Siniperca chuatsi rhabdovirus (SCRV) induces autophagy via PI3K/Akt-mTOR pathway in CPB cells

scTRIM44 Positively Regulated Siniperca Chuatsi Rhabdovirus Through RIG-I- and MDA5-Mediated Interferon Signaling

Tripartite Motif-Containing 44 (TRIM44) is responsible for cancers, neurodegenerative diseases, and viral infections. However, the role of Siniperca chuatsi TRIM44 (scTRIM44) during viral infection remains unclear. In the present study, we analyzed the molecular characteristics of scTRIM44 and its role in infectious spleen and kidney necrosis virus (ISKNV), largemouth bass virus (LMBV), and Siniperca chuatsi rhabdovirus (SCRV) infection. ScTRIM44 contained one B-box domain (B, 166-207 aa) and a coiled-coil domain (CC, 279-309 aa), but lacked the canonical RING domain of E3 ubiquitin ligases. The scTRIM44 mRNA was expressed relatively high in immune-related tissues. The mRNA expression of scTRIM44 significantly decreased in vivo and vitro post-ISKNV and -LMBV infection. However, the expression of scTRIM44 mRNA showed significant up-regulation post-SCRV infection. ScTRIM44 positively regulated SCRV infection in CPB cells, but copies of ISKNV and LMBV showed no significant alteration in over-expressed or knocked-down scTRIM44 cells. Moreover, scTRIM44 positively regulated RIG-I- and MDA5-mediated interferon molecule signaling. These data suggested that scTRIM44 promoted SCRV infection by positively regulating RIG-I- and MDA5-mediated interferon molecule signaling, but didn't regulate ISKNV and LMBV infection. This research provided a comprehensive insight into the antiviral activity of scTRIM44.

Akt inhibitors prevent CyHV-2 infection in vitro

Cyprinid herpesvirus 2 (CyHV-2) is a double-stranded DNA virus that infects goldfish (Carassius auratus) and crucian carp (C. carassius), resulting in substantial mortality rates and significant epidemiological implications. To gain deeper insights into CyHV-2-host interactions and identify potential therapeutic targets, quantitative proteomics analysis was conducted on CyHV-2-infected Ryukin goldfish fin (RyuF-2) cells. Our findings revealed significant alterations in the expression of proteins associated with the PI3K/Akt signaling pathway, which were up-regulated upon viral infection. Building on these observations, we employed LY294002, a specific inhibitor of PI3K, to investigate its impact on viral replication by inhibiting the PI3K/Akt pathway in GiCF cell line derived from the caudal fin of Carassius auratus gibelio (Bloch). Our results demonstrated the inhibition of both CyHV-2 replication and Akt phosphorylation within this pathway. Quercetin, a plant-derived analogue of LY294002, was further investigated for its anti-CyHV-2 effects in vitro as well as its underlying mechanism. The results suggested that quercetin exhibits antiviral properties against CyHV-2 and may exert its effects through mechanisms similar to those observed with LY294002. Given that aquaculture water serves as a vector for aquaculture viral diseases and the release of chemical compounds can lead to pollution of the aquatic environment, our study shifted focus to crude extracts obtained from plants. We confirmed crude quercetin extract derived from Cuminum anisum has antiviral activity against CyHV-2 in vitro. Therefore, based on our identification of the involvement of PI3K/Akt signaling pathway in CyHV-2 replication, along with verification of its antiviral mechanism using LY294002, we propose natural dietary quercetin as a promising candidate for development into a novel anti-CyHV-2 drug.

Autophagy induced by Cyprinid herpesvirus 3 (CyHV-3) facilitated intracellular viral replication and extracellular viral yields in common carp brain cells

Autophagy is a conservative and important process that exists in all eukaryotic cells in nature. Cyprinid herpesvirus 3 (CyHV-3), also known as KHV (Koi Herpesvirus), is a pathogen that mainly infecting common carp and koi. In the present study, we identified the CcLC3B gene, with a length of 379 bp and displaying a close evolutionary relationship with other sixteen different species, the tissue distribution and expression pattern of CcLC3 were also identified. We found that CyHV-3 infection could promote autophagy in CCB cells at the early stage but inhibit autophagy at the late stage by using confocal fluorescence microscopy, transmission electron microscopy and western blotting. And we measured the protein levels associated with the Akt/mTOR signalling pathway, intracellular replication of CyHV-3 at the mRNA and protein levels as well as viral titters. Collectively, the results taken together suggested that CyHV-3 infection could promote autophagy in CCB cells at the early stage but inhibit autophagy at the late stage via mTOR and that promoting autophagy could facilitate CyHV-3 intracellular replication and extracellular viral yields in CCB cells. These findings revealed the relationship between CyHV-3 and autophagy and provided a novel treatment strategy targeting the autophagy signalling pathway against CyHV-3 infection.

