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Infectious spleen and kidney necrosis virus (ISKNV) infections can trigger host cell death and are correlated with viral replication; however, they have rarely been considered in terms of the host organelle involvement. In the present study, we demonstrated that ISKNV triggered an oxidative stress signal in the Nrf2-mediated oxidative stress response and induced stress signals for Bax/Bak-mediated host cell death in fish GF-1 cells. The results showed that after ISKNV infection, the levels of reactive oxidative species (ROS) increased by 60–80% from day 3 to day 5, as assessed by an H2DCFDA assay for tracing hydrogen peroxide (H2O2), which was correlated with up to a one-fold change in the fish GF-1 cells. Furthermore, we found that ISKNV infection induced Nrf2-mediated ROS stress signals from D1 to D5, which were correlated with the upregulation of antioxidant enzymes, such as catalase, SOD1, and SOD2; these effects were blocked by the antioxidants GSH and NAC. By analyzing Nrf2-mediated ROS stress signals for cell death regulationviaan apoptotic assay, we found that treatment with antioxidants reduced annexin-V-positive signals by 10% (GSH) to 15% (NAC); moreover, necrotic-positive signals were reduced by 6% (GSH) and 32% (NAC) at day 5 (D5) in GF-1 cells, as indicated by PI staining. Furthermore, we found that Nrf2-mediated ROS stress regulated mitochondrion-mediated Bax/Bak death signals at D3 and D5; this was effectively blocked by antioxidant treatment in the GF-1 cells, as demonstrated by a JC1 assay (ΔΨm) and western blot analysis. In addition, we found that downstream signals for caspase-9 and -3 activation were apparently blocked by antioxidant treatment at D3 and D5. Finally, we found that treatment with GSH and NAC reduced major capsid protein (MCP) expression and virus titer (TCID50%) by up to 15-fold at D5 in GF-1 cells. Thus, our data suggest that ISKNV can induce ROS production, which triggers Nrf2-mediated stress signals. Then, these stress signals can regulate mitochondrion-mediated Bax/Bak apoptotic signaling, which is connected to downstream caspase-9 and -3 activation. If ISKNV-induced Nrf2-mediated stress signaling is blocked, then the antioxidants GSH and NAC can also suppress apoptotic signals or reduce viral replication. These findings may provide insights into the control and treatment of double-stranded DNA viruses.

The BH3-only molecule Bad regulates cell death via its differential protein phosphorylation, but very few studies address its effect on early embryonic development in vertebrate systems. In this work, we examined the novel role of zebrafish Bad in the initial programmed cell death (PCD) for brain morphogenesis through reducing environmental stress and cell death signaling. Bad was considered to be a material factor that because of the knockdown of Bad by morpholino oligonucleotides, PCD was increased and the reactive oxygen species (ROS) level was enhanced, which correlated to trigger a p53/caspase-8 involving cell death signaling. This Bad knockdown-mediated environmental stress and enhanced cell dying can delay normal cell migration in the formation of the three germ layers, especially the ectoderm, for further brain development. Furthermore, Bad defects involved in three-germ-layers development at 8 hpf were identified by in situ hybridization approach on cyp26, rtla, and Sox17 pattern expression markers. Finally, the Bad knockdown-induced severely defected brain was examined by tissue section from 24 to 48 h postfertilization (hpf), which correlated to induce dramatic malformation in the hindbrain. Our data suggest that the BH3-only molecule Bad regulates brain development via controlling programmed cell death on overcoming environmental stress for reducing secondary cell death signaling, which suggests that correlates to brain developmental and neurological disorders in this model system.

Megalocytiviruses are classified into three genotypes, infectious spleen and kidney necrosis virus (ISKNV), red seabream virus (RSIV), and turbo reddish body iridovirus (TRBIV), based on the major capsid protein and ATPase genes. However, only a few complete genome sequences have been obtained. This paper reports the complete genome sequence and phylogenetic analysis of an RSIV-Ku strain megalocytivirus. The genome sequence comprises 111,154 bp, has 132 putative open reading frames, and is homologous mostly to ISKNV, except for the sequence in the region 58981-66830, which is more closely related to that of the RSIV genotype. The results imply that RSIV-Ku is actually a natural recombinant virus.

// Hsuan-Wen Chiu 1 , Yu-Chin Su 1 and Jiann-Ruey Hong 1, 2 1 Department of Biotechnology and Bioindustry, Laboratory of Molecular Virology and Biotechnology, Institute of Biotechnology, National Cheng Kung University, Tainan 701, Taiwan 2 Department of Biotechnology and Bioindustry, National Cheng Kung University, Tainan 701, Taiwan Correspondence to: Jiann-Ruey Hong, email: jrhong@mail.ncku.edu.tw Keywords: B2 protein, cell death, p53, autophagy, lung cancer cell Received: July 27, 2017 Accepted: September 21, 2017 Published: October 06, 2017 ABSTRACT The betanodavirus B2 protein targets the mitochondria and acts as a “death factor”, but its effect on lung cancer cells is unknown. We examined the effect of the B2 protein on triggering apoptosis or necroptosis via P53-dependent and P53-independent pathways and increased in suppression of autophagy. The B2 protein targets the mitochondria of A549 (P53 +/+ ) and H1299 (P53 —/— ) lung cancer cells due to a specific signal sequence ( 41 RTFVISAHAA 50 ). This triggers generation of reactive oxygen species within the mitochondria, and a minor stress response in A549 cells, but a strong stress response in H1299 cells. We examined the molecular mechanism of this cell death pathway, and found that B2 protein induces the P53/Bax-mediated apoptotic pathway in A549 cells, and that a P53 specific inhibitor (pifithrin-α) switches this response to RIP3-mediated necroptosis. On the other hand, B2 induces RIP3-mediated necroptosis pathway in H1299 cells, and a necroptosis inhibitor (necrostatin-1) switches this response to the apoptotic pathway. Both types of cell death signals inhibited autophagy via a tightly increased balance of beclin-1 and Bcl-2. Thus, B2 protein triggers P53-dependent apoptosis in A549 cells and ROS/RIP3-mediated necroptosis in H1299 cells, and crosstalk of these pathways limits initiation of autophagy. These findings provide new insights into the possible control and treatment of lung cancer.

