Showing papers on "Integrated stress response published in 2019"
TL;DR: GDF15 expression is regulated by the integrated stress response and is induced in selected tissues in mice in these settings, and it is demonstrated that pharmacological GDF15 administration to mice can trigger conditioned taste aversion, suggesting that GDF 15 may induce an aversive response to nutritional stress.
244 citations
TL;DR: The evidence indicates that FGF21 is a local and systemic messenger of mtDNA stress in mice and humans with mitochondrial disease, and drives weight loss and glucose preference, and modifies metabolism and respiratory chain deficiency in a specific hippocampal brain region.
143 citations
TL;DR: It is demonstrated here that ISRIB inhibits low-level ISR activity, but does not affect strong ISR signaling, and the effects of pharmacological activation of eIF2B are tuned by P-eIF2α concentration, which provides a plausible mechanism of howISRIB counteracts toxic chronic ISRactivity, without disturbing the cytoprotective effects of a strong acute ISR.
Abstract: Activation of the integrated stress response (ISR) by a variety of stresses triggers phosphorylation of the α-subunit of translation initiation factor eIF2. P-eIF2α inhibits eIF2B, the guanine nucleotide exchange factor that recycles inactive eIF2•GDP to active eIF2•GTP. eIF2 phosphorylation thereby represses translation. Persistent activation of the ISR has been linked to the development of several neurological disorders, and modulation of the ISR promises new therapeutic strategies. Recently, a small-molecule ISR inhibitor (ISRIB) was identified that rescues translation in the presence of P-eIF2α by facilitating the assembly of more active eIF2B. ISRIB enhances cognitive memory processes and has therapeutic effects in brain-injured mice without displaying overt side effects. While using ISRIB to investigate the ISR in picornavirus-infected cells, we observed that ISRIB rescued translation early in infection when P-eIF2α levels were low, but not late in infection when P-eIF2α levels were high. By treating cells with varying concentrations of poly(I:C) or arsenite to induce the ISR, we provide additional proof that ISRIB is unable to inhibit the ISR when intracellular P-eIF2α concentrations exceed a critical threshold level. Together, our data demonstrate that the effects of pharmacological activation of eIF2B are tuned by P-eIF2α concentration. Thus, ISRIB can mitigate undesirable outcomes of low-level ISR activation that may manifest neurological disease but leaves the cytoprotective effects of acute ISR activation intact. The insensitivity of cells to ISRIB during acute ISR may explain why ISRIB does not cause overt toxic side effects in vivo.
133 citations
TL;DR: It is proposed that the ribosomal P-stalk could link GCN2 activation to translational stress, leading to initiation of the integrated stress response (ISR).
Abstract: Cells dynamically adjust their protein translation profile to maintain homeostasis in changing environments. During nutrient stress, the kinase general control nonderepressible 2 (GCN2) phosphorylates translation initiation factor eIF2α, initiating the integrated stress response (ISR). To examine the mechanism of GCN2 activation, we have reconstituted this process in vitro, using purified components. We find that recombinant human GCN2 is potently stimulated by ribosomes and, to a lesser extent, by tRNA. Hydrogen/deuterium exchange–mass spectrometry (HDX-MS) mapped GCN2–ribosome interactions to domain II of the uL10 subunit of the ribosomal P-stalk. Using recombinant, purified P-stalk, we showed that this domain of uL10 is the principal component of binding to GCN2; however, the conserved 14-residue C-terminal tails (CTTs) in the P1 and P2 P-stalk proteins are also essential for GCN2 activation. The HisRS-like and kinase domains of GCN2 show conformational changes upon binding recombinant P-stalk complex. Given that the ribosomal P-stalk stimulates the GTPase activity of elongation factors during translation, we propose that the P-stalk could link GCN2 activation to translational stress, leading to initiation of ISR.
114 citations
TL;DR: During recovery from stress, it is shown that mRNAs that were within SGs and PBs are translated and degraded at similar rates as their cytosolic counterparts.
106 citations
TL;DR: It is shown that introduction of a human VWM mutation into mice leads to persistent ISR induction in the central nervous system and long-term treatment with a small molecule eIF2B activator, 2BAct, prevents all measures of pathology and normalizes the transcriptome and proteome of VWM mice.
