Autophagy in antiviral innate immunity

Hypervirulent fowl adenovirus serotype 4 elicits early innate immune response and promotes virus-induced cellular autophagy in the spleen

The recent emergence of hepatitis-hydropericardium syndrome caused by highly pathogenic fowl adenovirus serotype 4 (FAdV-4) has resulted in significant economic losses to the poultry industry. However, the early innate immune response of immune organs within 24 hpi and the induction of autophagy in vivo after FAdV-4 infection have not been fully elucidated. In this study, 35-day-old specific pathogen-free (SPF) chickens were artificially infected with hypervirulent FAdV-4, which resulted in a mortality rate of up to 90%. The results showed that FAdV-4 infection rapidly triggered the innate immune response in vivo of chickens, with the spleen eliciting a stronger innate immune response than the thymus and bursa. During the early stage of viral infection within 24 hpi, the main receptors TLR3/7/21, MDA5, and cGAS were activated via the NF-κB and TBK1/IRF7-dependent signaling pathways, which up-regulated production of inflammatory cytokines and type I interferons. Additionally, the expression levels of the autophagy-related molecules LC3B, Beclin1, and ATG5 were significantly up-regulated at 24 hpi, while degradation of SQSTM1/p62 was observed, suggesting that FAdV-4 infection elicits a complete autophagy response in the spleen. Besides, the colocalization of Fiber2 and LC3B suggested that FAdV-4 infection induced autophagy which benefits FAdV-4 replication in vivo. This study provides new insights into the immunoregulation signal pathways of the early innate immunity in response to hypervirulent FAdV-4 infection in vivo within 24 hpi and the close relationship between viral replication and autophagy.

ISKNV Triggers AMPK/mTOR-Mediated Autophagy Signaling through Oxidative Stress, Inducing Antioxidant Enzyme Expression and Enhancing Viral Replication in GF-1 Cells

Infectious spleen and kidney necrosis virus (ISKNV) infections can induce the process of host cellular autophagy but have rarely been identified within the molecular autophagy signaling pathway. In the present study, we demonstrated that ISKNV induces ROS-mediated oxidative stress signals for the induction of 5'AMP-activated protein kinase/mechanistic target of rapamycin kinase (AMPK/mTOR)-mediated autophagy and upregulation of host antioxidant enzymes in fish GF-1 cells. We also examined ISKNV-induced oxidative stress, finding that reactive oxidative species (ROS) increased by 1.5-fold and 2.5-fold from day 2 to day 3, respectively, as assessed by the H2DCFDA assay for tracing hydrogen peroxide (H2O2), which was blocked by NAC treatment in fish GF-1 cells. Furthermore, ISKNV infection was shown to trigger oxidative stress/Nrf2 signaling from day 1 to day 3; this event was then correlated with the upregulation of antioxidant enzymes such as Cu/ZnSOD and MnSOD and was blocked by the antioxidant NAC. Using an MDC assay, TEM analysis and autophagy marker LC3-II/I ratio, we found that ROS stress can regulate autophagosome formation within the induction of autophagy, which was inhibited by NAC treatment in GF-1 cells. Through signal analysis, we found that AMPK/mTOR flux was modulated through inhibition of mTOR and activation of AMPK, indicating phosphorylation levels of mTOR Ser 2448 and AMPK Thr 172 from day 1 to day 3; however, this process was reversed by NAC treatment, which also caused a reduction in virus titer (TCID50%) of up to 1000 times by day 3 in GF-1 cells. Thus, ISKNV-induced oxidative stress signaling is blocked by antioxidant NAC, which can also either suppress mTOR/AMPK autophagic signals or reduce viral replication. These findings may provide the basis for the creation of DNA control and treatment strategies.

Deep sequencing identified miR-193b-3p as a positive regulator of autophagy targeting Akt3 in Ctenopharyngodon idella CIK cells during GCRV infection

Recent research has highlighted complex and close interaction between miRNAs, autophagy, and viral infection. In this study, we observed the autophagy status in CIK cells infected with GCRV at various time points. We found that GCRV consistently induced cellar autophagy from 0 h to 12 h post infection. Subsequently, we performed deep sequencing on CIK cells infected with GCRV at 0 h and 12 h respectively, identifying 38 DEMs and predicting 9581 target genes. With the functional enrichment analyses of GO and KEGG, we identified 35 autophagy-related target genes of these DEMs, among which akt3 was pinpointed as the most central hub gene using module assay of the PPI network. Then employing the miRanda and Targetscan programs for prediction, and verification through a double fluorescent enzyme system and qPCR method, we confirmed that miR-193 b-3p could target the 3'-UTR of grass carp akt3, reducing its gene expression. Ultimately, we illustrated that grass carp miR-193 b-3p could promote autophagy in CIK cells. Above results collectively indicated that miRNAs might play a critical role in autophagy of grass carp during GCRV infection and contributed significantly to antiviral immunity by targeting autophagy-related genes. This study may provide new insights into the intricate mechanisms involved in virus, autophagy, and miRNAs.

Inhibition of cellular activation induced by platelet factor 4 via the CXCR3 pathway ameliorates Japanese encephalitis and dengue viral infections

BACKGROUND

Activated platelets secrete platelet factor 4 (PF4), which contributes to viral pathogenesis. Recently, we reported the proviral role of PF4 in replication of closely related flaviviruses, Japanese encephalitis virus (JEV) and dengue virus (DENV).

OBJECTIVES

This study aimed to investigate the detailed mechanism of PF4-mediated virus replication.

METHODS

PF4-/- or wild-type (WT) mice were infected with JEV, and host defense mechanisms, including autophagic/interferon (IFN) responses, were assessed. WT mice were pretreated with the CXCR3 antagonist AMG487 that inhibits PF4:CXCR3 pathway. This pathway was tested in PF4-/- monocytes infected with DENV or in monocytes isolated from patients with DENV infection.

RESULTS

PF4-/- mice infected with JEV showed reduced viral load and improved brain inflammation and survival. PF4-/- mice synthesized more IFN-α/β with higher expression of phosphorylated IRF3 in the brain. PF4 treatment decreased IRF-3/7/9 and IFN-α/β expression and suppressed autophagic LC3-II flux and lysosomal degradation of viral proteins in JEV-infected cells. PF4 increased the expression of P-mTOR, P-p38, and P-ULK1Ser757 and decreased expression of LC3-II. Decreased autophagosome-lysosome fusion in turn promoted DENV2 replication. The above processes were reversed by AMG487. Uninfected PF4-/- monocytes showed elevated LC3-II and autophagosome-lysosome fusion. Microglia of JEV-infected PF4-/- mice exhibited elevated LC3-II inversely related to viral load. Similarly, monocytes from PF4-/- mice showed reduced infection by DENV2. In patients with DENV infection, higher plasma PF4 and viral load were inversely correlated with LC3-II, LAMP-1, and lysosomal degradation of DENV-NS1 in monocytes during the febrile phase.

CONCLUSION

These studies suggest that PF4 deficiency or inhibition of the PF4:CXCR3 pathway prevents JEV and DENV infection. The studies also highlight the PF4:CXCR3 axis as a potential target to develop treatment regimens against flaviviruses.

