Viral interactions with macroautophagy: a double-edged sword

Engineered bacterial outer membrane vesicles encapsulating oncolytic adenoviruses enhance the efficacy of cancer virotherapy by augmenting tumor cell autophagy

Oncolytic adenovirus (Ad) infection promotes intracellular autophagy in tumors. This could kill cancer cells and contribute to Ads-mediated anticancer immunity. However, the low intratumoral content of intravenously delivered Ads could be insufficient to efficiently activate tumor over-autophagy. Herein, we report bacterial outer membrane vesicles (OMVs)-encapsulating Ads as microbial nanocomposites that are engineered for autophagy-cascade-augmented immunotherapy. Biomineral shells cover the surface antigens of OMVs to slow their clearance during in vivo circulation, enhancing intratumoral accumulation. After entering tumor cells, there is excessive H₂O₂ accumulation through the catalytic effect of overexpressed pyranose oxidase (P₂O) from microbial nanocomposite. This increases oxidative stress levels and triggers tumor autophagy. The autophagy-induced autophagosomes further promote Ads replication in infected tumor cells, leading to Ads-overactivated autophagy. Moreover, OMVs are powerful immunostimulants for remolding the immunosuppressive tumor microenvironment, facilitating antitumor immune response in preclinical cancer models in female mice. Therefore, the present autophagy-cascade-boosted immunotherapeutic method can expand OVs-based immunotherapy.

Overexpression of Bcl2 and Bcl2L1 Can Suppress Betanodavirus-Induced Type III Cell Death and Autophagy Induction in GF-1 Cells

Betanodavirus infection induces viral nervous necrosis (VNN) in fish. However, the role of cell death and autophagy in the pathogenesis of VNN remains unknown. This study aimed to investigate the effect of red-spotted grouper nervous necrosis virus (RGNNV) infection on Bcl2 downregulation and overexpression on asymmetric interaction between cell death and autophagy. The mRFP-LC3 reporter system was used to identify autophagosome formation in GF-1 (Grouper fin-1) fish cells. We found that the RGNNV could strongly induce autophagosome formation 36 h post-infection (hpi) after autophagy inhibitor 3-MA had downregulated anti-apoptotic genes such as Bcl2 and Bcl2L1 (Bcl-xL). We proposed that the overexpression of Bcl2 and Bcl2L1 can modulate both cell death and autophagy. Then, we found that it can also reduce either type III cell death or autophagy, which are mildly correlated with reduced viral replication. Our data suggest that RGNNV-induced Bcl2 downregulation correlates with the asymmetrical interaction between cell death induction and the autophagy process, which resembles viral replication.

Autophagy Induced by the N-Terminus of the Classic Swine Fever Virus Nonstructural Protein 5A Protein Promotes Viral Replication

Although classic swine fever virus (CSFV) infection has been reported to induce autophagy, the specific induced mechanism remains unrevealed. Nonstructural protein 5A (NS5A) of CSFV is a multiphosphorylated protein with multiple functions to regulate viral replication and the host cell immune responses. Herein, we demonstrated that CSFV NS5A could induce cellular autophagy and promote viral replication. In the current study, we showed that NS5A expression significantly increased the levels of autophagy-related genes (ATGs), including light chain 3 (LC3), ATG5, and Beclin 1; conversely, degradation of P62/sequestosome 1 (SQSTM1) was observed by Western blotting. The number of autophagy-like vesicles was also obviously increased in NS5A-expressing cells, as analyzed by transmission electron microscopy (TEM). Furthermore, we observed the co-localization of the NS5A and LC3 proteins by confocal immunofluorescence analysis. Direct binding of NS5A to the autophagy-related LC3 protein was confirmed by coimmunoprecipitation in vivo and by a GST pulldown assay in vitro. Through segmentation and point mutation research on the NS5A protein, we found that the N-terminal region and the phosphorylation of amino acids 81 and 92 of the NS5A protein were essential for inducing autophagy. Finally, we demonstrated that the LC3 protein had a positive effect on CSFV replication. These findings emphasize a previously unascertained interaction relationship between NS5A and LC3 in the autophagy process. Furthermore, our research revealed a new role of CSFV NS5A, particularly its N-terminal amino acids serine 81 and serine 92, as a critical regulator of CSFV-induced autophagy and have significance for extending our understanding of the CSFV-autophagy interplay.

Phosphatase and Tensin Homolog (PTEN) of Japanese Flounder-Its Regulation by miRNA and Role in Autophagy, Apoptosis and Pathogen Infection

MicroRNAs (miRNAs) are small non-coding RNAs with important roles in diverse biological processes including immunity. Japanese flounder (Paralichthys olivaceus) is an aquaculture fish species susceptible to the infection of bacterial and viral pathogens including Edwardsiella tarda. In a previous study, pol-miR-novel_547, a novel miRNA of flounder with unknown function, was found to be induced by E. tarda. In the present study, we investigated the regulation and function of pol-miR-novel_547 and its target gene. We found that pol-miR-novel_547 was regulated differently by E. tarda and the viral pathogen megalocytivirus, and pol-miR-novel_547 repressed the expression of PTEN (phosphatase and tensin homolog) of flounder (PoPTEN). PoPTEN is ubiquitously expressed in multiple tissues of flounder and responded to bacterial and viral infections. Interference with PoPTEN expression in flounder cells directly or via pol-miR-novel_547 promoted E. tarda invasion. Consistently, in vivo knockdown of PoPTEN enhanced E. tarda dissemination in flounder tissues, whereas in vivo overexpression of PoPTEN attenuated E. tarda dissemination but facilitated megalocytivirus replication. Further in vitro and in vivo studies showed that PoPTEN affected autophagy activation via the AKT/mTOR pathway and also modulated the process of apoptosis. Together these results reveal for the first time a critical role of fish PTEN and its regulatory miRNA in pathogen infection, autophagy, and apoptosis.

Autophagy Induced by Simian Retrovirus Infection Controls Viral Replication and Apoptosis of Jurkat T Lymphocytes

Autophagy and apoptosis are two important evolutionarily conserved host defense mechanisms against viral invasion and pathogenesis. However, the association between the two pathways during the viral infection of T lymphocytes remains to be elucidated. Simian type D retrovirus (SRV) is an etiological agent of fatal simian acquired immunodeficiency syndrome (SAIDS), which can display disease features that are similar to acquired immunodeficiency syndrome in humans. In this study, we demonstrate that infection with SRV-8, a newly isolated subtype of SRV, triggered both autophagic and apoptotic pathways in Jurkat T lymphocytes. Following infection with SRV-8, the autophagic proteins LC3 and p62/SQSTM1 interacted with procaspase-8, which might be responsible for the activation of the caspase-8/-3 cascade and apoptosis in SRV-8-infected Jurkat cells. Our findings indicate that autophagic responses to SRV infection of T lymphocytes promote the apoptosis of T lymphocytes, which, in turn, might be a potential pathogenetic mechanism for the loss of T lymphocytes during SRV infection.

Japanese flounder pol-miR-3p-2 suppresses Edwardsiella tarda infection by regulation of autophagy via p53

MicroRNAs (miRNAs) are post-transcriptional regulators that play vital roles in diverse physiological processes including immunity. In this study, we investigated the regulatory mechanism and function of a novel Japanese flounder (Paralichthys olivaceus) miRNA, pol-miR-3p-2. pol-miR-3p-2 was responsive in expression to the infection of the bacterial pathogen Edwardsiella tarda. pol-miR-3p-2 negatively regulated the expression of p53 through interaction with the 3'UTR of p53. Overexpression of pol-miR-3p-2 promoted autophagy, resulting in augmented production of LC3-II, while knockdown of p53 increased the level of beclin, a key factor of autophagy. In vivo and in vitro studies showed that E. tarda infection induced autophagy in flounder, and pol-miR-3p-2 inhibited the infectivity of E. tarda. Together these results indicate that pol-miR-3p-2 regulates autophagy through the target gene p53, thus revealing a regulatory link between p53 and autophagy in teleost, and that pol-miR-3p-2 plays an important role in the immune defense against E. tarda.

