bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2021–03–14
fiveteen papers selected by
Matías Eduardo González Quiroz, Worker’s Hospital
  1. Molecular Evaluation of Endoplasmic Reticulum Homeostasis Meets Humoral Immunity.
  2. High dose expression of heme oxigenase-1 induces retinal degeneration through ER stress-related DDIT3.
  3. Immune responses to CRISPR-Cas protein.
  4. Death sentence: The tale of a fallen endoplasmic reticulum.
  5. FUS-dependent liquid-liquid phase separation is important for DNA repair initiation.
  6. Role of H2B mono-ubiquitination in the initiation and progression of cancer.
  7. Protein feature analysis of heat shock induced ubiquitination sites reveals preferential modification site localization.
  8. Detecting and Modulating ER Stress to Improve Generation of Induced Pluripotent Stem Cells.
  9. ORMDL3 Functions as a Negative Regulator of Antigen-Mediated Mast Cell Activation via an ATF6-UPR-Autophagy-Dependent Pathway.
  10. OTUB1 facilitates bladder cancer progression by stabilizing ATF6 in response to ER stress.
  11. Proteomic and transcriptomic profiling reveal different aspects of aging in the kidney.
  12. TP53/p53-FBXO22-TFEB controls basal autophagy to govern hormesis.
  13. CDK1 inhibitor controls G2/M phase transition and reverses DNA damage sensitivity.
  14. The Unfolded Protein Response Reveals eIF2α Phosphorylation as a Critical Factor for Direct MHC Class I Antigen Presentation.
  15. Localization of RNAs in the nucleus: cis- and trans- regulation.
  1. Trends Cell Biol. 2021 Mar 05. pii: S0962-8924(21)00029-5. [Epub ahead of print]
    Molecular Evaluation of Endoplasmic Reticulum Homeostasis Meets Humoral Immunity.
    Eelco van Anken, Anush Bakunts, Chih-Chi Andrew Hu, Sophie Janssens, Roberto Sitia.
      The biosynthesis of about one third of the human proteome, including membrane receptors and secreted proteins, occurs in the endoplasmic reticulum (ER). Conditions that perturb ER homeostasis activate the unfolded protein response (UPR). An 'optimistic' UPR output aims at restoring homeostasis by reinforcement of machineries that guarantee efficiency and fidelity of protein biogenesis in the ER. Yet, once the UPR 'deems' that ER homeostatic readjustment fails, it transitions to a 'pessimistic' output, which, depending on the cell type, will result in apoptosis. In this article, we discuss emerging concepts on how the UPR 'evaluates' ER stress, how the UPR is repurposed, in particular in B cells, and how UPR-driven counter-selection of cells undergoing homeostatic failure serves organismal homeostasis and humoral immunity.
    Keywords:  B cell development; RIDD; antibody production; endoplasmic reticulum; proteostasis; unfolded protein response
    DOI:  https://doi.org/10.1016/j.tcb.2021.02.004
  2. Mol Neurodegener. 2021 03 10. 16(1): 16
    High dose expression of heme oxigenase-1 induces retinal degeneration through ER stress-related DDIT3.
    Huirong Li, Bo Liu, Lili Lian, Jiajia Zhou, Shengjin Xiang, Yifan Zhai, Yu Chen, Xiaoyin Ma, Wencan Wu, Ling Hou.
       BACKGROUND: Oxidative stress is a common cause of neurodegeneration and plays a central role in retinal degenerative diseases. Heme oxygenase-1 (HMOX1) is a redox-regulated enzyme that is induced in neurodegenerative diseases and acts against oxidative stress but can also promote cell death, a phenomenon that is still unexplained in molecular terms. Here, we test whether HMOX1 has opposing effects during retinal degeneration and investigate the molecular mechanisms behind its pro-apoptotic role.
