EBV reduces autophagy, intracellular ROS and mitochondria to impair monocyte survival and differentiation

BRLF1-dependent viral and cellular transcriptomes and transcriptional regulation during EBV primary infection in B lymphoma cells

The immediate-early protein BRLF1 plays important roles in lytic infection of Epstein-Barr virus (EBV), in which it activates lytic viral transcription and replication. However, knowledge of the influence of BRLF1 on cellular gene expression and transcriptional reprogramming during the early lytic cycle remains limited. In the present study, deep RNA-sequencing analysis identified all differentially expressed genes (DEGs) and alternative splicing in B lymphoma cells subjected to wild-type and BRLF1-deficient EBV primary infection. The BRLF1-dependent cellular DEGs were annotated, and major differentially enriched pathways were related to DNA replication and transcription, immune and inflammatory responses, cytokine-receptor interactions and chemokine signaling and metabolic processes. Furthermore, analysis of BRLF1-binding proteins by mass spectrometry shows that BRLF1 binds to and cooperates with several transcription factors and components of the spliceosome and then influences both RNA polymerase II-dependent transcription and pre-mRNA splicing. The RTA-binding RRE motifs or specific motifs of unique cooperative transcription factors in viral and cellular DEG promoter regions indicate that BRLF1 employs different strategies for regulating viral and cellular transcription. Thus, our study characterized BRLF1-dependent cellular and viral transcriptional profile during primary infection and then revealed the comprehensive virus-cell interaction and alterations of transcription during EBV primary infection and lytic replication.

Fatty acids promote the expansion of NK-92 cells in vitro by improving energy metabolism

Natural killer-92 cells (NK-92 cells) need to be efficiently expanded by serum-free culture in vitro to meet clinical requirements. Fatty acids mainly provide substrates for energy production, which is of crucial importance to meet the energy demands of highly proliferating cells. This study optimized the medium (EM) for NK-92 cells by designing an experiment to expand cells efficiently. EM, an in-house designed chemically defined serum-free medium, was used as the basal medium. Fatty acids as additive ingredients were screened and optimized by the experimental design method. Three additives, arachidonic acid, myristic acid and palmitoleic acid, were screened; therefore, the optimized medium was named EM-FA. The total cell expansion of NK-92 cells in EM-FA was 72.61±11.95-fold on day 8, which was significantly higher than the 28.55±8.67-fold expansion in EM. To explore the mechanism by which fatty acids promote NK-92 cell expansion, the cell growth kinetics and metabolic characteristics in EM-FA were analyzed. The results showed that NK-92 cells in EM-FA were rapidly expanded while maintaining their cell phenotype and cytotoxicity and enhancing the oxygen consumption rate and mitochondrial function. Fatty acids promoted ATP production to elevate the energy flux for better cell expansion. This study developed an expansion strategy of NK-92 cells in vitro to facilitate their clinical application. KEY POINTS: • Arachidonic acid, myristic acid and palmitoleic acid in serum-free medium were optimized by experimental design to enable the rapid expansion of NK-92 cells in vitro. • Fatty acids upregulated oxidative phosphorylation levels and improved the energy metabolism of NK-92 cells.

ER Stress, UPR Activation and the Inflammatory Response to Viral Infection

The response to invading pathogens such as viruses is orchestrated by pattern recognition receptor (PRR) and unfolded protein response (UPR) signaling, which intersects and converges in the activation of proinflammatory pathways and the release of cytokines and chemokines that harness the immune system in the attempt to clear microbial infection. Despite this protective intent, the inflammatory response, particularly during viral infection, may be too intense or last for too long, whereby it becomes the cause of organ or systemic diseases itself. This suggests that a better understanding of the mechanisms that regulate this complex process is needed in order to achieve better control of the side effects that inflammation may cause while potentiating its protective role. The use of specific inhibitors of the UPR sensors or PRRs or the downstream pathways activated by their signaling could offer the opportunity to reach this goal and improve the outcome of inflammation-based diseases associated with viral infections.

