Inhibition of the integrated stress response by viral proteins that block p-eIF2-eIF2B association

The Translation Initiation Factor eIF2Bα Regulates Development, Stress Response, Amylase Production, and Kojic Acid Synthesis in the Fungus Aspergillus oryzae

Translation initiation, which involves numerous protein factors and coordinated control steps, represents the most complicated process during eukaryotic translation. However, the roles of eukaryotic translation initiation factor (eIF) in filamentous fungi are not well clarified. In this study, we investigated the function of eIF2Bα in Aspergillus oryzae, an industrially important filamentous fungus. The ΔeIF2Bα mutants showed slow colony growth and decreased conidia production, suggesting the critical roles of eIF2Bα in the growth and development of A. oryzae. In addition, the loss of eIF2Bα significantly impaired the ability to produce amylase and kojic acid, indicating the involvement of eIF2Bα in the amylase synthesis and secondary metabolite production. Interestingly, the elimination of eIF2Bα improved the tolerance of A. oryzae to diverse adverse stresses, including endoplasmic reticulum stress, oxidative stress, cell wall-perturbing stress, and cell membrane-damaging stress. Overall, our results indicate that eIF2Bα is a crucial regulator of growth, development, stress response, amylase production, and kojic acid synthesis in A. oryzae.

Targeting host integrated stress response: lead discovery of flavonoid compounds active against coronaviruses PEDV and PDCoV

Viral infections trigger the integrated stress response (ISR) in eukaryotic cells that leads to the activation of eIF2α kinases, the elevation of eukaryotic translation initiation factor 2α (eIF2α) phosphorylation, and thereby the shutdown of global protein synthesis that viruses rely on to replicate. Coronaviruses and other viruses have evolved various subversion mechanisms to counteract the antiviral ISR. These intricate host-virus interactions may be exploited by pharmacologically activating the host ISR for the development of host-directed antivirals (HDAs), an increasingly relevant area of research. In this study, we have discovered a new class of flavonoid-based ISR activators that exhibit potent antiviral activity against porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV). PEDV and PDCoV are animal coronaviruses of great veterinary and economic importance, for which there are currently no effective therapeutics. The mechanistic study indicated that lead compounds 1-B and 1-C inhibit PEDV and PDCoV replication via upregulating eIF2α phosphorylation and thereby downregulating global protein synthesis in host cells, suggesting they are HDA antivirals.

GCN2 in Viral Defence and the Subversive Tactics Employed by Viruses

The recent SARS-CoV-2 pandemic and associated COVID19 disease illustrates the important role of viral defence mechanisms in ensuring survival and recovery of the host or patient. Viruses absolutely depend on the host's protein synthesis machinery to replicate, meaning that impeding translation is a powerful way to counteract viruses. One major approach used by cells to obstruct protein synthesis is to phosphorylate the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α). Mammals possess four different eIF2α-kinases: PKR, HRI, PEK/PERK, and GCN2. While PKR is currently considered the principal eIF2α-kinase involved in viral defence, the other eIF2α-kinases have also been found to play significant roles. Unsurprisingly, viruses have developed mechanisms to counteract the actions of eIF2α-kinases, or even to exploit them to their benefit. While some of these virulence factors are specific to one eIF2α-kinase, such as GCN2, others target all eIF2α-kinases. This review critically evaluates the current knowledge of viral mechanisms targeting the eIF2α-kinase GCN2. A detailed and in-depth understanding of the molecular mechanisms by which viruses evade host defence mechanisms will help to inform the development of powerful anti-viral measures.

TOLLIP inhibits lipid accumulation and the integrated stress response in alveolar macrophages to control Mycobacterium tuberculosis infection

A polymorphism causing deficiencies in Toll-interacting protein (TOLLIP), an inhibitory adaptor protein affecting endosomal trafficking, is associated with increased tuberculosis (TB) risk. It is, however, unclear how TOLLIP affects TB pathogenesis. Here we show that TB severity is increased in Tollip-/- mice, characterized by macrophage- and T cell-driven inflammation, foam cell formation and lipid accumulation. Tollip-/- alveolar macrophages (AM) specifically accumulated lipid and underwent necrosis. Transcriptional and protein analyses of Mycobacterium tuberculosis (Mtb)-infected, Tollip-/- AM revealed increased EIF2 signalling and downstream upregulation of the integrated stress response (ISR). These phenotypes were linked, as incubation of the Mtb lipid mycolic acid with Mtb-infected Tollip-/- AM activated the ISR and increased Mtb replication. Correspondingly, the ISR inhibitor, ISRIB, reduced Mtb numbers in AM and improved Mtb control, overcoming the inflammatory phenotype. In conclusion, targeting the ISR offers a promising target for host-directed anti-TB therapy towards improved Mtb control and reduced immunopathology.