Abstract: The integrated stress response (ISR) attenuates the rate of protein synthesis while inducing expression of stress proteins in cells. Various insults activate kinases that phosphorylate the GTPase eIF2 leading to inhibition of its exchange factor eIF2B. Vanishing White Matter (VWM) is a neurological disease caused by eIF2B mutations that, like phosphorylated eIF2, reduce its activity. We show that introduction of a human VWM mutation into mice leads to persistent ISR induction in the central nervous system. ISR activation precedes myelin loss and development of motor deficits. Remarkably, long-term treatment with a small molecule eIF2B activator, 2BAct, prevents all measures of pathology and normalizes the transcriptome and proteome of VWM mice. 2BAct stimulates the remaining activity of mutant eIF2B complex in vivo, abrogating the maladaptive stress response. Thus, 2BAct-like molecules may provide a promising therapeutic approach for VWM and provide relief from chronic ISR induction in a variety of disease contexts.
105 citations
TL;DR: The integrated stress response—a signaling network that maintains proteostasis—was activated in the brains of DS mice and individuals with DS, reprogramming translation and reversed the changes in translation and inhibitory synaptic transmission and rescued the synaptic plasticity and long-term memory deficits in DS mice.
Abstract: Down syndrome (DS) is the most common genetic cause of intellectual disability. Protein homeostasis is essential for normal brain function, but little is known about its role in DS pathophysiology. In this study, we found that the integrated stress response (ISR)-a signaling network that maintains proteostasis-was activated in the brains of DS mice and individuals with DS, reprogramming translation. Genetic and pharmacological suppression of the ISR, by inhibiting the ISR-inducing double-stranded RNA-activated protein kinase or boosting the function of the eukaryotic translation initiation factor eIF2-eIF2B complex, reversed the changes in translation and inhibitory synaptic transmission and rescued the synaptic plasticity and long-term memory deficits in DS mice. Thus, the ISR plays a crucial role in DS, which suggests that tuning of the ISR may provide a promising therapeutic intervention.
96 citations
TL;DR: The authors present structures of the eIF2:eIF2B complex with and without phosphorylation, shedding light on how eIF1 phosphorylated regulates translation.
Abstract: Protein synthesis in eukaryotes is controlled by signals and stresses via a common pathway, called the integrated stress response (ISR). Phosphorylation of the translation initiation factor eIF2 alpha at a conserved serine residue mediates translational control at the ISR core. To provide insight into the mechanism of translational control we have determined the structures of eIF2 both in phosphorylated and unphosphorylated forms bound with its nucleotide exchange factor eIF2B by electron cryomicroscopy. The structures reveal that eIF2 undergoes large rearrangements to promote binding of eIF2α to the regulatory core of eIF2B comprised of the eIF2B alpha, beta and delta subunits. Only minor differences are observed between eIF2 and eIF2αP binding to eIF2B, suggesting that the higher affinity of eIF2αP for eIF2B drives translational control. We present a model for controlled nucleotide exchange and initiator tRNA binding to the eIF2/eIF2B complex.
92 citations
01 Jan 2019
TL;DR: The authors demonstrate that the mitochondrial pyruvate carrier (MPC), a critical metabolic conduit linking cytosolic and mitochondrial metabolism, is transcriptionally regulated by AR and that MPC inhibition suppresses tumour growth in hormone-responsive and castrate-resistant conditions.
Abstract: Specific metabolic underpinnings of androgen receptor (AR)-driven growth in prostate adenocarcinoma (PCa) are largely undefined, hindering the development of strategies to leverage the metabolic dependencies of this disease when hormonal manipulations fail. Here we show that the mitochondrial pyruvate carrier (MPC), a critical metabolic conduit linking cytosolic and mitochondrial metabolism, is transcriptionally regulated by AR. Experimental MPC inhibition restricts proliferation and metabolic outputs of the citric acid cycle (TCA) including lipogenesis and oxidative phosphorylation in AR-driven PCa models. Mechanistically, metabolic disruption resulting from MPC inhibition activates the eIF2α/ATF4 integrated stress response (ISR). ISR signaling prevents cell cycle progression while coordinating salvage efforts, chiefly enhanced glutamine assimilation into the TCA, to regain metabolic homeostasis. We confirm that MPC function is operant in PCa tumors in-vivo using isotopomeric metabolic flux analysis. In turn, we apply a clinically viable small molecule targeting the MPC, MSDC0160, to pre-clinical PCa models and find that MPC inhibition suppresses tumor growth in hormone-responsive and castrate-resistant conditions. Collectively, our findings characterize the MPC as a tractable therapeutic target in AR-driven prostate tumors.
90 citations
TL;DR: A mammalian CHO cell-based CRISPR-Cas9 mutagenesis screen for genes that contribute to ISR activation by amino acid starvation supports a model whereby lack of a cognate charged tRNA exposes a latent capacity of the ribosome P-stalk to activate GCN2 in cells and helps explain the emerging link between ribosomes stalling and IsR activation.