Modulation of Endosome Function, Vesicle Trafficking and Autophagy by Human Herpesviruses

Human herpesviruses are a ubiquitous family of viruses that infect individuals of all ages and are present at a high prevalence worldwide. Herpesviruses are responsible for a broad spectrum of diseases, ranging from skin and mucosal lesions to blindness and life-threatening encephalitis, and some of them, such as Kaposi’s sarcoma-associated herpesvirus (KSHV) and Epstein–Barr virus (EBV), are known to be oncogenic. Furthermore, recent studies suggest that some herpesviruses may be associated with developing neurodegenerative diseases. These viruses can establish lifelong infections in the host and remain in a latent state with periodic reactivations. To achieve infection and yield new infectious viral particles, these viruses require and interact with molecular host determinants for supporting their replication and spread. Important sets of cellular factors involved in the lifecycle of herpesviruses are those participating in intracellular membrane trafficking pathways, as well as autophagic-based organelle recycling processes. These cellular processes are required by these viruses for cell entry and exit steps. Here, we review and discuss recent findings related to how herpesviruses exploit vesicular trafficking and autophagy components by using both host and viral gene products to promote the import and export of infectious viral particles from and to the extracellular environment. Understanding how herpesviruses modulate autophagy, endolysosomal and secretory pathways, as well as other prominent trafficking vesicles within the cell, could enable the engineering of novel antiviral therapies to treat these viruses and counteract their negative health effects.

Mechanisms and therapeutic potential of interactions between human amyloids and viruses

The aggregation of specific proteins and their amyloid deposition in affected tissue in disease has been studied for decades assuming a sole pathogenic role of amyloids. It is now clear that amyloids can also encode important cellular functions, one of which involves the interaction potential of amyloids with microbial pathogens, including viruses. Human expressed amyloids have been shown to act both as innate restriction molecules against viruses as well as promoting agents for viral infectivity. The underlying molecular driving forces of such amyloid-virus interactions are not completely understood. Starting from the well-described molecular mechanisms underlying amyloid formation, we here summarize three non-mutually exclusive hypotheses that have been proposed to drive amyloid-virus interactions. Viruses can indirectly drive amyloid depositions by affecting upstream molecular pathways or induce amyloid formation by a direct interaction with the viral surface or specific viral proteins. Finally, we highlight the potential of therapeutic interventions using the sequence specificity of amyloid interactions to drive viral interference.

Mitochondria and immunity in chronic fatigue syndrome

It is widely accepted that the pathophysiology and treatment of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) could be considerably improved. The heterogeneity of ME/CFS and the confusion over its classification have undoubtedly contributed to this, although this would seem a consequence of the complexity of the array of ME/CFS presentations and high levels of diverse comorbidities. This article reviews the biological underpinnings of ME/CFS presentations, including the interacting roles of the gut microbiome/permeability, endogenous opioidergic system, immune cell mitochondria, autonomic nervous system, microRNA-155, viral infection/re-awakening and leptin as well as melatonin and the circadian rhythm. This details not only relevant pathophysiological processes and treatment options, but also highlights future research directions. Due to the complexity of interacting systems in ME/CFS pathophysiology, clarification as to its biological underpinnings is likely to considerably contribute to the understanding and treatment of other complex and poorly managed conditions, including fibromyalgia, depression, migraine, and dementia. The gut and immune cell mitochondria are proposed to be two important hubs that interact with the circadian rhythm in driving ME/CFS pathophysiology.

Viral Infection and Autophagy Dysregulation: The Case of HHV-6, EBV and KSHV

Human Herpes Virus-6 (HHV-6), Epstein-Barr Virus (EBV) and Kaposi Sarcoma Herpes Virus (KSHV) are viruses that share with other member of the Herpesvirus family the capacity to interfere with the autophagic process. In this paper, mainly based on the findings of our laboratory, we describe how, through different mechanisms, these viruses converge in reducing autophagy to impair DC immune function and how, by infecting and dysregulating autophagy in different cell types, they promote the pathologies associated with their infection, from the neurodegenerative diseases such Alzheimer’s disease to cancer.

The cross-talk between STAT1/STAT3 and ROS up-regulates PD-L1 and promotes the release of pro-inflammatory/immune suppressive cytokines in primary monocytes infected by HHV-6B

Programmed death ligand 1 (PD-L1) up-regulation on antigen presenting cells induces T cell dysfunction, strongly impairing immune response. Human Herpesviruses (HHV) 6B is a β-herpesvirus that, although displays a higher tropism for T cells, can infect other immune cells including monocytes and dendritic cells (DCs) and neuronal cells. We have previously shown that HHV-6B infection of primary monocytes reduced autophagy and induced Endoplasmic Reticulum (ER) stress/ Unfolded Protein Response (UPR), impairing their survival and differentiation into DCs. In this study, we found that PD-L1 expression was up-regulated by HHV-6B on the surface of infected monocytes and that its extracellular release also increased, effects known to lead to an impairment of anti-viral immune response. At molecular level, PD-L1 up-regulation correlated with the activation of a positive regulatory circuit between the increase of intracellular ROS and the activation of STAT1 and STAT3 induced by HHV-6B, accompanied by a high release of pro-inflammatory/immune suppressive cytokines. In conclusion, this study unveils new strategies put in place by HHV-6B to induce immune dysfunction and the underlying molecular pathways that could be targeted to counteract such immune suppressive effects.

