An IκB homologue (FcCactus) in Chinese shrimp Fenneropenaeus chinensis

PxDorsal Regulates the Expression of Antimicrobial Peptides and Affects the Bt Susceptibility of Plutella xylostella

The insect NF-κB pathway is primarily constituted by nuclear factor κB (NF-κB) and the inhibitor of κB (IκB), which plays a crucial role in the innate immune response. Dorsal and Cactus, as NF-κB and IκB factors, are important downstream regulators of the Toll pathway in Plutella xylostella. In this study, the PxDorsal and PxCactus genes of P. xylostella were cloned, and the molecular docking demonstrated that PxDorsal and PxCactus can interact with each other. RT-qPCR results indicated that PxDorsal and PxCactus were expressed in all stages, and the expression of PxDorsal, PxCactus, and antimicrobial peptides PxGloverin2, PxMoricin3, and PxLysozyme2 were significantly down-regulated under Bacillus thuringiensis (Bt8010) infection. Interestingly, silencing the PxDorsal gene by RNA interference (RNAi) significantly down-regulated the expression of PxGloverin2 and PxMoricin3 and increased the epidermis melanization of P. xylostella larvae fed with Bt8010. Our findings indicate that PxDorsal and PxCactus may interact with each other, and silencing PxDorsal inhibits the expression of downstream antimicrobial peptides, thereby enhance the susceptibility of P. xylostella to Bt8010. This study contributes a theoretical basis for further research on the Toll pathway of P. xylostella to pathogens and offers insights for screening effective biological control targets from the perspective of the immune system.

A scallop IκB protein involved in innate immunity acts as a key regulator of NF-κB

Chlamys farreri, a commercially important bivalve mollusk, is extensively cultivated in China. In recent years, the frequent occurrence of diseases has led to significant mortality in scallop farms. Despite this, our understanding of scallop's innate immune mechanisms remains limited. The NF-κB signaling pathway plays a crucial role in various biological processes, including cellular, developmental, and immune defense mechanisms. Inhibitors of NF-κB (IκB) proteins block the nuclear localization and DNA binding of NF-κB, thereby inhibiting its activity. However, the role of these proteins in invertebrates is not well understood. In this study, we identified a new homolog of the IκB gene in C. farreri, named CfIκB1. The open reading frame of CfIκB1 spans 1089 bp, encoding 362 amino acids. Through sequence comparison and phylogenetic analysis, CfIκB1 was classified as a member of the invertebrate IκB family. Quantitative real-time PCR revealed that CfIκB1 transcripts are present in all examined tissues, with the highest expression observed in hemocytes. Expression levels were significantly upregulated following exposure to lipopolysaccharide, peptidoglycan, and polyinosinic:polycytidylic acid. Co-immunoprecipitation studies confirmed that CfIκB1 interacts with NF-κB family proteins CfRel-1 and CfRel. Dual-luciferase reporter assays demonstrated that CfIκB1 inhibits CfRel-dependent activation of NF-κB, ISRE, IFNβ, and AP-1. These findings suggest that CfIκB1 plays a crucial role in regulating NF-κB activity, which is integral to the innate immunity of C. farreri. This research enhances our understanding of the innate immune system in invertebrates and provides a theoretical basis for developing disease-resistant scallops at the molecular level.