Abstract: The eukaryotic translation initiation factor 2α (eIF2α) kinase GCN2 is activated by amino acid starvation to elicit a rectifying physiological program known as the Integrated Stress Response (ISR). A role for uncharged tRNAs as activating ligands of yeast GCN2 is supported experimentally. However, mouse GCN2 activation has recently been observed in circumstances associated with ribosome stalling with no global increase in uncharged tRNAs. We report on a mammalian CHO cell-based CRISPR-Cas9 mutagenesis screen for genes that contribute to ISR activation by amino acid starvation. Disruption of genes encoding components of the ribosome P-stalk, uL10 and P1, selectively attenuated GCN2-mediated ISR activation by amino acid starvation or interference with tRNA charging without affecting the endoplasmic reticulum unfolded protein stress-induced ISR, mediated by the related eIF2α kinase PERK. Wildtype ribosomes isolated from CHO cells, but not those with P-stalk lesions, stimulated GCN2-dependent eIF2α phosphorylation in vitro. These observations support a model whereby lack of a cognate charged tRNA exposes a latent capacity of the ribosome P-stalk to activate GCN2 in cells and help explain the emerging link between ribosome stalling and ISR activation.
89 citations
TL;DR: Cryo–electron microscopy structures of e IF2 bound to eIF2B in the dephosphorylated state reveal that the eIF 2B decamer is a static platform upon which one or two flexible eIF1 trimers bind and align with eIF3B’s bipartite catalytic centers to catalyze nucleotide exchange.
Abstract: The integrated stress response (ISR) tunes the rate of protein synthesis. Control is exerted by phosphorylation of the general translation initiation factor eIF2. eIF2 is a guanosine triphosphatase that becomes activated by eIF2B, a two-fold symmetric and heterodecameric complex that functions as eIF2’s dedicated nucleotide exchange factor. Phosphorylation converts eIF2 from a substrate into an inhibitor of eIF2B. We report cryo–electron microscopy structures of eIF2 bound to eIF2B in the dephosphorylated state. The structures reveal that the eIF2B decamer is a static platform upon which one or two flexible eIF2 trimers bind and align with eIF2B’s bipartite catalytic centers to catalyze nucleotide exchange. Phosphorylation refolds eIF2α, allowing it to contact eIF2B at a different interface and, we surmise, thereby sequestering it into a nonproductive complex.
TL;DR: Cryo–electron microscopic and crystallographic structures are determined that explain how phosphorylated eIF2 dominantly inhibits the nucleotide exchange activity of eIF3B, a core event in the integrated stress response.
Abstract: A core event in the integrated stress response, an adaptive pathway common to all eukaryotic cells in response to various stress stimuli, is the phosphorylation of eukaryotic translation initiation factor 2 (eIF2). Normally, unphosphorylated eIF2 transfers the methionylated initiator tRNA to the ribosome in a guanosine 5'-triphosphate-dependent manner. By contrast, phosphorylated eIF2 inhibits its specific guanine nucleotide exchange factor, eIF2B. To elucidate how the eIF2 phosphorylation status regulates the eIF2B activity, we determined cryo-electron microscopic and crystallographic structures of eIF2B in complex with unphosphorylated or phosphorylated eIF2. The unphosphorylated and phosphorylated forms of eIF2 bind to eIF2B in completely different manners: the nucleotide exchange-active and -inactive modes, respectively. These structures explain how phosphorylated eIF2 dominantly inhibits the nucleotide exchange activity of eIF2B.
TL;DR: Pharmacological inhibition of GCN2 phenocopies eIF2B5 depletion and has therapeutic efficacy in tumour organoids demonstrates that a negative MYC–eIF2α feedback loop constitutes a targetable vulnerability of colorectal tumours.
Abstract: Tumours depend on altered rates of protein synthesis for growth and survival, which suggests that mechanisms controlling mRNA translation may be exploitable for therapy. Here, we show that loss of APC, which occurs almost universally in colorectal tumours, strongly enhances the dependence on the translation initiation factor eIF2B5. Depletion of eIF2B5 induces an integrated stress response and enhances translation of MYC via an internal ribosomal entry site. This perturbs cellular amino acid and nucleotide pools, strains energy resources and causes MYC-dependent apoptosis. eIF2B5 limits MYC expression and prevents apoptosis in APC-deficient murine and patient-derived organoids and in APC-deficient murine intestinal epithelia in vivo. Conversely, the high MYC levels present in APC-deficient cells induce phosphorylation of eIF2α via the kinases GCN2 and PKR. Pharmacological inhibition of GCN2 phenocopies eIF2B5 depletion and has therapeutic efficacy in tumour organoids, which demonstrates that a negative MYC-eIF2α feedback loop constitutes a targetable vulnerability of colorectal tumours.
