The unfolded protein response in virus infections

Porcine epidemic diarrhea virus E protein induces unfolded protein response through activating both PERK and ATF6 rather than IRE1 signaling pathway

Porcine epidemic diarrhea virus (PEDV) small envelope protein (E) plays important roles in virus budding, assembly, and release. Our previous study found that PEDV E protein localizes in the endoplasmic reticulum (ER) to trigger the unfolded protein response (UPR). However, how UPR is directly regulated by PEDV E protein remains elusive. Thus, in this study, we investigated the expression of ER chaperone glucose-regulated protein 78 (GRP78) and activations of the three main UPR signaling pathways to elucidate the underlying mechanisms of UPR triggered by PEDV E protein. The results showed that over-expression of PEDV E protein increased expression of GRP78 and induced stronger phosphorylation of both protein kinase RNA-like ER kinase (PERK) and eukaryotic initiation factor-2α (eIF2α), as well as caused the significant degradation of activating transcription factor 6 (ATF6), in both dose- and time-dependent manners. However, PEDV E protein did not induce UPR through the inositol-requiring enzyme 1 (IRE1) signaling pathway, as revealed by the splicing of XBP1 remaining unaffected and unchanged when PEDV E protein was overexpressed. Taken together, these results demonstrate that PEDV E protein induces UPR through activation of both PERK and ATF6 pathways rather than IRE1 signaling. This study not only provides mechanistic details of UPR induced by the PEDV E protein, but also provides insights into these new biologic functions to help us better understand the interactions between PEDV and host cells.

Enhanced antitumor activity induced by a DNA vaccine encoding E7 antigen fused to an ERAD-targeting sequence

The endoplasmic reticulum (ER) is a key organelle in cell homeostasis and cell health through antigen presentation to immune cells. Thus, the ER has become a therapeutic target to induce cellular immune responses. We previously reported the antitumor effect of a DNA vaccine that expresses the E7 antigen fused to the cyclooxygenase-2 (COX-2) protein. This inflammation-related enzyme contains a degradation cassette associated with the endoplasmic reticulum-associated degradation (ERAD) pathway. To avoid the use of full-length COX-2 and any risk of adverse effects due to the activity of its catalytic site, we designed new versions of the fusion protein. These new constructs encode the E7 antigen fused to the signal peptide and the ERAD sequence of COX-2 with or without the membrane-binding domain (MBD) as well as deletion of the catalytic site. We evaluated the antigen-specific antitumor effect of these DNA constructs in murine prophylactic and therapeutic cancer models. These assays showed that the ERAD cassette is the minimum sequence in the COX-2 protein that induces an antitumor effect when fused to the E7 antigen with the advantage of eliminating any potential adverse effects from the use of full-length COX-2.

Live and let die: signaling AKTivation and UPRegulation dynamics in SARS-CoVs infection and cancer

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the pathogen responsible for the coronavirus disease 2019 (COVID-19) pandemic. Of particular interest for this topic are the signaling cascades that regulate cell survival and death, two opposite cell programs whose control is hijacked by viral infections. The AKT and the Unfolded Protein Response (UPR) pathways, which maintain cell homeostasis by regulating these two programs, have been shown to be deregulated during SARS-CoVs infection as well as in the development of cancer, one of the most important comorbidities in relation to COVID-19. Recent evidence revealed two way crosstalk mechanisms between the AKT and the UPR pathways, suggesting that they might constitute a unified homeostatic control system. Here, we review the role of the AKT and UPR pathways and their interaction in relation to SARS-CoV-2 infection as well as in tumor onset and progression. Feedback regulation between AKT and UPR pathways emerges as a master control mechanism of cell decision making in terms of survival or death and therefore represents a key potential target for developing treatments for both viral infection and cancer. In particular, drug repositioning, the investigation of existing drugs for new therapeutic purposes, could significantly reduce time and costs compared to de novo drug discovery.

Pharmacological Inhibition of IRE-1 Alpha Activity in Herpes Simplex Virus Type 1 and Type 2-Infected Dendritic Cells Enhances T Cell Activation

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infections are life-long and highly prevalent in the human population. These viruses persist in the host, eliciting either symptomatic or asymptomatic infections that may occur sporadically or in a recurrent manner through viral reactivations. Clinical manifestations due to symptomatic infection may be mild such as orofacial lesions, but may also translate into more severe diseases, such as ocular infections that may lead to blindness and life-threatening encephalitis. A key feature of herpes simplex viruses (HSVs) is that they have evolved molecular determinants that hamper numerous components of the host’s antiviral innate and adaptive immune system. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), by inhibiting their T cell-activating capacity and eliciting their apoptosis after infection. Previously, we reported that HSV-2 activates the splicing of the mRNA of XBP1, which is related to the activity of the unfolded protein response (UPR) factor Inositol-Requiring Enzyme 1 alpha (IRE-1α). Here, we sought to evaluate if the activation of the IRE-1α pathway in DCs upon HSV infection may be related to impaired DC function after infection with HSV-1 or HSV-2. Interestingly, the pharmacological inhibition of the endonuclease activity of IRE-1α in HSV-1- and HSV-2-infected DCs significantly reduced apoptosis in these cells and enhanced their capacity to migrate to lymph nodes and activate virus-specific CD4⁺ and CD8⁺ T cells. These findings suggest that the activation of the IRE-1α-dependent UPR pathway in HSV-infected DCs may play a significant role in the negative effects that these viruses exert over these cells and that the modulation of this signaling pathway may be relevant for enhancing the function of DCs upon infection with HSVs.