New insights into the mechanism of ammonia toxicity: Focus on Cactus

The NF-κB signaling pathway is the most critical pathway in innate immunity. IκB (Cactus) is the primary cytoplasmic inhibitor of NF-κB (Dorsal). In this study, we found that ammonia exposure could significantly induce the expression of Cactus, in a dose-dependent manner in different tissues, with the highest expression in the gill of Corbicula fluminea. The expression pattern-related elements (Tube and Dorsal) in the NF-κB signaling pathway were also analyzed, showing significant up-regulation in 48 h. There was an inhibitory effect between up-regulated Cactus and Dorsal in 72 h, which may regulate Dorsal as a negative feedback pathway function to control the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). Besides, through molecular docking simulation, we found that the Cactus could be directly activated by NH₃, complementing the regulatory mechanism of the Cactus. To further test our hypothesis, the levels of pro-inflammatory cytokines decreased after adding PDTC (the antioxidant of Cactus/IκB), suggesting that PDTC can prevent the degradation of Cactus, inhibit Dorsal translocating into the nucleus, and activate the pro-inflammatory cytokines. This revealed the inhibitory effect of Cactus on activating Dorsal/NF-κB factors in the NF-κB signaling pathway. Thus, we suggested that the Cactus is an essential regulator of ammonia-activated inflammation in C. fluminea, which was reported to be activated only by bacteria and immune stimulators. Our study provides a new perspective on the mechanism of ammonia toxicity in invertebrates.

The ECSIT Mediated Toll3-Dorsal-ALFs Pathway Inhibits Bacterial Amplification in Kuruma Shrimp

The Toll signaling pathway plays an important role in animal innate immunity. However, its activation and signal transmission greatly differ across species and need to be investigated. Shrimp farming is a worldwide economic activity affected by bacterial disease from the 1990s, which promoted research on shrimp immunity. In this study, we first proved that, among the three identified Toll receptors in Marsupenaeus japonicus kuruma shrimp, Toll 3 plays a pivotal role in initiating the antibacterial response in vivo, especially upon anti-Staphylococcus aureus infection. Further research showed that this result was due to the activation of the Dorsal transcription factor, which induced the expression of two anti-lipopolysaccharide factors (Alfs). Moreover, the evolutionarily conserved signaling intermediate in Toll pathways, ECSIT, was proved to be needed for signal transmission from Toll 3 to Dorsal and the expression of anti-lipopolysaccharide factors. Finally, the mortality assay showed that a Toll3-ECSIT-Dorsal-Alf axis was functional in the anti-S.aureus immunity of M. japonicus shrimp. The results provide new insights into the function and signal transduction of the Toll pathway in aquatic species and offer basic knowledge for shrimp disease control and genetic breeding.

Yorkie Negatively Regulates the Expression of Antimicrobial Proteins by Inducing Cactus Transcription in Prawns Macrobrachium nipponense

The Hippo signaling pathway controls organ size and immune system in Drosophila and mammals. Yorkie acts as a transcriptional co-activator in the Hippo pathway and cross-talks with other essential pathways. In this study, a Yorkie gene and two Cactus isoforms (designated as MnYorkie, MnCactus-a, and MnCactus-b, respectively) were isolated and characterized from oriental river prawns (Macrobrachium nipponense). Results showed that MnYorkie includes 1620 bp open reading frame and encodes a protein of 539 amino acids (aa). MnCactus-a (377 aa) and MnCactus-b (471 aa) were produced by alternative splicing. MnYorkie and MnCactus were continuously expressed in all selected tissues. Upon Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Vibrio parahaemolyticus stimulation, the mRNA levels of MnYorkie and MnCactus in hemocytes and intestines underwent time-dependent enhancement. RNA interference studies showed that MnYorkie silencing remarkably downregulated the transcription of MnCactus but upregulated the expression of seven immune-related genes. In addition, MnYorkie silencing in vivo decreased the susceptibility of prawns to bacterial challenge. After S. aureus and V. parahaemolyticus infection, the survival rate of prawns increased significantly from 2 to 6 days, which corresponded to the period of MnYorkie knockdown. All these findings suggested that MnYorkie in the Hippo pathway might exhibit remarkable biological roles in the immune defense of M. nipponense by negatively regulating the expression of immune-related genes and promoting the transcription of MnCactus.