Deficiency of microglial Hv1 channel is associated with activation of autophagic pathway and ROS production in LPC-induced demyelination mouse model

BACKGROUND

Multiple sclerosis (MS) is an immune-mediated demyelinated disease of the central nervous system. Activation of microglia is involved in the pathogenesis of myelin loss.

OBJECTIVE

This study is focused on the role of Hv1 in regulating demyelination and microglial activation through reactive oxygen species (ROS) production after lysophosphatidylcholine (LPC)-mediated demyelination. We also explored autophagy in this process.

METHODS

A model of demyelination using two-point LPC injection into the corpus callosum was established. LFB staining, immunofluorescence, Western blot, and electron microscopy were used to study the severity of demyelination. Microglial phenotype and autophagy were detected by immunofluorescence and Western blot. Morris water maze was used to test spatial learning and memory ability.

RESULTS

We have identified that LPC-mediated myelin damage was reduced by Hv1 deficiency. Furthermore, we found that ROS and autophagy of microglia increased in the demyelination region, which was also inhibited by Hv1 knockout.

CONCLUSION

These results suggested that microglial Hv1 deficiency ameliorates demyelination through inhibition of ROS-mediated autophagy and microglial phenotypic transformation.

The Dynamic Interface of Viruses with STATs

Viruses commonly antagonize the antiviral type I interferon response by targeting signal transducer and activator of transcription 1 (STAT1) and STAT2, key mediators of interferon signaling. Other STAT family members mediate signaling by diverse cytokines important to infection, but their relationship with viruses is more complex. Importantly, virus-STAT interaction can be antagonistic or stimulatory depending on diverse viral and cellular factors. While STAT antagonism can suppress immune pathways, many viruses promote activation of specific STATs to support viral gene expression and/or produce cellular conditions conducive to infection. It is also becoming increasingly clear that viruses can hijack noncanonical STAT functions to benefit infection. For a number of viruses, STAT function is dynamically modulated through infection as requirements for replication change. Given the critical role of STATs in infection by diverse viruses, the virus-STAT interface is an attractive target for the development of antivirals and live-attenuated viral vaccines. Here, we review current understanding of the complex and dynamic virus-STAT interface and discuss how this relationship might be harnessed for medical applications.

Curcumin induces G2/M arrest and triggers autophagy, ROS generation and cell senescence in cervical cancer cells

Our study explored the tumor-suppressive effect of curcumin on cervical cancer cells. Cervical cancer is one of the most common cancers among women worldwide. Acquired resistance to chemotherapeutics and toxicity of such drugs has undermined the effectiveness of cervical cancer treatments. Therefore, the identification of novel chemotherapeutics is key to improving the survival of patients with cervical cancer. Curcumin has been shown to have various bioactivities, including antioxidant and antitumor effects; however, its effect on cervical cancer remains elusive. Here, we used the SiHa human cervical cancer cell line to test various concentrations of curcumin on the proliferation and apoptosis of cervical cancer cells. The involvement of autophagy and reactive oxygen species (ROS) in these effects were also tested by using specific autophagy inhibitors and ROS scavengers. Our results showed that curcumin induced ROS accumulation, apoptosis, autophagy, cell cycle arrest, and cellular senescence accompanied by upregulation of p53 and p21 proteins in SiHa cells.

KSHV dysregulates bulk macroautophagy, mitophagy and UPR to promote endothelial to mesenchymal transition and CCL2 release, key events in viral-driven sarcomagenesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of KS, an aggressive neoplasm that mainly occurs in immune-compromised patients. Spindle cells represent the main feature of this aggressive malignancy and arise from KSHV-infected endothelial cells undergoing endothelial to mesenchymal transition (EndMT), which changes their cytoskeletal composition and organization. As in epithelial to mesenchymal transition (EMT), EndMT is driven by transcription factors such as SNAI1 and ZEB1 and implies a cellular reprogramming mechanism regulated by several molecular pathways, particularly PI3K/AKT/MTOR. Here we found that KSHV activated MTOR and its targets 4EBP1 and ULK1 and reduced bulk macroautophagy and mitophagy to promote EndMT, activate ER stress/unfolded protein response (UPR), and increase the release of the pro-angiogenic and pro-inflammatory chemokine CCL2 by HUVEC cells. Our study suggests that the manipulation of macroautophagy, mitophagy and UPR and the interplay between the three could be a promising strategy to counteract EndMT, angiogenesis and inflammation, the key events of KSHV-driven sarcomagenesis.