Molecular Pathogenesis and Immune Evasion of Vesicular Stomatitis New Jersey Virus Inferred from Genes Expression Changes in Infected Porcine Macrophages

The molecular mechanisms associated with the pathogenesis of vesicular stomatitis virus (VSV) in livestock remain poorly understood. Several studies have highlighted the relevant role of macrophages in controlling the systemic dissemination of VSV during infection in different animal models, including mice, cattle, and pigs. To gain more insight into the molecular mechanisms used by VSV to impair the immune response in macrophages, we used microarrays to determine the transcriptomic changes produced by VSV infection in primary cultures of porcine macrophages. The results indicated that VSV infection induced the massive expression of multiple anorexic, pyrogenic, proinflammatory, and immunosuppressive genes. Overall, the interferon (IFN) response appeared to be suppressed, leading to the absence of stimulation of interferon-stimulated genes (ISG). Interestingly, VSV infection promoted the expression of several genes known to downregulate the expression of IFNβ. This represents an alternate mechanism for VSV control of the IFN response, beyond the recognized mechanisms mediated by the matrix protein. Although there was no significant differential gene expression in macrophages infected with a highly virulent epidemic strain compared to a less virulent endemic strain, the endemic strain consistently induced higher expression of all upregulated cytokines and chemokines. Collectively, this study provides novel insights into VSV molecular pathogenesis and immune evasion that warrant further investigation.

Endothelial Immunity Trained by Coronavirus Infections, DAMP Stimulations and Regulated by Anti-Oxidant NRF2 May Contribute to Inflammations, Myelopoiesis, COVID-19 Cytokine Storms and Thromboembolism

To characterize transcriptomic changes in endothelial cells (ECs) infected by coronaviruses, and stimulated by DAMPs, the expressions of 1311 innate immune regulatomic genes (IGs) were examined in 28 EC microarray datasets with 7 monocyte datasets as controls. We made the following findings: The majority of IGs are upregulated in the first 12 hours post-infection (PI), and maintained until 48 hours PI in human microvascular EC infected by middle east respiratory syndrome-coronavirus (MERS-CoV) (an EC model for COVID-19). The expressions of IGs are modulated in 21 human EC transcriptomic datasets by various PAMPs/DAMPs, including LPS, LPC, shear stress, hyperlipidemia and oxLDL. Upregulation of many IGs such as nucleic acid sensors are shared between ECs infected by MERS-CoV and those stimulated by PAMPs and DAMPs. Human heart EC and mouse aortic EC express all four types of coronavirus receptors such as ANPEP, CEACAM1, ACE2, DPP4 and virus entry facilitator TMPRSS2 (heart EC); most of coronavirus replication-transcription protein complexes are expressed in HMEC, which contribute to viremia, thromboembolism, and cardiovascular comorbidities of COVID-19. ECs have novel trained immunity (TI), in which subsequent inflammation is enhanced. Upregulated proinflammatory cytokines such as TNFα, IL6, CSF1 and CSF3 and TI marker IL-32 as well as TI metabolic enzymes and epigenetic enzymes indicate TI function in HMEC infected by MERS-CoV, which may drive cytokine storms. Upregulated CSF1 and CSF3 demonstrate a novel function of ECs in promoting myelopoiesis. Mechanistically, the ER stress and ROS, together with decreased mitochondrial OXPHOS complexes, facilitate a proinflammatory response and TI. Additionally, an increase of the regulators of mitotic catastrophe cell death, apoptosis, ferroptosis, inflammasomes-driven pyroptosis in ECs infected with MERS-CoV and the upregulation of pro-thrombogenic factors increase thromboembolism potential. Finally, NRF2-suppressed ROS regulate innate immune responses, TI, thrombosis, EC inflammation and death. These transcriptomic results provide novel insights on the roles of ECs in coronavirus infections such as COVID-19, cardiovascular diseases (CVD), inflammation, transplantation, autoimmune disease and cancers.

Zika Virus Induces an Atypical Tripartite Unfolded Protein Response with Sustained Sensor and Transient Effector Activation and a Blunted BiP Response

To study how the Zika virus (ZIKV) interacts with the host unfolded protein response (UPR), we undertook a kinetics study. We show that ZIKV infection triggers an atypical tripartite UPR in A549 cells involving transient activation of the effectors X-box-binding protein 1, activating transcription factor 4 (ATF4), CCAAT enhancer-binding protein-homologous protein, and growth arrest and DNA damage-inducible protein 34 during early infection and sustained activation of all three UPR sensors: RNA-activated protein kinase-like endoplasmic reticulum-resident kinase (PERK), inositol-requiring kinase-1α (IRE1α), and ATF6. Sustained phosphorylation of the eukaryotic translation initiation factor 2α and rRNA degradation coincide with host translational shutoff, cell lysis, and virus release during late infection. We show a blunted response of the master negative regulator, the immunoglobulin heavy-chain-binding protein (BiP), by chemical UPR inducers, and we show that ZIKV suppresses BiP transcription and translation, suggesting that it may be necessary to blunt the BiP response to sustain UPR sensor activation. The PERK inhibitor GSK2606414 alone has no effects but synergizes with the ATF6 inhibitor Ceapin-A7 to inhibit early and late infection, whereas Ceapin-A7 alone inhibits late infection. Likewise, 4-phenylbutyric acid inhibits ZIKV replication by attenuating the PERK and ATF6 pathways and potentiating the IRE1α pathway, suggesting that ZIKV infection is differentially and temporally regulated by different UPR arms. ZIKV infection is inhibited by pretreatment of chemical UPR inducers but is refractory to the inhibitory activity of chemical inducers once infection has been established, suggesting that ZIKV has anti-UPR mechanisms that may be able to modulate and co-opt the UPR in its life cycle.