Identification of an Apis cerana zinc finger protein 41 gene and its involvement in the oxidative stress response

Zinc finger proteins (ZFPs) are a class of transcription factors that contain zinc finger domains and play important roles in growth, aging, and responses to abiotic and biotic stresses. These proteins activate or inhibit gene transcription by binding to single-stranded DNA or RNA and through RNA/DNA bidirectional binding and protein-protein interactions. However, few studies have focused on the oxidation resistance functions of ZFPs in insects, particularly Apis cerana. In the current study, we identified a ZFP41 gene from A. cerana, AcZFP41, and verified its function in oxidative stress responses. Real-time quantitative polymerase chain reaction showed that the transcription level of AcZFP41 was upregulated to different degrees during exposure to oxidative stress, including that induced by extreme temperature, UV radiation, or pesticides. In addition, the silencing of AcZFP41 led to changes in the expression patterns of some known antioxidant genes. Moreover, the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and glutathione S-transferase (GST) in AcZFP41-silenced honeybees were higher than those in a control group. In summary, the data indicate that AcZFP41 is involved in the oxidative stress response. The results provide a theoretical basis for further studies of zinc finger proteins and improve our understanding of the antioxidant mechanisms of honeybees.

The white spot syndrome virus hijacks the expression of the Penaeus vannamei Toll signaling pathway to evade host immunity and facilitate its replication

The white spot syndrome virus (WSSV), the most lethal pathogen of shrimp, is a dsDNA virus with approximately a 300,000 base pairs and contains approximately 180-500 predicted open reading frames (ORFs), of which only 6% show homology to any known protein from other viruses or organisms. Although most of its ORFs encode enzymes for nucleotide metabolism, DNA replication, and protein modification, the WSSV uses some of its encoded proteins successfully to take control of the metabolism of the host and avoid immune responses. The contribution of the shrimp innate immune response to prevent viral invasions is recognized but yet not fully understood. Thus, the role of several components of Toll pathway of the shrimp Penaeus vannamei against WSSV has been previously described, and the consequential effects occurring through the cascade remain unknown. In the current study the effects of WSSV over various components of the shrimp Toll pathway were studied. The gene expression of Spätzle, Toll, Tube, Cactus and Dorsal was altered after 6-12 h post inoculation. The expression of LvToll3, LvCactus, LvDorsal, decreased ~4.4-, ~3.7- and ~7.3-fold at 48, 24 and 48 hpi, respectively. Furthermore, a remarkable reduction (~18-fold) in the expression of the gene encoding LvCactus in WSSV infected specimens was observed at 6 hpi. This may be a sophisticated strategy exploited by WSSV to evade the Toll-mediated immune action, and to promote its replication, thereby contributing to viral fitness.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Heat shock factor 1 regulates heat shock proteins and immune-related genes in Penaeus monodon under thermal stress

Heat shock factors (HSFs) participate in the response to environmental stressors and regulate heat shock protein (Hsp) expression. This study describes the molecular characterization and expression of PmHSF1 in black tiger shrimp Penaeus monodon under heat stress. PmHSF1 expression was detected in several shrimp tissues: the highest in the lymphoid organ and the lowest in the eyestalk. Significant up-regulation of PmHSF1 expression was observed in hemocytes (p < 0.05) following thermal stress. The expression of several PmHsps was rapidly induced following heat stress. Endogenous PmHSF1 protein was expressed in all three types of shrimp hemocyte and strongly induced under heat stress. The suppression of PmHSF1 expression by dsRNA-mediated gene silencing altered the expression of PmHsps, several antimicrobial genes, genes involved in the melanization process, and an antioxidant gene (PmSOD). PmHSF1 plays an important role in the thermal stress response, regulating the expression of Hsps and immune-related genes in P. monodon.

Silencing of a Kazal-type serine proteinase inhibitor SPIPm2 from Penaeus monodon affects YHV susceptibility and hemocyte homeostasis

In shrimp, the Kazal-type serine proteinase inhibitors (KPIs) are involved in host innate immune defense system against pathogenic microorganisms. A five-Kazal-domain SPIPm2 is the most abundant KPIs in the black tiger shrimp Penaeus monodon and up-regulated in response to yellow head virus (YHV) infection. In this study, the role of SPIPm2 in YHV infection was investigated. The expression of SPIPm2 in hemocytes, gill and heart from 48-h YHV-infected shrimp was increased. The expression of SPIPm2 in hemocytes was significantly increased after 12 h of infection and gradually increased higher afterwards. Silencing of SPIPm2 by dsRNA interference resulted in the increased expression of different apoptosis-related genes, the increased expression of transcriptional factors of antimicrobial synthesis pathways, the reduction of circulating hemocytes in the shrimp hemolymph, and the increased susceptibility of the silenced shrimp to YHV infection. The activities of caspase-3 and caspase-7 in the hemocytes of SPIPm2-silenced shrimp was also increased by 5.32-fold as compared with those of the control shrimp. The results suggested that the SPIPm2 was involved in the hemocyte homeostasis.