DEHP induces neutrophil extracellular traps formation and apoptosis in carp isolated from carp blood via promotion of ROS burst and autophagy

Di (2-ethylhexyl) phthalate (DEHP), a widely spreading environmental endocrine disruptor, has been confirmed to adversely affect the development of animals and humans. The formation of neutrophil extracellular traps (NETs) termed NETosis, is a recently identified antimicrobial mechanism for neutrophils. Though previous researches have investigated inescapable role of the immunotoxicity in DEHP-exposed model, relatively little is known about the effect of DEHP on NETs. In this study, carp peripheral blood neutrophils were treated with 40 and 200 μmol/L DEHP to investigate the underlying mechanisms of DEHP-induced NETs formation. Through the morphological observation of NETs and quantitative analysis of extracellular DNA, we found that DEHP exposure induced NETs formation. Moreover, our results proved that DEHP could increase reactive oxygen species (ROS) levels, decrease the expression of the anti-autophagy factor (mTOR) and the anti-apoptosis gene Bcl-2, and increase the expression of pro-autophagy genes (Dynein, Beclin-1 and LC3B) and the pro-apoptosis factors (BAX, Fas, FasL, Caspase3, Caspase8, and Caspase9), thus promoting autophagy and apoptosis. These results indicate that DEHP-induced ROS burst stimulates NETs formation mediated by autophagy and increases apoptosis in carp neutrophils.

Cognitive Protective Mechanism of Crocin Pretreatment in Rat Submitted to Acute High-Altitude Hypoxia Exposure

Inadequate oxygen availability at high altitude leads to oxidative stress, resulting in hippocampal neurodegeneration and memory impairment. In our previous study, we found that the cognitive dysfunction occurred when male SD rat was rapidly exposed to 4200 m of high altitude for 3 days. And we also found that crocin showed a cognitive protective effect under hypoxia by regulating SIRT1/PGC-1α pathways in rat's hippocampus. In this article, focused on factors related to SIRT1/PGC-1α pathways, we proposed to further elucidate crocin's pharmacological mechanism. Adult male Sprague-Dawley rats were randomly divided into five groups: control group, hypoxia group (rats were rapidly transported to high altitude of 4200 m for 72 h), and crocins+hypoxia groups (pretreatment with crocin of 25, 50, and 100 mg/kg/d for 3 days). The learning and memory ability was tested by Morris water maze analysis. Hippocampal histopathological changes were observed by HE staining and Nissl staining. The expression of NRF1, TFAM, Bcl-2, Bax, and caspase-3 was detected by immunohistochemistry, RT-PCR, and western blotting test. The contents of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GSHPx) were detected by the TBA, WST, and colorimetry method. Neuronal apoptosis was observed by TUNEL staining. After crocin pretreatment, the traveled distance was significantly reduced and the percentage of time in the target quadrant was significantly increased tested by Morris water maze. And neuronal damage in the hippocampus was also significantly ameliorated based on HE staining and Nissl staining. Furthermore, in hippocampus tissue, mitochondrial biosynthesis-related factors of NRF1, TFAM expression was increased; oxidative stress factors of SOD, GSH, and GSHPx expression level were increased, and MDA and glutathione disulfide (GSSG) level were decreased; antiapoptotic protein Bcl-2 expression was increased, and proapoptotic proteins Bax and caspase-3 expression were decreased, with a manner of crocin dose dependent. Therefore, the cognitive protective mechanism of crocin in rat under acute hypoxia was related to promoting mitochondrial biosynthesis, ameliorating oxidative stress injury, and decreasing neuronal apoptosis.

KSHV infection skews macrophage polarisation towards M2-like/TAM and activates Ire1 α-XBP1 axis up-regulating pro-tumorigenic cytokine release and PD-L1 expression

Background

Kaposi’s Sarcoma Herpesvirus (KSHV) is a gammaherpesvirus strongly linked to human cancer. The virus is also able to induce immune suppression, effect that contributes to onset/progression of the viral-associated malignancies. As KSHV may infect macrophages and these cells abundantly infiltrate Kaposi’s sarcoma lesions, in this study we investigated whether KSHV-infection could affect macrophage polarisation to promote tumorigenesis.