HCMV miR-UL70-3p downregulates the rapamycin-induced autophagy by targeting the autophagy-related protein 9A (ATG9A)

Human cytomegalovirus (HCMV) is a representative β-herpesvirus that establishes persistent infections in humans, and exhibits high seropositivity rates in adults. It has co-evolved with its human host and employs various strategies to evade antiviral mechanisms by utilizing a significant portion of its genome. HCMV-encoded proteins and miRNAs have been implicated in regulating these mechanisms, enabling viral survival within the human body. During viral infections, autophagy, a conserved catabolic process essential for cellular homeostasis, acts as an antiviral defense mechanism. Multiple studies have reported that HCMV can modulate autophagy through its proteins and miRNAs, thereby influencing its survival within the host. In this study, we showed the potential involvement of HCMV miRNAs in cellular autophagy. We employed various bioinformatic tools to predict putative HCMV miRNAs that target autophagy-related genes and their corresponding cellular autophagy genes. Our results show that the 3'UTR of autophagy-related genes, including ATG9A, ATG9B, ATG16L2, SQSTM1, and EIF2AK2, harbors potential binding sites for hcmv-miR-UL70-3p. Experimental manipulation involving ectopic expression of hcmv-miR-UL70-3p demonstrated a significant reduction in rapamycin-induced autophagy, with ATG9A as its functional target. These findings establish that hcmv-miR-UL70-3p acts as an autophagy inhibitor by suppressing the expression of ATG9A.

Regulation of Bombyx mori ferritin heavy-chain homolog on ROS induces multiple effects on BmNPV replication

Ferritin is an iron-binding protein composed of light-chain and heavy-chain homologs with a molecular weight of about 500 kDa. Free iron ions significantly affect reactive oxygen species (ROS) accumulation. Previous research has shown that Bombyx mori nucleopolyhedrosis virus (BmNPV) can increase ROS accumulation, activate autophagy, induce apoptosis, and upregulate the expression of B. mori ferritin heavy-chain homolog (BmFerHCH). However, the mechanism of mutual regulation between BmFerHCH and ROS-mediated autophagy and apoptosis induced by BmNPV remains unclear. In this study, we found that BmNPV induced the time-dependent accumulation of ROS in BmN cells, thereby promoting BmFerHCH expression. Interestingly, in BmFerHCH-overexpressed cells, BmNPV replication was inhibited in the first 18 h after infection but stimulated after 24 h. Further research on H2O2 or antioxidant-treated cells indicated that ROS-induced autophagy slightly increased in the early infection stage and increased BmNPV replication, while in the late stage, a large accumulation of ROS induced apoptosis and inhibited BmNPV replication. In this process, BmFerHCH inhibits BmNPV-induced ROS accumulation by chelating Fe2+. Taken together, BmFerHCH regulates ROS-mediated autophagy and apoptosis to achieve its various effects on BmNPV replication. These findings will help elucidate BmNPV-induced autophagy and apoptosis mediated by ROS and BmFerHCH, as well as the mutually fighting relationship between viruses and hosts.

Grouper Atg14 promotes Singapore grouper iridovirus (SGIV) replication by inhibiting the host innate immune response

As one of the important members of the autophagy-related protein family, Atg14 plays a key role in the formation and maturation of autophagosomes. However, little is known about the potential roles of fish Atg14 and its roles in virus infection. In the present study, the homolog of Atg14 (EcAtg14) from the orange-spotted grouper (Epinephelus coioides) was cloned and characterized. The open reading frame (ORF) of EcAtg14 consists of 1530 nucleotides, encoding 509 amino acids, with a predicted molecular weight of 56.9 kDa. EcAtg14 was distributed in all tested tissues, with higher expression in liver, blood and spleen. The expression of EcAtg14 was increased in grouper spleen (GS) cells after Singapore grouper iridovirus (SGIV) infection. EcAtg14 was distributed in the cytoplasm of GS cells. Overexpression of EcAtg14 promoted SGIV replication in GS cells and inhibited IFN3, ISRE and NF-κB promoter activities. Co-immunoprecipitation results showed that there was an interaction between EcAtg14 and EcBeclin. EcAtg14 also promoted the synthesis of LC3-II in GS cells. These findings provide a basis for understanding the innate immune mechanism of grouper against viral infection.

MicroRNAs in the Regulation of RIG-I-like Receptor Signaling Pathway: Possible Strategy for Viral Infection and Cancer

The retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) play a crucial role as pattern-recognition receptors within the innate immune system. These receptors, present in various cell and tissue types, serve as essential sensors for viral infections, enhancing the immune system's capacity to combat infections through the induction of type I interferons (IFN-I) and inflammatory cytokines. RLRs are involved in a variety of physiological and pathological processes, including viral infections, autoimmune disorders, and cancer. An increasing body of research has examined the possibility of RLRs or microRNAs as therapeutic targets for antiviral infections and malignancies, despite the fact that few studies have focused on the regulatory function of microRNAs on RLR signaling. Consequently, our main emphasis in this review is on elucidating the role of microRNAs in modulating the signaling pathways of RLRs in the context of cancer and viral infections. The aim is to establish a robust knowledge base that can serve as a basis for future comprehensive investigations into the interplay between microRNAs and RIG-I, while also facilitating the advancement of therapeutic drug development.

ATG16L1 negatively regulates MAVS-mediated antiviral signaling in black carp Mylopharyngodon piceus

Autophagy related 16 like 1 (ATG16L1) is a crucial component of autophagy that regulates the formation of the autophagosome. In mammals, ATG16L1 also performs important roles in immunity, including controlling viral replication and regulating innate immune signaling; however, investigation on the role of piscine ATG16L1 in immunity is rare. In this report, the ATG16L1 homolog of black carp Mylopharyngodon piceus (bcATG16L1) was cloned and identified, and its negative regulatory role in mitochondrial antiviral signaling protein (MAVS)-mediated antiviral signaling was described. The coding region of bcATG16L1 consists of 1830 nucleotides and encodes 609 amino acids, including one coiled-coil domain at the N-terminus, three low complexity region domains in the middle, and seven WD40 domains at the C-terminus. By immunofluorescence assay and immunoblotting, we found that bcATG16L1 is a cytosolic protein with a molecular weight of ∼74 kDa. In addition, over-expression of bcATG16L1 suppressed bcMAVS-mediated bcIFNa and DrIFNφ1 promoters transcriptional activity and inhibited bcMAVS-mediated antiviral activity. We further confirmed the co-localization of bcATG16L1 and bcMAVS by immunofluorescence assay and verified the protein interaction between bcATG16L1 and bcMAVS by immunoprecipitation assay. Our results report for the first time that black carp ATG16L1 suppresses MAVS-mediated antiviral signaling in teleost fish.

Severe acute respiratory syndrome coronavirus-2 accessory proteins ORF3a and ORF7a modulate autophagic flux and Ca2+ homeostasis in yeast

Virus infection involves the manipulation of key host cell functions by specialized virulence proteins. The Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) small accessory proteins ORF3a and ORF7a have been implicated in favoring virus replication and spreading by inhibiting the autophagic flux within the host cell. Here, we apply yeast models to gain insights into the physiological functions of both SARS-CoV-2 small open reading frames (ORFs). ORF3a and ORF7a can be stably overexpressed in yeast cells, producing a decrease in cellular fitness. Both proteins show a distinguishable intracellular localization. ORF3a localizes to the vacuolar membrane, whereas ORF7a targets the endoplasmic reticulum. Overexpression of ORF3a and ORF7a leads to the accumulation of Atg8 specific autophagosomes. However, the underlying mechanism is different for each viral protein as assessed by the quantification of the autophagic degradation of Atg8-GFP fusion proteins, which is inhibited by ORF3a and stimulated by ORF7a. Overexpression of both SARS-CoV-2 ORFs decreases cellular fitness upon starvation conditions, where autophagic processes become essential. These data confirm previous findings on SARS-CoV-2 ORF3a and ORF7a manipulating autophagic flux in mammalian cell models and are in agreement with a model where both small ORFs have synergistic functions in stimulating intracellular autophagosome accumulation, ORF3a by inhibiting autophagosome processing at the vacuole and ORF7a by promoting autophagosome formation at the ER. ORF3a has an additional function in Ca2+ homeostasis. The overexpression of ORF3a confers calcineurin-dependent Ca2+ tolerance and activates a Ca2+ sensitive FKS2-luciferase reporter, suggesting a possible ORF3a-mediated Ca2+ efflux from the vacuole. Taken together, we show that viral accessory proteins can be functionally investigated in yeast cells and that SARS-CoV-2 ORF3a and ORF7a proteins interfere with autophagosome formation and processing as well as with Ca2+ homeostasis from distinct cellular targets.

