bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2021‒12‒19
six papers selected by
Matías Eduardo González Quiroz
Worker’s Hospital

  1. Nat Commun. 2021 Dec 15. 12(1): 7310
      Inositol requiring enzyme 1 (IRE1) mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, in mammals RIDD seems to target only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1α-controlled mRNAs in human cells, we identify not only canonical endomotif-containing RIDD substrates, but also targets without such motifs-degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1α displays two basic endoribonuclease modalities: highly specific, endomotif-directed cleavage, minimally requiring dimers; and more promiscuous, endomotif-independent processing, requiring phospho-oligomers. An oligomer-deficient IRE1α mutant fails to support RIDDLE in vitro and in cells. Our results advance current mechanistic understanding of the UPR.
  2. Plant J. 2021 Dec 11.
      Proteostasis of the endoplasmic reticulum (ER) is controlled by sophisticated signaling pathways that are collectively called the unfolded protein response (UPR) and are initiated by specialized ER membrane-associated sensors. The evidence that complete loss-of-function mutations of the most conserved of the UPR sensors, inositol-requiring enzyme 1 (IRE1), dysregulates tissue growth and development in metazoans and plants raises the fundamental question as to how IRE1 is connected to organismal growth. To address this question, we interrogated the Arabidopsis primary root, an established model for organ development, using the tractable Arabidopsis IRE1 mutant ire1a ire1b, which has marked root development defects in the absence of exogenous stress. We demonstrate that IRE1 is required to reach maximum rates of cell elongation and root growth. We also established that in the actively growing ire1a ire1b mutant root tips the Target of Rapamycin (TOR) kinase, a widely conserved pro-growth regulator, is hyperactive, and that, unlike cell proliferation, the rate of cell differentiation is enhanced in ire1a ire1b in a TOR-dependent manner. By functionally connecting two essential growth regulators, these results underpin a novel and critical role of IRE1 in organ development and indicate that, as cells exit an undifferentiated state, IRE1 is required to monitor TOR activity to balance cell expansion and maturation during organ biogenesis.
    Keywords:   Arabidopsis thaliana ; IRE1; TOR; development; differentiation; unfolded protein response
  3. Andrologia. 2021 Dec 13. e14350
      Activating transcription factor 6 (ATF6), also known as ACHM7, ATF6A, encodes a transcription factor that activates target genes for the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress. It functions as nuclear transcription factor via a cis-acting ER stress response element (ERSE) that is presented in the promoters of genes encoding ER chaperones. Studies have shown that endoplasmic reticulum stress (ERS) can cause damage to spermatozoa and testes, leading to male sterility. And we find that the expression of ATF6 in spermatozoa of some infertile patients is significantly reduced. Then, we construct the Atf6 knockout mice model and interestingly find a decline in male fertility. The downstream gene testis-specific serine/threonine-protein kinase 4 (Tssk4) is screened based on transcriptome sequencing. We use Western blot and real-time PCR to confirm this result in both 293T cells and Atf6 knockout mice. TSSK4 is essential in male germ cell genesis and sperm maturation. Our results suggest that the expression of TSSK4 may be regulated by ATF6. The effect of Atf6 knockout on the reproductive development of male mice may be related to the low expression of TSSK4, which further verify that there may be some relationship between ERS and male reproduction.
    Keywords:  endoplasmic reticulum stress; male fertility; spermatogenesis; transcriptome sequencing
  4. J Biochem. 2021 Dec 15. pii: mvab140. [Epub ahead of print]
      Dysfunction caused by mGluR5 expression or activation is an important mechanism in the development of Parkinson's disease (PD). Early clinical studies on mGluR5 negative allosteric modulators have shown some limitations. It is therefore necessary to find a more specific approach to block mGluR5-mediated neurotoxicity. Here, we determined the role of NMDA receptor subunit NR2B in mGluR5-mediated ER stress and DNA damage. In vitro study, rotenone-induced ER stress and DNA damage were accompanied by an increase in mGluR5 expression, and overexpressed or activated mGluR5 with agonist CHPG induced ER stress and DNA damage, while blocking mGluR5 with antagonist MPEP alleviated the effect. Furthermore, the damage caused by CHPG was blocked by NMDA receptor antagonist MK-801. Additionally, rotenone or CHPG increased the p-Src and p-NR2B, which was inhibited by MPEP. Blocking p-Src or NR2B with PP2 or CP101,606 alleviated CHPG-induced ER stress and DNA damage. Overactivation of mGluR5 accompanied with the increase of p-Src and p-NR2B in the ER stress and DNA damage was found in rotenone-induced PD rat model. These findings suggest a new mechanism wherein mGluR5 induces ER stress and DNA damage through the NMDA receptor and propose NR2B as the molecular target for therapeutic strategy for PD.
    Keywords:  DNA damage; Endoplasmic reticulum stress; Metabotropic glutamate receptor 5; NR2B subunit; Parkinson’s disease
  5. Nature. 2021 Dec 15.
      Organelles move along differentially modified microtubules to establish and maintain their proper distributions and functions1,2. However, how cells interpret these post-translational microtubule modification codes to selectively regulate organelle positioning remains largely unknown. The endoplasmic reticulum (ER) is an interconnected network of diverse morphologies that extends promiscuously throughout the cytoplasm3, forming abundant contacts with other organelles4. Dysregulation of endoplasmic reticulum morphology is tightly linked to neurologic disorders and cancer5,6. Here we demonstrate that three membrane-bound endoplasmic reticulum proteins preferentially interact with different microtubule populations, with CLIMP63 binding centrosome microtubules, kinectin (KTN1) binding perinuclear polyglutamylated microtubules, and p180 binding glutamylated microtubules. Knockout of these proteins or manipulation of microtubule populations and glutamylation status results in marked changes in endoplasmic reticulum positioning, leading to similar redistributions of other organelles. During nutrient starvation, cells modulate CLIMP63 protein levels and p180-microtubule binding to bidirectionally move endoplasmic reticulum and lysosomes for proper autophagic responses.
  6. Methods Mol Biol. 2022 ;2400 75-85
      The bimolecular fluorescence complementation (BiFC) assay allows the visualization of protein-protein interactions in their native state within living systems. The BiFC assay is based on the in vivo complementation of nonfluorescent component parts of a fluorescent protein through the interaction or proximity target proteins, each fused to a different component of the fluorescent protein. Expansion of the BiFC toolkit with an increasing spectrum of fluorescence markers and catalog of Gateway-compatible vectors for high-throughput screening, has made BiFC an exceedingly powerful tool in discovering new protein interactions or providing backup evidence for known ones. Apart from the validation of protein-protein interactions, BiFC offers the additional benefit of providing information on the subcellular localization of protein interaction complexes. Subcellular localization to a specific subcellular compartment or organelle may be further validated by the coexpression of a fluorescence-labeled protein marker. Here we describe an efficient yet simple protocol for simultaneous determination and subcellular localization of protein-protein interactions in plant cells.
    Keywords:  Agroinfiltration; Bimolecular fluorescence complementation; Fluoresce microscopy; Protein–protein interaction; Subcellular localization; Transient expression