bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2021‒06‒13
thirteen papers selected by
Matías Eduardo González Quiroz
Worker’s Hospital

  1. Pediatr Surg Int. 2021 Jun 12.
      Endoplasmic reticulum (ER) is a dynamic organelle that has many functions including protein synthesis, lipid synthesis, and calcium metabolism. Any perturbation in the ER such as accumulation of unfolded or misfolded proteins in the ER lumen causes ER stress. ER stress has been implicated in many intestinal inflammatory diseases. However, the role of ER stress in acute intestinal epithelial injuries such as necrotizing enterocolitis in preterm neonates, remains incompletely understood. In this review, we introduce ER structure, functions and summarize the intracellular signaling pathways involved in unfolded protein response (UPR), a survival mechanism in which cells exert an adaptive function to restore homeostasis in the ER. However, intense and prolonged ER stress induces apoptotic response which results in apoptotic cell death. We also discuss and highlight recent advances that have improved our understanding of the molecular mechanisms that regulate the ER stress in acute intestinal epithelial injuries such as necrotizing enterocolitis (NEC). We focus on the role of ER stress in influencing gut homeostasis in the neonatal period and on the potential therapeutic interventions to alleviate ER stress-induced cell death in NEC.
    Keywords:  Acute intestinal injury; Endoplasmic reticulum stress; Intestinal epithelium homeostasis; Necrotizing enterocolitis; Unfolded protein response
  2. DNA Repair (Amst). 2021 Jun 08. pii: S1568-7864(21)00111-7. [Epub ahead of print]105 103155
      The accumulation of unrepaired DNA lesions is associated with many pathological outcomes in humans, particularly in neurodegenerative diseases and in normal aging. Evidence supporting a causal role for DNA damage in the onset and progression of neurodegenerative disease has come from rare human patients with mutations in DNA damage response genes as well as from model organisms; however, the generality of this relationship in the normal population is unclear. In addition, the relevance of DNA damage in the context of proteotoxic stress-the widely accepted paradigm for pathology during neurodegeneration-is not well understood. Here, observations supporting intertwined roles of DNA damage and proteotoxicity in aging-related neurological outcomes are reviewed, with particular emphasis on recent insights into the relationships between DNA repair and autophagy, the ubiquitin proteasome system, formation of protein aggregates, poly-ADP-ribose polymerization, and transcription-driven DNA lesions.
    Keywords:  DNA repair; Neurodegeneration; PARP; Protein aggregation; Protein homeostasis
  3. RNA. 2021 Jun 07. pii: rna.078776.121. [Epub ahead of print]
      Rifampicin, a broad-spectrum antibiotic, inhibits bacterial RNA polymerase. Here we show that rifampicin treatment of Escherichia coli results in a 50% decrease in cell size due to a terminal cell division. This decrease is a consequence of inhibition of transcription as evidenced by an isogenic rifampicin-resistant strain. There is also a 50% decrease in total RNA due mostly to a 90% decrease in 23S and 16S rRNA levels. Control experiments showed this decrease is not an artifact of our RNA purification protocol and therefore due to degradation in vivo. Since chromosome replication continues after rifampicin treatment, ribonucleotides from rRNA degradation could be recycled for DNA synthesis. Rifampicin-induced rRNA degradation occurs under different growth conditions and in different strain backgrounds. However, rRNA degradation is never complete thus permitting the re-initiation of growth after removal of rifampicin. The orderly shutdown of growth under conditions where the induction of stress genes is blocked by rifampicin is noteworthy. Inhibition of protein synthesis by chloramphenicol resulted in a partial decrease in 23S and 16S rRNA levels whereas kasugamycin treatment had no effect. Analysis of temperature-sensitive mutant strains implicate RNase E, PNPase and RNase R in rifampicin-induced rRNA degradation. We cannot distinguish between a direct role for RNase E in rRNA degradation versus an indirect role involving a slowdown of mRNA degradation. Since mRNA and rRNA appear to be degraded by the same ribonucleases, competition by rRNA is likely to result in slower mRNA degradation rates in the presence of rifampicin than under normal growth conditions.
    Keywords:  RNase E, PNPase, RNase R; cell size; mRNA degradation; ribosomal RNA degradation; rifampicin
  4. Bioessays. 2021 Jun 07. e2000311
      Genotoxic stress leads to DNA damage which can be detrimental to the cell. A well-orchestrated cellular response is mounted to manage and repair the genotoxic stress-induced DNA damage. Our understanding of genotoxic stress response is derived mainly from studies focused on transcription, mRNA splicing, and protein turnover. Surprisingly not as much is understood about the role of mRNA translation and decay in genotoxic stress response. This is despite the fact that regulation of gene expression at the level of mRNA translation and decay plays a critical role in a myriad of cellular processes. This review aims to summarize some of the known findings of the role of mRNA translation and decay by focusing on two categories of examples. We discuss examples of mRNA whose fates are regulated in the cytoplasm and RNA-binding proteins that regulate mRNA fates in response to genotoxic stress.