GAPDH mediates plant reovirus-induced incomplete autophagy for persistent viral infection in leafhopper vector

Macroautophagy/autophagy is a conserved mechanism launched by host organisms to fight against virus infection. Double-membraned autophagosomes in arthropod vectors can be remodeled by arboviruses to accommodate virions and facilitate persistent viral propagation, but the underlying mechanism is unknown. Rice gall dwarf virus (RGDV), a plant nonenveloped double-stranded RNA virus, induces the formation of virus-containing double-membraned autophagosomes to benefit persistent viral propagation in leafhopper vectors. In this study, it was found that the capsid protein P2 of RGDV alone induced autophagy. P2 specifically interacted with GAPDH (glyceraldehyde-3-phosphate dehydrogenase) and ATG4B both in vitro and in vivo. Furthermore, the GAPDH-ATG4B complex could be recruited to virus-induced autophagosomes. Silencing of GAPDH or ATG4B expression suppressed ATG8 lipidation, autophagosome formation, and efficient viral propagation. Thus, P2 could directly recruit the GAPDH-ATG4B complex to induce the formation of initial autophagosomes. Furthermore, such autophagosomes were modified to evade fusion with lysosomes for degradation, and thus could be persistently exploited by viruses to facilitate efficient propagation. GAPDH bound to ATG14 and inhibited the interaction of ATG14 with SNAP29, thereby preventing ATG14-SNARE proteins from mediating autophagosome-lysosome fusion. Taken together, these results highlight how RGDV activates GAPDH to initiate autophagosome formation and block autophagosome degradation, finally facilitating persistent viral propagation in insect vectors. The findings reveal a positive regulation of immune response in insect vectors during viral infection.

Sindbis virus is suppressed in the yellow fever mosquito Aedes aegypti by ATG-6/Beclin-1 mediated activation of autophagy

Autophagy is a critical modulator of pathogen invasion response in vertebrates and invertebrates. However, how it affects mosquito-borne viral pathogens that significantly burden public health remains underexplored. To address this gap, we use a genetic approach to activate macroautophagy/autophagy in the yellow fever mosquito (Aedes aegypti), infected with a recombinant Sindbis virus (SINV) expressing an autophagy activator. We first demonstrate a 17-amino acid peptide derived from the Ae. aegypti autophagy-related protein 6 (ATG-6/beclin-1-like protein) is sufficient to induce autophagy in C6/36 mosquito cells, as marked by lipidation of ATG-8 and puncta formation. Next, we engineered a recombinant SINV expressing this bioactive beclin-1-like peptide and used it to infect and induce autophagy in adult mosquitoes. We find that modulation of autophagy using this recombinant SINV negatively regulated production of infectious viruses. The results from this study improve our understanding of the role of autophagy in arboviruses in invertebrate hosts and also highlight the potential for the autophagy pathway to be exploited for arboviral control.

Interactions of Autophagy and the Immune System in Health and Diseases

Autophagy is a highly conserved process that utilizes lysosomes to selectively degrade a variety of intracellular cargo, thus providing quality control over cellular components and maintaining cellular regulatory functions. Autophagy is triggered by multiple stimuli ranging from nutrient starvation to microbial infection. Autophagy extensively shapes and modulates the inflammatory response, the concerted action of immune cells, and secreted mediators aimed to eradicate a microbial infection or to heal sterile tissue damage. Here, we first review how autophagy affects innate immune signaling, cell-autonomous immune defense, and adaptive immunity. Then, we discuss the role of non-canonical autophagy in microbial infections and inflammation. Finally, we review how crosstalk between autophagy and inflammation influences infectious, metabolic, and autoimmune disorders.

Molecular characterization and expression of the autophagy-related gene Atg14 in WSSV-infected Procambarus clarkii

Atg14 (autophagy-related gene 14), also known as Atg14L or Barkor (Beclin-1 associated autophagy-related key regulator), plays an important role in a variety of biological processes including immunity, development, tumor inhibition, longevity, and protection against some cardiac and neurodegenerative diseases. However, very few studies have characterized Atg14 expression in invertebrates, particularly crustaceans. Here, a novel Atg14 gene from Procambarus clarkii (named PcAtg14) was characterized via RACE technology. Bioinformatics analysis showed that the total length of the PcAtg14 gene sequence was 2,880 bp, and it was predicted to encode 488 amino acids. The results of homology comparison showed that PcAtg14 exhibited the highest homology with crustacean the American lobster (Homarus americanus). Quantitative real-time PCR expression analysis showed that PcAtg14 was expressed in all tissues of P. clarkii, with the hepatopancreas having the highest expression and the eyestalk exhibiting the lowest expression. Upon white spot syndrome virus (WSSV) infection, the relative expression of PcAtg14 in the hepatopancreas, muscle, hemocyte, gill, heart and epidermis were significantly up-regulated at different time periods. After PcAtg14 gene silencing via RNA interference (RNAi), the proliferation of WSSV in P. clarkii was significantly inhibited, which coincided with a significant increase in P. clarkii mortality and an increase in the expression of autophagy-related genes (ATGs). Transmission electron microscopy analysis demonstrated an increase in the number of autophagosomes in the hepatopancreas of the PcAtg14 gene silencing group compared to the control group after WSSV infection. Collectively, these results indicated that PcAtg14 suppressed autophagy by reduce the fusion of autophagosomes and lysosomes, thereby promoting WSSV replication in P. clarkii. The findings here therefore provide novel insights into the immune mechanisms through which P. clarkii responds to WSSV infection.

Soluble (PD-1) and Autophagy protein (ATG-5) in patients with tuberculosis

mmune checkpoints such as programmed cell death protein (PD-1) and autophagy-related protein 5 (ATG5) can directly affect the immune response and thus, interfere with infection with Mycobacterium tuberculosis (Mtb). This study aimed to determine the role of soluble ATG5 and soluble PD-1 proteins in tuberculosis (TB) patients. The study included a collection of 90 blood samples (47 samples from patients with confirmed tuberculosis and 43 samples from age and gender-matched healthy subjects to estimate the concentration of soluble autophagy (ATG-5) and programmed cell death protein (PD-1). Enzyme-linked immunosorbent assay was used to estimate the serum levels of these markers. The median value of ATG5 level in patients was 2.08 µg/ml, which is higher than the level of the control group (median = 0.93 µg/ml) with a highly significant difference. Similarly, the median value of PD-1 level in patients was 259.4 ng/ml (range 107.76-924.25 ng/ml), which was higher than that of the control (median = 146.4 ng/ml, range = 50.32-1117.1 ng/ml) and with a highly significant difference. It can be concluded that both soluble ATG5 and PD-1 increased significantly in patients with TB compared with controls. Keywords: tuberculosis, M. tuberculosis, Autophagy, Programmed cell death protein-1

A Comparative Transcriptomic Analysis Reveals That HSP90AB1 Is Involved in the Immune and Inflammatory Responses to Porcine Deltacoronavirus Infection