Autophagy is involved in assisting the replication of Bamboo mosaic virus in Nicotiana benthamiana

Autophagy plays a critical role in plants under biotic stress, including the response to pathogen infection. We investigated whether autophagy-related genes (ATGs) are involved in infection with Bamboo mosaic virus (BaMV), a single-stranded positive-sense RNA virus. Initially, we observed that BaMV infection in Nicotiana benthamiana leaves upregulated the expression of ATGs but did not trigger cell death. The induction of ATGs, which possibly triggers autophagy, increased rather than diminished BaMV accumulation in the leaves, as revealed by gene knockdown and transient expression experiments. Furthermore, the inhibitor 3-methyladenine blocked autophagosome formation and the autophagy inducer rapamycin, which negatively and positively affected BaMV accumulation, respectively. Pull-down experiments with an antibody against orange fluorescent protein (OFP)-NbATG8f, an autophagosome marker protein, showed that both plus- and minus-sense BaMV RNAs could associate with NbATG8f. Confocal microscopy revealed that ATG8f-enriched vesicles possibly derived from chloroplasts contained both the BaMV viral RNA and its replicase. Thus, BaMV infection may induce the expression of ATGs possibly via autophagy to selectively engulf a portion of viral RNA-containing chloroplast. Virus-induced vesicles enriched with ATG8f could provide an alternative site for viral RNA replication or a shelter from the host silencing mechanism.

The effects of autophagy on the replication of Nelson Bay orthoreovirus

BACKGROUND

Nelson Bay orthoreovirus (NBV) was first isolated over 40 years ago from a fruit bat in Australia. Normally, NBV does not cause human diseases, but recently several NBV strains have been associated with human respiratory tract infections, thus attracting clinical attention. Autophagy, an evolutionarily conserved process in eukaryotic cells, degrades intracellular substrates, participates in multiple physiological processes, and maintains cellular homeostasis. In addition, autophagy is intimately involved in viral infection.

METHODS

A new strain of NBV, isolated from a patient with a respiratory tract infection who returned to Japan from Bali, Indonesia, in 2007, was used in this study. NBV was rescued using a reverse genetics system involving cotransfection of BHK cells with 11 plasmids (pT7-L1 MB, pT7-L2 MB, pT7-L3 MB, pT7-M1 MB, pT7-M2 MB, pT7-M3 MB, pT7-S1 MB, pT7-S2 MB, pT7-S3 MB, pT7-S4 MB, and pcDNA3.1-T7), yielding NBV-MB. Recovered viruses were confirmed by immunofluorescence. The effect of NBV-MB on autophagy was evaluated by measuring the LC3-I/II proteins by immunoblot analysis after infection of BHK cells. Furthermore, after treatment with rapamycin (RAPA), 3-methyladenine (3-MA), chloroquine (CQ), or plasmid (GFP-LC3) transfection, the changes in expression of the LC3 gene and the amount of LC3-I/II protein were examined. In addition, variations in viral titer were assayed after treatment of BHK cells with drugs or after transfection with plasmids pCAGM3 and pCAGS3, which encode virus nonstructural proteins μNS and σNS, respectively.

RESULTS

NBV-MB infection induced autophagy in host cells; however, the level of induction was dependent on viral replication. Induction of autophagy increased viral replication. By contrast, inhibiting autophagy suppressed NBV replication, albeit not significantly. The NBV-MB nonstructural protein μNS was involved in the induction of autophagy with viral infection.

CONCLUSIONS

NBV-MB infection triggered autophagy. Also, the NBV nonstructural protein μNS may contribute to augmentation of autophagy upon viral infection.

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.

Extracellular Vesicles in Herpes Viral Spread and Immune Evasion

Extracellular vesicles (EVs) are involved in numerous processes during infections by both enveloped and non-enveloped viruses. Among them, herpes simplex virus type-1 (HSV-1) modulates secretory pathways, allowing EVs to exit infected cells. Many characteristics regarding the mechanisms of viral spread are still unidentified, and as such, secreted vesicles are promising candidates due to their role in intercellular communications during viral infection. Another relevant role for EVs is to protect virions from the action of neutralizing antibodies, thus increasing their stability within the host during hematogenous spread. Recent studies have suggested the participation of EVs in HSV-1 spread, wherein virion-containing microvesicles (MVs) released by infected cells were endocytosed by naïve cells, leading to a productive infection. This suggests that HSV-1 might use MVs to expand its tropism and evade the host immune response. In this review, we briefly describe the current knowledge about the involvement of EVs in viral infections in general, with a specific focus on recent research into their role in HSV-1 spread. Implications of the autophagic pathway in the biogenesis and secretion of EVs will also be discussed.

Bombyx mori Nuclear Polyhedrosis Virus (BmNPV) Induces Host Cell Autophagy to Benefit Infection

Bombyx mori nuclear polyhedrosis virus (BmNPV) is an important pathogen of silkworms. Despite extensive studies in recent decades, the interaction between BmNPV and host cells is still not clearly understood. Autophagy is an intrinsic innate immune mechanism and it controls infection autonomously in virus-infected cells. In this study, we found that BmNPV infection could trigger autophagy, as demonstrated by the formation of autophagosomes, fluorescent Autophagy-related gene 8-Green Fluorescent Protein (ATG8-GFP) punctate, and lipidated ATG8. Meanwhile, autophagic flux increased significantly when monitored by the ATG8-GFP-Red Fluorescent Protein (RFP) autophagy tandem sensor and protein degradation of p62. In addition, almost all of the identified autophagy-related genes (Atgs) had been up-regulated post infection in mRNA levels. Then, we screened Atgs with the greatest fold-change during virus infection. Interestingly, all of the screened Atgs positively regulated the expression of virus genes. Further studies showed that Atg7 and Atg9 could contribute to the level of autophagy caused by viral infection. Our results demonstrated that BmNPV induced host cell autophagy to benefit its infection. These results offer insight into the complex interactions between virus and host cell, and viral pathogenesis.

Autophagy induced by bovine viral diarrhea virus infection counteracts apoptosis and innate immune activation

Bovine viral diarrhea virus (BVDV) is an important pathogen of cattle that plays a complex role in disease. There are two biotypes of BVDV: non-cytopathic (NCP) and cytopathic (CP). One strategy that has been used to treat or prevent virus-associated diseases is the modulation of autophagy, which is used by the innate immune system to defend against viral infection; however, at present, the interplay between autophagy and BVDV remains unclear. Madin-Darby bovine kidney cells stably expressing microtubule-associated protein 1 light chain 3B (LC3B) with green fluorescent protein (GFP) (GFP-LC3-MDBK cells) and autophagy-deficient MDBKs (shBCN1-MDBK cells) were constructed. Then MDBK, GFP-LC3-MDBK and shBCN1-MDBK cells were infected with CP or NCP BVDV strains. The LC3-II turnover rate was estimated by western blot, autophagosomes were visualized by confocal microscopy, and ultrastructural analysis was performed using electron microscopy. Autophagy flux was observed using chloroquine as an inhibitor of the autophagic process. The influence of autophagy on BVDV replication and release was investigated using virus titration, and its effect on cell viability was also studied. The effect of BVDV-induced autophagy on the survival of BVDV-infected host cell, cell apoptosis, and interferon (IFN) signalling was studied by flow cytometric analysis and quantitative RT-(q)PCR using shBCN1-MDBK cells. we found that infection with either CP or NCP BVDV strains induced steady-state autophagy in MDBK cells, as evident by the increased number of double- or single-membrane vesicles, the accumulation of GFP- microtubule-associated protein 1 light chain 3 (LC3) dots, and the conversion of LC3-I (cytosolic) to LC3-II (membrane-bound) forms. The complete autophagic process was verified by monitoring the LC3-II turnover ratio, lysosomal delivery, and proteolysis. In addition, we found that CP and NCP BVDV growth was inhibited in MDBK cells treated with high levels of an autophagy inducer or inhibitor, or in autophagy deficient-MDBK cells. Furthermore, our studies also suggested that CP and NCP BVDV infection in autophagy-knockdown MDBK cells increased apoptotic cell death and enhanced the expression of the mRNAs for IFN-α, Mx1, IFN-β, and OAS-1 as compared with control MDBK cells. Our study provides strong evidence that BVDV infection induces autophagy, which facilitates BVDV replication in MDBK cells and impairs the innate immune response. These findings might help to illustrate the pathogenesis of persistent infection caused by BVDV.

