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

Characterization and expression profiling of fadd gene in response to exogenous Aeromonas hydrophila or Edwardsiella tarda challenge in the hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × P. vachelli ♂)

In mammals, fas-associated protein with death domain (FADD) is involved in the process of cell apoptosis and plays a key role in innate immune signaling. Nevertheless, its detailed molecular mechanisms underlying apoptosis and immune responses to exogenous bacterial infections in teleosts remain largely unknown. In this study, a group of 60 hybrid yellow catfish (with the body weight of 25 ± 0.5 g) were used in subsequent experiments, we examined the expression profiling of fadd gene through comparative genomics and comparative immunological methods. Our results showed that fadd in the hybrid yellow catfish (hycfadd) exhibited similar gene and spatial structures to those in other vertebrates, and formed an independent clade in phylogeny. An expression pattern analysis revealed that hycfadd widely transcribed in various tissues, with the highest transcription level in the liver. Furthermore, expression profiling of hycfadd when intraperitoneally infected with 50 μL of exogenous Aeromonas hydrophila (2.0 × 107 CFU/mL) or Edwardsiella tarda (2.0 × 107 CFU/mL) within 48 h were significantly up-regulated in the kidney, spleen, liver and intestine. Important genes in the toll like receptor (tlr) 1-tlr2- myeloid differentiation primary response 88 (MyD88)-fadd-caspase (casp) 8 cascades of TLR signaling pathway in liver were significantly up-regulated after the A. hydrophila stimulation, suggesting that apoptosis through the TLR signaling pathway may have been triggered and activated, which were further verified in the liver, kidney, spleen, intestine and gill by a TUNEL assay. Overall, this study provides solid evidence for the bacterial induction of fadd-related apoptosis in teleosts.

Grouper RIP2 inhibits Singapore grouper iridovirus infection by modulating ASC-caspase-1 interaction

Introduction

Receptor interacting protein 2 (RIP2), serves as a vital sensor of cell stress, is able to respond to cell survival or inflammation, and is involved in antiviral pathways. However, studies on the property of RIP2 in viral infections in fish have not been reported.

Methods

In this paper, we cloned and characterized RIP2 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP2) and further discussed the relevance of EcRIP2 to EcASC, comparing the influences of EcRIP2 and EcASC on the modulation of inflammatory factors and the NF-κB activation to reveal the mechanism of EcRIP2 in fish DNA virus infection.

Results

Encoded a 602 amino acid protein, EcRIP2 contained two structural domains: S-TKc and CARD. Subcellular localization signified that EcRIP2 existed in cytoplasmic filaments and dot aggregation patterns. After SGIV infection, the EcRIP2 filaments aggregated into larger clusters near the nucleus. The infection of SGIV could notably up-regulate the transcription level of the EcRIP2 gene compared with lipopolysaccharide (LPS) and red grouper nerve necrosis virus (RGNNV). Overexpression of EcRIP2 impeded SGIV replication. The elevated expression levels of inflammatory cytokines induced by SGIV were remarkably hindered by EcRIP2 treatment in a concentration-dependent manner. In contrast, EcASC treatment could up-regulate SGIV-induced cytokine expression in the presence of EcCaspase-1. Enhancing amounts of EcRIP2 could overcome the down regulatory effect of EcASC on NF-κB. Nevertheless, increasing doses of EcASC failed to restrain the NF-κB activation in the existence of EcRIP2. Subsequently, it was validated by a co-immunoprecipitation assay that EcRIP2 dose-dependently competed with EcASC binding to EcCaspase-1. With increasing time to SGIV infection, EcCaspase-1 gradually combined with more EcRIP2 than EcASC.

Discussion

Collectively, this paper highlighted that EcRIP2 may impede SGIV-induced hyperinflammation by competing with EcASC for binding EcCaspase-1, thereby suppressing viral replication of SGIV. Our work supplies novel viewpoints into the modulatory mechanism of RIP2-associated pathway and offers a novel view of RIP2-mediated fish diseases.

