bims-unfpre Biomed News
on Unfolded protein response
Issue of 2021‒06‒13
eight papers selected by
Susan Logue
University of Manitoba

  1. 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
  2. Front Oncol. 2021 ;11 654940
      The endoplasmic reticulum (ER) regulates protein folding, post-translational modifications, lipid synthesis, and calcium signaling to attenuate the accumulation of misfolded proteins causing ER stress and maintains cellular homeostasis. The tumor microenvironment is rich in soluble cytokines, chemokines, growth, and angiogenic factors and can drive the ER's abnormal functioning in healthy cells. Cancer cells adapt well to the tumor microenvironment induced ER stress. We identified that the inflammatory breast cancer (IBC) cells abundantly express osteoprotegerin (OPG) and their tumor microenvironment is rich in OPG protein. OPG also called osteoclast differentiation factor/osteoclastogenesis inhibitory factor (OCIF) is a soluble decoy receptor for receptor activator of nuclear factor-kappa B ligand (RANKL). Employing mass spectrometry analysis, we identified a set of ER chaperones associated with OPG in IBC cell lysates (SUM149PT, SUM1315MO2) compared to healthy human mammary epithelial cells (HMEC). Proximity ligation assay (PLA) and immunoprecipitation assay validated the interaction between OPG and ER chaperone and master regulator of unfolded protein response (UPR) GRP78/BiP (glucose-regulated protein/Binding immunoglobulin protein). We detected remarkably high gene expression of CCAAT enhancer-binding protein homologous protein (CHOP), inositol-requiring enzyme 1 (IRE1α), protein disulfide-isomerase (PDI), PKR-like ER kinase (PERK), activating transcription factor 4 (ATF4), X-box binding protein 1 (XBP-1) and growth arrest and DNA damage-inducible protein (GADD34) in SUM149PT and SUM190PT cells when compared to HMEC. Similarly, tissue sections of human IBC expressed high levels of ER stress proteins. We evaluated cell death and apoptosis upon Salubrinal and phenylbutyrate treatment in healthy and IBC cells by caspase-3 activity and cleaved poly (ADP-ribose) polymerase (PARP) protein assay. IBC (SUM149PT and SUM190PT) cells were chemosensitive to Salubrinal treatment, possibly via inhibition in OPG secretion, upregulating ATF4, and CHOP, thus ultimately driving caspase-3 mediated IBC cell death. Salubrinal treatment upregulated PDI, which connects ER stress to oxidative stress. We observed increased ROS production and reduced cell proliferation of Salubrinal treated IBC cells. Treatment with antioxidants could rescue IBC cells from ROS and aborted cell proliferation. Our findings implicate that manipulating ER stress with Salubrinal may provide a safer and tailored strategy to target the growth of inflammatory and aggressive forms of breast cancer.
    Keywords:  Salubrinal; endoplasmic reticulum stress; inflammatory breast cancer; osteoprotegerin; phenylbutyrate
  3. Cancer Sci. 2021 Jun 09.
      Pancreatic ductal adenocarcinoma (PDAC) is one of the most chemoresistant cancers. An understanding of the molecular mechanism by which PDAC cells have a high chemoresistant potential is important for improvement of the poor prognosis of patients with PDAC. Here we show for the first time that disruption of heat shock protein 47 (HSP47) enhances the efficacy of the therapeutic agent gemcitabine for PDAC cells and that the efficacy is suppressed by reconstituting HSP47 expression. HSP47 interacts with calreticulin (CALR) and the unfolded protein response transducer IRE1α in PDAC cells. Ablation of HSP47 promotes both the interaction of CALR with sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase 2 and interaction of IRE1α with inositol 1,4,5-triphosphate receptor, which generates a condition in which an increase in intracellular Ca2+ level is prone to be induced by oxidative stimuli. Disruption of HSP47 enhances NADPH oxidase-induced generation of intracellular reactive oxygen species (ROS) and subsequent increase in intracellular Ca2+ level in PDAC cells after treatment with gemcitabine, resulting in the death of PDAC cells by activation of the Ca2+ /caspases axis. Ablation of HSP47 promotes gemcitabine-induced suppression of tumor growth in PDAC cell-bearing mice. Overall, these results indicated that HSP47 confers chemoresistance on PDAC cells and suggested that disruption of HSP47 may improve the efficacy of chemotherapy for patients with PDAC.