Autophagy and its link to type II diabetes mellitus

Autophagy, a double-edged sword for cell survival, is the research object on 2016 Nobel Prize in Physiology or Medicine. Autophagy is a molecular mechanism for maintaining cellular physiology and promoting survival. Defects in autophagy lead to the etiology of many diseases, including diabetes mellitus (DM), cancer, neurodegeneration, infection disease and aging. DM is a metabolic and chronic disorder and has a higher prevalence in the world as well as in Taiwan. The character of diabetes mellitus is hyperglycemia resulting from defects in insulin secretion, insulin action, or both. Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and failure of producing insulin on pancreatic beta cells. In T2DM, autophagy is not only providing nutrients to maintain cellular energy during fasting, but also removes damaged organelles, lipids and miss-folded proteins. In addition, autophagy plays an important role in pancreatic beta cell dysfunction and insulin resistance. In this review, we summarize the roles of autophagy in T2DM.

Foot-and-mouth disease virus infection suppresses autophagy and NF-кB antiviral responses via degradation of ATG5-ATG12 by 3Cpro

Autophagy-related protein ATG5-ATG12 is an essential complex for the autophagophore elongation in autophagy, which has been reported to be involved in foot-and-mouth disease virus (FMDV) replication. Previous reports show that ATG5-ATG12 positively or negatively regulates type I interferon (IFN-α/β) pathway during virus infection. In this study, we found that FMDV infection rapidly induced LC3 lipidation and GFP-LC3 subcellular redistribution at the early infection stage in PK-15 cells. Along with infection time course to 2-5 h.p.i., the levels of LC3II and ATG5-ATG12 were gradually reduced. Further study showed that ATG5-ATG12 was degraded by viral protein 3Cpro, demonstrating that FMDV suppresses autophagy along with viral protein production. Depletion of ATG5-ATG12 by siRNA knock down significantly increased the FMDV yields, whereas overexpression of ATG5-ATG12 had the opposite effects, suggesting that degradation of ATG5-ATG12 benefits virus growth. Further experiment showed that overexpression of ATG5-ATG12 positively regulated NF-кB pathway during FMDV infection, marked with promotion of IKKα/β phosphorylation and IκBα degradation, inhibition of p65 degradation, and facilitation of p65 nuclear translocation. Meanwhile, ATG5-ATG12 also promoted the phosphorylation of TBK1 and activation of IRF3 via preventing TRAF3 degradation. The positive regulation of NF-кB and IRF3 pathway by ATG5-ATG12 resulted in enhanced expression of IFN-β, chemokines/cytokines, and IFN stimulated genes, including anti-viral protein PKR. Altogether, above findings suggest that ATG5-ATG12 positively regulate anti-viral NF-κB and IRF3 signaling during FMDV infection, thereby limiting FMDV proliferation. FMDV has evolved mechanisms to counteract the antiviral function of ATG5-ATG12, via degradation of them by viral protein 3Cpro.

Dissection and integration of the autophagy signaling network initiated by bluetongue virus infection: crucial candidates ERK1/2, Akt and AMPK

Bluetongue virus (BTV), a complex double-stranded segmented RNA virus, has been found to initiate cellular autophagy for its own benefit. Here, with a view to understanding the underlying mechanisms, we first systematically dissected the exact signaling network in BTV-induced autophagy. We found that the activity of mTOR, a crucial pivot, was inhibited by BTV1 infection, subsequently leading to downstream p70S6K suppression and autophagy initiation. We then explored the upstream regulators of mTOR and analyzed their activities via a series of assays. We found BTV1-induced autophagy to be independent of the ERK1/2 signaling pathway. However, the BTV1-induced inhibition of PI3K/Akt was found to be partially responsible for mTOR inactivation and subsequent autophagy initiation. Furthermore, we found unexpectedly that AMPK seemed to play a more important role in BTV1-induced autophagy. Elevated [Ca²⁺]_cyto-mediated activation of CaMKKβ exactly managed the activation of AMPK, which then positively regulated autophagy through suppressing mTOR. We must emphasize that TSC2 is a fatal mediator between upstream Akt or AMPK and downstream mTOR through its phosphorylation. Taken together, our data suggested that the BTV1-induced inhibition of the Akt-TSC2-mTOR pathway and the upregulation of the AMPK-TSC2-mTOR pathway both contributed to autophagy initiation and further favored virus replication.

Hepatitis B and C virus-induced hepatitis: Apoptosis, autophagy, and unfolded protein response

AIM

To investigate the co-incidence of apoptosis, autophagy, and unfolded protein response (UPR) in hepatitis B (HBV) and C (HCV) infected hepatocytes.

METHODS

We performed immunofluorescence confocal microscopy on 10 liver biopsies from HBV and HCV patients and tissue microarrays of HBV positive liver samples. We used specific antibodies for LC3β, cleaved caspase-3, BIP (GRP78), and XBP1 to detect autophagy, apoptosis and UPR, respectively. Anti-HCV NS3 and anti-HBs antibodies were also used to confirm infection. We performed triple blind counting of events to determine the co-incidence of autophagy (LC3β punctuate), apoptosis (cleaved caspase-3), and unfolded protein response (GRP78) with HBV and HCV infection in hepatocytes. All statistical analyses were performed using SPSS software for Windows (Version 16 SPSS Inc, Chicago, IL, United States). P-values < 0.05 were considered statistically significant. Statistical analyses were performed with Mann-Whitney test to compare incidence rates for autophagy, apoptosis, and UPR in HBV- and HCV-infected cells and adjacent non-infected cells.

RESULTS

Our results showed that infection of hepatocytes with either HBV and HCV induces significant increase (P < 0.001) in apoptosis (cleavage of caspase-3), autophagy (LC3β punctate), and UPR (increase in GRP78 expression) in the HCV- and HBV-infected cells, as compared to non-infected cells of the same biopsy sections. Our tissue microarray immunohistochemical expression analysis of LC3β in HBV(Neg) and HBV(Pos) revealed that majority of HBV-infected hepatocytes display strong positive staining for LC3β. Interestingly, although XBP splicing in HBV-infected cells was significantly higher (P < 0.05), our analyses show a slight increase of XBP splicing was in HCV-infected cells (P > 0.05). Furthermore, our evaluation of patients with HBV and HCV infection based on stage and grade of the liver diseases revealed no correlation between these pathological findings and induction of apoptosis, autophagy, and UPR.

CONCLUSION

The results of this study indicate that HCV and HBV infection activates apoptosis, autophagy and UPR, but slightly differently by each virus. Further studies are warranted to elucidate the interconnections between these pathways in relation to pathology of HCV and HBV in the liver tissue.

