Thiopurines activate an antiviral unfolded protein response that blocks influenza A virus glycoprotein accumulation

Influenza A viruses (IAVs) utilize host shutoff mechanisms to limit antiviral gene expression and redirect translation machinery to the synthesis of viral proteins. Previously, we showed that IAV replication is sensitive to protein synthesis inhibitors that block translation initiation and induce formation of cytoplasmic condensates of untranslated messenger ribonucleoprotein complexes called stress granules (SGs). In this study, using an image-based high-content screen, we identified two thiopurines, 6-thioguanine (6-TG) and 6-thioguanosine (6-TGo), that triggered SG formation in IAV-infected cells and blocked IAV replication in a dose-dependent manner without eliciting SG formation in uninfected cells. 6-TG and 6-TGo selectively disrupted the synthesis and maturation of IAV glycoproteins hemagglutinin (HA) and neuraminidase (NA) without affecting the levels of the viral RNAs that encode them. By contrast, these thiopurines had minimal effect on other IAV proteins or the global host protein synthesis. Disruption of IAV glycoprotein accumulation by 6-TG and 6-TGo correlated with activation of unfolded protein response (UPR) sensors activating transcription factor-6 (ATF6), inositol requiring enzyme-1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), leading to downstream UPR gene expression. Treatment of infected cells with the chemical chaperone 4-phenylbutyric acid diminished thiopurine-induced UPR activation and partially restored the processing and accumulation of HA and NA. By contrast, chemical inhibition of the integrated stress response downstream of PERK restored accumulation of NA monomers but did not restore processing of viral glycoproteins. Genetic deletion of PERK enhanced the antiviral effect of 6-TG without causing overt cytotoxicity, suggesting that while UPR activation correlates with diminished viral glycoprotein accumulation, PERK could limit the antiviral effects of drug-induced ER stress. Taken together, these data indicate that 6-TG and 6-TGo are effective host-targeted antivirals that trigger the UPR and selectively disrupt accumulation of viral glycoproteins. IMPORTANCE Secreted and transmembrane proteins are synthesized in the endoplasmic reticulum (ER), where they are folded and modified prior to transport. Many viruses rely on the ER for the synthesis and processing of viral glycoproteins that will ultimately be incorporated into viral envelopes. Viral burden on the ER can trigger the unfolded protein response (UPR). Much remains to be learned about how viruses co-opt the UPR to ensure efficient synthesis of viral glycoproteins. Here, we show that two FDA-approved thiopurine drugs, 6-TG and 6-TGo, induce the UPR, which represents a previously unrecognized effect of these drugs on cell physiology. This thiopurine-mediated UPR activation blocks influenza virus replication by impeding viral glycoprotein accumulation. Our findings suggest that 6-TG and 6-TGo may have broad antiviral effect against enveloped viruses that require precise tuning of the UPR to support viral glycoprotein synthesis.

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Thiopurines activate an antiviral unfolded protein response that blocks viral glycoprotein accumulation in cell culture infection model

10.1101/2020.09.30.319863 ◽

2020 ◽

Author(s):

Patrick Slaine ◽

Mariel Kleer ◽

Brett Duguay ◽

Eric S. Pringle ◽

Eileigh Kadijk ◽

...

Keyword(s):