Polyunsaturated fatty acids (PUFAs) play important roles in organisms, including the structure and liquidity of cell membranes, anti-oxidation and anti-inflammation. Very little has been done in terms of the effect of PUFAs on cell death, especially on DNA virus. In this study, we demonstrated that the infectious spleen and kidney necrosis virus (ISKNV) can induce host cell death via the apoptotic cell death pathway, which correlated to modulation by PUFAs in grouper fin cell line (GF-1) cells. We screened the PUFAs, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), for the ability of different dosages to prevent cell death in GF-1 cells with ISKNV infection. In the results, each 10 μM of DHA and EPA treatment enhanced host cell viability up to 80% at day 5 post-infection. Then, in Terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) assay, DHA- and EPA-treated groups reduced TUNEL positive signals 50% in GF-1 cells with ISKNV infection. Then, through studies of the mechanism of cell death, we found that ISKNV can induce both the Bax/caspase-3 and Fas/caspase-8/tBid death signaling pathways in GF-1 cells, especially at day 5 post-infection. Furthermore, we found that DHA and EPA treatment can either prevent caspase-3 activation on 17-kDa form cleavage or Bid cleaved (15-kDa form) for activation by caspase-8, apparently. On the other hand, the anti-apoptotic gene Bcl-2 was upregulated 0.3-fold and 0.15-fold at day 3 and day 5, respectively, compared to ISKNV-infected and DHA-treated cells; that this did not happen in the EPA-treated group showed that different PUFAs trigger different signals. Finally, ISKNV-infected GF-1 cells treated with either DHA or EPA showed a 5-fold difference in viral titer at day 5. Taken together, these results suggest that optimal PUFA treatment can affect cell death signaling through both the intrinsic and extrinsic death pathways, reducing viral expression and viral titer in GF-1 cells. This finding may provide insight in DNA virus infection and control.

Although serine/threonine (ST) kinase is known to induce host cell death in GF-1 cells, it remains unclear how ST kinase induces mitochondrial function loss. In the present study, we addressed the issue of mitochondrial function loss by determining whether the Bcl-2 family members Bcl-2 and Bcl-xL can prevent ST kinase-induced cell death activity via interacting with the pro-apoptotic gene Bax. Grouper fin cells (GF-1) carrying EGFP-Bal-xL and EGFP-Bcl-2 fused genes were selected, established in cell culture, and used to examine the involvement of Bcl-2 and Bcl-xL overexpression in protection of GF-1 cells from the effects of the giant sea perch iridovirus (GSIV) ST kinase gene. Using the TUNEL assay, we found that EGFP-Bcl-2 and EGFP-Bcl-xL reduced GSIV ST kinase-induced apoptosis to 20% all at 24 h and 48 h post-transfection (pt). Also, Bcl-2 and Bcl-xL substantially reduced the percentage of cells with GSIV ST kinase-induced loss of mitochondrial membrane potential (Δψps) at 24 and 48 hpt, respectively, and this reduction correlated with a 30% and 50% enhancement of host cell viability at 24 and 48 hpt as compared with vector control. Moreover, analysis of the effect of Bcl-2 and Bcl-xL interaction with Bax targeted to mitochondria during ST kinase expression at 48 hpt found that Bcl-2 and Bcl-xL also interacted with Bax to block cytochrome c release. Finally, Bcl-2 and Bcl-xL overexpression caused blockage of ST kinase function at 48 hpt, which was correlated with preventing caspase-9 and -3 cleavage and activation, thereby blocking downstream death signaling events. Taken together, our results suggest that the ST kinase-induced Bax/mitochondria-mediated cell death pathway can be blocked by the interaction of Bcl-2 and Bcl-xL with Bax to inhibit cytochrome c release during MMP loss. This rescue activity also correlated with inhibition of caspase-9 and -3 activation, thereby enhancing cell viability.

We report here the complete genome sequence of a megalocytivirus strain, GSIV-K1, isolated from a farmed giant sea perch ( Lates calcarifer ) in Kaohsiung, Taiwan. GSIV-K1 causes mortality in farmed marine fish, including giant sea perch and groupers. The genome sequence is nearly identical to the genome of the orange-spotted grouper iridovirus.

Gankyrin is a small ankyrin-repeat protein that previous research has confirmed to be overexpressed in hepatocellular carcinoma (HCC). Although relevant literature has reported on gankyrin functions in cellular proliferation and tumorigenesis, the exact role of gankyrin is poorly understood in animal model systems. This study analyzed hepatic lipid accumulation in gankyrin transgenic (GK) zebrafish. Bromodeoxyuridine (BrdU)-positive cells were predominantly increased in the liver bud of GK larvae, indicating that gankyrin functionally promoted cell proliferation at the larval stage in GK fish. However, over 90% of the viable GK adults showed an increased lipid content, leading in turn to liver steatosis. Liver histology and oil red O staining also indicated the accumulation of fatty droplets in GK fish, consistent with the specific pathological features of severe steatosis. Molecular analysis revealed that gankyrin overexpression induced hepatic steatosis and modulated the expression profiles of four hepatic microRNAs, miR-16, miR-27b, miR-122, and miR-126, and 22 genes involved in lipid metabolism. Moreover, significantly increased hepatic cell apoptosis resulted in liver damage in GK adults, leading to liver failure and death after approximately 10months. This study is the first to report gankyrin as a potential link between microRNAs and liver steatosis in zebrafish.