Maternal immunity and pregnancy outcome: focus on preconception and autophagy

Modulation of the maternal immune system before conception has a major role in determining subsequent pregnancy outcome. However, this has been a neglected area of investigation. There is a correlation between the length of time a woman is exposed to semen from her male partner and the development of regulatory T cells that limit a maternal antifetal immune response. Similarly, the composition of the vaginal microbiota influences the capacity of microorganisms to bypass the cervical barrier and colonize the uterus before pregnancy. The extent that this preconception colonization influences pre- and post-implantation gestational events depends on the types of microbes present, the genetic make-up of the mother and environmental influences on the magnitude and direction of her immune responses. Prepregnancy uterine and placental colonization with commensal bacteria may be beneficial to the fetus and newborn by generating tolerance to organisms that enhance postnatal well-being. Efforts to prevent or stop the progression of premature myometrial contractions have been limited because of an incomplete understanding of the mechanism(s) that trigger this occurrence. Based on recent studies of autophagy during gestation and parturition, inhibition of autophagy in myometrial cells may be the critical factor leading to a sequence of events culminating in induction of myometrial contractions either prematurely or at term.

Autophagy Activated by Bluetongue Virus Infection Plays a Positive Role in Its Replication

Bluetongue virus (BTV) is an important pathogen of wild and domestic ruminants. Despite extensive study in recent decades, the interplay between BTV and host cells is not clearly understood. Autophagy as a cellular adaptive response plays a part in many viral infections. In our study, we found that BTV1 infection triggers the complete autophagic process in host cells, as demonstrated by the appearance of obvious double-membrane autophagosome-like vesicles, GFP-LC3 dots accumulation, the conversion of LC3-I to LC3-II and increased levels of autophagic flux in BSR cells (baby hamster kidney cell clones) and primary lamb lingual epithelial cells upon BTV1 infection. Moreover, the results of a UV-inactivated BTV1 infection assay suggested that the induction of autophagy was dependent on BTV1 replication. Therefore, we investigated the role of autophagy in BTV1 replication. The inhibition of autophagy by pharmacological inhibitors (3-MA, CQ) and RNA interference (siBeclin1) significantly decreased viral protein synthesis and virus yields. In contrast, treating BSR cells with rapamycin, an inducer of autophagy, promoted viral protein expression and the production of infectious BTV1. These findings lead us to conclude that autophagy is activated by BTV1 and contributes to its replication, and provide novel insights into BTV-host interactions.

Autophagy is involved in oral rAAV/Aβ vaccine-induced Aβ clearance in APP/PS1 transgenic mice

The imbalance between ß-amyloid (Aß) generation and clearance plays a fundamental role in the pathogenesis of Alzheimer's disease (AD). The sporadic form of AD is characterized by an overall impairment in Aß clearance. Immunotherapy targeting Aß clearance is believed to be a promising approach and is under active clinical investigation. Autophagy is a conserved pathway for degrading abnormal protein aggregates and is crucial for Aß clearance. We previously reported that oral vaccination with a recombinant AAV/Aß vaccine increased the clearance of Aß from the brain and improved cognitive ability in AD animal models, while the underlying mechanisms were not well understood. In this study, we first demonstrated that oral vaccination with rAAV/Aß decreased the p62 level and up-regulated the LC3B-II/LC3B-I ratio in APP/PS1 mouse brain, suggesting enhanced autophagy. Further, inhibition of the Akt/mTOR pathway may account for autophagy enhancement. We also found increased anti-Aß antibodies in the sera of APP/PS1 mice with oral vaccination, accompanied by elevation of complement factors C1q and C3 levels in the brain. Our results indicate that autophagy is closely involved in oral vaccination-induced Aß clearance, and modulating the autophagy pathway may be an important strategy for AD prevention and intervention.

The induction of apoptosis and autophagy by Wasabia japonica extract in colon cancer

PURPOSE

Wasabia japonica (wasabi) has been shown to exhibit properties of detoxification, anti-inflammation and the induction of apoptosis in cancer cells. This study aimed to investigate the molecular mechanism of the cytotoxicity of wasabi extract (WE) in colon cancer cells to evaluate the potential of wasabi as a functional food for chemoprevention.

METHODS

Colo 205 cells were treated with different doses of WE, and the cytotoxicity was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide. Apoptosis and autophagy were detected by 4',6-diamidino-2-phenylindole, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-imidacarbo-yanine iodide and staining for acidic vascular organelles (AVOs), along with Western blotting.

RESULTS

The results demonstrated that WE induced the extrinsic pathway and mitochondrial death machinery through the activation of TNF-α, Fas-L, caspases, truncated Bid and cytochrome C. WE also induced autophagy by decreasing the phosphorylation of Akt and mTOR and promoting the expression of microtubule-associated protein 1 light chain 3-II and AVO formation. An in vivo xenograft model verified that tumor growth was delayed by WE treatment.

CONCLUSION

Our studies revealed that WE exhibits anti-colon cancer properties through the induction of apoptosis and autophagy. These results provide support for the application of WE as a chemopreventive functional food and as a prospective treatment of colon cancer.

Viral (hepatitis C virus, hepatitis B virus, HIV) persistence and immune homeostasis

Immune homeostasis is a host characteristic that maintains biological balance within a host. Humans have evolved many host defence mechanisms that ensure the survival of individuals upon encountering a pathogenic infection, with recovery or persistence from a viral infection being determined by both viral factors and host immunity. Chronic viral infections, such as hepatitis B virus, hepatitis C virus and HIV, often result in chronic fluctuating viraemia in the face of host cellular and humoral immune responses, which are dysregulated by multi-faceted mechanisms that are incompletely understood. This review attempts to illuminate the mechanisms involved in this process, focusing on immune homeostasis in the setting of persistent viral infection from the aspects of host defence mechanism, including interferon-stimulated genes, apolipoprotein B mRNA editing enzyme catalytic polypeptide 3 (APOBEC3), autophagy and interactions of various immune cells, cytokines and regulatory molecules.

Hijacking of an autophagy-like process is critical for the life cycle of a DNA virus infecting oceanic algal blooms

Marine photosynthetic microorganisms are the basis of marine food webs and are responsible for nearly 50% of the global primary production. Emiliania huxleyi forms massive oceanic blooms that are routinely terminated by large double-stranded DNA coccolithoviruses. The cellular mechanisms that govern the replication cycle of these giant viruses are largely unknown. We used diverse techniques, including fluorescence microscopy, transmission electron microscopy, cryoelectron tomography, immunolabeling and biochemical methodologies to investigate the role of autophagy in host-virus interactions. Hallmarks of autophagy are induced during the lytic phase of E. huxleyi viral infection, concomitant with up-regulation of autophagy-related genes (ATG genes). Pretreatment of the infected cells with an autophagy inhibitor causes a major reduction in the production of extracellular viral particles, without reducing viral DNA replication within the cell. The host-encoded Atg8 protein was detected within purified virions, demonstrating the pivotal role of the autophagy-like process in viral assembly and egress. We show that autophagy, which is classically considered as a defense mechanism, is essential for viral propagation and for facilitating a high burst size. This cellular mechanism may have a major impact on the fate of the viral-infected blooms, and therefore on the cycling of nutrients within the marine ecosystem.