SARS-CoV-2 variant-specific differences in inhibiting the effects of the PKR-activated integrated stress response

The integrated stress response (ISR) is a eukaryotic cell pathway that triggers translational arrest and the formation of stress granules (SGs) in response to various stress signals, including those caused by viral infections. The SARS-CoV-2 nucleocapsid protein has been shown to disrupt SGs, but SARS-CoV-2 interactions with other components of the pathway remains poorly characterized. Here, we show that SARS-CoV-2 infection triggers the ISR through activation of the eIF2α-kinase PKR while inhibiting a variety of downstream effects. In line with previous studies, SG formation was efficiently inhibited and the induced eIF2α phosphorylation only minimally contributed to the translational arrest observed in infected cells. Despite ISR activation and translational arrest, expression of the stress-responsive transcription factors ATF4 and CHOP was not induced in SARS-CoV-2 infected cells. Finally, we found variant-specific differences in the activation of the ISR between ancestral SARS-CoV-2 and the Delta and Omicron BA.1 variants in that Delta infection induced weaker PKR activation while Omicron infection induced higher levels of p-eIF2α, and greatly increased SG formation compared to the other variants. Our results suggest that different SARS-CoV-2 variants can affect normal cell functions differently, which can have an impact on pathogenesis and treatment strategies.

Protection of eIF2B from inhibitory phosphorylated eIF2: A viral strategy to maintain mRNA translation during the PKR-triggered integrated stress response

The integrated stress response (ISR) protects cells from a variety of insults. Once elicited (e.g., by virus infections), it eventually leads to the block of mRNA translation. Central to the ISR are the interactions between translation initiation factors eIF2 and eIF2B. Under normal conditions, eIF2 drives the initiation of protein synthesis through hydrolysis of GTP, which becomes replenished by the guanine nucleotide exchange factor eIF2B. The antiviral branch of the ISR is activated by the RNA-activated kinase PKR which phosphorylates eIF2, thereby converting it into an eIF2B inhibitor. Here, we describe the recently solved structures of eIF2B in complex with eIF2 and a novel escape strategy used by viruses. While unphosphorylated eIF2 interacts with eIF2B in its "productive" conformation, phosphorylated eIF2 [eIF2(αP)] engages a different binding cavity on eIF2B and forces it into the "nonproductive" conformation that prohibits guanine nucleotide exchange factor activity. It is well established that viruses express so-called PKR antagonists that interfere with double-strand RNA, PKR itself, or eIF2. However recently, three taxonomically unrelated viruses were reported to encode antagonists targeting eIF2B instead. For one antagonist, the S segment nonstructural protein of Sandfly fever Sicilian virus, atomic structures showed that it occupies the eIF2(αP)-binding cavity on eIF2B without imposing a switch to the nonproductive conformation. S segment nonstructural protein thus antagonizes the activity of PKR by protecting eIF2B from inhibition by eIF2(αP). As the ISR and specifically eIF2B are central to neuroprotection and a wide range of genetic and age-related diseases, these developments may open new possibilities for treatments.

SARS-CoV-2 nucleocapsid protein inhibits the PKR-mediated integrated stress response through RNA-binding domain N2b

The nucleocapsid protein N of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enwraps and condenses the viral genome for packaging but is also an antagonist of the innate antiviral defense. It suppresses the integrated stress response (ISR), purportedly by interacting with stress granule (SG) assembly factors G3BP1 and 2, and inhibits type I interferon responses. To elucidate its mode of action, we systematically deleted and over-expressed distinct regions and domains. We show that N via domain N2b blocks PKR-mediated ISR activation, as measured by suppression of ISR-induced translational arrest and SG formation. N2b mutations that prevent dsRNA binding abrogate these activities also when introduced in the intact N protein. Substitutions reported to block post-translation modifications of N or its interaction with G3BP1/2 did not have a detectable additive effect. In an encephalomyocarditis virus-based infection model, N2b - but not a derivative defective in RNA binding-prevented PKR activation, inhibited β-interferon expression and promoted virus replication. Apparently, SARS-CoV-2 N inhibits innate immunity by sequestering dsRNA to prevent activation of PKR and RIG-I-like receptors. Similar observations were made for the N protein of human coronavirus 229E, suggesting that this may be a general trait conserved among members of other orthocoronavirus (sub)genera.