A second FADD mediates coelomocyte apoptosis response to Vibrio splendidus infection in sea cucumber Apostichopus japonicus

Fas-associated protein with death domain (FADD) is a pivotal adaptor protein that functions in mediating cell death, cell cycle regulation, and particular in innate immunity by the main death receptors. In this study, a second FADD gene in sea cucumber Apostichopus japonicus (termed AjFADD-2) was cloned and its potential function in the innate responses was analyzed. The full-length cDNA of AjFADD-2 consists of 2405 bp and contains a 47 bp 5'-untranslated region (UTR), a 1629 bp 3'-UTR, and a 729 bp ORF encoding 242 amino acids. AjFADD-2 possesses two conserved domains of intracellular N-terminal death effector domain and an extracellular C-terminal death domain, which is different from the first cloned FADD gene in A. japonicus that only possesses the death domain. AjFADD-2 was examined in all sampled six tissues and was significantly induced in V. splendidus-challenged sea cucumbers and LPS-exposed coelomocytes. Subcellular localization detection showed that AjFADD-2 was primarily observed in the coelomocyte cytoplasm, and transferred to the nucleus post V. splendidus challenge. Consistently, AjFADD-2 knockdown significantly inhibited apoptosis in V. splendidus-challenged sea cucumbers and LPS-exposed coelomocytes. Taken together, our results provided evidence that AjFADD functioned as a positive regulator of coelomocytes apoptosis in response to pathogen V. splendidus challenge.

Expression and functional analysis of the BCL2-Associated agonist of cell death (BAD) gene in grass carp (Ctenopharyngodon idella) during bacterial infection

The BCL2-associated agonist of cell death protein is a key participant in apoptosis dependent on mitochondria and in disease progression that involves the regulation of cell death, such as tumorigenesis, diabetes, sepsis shock, and epilepsy. Nevertheless, the mechanisms underlying the immune responses to teleost BAD bacterial infection and mitochondrial-dependent apoptosis remains unclear. In order to elucidate the mechanisms involved, in this study, a Ctenopharyngodon idella (grass carp) BAD gene named GcBAD1 was firstly cloned and characterized. The results indicated that the ORF (open reading frame) of GcBAD1 was 438 bp in length, encoding a 145-amino acid putative protein of 16.66 kDa. This deduced amino acid sequence has a better identity than another teleost species according to a phylogenetic analysis, and contains a Bcl2-BAD-1 domain. In healthy grass carp fish, the mRNA transcripts of GcBAD1 were widely present in the studied tissues, which could be ranked as follows; spleen > brain > middle-kidney > head-kidney > liver > gills > intestines > heart and muscle. In addition, during infection by Aeromonas hydrophila and Staphylococcus aureus, the mRNA transcription and protein levels expression of GcBAD1 in the head-kidney, spleen, and liver tissues of the fish were significantly up-regulated. Moreover, when the C. idellus kidney cell line (CIK) cells were incubated with Lipopolysaccharide (LPS) and lipoteichoic acid (LTA), the GcBAD1 expression transcripts were also significantly up-regulated. Additionally, overexpression of GcBAD1 in CIK cells was able to activate apoptosis-related genes, including those encoding p53, Cytochrome C (CytoC), caspase-3, and caspase-9. Besides, in the TUNEL assays, when pEGFP-BAD1 was over-expressed, the number of red signals associated with apoptosis were significantly increased in the CIK cells infected with LPS or LTA at 12 h. This study demonstrates that GcBAD1 has a significant role in the mitochondrial apoptosis pathway of grass carp's innate immunity. Our findings provide new insight into the potential mechanisms of teleost antibacterial immunity.