Methods

FACS analysis was used to detect macrophage markers and PD-L1 expression. KSHV infection and the molecular pathways activated were investigated by western blot analysis and by qRT-PCR while cytokine release was assessed by Multi-analyte Kit.

Results

We found that KSHV infection reduced macrophage survival and skewed their polarisation towards M2 like/TAM cells, based on the expression of CD163, on the activation of STAT3 and STAT6 pathways and the release of pro-tumorigenic cytokines such as IL-10, VEGF, IL-6 and IL-8. We also found that KSHV triggered Ire1 α-XBP1 axis activation in infected macrophages to increase the release of pro-tumorigenic cytokines and to up-regulate PD-L1 surface expression.

Conclusions

The findings that KSHV infection of macrophages skews their polarisation towards M2/TAM and that activate Ire1 α-XBP1 to increase the release of pro-tumorigenic cytokines and the expression of PD-L1, suggest that manipulation of UPR could be exploited to prevent or improve the treatment of KSHV-associated malignancies.

Ferulic acid isolated from propolis inhibits porcine parvovirus replication potentially through Bid-mediate apoptosis

Propolis from honeybee hives, which is a traditional Chinese medicine, is widely used in veterinary clinics. Many compounds have been identified and isolated from propolis. Ferulic acid (FA), one of the propolis components, previous studies have proven that it has antiviral effects. To study the mechanism of FA antiviral effects, experiments such as immunofluorescence, quantitative real-time PCR and immunoblotting were introduced. In porcine kidney (PK-15) cells, PPV infection induced the expression of the proapoptotic genes Bid, Bad, Bim and Bak, disrupted mitochondrial membrane potential, promoted mitochondria-mediated, caspase-dependent apoptotic signaling and induced apoptosis. Furthermore, the infected PK-15 cells had increased intracellular reactive oxygen species (ROS) generation. FA treatment, however, reversed these effects and increased cell viability. FA treatment also significantly decreased the PPV-induced expression of Bid, Cyt-c and Apaf-1, suggesting that ROS were involved in the activation of the mitochondria-mediated apoptosis pathway. This in vitro study showed that the antiviral activity of FA was probably associated with inhibiting the replication of PPV by blocking proapoptotic factors such as Bid, Bcl-2 and Mcl-1, and attenuating the mitochondria-mediated response by inhibiting the activation of the Bid-related signaling pathway. Pharmacological inhibitors inhibited PPV-induced apoptosis by blocking Bid, and also suppressed the expression of Caspase family proteins in ppv-induced apoptosis. Taken together, our results suggested that PPV induced PK-15 cell apoptosis via activation of Bid and Bid-related signaling pathways and that the mitochondria act as the mediators of these pathways. FA effectively and extensively attenuated this PPV action, and thus is a potential antiviral agent against PPV.

Perturbation of bulk and selective macroautophagy, abnormal UPR activation and their interplay pave the way to immune dysfunction, cancerogenesis and neurodegeneration in ageing

A plethora of studies has indicated that ageing is characterized by an altered proteostasis, ROS accumulation and a status of mild/chronic inflammation, in which macroautophagy reduction and abnormal UPR activation play a pivotal role. The dysregulation of these inter-connected processes favors immune dysfunction and predisposes to a variety of several apparently unrelated pathological conditions including cancer and neurodegeneration. Given the progressive ageing of the population, a better understanding of the mechanisms regulating autophagy, UPR and their interplay is needed in order to design new therapeutic strategies able to counteract the effects of ageing and concomitantly restrain the onset/progression of age-related diseases that represent a private and public health problem.

Oxidative stress-induced RAC autophagy can improve the HUVEC functions by releasing exosomes

Retinal neovascularization (RNV) is a common pathological feature in many kinds of fundus oculi diseases. Sometimes RNV can even lead to severe vision loss. Oxidative injury is one of the main predisposing factors for RNV occurrence and development. The specific mechanism may be closely related to the special structural tissues of the retina. Retinal astrocytes (RACs) are mesenchymal cells located in the retinal neuroepithelial layer. RACs have an intimate anatomical relationship with microvascular endothelial cells. They have a variety of functions, but little is known about the mechanisms by which RACs regulate the function of endothelial cells. The molecules secreted by RACs, such as exosomes, have recently received a lot of attention and may provide potential clues to address the RAC‐mediated modulation of endothelial cells. In this study, we aimed to preliminarily explore the mechanisms of how RAC exosomes generated under oxidative stress are involved in the regulation of endothelial function. Our results showed that the apoptosis and autophagy levels in RACs were positively correlated with the oxidative stress level, and the exosomes generated from RACs under normal and oxidative stress conditions had different effects on the proliferation and migration of endothelial cells. However, the effect of RACs on endothelial cell function could be markedly reversed by the autophagy inhibitor 3‐methyladenine or the exosome inhibitor GW4869. Therefore, oxidative stress can lead to increased autophagy in RACs and can further promote RACs to regulate endothelial cell function by releasing exosomes.