IMPORTANCE The Zika virus originates from Africa and Asia but is emerging in other parts of the world. It usually causes an asymptomatic or mild, acute infection but can cause serious neurological complications, such as microcephaly and Guillain-Barré syndromes. Therefore, there is a pressing need for an antiviral. Viruses are obligative parasites and are dependent on the hosts for their propagation. As a result, we can target viruses by targeting host dependency. The host unfolded protein response is a cellular homeostatic response to stresses but can also be triggered by virus infections. We show here that Zika virus infection can cause stress and trigger the unfolded protein response. The Zika virus is able to manipulate, subvert, and co-opt the host unfolded protein response to aid its own replication. Understanding host dependency is important in the quest of a new class of antivirals called host-targeting agents.

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.

The Unfolded Protein Response and Autophagy on the Crossroads of Coronaviruses Infections

The ability to sense and adequately respond to variable environmental conditions is central for cellular and organismal homeostasis. Eukaryotic cells are equipped with highly conserved stress-response mechanisms that support cellular function when homeostasis is compromised, promoting survival. Two such mechanisms - the unfolded protein response (UPR) and autophagy - are involved in the cellular response to perturbations in the endoplasmic reticulum, in calcium homeostasis, in cellular energy or redox status. Each of them operates through conserved signaling pathways to promote cellular adaptations that include re-programming transcription of genes and translation of new proteins and degradation of cellular components. In addition to their specific functions, it is becoming increasingly clear that these pathways intersect in many ways in different contexts of cellular stress. Viral infections are a major cause of cellular stress as many cellular functions are coopted to support viral replication. Both UPR and autophagy are induced upon infection with many different viruses with varying outcomes - in some instances controlling infection while in others supporting viral replication and infection. The role of UPR and autophagy in response to coronavirus infection has been a matter of debate in the last decade. It has been suggested that CoV exploit components of autophagy machinery and UPR to generate double-membrane vesicles where it establishes its replicative niche and to control the balance between cell death and survival during infection. Even though the molecular mechanisms are not fully elucidated, it is clear that UPR and autophagy are intimately associated during CoV infections. The current SARS-CoV-2 pandemic has brought renewed interest to this topic as several drugs known to modulate autophagy - including chloroquine, niclosamide, valinomycin, and spermine - were proposed as therapeutic options. Their efficacy is still debatable, highlighting the need to better understand the molecular interactions between CoV, UPR and autophagy.

Obesity as a Risk Factor for Severe COVID-19 and Complications: A Review

Emerging data suggest that obesity is a major risk factor for the progression of major complications such as acute respiratory distress syndrome (ARDS), cytokine storm and coagulopathy in COVID-19. Understanding the mechanisms underlying the link between obesity and disease severity as a result of SARS-CoV-2 infection is crucial for the development of new therapeutic interventions and preventive measures in this high-risk group. We propose that multiple features of obesity contribute to the prevalence of severe COVID-19 and complications. First, viral entry can be facilitated by the upregulation of viral entry receptors, like angiotensin-converting enzyme 2 (ACE2), among others. Second, obesity-induced chronic inflammation and disruptions of insulin and leptin signaling can result in impaired viral clearance and a disproportionate or hyper-inflammatory response, which together with elevated ferritin levels can be a direct cause for ARDS and cytokine storm. Third, the negative consequences of obesity on blood coagulation can contribute to the progression of thrombus formation and hemorrhage. In this review we first summarize clinical findings on the relationship between obesity and COVID-19 disease severity and then further discuss potential mechanisms that could explain the risk for major complications in patients suffering from obesity.

The Epstein-Barr Virus Lytic Protein BMLF1 Induces Upregulation of GRP78 Expression through ATF6 Activation

The unfolded protein response (UPR) is an intracellular signaling pathway essential for alleviating the endoplasmic reticulum (ER) stress. To support the productive infection, many viruses are known to use different strategies to manipulate the UPR signaling network. However, it remains largely unclear whether the UPR signaling pathways are modulated in the lytic cycle of Epstein-Barr virus (EBV), a widely distributed human pathogen. Herein, we show that the expression of GRP78, a central UPR regulator, is up-regulated during the EBV lytic cycle. Our data further revealed that knockdown of GRP78 in EBV-infected cell lines did not substantially affect lytic gene expression; however, GRP78 knockdown in these cells markedly reduced the production of virus particles. Importantly, we identified that the early lytic protein BMLF1 is the key regulator critically contributing to the activation of the grp78 gene promoter. Mechanistically, we found that BMLF1 can trigger the proteolytic cleavage and activation of the UPR senor ATF6, which then transcriptionally activates the grp78 promoter through the ER stress response elements. Our findings therefore provide evidence for the connection between the EBV lytic cycle and the UPR, and implicate that the BMLF1-mediated ATF6 activation may play critical roles in EBV lytic replication.

Cross-talk between lipid homeostasis and endoplasmic reticulum stress in neurodegeneration: Insights for HIV-1 associated neurocognitive disorders (HAND)

The dysregulation of lipid homeostasis is emerging as a hallmark of many CNS diseases. As aberrant protein regulation is suggested to be a shared pathological feature amongst many neurodegenerative conditions, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), disruptions in neuronal lipid processing may contribute to disease progression in the CNS. Specifically, given the endoplasmic reticulum (ER) dual role in lipid homeostasis as well as protein quality control (PQC) via unfolded protein response (UPR), lipid dysregulation in the CNS may converge on ER functioning and constitute a crucial mechanism underlying aberrant protein aggregation. In the current review, we discuss the diverse roles of lipid species as essential components of the CNS. Moreover, given the importance of both lipid dysregulation and protein aggregation in pathology of CNS diseases, we attempt to assess the potential downstream cross-talk between lipid dysregulation and ER dependent PQC mechanisms, with special focus on HIV-associated neurodegenerative disorders (HAND).

