bims-unfpre Biomed News
on Unfolded protein response
Issue of 2023‒09‒24
nine papers selected by
Susan Logue, University of Manitoba

  1. J Cell Commun Signal. 2023 Sep 18.
      The unfolded protein response (UPR) is a cellular mechanism that protects cells during stress conditions in which there is an accumulation of misfolded proteins in the endoplasmic reticulum (ER). UPR activates three signaling pathways that function to alleviate stress conditions and promote cellular homeostasis and cell survival. During unmitigated stress conditions, however, UPR activation signaling changes to promote cell death through apoptosis. Interestingly, cancer cells take advantage of this pathway to facilitate survival and avoid apoptosis even during prolonged cell stress conditions. Here, we discuss different signaling pathways associated with UPR and focus specifically on one of the ER signaling pathways activated during UPR, inositol-requiring enzyme 1α (IRE1). The rationale is that the IRE1 pathway is associated with cell fate decisions and recognized as a promising target for cancer therapeutics. Here we discuss IRE1 inhibitors and how they might prove to be an effective cancer therapeutic.
    Keywords:  Basal RIDD; ER-stress; IRE1α; RIDD; UPR; XBP1
  2. J Cell Mol Med. 2023 Sep 20.
      Endoplasmic reticulum (ER) stress can stimulate the proliferation and metastasis of hepatocellular carcinoma (HCC) cells while hindering apoptosis and immune system function, but the molecular mechanism of ER stress in HCC has yet to be fully studied. We aim to investigate the molecular mechanism by which FAM134B inhibits autophagy of HCC cells by reducing the expression of ER stress-related degradation proteins. Clinical samples were collected for this study. Normal liver cell lines HL7702 and Hep3B and Huh7 HCC cell lines were cultured. Construction of FAM134B knockdown cell line. Cell proliferation was measured using the CCK-8 assay, while cell migration and invasion capabilities were detected using the plate colony formation assay. Flow cytometry was used to detect the apoptosis rate. Transmission electron microscopy was used to observe the formation of autophagosomes. qRT-PCR and WB detective expression changes related to autophagy proteins. Finally, the expression of the relevant proteins was observed by immunohistochemistry. The expression of FAM134B was significantly increased in human liver cancer tissue and HCC cell lines Hep3B and Huh7. After the lentiviral vector was transfected into Hep3B cells with sh-FAM134B, results showed that sh-FAM134B could effectively inhibit Hep3B cell proliferation and promote HCC cell apoptosis. Meanwhile, sh-FAM134B could effectively induce the autophagy of Hep3B liver cancer cells. Immunohistochemistry results showed that sh-FAM134B could effectively induce ER stress. FAM134B inhibits HCC cell autophagy and promotes the progression of liver cancer by inhibiting the expression of ER stress-related degradation factors such as DERL2, EDEM1, SEL1L and HRD1.
    Keywords:  FAM134B; cell autophagy; endoplasmic reticulum stress; hepatocellular carcinoma
  3. Life Sci. 2023 Sep 20. pii: S0024-3205(23)00742-7. [Epub ahead of print] 122107
      AIMS: Prolonged high levels of cytokines, glucose, or free fatty acids are associated with diabetes, elevation of cytosolic Ca2+ concentration ([Ca2+]C), and depletion of Ca2+ concentration in the endoplasmic reticulum (ER) of pancreatic beta cells. This Ca2+ imbalance induces ER stress and apoptosis. Lupenone, a lupan-type triterpenoid, is beneficial in diabetes; however, its mechanism of action is yet to be clarified. This study evaluated the protective mechanism of lupenone against thapsigargin-induced ER stress and apoptosis in pancreatic beta cells.MATERIALS AND METHODS: MIN6, INS-1, and native mouse islet cells were used. Western blot for protein expressions, measurement of [Ca2+]C, and in vivo glucose tolerance test were mainly performed.
    KEY FINDINGS: Thapsigargin increased the protein levels of cleaved caspase 3, cleaved PARP, and the phosphorylated form of JNK, ATF4, and CHOP. Thapsigargin increased the interaction between stromal interaction molecule1 (Stim1) and Orai1, enhancing store-operated calcium entry (SOCE). SOCE is further activated by protein tyrosine kinase 2 (Pyk2), which is Ca2+-dependent and phosphorylates the tyrosine residue at Y361 in Stim1. Lupenone inhibited thapsigargin-mediated Pyk2 activation, suppressed [Ca2+]C, ER stress, and apoptosis. Lupenone restored impaired glucose-stimulated insulin secretion effectuated by thapsigargin and glucose intolerance in a low-dose streptozotocin-induced diabetic mouse model.
    SIGNIFICANCE: These results suggested that lupenone attenuated thapsigargin-induced ER stress and apoptosis by inhibiting SOCE; this may be due to the hindrance of Pyk2-mediated Stim1 tyrosine phosphorylation. In beta cells that are inevitably exposed to frequent [Ca2+]C elevation, the attenuation of abnormally high SOCE would be beneficial for their survival.