    METHODS: Basal and induced levels of HMOX1 in retinas are examined during light-induced retinal degeneration in mice. Light damage-independent HMOX1 induction at two different expression levels is achieved by intraocular injection of different doses of an adeno-associated virus vector expressing HMOX1. Activation of Müller glial cells, retinal morphology and photoreceptor cell death are examined using hematoxylin-eosin staining, TUNEL assays, immunostaining and retinal function are evaluated with electroretinograms. Downstream gene expression of HMOX1 is analyzed by RNA-seq, qPCR examination and western blotting. The role of one of these genes, the pro-apoptotic DNA damage inducible transcript 3 (Ddit3), is analyzed in a line of knockout mice.
    RESULTS: Light-induced retinal degeneration leads to photoreceptor degeneration and concomitant HMOX1 induction. HMOX1 expression at low levels before light exposure prevents photoreceptor degeneration but expression at high levels directly induces photoreceptor degeneration even without light stress. Photoreceptor degeneration following high level expression of HMOX1 is associated with a mislocalization of rhodopsin in photoreceptors and an increase in the expression of DDIT3. Genetic deletion of Ddit3 in knockout mice prevents photoreceptor cell degeneration normally resulting from high level HMOX1 expression.
    CONCLUSION: The results reveal that the expression levels determine whether HMOX1 is protective or deleterious in the retina. Furthermore, in contrast to the protective low dose of HMOX1, the deleterious high dose is associated with induction of DDIT3 and endoplasmic reticulum stress as manifested, for instance, in rhodopsin mislocalization. Hence, future applications of HMOX1 or its regulated targets in gene therapy approaches should carefully consider expression levels in order to avoid potentially devastating effects.
    Keywords:  Antioxidant enzyme; CHOP pathway; Endoplasmic reticulum stress; Photoreceptor degeneration; Recombinant adeno-associated virus
    DOI:  https://doi.org/10.1186/s13024-021-00437-4
  3. Prog Mol Biol Transl Sci. 2021 ;pii: S1877-1173(20)30173-3. [Epub ahead of print]178 213-229
    Immune responses to CRISPR-Cas protein.
    Sobhan Roy.
      The clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated (Cas) protein technologies have evolved as promising, cost-effective, and efficient methods for editing genomes. Editing genomes with high specificity and precision is a daunting task, where errors can lead to undesirable outcomes. Many elegant studies have successfully shown that the CRISPR-Cas9 system can modify, disrupt, and add new DNA sequences directly into the genomes of the cells or animals being studied. As such, the CRISPR-Cas9 technology holds immense potential for biomedical research as well as agricultural and therapeutic applications, further emphasized by its unprecedented movement into the clinical setting. Throughout every stage of life, missense mutations can lead to highly unfavorable outcomes, syndromes, and diseases. Many of these mutations are transferred directly through the fertilization process and, thereby, acquired at birth and propagated to the next generation. As such, it has been of great interest to develop techniques to repair these mutations using genetic manipulation, prior to or following birth. CRISPR-Cas9 has many advantages in this regard over numerous other existing technologies. Regardless, editing bases within a genome can be associated with numerous challenges that were previously unrecognized and lead to unforeseen consequences. While the CRISPR-Cas9 method is perfectly suitable for editing cells outside the body with limited risk to the normal functioning of the cell, recent publications have illustrated a number of challenging conditions resulting from its use. One of them is directed to the host immune response toward CRISPR-Cas9. With this in mind, this review will discuss recent observations on the host immune response to CRISPR-Cas9 and the associated challenges that arise as a result.
    Keywords:  B cell; CRISPR-Cas; MHC; T cell; Therapeutic application
    DOI:  https://doi.org/10.1016/bs.pmbts.2020.12.003
  4. Biochim Biophys Acta Mol Cell Res. 2021 Mar 08. pii: S0167-4889(21)00055-0. [Epub ahead of print] 119001
    Death sentence: The tale of a fallen endoplasmic reticulum.
    Eoghan P McGrath, Federica G Centonze, Eric Chevet, Tony Avril, Elodie Lafont.