Biomolecular phase separation in stress granule assembly and virus infection

Liquid-liquid phase separation (LLPS) has emerged as a crucial mechanism for cellular compartmentalization. One prominent example of this is the stress granule. Found in various types of cells, stress granule is a biomolecular condensate formed through phase separation. It comprises numerous RNA and RNA-binding proteins. Over the past decades, substantial knowledge has been gained about the composition and dynamics of stress granules. SGs can regulate various signaling pathways and have been associated with numerous human diseases, such as neurodegenerative diseases, cancer, and infectious diseases. The threat of viral infections continues to loom over society. Both DNA and RNA viruses depend on host cells for replication. Intriguingly, many stages of the viral life cycle are closely tied to RNA metabolism in human cells. The field of biomolecular condensates has rapidly advanced in recent times. In this context, we aim to summarize research on stress granules and their link to viral infections. Notably, stress granules triggered by viral infections behave differently from the canonical stress granules triggered by sodium arsenite (SA) and heat shock. Studying stress granules in the context of viral infections could offer a valuable platform to link viral replication processes and host anti-viral responses. A deeper understanding of these biological processes could pave the way for innovative interventions and treatments for viral infectious diseases. They could potentially bridge the gap between basic biological processes and interactions between viruses and their hosts.

An old model with new insights: endogenous retroviruses drive the evolvement toward ASD susceptibility and hijack transcription machinery during development

The BTBR T+Itpr3tf/J (BTBR/J) strain is one of the most valid models of idiopathic autism, serving as a potent forward genetics tool to dissect the complexity of autism. We found that a sister strain with an intact corpus callosum, BTBR TF/ArtRbrc (BTBR/R), showed more prominent autism core symptoms but moderate ultrasonic communication/normal hippocampus-dependent memory, which may mimic autism in the high functioning spectrum. Intriguingly, disturbed epigenetic silencing mechanism leads to hyperactive endogenous retrovirus (ERV), a mobile genetic element of ancient retroviral infection, which increases de novo copy number variation (CNV) formation in the two BTBR strains. This feature makes the BTBR strain a still evolving multiple-loci model toward higher ASD susceptibility. Furthermore, active ERV, analogous to virus infection, evades the integrated stress response (ISR) of host defense and hijacks the transcriptional machinery during embryonic development in the BTBR strains. These results suggest dual roles of ERV in the pathogenesis of ASD, driving host genome evolution at a long-term scale and managing cellular pathways in response to viral infection, which has immediate effects on embryonic development. The wild-type Draxin expression in BTBR/R also makes this substrain a more precise model to investigate the core etiology of autism without the interference of impaired forebrain bundles as in BTBR/J.

Dysregulation of Stress-Induced Translational Control by Porphyromonas gingivalis in Host Cells

Porphyromonas gingivalis contributes to the chronic oral disease periodontitis, triggering the activation of host inflammatory responses, inducing cellular stresses such as oxidation. During stress, host cells can activate the Integrated Stress Response (ISR), a pathway which determines cellular fate, by either downregulating protein synthesis and initiating a stress–response gene expression program, or by initiating programmed cell death. Recent studies have implicated the ISR within both host antimicrobial defenses and the pathomechanism of certain microbes. In this study, using a combination of immunofluorescence confocal microscopy and immunoblotting, the molecular mechanisms by which P. gingivalis infection alters translation attenuation during oxidative stress-induced activation of the ISR in oral epithelial cells were investigated. P. gingivalis infection alone did not result in ISR activation. In contrast, infection coupled with stress caused differential stress granule formation and composition. Infection heightened stress-induced translational repression independently of core ISR mediators. Heightened translational repression during stress was observed with both P. gingivalis–conditioned media and outer membrane vesicles, implicating a secretory factor in this exacerbated translational repression. The effects of gingipain inhibitors and gingipain-deficient P. gingivalis mutants confirmed these pathogen-specific proteases as the effector of exacerbated translational repression. Gingipains are known to degrade the mammalian target of rapamycin (mTOR) and the findings of this study implicate the gingipain-mTOR axis as the effector of host translational dysregulation during stress.

A little less aggregation a little more replication: Viral manipulation of stress granules

Recent exciting studies have uncovered how membrane-less organelles, also known as biocondensates, are providing cells with rapid response pathways, allowing them to re-organize their cellular contents and adapt to stressful conditions. Their assembly is driven by the phase separation of their RNAs and intrinsically disordered protein components into condensed foci. Among these, stress granules (SGs) are dynamic cytoplasmic biocondensates that form in response to many stresses, including activation of the integrated stress response or viral infections. SGs sit at the crossroads between antiviral signaling and translation because they concentrate signaling proteins and components of the innate immune response, in addition to translation machinery and stalled mRNAs. Consequently, they have been proposed to contribute to antiviral activities, and therefore are targeted by viral countermeasures. Equally, SGs components can be commandeered by viruses for their own efficient replication. Phase separation processes are an important component of the viral life cycle, for example, driving the assembly of replication factories or inclusion bodies. Therefore, in this review, we will outline the recent understanding of this complex interplay and tug of war between viruses, SGs, and their components. This article is categorized under: RNA in Disease and Development > RNA in Disease Translation > Regulation RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Schweinfurthin induces ICD without ER stress and caspase activation