Fish RIP1 Mediates Innate Antiviral Immune Responses Induced by SGIV and RGNNV Infection

Receptor interacting protein 1 (RIP1) is an essential sensor of cellular stress, which may respond to apoptosis or cell survival and participate in antiviral pathways. To investigate the roles of fish RIP1 in Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) infection, a RIP1 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP1) was cloned and characterized. EcRIP1 encoded a 679 amino acid protein that shares 83.28% identity with that of Perca flavescens and contained a homologous N-terminal kinase (S-TKc) domain, a RIP isotype interaction motif (RHIM), and a C-terminal domain (DD). EcRIP1 was predominantly detected in immune tissues, and its expression was induced by RGNNV or SGIV infection in vitro. Subcellular localization showed that EcRIP1 was distributed in the cytoplasm with point-like uniform and dot-like aggregation forms. Overexpression of EcRIP1 inhibited SGIV and RGNNV replication and positively regulated the expression levels of interferon (IFN) and IFN-stimulated genes and pro-inflammatory factors. EcRIP1 may interact with grouper tumor necrosis factor receptor type 1-associated DEATH domain protein (EcTRADD) to promote SGIV-induced apoptosis, and interact with grouper Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-β (EcTRIF) and participate in Myeloid Differentiation Factor 88 (MyD88)-independent toll-like receptor (TLR) signaling. EcRIP1 may also interact with grouper tumor necrosis factor receptor-associated factors (TRAFs) as intracellular linker proteins and mediate the signaling of various downstream signaling pathways, including NF-κB and IFN. These results suggest that EcRIP1 may inhibit SGIV and RGNNV infection by regulating apoptosis and various signaling molecules. Our study offers new insights into the regulatory mechanism of RIP1-related signaling, and provides a novel perspective on fish diseases mediated by RIP1.

Fas-associated death domain (FADD) in sea cucumber (Apostichopus japonicus): Molecular cloning, characterization and pro-apoptotic function analysis

Fas-associated death domain (FADD) is an adaptor protein that functions in transferring the apoptotic signals regulated by the death receptors. In this study, a full-length cDNA of FADD homologue in sea cucumber Apostichopus japonicas (AjFADD) was cloned and characterized, and its functional roles in apoptosis investigated. In healthy sea cucumbers, AjFADD was expressed in all detected tissues, with higher levels in coelomocytes and intestine. AjFADD mRNA and protein levels were significantly expressed in coelomocytes after exposed with LPS or poly (I:C) in vitro, and challenged with Vibrio splendidus in vivo. Moreover, siRNA-mediated AjFADD knockdown in coelomocyte much decreased AjFADD mRNA and protein levels as well as the coelomocytes apoptosis levels. Furthermore, over-expression of the expression plasmid pcDNA3.1 encoding AjFADD (pcAjFADD) significantly increased the apoptosis levels in HEK293 cells. Taken together, our results support that AjFADD is a novel pro-apoptotic protein that might play key roles in defensing the bacterial and virus invasion in sea cucumber.

Grouper Atg12 negatively regulates the antiviral immune response against Singapore grouper iridovirus (SGIV) infection

Autophagy is an evolutionarily conserved, multi-step lysosomal degradation process used to maintain cell survival and homeostasis. A series of autophagy-related genes (Atgs) are involved in the autophagic pathway. In mammals, a growing number of studies have attributed functions to some Atgs that are distinct from their classical role in autophagosome biogenesis, such as resistance to pathogens. However, little is known about the functions of fish Atgs. In this study, we cloned and characterized an atg12 homolog from orange spotted grouper (Epinephelus coioides) (Ecatg12). Ecatg12 encodes a 117 amino acid protein that shares 94.0% and 76.8% identity with gourami (Anabas_testudineus) and humans (Homo sapiens), respectively. The transcription level of Ecatg12 was lower in cells infected with Singapore grouper iridovirus (SGIV) than in non-infected cells. Fluorescence microscopy revealed that EcAtg12 localized in the cytoplasm and nucleus in grouper spleen cells. Overexpression of EcAtg12 significantly increased the replication of SGIV, as evidenced by increased severity of the cytopathic effect, transcription levels of viral genes, levels of viral proteins, and progeny virus yield. Further studies showed that EcAtg12 overexpression decreased the expression levels of interferon (IFN) related molecules and pro-inflammatory factors and inhibited the promoter activity of IFN-3, interferon-stimulated response element, and nuclear factor-κB. Together, these results demonstrate that EcAtg12 plays crucial roles in SGIV replication by downregulating antiviral immune responses.

