Molecular clone and characterization of c-Jun N-terminal kinases 2 from orange-spotted grouper, Epinephelus coioides

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.

Grouper TRADD Mediates Innate Antiviral Immune Responses and Apoptosis Induced by Singapore Grouper Iridovirus (SGIV) Infection

Tumor necrosis factor (TNF) receptor type 1-associated DEATH domain protein (TRADD) is a TNFR1-associated signal transducer and an essential component of the TNFR1 complex that is involved in activating both apoptotic and nuclear factor (NF)-κB pathways as an adaptor. It also is required for TNFR-1-initiated neuronal apoptosis following in vitro infection with virus as an essential component of the antiviral response. To date, few studies have investigated the function of TRADD in lower vertebrates and its antiviral response to DNA virus infection. In the present study, a TRADD gene (named as EcTRADD) from the orange-spotted grouper (Epinephelus coioides) was cloned and characterized. The full-length cDNA of EcTRADD consists of 1,370 base pairs (bp) and contains a 44 bp 5′-terminal untranslated region (UTR), a 450 bp 3′-UTR including a poly (A) tail, and an 876 bp open reading frame encoding a putative 291 amino acid protein. EcTRADD has two conserved domains of N-terminal domain (TRADD-N) and a death domain (DD). EcTRADD was detected in all examined tissues. EcTRADD was up-regulated in the spleen after infection with Singapore grouper iridovirus (SGIV). Subcellular localization analysis revealed that EcTRADD and EcTRADD-DD exhibited a clear pattern of discrete and interconnecting cytoplasmic filaments resembling the death-effector filaments, while EcTRADD-N was observed in the cytoplasm. After infection with SGIV, EcTRADD, and EcTRADD-DD were transferred to the nucleus. Overexpression of EcTRADD and its domains inhibited replication of SGIV in vitro. Both EcTRADD and EcTRADD-DD induced the caspase-dependent apoptosis in control and infected cells, while EcTRADD-N inhibited the apoptosis. Additionally, EcTRADD and EcTRADD-DD significantly promoted activation of NF-κB and reporter gene p53, whereas EcTRADD-N had no significant effect on p53. The results may provide new insights into the role of fish TRADD in fish virus infection.

Engineered cell lines for fish health research

As fish farming continues to increase worldwide, the related research areas of fish disease and immunology are also expanding, aided by the revolution in access to genomic information and molecular technology. The genomes of most fish species of economic importance are now available and annotation based on sequence homology with characterised genomes is underway. However, while useful, functional homology is more difficult to determine, there being a lack of widely distributed and well characterised reagents such as monoclonal antibodies, traditionally used in mammalian studies, to help with confirming functions and cellular interactions of fish molecules. In this context, fish cell lines and the possibility of their genetic engineering offer good prospects for studying functional genomics with respect to fish diseases. In this review, we will give an overview of available permanently genetically engineered fish cell lines, as cell-based reporter systems or platforms for expression of endogenous immune or pathogen genes, to investigate interactions and function. The advantages of such systems and the technical challenge for their development will be discussed.

Molecular cloning and characterization of FADD from the orange-spotted grouper (Epinephelus coioides)

Fas-associated protein with death domain (FADD) is the key adaptor protein that transmits apoptotic signals mediated by the main death receptors. Besides being an essential instrument in cell death, FADD is also implicated in proliferation, cell cycle progression, tumor development, inflammation, innate immunity, and autophagy. In the present study, a FADD homologue (EcFADD) from the orange-spotted grouper (Epinephelus coioides) was cloned and its possible role in fish immunity was analyzed. The full length cDNA of EcFADD contains 808 base pairs (bp), including a 573 bp open reading frame that encodes a 190 amino acid protein with a predicted molecular mass of 21.81 kDa. Quantitative real-time polymerase chain reaction analysis indicated that EcFADD was distributed in all examined tissues. The expression of EcFADD in the spleen of E. coioides was differentially up-regulated when challenged with Singapore grouper iridovirus (SGIV) or polyinosine-polycytidylic acid(poly[I:C]). EcFADD was abundantly distributed in both the cytoplasm and nucleus in grouper spleen (GS) and fathead minnow (FHM) epithelial cells. Over-expression of EcFADD inhibited SGIV infection and replication and SGIV-induced apoptosis. To achieve antiviral and anti-apoptosis activities, FADD promoted the activation of interferon-stimulated response element (ISRE) and type I interferon (IFN) genes in the antiviral IFN signaling pathway and inhibited activation of apoptosis-related transcription factors p53. Our results not only characterize FADD but also reveal new immune functions and the molecular mechanisms by which FADD responds to virus infection and virus-induced apoptosis.