      Endoplasmic Reticulum (ER) stress signaling is an adaptive mechanism triggered when protein folding demand overcomes the folding capacity of this compartment, thereby leading to the accumulation of improperly folded proteins. This stress signaling pathway is named the Unfolded Protein Response (UPR) and aims at restoring ER homeostasis. However, if this fails, mechanisms orienting cells towards death processes are initiated. Herein, we summarize the most recent findings connecting ER stress and the UPR with identified death mechanisms including apoptosis, necrosis, pyroptosis, ferroptosis, and autophagy. We highlight new avenues that could be investigated and controlled through actionable mechanisms in physiology and pathology.
    Keywords:  Apoptosis; Autophagy; Cell death; Endoplasmic reticulum; Ferroptosis; Pyroptosis; Unfolded protein response
    DOI:  https://doi.org/10.1016/j.bbamcr.2021.119001
  5. J Cell Biol. 2021 May 03. pii: e202008030. [Epub ahead of print]220(5):
    FUS-dependent liquid-liquid phase separation is important for DNA repair initiation.
    Brunno R Levone, Silvia C Lenzken, Marco Antonaci, Andreas Maiser, Alexander Rapp, Francesca Conte, Stefan Reber, Jonas Mechtersheimer, Antonella E Ronchi, Oliver Mühlemann, Heinrich Leonhardt, M Cristina Cardoso, Marc-David Ruepp, Silvia M L Barabino.
      RNA-binding proteins (RBPs) are emerging as important effectors of the cellular DNA damage response (DDR). The RBP FUS is implicated in RNA metabolism and DNA repair, and it undergoes reversible liquid-liquid phase separation (LLPS) in vitro. Here, we demonstrate that FUS-dependent LLPS is necessary for the initiation of the DDR. Using laser microirradiation in FUS-knockout cells, we show that FUS is required for the recruitment to DNA damage sites of the DDR factors KU80, NBS1, and 53BP1 and of SFPQ, another RBP implicated in the DDR. The relocation of KU80, NBS1, and SFPQ is similarly impaired by LLPS inhibitors, or LLPS-deficient FUS variants. We also show that LLPS is necessary for efficient γH2AX foci formation. Finally, using superresolution structured illumination microscopy, we demonstrate that the absence of FUS impairs the proper arrangement of γH2AX nanofoci into higher-order clusters. These findings demonstrate the early requirement for FUS-dependent LLPS in the activation of the DDR and the proper assembly of DSB repair complexes.
    DOI:  https://doi.org/10.1083/jcb.202008030
  6. Bull Cancer. 2021 Mar 05. pii: S0007-4551(21)00049-7. [Epub ahead of print]
    Role of H2B mono-ubiquitination in the initiation and progression of cancer.
    Sa Zhou, Yuqiao Cai, Xinyi Liu, Lijun Jin, Xiaoqin Wang, Wenjian Ma, Tongcun Zhang.
      Numerous epigenetic alterations are observed in cancer cells, and dysregulation of mono-ubiquitination of histone H2B (H2Bub1) has often been linked to tumorigenesis. H2Bub1 is a dynamic post-translational histone modification associated with transcriptional elongation and DNA damage response. Histone H2B monoubiquitination occurs in the site of lysine 120, written predominantly by E3 ubiquitin ligases RNF20/RNF40 and deubiquitinated by ubiquitin specific peptidase 22 (USP22). RNF20/40 is often altered in the primary tumors including colorectal cancer, breast cancer, ovarian cancer, prostate cancer, and lung cancer, and the loss of H2Bub1 is usually associated with poor prognosis in tumor patients. The purpose of this review is to summarize the current knowledge of H2Bub1 in transcription, DNA damage response and primary tumors. This review also provides novel options for exploiting the potential therapeutic target H2Bub1 in personalized cancer therapy.
    Keywords:  Cancer cell; DNA damage response; E3 ubiquitin ligase; H2B mono6ubiquitination (H2Bub1); RNF20/RNF40; Transcription regulation
    DOI:  https://doi.org/10.1016/j.bulcan.2020.12.007
  7. J Proteomics. 2021 Mar 08. pii: S1874-3919(21)00081-6. [Epub ahead of print] 104182
    Protein feature analysis of heat shock induced ubiquitination sites reveals preferential modification site localization.
