bims-unfpre 2021-11-28 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2021–11–28
eleven papers selected by
Susan Logue, University of Manitoba

The IRE1/XBP1 signaling axis promotes skeletal muscle regeneration through a cell non-autonomous mechanism.
Crosstalk Between ER Stress, Autophagy and Inflammation.
Kinetic monitoring of neuronal stress response to proteostasis dysfunction.
Silencing of the ER and Integrative Stress Responses in the Liver of Mice with Error-Prone Translation.
IRE1-Mediated Unfolded Protein Response Promotes the Replication of Tick-Borne Flaviviruses in a Virus and Cell-Type Dependent Manner.
Endoplasmic reticulum stress increases LECT2 expression via ATF4.
The Unfolded Protein Response as a Guardian of the Secretory Pathway.
The ER Stress Sensor IRE1α Regulates the UV DNA Repair Response Through Control of Intracellular Calcium Homeostasis.
The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis.
Macrophage-Derived Immunoglobulin M Inhibits Inflammatory Responses via Modulating Endoplasmic Reticulum Stress.
Inhibition of USP14 influences alphaherpesvirus proliferation by degrading viral VP16 protein via ER stress-triggered selective autophagy.

Elife. 2021 Nov 23. pii: e73215. [Epub ahead of print]10

The IRE1/XBP1 signaling axis promotes skeletal muscle regeneration through a cell non-autonomous mechanism.

Anirban Roy, Meiricris Tomaz da Silva, Raksha Bhat, Kyle R Bohnert, Takao Iwawaki, Ashok Kumar.

  Skeletal muscle regeneration is regulated by coordinated activation of multiple signaling pathways activated in both injured myofibers and satellite cells. The unfolded protein response (UPR) is a major mechanism that detects and alleviates protein-folding stresses in ER. However, the role of individual arms of the UPR in skeletal muscle regeneration remain less understood. In the present study, we demonstrate that IRE1α (also known as ERN1) and its downstream target, XBP1, are activated in skeletal muscle of mice upon injury. Myofiber-specific ablation of IRE1 or XBP1 in mice diminishes skeletal muscle regeneration that is accompanied with reduced number of satellite cells and their fusion to injured myofibers. Ex vivo cultures of myofiber explants demonstrate that ablation of IRE1α reduces the proliferative capacity of myofiber-associated satellite cells. Myofiber-specific deletion of IRE1α dampens Notch signaling and canonical NF-kB pathway in skeletal muscle of mice. Our results also demonstrate that targeted ablation of IRE1α reduces skeletal muscle regeneration in the mdx mice, a model of Duchenne muscular dystrophy. Collectively, our results reveal that the IRE1α-mediated signaling promotes muscle regeneration through augmenting the proliferation of satellite cells in a cell non-autonomous manner.

Keywords:  cell biology; mouse; regenerative medicine; stem cells

DOI:  https://doi.org/10.7554/eLife.73215
Front Med (Lausanne). 2021 ;8 758311

Crosstalk Between ER Stress, Autophagy and Inflammation.

Sandhya Chipurupalli, Unni Samavedam, Nirmal Robinson.

  The endoplasmic reticulum (ER) is not only responsible for protein synthesis and folding but also plays a critical role in sensing cellular stress and maintaining cellular homeostasis. Upon sensing the accumulation of unfolded proteins due to perturbation in protein synthesis or folding, specific intracellular signaling pathways are activated, which are collectively termed as unfolded protein response (UPR). UPR expands the capacity of the protein folding machinery, decreases protein synthesis and enhances ER-associated protein degradation (ERAD) which degrades misfolded proteins through the proteasomes. More recent evidences suggest that UPR also amplifies cytokines-mediated inflammatory responses leading to pathogenesis of inflammatory diseases. UPR signaling also activates autophagy; a lysosome-dependent degradative pathwaythat has an extended capacity to degrade misfolded proteins and damaged ER. Thus, activation of autophagy limits inflammatory response and provides cyto-protection by attenuating ER-stress. Here we review the mechanisms that couple UPR, autophagy and cytokine-induced inflammation that can facilitate the development of novel therapeutic strategies to mitigate cellular stress and inflammation associated with various pathologies.