TL;DR: Overall, CHCHD10S55L mice recapitulate crucial aspects of human disease and reveal a novel toxic gain-of-function mechanism through maladaptive mtISR and metabolic dysregulation.
Abstract: Mutations in coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10), a mitochondrial protein of unknown function, cause a disease spectrum with clinical features of motor neuron disease, dementia, myopathy and cardiomyopathy. To investigate the pathogenic mechanisms of CHCHD10, we generated mutant knock-in mice harboring the mouse-equivalent of a disease-associated human S59L mutation, S55L in the endogenous mouse gene. CHCHD10S55L mice develop progressive motor deficits, myopathy, cardiomyopathy and accelerated mortality. Critically, CHCHD10 accumulates in aggregates with its paralog CHCHD2 specifically in affected tissues of CHCHD10S55L mice, leading to aberrant organelle morphology and function. Aggregates induce a potent mitochondrial integrated stress response (mtISR) through mTORC1 activation, with elevation of stress-induced transcription factors, secretion of myokines, upregulated serine and one-carbon metabolism, and downregulation of respiratory chain enzymes. Conversely, CHCHD10 ablation does not induce disease pathology or activate the mtISR, indicating that CHCHD10S55L-dependent disease pathology is not caused by loss-of-function. Overall, CHCHD10S55L mice recapitulate crucial aspects of human disease and reveal a novel toxic gain-of-function mechanism through maladaptive mtISR and metabolic dysregulation.
TL;DR: In this article, the authors showed that the stress response is suppressed during FMDV infection by using a chimeric recombinant encephalomyocarditis virus (EMCV), in which they functionally replaced the endogenous stress response antagonist by a leader protease (Lpro) or 3Cpro.
Abstract: Like other viruses, the picornavirus foot-and-mouth disease virus (FMDV; genus Aphthovirus), one of the most notorious pathogens in the global livestock industry, needs to navigate antiviral host responses to establish an infection. There is substantial insight into how FMDV suppresses the type I interferon (IFN) response, but it is largely unknown whether and how FMDV modulates the integrated stress response. Here, we show that the stress response is suppressed during FMDV infection. Using a chimeric recombinant encephalomyocarditis virus (EMCV), in which we functionally replaced the endogenous stress response antagonist by FMDV leader protease (Lpro) or 3Cpro, we demonstrate an essential role for Lpro in suppressing stress granule (SG) formation. Consistently, infection with a recombinant FMDV lacking Lpro resulted in SG formation. Additionally, we show that Lpro cleaves the known SG scaffold proteins G3BP1 and G3BP2 but not TIA-1. We demonstrate that the closely related equine rhinitis A virus (ERAV) Lpro also cleaves G3BP1 and G3BP2 and also suppresses SG formation, indicating that these abilities are conserved among aphthoviruses. Neither FMDV nor ERAV Lpro interfered with phosphorylation of RNA-dependent protein kinase (PKR) or eIF2α, indicating that Lpro does not affect SG formation by inhibiting the PKR-triggered signaling cascade. Taken together, our data suggest that aphthoviruses actively target scaffolding proteins G3BP1 and G3BP2 and antagonize SG formation to modulate the integrated stress response.IMPORTANCE The picornavirus foot-and-mouth disease virus (FMDV) is a notorious animal pathogen that puts a major economic burden on the global livestock industry. Outbreaks have significant consequences for animal health and product safety. Like many other viruses, FMDV must manipulate antiviral host responses to establish infection. Upon infection, viral double-stranded RNA (dsRNA) is detected, which results in the activation of the RNA-dependent protein kinase (PKR)-mediated stress response, leading to a stop in cellular and viral translation and the formation of stress granules (SG), which are thought to have antiviral properties. Here, we show that FMDV can suppress SG formation via its leader protease (Lpro). Simultaneously, we observed that Lpro can cleave the SG scaffolding proteins G3BP1 and G3BP2. Understanding the molecular mechanisms of the antiviral host response evasion strategies of FMDV may help to develop countermeasures to control FMDV infections in the future.
TL;DR: Various factors that may facilitateGCN2 activation are reviewed, including recent research showing that the P-stalk complex, a ribosome-associated heteropentameric protein complex, is a potent activator of GCN2.