    Erich R Kuechler, Amalia Rose, Marcel Bolten, Angel Madero, Shaima Kammoonah, Shane Colborne, Joerg Gsponer, Gregg B Morin, Thibault Mayor.
      Protein aggregation is indicative of failing protein quality control systems. These systems are responsible for the refolding or degradation of aberrant and misfolded proteins. Heat stress can cause proteins to misfold, triggering cellular responses and a marked increase in the ubiquitination of proteins. This response has been characterized in yeast, however more studies are needed within mammalian cells. Herein, we examine proteins that become ubiquitinated during heat shock in human tissue culture cells using diGly enrichment coupled with mass spectrometry. A majority of these proteins are localized in the nucleus or cytosol. Proteins which are conjugated under stress display longer sequence lengths, more interaction partners, and more hydrophobic patches than controls but do not show lower melting temperatures. Furthermore, heat-induced conjugation sites occur less frequently in disordered regions and are closer to hydrophobic patches than other ubiquitination sites; perhaps providing novel insight into the molecular mechanism mediating this response. Nuclear and cytosolic pools of modified proteins appear to have different protein features. Using a pulse-SILAC approach, we found that both long-lived and newly-synthesized proteins are conjugated under stress. Modified long-lived proteins are predominately nuclear and were distinct from newly-synthesized proteins, indicating that different pathways may mediate the heat-induced increase of polyubiquitination. SIGNIFICANCE: The maintenance of protein homeostasis requires a balance of protein synthesis, folding, and degradation. Under stress conditions, the cell must rapidly adapt by increasing its folding capacity to eliminate aberrant proteins. A major pathway for proteolysis is mediated by the ubiquitin proteasome system. While increased ubiquitination after heat stress was observed over 30 years ago, it remains unclear which proteins are conjugated during heat shock in mammalian cells and by what means this conjugation occurs. In this study, we combined SILAC-based mass spectrometry with computational analyses to reveal features associated to proteins ubiquitinated while under heat shock. Interestingly, we found that conjugation sites induced by the stress are less often located within disordered regions and more often located near hydrophobic patches. Our study showcases how proteomics can reveal distinct feature associated to a cohort of proteins that are modified post translationally and how the ubiquitin conjugation sites are preferably selected in these conditions. Our work opens a new path for delineating the molecular mechanisms leading to the heat stress response and the regulation of protein homeostasis.
    Keywords:  Heat shock; Intrinsic protein disorder; Mass spectrometry; Proteostasis; SILAC; Ubiquitin
    DOI:  https://doi.org/10.1016/j.jprot.2021.104182
  8. Methods Mol Biol. 2021 Mar 11.
    Detecting and Modulating ER Stress to Improve Generation of Induced Pluripotent Stem Cells.
    Alejandro Fuentes-Iglesias, Cristina Ameneiro, Diana Guallar, Miguel Fidalgo.
      The reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) has proven to be a powerful system creating new opportunities to interrogate molecular mechanisms controlling cell fate determination. Under standard conditions, the generation of iPSCs upon overexpression of OCT4, SOX2, KLF4, and c-MYC (OSKM) is generally slow and inefficient due to the presence of barriers that confer resistance to cell fate changes. Hyperactivated endoplasmic reticulum (ER) stress has emerged as a major reprogramming barrier that impedes the initial mesenchymal-to-epithelial transition (MET) step to form iPSCs from mesenchymal somatic cells. Here, we describe several systems to detect ER stress in the context of OSKM reprogramming and chemical interventions to modulate this process for improving iPSC formation.
    Keywords:  Cell fate change; Endoplasmic reticulum stress; Induced pluripotent stem cell; Mesenchymal-to-epithelial transition; Pluripotency; Unfolded protein response
    DOI:  https://doi.org/10.1007/7651_2021_354
  9. Front Immunol. 2021 ;12 604974
    ORMDL3 Functions as a Negative Regulator of Antigen-Mediated Mast Cell Activation via an ATF6-UPR-Autophagy-Dependent Pathway.
    Jia Li, Md Ashik Ullah, Hongping Jin, Yuting Liang, Lihui Lin, Juan Wang, Xia Peng, Huanjin Liao, Yanning Li, Yiqin Ge, Li Li.
