bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2022‒04‒03
nine papers selected by
Matías Eduardo González Quiroz
Worker’s Hospital

  1. Exp Hematol Oncol. 2022 Mar 31. 11(1): 18
      BACKGROUND: IRE1 is an unfolded protein response (UPR) sensor with kinase and endonuclease activity. It plays a central role in the endoplasmic reticulum (ER) stress response through unconventional splicing of XBP1 mRNA and regulated IRE1-dependent decay (RIDD). Multiple myeloma (MM) cells are known to exhibit an elevated level of baseline ER stress due to immunoglobulin production, however RIDD activity has not been well studied in this disease. In this study, we aimed to investigate the potential of RNA-sequencing in the identification of novel RIDD targets in MM cells and to analyze the role of these targets in MM cells.METHODS: In vitro IRE1-cleavage assay was combined with RNA sequencing. The expression level of RIDD targets in MM cell lines was measured by real-time RT-PCR and Western blot.
    RESULTS: Bioinformatic analysis revealed hundreds of putative IRE1 substrates in the in vitro assay, 32 of which were chosen for further validation. Looking into the secondary structure of IRE1 substrates, we found that the consensus sequences of IRF4, PRDM1, IKZF1, KLF13, NOTCH1, ATR, DICER, RICTOR, CDK12, FAM168B, and CENPF mRNAs were accompanied by a stem-loop structure essential for IRE1-mediated cleavage. In fact, we show that mRNA and protein levels corresponding to these targets were attenuated in an IRE1-dependent manner by treatment with ER-stress-inducing agents. In addition, a synergistic effect between IMiDs and ER-stress inducers was found.
    CONCLUSION: This study, using RNA sequencing, shows that IRE1 RNase has a broad range of mRNA substrates in myeloma cells and demonstrates for the first time that IRE1 is a key regulator of several proteins of importance in MM survival and proliferation.
    Keywords:  ER stress; IRE1; Multiple myeloma; RIDD; UPR
  2. RSC Chem Biol. 2021 Feb 01. 2(1): 47-76
      Damaging DNA is a current and efficient strategy to fight against cancer cell proliferation. Numerous mechanisms exist to counteract DNA damage, collectively referred to as the DNA damage response (DDR) and which are commonly dysregulated in cancer cells. Precise knowledge of these mechanisms is necessary to optimise chemotherapeutic DNA targeting. New research on DDR has uncovered a series of promising therapeutic targets, proteins and nucleic acids, with application notably via an approach referred to as combination therapy or combinatorial synthetic lethality. In this review, we summarise the cornerstone discoveries which gave way to the DNA being considered as an anticancer target, and the manipulation of DDR pathways as a valuable anticancer strategy. We describe in detail the DDR signalling and repair pathways activated in response to DNA damage. We then summarise the current understanding of non-B DNA folds, such as G-quadruplexes and DNA junctions, when they are formed and why they can offer a more specific therapeutic target compared to that of canonical B-DNA. Finally, we merge these subjects to depict the new and highly promising chemotherapeutic strategy which combines enhanced-specificity DNA damaging and DDR targeting agents. This review thus highlights how chemical biology has given rise to significant scientific advances thanks to resolutely multidisciplinary research efforts combining molecular and cell biology, chemistry and biophysics. We aim to provide the non-specialist reader a gateway into this exciting field and the specialist reader with a new perspective on the latest results achieved and strategies devised.
  3. Front Mol Neurosci. 2022 ;15 829365
      Cellular health depends on the integrity and functionality of the proteome. Each cell is equipped with a protein quality control machinery that maintains protein homeostasis (proteostasis) by helping proteins adopt and keep their native structure, and ensuring the degradation of damaged proteins. Postmitotic cells such as neurons are especially vulnerable to disturbances of proteostasis. Defects of protein quality control occur in aging and have been linked to several disorders, including neurodegenerative diseases. However, the exact nature and time course of such disturbances in the context of brain diseases remain poorly understood. Sensors that allow visualization and quantitative analysis of proteostasis capacity in neurons are essential for gaining a better understanding of disease mechanisms and for testing potential therapies. Here, I provide an overview of available biosensors for assessing the functionality of the neuronal proteostasis network, point out the advantages and limitations of different sensors, and outline their potential for biological discoveries and translational applications.