The Secretive Liaison of Particulate Matter and SARS-CoV-2. A Hypothesis and Theory Investigation

As the novel coronavirus disease sweeps across the world, there is growing speculation on the role that atmospheric factors may have played on the different distribution of SARS-CoV-2, and on the epidemiological characteristics of COVID-19. Knowing the role that environmental factors play in influenza virus outbreaks, environmental pollution and, in particular, atmospheric airborne (particulate matter, PM) has been considered as a potential key factor in the spread and mortality of COVID-19. A possible role of the PM as the virus carrier has also been debated. The role of PM in exacerbating respiratory and cardiovascular disease has been well recognized. Accumulating evidence support the hypothesis that PM can trigger inflammatory response at molecular, cellular and organ levels. On this basis, we developed the hypothesis that PM may play a role as a booster of COVID-19 rather than as a carrier of SARS-CoV-2. To support our hypothesis, we analyzed the molecular signatures detected in cells exposed to PM samples collected in one of the most affected areas by the COVID-19 outbreak, in Italy. T47D human breast adenocarcinoma cells were chosen to explore the global gene expression changes induced by the treatment with organic extracts of PM 2.5. The analysis of the KEGG's pathways showed modulation of several gene networks related to the leucocyte transendothelial migration, cytoskeleton and adhesion system. Three major biological process were identified, including coagulation, growth control and immune response. The analysis of the modulated genes gave evidence for the involvement of PM in the endothelial disease, coagulation disorders, diabetes and reproductive toxicity, supporting the hypothesis that PM, directly or through molecular interplay, affects the same molecular targets as so far known for SARS-COV-2, contributing to the cytokines storm and to the aggravation of the symptoms triggered by COVID-19. We provide evidence for a plausible cooperation of receptors and transmembrane proteins, targeted by PM and involved in COVID-19, together with new insights into the molecular interplay of chemicals and pathogens that could be of importance for sustaining public health policies and developing new therapeutic approaches.

Pan-Sigma Receptor Modulator RC-106 Induces Terminal Unfolded Protein Response In In Vitro Pancreatic Cancer Model

Pancreatic cancer (PC) remains one of the most lethal cancers worldwide. Sigma receptors (SRs) have been proposed as cancer therapeutic targets. Their main localization suggests they play a potential role in ER stress and in the triggering of the unfolded protein response (UPR). Here, we investigated the mechanisms of action of RC-106, a novel pan-SR modulator, to characterize therapeutically exploitable role of SRs in tumors. Two PC cell lines were used in all the experiments. Terminal UPR activation was evaluated by quantifying BiP, ATF4 and CHOP by Real-Time qRT-PCR, Western Blot, immunofluorescence and confocal microscopy. Cell death was studied by flow cytometry. Post-transcriptional gene silencing was performed to study the interactions between SRs and UPR key proteins. RC-106 activated ER stress sensors in a dose- and time-dependent manner. It also induced ROS production accordingly with ATF4 upregulation at the same time reducing cell viability of both cell lines tested. Moreover, RC-106 exerted its effect through the induction of the terminal UPR, as shown by the activation of some of the main transducers of this pathway. Post-transcriptional silencing studies confirmed the connection between SRs and these key proteins. Overall, our data highlighted a key role of SRs in the activation of the terminal UPR pathway, thus indicating pan-SR ligands as candidates for targeting the UPR in pancreatic cancer.

Induction of the Unfolded Protein Response during Bovine Alphaherpesvirus 1 Infection

Bovine herpesvirus 1 (BoHV-1) is an alphaherpesvirus that causes great economic losses in the cattle industry. Herpesvirus infection generally induces endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) in infected cells. However, it is not clear whether ER stress and UPR can be induced by BoHV-1 infection. Here, we found that ER stress induced by BoHV-1 infection could activate all three UPR sensors (the activating transcription factor 6 (ATF6), the inositol-requiring enzyme 1 (IRE1), and the protein kinase RNA-like ER kinase (PERK)) in MDBK cells. During BoHV-1 infection, the ATF6 pathway of UPR did not affect viral replication. However, both knockdown and specific chemical inhibition of PERK attenuated the BoHV-1 proliferation, and chemical inhibition of PERK significantly reduced the viral replication at the post-entry step of the BoHV-1 life cycle. Furthermore, knockdown of IRE1 inhibits BoHV-1 replication, indicating that the IRE1 pathway may promote viral replication. Further study revealed that BoHV-1 replication was enhanced by IRE1 RNase activity inhibition at the stage of virus post-entry in MDBK cells. Furthermore, IRE1 kinase activity inhibition and RNase activity enhancement decrease BoHV1 replication via affecting the virus post-entry step. Our study revealed that BoHV-1 infection activated all three UPR signaling pathways in MDBK cells, and BoHV-1-induced PERK and IRE1 pathways may promote viral replication. This study provides a new perspective for the interactions of BoHV-1 and UPR, which is helpful to further elucidate the mechanism of BoHV-1 pathogenesis.

Andrographolide Mitigates Unfolded Protein Response Pathway and Apoptosis Involved in Chikungunya Virus Infection

BACKGROUND

Chikungunya virus (CHIKV) is an arthropod-borne RNA virus which induces host Endoplasmic Reticulum (ER) stress by accumulating unfolded or misfolded proteins. ER stress activates the unfolded protein response (UPR) pathway to enable proper protein folding and maintain cellular homeostasis. There is no approved drug or vaccine available for CHIKV treatment, therefore, a pharmacological countermeasure is warranted for preventing CHIKV infection.

OBJECTIVE

With a view to find a treatment modality for chikungunya infection, "andrographolide", a plant-derived diterpenoid with reported antiviral, anti-inflammatory and immunomodulatory effects, was used to investigate its role in chikungunya induced unfolded protein stress and apoptosis.