A functional role for NS5ATP9 in the induction of HCV NS5A-mediated autophagy

Autophagy has been shown to facilitate replication of hepatitis C virus (HCV); however, the mechanism by which HCV induces autophagy has not been fully established. NS5A, a nonstructural protein expressed by HCV, regulates numerous cellular pathways, including autophagy, by up-regulating Beclin 1; however, the underlying mechanism remains unclear. To obtain new insights into HCV-regulated autophagy, NS5ATP9 was overexpressed in HepG2 and L02 cells, resulting in up-regulation of endogenous Beclin 1 mRNA and protein levels, respectively. The luciferase-reporter assay results showed that both NS5A and NS5ATP9 could transactivate Beclin 1 promoter activity, but that NS5A could not transactivate the Beclin 1 promoter in NS5ATP9-silenced HepG2 and L02 cells. Up-regulation of Beclin 1 mRNA and protein expression by NS5A could also be attenuated by NS5ATP9 knock-down. Furthermore, the HepG2 and L02 cells that transiently overexpressed NS5ATP9 had enhanced accumulation of vacuoles carrying the autophagy marker LC3, consistent with the conversion of endogenous LC3-I to LC3-II. In contrast, the conversion of endogenous LC3-I to LC3-II could not be enhanced by NS5A in NS5ATP9-silenced HepG2 cells. These results highlight an important potential role for NS5ATP9 in HCV NS5A-induced hepatocyte autophagy.

Comparative ultrastructural characterization of African horse sickness virus-infected mammalian and insect cells reveals a novel potential virus release mechanism from insect cells

African horse sickness virus (AHSV) is an arbovirus capable of successfully replicating in both its mammalian host and insect vector. Where mammalian cells show a severe cytopathic effect (CPE) following AHSV infection, insect cells display no CPE. These differences in cell death could be linked to the method of viral release, i.e. lytic or non-lytic, that predominates in a specific cell type. Active release of AHSV, or any related orbivirus, has, however, not yet been documented from insect cells. We applied an integrated microscopy approach to compare the nanomechanical and morphological response of mammalian and insect cells to AHSV infection. Atomic force microscopy revealed plasma membrane destabilization, integrity loss and structural deformation of the entire surface of infected mammalian cells. Infected insect cells, in contrast, showed no morphological differences from mock-infected cells other than an increased incidence of circular cavities present on the cell surface. Transmission electron microscopy imaging identified a novel large vesicle-like compartment within infected insect cells, not present in mammalian cells, containing viral proteins and virus particles. Extracellular clusters of aggregated virus particles were visualized adjacent to infected insect cells with intact plasma membranes. We propose that foreign material is accumulated within these vesicles and that their subsequent fusion with the cell membrane releases entrapped viruses, thereby facilitating a non-lytic virus release mechanism different from the budding previously observed in mammalian cells. This insect cell-specific defence mechanism contributes to the lack of cell damage observed in AHSV-infected insect cells.

Autophagy enhances the replication of classical swine fever virus in vitro

Autophagy plays an important role in cellular responses to pathogens. However, the impact of the autophagy machinery on classical swine fever virus (CSFV) infection is not yet confirmed. In this study, we showed that CSFV infection significantly increases the number of autophagy-like vesicles in the cytoplasm of host cells at the ultrastructural level. We also found the formation of 2 ubiquitin-like conjugation systems upon virus infection, including LC3-I/LC3-II conversion and ATG12–ATG5 conjugation, which are considered important indicators of autophagy. Meanwhile, high expression of ATG5 and BECN1 was detected in CSFV-infected cells; conversely, degradation of SQSTM1 was observed by immunoblotting, suggesting that CSFV infection triggered a complete autophagic response, most likely by the NS5A protein. Furthermore, by confocal immunofluorescence analysis, we discovered that both envelope protein E2 and nonstructural protein NS5A colocalized with LC3 and CD63 during CSFV infection. Examination by immunoelectron microscopy further confirmed the colocalization of both E2 and NS5A proteins with autophagosome-like vesicles, indicating that CSFV utilizes the membranes of these vesicles for replication. Finally, we demonstrated that alteration of cellular autophagy by autophagy regulators and shRNAs affects progeny virus production. Collectively, these findings provide strong evidence that CSFV infection needs an autophagy pathway to enhance viral replication and maturity in host cells.

Virus interactions with endocytic pathways in macrophages and dendritic cells

Macrophages and dendritic cells (DCs) are at the front line of defence against fungi, bacteria, and viruses. Together with physical barriers, such as mucus and a range of antimicrobial compounds, they constitute a major part of the intrinsic and innate immune systems. They have elaborate features, including pattern recognition receptors (PRRs) and specialized endocytic mechanisms, cytokines and chemokines, and the ability to call on reserves. As masters of manipulation and counter-attack, viruses shunt intrinsic and innate recognition, enter immune cells, and spread from these cells throughout an organism. Here, we review mechanisms by which viruses subvert endocytic and pathogen-sensing functions of macrophages and DCs, while highlighting possible strategic advantages of infecting cells normally tuned into pathogen destruction.

Detection of the HIV-1 minus-strand-encoded antisense protein and its association with autophagy

HIV-1 proteins are synthesized from a single transcript in an unspliced form or following splicing, but the existence of an antisense protein (ASP) expressed from an antisense polyadenylated transcript has been suggested. Difficulties linked to the detection of this protein in mammalian cells led us to codon optimize its cDNA. Codon-optimized ASP was indeed efficiently detected in various transfected cell lines following flow cytometry and confocal microscopy analyses. Western blot analyses also led to the detection of optimized ASP in transfected cells but also provided evidence of its instability and high multimerization potential. ASP was mainly distributed in the cytoplasm in a punctate manner, which was reminiscent of autophagosomes. In agreement with this observation, a significant increase in ASP-positive cells and loss of its punctate distribution was observed in transfected cells when autophagy was inhibited at early steps. Induction of autophagy was confirmed by Western blot analyses that showed an ASP-mediated increase in levels of LC3b-II and Beclin 1, as well as colocalization and interaction between ASP and LC3. Interestingly, Myc-tagged ASP was detected in the context of proviral DNA following autophagy inhibition with a concomitant increase in the level and punctate distribution of LC3b-II. Finally, 3-methyladenine treatment of transfected or infected U937 cells decreased extracellular p24 levels in wild-type proviral DNA and to a much lesser extent in ASP-mutated proviral DNA. This study provides the first detection of ASP in mammalian cells by Western blotting. ASP-induced autophagy might explain the inherent difficulty in detecting this viral protein and might justify its presumed low abundance in infected cells.

An autophagy-independent role for LC3 in equine arteritis virus replication

Equine arteritis virus (EAV) is an enveloped, positive-strand RNA virus. Genome replication of EAV has been associated with modified intracellular membranes that are shaped into double-membrane vesicles (DMVs). We showed by immuno-electron microscopy that the DMVs induced in EAV-infected cells contain double-strand (ds)RNA molecules, presumed RNA replication intermediates, and are decorated with the autophagy marker protein microtubule-associated protein 1 light chain 3 (LC3). Replication of EAV, however, was not affected in autophagy-deficient cells lacking autophagy-related protein 7 (ATG7). Nevertheless, colocalization of DMVs and LC3 was still observed in these knockout cells, which only contain the nonlipidated form of LC3. Although autophagy is not required, depletion of LC3 markedly reduced the replication of EAV. EAV replication could be fully restored in these cells by expression of a nonlipidated form of LC3. These findings demonstrate an autophagy-independent role for LC3 in EAV replication. Together with the observation that EAV-induced DMVs are also positive for ER degradation-enhancing α-mannosidase-like 1 (EDEM1), our data suggested that this virus, similarly to the distantly-related mouse hepatitis coronavirus, hijacks the ER-derived membranes of EDEMosomes to ensure its efficient replication.