      Antigen (Ag)-mediated mast cell activation plays a critical role in the immunopathology of IgE-dependent allergic diseases. Restraining the signaling cascade that regulates the release of mast cell-derived inflammatory mediators is an attractive therapeutic strategy to treat allergic diseases. Orosomucoid-like-3 (ORMDL3) regulates the endoplasmic reticulum stress (ERS)-induced unfolded protein response (UPR) and autophagy. Although ERS/UPR/autophagy pathway is crucial in Ag-induced mast cell activation, it is unknown whether ORMDL3 regulates the ERS/UPR/autophagy pathway during mast cell activation. In this study, we found that ORMDL3 expression was downregulated in Ag-activated MC/9 cells. Overexpression of ORMDL3 significantly inhibited degranulation, and cytokine/chemokine production, while the opposite effect was observed with ORMDL3 knockdown in MC/9 cells. Importantly, ORMDL3 overexpression upregulated mediators of ERS-UPR (SERCA2b, ATF6) and autophagy (Beclin 1 and LC3BII). Knockdown of ATF6 and/or inhibition of autophagy reversed the decreased degranulation and cytokine/chemokine expression caused by ORMDL3 overexpression. Moreover, in vivo knockdown of ORMDL3 and/or ATF6 enhanced passive cutaneous anaphylaxis (PCA) reactions in mouse ears. These data indicate that ORMDL3 suppresses Ag-mediated mast cell activation via an ATF6 UPR-autophagy dependent pathway and thus, attenuates anaphylactic reaction. This highlights a potential mechanism to intervene in mast cell mediated diseases.
    Keywords:  activating transcription factor 6; autophagy; degranulation; mast cell activation; orosomucoid-like 3; passive cutaneous anaphylaxis
    DOI:  https://doi.org/10.3389/fimmu.2021.604974
  10. Cancer Sci. 2021 Mar 09.
    OTUB1 facilitates bladder cancer progression by stabilizing ATF6 in response to ER stress.
    Hui-Hui Zhang, Chao Li, Jian-Wei Ren, Lian Liu, Xue-Hua Du, Jie Gao, Tao Liu, Shang-Ze Li.
      The unfolded protein response (UPR) plays an important role in carcinogenesis, but the functional role and mechanism of UPR-associated bladder carcinogenesis remain to be characterized. Upon UPR activation, ATF6α is activated to upregulate the transcription of UPR target genes. Although the mechanism of ATF6 activation has been studied extensively, the negative regulation of ATF6 stabilization is not well understood. Here, we report that the deubiquitinase otubain 1 (OTUB1) facilitates bladder cancer progression by stabilizing ATF6 in response to ER stress. OTUB1 expression is elevated in bladder cancer patients. Genetic ablation of OTUB1 markedly inhibited bladder cancer cell proliferation, viability and migration both in vitro and in vivo. Mechanistically, luciferase pathway screening showed that ATF6 signaling was clearly activated compared to other pathways. OTUB1 was found to activate ATF6 signaling by inhibiting its ubiquitylation, thereby remodeling the stressed cells through transcriptional regulation. Our results indicate that high OTUB1 expression promotes bladder cancer progression by stabilizing ATF6 and that OTUB1 is a potential therapeutic target in bladder cancer.
    Keywords:  ATF6; OTUB1; UPR; bladder cancer; deubiquitination
    DOI:  https://doi.org/10.1111/cas.14876
  11. Elife. 2021 Mar 09. pii: e62585. [Epub ahead of print]10
    Proteomic and transcriptomic profiling reveal different aspects of aging in the kidney.
    Yuka Takemon, Joel M Chick, Isabela Gerdes Gyuricza, Daniel A Skelly, Olivier Devuyst, Steven P Gygi, Gary A Churchill, Ron Korstanje.
