miR-homoHSV of Singapore grouper iridovirus (SGIV) inhibits expression of the SGIV pro-apoptotic factor LITAF and attenuates cell death

Antiviral role of grouper FoxO1 against RGNNV and SGIV infection

As a key regulator of the innate immune system, FoxO1 has a variety of activities in biological organisms. In the present study, grouper FoxO1 (EcFoxO1) was cloned and the antiviral activity in red grouper neuron necrosis virus (RGNNV) and Singapore grouper iridescent virus (SGIV) was examined. The open reading frame (ORF) of EcFoxO1 contains 2,034 base pairs that encode a protein of 677 amino acids with a predicted molecular weight of 73.21 kDa. EcFoxO1 was shown to be broadly distributed in healthy grouper tissues, and was up-regulated in vitro in response to stimulation by RGNNV and SGIV. EcFoxO1 has a whole-cell distribution in grouper spleen (GS) cells. EcFoxO1 decreased the replication of RGNNV and SGIV, and activated interferon (IFN) 3, IFN-stimulated response element (ISRE), and nuclear factor-κB (NF-κB) promoter activities. EcFoxO1 could interact with EcIRF3. Together, the results demonstrated that EcFoxO1 might be an important regulator of grouper innate immune response against RGNNV and SGIV infection.

Antiviral immunity of grouper MAP kinase phosphatase 1 to Singapore grouper iridovirus infection

Singapore grouper iridovirus (SGIV), with various mechanisms for evading and modulating host, has inflicted heavy economic losses in the grouper aquaculture. MAP kinase phosphatase 1 (MKP-1) regulates mitogen-activated protein kinases (MAPKs) to mediate the innate immune response. Here, we cloned EcMKP-1, an MKP-1 homolog from the orange-spotted grouper Epinephelus coioides, and investigated its role in the infection of SGIV. In juvenile grouper, EcMKP-1 was highly upregulated and peaked at different times after injection with lipopolysaccharide, polyriboinosinic polyribocytidylic acid and SGIV. EcMKP-1 expression in heterologous fathead minnow cells was able to suppress SGIV infection and replication. Furthermore, EcMKP-1 was a negative regulator of c-Jun N-terminal kinase (JNK) phosphorylation early in SGIV infection. EcMKP-1 decreased the apoptotic percentage and caspase-3 activity during the late stage of SGIV replication. Our results demonstrate critical functions of EcMKP-1 in antiviral immunity, JNK dephosphorylation and anti-apoptosis during SGIV infection.

Functional characterization of a putative lipopolysaccharide-induced TNF-alpha factor (LITAF) from blood clam Tegillarca granosa in innate immunity

Lipopolysaccharide-induced TNF-alpha factor (LITAF), as a transcription factor, activates the transcription of TNF and other cytokines in inflammatory response upon lipopolysaccharide (LPS) stimulation. In the present study, we cloned and identified the full-length cDNA of LITAF homolog from blood clam Tegillarca granosa for the first time. The full-length cDNA of TgLITAF was 1801 bp encoding a polypeptide of 147 amino acids with an estimated molecular mass of 16.13 kDa. TgLITAF contained a zf-LITAF-like zinc ribbon domain at the C-terminal of the protein and the TgLITAF domain showed 48-74% amino acid sequence identity with other known LITAFs from other species. Subcellular localization study showed that TgLITAF was mainly expressed in the nucleus. qRT-PCR analysis showed that the TgLITAF transcription expressed constitutively in all the examined tissues with the highest expression level in the gills. After LPS or V. alginolyticus treatment, expression of TgLITAF in hemocytes was both up-regulated significantly at 3-6 h. Furthermore, in vitro study indicated that overexpression of TgLITAF in HeLa cells resulted in the activation of TNFα, p53, and influenced the expression levels of apoptotic-related genes Bax, Bcl-2, Caspase-3, Caspase-6, and Caspase-7. The proliferation of HeLa cells was inhibited by overexpression of TgLITAF. Apoptotic fluorescence assay further revealed that TgLITAF participated in the apoptotic process of HeLa cells. Western blotting analysis showed that overexpression of TgLITAF increased endogenous level of cleaved Caspase-7. Taken together, these results revealed that TgLITAF participates in the innate immune response to the pathogen invasion in blood clams and induces apoptosis in HeLa cells.