METHODS

Cells and supernatant collected on andrographolide and VER-155008, a GRP78 inhibitor, treatment in CHIKV infected and mock-infected THP-1 cells were tested for differential expression of UPR pathway proteins including GRP78, PERK, EIF-2α, IRE-1α, XBP-1 and ATF6. Furthermore, the inflammasome and apoptosis pathway proteins, i.e., caspase-1, caspase-3 and PARP, were tested by immunoblotting, and cytokines, i.e., IL-1β, IL-6 and IFN-γ were tested by ELISA.

RESULTS

Andrographolide treatment in CHIKV infected THP-1 cells significantly reduced IRE1α and downstream spliced XBP1 protein expression. Furthermore, CHIKV induced apoptosis and viral protein expression were also reduced on andrographolide treatment. A comparative analysis of andrographolide versus VER-155008, confirmed that andrographolide surpasses the effects of VER-155008 in suppressing the CHIKV induced ER stress.

CONCLUSION

The study, therefore, confirms that andrographolide is a potential remedy for chikungunya infection and suppresses CHIKV induced ER stress and apoptosis.

Mycoplasma hyopneumoniae Inhibits Porcine Beta-Defensin 2 Production by Blocking the Unfolded Protein Response To Facilitate Epithelial Adhesion and Infection

Mycoplasma hyopneumoniae causes the disease porcine enzootic pneumonia, a highly contagious and chronic disease affecting pigs. Understanding the molecular mechanisms of its pathogenicity is critical for developing effective interventions to control this swine respiratory disease. Here, we describe a novel virulence mechanism by which M. hyopneumoniae interferes with the host unfolded protein response (UPR) and eventually facilitates bacterial adhesion and infection. We observed that M. hyopneumoniae infection suppressed the UPR target molecules GRP78 and CHOP by reducing PKR-like endoplasmic reticulum kinase/eukaryotic initiation factor 2 alpha (PERK/eIF2α) phosphorylation, ATF6 cleavage, and X-box binding protein 1 (XBP1) splicing. Interestingly, further analyses revealed that host UPR inhibition subsequently suppressed the NF-κB pathway, leading to the reduced production of porcine beta-defensin 2 (PBD-2), thus facilitating M. hyopneumoniae adherence and infection. This study provides new insights into the molecular pathogenesis of M. hyopneumoniae and sheds light upon its interactions with the host.

In Silico Discovery of Candidate Drugs against Covid-19

Previous studies reported that Angiotensin converting enzyme 2 (ACE2) is the main cell receptor of SARS-CoV and SARS-CoV-2. It plays a key role in the access of the virus into the cell to produce the final infection. In the present study we investigated in silico the basic mechanism of ACE2 in the lung and provided evidences for new potentially effective drugs for Covid-19. Specifically, we used the gene expression profiles from public datasets including The Cancer Genome Atlas, Gene Expression Omnibus and Genotype-Tissue Expression, Gene Ontology and pathway enrichment analysis to investigate the main functions of ACE2-correlated genes. We constructed a protein-protein interaction network containing the genes co-expressed with ACE2. Finally, we focused on the genes in the network that are already associated with known drugs and evaluated their role for a potential treatment of Covid-19. Our results demonstrate that the genes correlated with ACE2 are mainly enriched in the sterol biosynthetic process, Aryldialkylphosphatase activity, adenosylhomocysteinase activity, trialkylsulfonium hydrolase activity, acetate-CoA and CoA ligase activity. We identified a network of 193 genes, 222 interactions and 36 potential drugs that could have a crucial role. Among possible interesting drugs for Covid-19 treatment, we found Nimesulide, Fluticasone Propionate, Thiabendazole, Photofrin, Didanosine and Flutamide.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Calcium Influx Caused by ER Stress Inducers Enhances Oncolytic Adenovirus Enadenotucirev Replication and Killing through PKCα Activation

Oncolytic viruses represent an emerging approach to cancer therapy. However, better understanding of their interaction with the host cancer cell and approaches to enhance their efficacy are needed. Here, we investigate the effect of chemically induced endoplasmic reticulum (ER) stress on the activity of the chimeric group B adenovirus Enadenotucirev, its closely related parental virus Ad11p, and the archetypal group C oncolytic adenovirus Ad5. We show that treatment of colorectal and ovarian cancer cell lines with thapsigargin or ionomycin caused an influx of Ca2+, leading to an upregulation in E1A transcript and protein levels. Increased E1A protein levels, in turn, increased levels of expression of the E2B viral DNA polymerase, genome replication, late viral protein expression, infectious virus particle production, and cell killing during Enadenotucirev and Ad11p, but not Ad5, infection. This effect was not due to the induction of ER stress, but rather the influx of extracellular Ca2+ and consequent increase in protein kinase C activity. These results underscore the importance of Ca2+ homeostasis during adenoviral infection, indicate a signaling pathway between protein kinase C and E1A, and raise the possibility of using Ca2+ flux-modulating agents in the manufacture and potentiation of oncolytic virotherapies.

Enhanced Autophagy Contributes to Reduced Viral Infection in Black Flying Fox Cells

Bats are increasingly implicated as hosts of highly pathogenic viruses. The underlying virus⁻host interactions and cellular mechanisms that promote co-existence remain ill-defined, but physiological traits such as flight and longevity are proposed to drive these adaptations. Autophagy is a cellular homeostatic process that regulates ageing, metabolism, and intrinsic immune defense. We quantified basal and stimulated autophagic responses in black flying fox cells, and demonstrated that although black flying fox cells are susceptible to Australian bat lyssavirus (ABLV) infection, viral replication is dampened in these bat cells. Black flying fox cells tolerated prolonged ABLV infection with less cell death relative to comparable human cells, suggesting post-entry mechanisms interference with virus replication. An elevated basal autophagic level was observed and autophagy was induced in response to high virus doses. Pharmacological stimulation of the autophagy pathway reduced virus replication, indicating autophagy acts as an anti-viral mechanism. Enhancement of basal and virus-induced autophagy in bat cells connects related reports that long-lived species possess homeostatic processes that dampen oxidative stress and macromolecule damage. Exemplifying the potential that evolved cellular homeostatic adaptations like autophagy may secondarily act as anti-viral mechanisms, enabling bats to serve as natural hosts to an assortment of pathogenic viruses. Furthermore, our data suggest autophagy-inducing drugs may provide a novel therapeutic strategy for combating lyssavirus infection.