Keywords:  ER-stress; autophagy; cytokines; inflammation; unfolded protein response

DOI:  https://doi.org/10.3389/fmed.2021.758311
Mol Cell Neurosci. 2021 Nov 17. pii: S1044-7431(21)00095-6. [Epub ahead of print]118 103682

Kinetic monitoring of neuronal stress response to proteostasis dysfunction.

Angel J Santiago-Lopez, Ken Berglund, Robert E Gross, Claire-Anne N Gutekunst.

  Proteostasis dysfunction and activation of the unfolded protein response (UPR) are characteristic of all major neurodegenerative diseases. Nevertheless, although the UPR and proteostasis dysfunction has been studied in great detail in model organisms like yeast and mammalian cell lines, it has not yet been examined in neurons. In this study, we applied a viral vector-mediated expression of a reporter protein based on a UPR transcription factor, ATF4, and time-lapse fluorescent microscopy to elucidate how mouse primary neurons respond to pharmacological and genetic perturbations to neuronal proteostasis. In in vitro models of endoplasmic reticulum (ER) stress and proteasome inhibition, we used the ATF4 reporter to reveal the time course of the neuronal stress response relative to neurite degeneration and asynchronous cell death. We showed how potential neurodegenerative disease co-factors, ER stress and mutant α-synuclein overexpression, impacted neuronal stress response and overall cellular health. This work therefore introduces a viral vector-based reporter that yields a quantifiable readout suitable for non-cell destructive kinetic monitoring of proteostasis dysfunction in neurons by harnessing ATF4 signaling as part of the UPR activation.

Keywords:  Alpha-synuclein; Integrated stress response; Neurodegeneration; Proteostasis; Unfolded protein response

DOI:  https://doi.org/10.1016/j.mcn.2021.103682
Cells. 2021 Oct 23. pii: 2856. [Epub ahead of print]10(11):

Silencing of the ER and Integrative Stress Responses in the Liver of Mice with Error-Prone Translation.

James Moore, Ivan Osinnii, Amandine Grimm, Björn Oettinghaus, Anne Eckert, Stephan Frank, Erik C Böttger.

  Translational errors frequently arise during protein synthesis, producing misfolded and dysfunctional proteins. Chronic stress resulting from translation errors may be particularly relevant in tissues that must synthesize and secrete large amounts of secretory proteins. Here, we studied the proteostasis networks in the liver of mice that express the Rps2-A226Y ribosomal ambiguity (ram) mutation to increase the translation error rate across all proteins. We found that Rps2-A226Y mice lack activation of the eIF2 kinase/ATF4 pathway, the main component of the integrated stress response (ISR), as well as the IRE1 and ATF6 pathways of the ER unfolded protein response (ER-UPR). Instead, we found downregulation of chronic ER stress responses, as indicated by reduced gene expression for lipogenic pathways and acute phase proteins, possibly via upregulation of Sirtuin-1. In parallel, we observed activation of alternative proteostasis responses, including the proteasome and the formation of stress granules. Together, our results point to a concerted response to error-prone translation to alleviate ER stress in favor of activating alternative proteostasis mechanisms, most likely to avoid cell damage and apoptotic pathways, which would result from persistent activation of the ER and integrated stress responses.

Keywords:  ER stress; ER-UPR; RNA-Seq; Sirtuin-1; error-prone translation; liver; mistranslation; proteostasis; ribosomal misreading

DOI:  https://doi.org/10.3390/cells10112856
Viruses. 2021 Oct 27. pii: 2164. [Epub ahead of print]13(11):

IRE1-Mediated Unfolded Protein Response Promotes the Replication of Tick-Borne Flaviviruses in a Virus and Cell-Type Dependent Manner.

Veronika J M Breitkopf, Gerhard Dobler, Peter Claus, Hassan Y Naim, Imke Steffen.