Recent advances in researches on the innate immunity of shrimp in China

The annual production of shrimp culture in mainland of China has been over one million tons for several years. The major cultivated penaeidae species are Litopenaeus vannamei, Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Due to the importance of shrimp aquaculture in China, researchers have paid more attention to the molecular mechanism of shrimp disease occurrence and tried to develop an efficient control strategy for disease. This paper summarizes the research progress related to innate immunity of penaeid shrimp made in the last decade in Mainland China. Several pattern recognition receptors, such as lectin, toll, lipopolysaccharide and β-1,3-glucan binding protein (LGBP) and tetraspanin were identified. The major signal transduction pathways, including Toll pathway, IMD pathway, which might be involved in the immune response of shrimp, were focused on and most of the components in Toll pathway were identified. Also, cellular immune responses such as phagocytosis and apoptosis were regarded playing very important roles in anti-WSSV infection to shrimp. The molecules involved in the maintenance of the immune homeostasis of shrimp and the progress on molecular structure and pathogenic mechanism of WSSV were summarized. Therefore, the brief outline about the immune system of shrimp is drawn based on the recent data which will help us to understand the immune responses of shrimp to different pathogens.

Autophagy and the regulation of the immune response

Autophagy is a highly conserved mechanism of lysosomal-mediated protein degradation that plays a crucial role in maintaining cellular homeostasis by recycling amino acids, reducing the amount of damaged proteins and regulating protein levels in response to extracellular signals. In the last few years specific functions for different forms of autophagy have been identified in many tissues and organs. In the Immune System, autophagy functions range from the elimination infectious agents and the modulation of the inflammatory response, to the selection of antigens for presentation and the regulation of T cell homeostasis and activation. Here, we review the recent advances that have allowed us to better understand why autophagy is a crucial process in the regulation of the innate and adaptive immune responses.

West Nile virus (WNV) replication is independent of autophagy in mammalian cells

Autophagy is a homeostatic process responsible for recycling cytosolic proteins and organelles. Moreover, this pathway contributes to the cell's intrinsic innate defenses. While many viruses have evolved mechanisms to antagonize the antiviral effects of the autophagy pathway, others subvert autophagy to facilitate replication. Here, we have investigated the role of autophagy in West Nile virus (WNV) replication. Experiments in cell lines derived from a variety of sources, including the kidney, liver, skin, and brain, indicated that WNV replication does not upregulate the autophagy pathway. Furthermore, WNV infection did not inhibit rapamycin-induced autophagy, suggesting that WNV does not disrupt the authophagy signaling cascade. Perturbation of the autophagy pathway by depletion of the major autophagy factors Atg5 or Atg7 had no effect on WNV infectious particle production, indicating that WNV does not require a functional autophagy pathway for replication. Taken together, the results of our study provide evidence that WNV, unlike several other viruses of the family Flaviviridae, does not significantly interact with the conventional autophagy pathway in mammalian cells.

Oncolytic virotherapy with modified adenoviruses and novel therapeutic targets

INTRODUCTION

Numerous oncolytic viral mutants derived from a variety of strains have antitumor efficacy with limited or no toxicity to normal tissue. While all modes of administration were determined to be safe in patients with solid cancers refractory to current standard of care, this therapeutic approach requires further improvements to achieve definite efficacy.

AREAS COVERED

We review the most promising clinical developments with several oncolytic viruses. The focus is on preclinical and clinical findings with replication-selective adenoviral mutants including ONYX-015, H101 and Ad5ΔCR mutants that, to date, are the most studied oncolytic viruses. Cellular pathways reported to play a role in virus-induced cell killing are reviewed as potential targets for the development of more effective combinatorial therapies.

EXPERT OPINION

The most promising clinical outcomes for metastatic cancers have been reported for oncolytic vaccinia and herpes virus mutants expressing the cytokine GMCSF. However, highly efficacious and selective adenoviral mutants have been developed that interact synergistically with cytotoxic drugs in model systems. We anticipate that by delineating the cellular targets for synergistic cancer cell killing in response to adenoviral mutants and drugs such as apoptosis and autophagy signaling, greatly improved anticancer therapies will result in the near future.

Autophagy in the regulation of pathogen replication and adaptive immunity

Autophagy is an evolutionarily conserved homeostatic process by which cells deliver cytoplasmic material for degradation into lysosomes. Autophagy may have evolved as a nutrient-providing homeostatic pathway induced upon starvation, but with the acquisition of cargo receptors, autophagy has become an important cellular defence mechanism as well as a generator of antigenic peptides for major histocompatibility complex (MHC) presentation. We propose that autophagy efficiently protects against microbes encountering the cytosolic environment accidentally, for example, upon phagosomal damage, whereas pathogens routinely accessing the host cytosol have evolved to avoid or even benefit from autophagy.

Hepatitis C virus upregulates Beclin1 for induction of autophagy and activates mTOR signaling

Hepatitis C virus (HCV) induces autophagosome formation in infected human hepatocytes. We have previously reported that HCV exploits autophagic machinery in favor of virus growth and survival in host cells (S. Shrivastava et al., Hepatology 53:406-414, 2011); however, the mechanisms for autophagy induction is poorly understood. In the present study, we observed that HCV infection transcriptionally upregulates Beclin1, which forms complex with Vps34, the class III phosphatidylinositol 3-kinase, as a first step for autophagy initiation. Although Bcl-2 has an anti-autophagy effect by its association with Beclin1 in nutrient-deprived cells, our studies revealed that HCV-mediated autophagy occurs independent of Beclin1-Bcl-2 dissociation. Mammalian target of rapamycin (mTOR) is a positive regulator of cell growth and is recognized as an inhibitor of autophagy induction. Our results demonstrated that HCV infection enhances phospho-mTOR expression and its downstream target 4EBP1 activation, suggesting that mTOR is not a negative regulator of HCV-induced autophagy. On the other hand, HCV infection in autophagy-impaired cells reduced phospho-mTOR, mTOR, and phospho-4EBP1 expression. Together, these results suggested that HCV induces autophagy by upregulating Beclin1 and activates mTOR signaling pathway, which in turn may promote hepatocyte growth.

Inhibition of autophagy enhances the effects of E1A-defective oncolytic adenovirus dl922-947 against glioma cells in vitro and in vivo

Oncolytic viruses represent a novel therapeutic approach for aggressive tumors, such as glioblastoma multiforme, which are resistant to available treatments. Autophagy has been observed in cells infected with oncolytic viruses; however, its role in cell death/survival is unclear. To elucidate the potential therapeutic use of autophagy modulators in association with viral therapy, we analyzed autophagy induction in human glioma cell lines U373MG and U87MG infected with the oncolytic adenovirus dl922-947. dl922-947 infection triggered an autophagic cellular response, as shown by the development of acidic vesicular organelles, LC3-I→LC3-II conversion, and reduction of p62 levels. However, on infection, the Akt/mTOR/p70s6k pathway, which negatively regulates autophagy, was activated, whereas the ERK1/2 pathway, a positive regulator of autophagy, was inhibited. Accordingly, MEK inhibition by PD98059 sensitized glioma cells to dl922-947 effects, whereas autophagy induction by rapamycin protected cells from dl922-947-induced death. Treatment with two inhibitors of autophagy, chloroquine and 3-methyladenine, increased the cytotoxic effects of dl922-947 in vitro. In vivo, the growth of U87MG-induced xenografts was further reduced by adding chloroquine to the dl922-947 treatment. In conclusion, autophagy acts as a survival response in glioma cells infected with dl922-947, thus suggesting autophagy inhibitors as adjuvant/neoadjuvant drugs in oncolytic virus-based treatments.