Trazodone use and risk of dementia: A population-based cohort study

BACKGROUND

In vitro and animal studies have suggested that trazodone, a licensed antidepressant, may protect against dementia. However, no studies have been conducted to assess the effect of trazodone on dementia in humans. This electronic health records study assessed the association between trazodone use and the risk of developing dementia in clinical practice.

METHODS AND FINDINGS

The Health Improvement Network (THIN), an archive of anonymised medical and prescribing records from primary care practices in the United Kingdom, contains records of over 15 million patients. We assessed patients from THIN aged ≥50 years who received at least two consecutive prescriptions for an antidepressant between January 2000 and January 2017. We compared the risk of dementia among patients who were prescribed trazodone to that of patients with similar baseline characteristics prescribed other antidepressants, using a Cox regression model with 1:5 propensity score matching. Patients prescribed trazodone who met the inclusion criteria (n = 4,716; 59.2% female) were older (mean age 70.9 ± 13.1 versus 65.6 ± 11.4 years) and were more likely than those prescribed other antidepressants (n = 420,280; 59.7% female) to have cerebrovascular disease and use anxiolytic or antipsychotic drugs. After propensity score matching, 4,596 users of trazadone and 22,980 users of other antidepressants were analysed. The median time to dementia diagnosis for people prescribed trazodone was 1.8 years (interquartile range [IQR] = 0.5-5.0 years). Incidence of dementia among patients taking trazodone was higher than in matched users of other antidepressants (1.8 versus 1.1 per 100 person-years), with a hazard ratio (HR) of 1.80 (95% confidence interval [CI] 1.56-2.09; p < 0.001). However, our results do not suggest a causal association. When we restricted the control group to users of mirtazapine only in a sensitivity analysis, the findings were very similar to the results of the main analysis. The main limitation of our study is the possibility of indication bias, because people in the prodromal stage of dementia might be preferentially prescribed trazodone. Due to the observational nature of this study, we cannot rule out residual confounding.

CONCLUSIONS

In this study of UK population-based electronic health records, we found no association between trazodone use and a reduced risk of dementia compared with other antidepressants. These results suggest that the clinical use of trazodone is not associated with a reduced risk of dementia.

Naturally Occurring Hepatitis B Virus Mutations Leading to Endoplasmic Reticulum Stress and Their Contribution to the Progression of Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is a global health problem that causes a wide range of pathological outcomes, including cirrhosis and hepatocellular carcinoma (HCC). Endoplasmic reticulum (ER) stress induction by HBV infection has been implicated in liver carcinogenesis and disease progression with chronic inflammation via enhanced inflammation, oxidative stress-mediated DNA damage, and hepatocyte proliferation. In the natural course of HBV infection, the accumulation of naturally occurring mutations in the HBV genome can generate several mutant types of HBV-encoded proteins, including three different proteins in the S ORF (SHBs, MHBs, and LHBs) and HBcAg in the C ORF, which could contribute to enhanced ER stress in infected hepatocytes mainly via increased ER accumulation of mutant proteins. However, it seems that there may be distinct capacity and pathway in ER stress-induction and distinct resulting clinical outcomes between HBV variants. In addition, the role of HBxAg mutations in ER stress remains unknown. However, it has been reported that HBxAg itself could exert ER stress in infected cells, resulting in HCC generation in chronic HBV patients. To date, review papers regarding ER stress-mediated HBV mutation have been limited into a specific mutation type: preS2 deletion. So, in this review, we will discuss details about various mutation types in all four regions of the HBV genome (preS1, preS2, S, and C) related to ER stress and their distinct ER stress mechanisms and clinical outcomes in terms of mutation types.

Virus and tumor microenvironment induced ER stress and unfolded protein response: from complexity to therapeutics

Endoplasmic reticulum (ER) stress can be activated by various pathological and physiological conditions including the unfolded protein response (UPR) to restore homeostasis. The UPR signaling pathways initiated by double-stranded RNA-activated protein kinase (PKR) like ER kinase (PERK), inositol requiring enzyme 1 α (IRE1α), and activating transcription factor 6 (ATF6) are vital for tumor growth, aggressiveness, microenvironment remodeling, and resistance to cancer therapeutics. This review focuses on the role of ER stress and activity of UPR signaling pathways involved in tumor formation and uncontrolled cell proliferation during various cancers and viral malignancies.

Investigating the consequences of asymmetric endoplasmic reticulum inheritance in Saccharomyces cerevisiae under stress using a combination of single cell measurements and mathematical modelling

Adaptation allows organisms to maintain a constant internal environment, which is optimised for growth. The unfolded protein response (UPR) is an example of a feedback loop that maintains endoplasmic reticulum (ER) homeostasis, and is characteristic of how adaptation is often mediated by transcriptional networks. The more recent discovery of asymmetric division in maintaining ER homeostasis, however, is an example of how alternative non-transcriptional pathways can exist, but are overlooked by gold standard transcriptomic or proteomic population-based assays. In this study, we have used a combination of fluorescent reporters, flow cytometry and mathematical modelling to explore the relative roles of asymmetric cell division and the UPR in maintaining ER homeostasis. Under low ER stress, asymmetric division leaves daughter cells with an ER deficiency, necessitating activation of the UPR and prolonged cell cycle during which they can recover ER functionality before growth. Mathematical analysis of and simulation results from our mathematical model reinforce the experimental observations that low ER stress primarily impacts the growth rate of the daughter cells. These results demonstrate the interplay between homeostatic pathways and the importance of exploring sub-population dynamics to understand population adaptation to quantitatively different stresses.