    Keywords:  DNA damage response; RNA binding proteins; gadd45a; genotoxic stress; hnRNPs; mRNA decay; mRNA translation; p53; post-transcriptional regulation; ribosomal proteins
  5. Adv Protein Chem Struct Biol. 2021 ;pii: S1876-1623(21)00025-0. [Epub ahead of print]126 307-343
      The maintenance of cellular homeostasis involves the participation of multiple organelles, such as the endoplasmic reticulum (ER) and mitochondria. Specifically, ER plays a key role in calcium (Ca2+) storage, lipid synthesis, protein folding, and assembly, while mitochondria are the "energy factories" and provide energy to drive intracellular processes. Hence, alteration in ER or mitochondrial homeostasis has detrimental effects on cell survival, being linked to the triggering of apoptosis, a programmed form of cell death. Besides, ER stress conditions affect mitochondria functionality and vice-versa, as ER and mitochondria communicate via mitochondria-associated ER membranes (MAMs) to carry out a number of fundamental cellular functions. It is not surprising, thus, that also MAMs perturbations are involved in the regulation of apoptosis. This chapter intends to accurately discuss the involvement of MAMs in apoptosis, highlighting their crucial role in controlling this delicate cellular process.
    Keywords:  Apoptosis; Bioenergetics; Calcium signaling; ER-mitochondria contact sites; MAMs; Organelle tethering
  6. Cell Rep. 2021 Jun 08. pii: S2211-1247(21)00568-4. [Epub ahead of print]35(10): 109217
      The ubiquitous ribosome-associated complex (RAC) is a chaperone that spans ribosomes, making contacts near both the polypeptide exit tunnel and the decoding center, a position prime for sensing and coordinating translation and folding. Loss of RAC is known to result in growth defects and sensitization to translational and osmotic stresses. However, the physiological substrates of RAC and the mechanism(s) by which RAC is involved in responding to specific stresses in higher eukaryotes remain obscure. The data presented here uncover an essential function of mammalian RAC in the unfolded protein response (UPR). Knockdown of RAC sensitizes mammalian cells to endoplasmic reticulum (ER) stress and selectively interferes with IRE1 branch activation. Higher-order oligomerization of the inositol-requiring enzyme 1α (IRE1α) kinase/endoribonuclease depends upon RAC. These results reveal a surveillance function for RAC in the UPR, as follows: modulating IRE1α clustering as required for endonuclease activation and splicing of the substrate Xbp1 mRNA.
    Keywords:  IRE1 foci; UPR; Xbp1 mRNA; chaperone; ribosome stalling; ribosome-associated complex; translation
  7. Methods Mol Biol. 2021 ;2275 363-378
      In the last decades, membrane contact sites (MCSs) have been the object of intense investigation in different fields of cell physiology and pathology and their importance for the correct functioning of the cell is now widely recognized. MCS between any known intercellular organelles, including endoplasmic reticulum (ER), mitochondria, Golgi, endosomes, peroxisomes, lysosomes, lipid droplets, and the plasma membrane (PM), have been largely documented and in some cases the molecules responsible for the tethering also identified. They represent specific membrane hubs where a tightly coordinated exchange of ions, lipids, nutrients, and factors required to maintain proper cellular homeostasis takes place. Their delicate, dynamic, and sometimes elusive nature prevented and/or delayed the development of tools to easily image interorganelle proximity under physiological conditions and in living organisms. Nowadays, this aspect received great momentum due to the finding that MCSs' dysregulation is involved in several pathological conditions. We have recently developed modular, split-GFP-based contact site sensors (SPLICS) engineered to fluoresce when homo- and heterotypic juxtapositions between ER and mitochondria occur over a range of specific distances. Here we describe in detail, by highlighting strengths and weaknesses, the use and the application of these novel genetically encoded SPLICS sensors and how to properly quantify short- and long-range ER-mitochondria interactions.
    Keywords:  ER–Mitochondria tethering; Endoplasmic reticulum; Mitochondria; Organelle contact sites; SPLICS; Split GFP
  8. Nature. 2021 Jun;594(7862): 177
    Keywords:  History; Neuroscience; Philosophy; Sociology
  9. Front Oncol. 2021 ;11 654995
      Lung cancer is the most frequently diagnosed cancer and the main cause of cancer death in the world. X-box binding protein 1 (XBP1), which is an important transcription factor involved in regulating the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress, might act as a potent oncogenic protein in the processes of tumorigenesis, tumor proliferation and metastasis in various cancers. However, the clinical significance and pathological role of XBP1 in non-small cell lung cancer (NSCLC) remains unknown. In this study, we investigated the expression of XBP1s protein in the 104 NSCLC tumor tissues and matched adjacent normal lung tissues (ANLT) by Immunohistochemical (IHC), and we found overexpressed XBP1s protein was associated with NSCLC TNM stages, lymph node metastasis and poor prognosis. The further gain-and loss-of-function experiments indicated overexpression of XBP1s protein promoted cell invasion, migration and metastasis both in vitro and in vivo. Further study showed XBP1s protein could upregulate insulin-like growth factor binding protein-3 (IGFBP3) expression, and regulated NSCLC cells invasion and metastasis by regulating IGFBP3. Taken together, XBP1s protein is markedly overexpressed in NSCLC and serves as an oncogene that play a critical role in NSCLC tumorigenesis and development. Importantly, XBP1s protein might not only be a potential biomarker for metastasis and prognosis but also a potential therapeutic target in NSCLC.