FADD in Cancer: Mechanisms of Altered Expression and Function, and Clinical Implications

FADD was initially described as an adaptor molecule for death receptor-mediated apoptosis, but subsequently it has been implicated in nonapoptotic cellular processes such as proliferation and cell cycle control. During the last decade, FADD has been shown to play a pivotal role in most of the signalosome complexes, such as the necroptosome and the inflammasome. Interestingly, various mechanisms involved in regulating FADD functions have been identified, essentially posttranslational modifications and secretion. All these aspects have been thoroughly addressed in previous reviews. However, FADD implication in cancer is complex, due to pleiotropic effects. It has been reported either as anti- or protumorigenic, depending on the cell type. Regulation of FADD expression in cancer is a complex issue since both overexpression and downregulation have been reported, but the mechanisms underlying such alterations have not been fully unveiled. Posttranslational modifications also constitute a relevant mechanism controlling FADD levels and functions in tumor cells. In this review, we aim to provide detailed, updated information on alterations leading to changes in FADD expression and function in cancer. The participation of FADD in various biological processes is recapitulated, with a mention of interesting novel functions recently proposed for FADD, such as regulation of gene expression and control of metabolic pathways. Finally, we gather all the available evidence regarding the clinical implications of FADD alterations in cancer, especially as it has been proposed as a potential biomarker with prognostic value.

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.

Identification of fish CMPK2 as an interferon stimulated gene against SVCV infection

Cytidine/uridine monophosphate kinase 2 (CMPK2) is known as a nucleoside monophosphate kinase in mitochondria to maintains intracellular UTP/CTP, and could be induced by immunostimulants LPS and Poly (I:C) in mammals, suggesting its potential antiviral and antibacterial role. In this study, CMPK2 was cloned and characterized in Fathead minnow (FHM) cells. In vivo analysis of tissue distribution revealed that CMPK2 transcript was detected in all the tissues of zebrafish (Danio rerio) examined in this study, particularly abundant in liver, spleen and kidney. In addition, indirect immunofluorescence showed that CMPK2 was localized in the cytoplasm of FHM cells. Expression of CMPK2 mRNA was significantly up-regulated following challenge with Spring viraemia of carp virus (SVCV), poly(I:C), or zebrafish IFN1 and IFN3 both in vitro and in vivo. Furthermore, overexpression and RNA interference of CMPK2 in SVCV-infected FHM cells showed significantly antiviral effect. In summary, this study for the first time shows the presence and distribution of CMPK2 in different tissues of zebrafish, but also demonstrates its antiviral potential against SVCV infection in vivo. These new findings could contribute to explain the molecular mechanism of the CMPK2 mediated antiviral function.

The first cloned sea cucumber FADD from Holothuria leucospilota: Molecular characterization, inducible expression and involvement of apoptosis

In this study, a sea cucumber Fas-associated death domain (FADD) named HLFADD was first cloned from Holothuria leucospilota. The full-length cDNA of HLFADD is 2137 bp in size, containing a 116-bp 5'-untranslated region (UTR), a 1334-bp 3'-UTR and a 687-bp open reading frame (ORF) encoding a protein of 228 amino acids with a deduced molecular weight of 26.42 kDa. HLFADD protein contains a conserved death effector domain at its N-terminal and a conserved death domain at its C-terminal, structurally similar to its counterparts in vertebrates. The over-expressed HLFADD protein could induce apoptosis in HEK293 cells, suggesting a possible death receptor-mediated apoptosis pathway in echinoderms adapted with FADD. Moreover, HLFADD mRNA is ubiquitously expressed in all examined tissues, with the highest transcript level in the coelomocytes, followed by intestine. In vitro experiments performed in the H. leucospilota coelomocytes, the expression of HLFADD mRNA was significantly up-regulated by lipopolysaccharides (LPS) or polyriboinosinic-polyribocytidylic acid [poly (I:C)] challenge, suggesting that HLFADD might play important roles in the innate immune defense of sea cucumber against the invasion of bacteria and viruses.

