Correction: Surveillance-Activated Defenses Block the ROS-Induced Mitochondrial Unfolded Protein Response.
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ABSTRACT:
SUBMITTER: Runkel ED
PROVIDER: S-EPMC5065125 | biostudies-literature | 2016 Oct
REPOSITORIES: biostudies-literature
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Correction: Surveillance-Activated Defenses Block the ROS-Induced Mitochondrial Unfolded Protein Response.
Runkel Eva D ED Liu Shu S Baumeister Ralf R Schulze Ekkehard E
PLoS genetics 20161007 10
[This corrects the article DOI: 10.1371/journal.pgen.1003346.]. ...[more]
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Project description:Disturbance of cellular functions results in the activation of stress-signaling pathways that aim at restoring homeostasis. We performed a genome-wide screen to identify components of the signal transduction of the mitochondrial unfolded protein response (UPR(mt)) to a nuclear chaperone promoter. We used the ROS generating complex I inhibitor paraquat to induce the UPR(mt), and we employed RNAi exposure post-embryonically to allow testing genes whose knockdown results in embryonic lethality. We identified 54 novel regulators of the ROS-induced UPR(mt). Activation of the UPR(mt), but not of other stress-signaling pathways, failed when homeostasis of basic cellular mechanisms such as translation and protein transport were impaired. These mechanisms are monitored by a recently discovered surveillance system that interprets interruption of these processes as pathogen attack and depends on signaling through the JNK-like MAP-kinase KGB-1. Mutation of kgb-1 abrogated the inhibition of ROS-induced UPR(mt), suggesting that surveillance-activated defenses specifically inhibit the UPR(mt) but do not compromise activation of the heat shock response, the UPR of the endoplasmic reticulum, or the SKN-1/Nrf2 mediated response to cytosolic stress. In addition, we identified PIFK-1, the orthologue of the Drosophila PI 4-kinase four wheel drive (FWD), and found that it is the only known factor so far that is essential for the unfolded protein responses of both mitochondria and endoplasmic reticulum. This suggests that both UPRs may share a common membrane associated mechanism.
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Project description:The mitochondrial unfolded protein response (UPRmt ), a cellular protective program that ensures proteostasis in the mitochondria, has recently emerged as a regulatory mechanism for adult stem cell maintenance that is conserved across tissues. Despite the emerging genetic evidence implicating the UPRmt in stem cell maintenance, the underlying molecular mechanism is unknown. While it has been speculated that the UPRmt is activated upon stem cell transition from quiescence to proliferation, the direct evidence is lacking. In this study, we devised three experimental approaches that enable us to monitor quiescent and proliferating hematopoietic stem cells (HSCs) and provided the direct evidence that the UPRmt is activated upon HSC transition from quiescence to proliferation, and more broadly, mitochondrial integrity is actively monitored at the restriction point to ensure metabolic fitness before stem cells are committed to proliferation.
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Project description:Phosphorylation-dependent ubiquitination and degradation of the IFNAR1 chain of the type I interferon (IFN) receptor is regulated by two different pathways, one of which is ligand independent. We report that this ligand-independent pathway is activated by inducers of unfolded protein responses (UPR), including viral infection, and that such activation requires the endoplasmic reticulum-resident protein kinase PERK. Upon viral infection, activation of this pathway promotes phosphorylation-dependent ubiquitination and degradation of IFNAR1, specifically inhibiting type I IFN signaling and antiviral defenses. Knockin of an IFNAR1 mutant insensitive to virus-induced turnover or conditional knockout of PERK prevented IFNAR1 degradation, whether UPR-induced or virus-induced, and restored cellular responses to type I IFN and resistance to viruses. These data suggest that specific activation of the PERK component of UPR can favor viral replication. Interfering with PERK-dependent IFNAR1 degradation could therefore contribute to therapeutic strategies against viral infections.