PDCoV is an emerging enteropathogenic coronavirus that mainly causes acute diarrhea in piglets, seriously affecting pig breeding industries worldwide. To date, the molecular mechanisms of PDCoV-induced immune and inflammatory responses or host responses in LLC-PK cells in vitro are not well understood. HSP90 plays important roles in various viral infections. In this study, HSP90AB1 knockout cells (HSP90AB1^KO) were constructed and a comparative transcriptomic analysis between PDCoV-infected HSP90AB1^WT and HSP90AB1^KO cells was conducted using RNA sequencing to explore the effect of HSP90AB1 on PDCoV infection. A total of 1295 and 3746 differentially expressed genes (DEGs) were identified in PDCoV-infected HSP90AB1^WT and HSP90AB1^KO cells, respectively. Moreover, most of the significantly enriched pathways were related to immune and inflammatory response-associated pathways upon PDCoV infection. The DEGs enriched in NF-κB pathways were specifically detected in HSP90AB1^WT cells, and NF-κB inhibitors JSH-23, SC75741 and QNZ treatment reduced PDCoV infection. Further research revealed most cytokines associated with immune and inflammatory responses were upregulated during PDCoV infection. Knockout of HSP90AB1 altered the upregulated levels of some cytokines. Taken together, our findings provide new insights into the host response to PDCoV infection from the transcriptome perspective, which will contribute to illustrating the molecular basis of the interaction between PDCoV and HSP90AB1.

Autophagy Agents in Clinical Trials for Cancer Therapy: A Brief Review

Autophagy has been of novel interest since it was first demonstrated to have effect in Burkitt’s lymphoma. Since that time, the autophagy agents chloroquine and hydroxychloroquine have become the only FDA (Food and Drug Administration)-approved autophagy inhibitors. While not approved for cancer therapy, there are ongoing clinical trials to evaluate their safety and efficacy. Pevonedistat has emerged as a novel inhibitor through the neddylation pathway and is an autophagy activator. This paper summarizes and presents current clinical trials for hydroxychloroquine (HCQ), chloroquine (CQ), and Pevonedistat for the clinician.

Novirhabdoviruses versus fish innate immunity: A review

Novirhabdoviruses belong to the Rhabdoviridae family of RNA viruses. All of the four members are pathogenic for bony fish. Particularly, Infectious hematopoietic necrosis virus (IHNV) and Viral hemorrhagic septicemia virus (VHSV) often cause mass animal deaths and huge economic losses, representing major obstacles to fish farming industry worldwide. The interactions between fish and novirhabdoviruses are becoming better understood. In this review, we will present our current knowledge of fish innate immunity, particularly type I interferon (IFN-I) response, against novirhabdoviral infection, and the evasion strategies exploited by novirhabdoviruses. Members of Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs) appear to be involved in novirhabdovirus surveillance. NF-κB activation and IFN-I induction are primarily triggered for antiviral defense. Autophagy can also be induced by viral glycoprotein (G). Although sensitive to IFN-I, novirhabdoviruses have nucleoprotein (N), matrix protein (M), and non-virion protein (NV) to interfere with host signal transduction and gene expression steps toward antiviral state establishment. Moreover, novirhabdoviruses may exploit some microRNAs for immunosuppression.

Acute Infection of Viral Pathogens and Their Innate Immune Escape

Viral infections can cause rampant disease in human beings, ranging from mild to acute, that can often be fatal unless resolved. An acute viral infection is characterized by sudden or rapid onset of disease, which can be resolved quickly by robust innate immune responses exerted by the host or, instead, may kill the host. Immediately after viral infection, elements of innate immunity, such as physical barriers, various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, provide the first line of defense for viral clearance. Innate immunity not only plays a critical role in rapid viral clearance but can also lead to disease progression through immune-mediated host tissue injury. Although elements of antiviral innate immunity are armed to counter the viral invasion, viruses have evolved various strategies to escape host immune surveillance to establish successful infections. Understanding complex mechanisms underlying the interaction between viruses and host’s innate immune system would help develop rational treatment strategies for acute viral infectious diseases. In this review, we discuss the pathogenesis of acute infections caused by viral pathogens and highlight broad immune escape strategies exhibited by viruses.

MiR-30a sensitized lung cancer against neoadjuvant chemotherapy by depressing autophagy

OBJECTIVE

This study was aimed at exploring whether miR-30a enhanced sensitivity of non-small-cell lung cancer (NSCLC) cells against neoadjuvant chemotherapy through an autophagy-dependent way.

METHODS

We totally recruited 304 NSCLC patients who have underwent chemotherapy, as well as 185 NSCLC patients who did not receive chemotherapy. NSCLC cell lines (i.e. H1299 and H460) were also purchased, and they were transfected by miR-30a mimic/inhibitor. Furthermore, cisplatin (DDP)/pemetrexed (PEM) resistance of NSCLC cells was assessed utilizing MTT assay, and autophagic proteins isolated from NSCLC tissues and cells were quantitated by western blotting.

RESULTS

Lowly expressed miR-30a was reflective of lymph node metastasis, advanced TNM stage and poor 5-year survival among NSCLC patients treated by neoadjuvant chemotherapy (i.e. combined treatment of DDP and PEM) (P < 0.05). Moreover, DDP combined with PEM attenuated viability and proliferation, but, on the contrary, promoted autophagy of H1299 and H460 cell lines (P < 0.05). However, miR-30a undermined resistance of NSCLC cells against DDP and PEM (P < 0.05), and it suppressed DDP/PEM-induced autophagy and promoted DDP/PEM-triggered apoptosis of NSCLC cells (P < 0.05).

CONCLUSIONS

Intentionally elevating miR-30a expression was conducive to improving NSCLC prognosis after neoadjuvant chemotherapy, for its depressing drug-caused autophagy and resistance.

MiR-139 Induces an Interferon-β Response in Prostate Cancer Cells by Binding to RIG-1

BACKGROUND

We previously identified a panel of five miRNAs associated with prostate cancer recurrence and metastasis. Expression of one of the down-regulated miRNAs, miR-139-5p, was significantly associated with a lower incidence of biochemical recurrence and metastasis. Transcriptome profiling of miR-139-expressing prostate cancer cells revealed up-regulation of genes involved in interferon (IFN) stimulation. The association between miR-139 and IFN-β was further explored in this study.

MATERIALS AND METHODS

We examined miR-139 transfected PC3, Du145 and LNCaP cells and the associated IFN response by transcriptome sequencing, immunoblotting and pulldown assays.

RESULTS

Treatment of prostate cancer cells by miR-139 resulted in the up-regulation of IFN-related genes. Specifically, miR-139 induced expression of the IFN-β protein. The ability of miR-139 to induce IFN-β was due to its binding to RIG-1 and the induction of IFN-related genes was found to be dependent on RIG-1 expression.

CONCLUSION

miR-139 acts as an immune agonist of RIG-1 to enhance IFN-β response in prostate cancer cells.

Selective Autophagy Receptors in Antiviral Defense

Autophagy ensures the degradation of cytosolic substrates by the lysosomal pathway. Cargoes destined to be eliminated are confined within double-membrane vesicles called autophagosomes, prior to fusion with endolysosomal vacuoles. Autophagy receptors selectively interact with cargoes and route them to elongating autophagic membranes, a process referred to as selective autophagy. Besides contributing to cell homeostasis, selective autophagy constitutes an important cell-autonomous defense mechanism against viruses. We review observations related to selective autophagy receptor engagement during host cell responses to virus infection. We examine the distinct roles of autophagy receptors in antiviral autophagy, consider the strategies viruses have evolved to escape or oppose such restrictions, and delineate the contributions of selective autophagy to the tailoring of antiviral innate responses. Finally, we mention some open and emerging questions in the field.