    Keywords:  biosensor; neuron; protein folding; protein misfolding diseases; protein quality control; proteostasis
  4. Cell Biol Int. 2022 Mar 29.
      Endoplasmic reticulum (ER) stress and apoptosis play a critical role in liver injury. Endoplasmic reticulum oxidoreductase 1α (ERO1α) is an oxidase that exists in the luminal side of the ER membrane, participating in protein folding and secretion and inhibiting apoptosis, but the underlying mechanism on liver injury induced by homocysteine (Hcy) remains obscure. In this study, hyperhomocysteinemia (HHcy) mice model was established in cbs+/- mice by feeding a high-methionine diet for 12 weeks; and cbs+/- mice fed with high-methionine diet exhibited more severe liver injury compared to cbs+/+ mice. Mechanistically, we found that Hcy promoted ER stress and apoptosis of hepatocytes and thereby aggravated liver injury through inhibiting ERO1α expression; accordingly, over-expression of ERO1α remarkably alleviated ER stress and apoptosis of hepatocytes induced by Hcy. Epigenetic modification analysis revealed that Hcy significantly increased levels of DNA methylation and H3 lysine 9 dimethylation (H3K9me2) on ERO1α promoter, which attributed to up-regulated DNA methyltransferase 1 (DNMT1) and G9a respectively. Further study showed that DNMT1 and G9a cooperatively regulated ERO1α expression in hepatocytes exposed to Hcy. Taken together, our work demonstrates that Hcy activates ER stress and apoptosis of hepatocytes by downregulating ERO1α expression via cooperation between DNMT1 and G9a, which provides new insight into the mechanism of Hcy-induced ER stress and apoptosis of hepatocytes in liver injury. This article is protected by copyright. All rights reserved.
    Keywords:  DNMT1; ERO1α; Endoplasmic reticulum stress; G9a; Homocysteine; apoptosis
  5. Trends Genet. 2022 Mar 25. pii: S0168-9525(22)00037-3. [Epub ahead of print]
      The tumor protein TP53 gene, encoding the cellular tumor antigen p53, is the single most frequently mutated gene in human cancers. p53 plays a central role in responding to DNA damage and determines the outcome of the DNA damage checkpoint response by regulating cell cycle arrest and apoptosis. As a consequence of this function, dysfunctional p53 results in cells that, despite a damaged genome, continue to proliferate thus fueling malignant transformation. New insights have recently been gained into the complexity of the p53 regulation of the DNA damage response (DDR) and how it impacts a wide variety of cellular processes. In addition to cell-autonomous signaling mechanisms, non-cell-autonomous regulatory inputs influence p53 activity, which in turn can have systemic consequences on the organism. New inroads have also been made toward therapeutic targeting of p53 that for a long time has been anticipated.
    Keywords:  DNA damage; aging; cancer; p53; tumor suppression
  6. Bio Protoc. 2022 Feb 20. 12(4): e4331
      Mapping networks of RNA-protein interactions in cells is essential for understanding the inner workings of many biological processes, including RNA processing, trafficking, and translation. Current in vivo methods for studying protein-RNA interactions rely mostly on purification of poly(A) transcripts, which represent only ~2-3% of total RNAs (Figure 1). Alternate robust methods for tagging RNA molecules with an RNA aptamer (e.g., MS2-, U1A- and biotin-RNA aptamer) and capturing the RNA-protein complex by the respective aptamer-specific partner are not extensively studied. Here, we describe a protocol (Figure 2) in which a biotin-RNA aptamer, referred to as the RNA mimic of biotin (RMB), was conjugated separately to two small RNA secondary structures that contribute to trafficking and translating HAC1 mRNA in the budding yeast Saccharomyces cerevisiae. The RMB-tagged RNA was expressed in yeast cells from a constitutive promoter. The biotinylated RNA bound to proteins was pulled down from the cell lysate by streptavidin agarose beads. RNA was detected by RT-PCR (Figure 3) and associated proteins by mass spectrometry (Figure 4). Our findings show that an RNA aptamer tag to RNA molecule is an effective method to explore the functional roles of RNA-protein networks in vivo.