The role of autophagy during coxsackievirus infection of neural progenitor and stem cells

Coxsackievirus B3 (CVB3) has previously been shown to utilize autophagy in an advantageous manner during the course of infection of the host cell. However, few studies have determined whether stem cells induce autophagy in a similar fashion, and whether virus-induced autophagy occurs following infection of stem cells. Therefore, we compared the induction of autophagy following CVB3 infection of neural progenitor and stem cells (NPSCs), which we have recently shown to be highly susceptible to CVB3 infection, to HL-1 cells, a transformed cardiomyocyte cell line. As previously demonstrated for other susceptible host cells, HL-1 cells showed an increase in the activity of autophagic signaling following infection with a CVB3 expressing dsRed protein (dsRed-CVB3). Furthermore, viral titers in HL-1 cells increased in the presence of an inducer of autophagy (CCPA), while viral titers decreased in the presence of an inhibitor of autophagy (3-MA). In contrast, no change in autophagic signaling was seen in NPSCs following infection with dsRed-CVB3. Also, basal levels of autophagy in NPSCs were found to be highly elevated in comparison to HL-1 cells. Autophagy could be induced in NPSCs in the presence of rapamycin without altering levels of dsRed-CVB3 replication. In differentiated NPSC precursors, autophagy was activated during the differentiation process, and a decrease in autophagic signaling was observed within all three CNS lineages following dsRed-CVB3 infection. Hence, we conclude that the role of autophagy in modulating CVB3 replication appears cell type-specific, and stem cells may uniquely regulate autophagy in response to infection.

Membrane fusion-mediated autophagy induction enhances morbillivirus cell-to-cell spread

In the context of viral infections, autophagy induction can be beneficial or inhibitory. Within the Paramyxoviridae family, only morbilliviruses have been investigated and are reported to induce autophagy. Here we show that morbilliviruses rapidly induce autophagy and require this induction for efficient cell-to-cell spread. Coexpression of both glycoproteins in cells expressing one of the cellular receptors was required for autophagy induction, and LC3 punctum formation, indicative of autophagy, was mainly observed in syncytia. A similar correlation between syncytium formation and autophagy induction was also observed for other paramyxovirus glycoproteins, suggesting that membrane fusion-mediated autophagy may be common among paramyxoviruses and possibly other enveloped viruses.

Macroautophagy Regulation during HIV-1 Infection of CD4+ T Cells and Macrophages

Autophagy is an intracellular mechanism whereby pathogens, particularly viruses, are destroyed in autolysosomes after their entry into targets cells. Therefore, to survive and replicate in host cells, viruses have developed multiple strategies to either counteract or exploit this process. The aim of this review is to outline the known relationships between HIV-1 and autophagy in CD4+ T lymphocytes and macrophages, two main HIV-1 cell targets. The differential regulation of autophagy in these two cell-types is highlighted and its potential consequences in terms of viral replication and physiopathology discussed.

Effect of γ34.5 deletions on oncolytic herpes simplex virus activity in brain tumors

The ICP34.5 protein of herpes simplex virus (HSV) is involved in many aspects of viral pathogenesis; promoting neurovirulence, inhibiting interferon-induced shutoff of protein synthesis, interacting with PCNA and TBK1, inhibiting dendritic cell (DC) maturation, and binding to Beclin 1 to interfere with autophagy. Because of its key role in neuropathogenicity, the γ34.5 gene is deleted in all oncolytic HSVs (oHSVs) currently in clinical trial for treating malignant gliomas. Unfortunately, deletion of γ34.5 attenuates virus replication in cancer cells, especially human glioblastoma stem cells (GSCs). To develop new oHSVs for use in the brain and that replicate in GSCs, we explored the effect of deleting the γ34.5 Beclin 1 binding domain (BBD). To ensure cancer selectivity and safety, we inactivated the ICP6 gene (UL39, large subunit of ribonucleotide reductase), constructing ICP6 mutants with different γ34.5 genotypes: Δ68HR-6, intact γ34.5; Δ68H-6, γ34.5 BBD deleted; and 1716-6, γ34.5 deleted. Multimutated Δ68H-6 exhibited minimal neuropathogenicity in HSV-1-susceptible mice, as opposed to Δ68H and Δ68HR-6. It replicated well in human glioma cell lines and GSCs, effectively killing cells in vitro and prolonging survival of mice bearing orthotopic brain tumors. In contrast, 1716 and 1716-6 barely replicated in GSCs. Infection of glioma cells with Δ68H-6 and 1716-6 induced autophagy and increased phosphorylation of eIF2α, while inhibition of autophagy, by Beclin 1 short hairpin RNA (shRNA) knockdown or pharmacological inhibition, had no effect on virus replication or phosphorylated eIF2α (p-eIF2α) levels. Thus, Δ68H-6 represents a new oHSV vector that is safe and effective against a variety of brain tumor models.

Mapping of Chikungunya virus interactions with host proteins identified nsP2 as a highly connected viral component

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has been responsible for an epidemic outbreak of unprecedented magnitude in recent years. Since then, significant efforts have been made to better understand the biology of this virus, but we still have poor knowledge of CHIKV interactions with host cell components at the molecular level. Here we describe the extensive use of high-throughput yeast two-hybrid (HT-Y2H) assays to characterize interactions between CHIKV and human proteins. A total of 22 high-confidence interactions, which essentially involved the viral nonstructural protein nsP2, were identified and further validated in protein complementation assay (PCA). These results were integrated to a larger network obtained by extensive mining of the literature for reports on alphavirus-host interactions. To investigate the role of cellular proteins interacting with nsP2, gene silencing experiments were performed in cells infected by a recombinant CHIKV expressing Renilla luciferase as a reporter. Collected data showed that heterogeneous nuclear ribonucleoprotein K (hnRNP-K) and ubiquilin 4 (UBQLN4) participate in CHIKV replication in vitro. In addition, we showed that CHIKV nsP2 induces a cellular shutoff, as previously reported for other Old World alphaviruses, and determined that among binding partners identified by yeast two-hybrid methods, the tetratricopeptide repeat protein 7B (TTC7B) plays a significant role in this activity. Altogether, this report provides the first interaction map between CHIKV and human proteins and describes new host cell proteins involved in the replication cycle of this virus.

Avian reovirus triggers autophagy in primary chicken fibroblast cells and Vero cells to promote virus production

Avian reovirus (ARV) is an important cause of disease in poultry. Although ARV is known to induce apoptosis in infected cells, the interaction between ARV and its target cells requires further elucidation. In this report, we show that the ARV isolate strain GX/2010/1 induces autophagy in both Vero and primary chicken embryonic fibroblast (CEF) cells based on the appearance of an increased number of double-membrane vesicles, the presence of GFP-microtubule-associated protein 1 light chain 3 (GFP-LC3) dot formation, and the elevated production of LC3II. We further demonstrate that the class I phosphoinositide 3-kinase (PI3K)/Akt/mTOR pathway contributes to autophagic induction by ARV infection. Moreover, treatment of ARV-infected cells with the autophagy inducer rapamycin increased viral yields, while inhibition of the autophagosomal pathway using chloroquine led to a decrease in virus production. Altogether, our studies strongly suggest that autophagy may play a critical role in determining viral yield during ARV infection.

The role of programmed cell death in streptozotocin-induced early diabetic nephropathy

The mechanism of autophagy in diabetic nephropathy (DN) is still unclear. The study was performed on streptozotocin (STZ) rats to investigate whether programmed cell death contribute to the pathogenesis and progression of DN. STZ rats were induced by an single intravenous injection of STZ dissolved in citrate buffer, early DN (E-DN) for STZ rats was defined as the stage from modeling to the end of the 8th week according to previous studies. A total of 36 male Sprague-Dawley rats were randomly divided into two groups: an E-DN group and a control group. After the 1st, 4th, and 8th week, the rats were sacrificed. Beclin1 and microtubule associated protein 1 light chain 3 (LC3) were examined, apoptosis level in renal tissue was detected by Tunnel assay detected as the apoptotic index. An electron microscopic examination of kidney tissues was performed at end of the 4th and 8th week. Compared with the control group, Beclin1 expression increased since the 1st week after modeling in STZ rats kidney and peaked at the end of the 8th week in western blotting and immunohistochemical stain. Meanwhile the level of LC3-II in DN group was significantly lower from the end of the 1st to the 8th week. A small amount of autophagosomes were observed in both E-DN group and control group under electron microscopic examination, and there was no significant difference between the groups. These findings indicate that an abnormality on autophagy may play an important role in the pathogenesis of E-DN.