Innate Sensing of Influenza A Virus Hemagglutinin Glycoproteins by the Host Endoplasmic Reticulum (ER) Stress Pathway Triggers a Potent Antiviral Response via ER-Associated Protein Degradation

Innate immunity provides an immediate defense against infection after host cells sense danger signals from microbes. Endoplasmic reticulum (ER) stress arises from accumulation of misfolded/unfolded proteins when protein load overwhelms the ER folding capacity, which activates the unfolded protein response (UPR) to restore ER homeostasis. Here, we show that a mechanism for antiviral innate immunity is triggered after the ER stress pathway senses viral glycoproteins. When hemagglutinin (HA) glycoproteins from influenza A virus (IAV) are expressed in cells, ER stress is induced, resulting in rapid HA degradation via proteasomes. The ER-associated protein degradation (ERAD) pathway, an important UPR function for destruction of aberrant proteins, mediates HA degradation. Three class I α-mannosidases were identified to play a critical role in the degradation process, including EDEM1, EDEM2, and ERManI. HA degradation requires either ERManI enzymatic activity or EDEM1/EDEM2 enzymatic activity when ERManI is not expressed, indicating that demannosylation is a critical step for HA degradation. Silencing of EDEM1, EDEM2, and ERManI strongly increases HA expression and promotes IAV replication. Thus, the ER stress pathway senses influenza HA as "nonself" or misfolded protein and sorts HA to ERAD for degradation, resulting in inhibition of IAV replication.IMPORTANCE Viral nucleic acids are recognized as important inducers of innate antiviral immune responses that are sensed by multiple classes of sensors, but other inducers and sensors of viral innate immunity need to be identified and characterized. Here, we used IAV to investigate how host innate immunity is activated. We found that IAV HA glycoproteins induce ER stress, resulting in HA degradation via ERAD and consequent inhibition of IAV replication. In addition, we have identified three class I α-mannosidases, EDEM1, EDEM2, and ERManI, which play a critical role in initiating HA degradation. Knockdown of these proteins substantially increases HA expression and IAV replication. The enzymatic activities and joint actions of these mannosidases are required for this antiviral activity. Our results suggest that viral glycoproteins induce a strong innate antiviral response through activating the ER stress pathway during viral infection.

CSFV Infection Up-Regulates the Unfolded Protein Response to Promote Its Replication

Classical swine fever (CSF) is an OIE-listed, highly contagious animal disease caused by classical swine fever virus (CSFV). The endoplasmic reticulum (ER) is an organelle in which the replication of many RNA viruses takes place. During viral infection, a series of events elicited in cells can destroy the ER homeostasis that cause ER stress and induce an unfolded protein response (UPR). In this study, we demonstrate that ER stress was induced during CSFV infection as several UPR-responsive elements such as XBP1(s), GRP78 and CHOP were up-regulated. Specifically, CSFV transiently activated IRE1 pathway at the initial stage of infection but rapidly switched off, likely due to the reduction in cytoplasm Ca²⁺ after viral incubation. Additionally, our data show that the ER stress induced by CSFV can promote CSFV production, which the IRE1 pathway play an important role in it. Evidence of ER stress in vivo was also confirmed by the marked elevation of GRP78 in CSFV-infected pig PBMC and tissues. Collectively, these data indicate that the ER stress was induced upon CSFV infection and that the activation of the IRE1 pathway benefits CSFV replication.

Stress and the nonsense-mediated RNA decay pathway

Cells respond to internal and external cellular stressors by activating stress-response pathways that re-establish homeostasis. If homeostasis is not achieved in a timely manner, stress pathways trigger programmed cell death (apoptosis) to preserve organism integrity. A highly conserved stress pathway is the unfolded protein response (UPR), which senses excessive amounts of unfolded proteins in the ER. While a physiologically beneficial pathway, the UPR requires tight regulation to provide a beneficial outcome and avoid deleterious consequences. Recent work has demonstrated that a conserved and highly selective RNA degradation pathway-nonsense-mediated RNA decay (NMD)-serves as a major regulator of the UPR pathway. NMD degrades mRNAs encoding UPR components to prevent UPR activation in response to innocuous ER stress. In response to strong ER stress, NMD is inhibited by the UPR to allow for a full-magnitude UPR response. Recent studies have indicated that NMD also has other stress-related functions, including promoting the timely termination of the UPR to avoid apoptosis; NMD also regulates responses to non-ER stressors, including hypoxia, amino-acid deprivation, and pathogen infection. NMD regulates stress responses in species across the phylogenetic scale, suggesting that it has conserved roles in shaping stress responses. Stress pathways are frequently constitutively activated or dysregulated in human disease, raising the possibility that "NMD therapy" may provide clinical benefit by downmodulating stress responses.