Regulation of RIG-I-like receptor-mediated signaling: interaction between host and viral factors

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are RNA sensor molecules that play essential roles in innate antiviral immunity. Among the three RLRs encoded by the human genome, RIG-I and melanoma differentiation-associated gene 5, which contain N-terminal caspase recruitment domains, are activated upon the detection of viral RNAs in the cytoplasm of virus-infected cells. Activated RLRs induce downstream signaling via their interactions with mitochondrial antiviral signaling proteins and activate the production of type I and III interferons and inflammatory cytokines. Recent studies have shown that RLR-mediated signaling is regulated by interactions with endogenous RNAs and host proteins, such as those involved in stress responses and posttranslational modifications. Since RLR-mediated cytokine production is also involved in the regulation of acquired immunity, the deregulation of RLR-mediated signaling is associated with autoimmune and autoinflammatory disorders. Moreover, RLR-mediated signaling might be involved in the aberrant cytokine production observed in coronavirus disease 2019. Since the discovery of RLRs in 2004, significant progress has been made in understanding the mechanisms underlying the activation and regulation of RLR-mediated signaling pathways. Here, we review the recent advances in the understanding of regulated RNA recognition and signal activation by RLRs, focusing on the interactions between various host and viral factors.

Broad and Complex Roles of NBR1-Mediated Selective Autophagy in Plant Stress Responses

Selective autophagy is a highly regulated degradation pathway for the removal of specific damaged or unwanted cellular components and organelles such as protein aggregates. Cargo selectivity in selective autophagy relies on the action of cargo receptors and adaptors. In mammalian cells, two structurally related proteins p62 and NBR1 act as cargo receptors for selective autophagy of ubiquitinated proteins including aggregation-prone proteins in aggrephagy. Plant NBR1 is the structural and functional homolog of mammalian p62 and NBR1. Since its first reports almost ten years ago, plant NBR1 has been well established to function as a cargo receptor for selective autophagy of stress-induced protein aggregates and play an important role in plant responses to a broad spectrum of stress conditions including heat, salt and drought. Over the past several years, important progress has been made in the discovery of specific cargo proteins of plant NBR1 and their roles in the regulation of plant heat stress memory, plant-viral interaction and special protein secretion. There is also new evidence for a possible role of NBR1 in stress-induced pexophagy, sulfur nutrient responses and abscisic acid signaling. In this review, we summarize these progresses and discuss the potential significance of NBR1-mediated selective autophagy in broad plant responses to both biotic and abiotic stresses.

Vitamin D3 as Potential Treatment Adjuncts for COVID-19

Severe acute respiratory syndrome coronavirus type (SARS-CoV2, also known as COVID-19), which is the latest pandemic infectious disease, constitutes a serious risk to human health. SARS-CoV2 infection causes immune activation and systemic hyperinflammation which can lead to respiratory distress syndrome (ARDS). ARDS victims are characterized by a significant increase in IL-6 and IL-1. Macrophage activation, associated with the "cytokine storm", promotes the dysregulation of the innate immunity. So far, without vaccines or specific therapy, all efforts to design drugs or clinical trials are worthwhile. Vitamin D and its receptor vitamin D receptor (VDR) exert a critical role in infections due to their remarkable impact on both innate and adaptive immune responses and on the suppression of the inflammatory process. The protective properties of vitamin D supplementation have been supported by numerous observational studies and by meta-analysis of clinical trials for prevention of viral acute respiratory infection. In this review, we compare the mechanisms of the host immune response to SARS-CoV2 infection and the immunomodulatory actions that vitamin D exerts in order to consider the preventive effect of vitamin D supplementation on SARS-CoV2 viral infection.

Cell Clearing Systems as Targets of Polyphenols in Viral Infections: Potential Implications for COVID-19 Pathogenesis

The novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has generated the ongoing coronavirus disease-2019 (COVID-19) pandemic, still with an uncertain outcome. Besides pneumonia and acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), other features became evident in the context of COVID-19. These includes endothelial and coagulation dysfunction with disseminated intravascular coagulation (DIC), and multiple organ dysfunction syndrome (MODS), along with the occurrence of neurological alterations. The multi-system nature of such viral infection is a witness to the exploitation and impairment of ubiquitous subcellular and metabolic pathways for the sake of its life-cycle, ranging from host cell invasion, replication, transmission, up to a cytopathic effect and overt systemic inflammation. In this frame, alterations in cell-clearing systems of the host are emerging as a hallmark in the pathogenesis of various respiratory viruses, including SARS-CoV-2. Indeed, exploitation of the autophagy and proteasome pathways might contribute not only to the replication of the virus at the site of infection but also to the spreading of either mature virions or inflammatory mediators at both cellular and multisystem levels. In this frame, besides a pharmacological therapy, many researchers are wondering if some non-pharmacological substances might counteract or positively modulate the course of the infection. The pharmacological properties of natural compounds have gained increasing attention in the field of alternative and adjunct therapeutic approaches to several diseases. In particular, several naturally-occurring herbal compounds (mostly polyphenols) are reported to produce widespread antiviral, anti-inflammatory, and anti-oxidant effects while acting as autophagy and (immuno)-proteasome modulators. This article attempts to bridge the perturbation of autophagy and proteasome pathways with the potentially beneficial effects of specific phytochemicals and flavonoids in viral infections, with a focus on the multisystem SARS-CoV-2 infection.

Role of Endolysosomes in Severe Acute Respiratory Syndrome Coronavirus-2 Infection and Coronavirus Disease 2019 Pathogenesis: Implications for Potential Treatments

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an enveloped, single-stranded RNA virus. Humans infected with SARS-CoV-2 develop a disease known as coronavirus disease 2019 (COVID-19) with symptoms and consequences including acute respiratory distress syndrome (ARDS), cardiovascular disorders, and death. SARS-CoV-2 appears to infect cells by first binding viral spike proteins with host protein angiotensin-converting enzyme 2 (ACE2) receptors; the virus is endocytosed following priming by transmembrane protease serine 2 (TMPRSS2). The process of virus entry into endosomes and its release from endolysosomes are key features of enveloped viruses. Thus, it is important to focus attention on the role of endolysosomes in SARS-CoV-2 infection. Indeed, coronaviruses are now known to hijack endocytic machinery to enter cells such that they can deliver their genome at replication sites without initiating host detection and immunological responses. Hence, endolysosomes might be good targets for developing therapeutic strategies against coronaviruses. Here, we focus attention on the involvement of endolysosomes in SARS-CoV-2 infection and COVID-19 pathogenesis. Further, we explore endolysosome-based therapeutic strategies to restrict SARS-CoV-2 infection and COVID-19 pathogenesis.

Advances in Foot-and-Mouth Disease Virus Proteins Regulating Host Innate Immunity

Foot-and-mouth disease (FMD) is a highly contagious disease that affects cloven-hoofed animals such as pigs, cattle, and sheep. The disease is caused by the foot-and-mouth disease virus (FMDV) which has a non-enveloped virion with icosahedral symmetry that encapsulates a positive-sense, single-stranded RNA genome of ∼8.4 kb. FMDV infection causes obvious immunosuppressive effects on the host. In recent years, studies on the immunosuppressive mechanism of FMDV have become a popular topic. In addition, studies have shown that many FMDV proteins are involved in the regulation of host innate immunity and have revealed mechanisms by which FMDV proteins mediate host innate immunity. In this review, advances in studies on the mechanisms of interaction between FMDV proteins and host innate immunity are summarized to provide a comprehensive understanding of FMDV pathogenesis and the theoretical basis for FMD prevention and control.