Our previous study showed that one of the schweinfurthin compounds, 5’-methoxyschweinfurthin G (MeSG), not only enhances the anti-tumor effect of anti-PD1 antibody in the B16F10 murine melanoma model, but also provokes durable, protective anti-tumor immunity. Here we further investigated the mechanisms by which MeSG treatment induces immunogenic cell death (ICD). MeSG induced significant cell surface calreticulin (CRT) exposure in a time and concentration dependent manner as well as increased phagocytosis of tumor cells by dendritic cells in vitro. Interestingly, this CRT exposure differs from the canonical pathway in several aspects. MeSG does not cause ER stress and does not require PERK to induce CRT exposure. Caspase inhibitors partially rescue cells from MeSG-induced apoptosis, but fail to reduce CRT exposure. MeSG does not cause ERp57 exposure and the absence of ERp57 expression does not reduce CRT exposure. Finally, an intact ER to Golgi transport system is required for this phenomenon. These results lend support to the development of the schweinfurthin family as drugs to enhance clinical response to immunotherapy and highlight the need for additional research on the mechanisms of ICD induction.

Move and countermove: the integrated stress response in picorna- and coronavirus-infected cells

Viruses, when entering their host cells, are met by a fierce intracellular immune defense. One prominent antiviral pathway is the integrated stress response (ISR). Upon activation of the ISR - typically though not exclusively upon detection of dsRNA - translation-initiation factor eukaryotic initiation factor 2 (eIF2) becomes phosphorylated to act as an inhibitor of guanine nucleotide-exchange factor eIF2B. Thus, with the production of ternary complex blocked, a global translational arrest ensues. Successful virus replication hinges on effective countermeasures. Here, we review ISR antagonists and antagonistic mechanisms employed by picorna- and coronaviruses. Special attention will be given to a recently discovered class of viral antagonists that inhibit the ISR by targeting eIF2B, thereby allowing unabated translation initiation even at exceedingly high levels of phosphorylated eIF2.

Shielding the mRNA-translation factor eIF2B from inhibitory p-eIF2 as a viral strategy to evade protein kinase R-mediated innate immunity

The interferon-regulated kinase PKR (protein kinase RNA-activated) is a potent innate immune factor against a broad range of viruses. Being part of the integrated stress response (ISR), its restrictive effect is predominantly exerted by phosphorylating the eukaryotic translation-initiation factor eIF2, thereby turning it into an inhibitor of translation-initiation factor eIF2B. A plethora of viruses are known to evade the shutdown of cellular mRNA translation by interfering either with PKR activation or with eIF2 phosphorylation. Recently, a novel PKR evasion strategy was described: proteins from three taxonomically distinct RNA viruses allow for full PKR activation and eIF2 phosphorylation in the infected cell, but protect eIF2B from inhibition by phosphorylated eIF2, thus enabling mRNA translation in the presence of an activated ISR.

A common epigenetic mechanism across different cellular origins underlies systemic immune dysregulation in an idiopathic autism mouse model

Immune dysregulation plays a key role in the pathogenesis of autism. Changes occurring at the systemic level, from brain inflammation to disturbed innate/adaptive immune in the periphery, are frequently observed in patients with autism; however, the intrinsic mechanisms behind them remain elusive. We hypothesize a common etiology may lie in progenitors of different types underlying widespread immune dysregulation. By single-cell RNA sequencing (sc-RNA seq), we trace the developmental origins of immune dysregulation in a mouse model of idiopathic autism. It is found that both in aorta-gonad-mesonephros (AGM) and yolk sac (YS) progenitors, the dysregulation of HDAC1-mediated epigenetic machinery alters definitive hematopoiesis during embryogenesis and downregulates the expression of the AP-1 complex for microglia development. Subsequently, these changes result in the dysregulation of the immune system, leading to gut dysbiosis and hyperactive microglia in the brain. We further confirm that dysregulated immune profiles are associated with specific microbiota composition, which may serve as a biomarker to identify autism of immune-dysregulated subtypes. Our findings elucidate a shared mechanism for the origin of immune dysregulation from the brain to the gut in autism and provide new insight to dissecting the heterogeneity of autism, as well as the therapeutic potential of targeting immune-dysregulated autism subtypes.

Regulation and function of elF2B in neurological and metabolic disorders

Eukaryotic initiation factor 2B, eIF2B is a guanine nucleotide exchange, factor with a central role in coordinating the initiation of translation. During stress and disease, the activity of eIF2B is inhibited via the phosphorylation of its substrate eIF2 (p-eIF2α). A number of different kinases respond to various stresses leading to the phosphorylation of the alpha subunit of eIF2, and collectively this regulation is known as the integrated stress response, ISR. This targeting of eIF2B allows the cell to regulate protein synthesis and reprogramme gene expression to restore homeostasis. Advances within structural biology have furthered our understanding of how eIF2B interacts with eIF2 in both the productive GEF active form and the non-productive eIF2α phosphorylated form. Here, current knowledge of the role of eIF2B in the ISR is discussed within the context of normal and disease states focusing particularly on diseases such as vanishing white matter disease (VWMD) and permanent neonatal diabetes mellitus (PNDM), which are directly linked to mutations in eIF2B. The role of eIF2B in synaptic plasticity and memory formation is also discussed. In addition, the cellular localisation of eIF2B is reviewed and considered along with the role of additional in vivo eIF2B binding factors and protein modifications that may play a role in modulating eIF2B activity during health and disease.