Gene Expression ◽

Cell Culture ◽

Unfolded Protein Response ◽

Influenza Viruses ◽

Viral Glycoprotein ◽

Chemical Chaperone ◽

Aaa Atpase ◽

Unfolded Protein ◽

Viral Glycoproteins ◽

Protein Response

ABSTRACTEnveloped viruses, including influenza A viruses (IAVs) and coronaviruses (CoVs), utilize the host cell secretory pathway to synthesize viral glycoproteins and direct them to sites of assembly. Using an image-based high-content screen, we identified two thiopurines, 6-thioguanine (6-TG) and 6-thioguanosine (6-TGo), that selectively disrupted the processing and accumulation of IAV glycoproteins hemagglutinin (HA) and neuraminidase (NA). Selective disruption of IAV glycoprotein processing and accumulation by 6-TG and 6-TGo correlated with unfolded protein response (UPR) activation and HA accumulation could be partially restored by the chemical chaperone 4-phenylbutyrate (4PBA). Chemical inhibition of the integrated stress response (ISR) restored accumulation of NA monomers in the presence of 6-TG or 6-TGo, but did not restore NA glycosylation or oligomerization. Thiopurines inhibited replication of the human coronavirus OC43 (HCoV-OC43), which also correlated with UPR/ISR activation and diminished accumulation of ORF1ab and nucleocapsid (N) mRNAs and N protein, which suggests broader disruption of coronavirus gene expression in ER-derived cytoplasmic compartments. The chemically similar thiopurine 6-mercaptopurine (6-MP) had little effect on the UPR and did not affect IAV or HCoV-OC43 replication. Consistent with reports on other CoV Spike (S) proteins, ectopic expression of SARS-CoV-2 S protein caused UPR activation. 6-TG treatment inhibited accumulation of full length S0 or furin-cleaved S2 fusion proteins, but spared the S1 ectodomain. DBeQ, which inhibits the p97 AAA-ATPase required for retrotranslocation of ubiquitinated misfolded proteins during ER-associated degradation (ERAD) restored accumulation of S0 and S2 proteins in the presence of 6-TG, suggesting that 6-TG induced UPR accelerates ERAD-mediated turnover of membrane-anchored S0 and S2 glycoproteins. Taken together, these data indicate that 6-TG and 6-TGo are effective host-targeted antivirals that trigger the UPR and disrupt accumulation of viral glycoproteins. Importantly, our data demonstrate for the first time the efficacy of these thiopurines in limiting IAV and HCoV-OC43 replication in cell culture models.IMPORTANCESecreted and transmembrane proteins are synthesized in the endoplasmic reticulum (ER), where they are folded and modified prior to transport. During infection, many viruses burden the ER with the task of creating and processing viral glycoproteins that will ultimately be incorporated into viral envelopes. Some viruses refashion the ER into replication compartments where viral gene expression and genome replication take place. This viral burden on the ER can trigger the cellular unfolded protein response (UPR), which attempts to increase the protein folding and processing capacity of the ER to match the protein load. Much remains to be learned about how viruses co-opt the UPR to ensure efficient synthesis of viral glycoproteins. Here, we show that two FDA-approved thiopurine drugs, 6-TG and 6-TGo, induce the UPR in a manner that impedes viral glycoprotein accumulation for enveloped influenza viruses and coronaviruses. These drugs may impede the replication of viruses that require precise tuning of the UPR to support viral glycoprotein synthesis for the successful completion of a replication cycle.

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Chemical Genomics Identifies the PERK-Mediated Unfolded Protein Stress Response as a Cellular Target for Influenza Virus Inhibition

mBio ◽

10.1128/mbio.00085-16 ◽

2016 ◽

Vol 7 (2) ◽

Cited By ~ 8

Author(s):

Sara Landeras-Bueno ◽

Yolanda Fernández ◽

Ana Falcón ◽

Juan Carlos Oliveros ◽

Juan Ortín

Keyword(s):

Gene Expression ◽

Protein Synthesis ◽

Influenza Virus ◽

Virus Infection ◽

Unfolded Protein Response ◽

Influenza A ◽

Viral Protein Synthesis ◽

Cellular Targets ◽

Unfolded Protein ◽

Protein Response

ABSTRACTInfluenza A viruses generate annual epidemics and occasional pandemics of respiratory disease with important consequences for human health and the economy. Therefore, a large effort has been devoted to the development of new anti-influenza virus drugs directed to viral targets, as well as to the identification of cellular targets amenable to anti-influenza virus therapy. Here we have addressed the identification of such potential cellular targets by screening collections of drugs approved for human use. We reasoned that screening with a green fluorescent protein-based recombinant replicon system would identify cellular targets involved in virus transcription/replication and/or gene expression and hence address an early stage of virus infection. By using such a strategy, we identified Montelukast (MK) as an inhibitor of virus multiplication. MK inhibited virus gene expression but did not alter viral RNA synthesisin vitroor viral RNA accumulationin vivo. The low selectivity index of MK prevented its use as an antiviral, but it was sufficient to identify a new cellular pathway suitable for anti-influenza virus intervention. By deep sequencing of RNA isolated from mock- and virus-infected human cells, treated with MK or left untreated, we showed that it stimulates the PERK-mediated unfolded protein stress response. The phosphorylation of PERK was partly inhibited in virus-infected cells but stimulated in MK-treated cells. Accordingly, pharmacological inhibition of PERK phosphorylation led to increased viral gene expression, while inhibition of PERK phosphatase reduced viral protein synthesis. These results suggest the PERK-mediated unfolded protein response as a potential cellular target to modulate influenza virus infection.IMPORTANCEInfluenza A viruses are responsible for annual epidemics and occasional pandemics with important consequences for human health and the economy. The unfolded protein response is a defense mechanism fired by cells when the demand of protein synthesis and folding is excessive, for instance, during an acute virus infection. In this report, we show that influenza virus downregulates the unfolded protein response mediated by the PERK sensor, while Montelukast, a drug used to treat asthma in humans, specifically stimulated this response and downregulated viral protein synthesis and multiplication. Accordingly, we show that PERK phosphorylation was reduced in virus-infected cells and increased in cells treated with Montelukast. Hence, our studies suggest that modulation of the PERK-mediated unfolded protein response is a target for influenza virus inhibition.