Abstract: Cells must be able to sense and adapt to their surroundings to thrive in a dynamic environment. Key to adapting to a low nutrient environment is the Integrated Stress Response (ISR), a short-lived pathway that allows cells to either regain cellular homeostasis or facilitate apoptosis during periods of stress. Central to the ISR is the protein kinase General Control Non-depressible 2 (GCN2), which is responsible for sensing starvation. Upon amino acid deficiency, GCN2 is activated and initiates the ISR by phosphorylating the translation initiation factor eIF2α, stalling protein translation, and activating the transcription factor ATF4, which in turn up-regulates autophagy and biosynthesis pathways. A key outstanding question is how GCN2 is activated from an autoinhibited state. Until recently, a model of activation focussed on the increase of deacylated tRNA associated with amino acid starvation, with deacylated tRNA binding directly to GCN2 and releasing autoinhibition. However, in vivo experiments have pointed towards an alternative, deacylated-tRNA-independent mechanism of activation. Here, we review the various factors that may facilitate GCN2 activation, including recent research showing that the P-stalk complex, a ribosome-associated heteropentameric protein complex, is a potent activator of GCN2.
TL;DR: It is shown that cellular stress responses—the p53 transcriptional response and the integrated stress response (ISR)—are the most salient causes of spontaneous entry into the slow-cycling state and that cells’ ability to enter theSlow-Cycling state enhances their survival in stressful conditions.
Abstract: Slow-cycling subpopulations exist in bacteria, yeast, and mammalian systems. In the case of cancer, slow-cycling subpopulations have been proposed to give rise to drug resistance. However, the origin of slow-cycling human cells is poorly studied, in large part due to lack of markers to identify these rare cells. Slow-cycling cells pass through a noncycling period marked by low CDK2 activity and high p21 levels. Here, we use this knowledge to isolate these naturally slow-cycling cells from a heterogeneous population and perform RNA sequencing to delineate the transcriptome underlying the slow-cycling state. We show that cellular stress responses—the p53 transcriptional response and the integrated stress response (ISR)—are the most salient causes of spontaneous entry into the slow-cycling state. Finally, we show that cells’ ability to enter the slow-cycling state enhances their survival in stressful conditions. Thus, the slow-cycling state is hardwired to stress responses to promote cellular survival in unpredictable environments.
TL;DR: Results presented from the adoptive transfer of encephalitogenic T cells between wild-type and GADD34 mutant mice indicate that the beneficial effects of Sephin1 are mediated through a direct protective effect on the CNS, and suggest that a neuroprotective treatment based on the enhancement of the integrated stress response would likely have significant therapeutic value for multiple sclerosis patients.
Abstract: Multiple sclerosis is a chronic autoimmune demyelinating disorder of the CNS. Immune-mediated oligodendrocyte cell loss contributes to multiple sclerosis pathogenesis, such that oligodendrocyte-protective strategies represent a promising therapeutic approach. The integrated stress response, which is an innate cellular protective signalling pathway, reduces the cytotoxic impact of inflammation on oligodendrocytes. This response is initiated by phosphorylation of eIF2α to diminish global protein translation and selectively allow for the synthesis of protective proteins. The integrated stress response is terminated by dephosphorylation of eIF2α. The small molecule Sephin1 inhibits eIF2α dephosphorylation, thereby prolonging the protective response. Herein, we tested the effectiveness of Sephin1 in shielding oligodendrocytes against inflammatory stress. We confirmed that Sephin1 prolonged eIF2α phosphorylation in stressed primary oligodendrocyte cultures. Moreover, by using a mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis, we demonstrated that Sephin1 delayed the onset of clinical symptoms, which correlated with a prolonged integrated stress response, reduced oligodendrocyte and axon loss, as well as diminished T cell presence in the CNS. Sephin1 is reportedly a selective inhibitor of GADD34 (PPP1R15A), which is a stress-induced regulatory subunit of protein phosphatase 1 complex that dephosphorylates eIF2α. Consistent with this possibility, GADD34 mutant mice presented with a similar ameliorated experimental autoimmune encephalomyelitis phenotype as Sephin1-treated mice, and Sephin1 did not provide additional therapeutic benefit to the GADD34 mutant animals. Results presented from the adoptive transfer of encephalitogenic T cells between wild-type and GADD34 mutant mice further indicate that the beneficial effects of Sephin1 are mediated through a direct protective effect on the CNS. Of particular therapeutic relevance, Sephin1 provided additive therapeutic benefit when combined with the first line multiple sclerosis drug, interferon β. Together, our results suggest that a neuroprotective treatment based on the enhancement of the integrated stress response would likely have significant therapeutic value for multiple sclerosis patients.