  Tick-borne flaviviruses (TBFV) can cause severe neurological complications in humans, but differences in tissue tropism and pathogenicity have been described for individual virus strains. Viral protein synthesis leads to the induction of the unfolded protein response (UPR) within infected cells. The IRE1 pathway has been hypothesized to support flavivirus replication by increasing protein and lipid biogenesis. Here, we investigated the role of the UPR in TBFV infection in human astrocytes, neuronal and intestinal cell lines that had been infected with tick-borne encephalitis virus (TBEV) strains Neudoerfl and MucAr-HB-171/11 as well as Langat virus (LGTV). Both TBEV strains replicated better than LGTV in central nervous system (CNS) cells. TBEV strain MucAr-HB-171/11, which is associated with gastrointestinal symptoms, replicated best in intestinal cells. All three viruses activated the inositol-requiring enzyme 1 (IRE1) pathway via the X-box binding protein 1 (XBP1). Interestingly, the neurotropic TBEV strain Neudoerfl induced a strong upregulation of XBP1 in all cell types, but with faster kinetics in CNS cells. In contrast, TBEV strain MucAr-HB-171/11 failed to activate the IRE1 pathway in astrocytes. The low pathogenic LGTV led to a mild induction of IRE1 signaling in astrocytes and intestinal cells. When cells were treated with IRE1 inhibitors prior to infection, TBFV replication in astrocytes was significantly reduced. This confirms a supporting role of the IRE1 pathway for TBFV infection in relevant viral target cells and suggests a correlation between viral tissue tropism and the cell-type dependent induction of the unfolded protein response.

Keywords:  ER stress; Langat virus; flavivirus; neuroinfection; tick-borne encephalitis virus; unfolded protein response; viral replication

DOI:  https://doi.org/10.3390/v13112164
Biochem Biophys Res Commun. 2021 Nov 16. pii: S0006-291X(21)01549-7. [Epub ahead of print]585 169-176

Endoplasmic reticulum stress increases LECT2 expression via ATF4.

Chan Yoon Park, Seul Ki Lee, Jimin Kim, Donguk Kim, Han Choe, Ji-Hoon Jeong, Kyung-Chul Choi, Hye Soon Park, Sung Nim Han, Yeon Jin Jang.

  Non-alcoholic fatty liver disease (NAFLD) is frequently associated with obesity, insulin resistance, and endoplasmic reticulum (ER) stress. Elevated circulating levels of the hepatokine leukocyte cell-derived chemotaxin-2 (LECT2) have also been noted in NAFLD; however, the mechanism underlying this association is unclear. To investigate a possible link between ER stress/unfolded protein response (UPR) signaling and LECT2 secretion, HepG2 cells were incubated with ER stress inducers with or without an ER stress-reducing chemical chaperone. Additionally, UPR pathway genes were knocked down and overexpressed, and a ChIP assay was performed. In diet-induced obese mice, hepatic expression of LECT2 and activating transcription factor 4 (ATF4) was measured. In HepG2 cells, LECT2 expression was increased by ER stressors, an effect blocked by the chemical chaperone. Among UPR pathway proteins, only knockdown of ATF4 suppressed ER stress-induced LECT2 expression, while overexpression of ATF4 enhanced LECT2 expression. The ChIP assay revealed that ATF4 binds to three putative binding sites on the LECT2 promoter and binding is promoted by an ER stress inducer. In steatotic livers of obese mice, LECT2 and ATF4 expression was concomitantly elevated. Our data indicate that activation of ER stress/UPR signaling induces LECT2 expression in steatotic liver; specifically, ATF4 appears to mediate upregulation of LECT2 transcription.

Keywords:  ATF4; ER stress; Hepatokine; LECT2; NAFLD; Obesity

DOI:  https://doi.org/10.1016/j.bbrc.2021.11.038
Cells. 2021 Oct 31. pii: 2965. [Epub ahead of print]10(11):

The Unfolded Protein Response as a Guardian of the Secretory Pathway.

Toni Radanović, Robert Ernst.