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Inhibition of protein synthesis leading to unfolded protein response is the major event in abrin-mediated apoptosis

Molecular and Cellular Biochemistry ◽

10.1007/s11010-015-2355-9 ◽

2015 ◽

Vol 403 (1-2) ◽

pp. 255-265 ◽

Cited By ~ 9

Author(s):

Ritu Mishra ◽

Meenakshi Sundaram Kumar ◽

Anjali A. Karande

Keyword(s):

Protein Synthesis ◽

Unfolded Protein Response ◽

Major Event ◽

Unfolded Protein ◽

Inhibition Of Protein Synthesis ◽

Protein Response

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Activation of the Unfolded Protein Response by 2-Deoxy-d-Glucose Inhibits Kaposi's Sarcoma-Associated Herpesvirus Replication and Gene Expression

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01126-12 ◽

2012 ◽

Vol 56 (11) ◽

pp. 5794-5803 ◽

Cited By ~ 27

Author(s):

Howard J. Leung ◽

Elda M. Duran ◽

Metin Kurtoglu ◽

Samita Andreansky ◽

Theodore J. Lampidis ◽

...

Keyword(s):

Protein Synthesis ◽

Er Stress ◽

Unfolded Protein Response ◽

Kaposi's Sarcoma ◽

Kaposi’S Sarcoma ◽

Lytic Replication ◽

Unfolded Protein ◽

Kaposi's Sarcoma Associated Herpesvirus ◽

Protein Response ◽

Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTLytic replication of the Kaposi's sarcoma-associated herpesvirus (KSHV) is essential for the maintenance of both the infected state and characteristic angiogenic phenotype of Kaposi's sarcoma and thus represents a desirable therapeutic target. During the peak of herpesvirus lytic replication, viral glycoproteins are mass produced in the endoplasmic reticulum (ER). Normally, this leads to ER stress which, through an unfolded protein response (UPR), triggers phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α), resulting in inhibition of protein synthesis to maintain ER and cellular homeostasis. However, in order to replicate, herpesviruses have acquired the ability to prevent eIF2α phosphorylation. Here we show that clinically achievable nontoxic doses of the glucose analog 2-deoxy-d-glucose (2-DG) stimulate ER stress, thereby shutting down eIF2α and inhibiting KSHV and murine herpesvirus 68 replication and KSHV reactivation from latency. Viral cascade genes that are involved in reactivation, including the master transactivator (RTA) gene, glycoprotein B, K8.1, and angiogenesis-regulating genes are markedly decreased with 2-DG treatment. Overall, our data suggest that activation of UPR by 2-DG elicits an early antiviral response via eIF2α inactivation, which impairs protein synthesis required to drive viral replication and oncogenesis. Thus, induction of ER stress by 2-DG provides a new antiherpesviral strategy that may be applicable to other viruses.

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Transcriptome Analysis of Recombinant Protein Secretion by Aspergillus nidulans and the Unfolded-Protein Response In Vivo

Applied and Environmental Microbiology ◽

10.1128/aem.71.5.2737-2747.2005 ◽

2005 ◽

Vol 71 (5) ◽

pp. 2737-2747 ◽

Cited By ~ 61

Author(s):

Andrew H. Sims ◽

Manda E. Gent ◽

Karin Lanthaler ◽

Nigel S. Dunn-Coleman ◽

Stephen G. Oliver ◽

...

Keyword(s):

Gene Expression ◽

Recombinant Protein ◽

Unfolded Protein Response ◽

Aspergillus Nidulans ◽

Filamentous Fungi ◽

Protein Secretion ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

ABSTRACT Filamentous fungi have a high capacity for producing large amounts of secreted proteins, a property that has been exploited for commercial production of recombinant proteins. However, the secretory pathway, which is key to the production of extracellular proteins, is rather poorly characterized in filamentous fungi compared to yeast. We report the effects of recombinant protein secretion on gene expression levels in Aspergillus nidulans by directly comparing a bovine chymosin-producing strain with its parental wild-type strain in continuous culture by using expressed sequence tag microarrays. This approach demonstrated more subtle and specific changes in gene expression than those observed when mimicking the effects of protein overproduction by using a secretion blocker. The impact of overexpressing a secreted recombinant protein more closely resembles the unfolded-protein response in vivo.

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Enforced dimerization between XBP1s and ATF6f enhances the protective effects of the unfolded protein response (UPR) in models of neurodegeneration

10.1101/2020.11.17.387480 ◽

2020 ◽

Author(s):

René L. Vidal ◽

Denisse Sepulveda ◽

Paulina Troncoso-Escudero ◽

Paula Garcia-Huerta ◽

Constanza Gonzalez ◽

...