TL;DR: HRI-ISR has emerged as a potential therapeutic target for hemoglobinopathies through two key signaling pathways, ISR and mTORC1, coordinated by HRI to circumvent ineffective erythropoiesis.
TL;DR: Endoplasmic reticulum controls mitochondrial clearance by activating eIF2α-LONP1 signaling, contributing to an amplified oxidative stress response that triggers robust inflammasome activation and interleukin-1β secretion by dietary fats.
TL;DR: It is shown that activation of the PKR/eIF2α-P pathway exhibits anti-tumor effects in HER2+ cancer and is required for the response to Trastuzumab.
Abstract: Trastuzumab is integral to HER2+ cancer treatment, but its therapeutic index is narrowed by the development of resistance. Phosphorylation of the translation initiation factor eIF2α (eIF2α-P) is the nodal point of the integrated stress response, which promotes survival or death in a context-dependent manner. Here, we show an anti-tumor function of the protein kinase PKR and its substrate eIF2α in a mouse HER2+ breast cancer model. The anti-tumor function depends on the transcription factor ATF4, which upregulates the CDK inhibitor P21CIP1 and activates JNK1/2. The PKR/eIF2α-P arm is induced by Trastuzumab in sensitive but not resistant HER2+ breast tumors. Also, eIF2α-P stimulation by the phosphatase inhibitor SAL003 substantially increases Trastuzumab potency in resistant HER2+ breast and gastric tumors. Increased eIF2α-P prognosticates a better response of HER2+ metastatic breast cancer patients to Trastuzumab therapy. Hence, the PKR/eIF2α-P arm antagonizes HER2 tumorigenesis whereas its pharmacological stimulation improves the efficacy of Trastuzumab therapy.
TL;DR: The precis presented here provides a comprehension on the multifarious actions of NO and H2S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their “Janus bifrons” effect in IS milieu together with plausible therapeutic implications.
Abstract: Nitric oxide (NO) and hydrogen sulfide (H2S) are the key gasotransmitters with an imperious role in the maintenance of cerebrovascular homeostasis. A decline in their levels contributes to endothelial dysfunction that portends ischemic stroke (IS) or cerebral ischemia/reperfusion (CI/R). Nevertheless, their exorbitant production during CI/R is associated with exacerbation of cerebrovascular injury in the post-stroke epoch. NO-producing nitric oxide synthases are implicated in IS pathology and their activity is regulated, inter alia, by various post-translational modifications and chromatin-based mechanisms. These account for heterogeneous alterations in NO production in a disease setting like IS. Interestingly, NO per se has been posited as an endogenous epigenetic modulator. Further, there is compelling evidence for an ingenious crosstalk between NO and H2S in effecting the canonical (direct) and non-canonical (off-target collateral) functions. In this regard, NO-mediated S-nitrosylation and H2S-mediated S-sulfhydration of specific reactive thiols in an expanding array of target proteins are the principal modalities mediating the all-pervasive influence of NO and H2S on cell fate in an ischemic brain. An integrated stress response subsuming unfolded protein response and autophagy to cellular stressors like endoplasmic reticulum stress, in part, is entrenched in such signaling modalities that substantiate the role of NO and H2S in priming the cells for stress response. The precis presented here provides a comprehension on the multifarious actions of NO and H2S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their "Janus bifrons" effect in IS milieu together with plausible therapeutic implications.
TL;DR: This work elucidates the mechanism of action of MGO in the production of pain at pathophysiologically relevant concentrations and suggests a new pharmacological avenue for the treatment of diabetic and other types of M GO-driven neuropathic pain.
Abstract: Methylglyoxal (MGO) is a reactive glycolytic metabolite associated with painful diabetic neuropathy at plasma concentrations between 500 nM and 5 μM. The mechanisms through which MGO causes neuropathic pain at these pathological concentrations are not known. Because MGO has been linked to diabetic neuropathic pain, which is prevalent and poorly treated, insight into this unsolved biomedical problem could lead to much needed therapeutics. Our experiments provide compelling evidence that ∼1-μM concentrations of MGO activate the integrated stress response (ISR) in IB4-positive nociceptors in the dorsal root ganglion (DRG) of mice in vivo and in vitro. Blocking the integrated stress response with a specific inhibitor (ISRIB) strongly attenuates and reverses MGO-evoked pain. Moreover, ISRIB reduces neuropathic pain induced by diabetes in both mice and rats. Our work elucidates the mechanism of action of MGO in the production of pain at pathophysiologically relevant concentrations and suggests a new pharmacological avenue for the treatment of diabetic and other types of MGO-driven neuropathic pain.