  The endoplasmic reticulum (ER) is the major site of membrane biogenesis in most eukaryotic cells. As the entry point to the secretory pathway, it handles more than 10,000 different secretory and membrane proteins. The insertion of proteins into the membrane, their folding, and ER exit are affected by the lipid composition of the ER membrane and its collective membrane stiffness. The ER is also a hotspot of lipid biosynthesis including sterols, glycerophospholipids, ceramides and neural storage lipids. The unfolded protein response (UPR) bears an evolutionary conserved, dual sensitivity to both protein-folding imbalances in the ER lumen and aberrant compositions of the ER membrane, referred to as lipid bilayer stress (LBS). Through transcriptional and non-transcriptional mechanisms, the UPR upregulates the protein folding capacity of the ER and balances the production of proteins and lipids to maintain a functional secretory pathway. In this review, we discuss how UPR transducers sense unfolded proteins and LBS with a particular focus on their role as guardians of the secretory pathway.

Keywords:  ATF6; ER; IRE1; PERK; UPR; hydrophobic mismatch; lipid bilayer stress; membrane stiffness; membrane thickness; proteotoxic stress; secretory pathway

DOI:  https://doi.org/10.3390/cells10112965
J Invest Dermatol. 2021 Nov 19. pii: S0022-202X(21)02508-2. [Epub ahead of print]

The ER Stress Sensor IRE1α Regulates the UV DNA Repair Response Through Control of Intracellular Calcium Homeostasis.

Jeongin Son, Saie Mogre, Fiona E Chalmers, Jack Ibinson, Stephen Worrell, Adam B Glick.

  The unfolded protein response is activated by UVB irradiation, but the role of a key mediator, inositol requiring enzyme 1a (IRE1α), is not clear. Here, we show that mice with an epidermal IRE1α deletion are sensitized to UV with increased apoptosis, rapid loss of UV-induced cyclopyrimidine dimer (CPD) positive keratinocytes and sloughing of the epidermis. In vitro, IRE1α deficient keratinocytes have increased UVB sensitivity, reduced CPD repair and reduced accumulation of γH2AX and p-ATR, suggesting defective the activation of nucleotide excision repair. Knockdown of XBP1 or pharmacological inhibition of the IRE1α RNase did not phenocopy IRE1α deficiency. The altered UV response was linked to elevated intracellular calcium levels and ROS, and this was due to dysregulation of the ER calcium channel inositol triphosphate receptor (InsP3R). Pharmacologic, genetic, and biochemical studies linked regulation of the Ins3PR, intracellular calcium and normal UV DNA damage response to calcium and integrin binding protein 1 (CIB1) and the IRE1α-TRAF2-ASK1 complex. These results suggest a model where IRE1α activation state drives CIB1 binding either to the InsP3R or ASK1 to regulate ER calcium efflux, ROS and DNA repair responses following UV.

Keywords:  DNA damage response; ER stress; IRE1α; Intracellular calcium; Skin; UVB; Unfolded Protein Response

DOI:  https://doi.org/10.1016/j.jid.2021.11.010
Cells. 2021 Nov 02. pii: 2980. [Epub ahead of print]10(11):

The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis.

Pascal Trouvé, Claude Férec, Emmanuelle Génin.

  In cystic fibrosis (CF), p.Phe508del is the most frequent mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The p.Phe508del-CFTR protein is retained in the ER and rapidly degraded. This retention likely triggers an atypical Unfolded Protein Response (UPR) involving ATF6, which reduces the expression of p.Phe508del-CFTR. There are still some debates on the role of the UPR in CF: could it be triggered by the accumulation of misfolded CFTR proteins in the endoplasmic reticulum as was proposed for the most common CFTR mutation p.Phe508del? Or, is it the consequence of inflammation and infection that occur in the disease? In this review, we summarize recent findings on UPR in CF and show how infection, inflammation and UPR act together in CF. We propose to rethink their respective role in CF and to consider them as a whole.

