Molecular cloning, subcelluar location and expression profile of signal transducer and activator of transcription 2 (STAT2) from turbot, Scophthalmus maximus

STAT2 negatively regulates RIG-I in the antiviral innate immunity of black carp

The signal transducer and activator of transcription 2 (STAT2), a downstream factor of type I interferons (IFNs), is a key component of the cellular antiviral immunity response. However, the role of STAT2 in the upstream of IFN signaling, such as the regulation of pattern recognition receptors (PRRs), remains unknown. In this study, STAT2 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized. The open reading frame (ORF) of bcSTAT2 comprises 2523 nucleotides and encodes 841 amino acids, which presents the conserved structure to that of mammalian STAT2. The dual-luciferase reporter assay and the plaque assay showed that bcSTAT2 possessed certain IFN-inducing ability and antiviral ability against both spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV). Interestingly, we detected the association between bcSTAT2 and bcRIG-I through co-immunoprecipitation (co-IP) assay. Moreover, when bcSTAT2 was co-expressed with bcRIG-I, bcSTAT2 obviously suppressed bcRIG-I-induced IFN expression and antiviral activity. The subsequent co-IP assay and immunoblotting (IB) assay further demonstrated that bcSTAT2 inhibited K63-linked polyubiquitination but not K48-linked polyubiquitination of bcRIG-I, however, did not affect the oligomerization of bcRIG-I. Thus, our data conclude that black carp STAT2 negatively regulates RIG-I through attenuates its K63-linked ubiquitination, which sheds a new light on the regulation of the antiviral innate immunity cascade in vertebrates.

Molecular characterization, expression analysis and subcellular location of the members of STAT family from spotted seabass (Lateolabrax maculatus)

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway is a pervasive intracellular signal transduction pathway, involving in biological processes such as cell proliferation, differentiation, apoptosis and immune regulation. In this study, seven STAT genes, STAT1, STAT1-like, STAT2, STAT3, STAT4, STAT5a and STAT5b, were identified and characterized in spotted seabass (Lateolabrax maculatus). Analyses of multiple sequence alignment, genomic organization, phylogeny and conserved synteny were conducted to infer the evolutionary conservation of these genes in the STAT family. The results of the bioinformatics analysis assumed that STAT1 and STAT1-like might be homologous to STAT1a and STAT1b, respectively. Furthermore, the expression of the seven genes were detected in eight tissues of healthy spotted seabass, which revealed that they were expressed in a variety of tissues, mainly in gill, spleen and muscle, and extremely under-expression in liver. The expression of the seven genes in gill, head-kidney, spleen and intestine were significantly induced by lipopolysaccharide (LPS) or Edwardsiella tarda challenge. The expression of most of the LmSTATs were up-regulated, and the highest expression levels at 12 h after LPS stimulation, however, the LmSTATs were down-regulated by E. tarda infection. The results of subcellular localization show that the native LmSTAT1, LmSTAT1-like, LmSTAT2, LmSTAT3 and LmSTAT5a were localized in the cytoplasm, but they were translocated into the nucleus after LPS stimulation. Whereas, LmSTAT4 and LmSTAT5b were translocation into the nucleus whether with LPS stimulation or not. Overall, this is the first study to systematically revealed the localization of STAT members in fish, and indicated that LmSTATs participate in the process of protecting the host from pathogens invasion in the form of entry into nucleus.

Molecular cloning, expression and functional analysis of STAT2 in orange-spotted grouper, Epinephelus coioides