Melatonin potentials against viral infections including COVID-19: Current evidence and new findings

Viral infections are dangerous diseases for human health worldwide, which lead to significant morbidity and mortality each year. Because of their importance and the lack of effective therapeutic approaches, further attempts should be made to discover appropriate alternative or complementary treatments. Melatonin, a multifunctional neurohormone mainly synthesized and secreted by the pineal gland, plays some roles in the treatment of viral infections. Regarding a deadly outbreak of COVID-19 across the world, we decided to discuss melatonin functions against various viral infections including COVID-19. Therefore, in this review, we summarize current evidence on melatonin therapy for viral infections with focus on possible underlying mechanisms of melatonin actions.

Crimean-Congo hemorrhagic fever virus replication imposes hyper-lipidation of MAP1LC3 in epithelial cells

Crimean-Congo hemorrhagic fever virus (CCHFV) is a virus that causes severe liver dysfunctions and hemorrhagic fever, with high mortality rate. Here, we show that CCHFV infection caused a massive lipidation of LC3 in hepatocytes. This lipidation was not dependent on ATG5, ATG7 or BECN1, and no signs for recruitment of the alternative ATG12-ATG3 pathway for lipidation was found. Both virus replication and protein synthesis were required for the lipidation of LC3. Despite an augmented transcription of SQSTM1, the amount of proteins did not show a massive and sustained increase in infected cells, indicating that degradation of SQSTM1 by macroautophagy/autophagy was still occurring. The genetic alteration of autophagy did not influence the production of CCHFV particles demonstrating that autophagy was not required for CCHFV replication. Thus, the results indicate that CCHFV multiplication imposes an overtly elevated level of LC3 mobilization that involves a possibly novel type of non-canonical lipidation. Abbreviations: BECN1: Beclin 1; CCHF: Crimean-Congo hemorrhagic fever; CCHFV: Crimean-Congo hemorrhagic fever virus; CHX: cycloheximide; ER: endoplasmic reticulum; GFP: green fluorescent protein; GP: glycoproteins; MAP1LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; n.i.: non-infected; NP: nucleoprotein; p.i.: post-infection; SQSTM1: sequestosome 1.

Molecular Mechanisms of Immune Escape for Foot-and-Mouth Disease Virus

Foot-and-mouth disease virus (FMDV) causes a highly contagious vesicular disease in cloven-hoofed livestock that results in severe consequences for international trade, posing a great economic threat to agriculture. The FMDV infection antagonizes the host immune responses via different signaling pathways to achieve immune escape. Strategies to escape the cell immune system are key to effective infection and pathogenesis. This review is focused on summarizing the recent advances to understand how the proteins encoded by FMDV antagonize the host innate and adaptive immune responses.

Aichi virus 3C protease modulates LC3- and SQSTM1/p62-involved antiviral response

Rationale: Autophagy is an essential, homeostatic process by which cells break down their own components, it also contributes to restricting bacterial infection in host defense systems; yet, how autophagy regulates viral infection remains inconclusive. Aichi virus (AiV), belonging to the genus Kobuvirus in the Picornaviridae family, causes acute gastroenteritis in human. The role of autophagy-mediated anti-viral activity on AiV infection was investigated in this study. Methods: The effect of autophagy-associated molecules in retinoic acid-inducible gene-I (RIG-I)-like receptor (RLR) antiviral signal axis was analyzed in AiV infected cells by using biochemistry and pharmacologic approaches. In addition, the AiV viral protein regulating autophagy-associated RLR activity was also evaluated. Results: In AiV-infected cells, autophagic flux including the formation of autophagic vacuoles, as well as degradation of microtubule-associated protein light chain 3 (LC3) and sequestosome-1 (SQSTM1/p62) were observed. Ectopic overexpression of LC3 and p62, but not Atg proteins, contributed to RLR antiviral signal axis, shRNA knockdown of LC3 and p62 led to a downregulation of antiviral inflammation. Moreover, AiV infection inhibited double-stranded RNA (dsRNA)-activated RLR activity by the viral protein 3C protease but not H42D, C143S protease dead mutants. AiV 3C protease caused the degradation of LC3 and p62, and also RLR signal proteins. Conclusion: This study reveals a possible mechanism of autophagy-associated proteins regulating virus replication. Maintaining a cellular level of LC3 and p62 during the viral infection period might help restrict virus replication. Although, AiV 3C protease dampens the LC3 and p62-mediated host antiviral machinery for AiV replication. Results obtained provide a better understanding of the molecular pathogenesis of AiV for developing methods of prevention and treatment.

Apoptosis and autophagy as a turning point in viral–host interactions: the case of human norovirus and its surrogates

Human gastroenteritis viruses are amid the major causes of disease worldwide, responsible for more than 2 million deaths per year. Human noroviruses play a leading role in the gastroenteritis outbreaks and the continuous emergence of new strains contributes to the significant morbidity and mortality. Many aspects of the viral entry and infection process remain unclear, including the major response of the host cell to the virus, which is the trigger of several programmed cell death related mechanisms. In this review, we assessed apoptosis and autophagy at various stages in the infection process to provide better understanding of the viral–host interaction. This brings us closer to fully understanding how noroviruses work, thus allowing the development of specific antiviral therapies.

Characterization of virus-mediated immunogenic cancer cell death and the consequences for oncolytic virus-based immunotherapy of cancer

Oncolytic viruses have the potential to induce immunogenic cell death (ICD) that may provoke potent and long-lasting anti-cancer immunity. Here we aimed to characterize the ICD-inducing ability of wild-type Adenovirus (Ad), Semliki Forest virus (SFV) and Vaccinia virus (VV). We did so by investigating the cell death and immune-activating properties of virus-killed tumor cells. Ad-infection of tumor cells primarily activates autophagy, but also activate events of necroptotic and pyroptotic cell death. SFV infection on the other hand primarily activates immunogenic apoptosis while VV activates necroptosis. All viruses mediated lysis of tumor cells leading to the release of danger-associated molecular patterns, triggering of phagocytosis and maturation of dendritic cells (DCs). However, only SFV-infected tumor cells triggered significant T helper type 1 (Th1)-cytokine release by DCs and induced antigen-specific T-cell activation. Our results elucidate cell death processes activated upon Ad, SFV, and VV infection and their potential to induce T cell-mediated anti-tumor immune responses. This knowledge provides important insight for the choice and design of therapeutically successful virus-based immunotherapies.

Combination therapies enhance immunoregulatory properties of MIAMI cells

Background

Mesenchymal stromal cells (MSCs), adult stromal cells most commonly isolated from bone marrow (BM), are being increasingly utilized in various therapeutic applications including tissue repair via immunomodulation, which is recognized as one of their most relevant mechanism of action. The promise of MSC-based therapies is somewhat hindered by their apparent modest clinical benefits, highlighting the need for approaches that would increase the efficacy of such therapies. Manipulation of cellular stress-response mechanism(s) such as autophagy, a catabolic stress-response mechanism, with small molecules prior to or during MSC injection could improve MSCs’ therapeutic efficacy. Unfortunately, limited information exists on how manipulation of autophagy affects MSCs’ response to inflammation and subsequent immunoregulatory properties.

Methods

In this study, we exposed BM-MSC precursor cells, “marrow-isolated adult multilineage inducible” (MIAMI) cells, to autophagy modulators tamoxifen (TX) or chloroquine (CQ), together with IFN-γ. Exposed cells then underwent RNA sequencing (RNAseq) to determine the effects of TX or CQ co-treatments on cellular response to IFN-γ at a molecular level. Furthermore, we evaluated their immunoregulatory capacity using activated CD4+ T cells by analyzing T cell activation marker CD25 and the percentage of proliferating T cells after co-culturing the cells with MIAMI cells treated or not with TX or CQ.