      Little is known about the molecular changes that take place in the kidney during the aging process. In order to better understand these changes, we measured mRNA and protein levels in genetically diverse mice at different ages. We observed distinctive change in mRNA and protein levels as a function of age. Changes in both mRNA and protein are associated with increased immune infiltration and decreases in mitochondrial function. Proteins show a greater extent of change and reveal changes in a wide array of biological processes including unique, organ-specific features of aging in kidney. Most importantly, we observed functionally important age-related changes in protein that occur in the absence of corresponding changes in mRNA. Our findings suggest that mRNA profiling alone provides an incomplete picture of molecular aging in the kidney and that examination of changes in proteins is essential to understand aging processes that are not transcriptionally regulated.
    Keywords:  computational biology; mouse; systems biology
    DOI:  https://doi.org/10.7554/eLife.62585
  12. Autophagy. 2021 Mar 11. 1-18
    TP53/p53-FBXO22-TFEB controls basal autophagy to govern hormesis.
    Narumi Suzuki, Yoshikazu Johmura, Teh-Wei Wang, Toshiro Migita, Wenwen Wu, Rei Noguchi, Kiyoshi Yamaguchi, Yoichi Furukawa, Shuhei Nakamura, Ichiro Miyoshi, Tamotsu Yoshimori, Tomohiko Ohta, Makoto Nakanishi.
      Preconditioning with a mild stressor such as fasting is a promising way to reduce severe side effects from subsequent chemo- or radiotherapy. However, the underlying mechanisms have been largely unexplored. Here, we demonstrate that the TP53/p53-FBXO22-TFEB (transcription factor EB) axis plays an essential role in this process through upregulating basal macroautophagy/autophagy. Mild stress-activated TP53 transcriptionally induced FBXO22, which in turn ubiquitinated KDM4B (lysine-specific demethylase 4B) complexed with MYC-NCOR1 suppressors for degradation, leading to transcriptional induction of TFEB. Upregulation of autophagy-related genes by increased TFEB dramatically enhanced autophagic activity and cell survival upon following a severe stressor. Mitogen-induced AKT1 activation counteracted this process through the phosphorylation of KDM4B, which inhibited FBXO22-mediated ubiquitination. Additionally, fbxo22-/- mice died within 10 h of birth, and their mouse embryonic fibroblasts (MEFs) showed a lowered basal autophagy, whereas FBXO22-overexpressing mice were resistant to chemotherapy. Taken together, these results suggest that TP53 upregulates basal autophagy through the FBXO22-TFEB axis, which governs the hormetic effect in chemotherapy.Abbreviations: BBC3/PUMA: BCL2 binding component 3; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; ChIP-seq: chromatin immunoprecipitation followed by sequencing; DDB2: damage specific DNA binding protein 2; DRAM: DNA damage regulated autophagy modulator; ESR/ER: estrogen receptor 1; FMD: fasting mimicking diet; HCQ: hydroxychloroquine; KDM4B: lysine-specific demethylase 4B; MAP1LC3/LC3: microtubule associated protein 1 light chain 3 alpha; MEFs: mouse embryonic fibroblasts; MTOR: mechanistic target of rapamycin kinase; NCOR1: nuclear receptor corepressor 1; SCF: SKP1-CUL-F-box protein; SQSTM1: sequestosome 1; TFEB: transcription factor EB.
    Keywords:  AKT1; FBXO22; KDM4B; MYC; TP53; autophagy; hormesis; ubiquitination
    DOI:  https://doi.org/10.1080/15548627.2021.1897961
  13. Biochem Biophys Res Commun. 2021 Mar 05. pii: S0006-291X(21)00346-6. [Epub ahead of print]550 56-61
    CDK1 inhibitor controls G2/M phase transition and reverses DNA damage sensitivity.
    Shigeaki Sunada, Hiroko Saito, Doudou Zhang, Zeyu Xu, Yoshio Miki.