1.

tBHP‐induced oxidative stress can increase the level of autophagy in retinal (RAC) astrocytes.

2.

RAC with high‐autophagy level has a completely opposite effect on HUVEC functions when compared with normal RAC.

3.

RACs under different states have different effects on endothelial cell functions by releasing exosomes

An Isolated Complex V Inefficiency and Dysregulated Mitochondrial Function in Immortalized Lymphocytes from ME/CFS Patients

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is an enigmatic condition characterized by exacerbation of symptoms after exertion (post-exertional malaise or “PEM”), and by fatigue whose severity and associated requirement for rest are excessive and disproportionate to the fatigue-inducing activity. There is no definitive molecular marker or known underlying pathological mechanism for the condition. Increasing evidence for aberrant energy metabolism suggests a role for mitochondrial dysfunction in ME/CFS. Our objective was therefore to measure mitochondrial function and cellular stress sensing in actively metabolizing patient blood cells. We immortalized lymphoblasts isolated from 51 ME/CFS patients diagnosed according to the Canadian Consensus Criteria and an age- and gender-matched control group. Parameters of mitochondrial function and energy stress sensing were assessed by Seahorse extracellular flux analysis, proteomics, and an array of additional biochemical assays. As a proportion of the basal oxygen consumption rate (OCR), the rate of ATP synthesis by Complex V was significantly reduced in ME/CFS lymphoblasts, while significant elevations were observed in Complex I OCR, maximum OCR, spare respiratory capacity, nonmitochondrial OCR and “proton leak” as a proportion of the basal OCR. This was accompanied by a reduction of mitochondrial membrane potential, chronically hyperactivated TOR Complex I stress signaling and upregulated expression of mitochondrial respiratory complexes, fatty acid transporters, and enzymes of the β-oxidation and TCA cycles. By contrast, mitochondrial mass and genome copy number, as well as glycolytic rates and steady state ATP levels were unchanged. Our results suggest a model in which ME/CFS lymphoblasts have a Complex V defect accompanied by compensatory upregulation of their respiratory capacity that includes the mitochondrial respiratory complexes, membrane transporters and enzymes involved in fatty acid β-oxidation. This homeostatically returns ATP synthesis and steady state levels to “normal” in the resting cells, but may leave them unable to adequately respond to acute increases in energy demand as the relevant homeostatic pathways are already activated.

Epstein-Barr Virus and Innate Immunity: Friends or Foes?

Epstein–Barr virus (EBV) successfully persists in the vast majority of adults but causes lymphoid and epithelial malignancies in a small fraction of latently infected individuals. Innate immunity is the first-line antiviral defense, which EBV has to evade in favor of its own replication and infection. EBV uses multiple strategies to perturb innate immune signaling pathways activated by Toll-like, RIG-I-like, NOD-like, and AIM2-like receptors as well as cyclic GMP-AMP synthase. EBV also counteracts interferon production and signaling, including TBK1-IRF3 and JAK-STAT pathways. However, activation of innate immunity also triggers pro-inflammatory response and proteolytic cleavage of caspases, both of which exhibit proviral activity under some circumstances. Pathogenic inflammation also contributes to EBV oncogenesis. EBV activates NFκB signaling and induces pro-inflammatory cytokines. Through differential modulation of the proviral and antiviral roles of caspases and other host factors at different stages of infection, EBV usurps cellular programs for death and inflammation to its own benefits. The outcome of EBV infection is governed by a delicate interplay between innate immunity and EBV. A better understanding of this interplay will instruct prevention and intervention of EBV-associated cancers.

Kaposi Sarcoma Herpes Virus (KSHV) infection inhibits macrophage formation and survival by counteracting Macrophage Colony-Stimulating Factor (M-CSF)-induced increase of Reactive Oxygen Species (ROS), c-Jun N-terminal kinase (JNK) phosphorylation and autophagy

Kaposi Sarcoma Herpes Virus (KSHV) is an oncovirus belonging to the human gammaherpesvirus family, able to infect several immune cell types including B cells, dendritic cells (DCs) and monocytes. In this study, we found that KSHV infection of monocytes counteracted the Reactive Oxygen Species (ROS) increase induced by Macrophage Colony-Stimulating Factor (M-CSF), prevented c-Jun N-terminal kinase (JNK) and B-cell lymphoma-2 (Bcl-2) phosphorylation and inhibited autophagy, leading to an impairment of cell survival and differentiation into macrophages. We also show that, to further dysregulate immune response in monocytes, KSHV reduced the production of pro-inflammatory cytokines such as Tumor necrosis factor alpha (TNF α) while increased the release of the immune suppressive cytokine Interleukin-10 (IL-10). These results unveils new strategies put in place by KSHV to induce immune suppression and to persist into the infected host.

