YY1) is a multifunctional zinc finger transcription factor that regulates many key cellular processes. In this study, we report the cloning of YY1 from Litopenaeus vannamei shrimp (LvYY1). This study shows that LvYY1 is ubiquitously expressed in shrimp tissues, and knockdown of LvYY1 expression by double-stranded RNA (dsRNA) injection in white spot syndrome virus (WSSV)-infected shrimp reduced both mRNA levels of the WSSV immediate early gene ie1 as well as overall copy numbers of the WSSV genome. The cumulative mortality rate of infected shrimp also declined with LvYY1 dsRNA injection. Using an insect cell model, we observed that LvYY1 activates ie1 expression, and a mutation introduced into the ie1 promoter subsequently repressed this capability. Moreover, reporter assay results suggested that LvYY1 is involved in basal transcriptional regulation via an interaction with L. vannamei TATA-binding protein (LvTBP). Electrophoretic mobility shift assay (EMSA) results further indicated that LvYY1 binds to a YY1-binding site in the region between positions -119 and -126 in the ie1 promoter. Chromatin immunoprecipitation analysis also confirmed that LvYY1 binds to the ie1 promoter in WSSV-infected shrimp. Taken together, these results indicate that WSSV uses host LvYY1 to enhance ie1 expression via a YY1-binding site and the TATA box in the ie1 promoter, thereby facilitating lytic activation and viral replication.IMPORTANCE WSSV has long been a scourge of the shrimp industry and remains a serious global threat. Thus, there is a pressing need to understand how the interactions between WSSV and its host drive infection, lytic development, pathogenesis, and mortality. Our successful cloning of L. vannamei YY1 (LvYY1) led to the elucidation of a critical virus-host interaction between LvYY1 and the WSSV immediate early gene ie1 We observed that LvYY1 regulates ie1 expression via a consensus YY1-binding site and TATA box. LvYY1 was also found to interact with L. vannamei TATA-binding protein (LvTBP), which may have an effect on basal transcription. Knockdown of LvYY1 expression inhibited ie1 transcription and subsequently reduced viral DNA replication and decreased cumulative mortality rates of WSSV-infected shrimp. These findings are expected to contribute to future studies involving WSSV-host interactions.

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.

Transcriptome Analysis of the Hepatopancreas in the Pacific White Shrimp (Litopenaeus vannamei) under Acute Ammonia Stress

In the practical farming of Litopenaeus vannamei, the intensive culture system and environmental pollution usually results in a high concentration of ammonia, which usually brings large detrimental effects to shrimp, such as increasing the susceptibility to pathogens, reducing growth, decreasing osmoregulatory capacity, increasing the molting frequency, and even causing high mortality. However, little information is available on the molecular mechanisms of the detrimental effects of ammonia stress in shrimp. In this study, we performed comparative transcriptome analysis between ammonia-challenged and control groups from the same family of L. vannamei to identify the key genes and pathways response to ammonia stress. The comparative transcriptome analysis identified 136 significantly differentially expressed genes that have high homologies with the known proteins in aquatic species, among which 94 genes are reported potentially related to immune function, and the rest of the genes are involved in apoptosis, growth, molting, and osmoregulation. Fourteen GO terms and 6 KEGG pathways were identified to be significantly changed by ammonia stress. In these GO terms, 13 genes have been studied in aquatic species, and 11 of them were reported potentially involved in immune defense and two genes were related to molting. In the significantly changed KEGG pathways, all the 7 significantly changed genes have been reported in shrimp, and four of them were potentially involved in immune defense and the other three were related to molting, defending toxicity, and osmoregulation, respectively. In addition, majority of the significantly changed genes involved in nitrogen metabolisms that play an important role in reducing ammonia toxicity failed to perform the protection function. The present results have supplied molecular level support for the previous founding of the detrimental effects of ammonia stress in shrimp, which is a prerequisite for better understanding the molecular mechanism of the immunosuppression from ammonia stress.

Spring Viremia of Carp Virus N Protein Suppresses Fish IFNφ1 Production by Targeting the Mitochondrial Antiviral Signaling Protein

For a virus to replicate efficiently, it must try and inhibit host IFN expression because IFN is an important host defense at early stages after viral infection. For aquatic viruses, the mechanisms used to escape the hosts IFN system are still unclear. In this study, we show that the N protein of spring viremia of carp virus (SVCV) inhibits zebrafish IFNφ1 production by degrading the mitochondrial antiviral signaling protein (MAVS). First, the upregulation of IFNφ1 promoter activity stimulated by polyinosinic:polycytidylic acid, retinoic acid-inducible gene I (RIG-I) or MAVS was suppressed by the SVCV infection. However, the upregulation by the downstream factor of the RIG-I-like receptor signaling pathway, TANK-binding kinase 1, was not affected. Notably, at the protein level, MAVS decreased remarkably when cells were infected with SVCV. Second, consistent with the result of the SVCV infection, overexpression of the N protein of SVCV blocked the IFNφ1 transcription activated by MAVS and downregulated MAVS expression at the protein level but not at the mRNA level. Further analysis demonstrated that the N protein targeted MAVS for K48-linked ubiquitination, which promoted the degradation of MAVS. These data indicated that fish MAVS could be degraded by the N protein of SVCV through the ubiquitin-proteasome pathway. To our knowledge, this is the first article of a fish RIG-I-like receptor pathway interfered by an aquatic virus in an ubiquitin-proteasome manner, suggesting that immune evasion of a virus also exists in lower vertebrates.