Autophagy is involved in the early step of Japanese encephalitis virus infection

Japanese encephalitis virus (JEV), an enveloped Flavivirus with a positive-sense RNA genome, causes acute encephalitis with high mortality in humans. We used a virulent (RP-9) and an attenuated (RP-2ms) JEV strain to assess the role of autophagy in JEV infection. By monitoring the levels of lipidated LC3, we found that autophagy was induced in human NT-2 cells infected with RP-2ms, especially at the late stage, and to a lesser extent with RP-9. The induction of autophagy by rapamycin increased viral production, whereas the inhibition of autophagy by 3-methyladenine reduced viral yields for both RP-9 and RP-2ms. The viral replication of RP-9 and RP-2ms was also reduced in cells with downregulated ATG5 or Beclin 1 expression, suggesting a proviral role of autophagy in JEV replication. To determine the step of JEV life cycle affected by autophagy, we used an mCherry-LC3 fusion protein as the autophagosome marker. Little of no colocalization of LC3 puncta with dsRNA was noted, whereas the input JEV particles were targeted to autophagosomes stained positive for early endosome marker. Overall, we show for the first time that the cellular autophagy process is involved in JEV infection and the inoculated viral particles traffic to autophagosomes for subsequent steps of viral infection.

Rab5 and class III phosphoinositide 3-kinase Vps34 are involved in hepatitis C virus NS4B-induced autophagy

Autophagy has been shown to facilitate replication or production of hepatitis C virus (HCV); nevertheless, how HCV induces autophagy remains unclear. Here, we demonstrate that HCV nonstructural protein 4B (NS4B) alone can induce autophagy signaling; amino acid residues 1 to 190 of NS4B are sufficient for this induction. Further studies showed that the phosphorylation levels of S6K and 4E-BP1 were not altered, suggesting that the mTOR/S6 kinase pathway and mTOR/4E-BP1 pathway did not contribute to NS4B- or HCV-induced autophagy. Inhibition of Rab5 function by silencing Rab5 or overexpressing dominant-negative Rab5 mutant (S34N) resulted in significant reduction of NS4B- or HCV-induced autophagic vesicle formation. Moreover, the autophagy induction was impaired by inhibition of class III phosphoinositide 3-kinase (PI 3-kinase) Vps34 function. Finally, the coimmunoprecipitation assay indicated that NS4B formed a complex with Rab5 and Vps34, supporting the notion that Rab5 and Vps34 are involved in NS4B-induced autophagy. Taken together, these results not only reveal a novel role of NS4B in autophagy but also offer a clue to the mechanism of HCV-induced autophagy.

Autophagosome formation during varicella-zoster virus infection following endoplasmic reticulum stress and the unfolded protein response

Autophagy is a recently recognized component of the life cycle of varicella-zoster virus (VZV). We have documented abundant autophagosome formation in skin vesicles (final site of virion assembly) from randomly selected cases of varicella and zoster. The fact that autophagy was an early event in the VZV replication cycle was documented by finding infected vesicle cells with the VZV IE62 protein confined to the nucleus. Next, we pursued studies in VZV-infected cultured cells to define whether autophagy was preceded by endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). First, we demonstrated that autophagosome formation in infected cells closely resembled that seen after treatment of cells with tunicamycin, a potent initiator of ER stress. Second, we demonstrated a marked expansion of ER size in both VZV-infected cells and cells transfected with the predominant VZV glycoprotein complex gE/gI. An enlarged ER is critical evidence of ER stress, which in turn is relieved by the UPR. To this end, we documented the UPR by detecting the alternatively spliced form of the XBP1 protein as well as CHOP (C/EBP homologous protein), both transcriptional activators of other UPR genes in an ER stress-dependent manner. Because VZV does not encode inhibitors of autophagy, the above results suggested that autophagy was a common event in VZV-infected cells and that it was provoked at least in part by ER stress secondary to overly abundant VZV glycoprotein biosynthesis, which led to UPR activation in an attempt to maintain cellular homeostasis.

Mutation of the elongin C binding domain of human respiratory syncytial virus non-structural protein 1 (NS1) results in degradation of NS1 and attenuation of the virus

Background

Human respiratory syncytial virus (RSV) is an important cause of lower respiratory tract disease in the paediatic population, immunocompromised individuals and the elderly worldwide. However, despite global efforts over the past several decades there are no commercially available vaccines. RSV encodes 2 non-structural proteins, NS1 and NS2, that are type I interferon antagonists. RSV restricts type I interferon signaling and the expression of antiviral genes by degrading STAT2. It has been proposed that NS1 binds to elongin C to form a ubiquitin ligase (E3) complex that targets STAT2 for ubiquitination and proteosomal degradation.

Results

Here, we have engineered a live recombinant RSV in which the 3 consensus amino acids of the NS1 elongin C binding domain have been replaced with alanine (NS1F-ELCmut). Mutation of this region of NS1 resulted in attenuation of RSV replication in A549 cells to levels similar to that observed when the NS1 gene is completely deleted (ΔNS1). This mutation also resulted in moderate attenuation in Vero cells. Attenuation was correlated to intracellular degradation of the mutated NS1 protein. Time course analysis showed that mutant NS1 protein accumulated in cytoplasmic bodies that contained the lysosomal marker LAMP1. However lack of cleavage of LC3 suggested that autophagy was not involved. Induction of IFN-β mRNA expression also was observed in association with the degradation of NS1 protein and attenuation of viral growth.

Conclusions

These results indicate that the elongin C binding region of NS1 is crucial for survival of the protein and that disruption of this region results in the degradation of NS1 and restriction of RSV replication.

Macroautophagy during Innate Immune Activation

Innate immune activation is initiated by recognition of pathogen associated molecular patterns (PAMPs). Delivery of PAMPs to their respective receptors, regulation of receptor activity, and effector functions downstream from these receptors, which constitute part of the initiated innate immune control, are in part mediated via macroautophagy, an evolutionary conserved pathway for cytoplasmic constituent degradation in lysosomes. In this review these facets of the recently unveiled involvement of macroautophagy in innate immunity will be summarized, and aspects that need additional investigations will be high-lighted. The improved understanding of the capabilities of macroautophagy for immunity suggests that this pathway should be harnessed in immunotherapies against infectious diseases.

Autophagy basics

Autophagy (macroautophagy) is a dynamic process for degradation of cytosolic components. Autophagy has intracellular anti-viral and anti-bacterial functions, and plays a role in the initiation of innate and adaptive immune system responses to viral and bacterial infections. Some viruses encode virulence factors for blocking autophagy, whereas others utilize some autophagy components for their intracellular growth or cellular budding. The "core" autophagy-related (Atg) complexes in mammals are ULK1 protein kinase, Atg9-WIPI-1 and Vps34-beclin1 class III PI3-kinase complexes, and the Atg12 and LC3 conjugation systems. In addition, PI(3)-binding proteins, PI3-phosphatases, and Rab proteins contribute to autophagy. The autophagy process consists of continuous dynamic membrane formation and fusion. In this review, the relationships between these Atg complexes and each process are described. Finally, the critical points for monitoring autophagy, including the use of GFP-LC3 and GFP-Atg5, are discussed.