Results

RNAseq data indicate that the co-treatments alter both mRNA and protein levels of key genes responsible for MSCs’ immune-regulatory properties. Interestingly, TX and CQ also altered some of the microRNAs targeting such key genes. In addition, while IFN-γ treatment alone increased the surface expression of PD-L1 and secretion of IDO, this increase was further enhanced with TX. An improvement in MIAMI cells’ ability to decrease the activation and proliferation of T cells was also observed with TX, and to a lesser extent, CQ co-treatments.

Conclusion

Altogether, this work suggests that both TX and CQ have a potential to enhance MIAMI cells’ immunoregulatory properties. However, this enhancement is more pronounced with TX co-treatment.

Autophagy protects against retinal cell death in mouse model of cytomegalovirus retinitis

BACKGROUND

Extensive death of uninfected bystander neuronal cells is an important component of the pathogenesis of cytomegalovirus retinitis (CMV). Our previous results have shown that there is a functional relationship between autophagy and apoptosis during MCMV infection of retinal pigment epithelium (RPE). The purpose of this study was to determine whether autophagy plays a significant role in the death of retinal cells during MCMV retinitis.

METHODS

The retinas of adult BALB/c mice were infected with MCMV via supraciliary injection. Rapamycin, a mTOR inhibitor, was injected to MCMV-infected BALB/c mice intraperitoneally. Immunohistochemistry and western blot were performed to observe the spread pattern of virus in retinas and the levels of targeted proteins. Plaque assay was performed to determine the virus titer in different groups. Since Atg5 is a key gene regulating autophagy, we bred Atg5^flox/flox; Nestin-Cre mice to deeply elucidate the role of autophagy during MCMV retinitis. Atg5^flox/flox; Nestin-Cre mice were genotyped and infected with MCMV. Immunohistochemistry was performed to observe the type of virus-infected cells and apoptosis in retinas during MCMV retinitis.

RESULTS

In MCMV mouse model, MCMV infection in outer nuclear layer (ONL) and inner nuclear layer (INL) in the retinas caused cleaved caspase 3 positive apoptosis, which is not co-localized with early antigen (EA) positive virus infected cells in rapamycin treated group. Rapamycin treatment increased the levels of LC3B-II by inhibiting mTOR and decreased the levels of cleaved caspase-3 during MCMV retinitis. However, virus propagation was not affected by rapamycin. In Atg5^flox/flox; Nestin-Cre mice, RPE and glial cells were the main targets of viral infection, and number of EA positive retinal cells and TUNEL positive retinal cells was significantly increased compared to Atg5^flox/+; Nestin-Cre mice though there was no difference of virus propagation between Atg5^flox/flox; Nestin-Cre mice and Atg5^flox/+; Nestin-Cre mice.

CONCLUSIONS

Autophagy protects retinal cells from MCMV infection induced apoptosis through mTOR-mediated signaling pathway.

Flavivirus Replication Organelle Biogenesis in the Endoplasmic Reticulum: Comparison with Other Single-Stranded Positive-Sense RNA Viruses

Some single-stranded positive-sense RNA [ssRNA(+)] viruses, including Flavivirus, generate specific organelle-like structures in the host endoplasmic reticulum (ER). These structures are called virus replication organelles and consist of two distinct subdomains, the vesicle packets (VPs) and the convoluted membranes (CMs). The VPs are clusters of small vesicle compartments and are considered to be the site of viral genome replication. The CMs are electron-dense amorphous structures observed in proximity to the VPs, but the exact roles of CMs are mostly unknown. Several recent studies have revealed that flaviviruses recruit several host factors that are usually used for the biogenesis of other conventional organelles and usurp their function to generate virus replication organelles. In the current review, we summarize recent studies focusing on the role of host factors in the formation of virus replication organelles and discuss how these intricate membrane structures are organized.

Phosphoenolpyruvate carboxykinase is involved in antiviral immunity against Bombyx mori nucleopolyhedrovirus

Phosphoenolpyruvate carboxykinase (PEPCK) has cytoplasmic isoform (PEPCK-C) and a mitochondrial isoform (PEPCK-M). PEPCK-C plays an important role in gluconeogenesis, but the function of PEPCK-M is largely unknown. In this study, we cloned two isoforms of PEPCK (BmPEPCK-1 and BmPEPCK-2; both of PEPCK-M) from the lepidopteran model Bombyx mori. BmPEPCK-1 and BmPEPCK-2 were adjacently located in the silkworm genome, and both contained 13 exons. The main difference in the sequences was the 13th exon and 3'UTR. The expression of BmPEPCK-1 was higher than that of BmPEPCK-2, the overexpression of which did not affect BmNPV proliferation. The expression levels of BmPEPCK-2 and ATG6/7/8/13 decreased after BmNPV infection. Overexpression of BmPEPCK-2 increased the expression of ATG6/7/8 and significantly decreased viral fluorescence and content, suggesting that BmPEPCK-2 suppressed the multiplication of BmNPV by increasing ATGs expression. These results revealed that PEPCK-M has an important function in antiviral immunity.

Autophagy in Zika Virus Infection: A Possible Therapeutic Target to Counteract Viral Replication

Zika virus (ZIKV) still constitutes a public health concern, however, no vaccines or therapies are currently approved for treatment. A fundamental process involved in ZIKV infection is autophagy, a cellular catabolic pathway delivering cytoplasmic cargo to the lysosome for degradation—considered as a primordial form of innate immunity against invading microorganisms. ZIKV is thought to inhibit the Akt-mTOR signaling pathway, which causes aberrant activation of autophagy promoting viral replication and propagation. It is therefore appealing to study the role of autophagic molecular effectors during viral infection to identify potential targets for anti-ZIKV therapeutic intervention.

Crosstalk between Autophagy and Type I Interferon Responses in Innate Antiviral Immunity

Autophagy exhibits dual effects during viral infections, promoting the clearance of viral components and activating the immune system to produce antiviral cytokines. However, some viruses impair immune defenses by collaborating with autophagy. Mounting evidence suggests that the interaction between autophagy and innate immunity is critical to understanding the contradictory roles of autophagy. Type I interferon (IFN-I) is a crucial antiviral factor, and studies have indicated that autophagy affects IFN-I responses by regulating IFN-I and its receptors expression. Similarly, IFN-I and interferon-stimulated gene (ISG) products can harness autophagy to regulate antiviral immunity. Crosstalk between autophagy and IFN-I responses could be a vital aspect of the molecular mechanisms involving autophagy in innate antiviral immunity. This review briefly summarizes the approaches by which autophagy regulates antiviral IFN-I responses and highlights the recent advances on the mechanisms by which IFN-I and ISG products employ autophagy against viruses.

The Intertwined Life Cycles of Enterovirus and Autophagy

Enteroviruses (EVs) are the most common human pathogens worldwide. Recent international outbreaks in North America and South East Asia have emphasized the need for more effective anti-viral therapies. As obligate parasites, EVs rely on the host cellular machinery for effective viral propagation. Accumulating evidence has indicated that EVs subvert and disrupt the cellular autophagy pathway to facilitate productive infection, and consequently leading to host pathogenesis. Given that defective autophagy is a common factor in various human diseases, including neurodegeneration, cardiomyopathy, and metabolic disorders, a clear understanding of the relationship between EV infection and autophagy is warranted. In this review, we highlight recent advances in understanding the molecular mechanisms by which EVs exploit the autophagy pathway during different steps of viral life cycle, from entry, replication, and maturation to release. We also provide an overview of recent progress in EV subversion of the autophagy for immune evasion.