Keyword(s):

Gene Expression ◽

Unfolded Protein Response ◽

Target Genes ◽

Cell Function ◽

Alpha Synuclein ◽

Protective Effects ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

AbstractAlteration to endoplasmic reticulum (ER) proteostasis is observed on a variety of neurodegenerative diseases associated with abnormal protein aggregation. Activation of the unfolded protein response (UPR) enables an adaptive reaction to recover ER proteostasis and cell function. The UPR is initiated by specialized stress sensors that engage gene expression programs through the concerted action of the transcription factors ATF4, ATF6f, and XBP1s. Although UPR signaling is generally studied as unique linear signaling branches, correlative evidence suggests that ATF6f and XBP1s may physically interact to regulate a subset of UPR-target genes. Here, we designed an ATF6f-XBP1s fusion protein termed UPRplus that behaves as a heterodimer in terms of its selective transcriptional activity. Cell-based studies demonstrated that UPRplus has stronger an effect in reducing the abnormal aggregation of mutant huntingtin and alpha-synuclein when compared to XBP1s or ATF6 alone. We developed a gene transfer approach to deliver UPRplus into the brain using adeno-associated viruses (AAVs) and demonstrated potent neuroprotection in vivo in preclinical models of Parkinson’s and Huntington’s disease. These results support the concept where directing UPR-mediated gene expression toward specific adaptive programs may serve as a possible strategy to optimize the beneficial effects of the pathway in different disease conditions.

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PERK/eIF2α signaling inhibits HIF-induced gene expression during the unfolded protein response via YB1-dependent regulation of HIF1α translation

Nucleic Acids Research ◽

10.1093/nar/gky127 ◽

2018 ◽

Vol 46 (8) ◽

pp. 3878-3890 ◽

Cited By ~ 11

Author(s):

Iglika G Ivanova ◽

Catherine V Park ◽

Adrian I Yemm ◽

Niall S Kenneth

Keyword(s):

Gene Expression ◽

Unfolded Protein Response ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

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Development and validation of an unfolded protein response-related gene signature to predict overall survival in HNSCC.

Journal of Clinical Oncology ◽

10.1200/jco.2021.39.15_suppl.e18033 ◽

2021 ◽

Vol 39 (15_suppl) ◽

pp. e18033-e18033

Author(s):

Jun Chen ◽

Bei Zhang

Keyword(s):

Gene Expression ◽

Overall Survival ◽

Unfolded Protein Response ◽

Cox Regression ◽

Risk Group ◽

Gene Signature ◽

Related Gene ◽

Hallmarks Of Cancer ◽

Unfolded Protein ◽

Protein Response

e18033 Background: Genomic expression profiles have enabled the classification of head and neck squamous cell carcinoma (HNSCC) into molecular sub-types and provide prognostic information, which have implications for the personalized treatment of HNSCC beyond clinical and pathological features. Methods: Gene-expression profiling was identified in TCGA- HNSCC (n = 492) and validated with the Gene Expression Ominibus (GEO) dataset(n = 270) for which RNA sequencing data and clinical covariates were available. A single-sample gene set enrichment analysis (ssGSEA) algorithm were used to quantified the levels of various hallmarks of cancer. And LASSO Cox regression model was used to screen robust prognostic biomarkers to identify the best set of survival-associated gene signatures in HNSCC. Statistical analyses were performed using R version 3.4.4. Results: We identified unfolded protein response as the primary risk factor for survival（cox coefficient = 17.4 [8.4-26.3], P < 0.001）among various hallmarks of cancer in TCGA- HNSCC. And unfolded protein response ssGESA scores were significantly elevated in patients who died during follow up (P = 0.009). Kaplan-Meier analysis showed that patients with low ssGSEA scores of unfolded protein response exhibited better OS (HR = 0.69, P = 0.008). And we established an unfolded protein response-related gene signature based on lasso cox. We then apply the unfolded protein response -related gene signature to classify patients into the high risk group and the low risk group with the cutoff of 0.18. Adjusted for stage，age，gender, our signature was an independent risk factor for overall survival in TCGA cohorts (HR = 0.39 [0.28-0.53],P = < 0.001). In external independent cohorts, similar results were observed. In the validation cohort GEO65858, the patients with high unfolded protein response score showed longer survival (HR = 0.62 [0.38-1.0], P = 0.049). And adjusted for stage，age，HPV state, the multivariate cox regression analysis showed that unfolded protein response-related gene signature exhibited an independent risk prediction for overall survival in 270 patients with HNSCC (HR = 0.57 [0.35-0.94], P = 0.026). Conclusions: By analyzing the gene-expression data with bioinformation approach, we developed and validated a risk prediction model with unfolded protein response -related expression scores in HNSCC, which have the potential to identify patients who could have better overall survival.

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