The immune evasion strategies of fish viruses

Viral infection of a host rapidly triggers intracellular signaling events that induce interferon production and a cellular antiviral state. Viral diseases are important concerns in fish aquaculture. The major mechanisms of the fish antiviral immune response are suggested to be similar to those of mammals, although the specific details of the process require further studies. Throughout the process of pathogen-host coevolution, fish viruses have developed a battery of distinct strategies to overcome the biochemical and immunological defenses of the host. Such strategies include signaling interference, effector modulation, and manipulation of host apoptosis. This review provide an overview of the different mechanisms that fish viruses use to evade host immune responses. The basic mechanisms of immune evasion of fish virus are discussed, and some examples are provided to illustrate particular points.

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.

Non-coding RNAs Function as Immune Regulators in Teleost Fish

Non-coding RNAs (ncRNAs) are functional RNA molecules that are transcribed from DNA but not translated into proteins. ncRNAs function as key regulators of gene expression and chromatin modification. Recently, the functional role of ncRNAs in teleost fish has been extensively studied. Teleost fish are a highly diverse group among the vertebrate lineage. Fish are also important in terms of aquatic ecosystem, food production and human life, being the source of animal proteins worldwide and models of biomedical research. However, teleost fish always suffer from the invasion of infectious pathogens including viruses and bacteria, which has resulted in a tremendous economic loss to the fishing industry worldwide. Emerging evidence suggests that ncRNAs, especially miRNAs and lncRNAs, may serve as important regulators in cytokine and chemokine signaling, antigen presentation, complement and coagulation cascades, and T cell response in teleost fish. In this review, we summarize current knowledge and understanding of the roles of both miRNAs and lncRNAs in immune regulation in teleost fish. Molecular mechanism insights into the function of ncRNAs in fish immune response may contribute to the development of potential biomarkers and therapeutic targets for the prevention and treatment of fish diseases.

Giant seaperch iridovirus infection upregulates Bas and Bak expression, leading to apoptotic death of fish cells

The giant seaperch iridovirus (GSIV) induces host cell apoptosis by a poorly-understood process. In this study, GSIV is shown to upregulate the pro-apoptotic death genes Bax and Bak at the middle replication stage, and factors in the grouper fin cell line (GF-1) are shown to modulate this process. Studying the mechanism of cell death, we found that upregulated, de novo-synthesized Bax and Bak proteins formed heterodimers. This up-regulation process correlated with mitochondrial membrane potential (MMP) loss, increased caspase-3 activity, and increased apoptotic cell death. All effects were diminished by treatment of infected GF-1 cells with the protein synthesis inhibitor cycloheximide. Interestingly, overexpression of the anti-apoptotic gene Bcl-xL also diminished GSIV-induced mitochondria-mediated cell death, increasing host cell viability and decreasing MMP loss at the early replication stage. Our data suggest that GSIV induces GF-1 apoptotic cell death through up-regulation of the pro-apoptotic genes Bax and Bak, which are regulated by Bcl-xL overexpression on mitochondria in GF-1 cells.

ORF75 of megalocytivirus RBIV-C1: A global transcription regulator and an effective vaccine candidate

Megalocytivirus, a DNA virus belonging to the Iridoviridae family, is a severe pathogen to a wide range of marine and freshwater fish. In this study, using turbot (Scophthalmus maximus) as a host model, we examined the immunoprotective property of one megalocytivirus gene, ORF75, in the form of DNA vaccine (named pORF75). Immunofluorescence microscopy and RT-PCR analysis showed that P444, the protein encoded by ORF75, was naturally produced in the tissues of turbot during megalocytivirus infection, and that the vaccine gene in pORF75 was expressed in fish cells transfected with pORF75 and in the tissues of turbot immunized with pORF75. Following vaccination of turbot with pORF75, a high level of survival (73%) was observed against a lethal megalocytivirus challenge. Consistently, viral replication in the vaccinated fish was significantly inhibited. Immune response analysis showed that pORF75-vaccinated fish (i) exhibited upregulated expression of the genes involved in innate and adaptive immunity, (ii) possessed specific memory immune cells that showed significant response to secondary antigen stimulation, and (iii) produced specific serum antibodies which, when co-introduced into turbot with megalocytivirus, blocked viral replication. Furthermore, whole-genome transcriptome analysis revealed that ORF75 knockdown altered the transcription of 43 viral genes. Taken together, these results indicate that ORF75 encoded a highly protective immunogen that is also a global transcription regulator of megalocytivirus.