The infectious pancreatic necrosis virus (IPNV) belongs to the Birnaviridae family of viruses and causes acute contagious diseases in a number of economically important freshwater and marine fish. In this study, we infected zebrafish embryonic cells (ZF4) with IPNV and analyzed the gene expression patterns of normal and infected cells using quantitative real-time PCR. We identified a number of immune response genes, including ifna, ifng, mx, irf1, irf2, irf4, tnfa, tnfb, il-1b, il-15, il-26, ccl4 and mmp family genes, that are induced after viral infection. Transcriptional regulators, including cebpb, junb, nfkb and stat1, stat4 and stat5, were also upregulated in IPNV-infected cells. In addition, we used Pathway Studio software to identify TNFα as having the greatest downstream influence among these altered genes. Treating virus-infected cells with an siRNA targeting TNFα inhibited NF-κB expression. To further interrupt the TNFα/NF-κB-mediated pathway, the expression levels of cytokines and metalloproteinases were inhibited in IPNV-infected cells. These data suggest that, during IPNV infection, the expression of cytokines and metalloproteinases might be initiated through the TNFα/NF-κB-mediated pathway. The modulation of TNFα/NF-κB-related mechanisms may provide a therapeutic strategy for inhibiting viral infection in teleosts.

The betanodavirus non-structural protein B2 is a newly discovered necrotic death factor with a still unknown role in regulation of mitochondrial function. In the present study, we examined protein B2-mediated inhibition of mitochondrial complex II activity, which results in ATP depletion and thereby in a bioenergetic crisis in vitro and in vivo. Expression of protein B2 was detected early at 24 h postinfection with red-spotted grouper nervous necrosis virus in the cytoplasm. Later B2 was found in mitochondria using enhanced yellow fluorescent protein (EYFP) and immuno-EM analysis. Furthermore, the B2 mitochondrial targeting signal peptide was analyzed by serial deletion and specific point mutation. The sequence of the B2 targeting signal peptide ((41)RTFVISAHAA(50)) was identified and its presence correlated with loss of mitochondrial membrane potential in fish cells. Protein B2 also was found to dramatically inhibit complex II (succinate dehydrogenase) activity, which impairs ATP synthesis in fish GF-1 cells as well as human embryonic kidney 293T cells. Furthermore, when B2 was injected into zebrafish embryos at the one-cell stage to determine its cytotoxicity and ability to inhibit ATP synthesis, we found that B2 caused massive embryonic cell death and depleted ATP resulting in further embryonic death at 10 and 24 h post-fertilization. Taken together, our results indicate that betanodavirus protein B2-induced cell death is due to direct targeting of the mitochondrial matrix by a specific signal peptide that targets mitochondria and inhibits mitochondrial complex II activity thereby reducing ATP synthesis.

The RNA nervous necrosis virus induces necrotic cell death in fish; however, the molecular mechanism remains unknown. In this study, we demonstrated that beta-nodavirus-induced mitochondria-mediated dependent cell death is through newly synthesized protein dependent pathway in replication cycle. We determined that newly synthesized protein dependent pathway is required for red-spotted grouper nervous necrosis virus (RGNNV)-induced cell death. UV irradiation of the virus effectively blocked viral replication and cell death. Next, RGNNV RNA-dependent RNA polymerase (RdRp or protein A) was cloned and its involvement in RNA genome replication and viral protein synthesis was analyzed. Protein A was initially expressed 48 h post-infection and localized to the cytoplasm. Knockdown of protein A expression completely blocked viral genomic replication and expression of viral protein expression RNA1 small hairpin RNA (shRNA) producing cell lines, which coincided with inhibition of phosphatidylserine exposure, mitochondria-mediated death signaling, and increased cell viability 72 h post-infection. Furthermore, RGNNV-induced mitochondria-mediated caspase-3-independent necrotic cell death is dependent on viral synthesized protein dependent pathway at the middle-late replication stage. Taken together, for instance these results suggested that RGNNV induces cell death may require newly synthesized protein for triggering host mitochondria-mediated cell death. These findings may provide new insights into RNA viral pathogenesis.

Aquatic birnavirus induces post-apoptotic necrotic cell death via a newly synthesized protein-dependent pathway. However, the involvement of viral genome-encoded protein(s) in this death process remains unknown. In the present study, we demonstrated that the submajor capsid protein, VP3, up-regulates the pro-apoptotic protein, Bad, in fish and mouse cells. Western blot analysis revealed that VP3 was expressed in CHSE-214 cells at 4 h post-infection (pi), indicating an early role during viral replication. We cloned the VP3 gene and tested its function in fish and mouse cells; VP3 overexpression induced apoptotic cell death by TUNEL assay. In addition, it up-regulated Bad gene expression in zebrafish ZLE cells by threefold at 12 h post-transfection (pt) and in mouse NIH3T3 cells by tenfold at 24 h pt. VP3 up-regulation of Bad expression altered mitochondria function, inducing mitochondrial membrane potential (MMP) loss and activating initiator caspase-9 and effector caspase-3. Furthermore, reduced Bad expression (65% reduction), MMP loss (up to 40%), and enhanced cell viability (up to 60%) upon expression of VP3 antisense RNA in CHSE-214 cells at 24 h post-IPNV infection was observed. Finally, overexpression of the anti-apoptotic gene, zfBcl-xL, reduced VP3-induced apoptotic cell death and caspase-3 activation at 24 h in fish cells. Taken together, these results suggest that aquatic birnavirus VP3 induces apoptosis via up-regulation of Bad expression and mitochondrial disruption, which activates a downstream caspase-3-mediated death pathway that is blocked by zfBcl-xL.

Aquatic birnavirus induces necrotic cell death by an ill-understood process. Presently, we demonstrate that infectious pancreatic necrosis virus (IPNV) induces post-apoptotic necrotic cell death through loss of mitochondrial membrane potential (MMP) followed by caspase-3 activation in CHSE-214 cells. Progressive phosphatidylserine externalization was observed at 6 h post-infection (p.i.). This was followed by the development of bulb-like vesicles (bleb formation) at 8 h p.i. Progressive loss of MMP was also observed in IPNV-infected CHSE-214 cells beginning at 6 h p.i. At 8 h and 12 h p.i., IPNV-infected cells demonstrated a dramatic increase in MMP loss, rapid entry into necrotic cell death, and activation of caspase-9 and -3. Additionally, treatment with an inhibitor of MMP loss, bongkrekic acid, an adenine nucleotide translocase inhibitor, blocked IPNV-induced PS exposure and MMP loss, as well as reduced the activation of caspase-3. Taken together, our results suggest that IPNV induces apoptotic cell death via loss of MMP, thereby triggering secondary necrosis and caspases-3 activation. Furthermore, this death-signaling pathway is disrupted by bongkrekic acid in fish cells, indicating that this drug may serve to modulate IPNV-induced pathogenesis.