    Keywords:  HSP47; IRE1α; PDAC; calreticulin; chemoresistance
  4. 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
  5. Eur J Pharmacol. 2021 Jun 08. pii: S0014-2999(21)00400-3. [Epub ahead of print] 174247
      Endoplasmic reticulum (ER) stress is an inflammatory response that contributes to endothelial dysfunction, a hallmark of cardiovascular diseases, in close interplay with oxidative stress. Recently, Sestrin2 (SESN2) emerged as a novel stress-inducible protein protecting cells from oxidative stress. We investigated here, for the first time, the impact of SESN2 suppression on oxidative stress and cell survival in human endothelial cells subjected to pharmacologically (thapsigargin)-induced ER stress and studied the underlying cellular pathways. We found that SESN2 silencing, though did not specifically induce ER stress, it aggravated the effects of thapsigargin-induced ER stress on oxidative stress and cell survival. This was associated with a dysregulation of Nrf-2, AMPK and mTORC1 signaling pathways. Furthermore, SESN2 silencing aggravated, in an additive manner, apoptosis caused by thapsigargin. Importantly, SESN2 silencing, unlike thapsigargin, caused a dramatic decrease in protein expression and phosphorylation of Akt, a critical pro-survival hub and component of the AMPK/Akt/mTORC1 axis. Our findings suggest that patients with conditions characterized by ER stress activation, such as diabetes, may be at higher risk for cardiovascular complications if their endogenous ability to stimulate and/or maintain expression levels of SESN2 is disturbed or impaired. Therefore, identifying novel or repurposing existing pharmacotherapies to enhance and/or maintain SESN2 expression levels would be beneficial in these conditions.
    Keywords:  Cardiovascular disease; Sestrin2; cell survival; endoplasmic reticulum (ER) stress; endothelial dysfunction; oxidative stress
  6. Cell Death Dis. 2021 Jun 11. 12(6): 606
      Increased neutrophil extracellular traps (NETs) formation has been found to be associated with intestinal inflammation, and it has been reported that NETs may drive the progression of gut dysregulation in sepsis. However, the biological function and regulation of NETs in sepsis-induced intestinal barrier dysfunction are not yet fully understood. First, we found that both circulating biomarkers of NETs and local NETs infiltration in the intestine were significantly increased and had positive correlations with markers of enterocyte injury in abdominal sepsis patients. Moreover, the levels of local citrullinated histone 3 (Cit H3) expression were associated with the levels of BIP expression. To further confirm the role of NETs in sepsis-induced intestinal injury, we compared peptidylarginine deiminase 4 (PAD4)-deficient mice and wild-type (WT) mice in a lethal septic shock model. In WT mice, the Cit H3-DNA complex was markedly increased, and elevated intestinal inflammation and endoplasmic reticulum (ER) stress activation were also found. Furthermore, PAD4 deficiency alleviated intestinal barrier disruption and decreased ER stress activation. Notably, NETs treatment induced intestinal epithelial monolayer barrier disruption and ER stress activation in a dose-dependent manner in vitro, and ER stress inhibition markedly attenuated intestinal apoptosis and tight junction injury. Finally, TLR9 antagonist administration significantly abrogated NETs-induced intestinal epithelial cell death through ER stress inhibition. Our results indicated that NETs could contribute to sepsis-induced intestinal barrier dysfunction by promoting inflammation and apoptosis. Suppression of the TLR9-ER stress signaling pathway can ameliorate NETs-induced intestinal epithelial cell death.