TL;DR: Insulin via ERK activation increases the expression of MSR genes in vitro as well as in the hypothalamus of streptozotocin-treated mice, and regulation propagates mitochondrial function by controlling mitochondrial proteostasis and preventing excessive autophagy under serum deprivation.
Abstract: Objective Insulin action in the brain controls metabolism and brain function, which is linked to proper mitochondrial function. Conversely, brain insulin resistance associates with mitochondrial stress and metabolic and neurodegenerative diseases. In the present study, we aimed to decipher the impact of hypothalamic insulin action on mitochondrial stress responses, function and metabolism. Methods To investigate the crosstalk of insulin action and mitochondrial stress responses (MSR), namely the mitochondrial unfolded protein response (UPRmt) and integrated stress response (ISR), qPCR, western blotting, and mitochondrial activity assays were performed. These methods were used to analyze the hypothalamic cell line CLU183 treated with insulin in the presence or absence of the insulin receptor as well as in mice fed a high fat diet (HFD) for three days and STZ-treated mice without or with insulin therapy. Intranasal insulin treatment was used to investigate the effect of acute brain insulin action on metabolism and mitochondrial stress responses. Results Acute HFD feeding reduces hypothalamic mitochondrial stress responsive gene expression of Atf4, Chop, Hsp60, Hsp10, ClpP, and Lonp1 in C57BL/6N mice. We show that insulin via ERK activation increases the expression of MSR genes in vitro as well as in the hypothalamus of streptozotocin-treated mice. This regulation propagates mitochondrial function by controlling mitochondrial proteostasis and prevents excessive autophagy under serum deprivation. Finally, short-term intranasal insulin treatment activates MSR gene expression in the hypothalamus of HFD-fed C57BL/6N mice and reduces food intake and body weight development. Conclusions We define hypothalamic insulin action as a novel master regulator of MSR, ensuring proper mitochondrial function by controlling mitochondrial proteostasis and regulating metabolism.
TL;DR: Current recognized contributions of the mitochondria to AD are reviewed, with an emphasis on their potential contribution to brain stress responses.
Abstract: Alzheimer’s disease (AD) patients display widespread mitochondrial defects. Brain hypometabolism occurs alongside mitochondrial defects, and correlates well with cognitive decline. Numerous theories attempt to explain AD mitochondrial dysfunction. Groups propose AD mitochondrial defects stem from: (1) mitochondrial-nuclear DNA interactions/variations; (2) amyloid and neurofibrillary tangle interactions with mitochondria, and (3) mitochondrial quality control defects and oxidative damage. Cells respond to mitochondrial dysfunction through numerous retrograde responses including the Integrated Stress Response (ISR) involving eukaryotic initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP). AD brains activate the ISR and we hypothesize mitochondrial defects may contribute to ISR activation. Here we review current recognized contributions of the mitochondria to AD, with an emphasis on their potential contribution to brain stress responses.
TL;DR: A critical role for ISR is reported in regulating the mammalian circadian clock and a potential link between dysregulated ISR and circadian dysfunction in brain diseases is provided.
TL;DR: Murine norovirus infection stalls host protein translation and the production of antiviral and proinflammatory cytokines, but MNV regulates the ISR by activating and recruiting key ISR host factors and promotes immune evasion of the virus by altering protein translation.