Previous studies have shown that GSIV induces apoptotic cell death through upregulation of the pro-apoptotic genes Bax and Bak in Grouper fin cells (GF-1 cells). However, the role of viral genome-encoded protein(s) in this death process remains unknown. In this study, we demonstrated that the Giant seaperch iridovirus (GSIV) genome encoded a serine/threonine kinase (ST kinase) protein, and induced apoptotic cell death via a p53-mediated Bax upregulation approach and a downregulation of Bcl-2 in fish cells. The ST kinase expression profile was identified through Western blot analyses, which indicated that expression started at day 1 h post-infection (PI), increased up to day 3, and then decreased by day 5 PI. This profile indicated the role of ST kinase expression during the early and middle phases of viral replication. We then cloned the ST kinase gene and tested its function in fish cells. The ST kinase was transiently expressed and used to investigate possible novel protein functions. The transient expression of ST kinase in GF-1 cells resulted in apoptotic cell features, as revealed with Terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling (TUNEL) assays and Hoechst 33258 staining at 24 h (37 %) and 48 h post-transfection (PT) (49 %). Then, through studies on the mechanism of cell death, we found that ST kinase overexpression could upregulate the anti-stress gene p53 and the pro-apoptotic gene Bax at 48 h PT. Interestingly, this upregulation of p53 and Bax also correlated to alterations in the mitochondria function that induced loss of mitochondrial membrane potential (MMP) and activated the initiator caspase-9 and the effector caspase-3 in the downstream. Moreover, when the p53-dependent transcriptional downstream gene was blocked by a specific transcriptional inhibitor, it was found that pifithrin-α not only reduced Bax expression, but also averted cell death in GF-1 cells during the ST kinase overexpression. Taken altogether, these results suggested that aquatic GSIV ST kinase could induce apoptosis via upregulation of p53 and Bax expression, resulting in mitochondrial disruption, which activated a downstream caspases-mediated cell death pathway.

Fish nodaviruses are causative agents of viral nervous necrosis (VNN) disease, which is also known as viral encephalopathy and retinopathy ( VER ). In the past two decades, VNN has caused mass mortality in many species of cultured marine fish worldwide. Fish nodavirus is a nonenveloped icosahedral virion with diameter of 25–30 nm, containing two single-stranded, positive-sense genomic RNAs, and is classified as the Betanodavirus of Nodaviridae . There are four genotypes of betanodavirus with different optimal growth temperatures and different host ranges. In this chapter, the characteristics of the betanodavirus, the phylogenic relationship, the interaction between virus and host fish, the transmission pathways, the progression of viral infection, viral replication cycle, viral protein-induced cytopathogenesis, the diagnosis and control strategies are carefully reviewed and discussed.

The self-destruction of cells infected with viruses undergoes the process of apoptosis generally to restrict infection and the spread of viral progeny. To avoid infection host has evolved interconnected complex defence network that comprises innate and acquired immune response. Mitochondria being considered as powerhouse of a cell is not limited to only energy production, but mitochondria perform various other functions in (disease, apoptosis and host innate immune system) which make them absolutely indispensable to the cell. This makes them a target of almost all the invading pathogens including viruses. Therefore being a multifunctional organelle, the viruses choose mitochondria as a favourite organelle as they can easily take control of the whole cell and make it to promote or block apoptosis as per their need.

Nervous necrosis virus (NNV)-induced, host cell apoptosis mediates secondary necrosis by an ill-understood process. In this study, redspotted grouper nervous necrosis virus (RGNNV) is shown to induce mitochondria-mediated necrotic cell death in GL-av cells (fish cells) via cytochrome c release, and anti-apoptotic proteins are shown to protect these cells from death. Western blots revealed that cytochrome c release coincided with disruption of mitochondrial ultrastructure and preceded necrosis, but did not correlate with caspases activation. To identify the mediator(s) of this necrotic process, a protein synthesis inhibitor (cycloheximide; CHX; 0.33 microg/ml) was used to block cytochrome c release as well as PS exposure and mitochondrial membrane permeability transition pore (MMP) loss. CHX (0.33 microg/ml) completely blocked viral protein B2 expression, and partly blocked protein A, protein alpha, and a pro-apoptotic death protein (Bad) expression. Overexpression of B2 gene increased necrotic-like cell death up to 30% at 48 h post-transfection, suggesting that newly synthesized protein (B2) may be involved in this necrotic process. Finally, necrotic death was prevented by overexpression of Bcl-2 family proteins, zfBcl-x(L) and xfMcl-1a. Thus, new protein synthesis and release of cytochrome c are required for RGNNV-induced necrotic cell death, which can be blocked by anti-apoptotic Bcl-2 members.

Virus infections of mammalian and animal cells consist of a series of events. As intracellular parasites, viruses rely on the use of host cellular machinery. Through the use of cell culture and molecular approaches over the past decade, our knowledge of the biology of aquatic viruses has grown exponentially. The increase in aquaculture operations worldwide has provided new approaches for the transmission of aquatic viruses that include RNA and DNA viruses. Therefore, the struggle between the virus and the host for control of the cell's death machinery is crucial for survival. Viruses are obligatory intracellular parasites and, as such, must modulate apoptotic pathways to control the lifespan of their host to complete their replication cycle. This paper updates the discussion on the detailed mechanisms of action that various aquatic viruses use to induce cell death pathways in the host, such as Bad-mediated, mitochondria-mediated, ROS-mediated and Fas-mediated cell death circuits. Understanding how viruses exploit the apoptotic pathways of their hosts may provide great opportunities for the development of future potential therapeutic strategies and pathogenic insights into different aquatic viral diseases.