A Review of Functional Motifs Utilized by Viruses

Short linear motifs (SLiM) are short peptides that facilitate protein function and protein-protein interactions. Viruses utilize these motifs to enter into the host, interact with cellular proteins, or egress from host cells. Studying functional motifs may help to predict protein characteristics, interactions, or the putative cellular role of a protein. In virology, it may reveal aspects of the virus tropism and help find antiviral therapeutics. This review highlights the recent understanding of functional motifs utilized by viruses. Special attention was paid to the function of proteins harboring these motifs, and viruses encoding these proteins. The review highlights motifs involved in (i) immune response and post-translational modifications (e.g., ubiquitylation, SUMOylation or ISGylation); (ii) virus-host cell interactions, including virus attachment, entry, fusion, egress and nuclear trafficking; (iii) virulence and antiviral activities; (iv) virion structure; and (v) low-complexity regions (LCRs) or motifs enriched with residues (Xaa-rich motifs).

Molecular Mechanisms of White Spot Syndrome Virus Infection and Perspectives on Treatments

Since its emergence in the 1990s, White Spot Disease (WSD) has had major economic and societal impact in the crustacean aquaculture sector. Over the years shrimp farming alone has experienced billion dollar losses through WSD. The disease is caused by the White Spot Syndrome Virus (WSSV), a large dsDNA virus and the only member of the Nimaviridae family. Susceptibility to WSSV in a wide range of crustacean hosts makes it a major risk factor in the translocation of live animals and in commodity products. Currently there are no effective treatments for this disease. Understanding the molecular basis of disease processes has contributed significantly to the treatment of many human and animal pathogens, and with a similar aim considerable efforts have been directed towards understanding host-pathogen molecular interactions for WSD. Work on the molecular mechanisms of pathogenesis in aquatic crustaceans has been restricted by a lack of sequenced and annotated genomes for host species. Nevertheless, some of the key host-pathogen interactions have been established: between viral envelope proteins and host cell receptors at initiation of infection, involvement of various immune system pathways in response to WSSV, and the roles of various host and virus miRNAs in mitigation or progression of disease. Despite these advances, many fundamental knowledge gaps remain; for example, the roles of the majority of WSSV proteins are still unknown. In this review we assess current knowledge of how WSSV infects and replicates in its host, and critique strategies for WSD treatment.

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.

The interaction of nonstructural protein 9 with retinoblastoma protein benefits the replication of genotype 2 porcine reproductive and respiratory syndrome virus in vitro

The nonstructural protein 9 (Nsp9) of porcine reproductive and respiratory syndrome virus (PRRSV) is a RNA-dependent RNA polymerase (RdRp) that plays a vital role in viral replication. This study first demonstrated that the Nsp9 of genotype 2 PRRSV interacted with cellular retinoblastoma protein (pRb), and Nsp9 co-localized with pRb in the cytoplasm of PRRSV-infected MARC-145 cells and pulmonary alveolar macrophages (PAMs). Next, the overexpression of truncated pRb was shown to inhibit the PRRSV replication and silencing the pRb gene could facilitate the PRRSV replication in MARC-145 cells. Finally, the pRb level was confirmed to be down-regulated in PRRSV-infected MARC-145 cells, and Nsp9 was shown to promote the pRb degradation by proteasome pathway. These findings indicate that the interaction of Nsp 9 with pRb benefits the replication of genotype 2 PRRSV in vitro, helping to understand the roles of Nsp9 in the replication and pathogenesis of PRRSV.

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The Nsp9 of genotype 2 PRRSV interacted with retinoblastoma protein (pRb).

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The pRb level was down-regulated in PRRSV-infected MARC-145 cells.

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The Nsp9 of genotype 2 PRRSV promoted the pRb degradation by proteasome pathway.

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The interaction of Nsp 9 with pRb benefits the genotype 2 PRRSV replication in vitro.

Exploration of panviral proteome: high-throughput cloning and functional implications in virus-host interactions

Throughout the long history of virus-host co-evolution, viruses have developed delicate strategies to facilitate their invasion and replication of their genome, while silencing the host immune responses through various mechanisms. The systematic characterization of viral protein-host interactions would yield invaluable information in the understanding of viral invasion/evasion, diagnosis and therapeutic treatment of a viral infection, and mechanisms of host biology. With more than 2,000 viral genomes sequenced, only a small percent of them are well investigated. The access of these viral open reading frames (ORFs) in a flexible cloning format would greatly facilitate both in vitro and in vivo virus-host interaction studies. However, the overall progress of viral ORF cloning has been slow. To facilitate viral studies, we are releasing the initiation of our panviral proteome collection of 2,035 ORF clones from 830 viral genes in the Gateway® recombinational cloning system. Here, we demonstrate several uses of our viral collection including highly efficient production of viral proteins using human cell-free expression system in vitro, global identification of host targets for rubella virus using Nucleic Acid Programmable Protein Arrays (NAPPA) containing 10,000 unique human proteins, and detection of host serological responses using micro-fluidic multiplexed immunoassays. The studies presented here begin to elucidate host-viral protein interactions with our systemic utilization of viral ORFs, high-throughput cloning, and proteomic technologies. These valuable plasmid resources will be available to the research community to enable continued viral functional studies.