Remodeling of host membranes during herpesvirus assembly and egress

Many viruses, enveloped or non-enveloped, remodel host membrane structures for their replication, assembly and escape from host cells. Herpesviruses are important human pathogens and cause many diseases. As large enveloped DNA viruses, herpesviruses undergo several complex steps to complete their life cycles and produce infectious progenies. Firstly, herpesvirus assembly initiates in the nucleus, producing nucleocapsids that are too large to cross through the nuclear pores. Nascent nucleocapsids instead bud at the inner nuclear membrane to form primary enveloped virions in the perinuclear space followed by fusion of the primary envelopes with the outer nuclear membrane, to translocate the nucleocapsids into the cytoplasm. Secondly, nucleocapsids obtain a series of tegument proteins in the cytoplasm and bud into vesicles derived from host organelles to acquire viral envelopes. The vesicles are then transported to and fuse with the plasma membrane to release the mature virions to the extracellular space. Therefore, at least two budding and fusion events take place at cellular membrane structures during herpesviruses assembly and egress, which induce membrane deformations. In this review, we describe and discuss how herpesviruses exploit and remodel host membrane structures to assemble and escape from the host cell.

Poliovirus induces autophagic signaling independent of the ULK1 complex

Poliovirus (PV), like many positive-strand RNA viruses, subverts the macroautophagy/autophagy pathway to promote its own replication. Here, we investigate whether the virus uses the canonical autophagic signaling complex, consisting of the ULK1/2 kinases, ATG13, RB1CC1, and ATG101, to activate autophagy. We find that the virus sends autophagic signals independent of the ULK1 complex, and that the members of the autophagic complex are not required for normal levels of viral replication. We also show that the SQSTM1/p62 receptor protein is not degraded in a conventional manner during infection, but is likely cleaved in a manner similar to that shown for coxsackievirus B3. This means that SQSTM1, normally used to monitor autophagic degradation, cannot be used to accurately monitor degradation during poliovirus infection. In fact, autophagic degradation may be affected by the loss of SQSTM1 at the same time as autophagic signals are being sent. Finally, we demonstrate that ULK1 and ULK2 protein levels are greatly reduced during PV infection, and ATG13, RB1CC1, and ATG101 protein levels are reduced as well. Surprisingly, autophagic signaling appears to increase as ULK1 levels decrease. Overexpression of wild-type or dominant-negative ULK1 constructs does not affect virus replication, indicating that ULK1 degradation may be a side effect of the ULK1-independent signaling mechanism used by PV, inducing complex instability. This demonstration of ULK1-independent autophagic signaling is novel and leads to a model by which the virus is signaling to generate autophagosomes downstream of ULK1, while at the same time, cleaving cargo receptors, which may affect cargo loading and autophagic degradative flux. Our data suggest that PV has a finely-tuned relationship with the autophagic machinery, generating autophagosomes without using the primary autophagy signaling pathway.

ABBREVIATIONS

ACTB - actin beta; ATG13 - autophagy related 13; ATG14 - autophagy related 14; ATG101 - autophagy related 101; BECN1 - beclin 1; CVB3 - coxsackievirus B3; DMV - double-membraned vesicles; EM - electron microscopy; EMCV - encephalomyocarditis virus; EV-71 - enterovirus 71; FMDV - foot and mouth disease virus; GFP - green fluorescent protein; MAP1LC3B/LC3B - microtubule associated protein 1 light chain 3 beta; MOI - multiplicity of infection; MTOR - mechanistic target of rapamycin kinase; PIK3C3 - phosphatidylinositol 3-kinase catalytic subunit type 3; PRKAA2 - protein kinase AMP-activated catalytic subunit alpha 2; PSMG1 - proteasome assembly chaperone 1; PSMG2 - proteasome assembly chaperone 2PV - poliovirus; RB1CC1 - RB1 inducible coiled-coil 1; SQSTM1 - sequestosome 1; ULK1 - unc-51 like autophagy activating kinase 1; ULK2 - unc-51 like autophagy activating kinase 2; WIPI1 - WD repeat domain, phosphoinositide interacting 1.

miRNAs in Tuberculosis: New Avenues for Diagnosis and Host-Directed Therapy

Tuberculosis (TB) is one of the most fatal infectious diseases and a leading cause of mortality, with 95% of these deaths occurring in developing countries. The causative agent, Mycobacterium tuberculosis (Mtb), has a well-established ability to circumvent the host's immune system for its intracellular survival. microRNAs (miRNAs) are small, non-coding RNAs having an important function at the post-transcriptional level and are involved in shaping immunity by regulating the repertoire of genes expressed in immune cells. It has been established in recent studies that the innate immune response against TB is significantly regulated by miRNAs. Moreover, differential expression of miRNA in Mtb infection can reflect the disease progression and may help distinguish between active and latent TB infection (LTBI). These findings encouraged the application of miRNAs as potential biomarkers. Similarly, active participation of miRNAs in modulation of autophagy and apoptosis responses against Mtb opens an exciting avenue for the exploitation of miRNAs as host directed therapy (HDT) against TB. Nanoparticles mediated delivery of miRNAs to treat various diseases has been reported and this technology has a great potential to be used in TB. In reality, this exploitation of miRNAs as biomarkers and in HDT is still in its infancy stage, and more studies using animal models mimicking human TB are advocated to assess the role of miRNAs as biomarkers and therapeutic targets. In this review, we attempt to summarize the recent advancements in the role of miRNAs in TB as immune modulator, miRNAs' capability to distinguish between active and latent TB and, finally, usage of miRNAs as therapeutic targets against TB.

Autophagy in Negative-Strand RNA Virus Infection

Autophagy is a homoeostatic process by which cytoplasmic material is targeted for degradation by the cell. Viruses have learned to manipulate the autophagic pathway to ensure their own replication and survival. Although much progress has been achieved in dissecting the interplay between viruses and cellular autophagic machinery, it is not well understood how the cellular autophagic pathway is utilized by viruses and manipulated to their own advantage. In this review, we briefly introduce autophagy, viral xenophagy and the interaction among autophagy, virus and immune response, then focus on the interplay between NS-RNA viruses and autophagy during virus infection. We have selected some exemplary NS-RNA viruses and will describe how these NS-RNA viruses regulate autophagy and the role of autophagy in NS-RNA viral replication and in immune responses to virus infection. We also review recent advances in understanding how NS-RNA viral proteins perturb autophagy and how autophagy-related proteins contribute to NS-RNA virus replication, pathogenesis and antiviral immunity.

Foot-and-mouth disease virus capsid protein VP2 activates the cellular EIF2S1-ATF4 pathway and induces autophagy via HSPB1

Foot-and-mouth disease virus (FMDV) can result in economical destruction of cloven-hoofed animals. FMDV infection has been reported to induce macroautophagy/autophagy; however, the precise molecular mechanisms of autophagy induction and effect of FMDV capsid protein on autophagy remain unknown. In the present study, we report that FMDV infection induced a complete autophagy process in the natural host cells of FMDV, and inhibition of autophagy significantly decreased FMDV production, suggesting that FMDV-induced autophagy facilitates viral replication. We found that the EIF2S1-ATF4 pathway was activated and the AKT-MTOR signaling pathway was inhibited by FMDV infection. We also observed that ultraviolet (UV)-inactivated FMDV can induce autophagy. Importantly, our work provides the first piece of evidence that expression of FMDV capsid protein VP2 can induce autophagy through the EIF2S1-ATF4-AKT-MTOR cascade, and we found that VP2 interacted with HSPB1 (heat shock protein family B [small] member 1) and activated the EIF2S1-ATF4 pathway, resulting in autophagy and enhanced FMDV replication. In addition, we show that VP2 induced autophagy in a variety of mammalian cell lines and decreased aggregates of a model mutant HTT (huntingtin) polyglutamine expansion protein (HTT103Q). Overall, our results demonstrate that FMDV capsid protein VP2 induces autophagy through interaction with HSPB1 and activation of the EIF2S1-ATF4 pathway.