Glycosite-deleted mRNA of SARS-CoV-2 spike protein as a broad-spectrum vaccine

Development of the messenger RNA (mRNA) vaccine has emerged as an effective and speedy strategy to control the spread of new pathogens. After vaccination, the mRNA is translated into the real protein vaccine, and there is no need to manufacture the protein in vitro. However, the fate of mRNA and its posttranslational modification inside the cell may affect immune response. Here, we showed that the mRNA vaccine of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein with deletion of glycosites in the receptor-binding domain (RBD) or especially the subunit 2 (S2) domain to expose more conserved epitopes elicited stronger antibody and CD8+ T cell responses with broader protection against the alpha, beta, gamma, delta, and omicron variants, compared to the unmodified mRNA. Immunization of such mRNA resulted in accumulation of misfolded spike protein in the endoplasmic reticulum, causing the up-regulation of BiP/GRP78, XBP1, and p-eIF2α to induce cell apoptosis and strong CD8+ T cell response. In addition, dendritic cells (DCs) incubated with S2-glysosite deleted mRNA vaccine increased class I major histocompatibility complex (MHC I) expression. This study provides a direction for the development of broad-spectrum mRNA vaccines which may not be achieved with the use of expressed proteins as antigens.

Immunogenic cell stress and death

Dying mammalian cells emit numerous signals that interact with the host to dictate the immunological correlates of cellular stress and death. In the absence of reactive antigenic determinants (which is generally the case for healthy cells), such signals may drive inflammation but cannot engage adaptive immunity. Conversely, when cells exhibit sufficient antigenicity, as in the case of infected or malignant cells, their death can culminate with adaptive immune responses that are executed by cytotoxic T lymphocytes and elicit immunological memory. Suggesting a key role for immunogenic cell death (ICD) in immunosurveillance, both pathogens and cancer cells evolved strategies to prevent the recognition of cell death as immunogenic. Intriguingly, normal cells succumbing to conditions that promote the formation of post-translational neoantigens (for example, oxidative stress) can also drive at least some degree of antigen-specific immunity, pointing to a novel implication of ICD in the etiology of non-infectious, non-malignant disorders linked to autoreactivity.

Minding the message: tactics controlling RNA decay, modification, and translation in virus-infected cells

With their categorical requirement for host ribosomes to translate mRNA, viruses provide a wealth of genetically tractable models to investigate how gene expression is remodeled post-transcriptionally by infection-triggered biological stress. By co-opting and subverting cellular pathways that control mRNA decay, modification, and translation, the global landscape of post-transcriptional processes is swiftly reshaped by virus-encoded factors. Concurrent host cell-intrinsic countermeasures likewise conscript post-transcriptional strategies to mobilize critical innate immune defenses. Here we review strategies and mechanisms that control mRNA decay, modification, and translation in animal virus-infected cells. Besides settling infection outcomes, post-transcriptional gene regulation in virus-infected cells epitomizes fundamental physiological stress responses in health and disease.

Viral evasion of the integrated stress response through antagonism of eIF2-P binding to eIF2B

Viral infection triggers activation of the integrated stress response (ISR). In response to viral double-stranded RNA (dsRNA), RNA-activated protein kinase (PKR) phosphorylates the translation initiation factor eIF2, converting it from a translation initiator into a potent translation inhibitor and this restricts the synthesis of viral proteins. Phosphorylated eIF2 (eIF2-P) inhibits translation by binding to eIF2's dedicated, heterodecameric nucleotide exchange factor eIF2B and conformationally inactivating it. We show that the NSs protein of Sandfly Fever Sicilian virus (SFSV) allows the virus to evade the ISR. Mechanistically, NSs tightly binds to eIF2B (KD = 30 nM), blocks eIF2-P binding, and rescues eIF2B GEF activity. Cryo-EM structures demonstrate that SFSV NSs and eIF2-P directly compete, with the primary NSs contacts to eIF2Bα mediated by five 'aromatic fingers'. NSs binding preserves eIF2B activity by maintaining eIF2B's conformation in its active A-State.