Signal transducer and activator of transcription 2 (STAT2) is an important molecule involved in the type I interferon signaling pathway. To better understand the functions of STAT2 in fish immune response, a STAT2 gene from orange-spotted grouper (Epinephelus coioides) (EcSTAT2) was cloned and characterized in this study. EcSTAT2 encoded a 802-amino acid peptide which shared 99.5% and 91.5% identity with giant grouper (Epinephelus lanceolatus) and leopard coral grouper (Plectropomus leopardus), respectively. Amino acid alignment analysis showed that EcSTAT2 contained five conserved domains, including N-terminal protein interaction domain, coiled coil domain (CCD), DNA binding domain (DBD), Src-homology 2 (SH2) domain, and C-terminal transactivation domain (TAD). Phylogenetic analysis indicated that EcSTAT2 clustered into fish STAT2 group and showed the nearest relationship to giant grouper STAT2. In healthy grouper, EcSTAT2 was distributed in all tissues tested, and the expression of EcSTAT2 was predominantly detected in spleen, kidney and gill. In vitro, EcSTAT2 expression was significantly increased in response to polyinosinic:polycytidylic acid [poly (I:C)] stimulation and red-spotted grouper nervous necrosis virus (RGNNV) infection. Subcellular localization showed that EcSTAT2 was located in the cytoplasm in a punctate manner. EcSTAT2 overexpression significantly inhibited RGNNV replication, as evidenced by the decreased severity of cytopathic effect (CPE) and the reduced expression levels of viral genes and protein. Consistently, knockdown of EcSTAT2 using small interfering RNA (siRNA) promoted RGNNV replication. Furthermore, EcSTAT2 overexpression increased both interferon (IFN) and interferon stimulated genes (ISGs) expression. In addition, EcSTAT2 knockdown decreased the transcription levels of IFN and ISGs. Together, our data demonstrated that EcSTAT2 exerted antiviral activity against RGNNV through up-regulation of host interferon response.

Molecular insight, expression profile and subcellular localization of two STAT family members, STAT1a and STAT2, from Japanese eel, Anguilla japonica

Signal transducer and activator of transcription 1 (STAT1) and STAT2 are critical components of type I and type II IFNs signaling. To date, seven STAT family proteins have been identified from mammals. However, the information on STAT genes in teleost fish is still limited. In the present study, two STAT family genes (STAT1a and STAT2) were identified from Japanese eel, Anguilla japonica and designated as AjSTAT1a and AjSTAT2. The open reading frames of AjSTAT1a and AjSTAT2 are 2244 bp and 2421 bp, encoding for polypeptides of 747 aa and 806 aa, respectively. Both AjSTAT1a and AjSTAT2 contain the conserved domains of STAT proteins. Phylogenetic analysis was performed based on the STATs protein sequences, and showed that AjSTAT1a and AjSTAT2 shared the closest relationship with Oncorhynchus mykiss. Quantitative real-time PCR analysis revealed that AjSTAT1a and AjSTAT2 were expressed in most examined tissues, with the highest expression both in blood. Significantly up-regulated transcripts of AjSTAT1a and AjSTAT2 were detected in response to poly I:C stimulation, and Edwardsiella tarda induced increase in the expression of AjSTAT1a and AjSTAT2 genes. Subcellular localization analysis showed that in both IFNγ-stimulated and unstimulated EPC cells AjSTAT1a and AjSTAT2 were mainly distributed in the cytoplasm, but few AjSTAT1a was distributed in the nucleus. All these results suggested that AjSTAT1a and AjSTAT2 may be critical for regulating the host innate immune defense against pathogens invasion.

Cloning, expression prolife, and immune characterization of a novel stat family member (stat5bl) in Chinese tongue sole (Cynoglossus semilaevis)

STAT plays important roles in innate immunity during JAK/STAT signaling pathway, and STAT5 is particularly focused due to the existence of duplicated forms in fish and mammal. In Chinese tongue sole, stat5bl was suggested to be a candidate related to Vibrio harveyi resistance based on previous QTL screening. In this study, the full length of stat5bl cDNA was cloned and its expression patterns were analyzed. stat5bl was predominantly expressed in immune tissues, where the highest level was observed in liver, followed by skin and gill. Time course expression patterns were examined in six tissues (liver, skin, gill, kidney, intestine, spleen) after V. harveyi infection. stat5bl could be up-regulated by V. harveyi infection in all tissues except liver, despite the timepoints of peak were different. In contrast, stat5bl was significantly downregulated in liver. To elucidate the role of stat5bl in liver, in vitro RNAi were performed using primary liver cell culture. Knockdown of stat5bl could regulate the expression of genes closely related to JAK/STAT pathway. This study would enlarge our understanding of stat5bl in fish immunity.