Molecular cloning and characterization of FADD from the manila clam Ruditapes philippinarum

Fas-associated protein with death domain (FADD) is an essential element in cell death, and also implicates in cell cycle progression, inflammation and innate immunity. In the study, an FADD (designated as RpFADD) was identified and characterized from manila clam, Ruditapes philippinarum. Multiple alignments and phylogenetic analysis strongly suggested that RpFADD was a new member of the FADD family. The RpFADD transcripts were constitutively expressed in a wide range of tissues, and dominantly expressed in hemocytes. After challenged with Vibrio anguillarum or Micrococcus luteus, the expression level of RpFADD transcripts was significantly induced and reached the maximum level at 72 h and 48 h, respectively. Knockdown of RpFADD down-regulated the transcript levels of RpIKK, RpTAK1 and RpNF-κB with the exception of RpIκB. Moreover, RpFADD primarily localized in the cell cytoplasm, and its over-expression promoted the apoptosis of HeLa cells. These results revealed that RpFADD perhaps regulated the NF-κB signaling pathways positively, which provided a better understanding of RpFADD in innate immunity.

Fish Autophagy Protein 5 Exerts Negative Regulation on Antiviral Immune Response Against Iridovirus and Nodavirus

Autophagy is an important biological activity that maintains homeostasis in eukaryotic cells. However, little is known about the functions of fish autophagy-related genes (Atgs). In this study, we cloned and characterized Atg5, a key gene in the autophagy gene superfamily, from orange-spotted grouper (Epinephelus coioides) (EcAtg5). EcAtg5 encoded a 275-amino acid protein that shared 94 and 81% identity to seabass (Lates calcarifer) and humans (Homo sapiens), respectively. The transcription level of EcAtg5 was significantly increased in cells infected with red-spotted grouper nervous necrosis virus (RGNNV). In cells infected with Singapore grouper iridovirus (SGIV), EcAtg5 expression declined during the early stage of infection and increased in the late stage. Fluorescence microscopy revealed that EcAtg5 mainly localized with a dot-like pattern in the cytoplasm of grouper cells. Overexpression of EcAtg5 significantly increased the replication of RGNNV and SGIV at different levels of detection, as indicated by increased severity of the cytopathic effect, transcription levels of viral genes, and levels of viral proteins. Knockdown of EcAtg5 decreased the replication of RGNNV and SGIV. Further studies showed that overexpression EcAtg5 activated autophagy, decreased expression levels of interferon related cytokines or effectors and pro-inflammatory factors, and inhibited the activation of nuclear factor κB, IFN-sensitive response element, and IFNs. In addition, ectopic expression of EcAtg5 affected cell cycle progression by hindering the G1/S transition. Taken together, our results demonstrated that fish Atg5 exerted a crucial role in virus replication by promoting autophagy, down-regulating antiviral IFN responses, and affecting the cell cycle.

SPOP promotes FADD degradation and inhibits NF-κB activity in non-small cell lung cancer

FAS-associated protein with death domain (FADD) is the pivotal adaptor protein, which transmits apoptotic signals mediated by the death receptors. Here we report that high FADD protein level predicts poor prognosis of non-small cell lung cancer (NSCLC) patients and its protein level is mainly regulated by the 26S proteasome. We also found that ubiquitin ligase SPOP (speckle-type POZ protein) binds to FADD and mediates its degradation, which can be blocked by MG132 treatment. Notably, SPOP inhibits NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity and its target genes expression via FADD. These results reveal the function of SPOP-FADDNFκB axis in NSCLC cells, which is associated with prognosis of NSCLC patients.