eIF2B-capturing viral protein NSs suppresses the integrated stress response

Various stressors such as viral infection lead to the suppression of cap-dependent translation and the activation of the integrated stress response (ISR), since the stress-induced phosphorylated eukaryotic translation initiation factor 2 [eIF2(αP)] tightly binds to eIF2B to prevent it from exchanging guanine nucleotide molecules on its substrate, unphosphorylated eIF2. Sandfly fever Sicilian virus (SFSV) evades this cap-dependent translation suppression through the interaction between its nonstructural protein NSs and host eIF2B. However, its precise mechanism has remained unclear. Here, our cryo-electron microscopy (cryo-EM) analysis reveals that SFSV NSs binds to the α-subunit of eIF2B in a competitive manner with eIF2(αP). Together with SFSV NSs, eIF2B retains nucleotide exchange activity even in the presence of eIF2(αP), in line with the cryo-EM structures of the eIF2B•SFSV NSs•unphosphorylated eIF2 complex. A genome-wide ribosome profiling analysis clarified that SFSV NSs expressed in cultured human cells attenuates the ISR triggered by thapsigargin, an endoplasmic reticulum stress inducer. Furthermore, SFSV NSs introduced in rat hippocampal neurons and human induced-pluripotent stem (iPS) cell-derived motor neurons exhibits neuroprotective effects against the ISR-inducing stress. Since ISR inhibition is beneficial in various neurological disease models, SFSV NSs may be a promising therapeutic ISR inhibitor.

Resveratrol and related stilbene derivatives induce stress granules with distinct clearance kinetics

Stress granules (SGs) are ribonucleoprotein functional condensates that form under stress conditions in all eukaryotic cells. Although their stress-survival function is far from clear, SGs have been implicated in the regulation of many vital cellular pathways. Consequently, SG dysfunction is thought to be a mechanistic point of origin for many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Additionally, SGs are thought to play a role in pathogenic pathways as diverse as viral infection and chemotherapy resistance. There is a growing consensus on the hypothesis that understanding the mechanistic regulation of SG physical properties is essential to understanding their function. Although the internal dynamics and condensation mechanisms of SGs have been broadly investigated, there have been fewer investigations into the timing of SG formation and clearance in live cells. Because the lifetime of SG persistence can be a key factor in their function and tendency toward pathological dysregulation, SG clearance mechanisms deserve particular attention. Here we show that resveratrol and its analogues piceatannol, pterostilbene, and 3,4,5,4'-tetramethoxystilbene induce G3BP-dependent SG formation with atypically rapid clearance kinetics. Resveratrol binds to G3BP, thereby reducing its protein-protein association valency. We suggest that altering G3BP valency is a pathway for the formation of uniquely transient SGs.

Patients with Coronary Artery Disease Have Lower Levels of Antibody to Heat-Stressed Fibroblast Derived Proteins, versus Normal Subjects

Cellular stress response plays an important role in the pathophysiology of coronary artery disease (CAD). Inhibition of cellular stress may provide a novel clinical approach regarding the diagnosis and treatment of CAD. Fibroblasts constitute 60-70% of cardiac cells and have a crucial role in cardiovascular function. Hence, the aim of this study was to show a potential therapeutic application of proteins derived from heat-stressed fibroblast in CAD patients. Fibroblasts were isolated from the foreskin and cultured under heat stress conditions. Surprisingly, 1.06% of the cells exhibited a necrotic death pattern. Furthermore, heat-stressed fibroblasts produced higher level of total proteins than control cells. In SDS-PAGE analysis, a 70 kDa protein band was observed in stressed cell culture supernatants which appeared as two acidic spots with close pI in the two-dimensional electrophoresis. To evaluate the immunogenic properties of fibroblast-derived heat shock proteins (HSPs), the serum immunoglobulin-G (IgG) was measured by ELISA in 50 CAD patients and 50 normal subjects who had been diagnosed through angiography. Interestingly, the level of anti-HSP antibody was significantly higher in non-CAD individuals in comparison with the patient's group (p < 0.05). The odds ratio for CAD was 5.06 (95%CI = 2.15‐11.91) in cut-off value of 30 AU/mL of anti-HSP antibody. Moreover, ROC analysis showed that anti-HSP antibodies had a specificity of 74% and a sensitivity of 64%, which is almost equal to 66% sensitivity of exercise stress test (EST) as a CAD diagnostic method. These data revealed that fibroblast-derived HSPs are suitable for the diagnosis and management of CAD through antibody production.

CD177, a specific marker of neutrophil activation, is associated with coronavirus disease 2019 severity and death

The identification of patients with coronavirus disease 2019 and high risk of severe disease is a challenge in routine care. We performed cell phenotypic, serum, and RNA sequencing gene expression analyses in severe hospitalized patients (n = 61). Relative to healthy donors, results showed abnormalities of 27 cell populations and an elevation of 42 cytokines, neutrophil chemo-attractants, and inflammatory components in patients. Supervised and unsupervised analyses revealed a high abundance of CD177, a specific neutrophil activation marker, contributing to the clustering of severe patients. Gene abundance correlated with high serum levels of CD177 in severe patients. Higher levels were confirmed in a second cohort and in intensive care unit (ICU) than non-ICU patients (P < 0.001). Longitudinal measurements discriminated between patients with the worst prognosis, leading to death, and those who recovered (P = 0.01). These results highlight neutrophil activation as a hallmark of severe disease and CD177 assessment as a reliable prognostic marker for routine care.