Shrimp humoral responses against pathogens: antimicrobial peptides and melanization

Diseases have caused tremendous economic losses and become the major problem threatening the sustainable development of shrimp aquaculture. The knowledge of host defense mechanisms against invading pathogens is essential for the implementation of efficient strategies to prevent disease outbreaks. Like other invertebrates, shrimp rely on the innate immune system to defend themselves against a range of microbes by recognizing and destroying them through cellular and humoral immune responses. Detection of microbial pathogens triggers the signal transduction pathways including the NF-κB signaling, Toll and Imd pathways, resulting in the activation of genes involved in host defense responses. In this review, we update the discovery of components of the Toll and Imd pathways in shrimp and their participation in the regulation of shrimp antimicrobial peptide (AMP) synthesis. We also focus on a recent progress on the two most powerful and the best-studied shrimp humoral responses: AMPs and melanization. Shrimp AMPs are mainly cationic peptides with sequence diversity which endues them the broad range of activities against microorganisms. Melanization, regulated by the prophenoloxidase activating cascade, also plays a crucial role in killing and sequestration of invading pathogens. The progress and emerging research on mechanisms and functional characterization of components of these two indispensable humoral responses in shrimp immunity are summarized and discussed. Interestingly, the pattern recognition protein (PRP) crosstalk is evidenced between the proPO activating cascade and the AMP synthesis pathways in shrimp, which enables the innate immune system to build up efficient immune responses.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) participates in anti-lipopolysaccharide factors (ALFs) gene expression in mud crab

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key cytoplasm signal adaptor that mediates signals activated by tumor necrosis factor receptor (TNFR) superfamily and the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. The full-length 2492 bp TRAF6 (Sp-TRAF6) from Scylla paramamosain contains 1800 bp of open reading frame (ORF) encoding 598 amino acids, including an N-terminal RING-type zinc finger, two TRAF-type zinc fingers and a conserved C-terminal meprin and TRAF homology (MATH) domain. Multiple alignment analysis shows that the putative amino acid sequence of Sp-TRAf6 has highest identity of 88% with Pt-TRAF6 from Portunus trituberculatus, while the similarity of Sp-TRAF6 with other crustacean sequences was 54-55%. RT-PCR analysis indicated that Sp-TRAF6 transcripts were predominantly expressed in the hepatopancreas and stomach, whereas it was barely detected in the heart and hemocytes in our study. Moreover, Sp-TRAF6 transcripts were significantly up-regulated after Vibrio parahemolyticus and LPS challenges. RNA interference assay was carried out used by siRNA to investigate the genes expression patterns regulated by Sp-TRAF6. The qRT-PCR results showed that silencing Sp-TRAF6 gene could inhibit SpALF1, SpALF2, SpALF5 and SpALF6 expression in hemocytes, while inhibit SpALF1, SpALF3, SpALF4, SpALF5 and SpALF6 expression in hepatopancreas. Taken together, the acute-phase response to immune challenges and the inhibition of SpALFs gene expression indicate that Sp-TRAF6 plays an important role in host defense against pathogen invasions via regulation of ALF gene expression in S. paramamosain.