Giant seaperch iridovirus (GSIV) induces cell death by an unknown mechanism. We postulated that this mechanism involves mitochondria-mediated cell death. Cell viability assays revealed a steady increase in dead grouper fin cells (GF-1) after GSIV infection, from 11% at 2 days post-infection (dpi) to 67% at 5 dpi. Annexin V/PI staining revealed GSIV infection induced apoptosis in a steadily increasing fraction of cells, from 4% at 1 dpi to 29% at 5 dpi. Furthermore, post-apoptotic necrosis was apparent at 4 and 5 dpi in the late replication stage. In the early replication stage, JC-1 dye revealed mitochondrial membrane potential (ΔΨm) loss in 42% of infected cells at 1 dpi, increasing to 98% at 3 dpi. Phosphatidylserine (PS) exposure and loss of ΔΨm from apoptosis/necrosis was attenuated by treatment with the adenine nucleotide translocase inhibitor bongkrekic acid (BKA) and the protein synthesis inhibitor cyclohexamide (CHX). These data suggest GSIV induces GF-1 apoptotic/necrotic cell death through pathways that require newly synthesized protein and involve the mitochondrial function.

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.

VP5, a 5′-terminal, small open reading frame in segment A of the aquatic birnavirus (infectious pancreatic necrosis virus, IPNV) genome, encodes a 17-kDa nonstructural protein. We previously reported apoptosis induced by IPNV in a fish cell line. In the present study, we cloned and identified VP5 and tested its function. Comparisons of the amino acid sequence of VP5 with well-known Bcl-2 family member proteins showed that the VP5 protein contains Bcl-2 homology (BH) domains BH1, BH2, BH3, and BH4 but without the transmembrane region. VP5-stable clones enhanced viability, prevented membrane blebbing, delayed DNA internucleosomal cleavage, and decreased virus titer during IPNV infection but, when deleted, BH domains 1 and 2 could lose the preventable ability. In addition, VP5 was demonstrated to be able to enhance or assist in maintaining the functional half-life of survival factor Mcl-1 and regulate specific viral protein expression during the early replication cycle. Finally, we found that VP5 was capable of enhancing cell viability when cells were exposed to UV irradiation. In summary, these results suggest that the aquatic birnavirus may utilize a notable strategy via VP5 to regulate the host apoptosis-off system for enhancing progeny production.

A Bcl-2 related family member, Bad, promotes cell death, and its function is regulated by phosphorylation. In this study, we show how the IPNV elicits the induction of Bad gene expression and promotes host apoptotic death. Anti-IPNV-E1S polyclonal and anti-VP3 monoclonal antibodies are used to neutralize the virus that blocks the prime death signal via the virus receptor. In the viability assay, each antibody could also enhance cell viability during IPNV infection. We tested tyrosine kinase inhibitors on IPNV-infected cells in order to assess their effect on blocking the death signal. With 100 microg/ml genistein treatment, Bad-like gene expression was blocked, either by rescuing the IPNV-infected CHSE-214 cells or by blocking internucleosomal DNA cleavage; but the tyrphostin group did not block Bad expression. For CHSE-214 cells, treatment with the protein synthesis-inhibitor, cycloheximide (1microg/ml), blocked new protein synthesis via activated tyrosine kinase during IPNV infection. We found that Bad protein expression could be blocked, and apoptotic death prevented. Together, these results demonstrate that the IPNV exerts up-regulation of a pro-apoptotic death gene (Bad), the expression of which serves to trigger apoptotic cell death. Our data also suggests that the IPNV induces apoptotic death via a viral receptor which triggers death effector Bad gene expression, possibly through a tyrosine kinase-dependent pathway.

The phosphatidylserine receptor (PSR) recognizes a surface marker on apoptotic cells and initiates engulfment. This receptor is important for effective apoptotic cell clearance and maintains normal tissue homeostasis and regulation of the immune response. However, the regulation of PSR expression remains poorly understood. In this study, we determined that interferon regulatory factor-1 (IRF-1) was dramatically upregulated upon viral infection in the fish cell. We observed apoptosis in virus-infected cells and found that both PSR and IRF-1 increased simultaneously. Based on a bioinformatics promoter assay, IRF-1 binding sites were identified in the PSR promoter. Compared to normal viral infection, we found that PSR expression was delayed, viral replication was increased and virus-induced apoptosis was inhibited following IRF-1 suppression with morpholino oligonucleotides. A luciferase assay to analyze promoter activity revealed a decreasing trend after the deletion of the IRF-1 binding site on PSR promoter. The results of this study indicated that infectious pancreatic necrosis virus (IPNV) infection induced both the apoptotic and interferon (IFN) pathways, and IRF-1 was involved in regulating PSR expression to induce anti-viral effects. Therefore, this work suggests that PSR expression in salmonid cells during IPNV infection is activated when IRF-1 binds the PSR promoter. This is the first report to show the potential role of IRF-1 in triggering the induction of apoptotic cell clearance-related genes during viral infection and demonstrates the extensive crosstalk between the apoptotic and innate immune response pathways.

The importance of the Bcl-2 family proteins in normal vertebrate embryogenesis is being recognized; however, their regulatory mechanism is poorly understood. We report here the cloning and characterization of a novel zebrafish Bcl-2 family protein, zfBLP1. The zfBLP1 cDNA is 1942 nucleotides long, encoding a polypeptide of 238 amino acids. The primary sequence of zfBLP1 shares 50% identity to human Bcl-XL, and contains all four conserved BH domains of the Bcl-2 family proteins. Primary sequence analysis identified a consensus ER retention signal at the C-terminal end of zfBLP1. Northern blot analysis indicated that there were two major and two minor zfBLP1 mRNA species expressed during embryonic development. Among the two major mRNA species, the short one, approx. 3 kb in size, was expressed throughout embryonic development, while the long one, approx. 7 kb long, was not detectable until the gastrula stage. These results suggest that zfBLP1 is a novel Bcl-2 family protein under complicated regulations, and is likely to play an important role in zebrafish oogenesis and embryogenesis.