Autophagy regulation of virus infection in aquatic animals

Autophagy is a conserved intracellular degradation process that is required to maintain host homeostasis and cope with invading pathogens. Over the past few decades, studies on mammals have greatly increased our understanding of the relationship between autophagy and virus infection. Autophagy may convey the invader to lysosomes to degrade or activate the host immune response against virus replication. However, many viruses have developed some strategies that evade the degradative nature of autophagy or hijack this pathway for their gain. It follows that autophagy during viral infection is a double‐edged sword. In contrast to mammals, the review on autophagy modulated by the aquatic animal virus is limited. Here, after a brief description of the main information about autophagy, we highlight current progress on the interplays between autophagy and virus infection in aquatic animals, including the phenomenon of autophagy upon virus infection, the effect of modulating autophagy on virus replication, and the crosstalk between autophagy and immune response during virus infection. This review will help us better understand the pathogenic mechanism of aquatic animal viruses and develop proper antiviral countermeasures aimed at modulating autophagy.

Molecular cloning and functional analysis of polymeric immunoglobulin receptor, pIgR, gene in mandarin fish Siniperca chuatsi

Polymeric immunoglobulin receptor (pIgR) can bind and transport immunoglobulins (Igs), thus playing a role in mucosal immunity. In this study, pIgR gene was cloned in mandarin fish, Siniperca chuatsi, with the open reading frame (ORF) of 1011 bp, encoding 336 amino acids. The pIgR protein consists of a signal peptide, an extracellular domain, a transmembrane domain and an intracellular region, with the presence of two Ig-like domains (ILDs) in the extracellular domain, as reported in other species of fish. The pIgR gene was expressed in all organs/tissues of healthy mandarin fish, with higher level observed in liver and spleen. Following the immersion infection of Flavobacterium columnare, pIgR transcripts were detected in immune related, especially mucosal tissues, with significantly increased transcription during the first two days of infection. Through transfection of plasmids expressing pIgR, IgT and IgM, pIgR was found to be interacted with IgT and IgM as revealed by co-immunoprecipitation and immunofluorescence.

Harmine suppresses the malignant phenotypes and PI3K activity in breast cancer

Breast cancer remains a serious threaten to the women's health, discovery of potent treatment would help to improve the outcomes of breast cancer patients. Harmine extracted from Peganum harmala L , has been reported to exert tumor suppressive activity in several malignancies. Our objective was to demonstrate the effects of harmine on the malignant phenotypes of breast cancer cells. Breast cancer cell lines (MDA-MB-231, SKBR3, and MCF-7) and human normal breast cell line MCF-10A were employed in the present study. The MTT and colony formation assays were applied to the detection of cell viability and proliferation. Wound healing and transwell assays were performed to evaluate the alterations of cell migration and invasion after harmine treatment. Flow cytometry was applied to assess the effect of harmine in inducing cell apoptosis. Furthermore, western blotting assay was used to detect the biomarkers of epithelial-mesenchymal transition and phosphatidylinositol 3 kinase (PI3K) signaling pathway. The tumorigenesis ability was detected by subcutaneous implantation. Harmine dose-dependently suppressed the viability and proliferative capacity of breast cancer cells. Flow cytometry showed that harmine induced apoptosis in MCF-7 and MDA-MB-231 cells. In addition, harmine effectively inhibited the migration and invasion abilities of breast cancer cells. Western blotting indicated harmine significantly promoted E-cadherin and PTEN expression, while suppressed N-cadherin, vimentin, PI3K, p-mTOR, and AKT levels. Interfering the PTEN expression by siRNA partly rescued the activity of PI3K signaling pathway. Moreover, harmine injection also suppressed the tumorigenesis of breast cancer cells. Our results suggested that Hermine could suppress multiple malignant phenotypes and inhibit PI3K signaling, which supports that harmine might be a potential tumor-suppressive natural compound against breast cancer.

Grass Carp Reovirus triggers autophagy enhancing virus replication via the Akt/mTOR pathway

Autophagy impacts the replication cycle of many viruses. Grass Carp Reovirus (GCRV) is an agent that seriously affects the development of the grass carp aquaculture industry. The role of autophagy in GCRV infection is not clearly understood. In this study, we identified that GCRV infection triggered autophagy in CIK cells, which was demonstrated by transmission electron microscopy, the conversion of LC3B I to LC3B II and the level of autophagy substrate p62. Furthermore, we found that GCRV infection activated Akt-mTOR signaling pathway, and the conversion of LC3B I to LC3B II was increased by inhibiting mTOR with rapamycin (Rap) but decreased by activating Akt with insulin. We then assessed the effects of autophagy on GCRV replication. We found that inducing autophagy with Rap promoted GCRV proliferation but inhibiting autophagy with 3 MA or CQ inhibited GCRV replication in CIK cells. Moreover, it was found that enhancing Akt-mTOR activity by insulin, GCRV VP7 protein and viral titers of GCRV were decreased. Collectively, these results indicated that GCRV infection induced autophagy involved in GCRV replication via the Akt-mTOR signal pathway. Thus, new insights into GCRV pathogenesis and antiviral treatment strategies are provided.