Bacterial Manipulation of the Integrated Stress Response: A New Perspective on Infection

Host immune activation forms a vital line of defence against bacterial pathogenicity. However, just as hosts have evolved immune responses, bacteria have developed means to escape, hijack and subvert these responses to promote survival. In recent years, a highly conserved group of signalling cascades within the host, collectively termed the integrated stress response (ISR), have become increasingly implicated in immune activation during bacterial infection. Activation of the ISR leads to a complex web of cellular reprogramming, which ultimately results in the paradoxical outcomes of either cellular homeostasis or cell death. Therefore, any pathogen with means to manipulate this pathway could induce a range of cellular outcomes and benefit from favourable conditions for long-term survival and replication. This review aims to outline what is currently known about bacterial manipulation of the ISR and present key hypotheses highlighting areas for future research.

Duck Hepatitis A Virus Type 1 Induces eIF2α Phosphorylation-Dependent Cellular Translation Shutoff via PERK/GCN2

Duck hepatitis A virus type 1 (DHAV-1) is one of the most deadly pathogens that endanger the duck industry. Most viruses usually turn off host translation after infection to facilitate viral replication and translation. For the first time report to our knowledge, DHAV-1 can induce eIF2α phosphorylation and inhibit cellular translation in duck embryo fibroblasts (DEFs). Moreover, the activity of DHAV-1 in the cells caused obvious eIF2α phosphorylation, which has nothing to do with the viral protein. Subsequently, we screened two kinases (PERK and GCN2) that affect eIF2α phosphorylation through inhibitors and shRNA. Notably, the role of GCN2 in other picornaviruses has not been reported. In addition, when the phosphorylation of eIF2α induced by DHAV-1 is inhibited, the translation efficiency of DEFs restores to a normal level, indicating that DHAV-1 induced cellular translation shutoff is dependent on eIF2α phosphorylation.

eIF2B conformation and assembly state regulate the integrated stress response

The integrated stress response (ISR) is activated by phosphorylation of the translation initiation factor eIF2 in response to various stress conditions. Phosphorylated eIF2 (eIF2-P) inhibits eIF2's nucleotide exchange factor eIF2B, a twofold symmetric heterodecamer assembled from subcomplexes. Here, we monitor and manipulate eIF2B assembly in vitro and in vivo. In the absence of eIF2B's α-subunit, the ISR is induced because unassembled eIF2B tetramer subcomplexes accumulate in cells. Upon addition of the small-molecule ISR inhibitor ISRIB, eIF2B tetramers assemble into active octamers. Surprisingly, ISRIB inhibits the ISR even in the context of fully assembled eIF2B decamers, revealing allosteric communication between the physically distant eIF2, eIF2-P, and ISRIB binding sites. Cryo-electron microscopy structures suggest a rocking motion in eIF2B that couples these binding sites. eIF2-P binding converts eIF2B decamers into 'conjoined tetramers' with diminished substrate binding and enzymatic activity. Canonical eIF2-P-driven ISR activation thus arises due to this change in eIF2B's conformational state.

Arthropods Under Pressure: Stress Responses and Immunity at the Pathogen-Vector Interface

Understanding what influences the ability of some arthropods to harbor and transmit pathogens may be key for controlling the spread of vector-borne diseases. Arthropod immunity has a central role in dictating vector competence for pathogen acquisition and transmission. Microbial infection elicits immune responses and imparts stress on the host by causing physical damage and nutrient deprivation, which triggers evolutionarily conserved stress response pathways aimed at restoring cellular homeostasis. Recent studies increasingly recognize that eukaryotic stress responses and innate immunity are closely intertwined. Herein, we describe two well-characterized and evolutionarily conserved mechanisms, the Unfolded Protein Response (UPR) and the Integrated Stress Response (ISR), and examine evidence that these stress responses impact immune signaling. We then describe how multiple pathogens, including vector-borne microbes, interface with stress responses in mammals. Owing to the well-conserved nature of the UPR and ISR, we speculate that similar mechanisms may be occurring in arthropod vectors and ultimately impacting vector competence. We conclude this Perspective by positing that novel insights into vector competence will emerge when considering that stress-signaling pathways may be influencing the arthropod immune network.