Morphologically, apoptotic cells are characterized by highly condensed membrane blebbing and formation of apoptotic bodies. Recently, we reported that apoptosis precedes necrosis in a fish cell line infected with infectious pancreatic necrosis virus (IPNV). In the present study, we tested the possibility that nontypical apoptosis is a component of IPNV-induced fish cell death. A variant type of green fluorescent protein (EGFP) was expressed in a fish cell line such that EGFP served as a protein marker for visualizing dynamic apoptotic cell morphological changes and for tracing membrane integrity changes during IPNV infection. Direct morphological changes were visualized by fluorescence microscopy by EGFP in living cells infected with IPNV. The nontypical apoptotic morphological change stage occurred during the pre-late stage (6 to 7 h postinfection). Nontypical apoptotic features, including highly condensed membrane blebbing, occurred during the middle apoptotic stage. At the pre-late apoptotic stage, membrane vesicles quickly formed, blebbed, and were finally pinched off from the cell membrane. At the same time, at this pre-late apoptotic stage, apoptotic cells formed unique small holes in their membranes that ranged from 0.39 to 0.78 μm according to examination by scanning electron microscopy and immunoelectron microscopy. Quantitation of the intra- and extracellular release of EGFP by CHSE-214-EGFP cells after IPNV infection was done by Western blotting and fluorometry. Membrane integrity was quickly lost during the late apoptotic stage (after 8 h postinfection), and morphological change and membrane integrity loss could be prevented and blocked by treatment with apoptosis inhibitors such as cycloheximide, genistein, and EDTA before IPNV infection. Together, these findings show the apoptotic features at the onset of pathology in host cells (early and middle apoptotic stages), followed secondarily by nontypical apoptosis (pre-late apoptotic stage) and then by postapoptotic necrosis (late apoptotic stage), of a fish cell line. Our results demonstrate that nontypical apoptosis is a component of IPNV-induced fish cell death.

Infectious pancreatic necrosis virus (IPNV) causes an acute, contagious disease in a number of economically important fish species (Pilcher & Fryer 1980). It is a member of the Birnaviridae (Brown 1986). In this study, the present authors first characterized the process of fish cell damage caused by IPNV infection in cultured cells, and found that it induced fragmentation of chromosomal DNA into oligonucleosomes and also caused nuclear fragmentation by secondary necrosis.

An investigation of virus-specific protein maturation in infectious pancreatic necrosis virus (IPNV) infected Chinook salmon embryo cells (CHSE-214) was undertaken. The precursor protein (pVP2‐1) of the major mature capsid protein (VP2) was processed sequentially from pVP2‐1 to pVP2‐ 2 and VP2. Experiments using serine proteinase inhibitors showed that the maturation of the VP2 was blocked in the pVP2‐1 post-translational cleavage steps. A protinin, a potent proteinase inhibitor, at 800 μ gm l ‐1 blocked pVP2‐2 to VP2 and the cleavage of VP4 (28 kDa) to VP4‐1 (25 kDa). Therefore, our data showed that the maturation of the capsid protein (VP2) and cleavage of VP4 (NS proteinase) can be blocked by serine proteinase inhibitors.

Aquaculture is one of the most important economic activities in Asia and is presently the fastest growing sector of food production in the world. Explosive increases in global fish farming have been accompanied by an increase in viral diseases. Viral infections are responsible for huge economic losses in fish farming, and control of these viral diseases in aquaculture remains a serious challenge. Recent advances in biotechnology have had a significant impact on disease reduction in aquaculture. RNAi is one of the most important technological breakthroughs in modern biology, allowing us to directly observe the effects of the loss of specific genes in living systems. RNA interference technology has emerged as a powerful tool for manipulating gene expression in the laboratory. This technology represents a new therapeutic approach for treating aquatic diseases, including viral infections. RNAi technology is based on a naturally occurring post-transcriptional gene silencing process mediated by the formation of dsRNA. RNAi has been proven widely effective for gene knockdown in mammalian cultured cells, but its utility in fish remains unexplored. This review aims to highlight the RNAi technology that has made significant contributions toward the improvement of aquatic animal health and will also summarize the current status and future strategies concerning the therapeutic applications of RNAi to combat viral disease in aquacultured organisms.

Iridoviruses are large DNA viruses that infect invertebrates and poikilothermic vertebrates, such as insects, fish, amphibians, reptiles, crustaceans, and mollusks. The emergence of deadly iridoviral disease in aquatic fish has led to a growing interest in the mechanism of iridovirus-induced host cell death. In this present, we found that infectious spleen and kidney necrosis virus (ISKNV) can trigger a host cellular death via ROS signaling in grouper fin (GF-1) cells. ISKNV infection can induce reactive oxygen species (ROS) production by using H2DCFDA assay at early replication stage. Then, this ROS signaling can upregulate the pro-apoptotic genes Bax and Bak expressions at middle replication stage. Moreover, ISKNV-induced ROS-mediated signals triggered the mitochondrial membrane potential (MMP) loss, which correlated to activate downstream caspases such as caspase-8, caspase-9 and caspase-3 at late replication stage. Final, we found that antioxidants treatment dramatically reduced ISKNV-induced host cellular death in GF-1 cells. Taken together our data show that ISKNV used a novel strategy to regulate the mitochondria/caspase-mediated cell death pathway via ROS signaling, which may provide new insight into DNA virus control and treatment.

Betanodaviruses cause viral nervous necrosis, an infectious neuropathological condition in fish that is characterized by necrosis of the central nervous system, including the brain and retina. This disease can cause mass mortality in larval and juvenile populations of several teleost species and is of global economic importance. The mechanism of brain and retina damage during betanodavirus infection is poorly understood. In this review, we will focus recent results that highlight betanodavirus infection-induced molecular death mechanisms in vitro. Betanodavirus can induce host cellular death and post-apoptotic necrosis in fish cells. Betanodavirus-induced necrotic cell death is also correlated with loss of mitochondrial membrane potential in fish cells, as this necrotic cell death is blocked by the mitochondrial membrane permeability transition pore inhibitor bongkrekic acid and the expression of the anti-apoptotic Bcl-2 family member zfBcl-xL. Moreover, this mitochondria-mediated necrotic cell death may require a caspase-independent pathway. A possible cellular death pathway involving mitochondrial function and the modulator zfBcl-xs is discussed which may provide new insights into the necrotic pathogenesis of betanodavirus.