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Project description:In an accompanying paper, we show that the mitochondrial Unfolded Protein Response or mtUPR is initiated by the activation of transcription of chop through an AP-1 element in the chop promoter. Further, we show that the c/ebp beta gene is similarly activated and CHOP and C/EBP beta subsequently hetero-dimerise to activate transcription of mtUPR responsive genes. Here, we report the discovery of six additional mtUPR responsive genes. We found that these genes encoding mitochondrial proteases YME1L1 and MPP beta, import component Tim17A and enzymes NDUFB2, endonuclease G and thioredoxin 2, all contain a CHOP element in their promoters. In contrast, genes encoding mitochondrial proteins Afg3L2, Paraplegin, Lon and SAM 50, which do not have a CHOP element, were not up-regulated. Conversely, genes with CHOP elements encoding cytosolic proteins were not induced by the accumulation of unfolded proteins in mitochondria. These results indicate that mtUPR responsive genes appear to share a requirement for a CHOP element, but that this is not sufficient for the regulation of the mtUPR. A more detailed analysis of promoters of mtUPR responsive genes revealed at least two additional highly conserved, putative regulatory sites either side of the CHOP element, one a motif of 12 bp which lies 14 bp upstream of the CHOP site and another 9 bp element, 2 bp downstream of the CHOP site. Both of these additional elements are conserved in the promoters of 9 of the ten mtUPR responsive genes we have identified so far, the exception being the Cpn60/10 bidirectional promoter. Mutation of each of these elements substantially reduced the mtUPR responsiveness of the promoters suggesting that these elements coordinately regulate mtUPR.
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Project description:BackgroundMitochondrial dysfunction causes or contributes to a wide variety of pathologies, including neurodegenerative diseases, cancer, metabolic diseases, and aging. Cells actively surveil a number of mitochondrial readouts to ensure that cellular homeostasis is maintained.ResultsIn this article, we characterize the role of the ethanol and stress response element (ESRE) pathway in mitochondrial surveillance and show that it is robustly activated when the concentration of reactive oxygen species (ROS) in the cell increases. While experiments were mostly performed in Caenorhabditis elegans, we observed similar gene activation profile in human cell lines. The linear relationship between ROS and ESRE activation differentiates ESRE from known mitochondrial surveillance pathways, such as the mitochondrial unfolded protein response (UPRmt), which monitor mitochondrial protein import. The ability of the ESRE network to be activated by increased ROS allows the cell to respond to oxidative and reductive stresses. The ESRE network works in tandem with other mitochondrial surveillance mechanisms as well, in a fashion that suggests a partially redundant hierarchy. For example, mutation of the UPRmt pathway results in earlier and more robust activation of the ESRE pathway. Interestingly, full expression of ATFS-1, a key transcription factor for the UPRmt, requires the presence of an ESRE motif in its promoter region.ConclusionThe ESRE pathway responds to mitochondrial damage by monitoring ROS levels. This response is conserved in humans. The ESRE pathway is activated earlier when other mitochondrial surveillance pathways are unavailable during mitochondrial crises, potentially to mitigate stress and restore health. However, the exact mechanisms of pathway activation and crosstalk remain to be elucidated. Ultimately, a better understanding of this network, and its role in the constellation of mitochondrial and cellular stress networks, will improve healthspan.
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Project description:An unfolded protein response (UPR) in addition to oxidative stress and the inflammatory response is known to be activated in age-related ocular disorders, such as macular degeneration, diabetic retinopathy, glaucoma, and cataracts. Therefore, we aimed to investigate whether healthy aged retinas display UPR hallmarks, in order to establish a baseline for the activated UPR markers for age-related ocular diseases. Using western blotting, we determined that the hallmarks of the UPR PERK arm, phosphorylated (p) eIF2a, ATF4, and GADD34, were significantly altered in aged vs. young rat retinas. The cleaved pATF6 (50) and CHOP proteins were dramatically upregulated in the aged rodent retinas, indicating the activation of the ATF6 UPR arm. The UPR activation was associated with a drop in rhodopsin expression and in the NRF2 and HO1 levels, suggesting a decline in the anti-oxidant defense in aged retinas. Moreover, we observed down-regulation of anti-inflammatory IL-10 and IL-13 and upregulation of pro-inflammatory RANTES in the healthy aged retinas, as measured using the Bio-plex assay. Our results suggest that cellular homeostasis in normal aged retinas is compromised, resulting in the concomitant activation of the UPR, oxidative stress, and inflammatory signaling. This knowledge brings us closer to understanding the cellular mechanisms of the age-related retinopathies and ocular disorders characterized by an ongoing UPR, and highlight the UPR signaling molecules that should be validated as potential therapeutic targets.
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Project description:Mitogen-activated protein kinase kinase kinase 7 (MAP3K7), known as TAK1, is an intracellular signaling intermediate of inflammatory responses. However, a series of mouse Tak1 gene deletion analyses have revealed that ablation of TAK1 does not prevent but rather elicits inflammation, which is accompanied by elevation of reactive oxygen species (ROS). This has been considered a consequence of impaired TAK1-dependent maintenance of tissue integrity. Contrary to this view, here we propose that TAK1 inhibition-induced ROS are an active cellular process that targets intracellular bacteria. Intracellular bacterial effector proteins such as Yersinia's outer membrane protein YopJ are known to inhibit TAK1 to circumvent the inflammatory host responses. We found that such TAK1 inhibition induces mitochondrial-derived ROS, which effectively destroys intracellular bacteria. Two cell death-signaling molecules, caspase 8 and RIPK3, cooperatively participate in TAK1 inhibition-induced ROS and blockade of intracellular bacterial growth. Our results reveal a previously unrecognized host defense mechanism, which is initiated by host recognition of pathogen-induced impairment in a host protein, TAK1, but not directly of pathogens.