    Keywords:  IGFBP3; NSCLC; XBP1; invasion; metastasis
  10. Mol Biol. 2021 May 30. 1-31
      Spatial organization of protein biosynthesis in the eukaryotic cell has been studied for more than fifty years, thus many facts have already been included in textbooks. According to the classical view, mRNA transcripts encoding secreted and transmembrane proteins are translated by ribosomes associated with endoplasmic reticulum membranes, while soluble cytoplasmic proteins are synthesized on free polysomes. However, in the last few years, new data has emerged, revealing selective translation of mRNA on mitochondria and plastids, in proximity to peroxisomes and endosomes, in various granules and at the cytoskeleton (actin network, vimentin intermediate filaments, microtubules and centrosomes). There are also long-standing debates about the possibility of protein synthesis in the nucleus. Localized translation can be determined by targeting signals in the synthesized protein, nucleotide sequences in the mRNA itself, or both. With RNA-binding proteins, many transcripts can be assembled into specific RNA condensates and form RNP particles, which may be transported by molecular motors to the sites of active translation, form granules and provoke liquid-liquid phase separation in the cytoplasm, both under normal conditions and during cell stress. The translation of some mRNAs occurs in specialized "translation factories," assemblysomes, transperons and other structures necessary for the correct folding of proteins, interaction with functional partners and formation of oligomeric complexes. Intracellular localization of mRNA has a significant impact on the efficiency of its translation and presumably determines its response to cellular stress. Compartmentalization of mRNAs and the translation machinery also plays an important role in viral infections. Many viruses provoke the formation of specific intracellular structures, virus factories, for the production of their proteins. Here we review the current concepts of the molecular mechanisms of transport, selective localization and local translation of cellular and viral mRNAs, their effects on protein targeting and topogenesis, and on the regulation of protein biosynthesis in different compartments of the eukaryotic cell. Special attention is paid to new systems biology approaches, providing new cues to the study of localized translation.
    Keywords:  SARS-CoV-2 induced COVID-19; assemblysomes; endoplasmic reticulum; localized translation; mRNA transport; mitochondria; nuclear translation; stress granules; translation factories; viral factories
  11. Nature. 2021 Jun;594(7862): 289-291
    Keywords:  Careers; Education; Lab life
  12. Methods Mol Biol. 2021 ;2275 301-314
      Our group has previously established a strategy utilizing fluorescence lifetime probes to image membrane protein supercomplex (SC) formation in situ. We showed that a probe at the interface between individual mitochondrial respiratory complexes exhibits a decreased fluorescence lifetime when a supercomplex is formed. This is caused by electrostatic interactions with the adjacent proteins. Fluorescence lifetime imaging microscopy (FLIM) records the resulting decrease of the lifetime of the SC-probe. Here we present the details of our method for performing SC-FLIM, including the evaluation of fluorescence lifetimes from the FLIM images. To validate the feasibility of the technique for monitoring adaptive SC formation, we compare data obtained under different metabolic conditions. The results confirm that SC formation is dynamic.
    Keywords:  FLIM; Fluorescence sensor; Live cell imaging; Mitochondria; Respiratory supercomplexes
  13. EMBO Mol Med. 2021 Jun 07. e13591
      Cachexia syndrome develops in patients with diseases such as cancer and sepsis and is characterized by progressive muscle wasting. While iNOS is one of the main effectors of cachexia, its mechanism of action and whether it could be targeted for therapy remains unexplored. Here, we show that iNOS knockout mice and mice treated with the clinically tested iNOS inhibitor GW274150 are protected against muscle wasting in models of both septic and cancer cachexia. We demonstrate that iNOS triggers muscle wasting by disrupting mitochondrial content, morphology, and energy production processes such as the TCA cycle and acylcarnitine transport. Notably, iNOS inhibits oxidative phosphorylation through impairment of complexes II and IV of the electron transport chain and reduces ATP production, leading to energetic stress, activation of AMPK, suppression of mTOR, and, ultimately, muscle atrophy. Importantly, all these effects were reversed by GW274150. Therefore, our data establish how iNOS induces muscle wasting under cachectic conditions and provide a proof of principle for the repurposing of iNOS inhibitors, such as GW274150 for the treatment of cachexia.
    Keywords:  cachexia; cancer; iNOS; inflammation; metabolism