β-Arrestins Negatively Regulate the Toll Pathway in Shrimp by Preventing Dorsal Translocation and Inhibiting Dorsal Transcriptional Activity

The Toll signaling pathway plays an important role in the innate immunity ofDrosophila melanogasterand mammals. The activation and termination of Toll signaling are finely regulated in these animals. Although the primary components of the Toll pathway were identified in shrimp, the functions and regulation of the pathway are seldom studied. We first demonstrated that the Toll signaling pathway plays a central role in host defense againstStaphylococcus aureusby regulating expression of antimicrobial peptides in shrimp. We then found that β-arrestins negatively regulate Toll signaling in two different ways. β-Arrestins interact with the C-terminal PEST domain of Cactus through the arrestin-N domain, and Cactus interacts with the RHD domain of Dorsal via the ankyrin repeats domain, forming a heterotrimeric complex of β-arrestin·Cactus·Dorsal, with Cactus as the bridge. This complex prevents Cactus phosphorylation and degradation, as well as Dorsal translocation into the nucleus, thus inhibiting activation of the Toll signaling pathway. β-Arrestins also interact with non-phosphorylated ERK (extracellular signal-regulated protein kinase) through the arrestin-C domain to inhibit ERK phosphorylation, which affects Dorsal translocation into the nucleus and phosphorylation of Dorsal at Ser(276)that impairs Dorsal transcriptional activity. Our study suggests that β-arrestins negatively regulate the Toll signaling pathway by preventing Dorsal translocation and inhibiting Dorsal phosphorylation and transcriptional activity.

YHV-responsive gene expression under the influence of PmRelish regulation

In animals, infection by Gram-negative bacteria and certain viruses activates the Imd signaling pathway wherein the a NF-κB transcription factor, Relish, is a key regulatory protein for the synthesis of antimicrobial proteins. Infection by yellow head virus (YHV) activates the Imd pathway. To investigate the expression of genes involved in YHV infection and under the influence of PmRelish regulation, RNA interference and suppression subtractive hybridization (SSH) are employed. The genes in forward library expressed in shrimp after YHV infection and under the activity of PmRelish were obtained by subtracting the cDNAs from YHV-infected and PmRelish-knockdown shrimp with cDNAs from YHV-infected shrimp. Opposite subtraction gave a reverse library whereby an alternative set of genes under YHV infection and no PmRelish expression were obtained. Nucleotide sequences of 252 and 99 cDNA clones from the forward and reverse libraries, respectively, were obtained and annotated through blast search against the GenBank sequences. Genes involved in defense and homeostasis were abundant in both libraries, 31% and 23% in the forward and reverse libraries, respectively. They were predominantly antimicrobial proteins, proteinases and proteinase inhibitors. The expression of antimicrobial protein genes, ALFPm3, crustinPm1, penaeidin3 and penaeidin5 were tested under PmRelish silencing and Gram-negative bacterium Vibrio harveyi infection. Together with the results using YHV infection previously reported, the expression of penaeidin5 and also penaeidin3 but not ALFPm3 and crustinPm1 were under the regulation of PmRelish in the Imd pathway.

Activation of PmRelish from Penaeus monodon by yellow head virus

Humoral innate immune response against pathogenic infection is partly responsible by the Imd pathway in which a transcription factor Relish relays the infection signals to the nuclei for the expression of antimicrobial proteins. A PmRelish gene which encoded a protein of 1195 amino acids was cloned. The PmRelish was constitutively expressed in all tissues tested and mostly up-regulated upon YHV infection. In hemocytes, the PmRelish expression was up-regulated upon Vibrio harveyi, yellow head virus (YHV) and white spot syndrome virus (WSSV) challenges. Using dsRNA silencing of PmRelish gene, it was shown that the expression of penaeidin5 but not anti-lipopolysaccharide factor ALFPm3, crustinPm1 and penaeidin3 was under the regulation of Imd pathway. Under PmRelish silencing, the shrimp were more susceptible to infection by YHV with the 50% survival rate reduced from about 72 h to 42 h. The PmRelish was detected in the cytoplasm of all the hemocytes from both uninfected and YHV-infected shrimp. The accumulation of activated PmRelish in the nuclei was not clearly observed but the activated PmRelish was detected in the YHV-infected hemocytes by Western blot analysis. Thus, the PmRelish and, hence, the Imd pathway respond to the YHV infection.