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Project description:ObjectiveInflammatory bowel diseases (IBDs) feature multiple cellular stress responses, including endoplasmic reticulum (ER) unfolded protein responses (UPRs). UPRs represent autoregulatory pathways that adjust organelle capacity to cellular demand. A similar mechanism, mitochondrial UPR (mtUPR), has been described for mitochondria. ER UPR in intestinal epithelial cells (IECs) contributes to the development of intestinal inflammation, and since mitochondrial alterations and dysfunction are implicated in the pathogenesis of IBDs, the authors characterised mtUPR in the context of intestinal inflammation.MethodsTruncated ornithine transcarbamylase was used to selectively induce mtUPR in a murine IEC line. Dextran sodium sulphate (DSS) was administered to PKR (double-stranded-RNA-activated protein kinase) knockout mice to induce IEC stress in vivo and to test for their susceptibility to DSS-induced colitis. Expression levels of the mitochondrial chaperone chaperonin 60 (CPN60) and PKR were quantified in IECs from patients with IBDs and from murine models of colitis using immunohistochemistry and Western blot analysis.ResultsSelective mtUPR induction by truncated ornithine transcarbamylase transfection triggered the phosphorylation of eukaryotic translation initiation factor (eIF) 2α and cJun through the recruitment of PKR. Using pharmacological inhibitors and small inhibitory RNA, the authors identified mtUPR-induced eIF2α phosphorylation and transcription factor activation (cJun/AP1) as being dependent on the activities of the mitochondrial protease ClpP and the cytoplasmic kinase PKR. Pkr(-/-) mice failed to induce CPN60 in IECs upon DSS treatment at early time points and subsequently showed an almost complete resistance to DSS-induced colitis. Under inflammatory conditions, primary IECs from patients with IBDs and two murine models of colitis exhibited a strong induction of the mtUPR marker protein CPN60 associated with enhanced expression of PKR.ConclusionPKR integrates mtUPR into the disease-relevant ER UPR via eIF2α phosphorylation and AP1 activation. Induction of mtUPR and PKR was observed in IECs from murine models and patients with IBDs. The authors' results indicate that PKR might link mitochondrial stress to intestinal inflammation.
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Project description:The mitochondria of cancer cells are characterized by elevated oxidative stress caused by reactive oxygen species (ROS). Such an elevation in ROS levels contributes to mitochondrial reprogramming and malignant transformation. However, high levels of ROS can cause irreversible damage to proteins, leading to their misfolding, mitochondrial stress, and ultimately cell death. Therefore, mechanisms to overcome mitochondrial stress are needed. The unfolded protein response (UPR) triggered by accumulation of misfolded proteins in the mitochondria (UPR(mt)) has been reported recently. So far, the UPR(mt) has been reported to involve the activation of CHOP and estrogen receptor alpha (ERα). The current study describes a novel role of the mitochondrial deacetylase SirT3 in the UPR(mt). Our data reveal that SirT3 acts to orchestrate two pathways, the antioxidant machinery and mitophagy. Inhibition of SirT3 in cells undergoing proteotoxic stress severely impairs the mitochondrial network and results in cellular death. These observations suggest that SirT3 acts to sort moderately stressed from irreversibly damaged organelles. Since SirT3 is reported to act as a tumor suppressor during transformation, our findings reveal a dual role of SirT3. This novel role of SirT3 in established tumors represents an essential mechanism of adaptation of cancer cells to proteotoxic and mitochondrial stress.
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Project description:Maintenance of the mitochondrial proteome is performed primarily by chaperones, which fold and assemble proteins, and by proteases, which degrade excess damaged proteins. Upon various types of mitochondrial stress, triggered genetically or pharmacologically, dysfunction of the proteome is sensed and communicated to the nucleus, where an extensive transcriptional program, aimed to repair the damage, is activated. This feedback loop, termed the mitochondrial unfolded protein response (UPR(mt)), synchronizes the activity of the mitochondrial and nuclear genomes and as such ensures the quality of the mitochondrial proteome. Here we review the recent advances in the UPR(mt) field and discuss its induction, signaling, communication with the other mitochondrial and major cellular regulatory pathways, as well as its potential implications on health and lifespan.
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