Mutant p53, Stabilized by Its Interplay with HSP90, Activates a Positive Feed-Back Loop Between NRF2 and p62 that Induces Chemo-Resistance to Apigenin in Pancreatic Cancer Cells

Pancreatic cancer is one of the most aggressive cancers whose prognosis is worsened by the poor response to the current chemotherapies. In this study, we investigated the cytotoxic effect of Apigenin, against two pancreatic cell lines, namely Panc1 and PaCa44, harboring different p53 mutations. Apigenin is a flavonoid widely distributed in nature that displays anti-inflammatory and anticancer properties against a variety of cancers. Here we observed that Apigenin exerted a stronger cytotoxic effect against Panc1 cell line in comparison to PaCa44. Searching for mechanisms responsible for such different effect, we found that the higher cytotoxicity of Apigenin correlated with induction of higher level of intracellular ROS, reduction of mutant (mut) p53 and HSP90 expression and mTORC1 inhibition. Interestingly, we found that mutp53 was stabilized by its interplay with HSP90 and activates a positive feed-back loop between NRF2 and p62, up-regulating the antioxidant response and reducing the cytotoxicity of Apigenin. These results suggest that targeting the molecules involved in the mTOR-HSP90-mutp53-p62-NRF2-antioxidant response axis could help to overcome the chemo-resistance of pancreatic cancer to Apigenin.

p62-mediated Selective autophagy endows virus-transformed cells with insusceptibility to DNA damage under oxidative stress

DNA damage response (DDR) and selective autophagy both can be activated by reactive oxygen/nitrogen species (ROS/RNS), and both are of paramount importance in cancer development. The selective autophagy receptor and ubiquitin (Ub) sensor p62 plays a key role in their crosstalk. ROS production has been well documented in latent infection of oncogenic viruses including Epstein-Barr Virus (EBV). However, p62-mediated selective autophagy and its interplay with DDR have not been investigated in these settings. In this study, we provide evidence that considerable levels of p62-mediated selective autophagy are spontaneously induced, and correlate with ROS-Keap1-NRF2 pathway activity, in virus-transformed cells. Inhibition of autophagy results in p62 accumulation in the nucleus, and promotes ROS-induced DNA damage and cell death, as well as downregulates the DNA repair proteins CHK1 and RAD51. In contrast, MG132-mediated proteasome inhibition, which induces rigorous autophagy, promotes p62 degradation but accumulation of the DNA repair proteins CHK1 and RAD51. However, pretreatment with an autophagy inhibitor offsets the effects of MG132 on CHK1 and RAD51 levels. These findings imply that p62 accumulation in the nucleus in response to autophagy inhibition promotes proteasome-mediated CHK1 and RAD51 protein instability. This claim is further supported by the findings that transient expression of a p62 mutant, which is constitutively localized in the nucleus, in B cell lines with low endogenous p62 levels recaptures the effects of autophagy inhibition on CHK1 and RAD51 protein stability. These results indicate that proteasomal degradation of RAD51 and CHK1 is dependent on p62 accumulation in the nucleus. However, small hairpin RNA (shRNA)-mediated p62 depletion in EBV-transformed lymphoblastic cell lines (LCLs) had no apparent effects on the protein levels of CHK1 and RAD51, likely due to the constitutive localization of p62 in the cytoplasm and incomplete knockdown is insufficient to manifest its nuclear effects on these proteins. Rather, shRNA-mediated p62 depletion in EBV-transformed LCLs results in significant increases of endogenous RNF168-γH2AX damage foci and chromatin ubiquitination, indicative of activation of RNF168-mediated DNA repair mechanisms. Our results have unveiled a pivotal role for p62-mediated selective autophagy that governs DDR in the setting of oncogenic virus latent infection, and provide a novel insight into virus-mediated oncogenesis.

Could autophagy dysregulation link neurotropic viruses to Alzheimer's disease?