Reovirus and the Host Integrated Stress Response: On the Frontlines of the Battle to Survive

Cells are continually exposed to stressful events, which are overcome by the activation of a number of genetic pathways. The integrated stress response (ISR) is a large component of the overall cellular response to stress, which ultimately functions through the phosphorylation of the alpha subunit of eukaryotic initiation factor-2 (eIF2α) to inhibit the energy-taxing process of translation. This response is instrumental in the inhibition of viral infection and contributes to evolution in viruses. Mammalian orthoreovirus (MRV), an oncolytic virus that has shown promise in over 30 phase I–III clinical trials, has been shown to induce multiple arms within the ISR pathway, but it successfully evades, modulates, or subverts each cellular attempt to inhibit viral translation. MRV has not yet received Food and Drug Administration (FDA) approval for general use in the clinic; therefore, researchers continue to study virus interactions with host cells to identify circumstances where MRV effectiveness in tumor killing can be improved. In this review, we will discuss the ISR, MRV modulation of the ISR, and discuss ways in which MRV interaction with the ISR may increase the effectiveness of cancer therapeutics whose modes of action are altered by the ISR.

Targeting the integrated stress response in ophthalmology

Purpose: To summarize the Integrated Stress Response (ISR) in the context of ophthalmology, with special interest on the cornea and anterior segment. Results: The ISR is a powerful and conserved signaling pathway that allows for cells to respond to a diverse array of both intracellular and extracellular stressors. The pathway is classically responsible for coordination of the cellular response to amino acid starvation, ultraviolet light, heme dysregulation, viral infection, and unfolded protein. Under normal circumstances, it is considered pro-survival and a necessary mechanism through which protein translation is controlled. However, in cases of severe or prolonged stress the pathway can promote apoptosis, and loss of normal cellular phenotype. The activation of this pathway culminates in the global inhibition of cap-dependent protein translation and the canonical expression of the activating transcription factor 4 (ATF4). Conclusion:The eye is uniquely exposed to ISR responsive stressors due to its environmental exposure and relative isolation from the circulatory system which are necessary for its function. We will discuss how this pathway is critical for the proper function of the tissue, its role in development, as well as how targeting of the pathway could alleviate key aspects of diverse ophthalmic diseases.

Lysosomotropic agents including azithromycin, chloroquine and hydroxychloroquine activate the integrated stress response

The integrated stress response manifests with the phosphorylation of eukaryotic initiation factor 2α (eIF2α) on serine residue 51 and plays a major role in the adaptation of cells to endoplasmic reticulum stress in the initiation of autophagy and in the ignition of immune responses. Here, we report that lysosomotropic agents, including azithromycin, chloroquine, and hydroxychloroquine, can trigger eIF2α phosphorylation in vitro (in cultured human cells) and, as validated for hydroxychloroquine, in vivo (in mice). Cells bearing a non-phosphorylatable eIF2α mutant (S51A) failed to accumulate autophagic puncta in response to azithromycin, chloroquine, and hydroxychloroquine. Conversely, two inhibitors of eIF2α dephosphorylation, nelfinavir and salubrinal, enhanced the induction of such autophagic puncta. Altogether, these results point to the unexpected capacity of azithromycin, chloroquine, and hydroxychloroquine to elicit the integrated stress response.

Cell-Type-Specific Immune Dysregulation in Severely Ill COVID-19 Patients

Recent studies have demonstrated immunologic dysfunction in severely ill coronavirus disease 2019 (COVID-19) patients. We use single-cell RNA sequencing (scRNA-seq) to analyze the transcriptome of peripheral blood mononuclear cells (PBMCs) from healthy (n = 3) and COVID-19 patients with moderate disease (n = 5), acute respiratory distress syndrome (ARDS, n = 6), or recovering from ARDS (n = 6). Our data reveal transcriptomic profiles indicative of defective antigen presentation and interferon (IFN) responsiveness in monocytes from ARDS patients, which contrasts with higher responsiveness to IFN signaling in lymphocytes. Furthermore, genes involved in cytotoxic activity are suppressed in both natural killer (NK) and CD8 T lymphocytes, and B cell activation is deficient, which is consistent with delayed viral clearance in severely ill COVID-19 patients. Our study demonstrates that COVID-19 patients with ARDS have a state of immune imbalance in which dysregulation of both innate and adaptive immune responses may be contributing to a more severe disease course.

Fasnall Induces Atypically Transient Stress Granules Independently of FASN Inhibition

Stress Granule formation has been linked to the resistance of some cancer cells to chemotherapeutic intervention. A number of studies have proposed that certain anti-tumor compounds promote cancer cell survival by inducing Stress Granule formation, leading to increased cellular fitness and apoptosis avoidance. Here we show that a potent fatty acid synthase inhibitor, fasnall, known for its anti-tumor capabilities, triggers the formation of atypical Stress Granules, independently of fatty acid synthase inhibition, characterized by high internal mobility and rapid turnover.