Gene expression profiles associated with lymphocystis disease virus (LCDV) in experimentally infected Senegalese sole (Solea senegalensis)

In the present study, the pathogenesis of lymphocystis disease virus (LCDV) and the immune gene expression patterns associated with this viral infection were determined in the flatfish Senegalese sole. The results indicate that LCDV spreads rapidly from the peritoneal cavity through the bloodstream to reach target organs such as kidney, gut, liver, and skin/fin. The viral load was highest in kidney and reduced progressively thorough the experiment in spite of the viral major capsid protein gene was transcribed. The LCDV injection activated a similar set of differentially expressed transcripts in kidney and intestine although with some differences in the intensity and time-course response. This set included antiviral-related transcripts (including the mx and interferon-related factors irf1, irf2, irf3, irf7, irf8, irf9, irf10), cytokines (il1b, il6, il8, il12 and tnfa) and their receptors (il1r, il8r, il10r, il15ra, il17r), chemokines (CXC-type, CC-type and IL-8), prostaglandins (cox-2), g-type lysozymes, hepcidin, complement fractions (c2, c4-1 and c4-2) and the antigen differentiation factors cd4, cd8a, and cd8b. The expression profile observed indicated that the host triggered a systemic defensive response including inflammation able to cope with the viral challenge.

Interaction of IRF9 and STAT2 synergistically up-regulates IFN and PKR transcription in Ctenopharyngodon idella

IRF9 is a key factor in the JAK-STAT pathway. Under the stimulation of type I IFN, IRF9 interacts with STAT1 and STAT2 to form the IFN-I-stimulated gene factor 3 (ISGF3) which activates the transcription of ISG. However, many studies also showed that the dimmer IRF9/STAT2 rather than the tripolymer IRF9/STAT1/STAT2 acts as the ISGF3 in cells in response to IFN signals. In the present study, the full-length cDNA sequence of IRF9 (termed CiIRF9, KT601055) and STAT2 (term CiSTAT2, KT781914) from grass carp were cloned and identified. A low level of constitutive expression of CiIRF9 was detected by RT-PCR in grass carp tissues, but it was significantly up-regulated by LPS and poly I:C stimulation. In vitro, a high-affinity interaction between CiIRF9 and the promoter of CiIFN or CiPKR was demonstrated by gel mobility shift assay. In vivo, the promoter activities of CiIFN and CiPKR were not only increased by transient transfection of CiIRF9, but also prominently increased by co-transfection of CiIRF9 and CiSTAT2. Moreover, the interaction of CiIRF9 and CiSTAT2 was further investigated by in vivo and in vitro protein interaction assays. Recombinant CiIRF9 and CiSTAT2, both tagged with FLAG (or HA), were expressed in HEK 293T cells by transient transfection experiment. Co-immunoprecipitation assays showed that CiIRF9 can interact with CiSTAT2 in vivo. Soluble GST-ST2-936 (containing the N-terminal and coiled-coil domain of CiSTAT2) was expressed and purified from E. coli. A GST pull-down assay suggested that GST-tagged ST2-936 efficiently bound to FLAG-tagged IRF9. The data indicated that interaction of IRF9 and STAT2 synergistically up-regulated the transcriptional level of IFN and ISG genes.