The SAT Protein of Porcine Parvovirus Accelerates Viral Spreading through Induction of Irreversible Endoplasmic Reticulum Stress

The SAT protein (SATp) of porcine parvovirus (PPV) accumulates in the endoplasmic reticulum (ER), and SAT deletion induces the slow-spreading phenotype. The in vitro comparison of the wild-type Kresse strain and its SAT knockout (SAT^-) mutant revealed that prolonged cell integrity and late viral release are responsible for the slower spreading of the SAT^- virus. During PPV infection, regardless of the presence or absence of SATp, the expression of downstream ER stress response proteins (Xbp1 and CHOP) was induced. However, in the absence of SATp, significant differences in the quantity and the localization of CHOP were detected, suggesting a role of SATp in the induction of irreversible ER stress in infected cells. The involvement of the induction of irreversible ER stress in porcine testis (PT) cell necrosis and viral egress was confirmed by treatment of infected cells by ER stress-inducing chemicals (MG132, dithiothreitol, and thapsigargin), which accelerated the egress and spreading of both the wild-type and the SAT^- viruses. UV stress induction had no beneficial effect on PPV infection, underscoring the specificity of ER stress pathways in the process. However, induction of CHOP and its nuclear translocation cannot alone be responsible for the biological effect of SAT, since nuclear CHOP could not complement the lack of SAT in a coexpression experiment.IMPORTANCE SATp is encoded by an alternative open reading frame of the PPV genome. Earlier we showed that SATp of the attenuated PPV NADL-2 strain accumulates in the ER and accelerates virus release and spreading. Our present work revealed that slow spreading is a general feature of SAT^- PPVs and is the consequence of prolonged cell integrity. PPV infection induced ER stress in infected cells regardless of the presence of SATp, as demonstrated by the morphological changes of the ER and expression of the stress response proteins Xbp1 and CHOP. However, the presence of SATp made the ER stress more severe and accelerated cell death during infection, as shown by the higher rate of expression of CHOP and alteration of the localization of CHOP. The beneficial effect of irreversible ER stress on PPV spread was confirmed by treatment of infected cells with ER stress-inducing chemicals.

New insight into the interaction of TRAF2 C-terminal domain with lipid raft microdomains

In this study we provide the first evidence of the interaction of a truncated-TRAF2 with lipid raft microdomains. We have analyzed this interaction by measuring the diffusion coefficient of the protein in large and giant unilamellar vesicles (LUVs and GUVs, respectively) obtained both from synthetic lipid mixtures and from natural extracts. Steady-state fluorescence measurements performed with synthetic vesicles indicate that this truncated form of TRAF2 displays a tighter binding to raft-like LUVs with respect to the control (POPC-containing LUVs), and that this process depends on the protein oligomeric state. Generalized Polarization measurements and spectral phasor analysis revealed that truncated-TRAF2 affects the membrane fluidity, especially when vesicles are heated up at physiological temperature. The addition of nanomolar concentration of TRAF2 in GUVs also seems to exert a mechanical action, as demonstrated by the formation of intraluminal vesicles, a process in which ganglioside GM1 plays a crucial role.

ER Stress, UPR and Virus Infections in Plants

The endoplasmic reticulum (ER) endomembrane is a central site for protein synthesis. Perturbation of ER homeostasis can result in an accumulation of unfolded proteins within the ER lumen, causing ER stress and the unfolded protein response (UPR). In humans, ER stress and UPR are closely associated with a vast number of diseases, including viral diseases. In plants, two arms that govern the UPR signaling network have been described: one that contains two ER membrane–associated transcription factors (bZIP17 and bZIP28) and the other that encompasses a dual protein kinase (RNA-splicing factor IRE1) and its target RNA (bZIP60). Although early studies mainly focus on the essential roles of the UPR in abiotic stresses, the significance of UPR in plant diseases caused by virus infections has recently drawn much attention. This chapter summarizes the latest scenario of ER stress and UPR in virus-infected plant cells, highlights the emerging roles of the IRE1 pathway in virus infections, and outlines exciting future directions to spark more research interest in the UPR field in plants.

The Malat1 long non-coding RNA is upregulated by signalling through the PERK axis of unfolded protein response during flavivirus infection

Flavivirus infection causes host cell death by initiation of an unfolded protein response (UPR). UPR is initiated following activation of three ER-membrane resident sensors, PERK, IRE1α and ATF6, which are otherwise kept inactive through association with the ER-chaperone GRP78. Activation precedes cellular and molecular changes that act to restore homeostasis but might eventually initiate apoptosis. These changes involve influencing function of multiple genes by either transcriptional or post-transcriptional or post-translational mechanisms. Transcriptional control includes expression of transcription factor cascades, which influence cognate gene expression. Malat1 is a long non-coding RNA which is over-expressed in many human oncogenic tissues and regulates cell cycle and survival. In this report, for the first time we show activation of Malat1 following infection by two flaviviruses, both of which activate the UPR in host cells. The temporal kinetics of expression was restricted to later time points. Further, Malat1 was also activated by pharmacological inducer of UPR, to a similar degree. Using drugs that specifically inhibit or activate the PERK or IRE1α sensors, we demonstrate that signalling through the PERK axis activates this expression, through a transcriptional mechanism. To our knowledge, this is the first report of an UPR pathway regulating the expression of an lncRNA.

Degradation of polyomavirus JC T-antigen by stress involves the LIP isoform of C/EBP

Endoplasmic reticulum (ER) stress is caused by the accumulation of misfolded or unfolded proteins in the lumen of the endoplasmic reticulum. CCAAT/enhancer binding proteins are one of the cellular proteins whose expression is upregulated during ER stress. Previously, we have identified C/EBPbeta isoforms, especially LIP, as a negative regulator of polyomavirus JC (JCV), the causative agent of the demyelinating disease progressive multifocal leukoencephalopathy (PML). Here, we show that the induction of ER stress by thapsigargin increase the expression of endogenous LIP and the degradation of JCV T-antigen in a JCV-transgenic mouse tumor cell line. Our results also revealed that overexpression of LIP significantly reduced the level of T-Ag and this effect is reversed upon siRNA-mediated silencing of LIP. Immunoprecipitation/Western blot experiments indicated that LIP interacts with T-antigen directly. Treatment of cells that overexpress LIP with MG115, a proteasome inhibitor, partially rescued LIP-mediated degradation of T-antigen. Our observations point to a role of LIP in ER stress regulation of T-antigen stability and may open a new avenue to study host-virus interaction during ER stress.