  7. Front Oncol. 2021 ;11 641487
      Hepatocellular carcinoma (HCC) is one of the most common types of cancer worldwide and its incidence continues to increase year by year. Endoplasmic reticulum stress (ERS) caused by protein misfolding within the secretory pathway in cells and has an extensive and deep impact on cancer cell progression and survival. Growing evidence suggests that the genes related to ERS are closely associated with the occurrence and progression of HCC. This study aimed to identify an ERS-related signature for the prospective evaluation of prognosis in HCC patients. RNA sequencing data and clinical data of patients from HCC patients were obtained from The Cancer Genome Atlas (TCGA) and The International Cancer Genome Consortium (ICGC). Using data from TCGA as a training cohort (n=424) and data from ICGC as an independent external testing cohort (n=243), ERS-related genes were extracted to identify three common pathways IRE1, PEKR, and ATF6 using the GSEA database. Through univariate and multivariate Cox regression analysis, 5 gene signals in the training cohort were found to be related to ERS and closely correlated with the prognosis in patients of HCC. A novel 5-gene signature (including HDGF, EIF2S1, SRPRB, PPP2R5B and DDX11) was created and had power as a prognostic biomarker. The prognosis of patients with high-risk HCC was worse than that of patients with low-risk HCC. Multivariate Cox regression analysis confirmed that the signature was an independent prognostic biomarker for HCC. The results were further validated in an independent external testing cohort (ICGC). Also, GSEA indicated a series of significantly enriched oncological signatures and different metabolic processes that may enable a better understanding of the potential molecular mechanism mediating the progression of HCC. The 5-gene biomarker has a high potential for clinical applications in the risk stratification and overall survival prediction of HCC patients. In addition, the abnormal expression of these genes may be affected by copy number variation, methylation variation, and post-transcriptional regulation. Together, this study indicated that the genes may have potential as prognostic biomarkers in HCC and may provide new evidence supporting targeted therapies in HCC.
    Keywords:  The Cancer Genome Atlas; endoplasmic reticulum stress; hepatocellular carcinoma; multi-omics; prognosis; signature
  8. Eur J Pharmacol. 2021 Jun 08. pii: S0014-2999(21)00402-7. [Epub ahead of print] 174249
      Endoplasmic reticulum (ER) stress plays a critical role in progression of diabetes and development of complications, notably cardiovascular disease. Some of the contemporary anti-hyperglycemic drugs have been shown to inhibit ER stress. To extend these observations, the effects of various anti-hyperglycemic agents were screened for their effects on ER stress. Seven classes of anti-hyperglycemic drugs were screened including sulfonylureas, meglitinides, metformin, α glucosidase inhibitors, thiazolidinedione, glucagon like peptide 1 (GLP-1) receptor agonists and sodium-glucose cotransporter 2 (SGLT-2) inhibitors. ER stress was measured in human coronary artery endothelial cells (HCAEC) either treated with tunicamycin (TM) or cultured in hyperglycemic conditions (27.5 mM dextrose). The ER stress was measured with the secreted alkaline phosphatase (ES-TRAP) assay. Mediators of the unfolded protein response, including activating transcription factor 6 (ATF6), glucose-regulated protein 78 (GRP78), phospho-inositol-requiring enzyme 1α (pIRE1α), IRE1α, phospho-protein kinase R (PKR)-like endoplasmic reticulum kinase (pPERK), and PERK were measured by Western blot. Metformin, GLP-1 receptor agonists (GLP-1, exendin 4, liraglutide, albiglutide, and lixisenatide) and SGLT-2 inhibitors (canagliflozin, dapagliflozin, and empagliflozin) were the only anti-hyperglycemic drugs screened that reduced ER stress caused by pharmacological (tunicamycin) or hyperglycemic conditions. High-dextrose and TM increased IRE1α and PERK phosphorylation and ATF6 and GRP78 expression, while treatment with metformin, liraglutide (a GLP-1 receptor agonist) and dapagliflozin (a SGLT-2 inhibitor), suppressed IRE1α and PERK phosphorylation as well as ATF6 and GRP78 expression. The cardioprotective effects of metformin, some of the GLP-1 receptor agonists and SGLT2 inhibitors may be partly related to their ability to reduce ER stress.
    Keywords:  GLP-1; HCAEC; unfolded protein response