Neurotropic herpesviruses have been associated with the onset and progression of Alzheimer’s disease, a common form of dementia that afflicts a large percentage of elderly individuals. Interestingly, among the neurotropic herpesviruses, herpes simplex virus-1, human herpesvirus-6A, and human herpesvirus-6B have been reported to infect several cell types present in the central nervous system and to dysregulate autophagy, a process required for homeostasis of cells, especially neurons. Indeed autophagosome accumulation, indicating an unbalance between autophagosome formation and autophagosome degradation, has been observed in neurons of Alzheimer’s disease patients and may play a role in the intracellular and extracellular accumulation of amyloid β and in the altered protein tau metabolism. Moreover, herpesvirus infection of central nervous system cells such as glia and microglia can increase the production of oxidant species through the alteration of mitochondrial dynamics and promote inflammation, another hallmark of Alzheimer’s disease. This evidence suggests that it is worth further investigating the role of neurotropic herpesviruses, particularly human herpesvirus-6A/B, in the etiopathogenesis of Alzheimer’s disease.

Cytotoxic Drugs Activate KSHV Lytic Cycle in Latently Infected PEL Cells by Inducing a Moderate ROS Increase Controlled by HSF1, NRF2 and p62/SQSTM1

Previous studies have indicated that cytotoxic treatments may induce or not activate viral lytic cycle activation in cancer cells latently infected by Kaposi’s sarcoma-associated herpesvirus (KSHV). To investigate the molecular mechanisms responsible for such an effect, we compared two cytotoxic treatments able to induce the viral lytic cycle, named 12-O-tetradecanoylphorbol 13-acetate (TPA) (T) in combination with sodium butyrate (B) and bortezomib (BZ), with two cytotoxic treatments that did not activate this process, named metformin (MET) and quercetin (Q). Our results indicated that TB and bortezomib increased levels of oxygen reactive species (ROS) while metformin and quercetin reduced them. The finding that N-acetylcysteine (NAC), a reactive oxigen species (ROS) scavenger, counteracted K-bZIP expression induced by TB or bortezomib, confirmed that an ROS increase played a role in KSHV lytic cycle activation. Moreover, we found that TB and bortezomib up-regulated p62/Sequestosome1(p62/SQSTM1) protein, while metformin and quercetin down-regulated it. p62/SQSTM1 silencing or the inhibition of NF-E2-related factor 2 (NRF2) or Heat Shock Factor 1 (HSF1), that mediate p62/SQSTM1 transcription, also reduced KSHV lytic antigen expression induced by TB or bortezomib. Interestingly, such combination treatments further increased intracellular ROS and cytotoxicity induced by the single TB or bortezomib treatment, suggesting that NRF2, HSF1 and p62/SQSTM1 keep the ROS level under control, allowing primary effusion lymphoma (PEL) cells to continue to survive and KSHV to replicate.

EBV and KSHV Infection Dysregulates Autophagy to Optimize Viral Replication, Prevent Immune Recognition and Promote Tumorigenesis

Autophagy is a catabolic process strongly involved in the immune response, and its dysregulation contributes to the onset of several diseases including cancer. The human oncogenic gammaherpesviruses, Epstein—Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV), manipulate autophagy, either during the de novo infection or during the lytic reactivation, in naturally latently-infected lymphoma cells. In particular, the gammaherpesvirus infection reduces autophagy in immune cells, such as monocytes, resulting in the impairment of cell survival and cell differentiation into dendritic cells (DCs), which are essential for initiating and regulating the immune response. In the case of EBV, the reduction of autophagy in these cells, leading to p62 accumulation, activated the p62-NRF2-antioxidant response, reducing ROS, and further inhibiting autophagy. KSHV inhibits autophagy in monocytes by de-phosphorylating JNK2, altering the calpains–calpastatin balance and increasing the calpain activity responsible for the cleavage of ATG5. To further impair the immune response, KSHV also inhibits autophagy in differentiated DCs by hyper-phosphorylating STAT3. Conversely, when the lytic cycle is induced in vitro in latently-infected lymphoma B cells, both EBV and KSHV promote autophagy to enhance their replication, although the final autophagic steps are blocked through the down-regulation of Rab7. This strategy allows viruses to avoid the destructive environment of lysosomes, and to exploit the autophagic machinery for intracellular transportation. EBV and KSHV encode for proteins that may either inhibit or promote autophagy and, in addition, they can modulate the cellular pathways that control this process. In this review we will discuss the findings that indicate that autophagy is dysregulated by gammaherpesvirus to promote immune suppression, facilitate viral replication and contribute to the onset and maintenance of gammaherpesvirus-associated malignancies.