Toll-pathway in tiger shrimp (Penaeus monodon) responds to white spot syndrome virus infection: evidence through molecular characterisation and expression profiles of MyD88, TRAF6 and TLR genes

The Toll-pathway plays key roles in regulating the innate immune response in invertebrates. Myeloid differentiation factor 88 (MyD88) and Tumour necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) are key molecules in this signalling pathway. To investigate the role of Toll-pathway in innate immune response of shrimp, Penaeus monodon, MyD88 (PmMyD88) and TRAF6 (PmTRAF6) were identified and characterised. PmMyD88 cDNA is 1716 bp long with an open reading frame (ORF) of 1449 bp encoding a putative protein of 482 amino acids, with a death domain, a TIR domain and C-terminal extension domain. PmTRAF6 cDNA is 2563 bp long with an ORF of 1785 bp (594 amino acids) with an N-terminal RING-type zinc finger domain, two TRAF-type zinc finger domains, a coiled region and a MATH domain. In healthy shrimp, PmMyD88, PmTRAF6 and PmToll were detected in 15 tissues with the highest expression in midgut, eyestalk and lymphoid organ, respectively. Responses of these genes to WSSV in experimentally-infected P. monodon as well as in cultured haemocytes and also effect of poly I:C on the gene expression in vitro was investigated at six time-points in seven tissues. PmToll showed significant up-regulation at all time-points of infection in six tissues and until 24 h post-infection in vitro. However, poly I:C-induced haemocytes showed up-regulation of the gene until 48 h post-exposure. WSSV caused significant up-regulation of PmMyD88 in most of the tissues tested. The virus challenge as well as poly I:C induction in vitro also resulted in significant up-regulation of the gene. Up-regulated expression of PmTRAF6 was detected in haemocytes and lymphoid organ at late stage of infection. In vitro virus challenge showed significant up-regulation of PmTRAF6 at almost all time-points whereas no significant change in the expression was observed on poly I:C induction. The responses of these key genes, observed in the present study, suggest that Toll-pathway as a whole may play a crucial role in the immune response against viruses in shrimp.

Identification and functional characterization of heat shock transcription factor1 in Litopenaeus vannamei

Heat shock transcription factors belong to the heat shock factor (HSF) protein family, which are involved in heat shock protein (HSP) gene regulation. They are critical for cell survival upon exposure to harmful conditions. In this study, we identified and characterized a HSF1 (LvHSF1) gene in Litopenaeus vannamei, with a full-length cDNA of 2841 bp and an open reading frame encoding a putative protein of 632 amino acids. Through multiple sequence alignment and phylogenetic analysis, it was revealed that LvHSF1 was closed to insect HSF family, which contained a highly conserved DNA-binding domain, oligomerization domains with HR-A/B, and a nuclear localization signal. Tissues distribution showed that LvHSF1 was widely expressed in all tissues tested. And it was upregulated in hemocytes and gills after Vibrio alginolyticus or Staphylococcus aureus infection. Dual-luciferase reporter assays indicated that LvHSF1 activated the promoters of L. vannamei HSP70 (LvHSP70) and L. vannamei Cactus (LvCactus), while inhibited the expressions of Drosophila antimicrobial peptide (AMP) Atta, Mtk, and L. vannamei AMP PEN4 through NF-κB signal transduction pathway modification. Knocked-down expression of LvHSF1 by dsRNA resulted in downregulations of LvHSP70 and LvCactus, as well as cumulative mortality decreasing under V. alginolyticus or S. aureus infection in L. vannamei. Taken together, our data strongly suggest that LvHSF1 is involved in LvHSP70 regulation, therefore plays a great role in stress resistance. And it also takes part in LvCactus/LvDorsal feedback regulatory pathway modification of L. vannamei, which is in favor of V. alginolyticus or S. aureus infection.