Isolation and Expression Analysis of STAT Members from Synechogobius hasta and Their Roles in Leptin Affecting Lipid Metabolism

Signal transducers and activators of transcription proteins (STATs) act as important mediators in multiple biological processes induced by a large number of cytokines. In the present study, full-length cDNA sequences of seven STAT members, including some splicing variants different from those in mammals, were obtained from Synechogobius hasta. The phylogenetic analysis revealed that the seven STAT members were derived from paralogous genes that might have arisen by whole genome duplication (WGD) events during vertebrate evolution. All of these members share similar domain structure compared with those of mammals, and were widely expressed across the tested tissues (brain, gill, heart, intestine, liver, muscle and spleen), but at variable levels. Incubation in vitro of recombinant human leptin changed the intracellular triglyceride (TG) content and mRNA levels of several STATs members, as well as expressions and activities of genes involved in lipid metabolism. Furthermore, Tyrphostin B42 (AG490), a specific inhibitor of the Janus Kinase 2(JAK2)-STAT pathway, partially reversed leptin-induced change on STAT3 and its two spliced isoforms expression, as well as expressions and activities of genes involved in lipid metabolism. As a consequence, the decrease of TG content was also reversed. Thus, our study suggests that STAT3 is the requisite for the leptin signal and the activation of the STAT3 member may account for the leptin-induced changes in lipid metabolism in S. hasta.

JAK and STAT members of yellow catfish Pelteobagrus fulvidraco and their roles in leptin affecting lipid metabolism

The present study clones and characterizes the full-length cDNA sequences of members in JAK-STAT pathway, explores their mRNA tissue expression and the biological role in leptin influencing lipid metabolism in yellow catfish Pelteobagrus fulvidraco. Full-length cDNA sequences of five JAKs and seven STAT members, including some splicing variants, were obtained from yellow catfish. Compared to mammals, more members of the JAKs and STATs family were found in yellow catfish, which provided evidence that the JAK and STAT family members had arisen by the whole genome duplications during vertebrate evolution. All of these members were widely expressed across the eleven tissues (liver, white muscle, spleen, brain, gill, mesenteric fat, anterior intestine, heart, mid-kidney, testis and ovary) but at the variable levels. Intraperitoneal injection in vivo and incubation in vitro of recombinant human leptin changed triglyceride content and mRNA expression of several JAKs and STATs members, and genes involved in lipid metabolism. AG490, a specific inhibitor of JAK2-STAT pathway, partially reversed leptin-induced effects, indicating that the JAK2a/b-STAT3 pathway exerts main regulating actions of leptin on lipid metabolism at transcriptional level. Meanwhile, the different splicing variants were differentially regulated by leptin incubation. Thus, our data suggest that leptin activated the JAK/STAT pathway and increases the expression of target genes, which partially accounts for the leptin-induced changes in lipid metabolism in yellow catfish.

Structural and functional characterization of salmon STAT1, STAT2 and IRF9 homologs sheds light on interferon signaling in teleosts

Mammalian IRF9 and STAT2, together with STAT1, form the ISGF3 transcription factor complex, which is critical for type I interferon (IFN)-induced signaling, while IFNγ stimulation is mediated by homodimeric STAT1 protein. Teleost fish are known to possess most JAK and STAT family members, however, description of their functional activity in lower vertebrates is still scarce. In the present study we have identified two different STAT2 homologs and one IRF9 homolog from Atlantic salmon (Salmo salar). Both proteins have domain-like structures with functional motifs that are similar to higher vertebrates, suggesting that they are orthologs to mammalian STAT2 and IRF9. The two identified salmon STAT2s, named STAT2a and STAT2b, showed high sequence identity but were divergent in their transactivation domain (TAD). Like STAT1, ectopically expressed STAT2a and b were shown to be tyrosine phosphorylated by type I IFNs and, interestingly, also by IFNγ. Microscopy analyses demonstrated that STAT2 co-localized with STAT1a in the cytoplasm of unstimulated cells, while IFNa1 and IFNγ stimulation seemed to favor their nuclear localization. Overexpression of STAT2a or STAT2b together with STAT1a activated a GAS-containing reporter gene construct in IFNγ-stimulated cells. The highest induction of GAS promoter activation was found in IFNγ-stimulated cells transfected with IRF9 alone. Taken together, these data suggest that salmon STAT2 and IRF9 may have a role in IFNγ-induced signaling and promote the expression of GAS-driven genes in bony fish. Since mammalian STAT2 is primarily an ISGF3 component and not involved in IFNγ signaling, our finding features a novel role for STAT2 in fish.