Infectious pancreatic necrosis virus (IPNV) is a fish pathogen and the prototype of the Birnaviridae virus family (Dobos et al., 1979). IPNV causes infectious pancreatic necrosis, an acute and serious disease in juvenile salmonid fish worldwide (Hill and Way, 1995) Birnaviruses possess a bi-segmented, double-stranded RNA genome contained within a medium-sized, unenveloped, icosahedral capsid. The protein products of four unrelated major genes undergo various post-translational cleavage processes to generate three to five different structural proteins (Dobos, 1995). The largest of these proteins (VP1; 90–110 kDa) is encoded by the smaller segment B RNA (Wu et al., 1998). The larger genome segment A contains a large open reading frame (ORF; which encodes VP3 [32-kDa; a minor capsid protein] [Wu et al., 1998], VP4 [28 kDa], and VP2 [the major capsid protein; 46 kDa] [Wu et al., 1998]) and a small ORF, which encodes VP5 (17 kDa; a non-structural protein with antiapoptotic activity) (Hong et al., 2002a; Hong and Wu, 2002c).

The role of oxidative stress in the pathogenesis of RNA nervous necrosis virus infection is still unknown. Red-spotted grouper nervous necrosis virus (RGNNV) induced free radical species (ROS) production at 12–24 h post-infection (pi; early replication stage) in fish GF-1 cells, and then at middle replication stage (24–48 h pi), this ROS signal may upregulate some expressions of the anti-oxidant enzymes Cu/Zn SOD and catalase, and eventually expression of the transcription factor Nrf2. Furthermore, both antioxidants diphenyliodonium and N-acetylcysteine or overexpression of zebrafish catalase in GF-1 cells also reduced ROS production and protected cells for enhancing host survival rate due to RGNNV infection. Furthermore, localization of ROS production using esterase activity and Mitotracker staining assays found that the ROS generated can affect mitochondrial morphology changes and causes ΔΨ loss, both of which can be reversed by antioxidant treatment. Taken together, our data suggest that RGNNV induced oxidative stress response for playing dual role that can initiate the host oxidative stress defense system to upregulate expression of antioxidant enzymes and induces cell death via disrupting the mitochondrial morphology and inducing ΔΨ loss, which can be reversed by anti-oxidants and zfcatalase, which provide new insight into betanodavirus-induced ROS-mediated pathogenesis.

The aquatic birnavirus induces mitochondria-mediated cell death in fish; however, the molecular mechanism remains unknown. In the present study, we demonstrated that aquatic birnavirus-induced mitochondria-mediated cell death is regulated by the anti-apoptotic Bcl-2 family member, zfBcl-xL, which is anti-apoptotic and enhances host cell viability. First, CHSE-214 cells carrying EGFP-zfBcl-xL fused genes were selected, established in culture, and used to examine the involvement of zfBcl-xL in host cell protection from the effects of viral infection. EGFP-zfBcl-xL was found to prevent infectious pancreatic necrosis virus (IPNV)-induced phosphatidylserine exposure up to 40% at 12 h and 24 h post-infection (p.i.), block IPNV-induced loss of mitochondrial membrane potential (ΔΨm), and enhance host viability at the middle and late replication stages. In addition, zfBcl-xL overexpression prevented IPNV-induced caspase-9 activation up to 25% and 85% at the middle (12 h p.i.) and late (24 h p.i.) replication stages without affecting expression of viral proteins such as VP3 (as a viral death protein) protein. In the present study, we demonstrated that aquatic birnavirus-induced cell death is prevented by the anti-apoptotic Bcl-2 family member, zfBcl-xL, which enhances host cell viability through blockage of mitochondrial disruption and caspase-9 activation.

Infectious pancreatic necrosis virus (IPNV) can induce Bad-mediated apoptosis followed by secondary necrosis in fish cells, but it is not known how these two types of cell death are regulated by IPNV. We found that IPNV infection can regulate Bad/Bid-mediated apoptotic and Rip1/ROS-mediated necrotic death pathways via the up-regulation of TNFα in zebrafish ZF4 cells. Using a DNA microarray and quantitative RT-PCR analyses, two major subsets of differentially expressed genes were characterized, including the innate immune response gene TNFα and the pro-apoptotic genes Bad and Bid. In the early replication stage (0-6 h post-infection, or p.i.), we observed that the pro-inflammatory cytokine TNFα underwent a rapid six-fold induction. Then, during the early-middle replication stages (6-12 h p.i.), TNFα level was eight-fold induction and the pro-apoptotic Bcl-2 family members Bad and Bid were up-regulated. Furthermore, specific inhibitors of TNFα expression (AG-126 or TNFα-specific siRNA) were used to block apoptotic and necrotic death signaling during the early or early-middle stages of IPNV infection. Inhibition of TNFα expression dramatically reduced the Bad/Bid-mediated apoptotic and Rip1/ROS-mediated necrotic cell death pathways and rescued host cell viability. Moreover, we used Rip1-specific inhibitors (Nec-1 and Rip1-specific siRNA) to block Rip1 expression. The Rip1/ROS-mediated secondary necrotic pathway appeared to be reduced in IPNV-infected fish cells during the middle-late stage of infection (12-18 h p.i.). Taken together, our results indicate that IPNV triggers two death pathways via up-stream induction of the pro-inflammatory cytokine TNFα, and these results may provide new insights into the pathogenesis of RNA viruses.