Analysis of expression, cellular localization, and function of three inhibitors of apoptosis (IAPs) from Litopenaeus vannamei during WSSV infection and in regulation of antimicrobial peptide genes (AMPs)

Inhibitors of apoptosis (IAPs) play important roles in apoptosis and NF-κB activation. In this study, we cloned and characterized three IAPs (LvIAP1-3) from the Pacific white shrimp, Litopenaeusvannamei. LvIAP1-3 proteins shared signature domains and exhibited significant similarities with other IAP family proteins. The tissue distributions of LvIAP1-3 were studied. The expression of LvIAP1-3 was induced in the muscle after white spot syndrome virus (WSSV) infection. LvIAP1 expression in the gill, hemocytes, hepatopancreas, and intestine was responsive to WSSV and Vibrioalginolyticus infections. LvIAP2 expression in the gill, hemocytes, and hepatopancreas was also responsive to WSSV infection. The expression of LvIAP3 in the gill, hemocytes, and intestine was reduced after V. alginolyticus infection. When overexpressed in Drosophila S2 cells, GFP labeled-LvIAP2 was distributed in the cytoplasm and appeared as speck-like aggregates in the nucleus. Both LvIAP1 and LvIAP3 were widely distributed throughout the cytoplasm and nucleus. The expression of LvIAP1, LvIAP2, and LvIAP3 was significantly knocked down by dsRNA-mediated gene silencing. In the gill of LvIAP1- or LvIAP3-silenced shrimp, the expression of WSSV VP28 was significantly higher than that of the dsGFP control group, suggesting that LvIAP1 and LvIAP3 may play protective roles in host defense against WSSV infection. Intriguingly, the LvIAP2-silenced shrimp all died within 48 hours after dsLvIAP2 injection. In the hemocytes of LvIAP2-silenced shrimps, the expression of antimicrobial peptide genes (AMPs), including Penaeidins, lysozyme, crustins, Vibriopenaeicidae-induced cysteine and proline-rich peptides (VICPs), was significantly downregulated, while the expression of anti-lipopolysaccharide factors (ALFs) was upregulated. Moreover, LvIAP2 activated the promoters of the NF-κB pathway-controlled AMPs, such as shrimp Penaeidins and Drosophila drosomycin and attacin A, in Drosophila S2 cells. Taken together, these results reveal that LvIAP1 and LvIAP3 might participate in the host defense against WSSV infection, and LvIAP2 might be involved in the regulation of shrimp AMPs.

Litopenaeus vannamei Toll-interacting protein (LvTollip) is a potential negative regulator of the shrimp Toll pathway involved in the regulation of the shrimp antimicrobial peptide gene penaeidin-4 (PEN4)

The Toll-like receptor (TLR)-nuclear factor (NF)-κB signaling pathway is evolutionarily conserved from insects to mammals as a regulator of the expression of immune-related genes. In mammals, TLR-NF-κB signaling is tightly controlled because excessive activation of this pathway can result in severe damage to the host. The mammalian Toll-interacting protein (Tollip) has an important function in the negative regulation of this pathway, but no reports about invertebrate Tollip have been published to date. In this study, we cloned Litopenaeus vannamei Tollip (LvTollip) and investigated its function in the regulation of the NF-κB pathway-controlled antimicrobial peptide genes (AMPs). The LvTollip full-length cDNA is 1231bp long and contains an open reading frame of 813bp that encodes a 270-amino acid protein. LvTollip shares significant similarities to mammalian Tollips, which contain a centrally localized protein kinase C conserved region 2 (C2) domain and a C-terminal CUE domain. After challenges with the white spot syndrome virus (WSSV) or Vibrio alginolyticus, the expression levels of LvTollip were altered in the gill, hemocyte, hepatopancreatic, intestinal, and muscle tissues. In Drosophila S2 cells, LvTollip localized in the membrane and the cytoplasm and significantly inhibited the promoter activities of the NF-κB pathway-controlled AMP penaeidin-4 (PEN4). In LvTollip-knockdown shrimp, the expression level of AMP PEN4 was increased. However, the mortality rates of LvTollip-knockdown shrimp in response to WSSV or V. alginolyticus infections were not significantly different from those of the control group. Our results suggested that LvTollip might be involved in the negative regulation of PEN4 and that LvTollip expression was responsive to microbial infections.