    Keywords:  Biotinylated RNA; HAC1 mRNA; RNA aptamer; RNA binding protein (RBP); RNA mimic of biotin
  7. Cancer Sci. 2022 Mar 31.
      Infection with cagA-positive Helicobacter pylori strains plays an etiological role in the development of gastric cancer. The CagA protein is injected into gastric epithelial cells through a bacterial Type IV secretion system. Inside the host cells, CagA promiscuously associates with multiple host cell proteins including the prooncogenic phosphatase SHP2 that is required for full activation of the RAS-ERK pathway. CagA-SHP2 interaction aberrantly activates SHP2 and thereby deregulates RAS-ERK signaling. Cancer is regarded as a disease of the genome, indicating that H. pylori-mediated gastric carcinogenesis is also associated with genomic alterations in the host cell. Indeed, accumulating evidence has indicated that H. pylori infection provokes DNA double-strand breaks (DSBs) by both CagA-dependent and -independent mechanisms. DSBs are repaired by either error-free homologous recombination (HR) or error-prone non-homologous end joining (NHEJ) or microhomology-mediated end joining (MMEJ). Infection with cagA-positive H. pylori inhibits RAD51 expression while dampening cytoplasmic-to-nuclear translocalization of BRCA1, causing replication fork instability and HR defects (known as "BRCAness"), which collectively provoke genomic hypermutation via non-HR-mediated DSB repair. H. pylori also subverts multiple DNA damage responses including DNA repair systems. Infection with H. pylori additionally inhibits the function of the p53 tumor suppressor, thereby dampening DNA damage-induced apoptosis while promoting proliferation of CagA-delivered cells. Thus, H. pylori cagA-positive strains promote abnormal expansion of cells with BRCAness, which dramatically increases the chance of generating driver gene mutations in the host cells. Once such driver mutations are acquired, H. pylori CagA is no longer required for subsequent gastric carcinogenesis (Hit-and-Run carcinogenesis).
    Keywords:   Helicobacter pylori ; CagA; DNA damage response; DNA double-strand break; genome instability
  8. Sci Rep. 2022 Mar 30. 12(1): 5377
      Regulatory T cells (Tregs) suppress the host immune response and maintain immune homeostasis. Tregs also promote cancer progression and are involved in resistance to immune checkpoint inhibitor treatments. Recent studies identified selective CCR8 expression on tumor-infiltrating Tregs; CCR8+ Tregs have been indicated as a possible new target of cancer immunotherapy. Here, we investigated the features of CCR8+ Tregs in lung cancer patients. CCR8+ Tregs were highly activated and infiltration of CCR8+ Tregs in tumors was associated with poor prognosis in lung cancer patients. We also investigated their immune suppressive function, especially the influence on cytotoxic T lymphocyte cell function. The Cancer Genome Atlas analysis revealed that CD8 T cell activities were suppressed in high CCR8-expressing tumors. Additionally, depletion of CCR8+ cells enhanced CD8 T cell function in an ex vivo culture of lung tumor-infiltrating cells. Moreover, CCR8+ Tregs, but not CCR8- Tregs, induced from human PBMCs markedly suppressed CD8 T cell cytotoxicity. Finally, we demonstrated the therapeutic effect of targeting CCR8 in a murine model of lung cancer. These findings reveal the significance of CCR8+ Tregs for immunosuppression in lung cancer, especially via cytotoxic T lymphocyte cell suppression, and suggest the potential value of CCR8-targeted therapy for cancer treatment.
  9. Aging Cell. 2022 Mar 29. e13603
      Protein quality control ensures the degradation of damaged and misfolded proteins. Derangement of proteostasis is a primary cause of aging and age-associated diseases. The ubiquitin-proteasome and autophagy-lysosome play key roles in proteostasis but, in addition to these systems, the human genome encodes for ~600 proteases, also known as peptidases. Here, we examine the role of proteases in aging and age-related neurodegeneration. Proteases are present across cell compartments, including the extracellular space, and their substrates encompass cellular constituents, proteins with signaling functions, and misfolded proteins. Proteolytic processing by proteases can lead to changes in the activity and localization of substrates or to their degradation. Proteases cooperate with the autophagy-lysosome and ubiquitin-proteasome systems but also have independent proteolytic roles that impact all hallmarks of cellular aging. Specifically, proteases regulate mitochondrial function, DNA damage repair, cellular senescence, nutrient sensing, stem cell properties and regeneration, protein quality control and stress responses, and intercellular signaling. The capacity of proteases to regulate cellular functions translates into important roles in preserving tissue homeostasis during aging. Consequently, proteases influence the onset and progression of age-related pathologies and are important determinants of health span. Specifically, we examine how certain proteases promote the progression of Alzheimer's, Huntington's, and/or Parkinson's disease whereas other proteases protect from neurodegeneration. Mechanistically, cleavage by proteases can lead to the degradation of a pathogenic protein and hence impede disease pathogenesis. Alternatively, proteases can generate substrate byproducts with increased toxicity, which promote disease progression. Altogether, these studies indicate the importance of proteases in aging and age-related neurodegeneration.
    Keywords:  aging; extracellular proteostasis; neurodegeneration; peptidase; protease; proteolysis