Whether viral pathogens that induce ER stress responses benefit the host or the virus remains controversial. In this study we show that betanodavirus induced ER stress responses up-regulate GRP78, which regulates the viral replication and host cellular mitochondrial-mediated cell death. Betanodavirus (redspotted grouper nervous necrosis virus, RGNNV) infection resulted in the following increased ER stress responses in fish GF-1 grouper fin cells: (1) IRE-1 and ATF-6 sensors at 48 h post-infection (p.i.) that up-regulated chaperone protein GRP78; (2) activation of caspase-12; and (3) PERK phosphorylation and down-regulation of Bcl-2. Analyses of GRP78 functions during viral replication using either loss-of-function or gain-of-function approaches showed that GRP78 over-expression also enhanced viral replication and induced cell death. Then, we found that zfGRP78 localization gradually increased in mitochondria after RGNNV infection by EGFP tagging approach. Furthermore, zfGRP78 can interact with viral RNA-dependent RNA polymerase (RdRp) by using immunofluorescent and immunoprecipitation assays. Finally, we found that blocking GRP78-mediated ER signals can reduce the viral death factors protein α and protein B2 expression and decrease the Bcl-2 down-regulation mediated mitochondria-dependent cell death, which also enhances host cellular viability. Taken together, our results suggest that RGNNV infection and expression can trigger ER stress responses, which up-regulate the chaperone GRP78 at early replication stage. Then, GRP78 can interact with RdRp that may enhance the viral replication for increasing viral death factors’ expressions at middle-late replication stage, which can enhance mitochondrial-mediated cell death pathway and viral spreading. These results may provide new insights into the mechanism of ER stress-mediated cell death in RNA viruses.

To generate a zebrafish model of inducible male sterility, we expressed an Escherichia coli nitroreductase (Ntr) gene in the male germ line of zebrafish. The Ntr gene encodes an enzyme that can convert prodrugs such as metronidazole (Met) to cytotoxins. A fusion protein eGFP:Ntr (fusing Ntr to eGFP) under control of approximately 2 kb putative promoters of the zebrafish testis-specific genes, A-kinase anchoring protein-associated protein (Asp), outer dense fibers (Odf), and sperm acrosomal membrane-associated protein (Sam) was expressed in the male germ line. Three independent and four compound transgenic zebrafish lines expressing eGFP:Ntr were established. Female carriers were fertile, while males exhibited different levels of sterility and appeared normal, otherwise. Developmental analysis shows that germ cells survived and testes were normal before Met treatment, but that the testes of all male transgenic zebrafish exhibited variously depleted prospermatogonia after Met treatment. Particularly in a triple-transgenic line, Tg(AOS-eGFP:Ntr)[Tg(Asp-eGFP:Ntr; Odf-eGFP:Ntr; Sam-eGFP:Ntr)], the transgenic males had very small testes that were virtually devoid of germ cells, and the residual germ cells had almost completely disappeared after 2 weeks of Met treatment. These zebrafish transgenic lines show the complete testis specificity of inducible male sterility after Met treatment and reveal a period of the Ntr/Met ablation activity just prior to formation of the definitive adult spermatogonial cell population. This study demonstrates that combined genetic and pharmacological methods for developing an "infertile breeding technology" have practical application in controlling genetically modified (GM) fish breeding and meet the standards of biological and environment safety for other GM species.

The functions of the Betanodavirus non-structural protein B1 is still unknown. We examined B1 expression patterns and investigated novel cell death regulatory functions for this viral protein following RGNNV infection in fish cells. The B1 gene (336 nt) was cloned from the redspotted grouper nervous necrosis virus (RGNNV) genome. B1 mRNA was rapidly expressed in the fish cells from viral RNA3 at 12 h post-infection (p.i.). At the protein level, expression was low at 12 h p.i., and then increased rapidly between 24 h and 72 h p.i. In RGNNV-infected, B1-containing fish cells, over expression of RGNNV B1 reduced Annexin-V positive cells by 50% and 65% at 48 h and 72 h p.i., respectively, and decreased loss of mitochondrial membrane potential (MMP) by 20% and 70% at 48 h and 72 h p.i., respectively. Finally, B1 knockdown during RGNNV infection using anti-sense RNA increased necrotic cell death and reduced cell viability during the early replication cycle (24 h p.i.). Our results suggest that B1 is an early expression protein that has an anti-necrotic cell death function which reduces the MMP loss and enhances viral host cell viability. This finding provides new insights into RNA viral pathogenesis and disease control.

Our previous studies found that infectious pancreatic necrosis virus (IPNV) induces host apoptotic cell death, possibly through a newly synthesized protein trigger. Here, we examine whether IPNV infection can induce NF-kappaB activation through tyrosine kinase signalling of CHSE-214 cell death (host cell death). Using the electrophoretic mobility shift assay (EMSA) to detect transcription factor activation, we found that NF-kappaB is apparently activated 6-8 h post-IPNV infection. Using genistein (100 microg mL(-1); a tyrosine kinase inhibitor) to determine whether NF-kappaB activation requires tyrosine kinase activation, we found genistein blocks NF-kappaB activation at 8 h post-infection (p.i), and either enhances cell viability up to 50% at 12 h p.i. or blocks DNA fragmentation at 24 h p.i. Furthermore, the proteasome inhibitors PSI-I and PSI-II (both at 40 microm) also effectively blocked the NF-kappaB activation as well as stimulating a 30% increase in cell viability (30% decrease in apoptosis) at 8 and 12 h p.i. Taken together our data suggest that IPNV may induce NF-kappaB activation through tyrosine kinase signalling, which may be associated with induction of apoptosis.

Betanodavirus, a small positive-sense bipartite RNA virus notoriously affecting marine aquaculture worldwide has been extensively studied in vitro. However, impending studies in elucidating virus-host interactions have been limiting due to the lack of appropriate animal disease models. Therefore, in this study, we have attempted to successfully establish NNV infection in zebrafish (Danio rerio) showing typical NNV symptoms and which could potentially serve as an in vivo model for studying virus pathogenesis. Zebrafish being already a powerful research tool in developmental biology and having its genome completely sequenced by the end of 2007 would expedite NNV research. We have observed viral titers peaked at 3 days post-infection and histological study showing lesions in brain tissues similar to natural host infection. Further, we used this infection model to study the acute and persistence infection during NNV infection. Interestingly, RT-PCR and immunoblotting assays revealed that the acute infection in larvae and juveniles is largely due to inactive interferon response as opposed to activated innate immune response during persistent infection in adult stage. This study is the first to demonstrate NNV infection of zebrafish, which could serve as a potential animal model to study virus pathogenesis and neuron degeneration research.