Abstract: The integrated stress response (ISR) is a cellular response system activated upon different types of stresses, including viral infection, to restore cellular homeostasis. However, many viruses manipulate this response for their own advantage. In this study, we investigated the association between murine norovirus (MNV) infection and the ISR and demonstrate that MNV regulates the ISR by activating and recruiting key ISR host factors. We observed that during MNV infection, there is a progressive increase in phosphorylated eukaryotic initiation factor 2α (p-eIF2α), resulting in the suppression of host translation, and yet MNV translation still progresses under these conditions. Interestingly, the shutoff of host translation also impacts the translation of key signaling cytokines such as beta interferon, interleukin-6, and tumor necrosis factor alpha. Our subsequent analyses revealed that the phosphorylation of eIF2α was mediated via protein kinase R (PKR), but further investigation revealed that PKR activation, phosphorylation of eIF2α, and translational arrest were uncoupled during infection. We further observed that stress granules (SGs) are not induced during MNV infection and that MNV can restrict SG nucleation and formation. We observed that MNV recruited the key SG nucleating protein G3BP1 to its replication sites and intriguingly the silencing of G3BP1 negatively impacts MNV replication. Thus, it appears that MNV utilizes G3BP1 to enhance replication but equally to prevent SG formation, suggesting an anti-MNV property of SGs. Overall, this study highlights MNV manipulation of SGs, PKR, and translational control to regulate cytokine translation and to promote viral replication.IMPORTANCE Viruses hijack host machinery and regulate cellular homeostasis to actively replicate their genome, propagate, and cause disease. In retaliation, cells possess various defense mechanisms to detect, destroy, and clear infecting viruses, as well as signal to neighboring cells to inform them of the imminent threat. In this study, we demonstrate that the murine norovirus (MNV) infection stalls host protein translation and the production of antiviral and proinflammatory cytokines. However, virus replication and protein translation still ensue. We show that MNV further prevents the formation of cytoplasmic RNA granules, called stress granules (SGs), by recruiting the key host protein G3BP1 to the MNV replication complex, a recruitment that is crucial to establishing and maintaining virus replication. Thus, MNV promotes immune evasion of the virus by altering protein translation. Together, this evasion strategy delays innate immune responses to MNV infection and accelerates disease onset.
TL;DR: The findings reveal a novel mechanism for paclitaxel resistance and suggest that targeting EIF2A combined with ISR agonist may be a potential treatment regimen to overcome drug resistance for breast cancer.
Abstract: The integrated stress response (ISR) is critical for cancer cell survival during stress stimuli and has been implicated in the resistance to cancer therapeutics, in which the mechanism, however, is poorly understood. Here, we showed that paclitaxel, the major chemotherapy drug for breast cancer, induced ISR and phosphorylated ser51 residue of EIF2S1 by EIF2AK3 and EIF2AK4. When exposed to paclitaxel, cancer cells activated the EIF2AK3/EIF2AK4-pEIF2S1-ATF4 axis and maintained redox homoeostasis by inducing expression of the major antioxidant enzymes HMOX1, SHMT2 and SLC7A11. Paclitaxel-mediated cell death was significantly increased following loss of ISR or ATF4 expression. This sensitizing effect could be partially rescued by Trolox, a ROS scavenger. We demonstrated that the alternative initiation factor EIF2A was essential for cancer cell survival after paclitaxel-mediated ISR both in vitro and in vivo. Moreover, patients with breast cancer exhibited higher ISR after chemotherapy, and the elevated mRNA levels of HMOX1, SHMT2 and EIF2A were correlated with poor prognosis. Collectively, our findings reveal a novel mechanism for paclitaxel resistance and suggest that targeting EIF2A combined with ISR agonist may be a potential treatment regimen to overcome drug resistance for breast cancer.
TL;DR: It is proposed that, in human cells, oxidative stress triggers tRNA retrograde transport, which is rapid, reversible, and selective for certain tRNA species, mostly with shorter 3′ ends, and is part of the cellular response to oxidative stress.
TL;DR: Results suggest ONC212 as a novel therapeutic agent for AML as well as potential eradication of AML initiating cells in an NSG PDX model and was highly synergistic in combination with ABT-199.
Abstract: Imipridones constitute a novel class of antitumor agents. Here, we report that a second-generation imipridone, ONC212, possesses highly increased antitumor activity compared to the first-generation compound ONC201. In vitro studies using human acute myeloid leukemia (AML) cell lines, primary AML, and normal bone marrow (BM) samples demonstrate that ONC212 exerts prominent apoptogenic effects in AML, but not in normal BM cells, suggesting potential clinical utility. Imipridones putatively engage G protein-coupled receptors (GPCRs) and/or trigger an integrated stress response in hematopoietic tumor cells. Comprehensive GPCR screening identified ONC212 as activator of an orphan GPCR GPR132 and Gαq signaling, which functions as a tumor suppressor. Heterozygous knock-out of GPR132 decreased the antileukemic effects of ONC212. ONC212 induced apoptogenic effects through the induction of an integrated stress response, and reduced MCL-1 expression, a known resistance factor for BCL-2 inhibition by ABT-199. Oral administration of ONC212 inhibited AML growth in vivo and improved overall survival in xenografted mice. Moreover, ONC212 abrogated the engraftment capacity of patient-derived AML cells in an NSG PDX model, suggesting potential eradication of AML initiating cells, and was highly synergistic in combination with ABT-199. Collectively, our results suggest ONC212 as a novel therapeutic agent for AML.