Keywords:  cystic fibrosis; infection; inflammation; unfolded protein response

DOI:  https://doi.org/10.3390/cells10112980
Cells. 2021 Oct 20. pii: 2812. [Epub ahead of print]10(11):

Macrophage-Derived Immunoglobulin M Inhibits Inflammatory Responses via Modulating Endoplasmic Reticulum Stress.

Xiaoting Gong, Huige Yan, Junfan Ma, Zhu Zhu, Shenghua Zhang, Weiyan Xu, Jing Huang, Xiaoyan Qiu.

  Immunoglobulin (Ig), a characteristic marker of B cells, is a multifunctional evolutionary conserved antibody critical for maintaining tissue homeostasis and developing fully protective humoral responses to pathogens. Increasing evidence revealed that Ig is widely expressed in non-immune cells; moreover, Ig produced by different lineages cells plays different biological roles. Recently, it has been reported that monocytes or macrophages also express Ig. However, its function remains unclear. In this study, we further identified that Ig, especially Ig mu heavy chain (IgM), was mainly expressed in mice macrophages. We also analyzed the IgM repertoire characteristic in macrophages and found that the VHDJH rearrangements of macrophage-derived IgM showed a restricted and conservative VHDJH pattern, which differed from the diverse VHDJH rearrangement pattern of the B cell-expressed IgM in an individual. Functional investigation showed that IgM knockdown significantly promoted macrophage migration and FAK/Src-Akt axis activation. Furthermore, some inflammatory cytokines such as MCP1 and IL-6 increased after IgM knockdown under LPS stimulation. A mechanism study revealed that the IgM interacted with binding immunoglobulin protein (Bip) and inhibited inflammatory response and unfolded protein response (UPR) activation in macrophages. Our data elucidate a previously unknown function of IgM in macrophages that explains its ability to act as a novel regulator of Bip to participate in endoplasmic reticulum stress and further regulate the inflammatory response.

Keywords:  Bip; ER stress; IgM; inflammatory response; macrophage

DOI:  https://doi.org/10.3390/cells10112812
Autophagy. 2021 Nov 25. 1-21

Inhibition of USP14 influences alphaherpesvirus proliferation by degrading viral VP16 protein via ER stress-triggered selective autophagy.

Sheng-Li Ming, Shuang Zhang, Qi Wang, Lei Zeng, Lu-Yu Zhou, Meng-Di Wang, Ying-Xian Ma, Li-Qiang Han, Kai Zhong, He-Shui Zhu, Yi-Lin Bai, Guo-Yu Yang, Jiang Wang, Bei-Bei Chu.

  Alphaherpesvirus infection results in severe health consequences in a wide range of hosts. USPs are the largest subfamily of deubiquitinating enzymes that play critical roles in immunity and other cellular functions. To investigate the role of USPs in alphaherpesvirus replication, we assessed 13 USP inhibitors for PRV replication. Our data showed that all the tested compounds inhibited PRV replication, with the USP14 inhibitor b-AP15 exhibiting the most dramatic effect. Ablation of USP14 also influenced PRV replication, whereas replenishment of USP14 in USP14 null cells restored viral replication. Although inhibition of USP14 induced the K63-linked ubiquitination of PRV VP16 protein, its degradation was not dependent on the proteasome. USP14 directly bound to ubiquitin chains on VP16 through its UBL domain during the early stage of viral infection. Moreover, USP14 inactivation stimulated EIF2AK3/PERK- and ERN1/IRE1-mediated signaling pathways, which were responsible for VP16 degradation through SQSTM1/p62-mediated selective macroautophagy/autophagy. Ectopic expression of non-ubiquitinated VP16 fully rescued PRV replication. Challenge of mice with b-AP15 activated ER stress and autophagy and inhibited PRV infection in vivo. Our results suggested that USP14 was a potential therapeutic target to treat alphaherpesvirus-induced infectious diseases.

Keywords:  Alphaherpesvirus; ER stress; PRV VP16; USP14; selective autophagy

DOI:  https://doi.org/10.1080/15548627.2021.2002101