      CDK1 plays key roles in cell cycle progression through the G2/M phase transition and activation of homologous recombination (HR) DNA repair pathway. Accordingly, various CDK1 inhibitors have been developed for cancer therapy that induce prolonged G2 arrest and/or sensitize cells to DNA damaging agents in tumor cells, resulting in cell death. However, CDK1 inhibition can induce resistance to DNA damage in certain conditions. The mechanism of different DNA damage sensitivity is not completely understood. We performed immunofluorescence and flow cytometry analysis to investigate DNA damage responses in human tumor cells during low and high dose treatments with RO-3306, a selective CDK1 inhibitor. This comparative investigation demonstrated that RO-3306-induced G2 arrest prevented cells with DNA double-strand breaks from transitioning into the M-phase and that the cells maintained their DNA repair capacity in G2-phase, even under RO-3306 dose-dependent DNA repair inhibition. These findings reveal that CDK1 inhibitor-induced DNA repair inhibition and cell cycle control, which regulate each other during the G2/M phase transition determine the cellular sensitivity to DNA damage, providing insight useful for developing clinical strategies targeting CDK1 inhibition in tumor cells.
    Keywords:  CDK inhibitor; DNA damage Response; DSB repair; G2 arrest; Homologous recombination
    DOI:  https://doi.org/10.1016/j.bbrc.2021.02.117
  14. Immunohorizons. 2021 Mar 08. 5(3): 135-146
    The Unfolded Protein Response Reveals eIF2α Phosphorylation as a Critical Factor for Direct MHC Class I Antigen Presentation.
    Brandy S Nagamine, Jamila Godil, Brian P Dolan.
      The ability to modulate direct MHC class I (MHC I) Ag presentation is a desirable goal for the treatment of a variety of conditions, including autoimmune diseases, chronic viral infections, and cancers. It is therefore necessary to understand how changes in the cellular environment alter the cells' ability to present peptides to T cells. The unfolded protein response (UPR) is a signaling pathway activated by the presence of excess unfolded proteins in the endoplasmic reticulum. Previous studies have indicated that chemical induction of the UPR decreases direct MHC I Ag presentation, but the precise mechanisms are unknown. In this study, we used a variety of small molecule modulators of different UPR signaling pathways to query which UPR signaling pathways can alter Ag presentation in both murine and human cells. When signaling through the PERK pathway, and subsequent eIF2α phosphorylation, was blocked by treatment with GSK2656157, MHC I Ag presentation remain unchanged, whereas treatment with salubrinal, which has the opposite effect of GSK2656157, decreases both Ag presentation and overall cell-surface MHC I levels. Treatment with 4μ8C, an inhibitor of the IRE1α UPR activation pathway that blocks splicing of Xbp1 mRNA, also diminished MHC I Ag presentation. However, 4μ8C treatment unexpectedly led to an increase in eIF2α phosphorylation in addition to blocking IRE1α signaling. Given that salubrinal and 4μ8C lead to eIF2α phosphorylation and similar decreases in Ag presentation, we conclude that UPR signaling through PERK, leading to eIF2α phosphorylation, results in a modest decrease in direct MHC I Ag presentation.
    DOI:  https://doi.org/10.4049/immunohorizons.2100012
  15. RNA Biol. 2021 Mar 08. 1-14
    Localization of RNAs in the nucleus: cis- and trans- regulation.
    Chong Tong, Yafei Yin.
      The subcellular localization of RNAs correlates with their function and how they are regulated. Most protein-coding mRNAs are exported into the cytoplasm for protein synthesis, while some mRNA species, long noncoding RNAs, and some regulatory element-associated unstable transcripts tend to be retained in the nucleus, where they function as a regulatory unit and/or are regulated by nuclear surveillance pathways. While the mechanisms regulating mRNA export and localization have been well summarized, the mechanisms governing nuclear retention of RNAs, especially of noncoding RNAs, are seldomly reviewed. In this review, we summarize recent advances in the mechanistic study of RNA nuclear retention, especially for noncoding RNAs, from the angle of cis-acting elements embedded in RNA transcripts and their interaction with trans-acting factors. We also try to illustrate the general principles of RNA nuclear retention and we discuss potential areas for future investigation.
    Keywords:  Noncoding RNA; RNA decay; chromatin association; hnrnpk; nuclear retention; repeat; splicing; u1 snRNP; xist
    DOI:  https://doi.org/10.1080/15476286.2021.1894025
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