The mTOR/PGC-1α/SIRT3 Pathway Drives Reductive Glutamine Metabolism to Reduce Oxidative Stress Caused by ISKNV in CPB Cells

Under oxidative stress, viruses prefer glycolysis as an ATP source, and glutamine is required as an anaplerotic substrate to replenish the TCA cycle. Infectious spleen and kidney necrosis virus (ISKNV) induces reductive glutamine metabolism in the host cells. Here we report that ISKNV infection the increased NAD+/NADH ratio and the gene expression of glutaminase 1 (GLS1), glutamate dehydrogenase (GDH), and isocitrate dehydrogenase (IDH2) resulted in the phosphorylation and activation of mammalian target of rapamycin (mTOR) in CPB cells. Inhibition of mTOR signaling attenuates ISKNV-induced the upregulation of GLS1, GDH, and IDH2 genes expression, and exhibits significant antiviral activity. Moreover, the expression of silent information regulation 2 homolog 3 (SIRT3) in mRNA level is increased to enhance the reductive glutamine metabolism in ISKNV-infected cells. And those were verified by the expression levels of metabolic genes and the activities of metabolic enzymes in SIRT3-overexpressed or SIRT3-knocked down cells. Remarkably, activation of mTOR signaling upregulates the expression of the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) gene, leading to increased expression of SIRT3 and metabolic genes. These results indicate that mTOR signaling manipulates reductive glutamine metabolism in ISKNV-infected cells through PGC-1α-dependent regulation of SIRT3. Our findings reveal new insights on ISKNV-host interactions and will contribute new cellular targets to antiviral therapy. IMPORTANCE Infectious spleen and kidney necrosis virus (ISKNV) is the causative agent of farmed fish disease that has caused huge economic losses in fresh and marine fish aquaculture. The redox state of cells is shaped by virus into a favorable microenvironment for virus replication and proliferation. Our previous study demonstrated that ISKNV replication induced glutamine metabolism reprogramming, and it is necessary for the ISKNV multiplication. In this study, the mechanistic link between the mTOR/PGC-1α/SIRT3 pathway and reductive glutamine metabolism in the ISKNV-infected cells was provided, which will contribute new insights into the pathogenesis of ISKNV and antiviral treatment strategies.

Autophagy Delays Apoptotic Cell Death Induced by Siniperca chuatsi Rhabdovirus in Epithelioma Papulosum Cyprinid Cells

Autophagy and apoptosis are two key cell fate determination pathways, which play vital roles in the interaction between viruses and host cells. Previous research had confirmed that one strain of fish rhabdoviruses, Siniperca chuatsi rhabdovirus (SCRV), could induce apoptosis and autophagy after infection. In the current study, we continued to analyze the interaction of autophagy and apoptosis in SCRV-infected EPC cell lines after treatment with different autophagy or apoptosis inhibitors. We found that SCRV infection could activate the mitochondrial apoptotic pathway by the detection of the activities of the caspase-3 and caspase-9 and by flow cytometry analysis in JC-1-stained cells, respectively. Furthermore, no significant autophagy-related factors were disturbed in SCRV-infected cell after apoptosis inhibitor Z-VAD-FMK treatment, while autophagy inducer rapamycin could obviously delay the occurrence of CPE and cell death. Meanwhile, rapamycin was able to reduce the proportion of apoptotic cells. Besides that, rapamycin could disturb the expression of p62 and LC3B-II, and the transcription level of SCRV nucleoprotein mRNA. The progeny virus titers did not show a big difference between the rapamycin treatment or without it. Collectively, our data preliminarily confirmed that SCRV-activated autophagy could delay apoptosis in EPC cells and may not affect virus production. Further study may need to focus on the crosstalk regulation and its roles on the SCRV infection.

Molecular Characterization of Paralichthys olivaceus MAF1 and Its Potential Role as an Anti-Viral Hemorrhagic Septicaemia Virus Factor in Hirame Natural Embryo Cells

MAF1 is a global suppressor of RNA polymerase III-dependent transcription, and is conserved from yeast to human. Growing evidence supports the involvement of MAF1 in the immune response of mammals, but its biological functions in fish are unknown. We isolated and characterized Maf1 from the olive flounder Paralichthys olivaceus (PoMaf1). The coding region of PoMaf1 comprised 738 bp encoding a 245-amino-acid protein. The deduced PoMAF1 amino acid sequence shared features with those of MAF1 orthologues from vertebrates. PoMaf1 mRNA was detected in all tissues examined, and the levels were highest in eye and muscle tissue. The PoMaf1 mRNA level increased during early development. In addition, the PoMaf1 transcript level decreased during viral hemorrhagic septicemia virus (VHSV) infection of flounder hirame natural embryo (HINAE) cells. To investigate the role of PoMaf1 in VHSV infection, single-cell-derived PoMaf1 knockout HINAE cells were generated using the clustered regularly interspaced short palindromic repeats/CRISPR-associated-9 (CRISPR/Cas9) system, and cell clones with complete disruption of PoMaf1 were selected. PoMaf1 disruption increased the VHSV glycoprotein (G) mRNA levels during VHSV infection of HINAE cells, implicating PoMAF1 in the immune response to VSHV infection. To our knowledge, this is the first study to characterize fish Maf1, which may play a role in the response to viral infection.