c-Jun N-terminal kinases 3 (JNK3) from orange-spotted grouper, Epinephelus coioides, inhibiting the replication of Singapore grouper iridovirus (SGIV) and SGIV-induced apoptosis

C-Jun N-terminal kinases (JNKs), a subgroup of serine-threonine protein kinases that activated by phosphorylation, are involve in physiological and pathophysiological processes. JNK3 is one of JNK proteins involved in JNK3 signaling transduction. In the present study, two JNK3 isoforms, Ec-JNK3 X1 and Ec-JNK3 X2, were cloned from orange-spotted grouper, Epinephelus coioides. Both Ec-JNK3 X1 and Ec-JNK3 X2 were mainly expressed in liver, gill, skin, brain and muscle of juvenile grouper. The relative expression of Ec-JNK3 X2 mRNA was much higher in muscle and gill than that of Ec-JNK3 X1. Isoform-specific immune response to challenges was revealed by the expression profiles in vivo. Immunofluorescence staining indicated that JNK3 was localized in the cytoplasm of grouper spleen (GS) cells and shown immune response to SGIV infection in vitro. Over-expressing Ec-JNK3 X1 and/or Ec-JNK3 X2 inhibited the SGIV infection and replication and the SGIV-induced apoptosis. To achieve the antiviral and anti-apoptosis activities, JNK3 promoted the activation of genes ISRE and type I IFN in the antiviral IFN signaling pathway, and inhibited the activation of transcription factors NF-κB and p53 relating to apoptosis, respectively. Ec-JNK3 X2 showed stronger activities in antivirus and anti-apoptosis than that of Ec-JNK3 X1. Our results not only define the characterization of JNK3 but also reveal new immune functions and the molecular mechanisms of JNK3 on iridoviruses infection and the virus-induced apoptosis.

MKK7 confers different activities to viral infection of Singapore grouper iridovirus (SGIV) and nervous necrosis virus (NNV) in grouper

Mitogen-activated protein kinase 7 (MKK7) is one of the major stress-activated protein kinase (SAPK)-activating kinases in response to environmental or physiological stimuli. Here a MKK7 named as Ec-MKK7 was identified from orange-spotted grouper, Epinephelus coioides. The full-length cDNA of Ec-MKK7 was 1853 bp, with an open reading frame (ORF) of 1272 bp encoding a putative protein of 423 amino acids. A characteristic S-K-A-K-T motif was contained in the domain of dual-specificity protein kinase, mitogen-activated protein kinase kinase 7 (PKc_MKK7). Intracellular localization showed that Ec-MKK7 was localized in both the cytoplasm and the nucleus of grouper spleen (GS) and/or grouper brain (EAGB) cells. Moreover, Ec-MKK7 was universally expressed in all examined tissues and showed expression modulation to challenges of lipopolysacchride (LPS), Singapore grouper iridovirus (SGIV) and polyriboinosinic polyribocytidylic acid (poly I:C) in vivo. A gene targeting strategy over-expressing Ec-MKK7 was performed to examine the activities of MKK7 to viral infection in vitro. Our data showed that Ec-MKK7 was involved in the evasion and replication of SGIV but played an antiviral role to the infection of nervous necrosis virus (NNV). All results demonstrated that Ec-MKK7 could play important roles in grouper innate immunity and show distinct functions on virus infection.