    Keywords:  2-Aminoethoxydiphenyl borate (PubChem CID: 1598); 4-Phenylbutyric acid (PubChem CID: 4775); Apoptosis; Beta-cell; Cyclopiazonic acid (PubChem CID: 54695722); ER stress; KN-93 (PubChem CID: 5312122); Lupenone; Lupenone (PubChem CID: 92158); Protein tyrosine kinase 2; SP600125 (PubChem CID: 8515); Sodium orthovanadate (PubChem CID: 61671); Store-operated calcium entry; Streptozotocin (PubChem CID: 29327); Thapsigargin (PubChem CID: 446378); W-7 (PubChem CID: 124887)
  4. Cell Stress Chaperones. 2023 Sep 22.
      Ischemic heart failure (HF) is one of the leading causes of global morbidity and mortality; blocking the apoptotic cascade could help improve adverse outcomes of it. RNA-binding motif protein 25 (RBM25) is an RNA-binding protein related to apoptosis; however, its role remains unknown in ischemic HF. The main purpose of this study is to explore the mechanism of RBM25 in ischemic HF. Establishing an ischemic HF model and oxygen-glucose deprivation (OGD) model. ELISA was performed to evaluate the BNP level in the ischemic HF model. Echocardiography and histological analysis were performed to assess cardiac function and infarct size. Proteins were quantitatively and locationally analyzed by western blotting and immunofluorescence. The morphological changes of endoplasmic reticulum (ER) were observed with ER-tracker. Cardiac function and myocardial injury were observed in ischemic HF rats. RBM25 was elevated in cardiomyocytes of hypoxia injury hearts and localized in nucleus both in vitro and in vivo. In addition, cell apoptosis was significantly increased when overexpressed RBM25. Moreover, ER stress stimulated upregulation of RBM25 and promoted cell apoptosis through the CHOP related pathway. Finally, inhibiting the expression of RBM25 could ameliorate the apoptosis and improve cardiac function through blocking the activation of CHOP signaling pathway. RBM25 is significantly upregulated in ischemic HF rat heart and OGD model, which leads to apoptosis by modulating the ER stress through CHOP pathway. Knockdown of RBM25 could reverse apoptosis-mediated cardiac dysfunction. RBM25 may be a promising target for the treatment of ischemic HF.
    Keywords:  Apoptosis; Endoplasmic reticulum stress; Ischemic heart failure; Myocardial infarction; RBM25
  5. Biochim Biophys Acta Mol Cell Res. 2023 Sep 20. pii: S0167-4889(23)00161-1. [Epub ahead of print] 119588
      Protein phosphatase 4 (PP4) plays an indispensable regulatory part in the development and malignant progression of multifarious tumors. Nevertheless, the function of protein phosphatase 4 regulatory subunit 1 (PP4R1), a vital regulatory subunit of PP4, in tumors especially in lung cancer remains blurred. Therefore, this study aimed to investigate the function and mechanism of PP4R1 in the development of non-small cell lung cancer (NSCLC). We analyzed the clinical correlation of PP4R1 based on the TCGA database by UALCAN ( and found that hyper-expression of PP4R1 mRNA was related to the severe prognosis in NSCLC. The subsequent cellular experiments confirmed that the proliferation, colony growth, migration as well as invasion of H1299 and HCC827 were significantly enhanced after PP4R1 overexpression treatment in vitro. Results from animal experiments pointed out that tumors exhibited stronger growth and lung metastatic capacities due to the overexpression of PP4R1. The bioinformatics analysis, including RNA-seq, showed us that PP4R1 significantly promoted the expression of several HSP70 family member genes, with a particularly marked increase in HSPA6, and the enrichment analyses illustrated that the differentially expressed genes (DEGs) were enriched in those pathways related to protein folding. More importantly, the overexpression of HSPA6 resulted in the same malignant progression of NSCLC as PP4R1 overexpression, and both concomitant with the activation of endoplasmic reticulum (ER) stress. In aggregate, PP4R1 contributed to the malignant progression of NSCLC via up-regulating HSPA6 expression and then activating ER stress.
    Keywords:  ER stress; HSPA6; NSCLC; PP4R1
  6. Autophagy. 2023 Sep 21.
      The VPS37A gene encodes a subunit of the endosomal sorting complex required for transport (ESCRT)-I complex that is frequently lost in a wide variety of human solid cancers. We have previously demonstrated the role of VPS37A in directing the ESCRT membrane scission machinery to seal the phagophore for autophagosome completion. Here, we report that VPS37A-deficient cells exhibit an accumulation of the apoptotic initiator CASP8 (caspase 8) on the phagophore and are primed to undergo rapid apoptosis through the intracellular death-inducing signaling complex (iDISC)-mediated CASP8 activation upon exposure to endoplasmic reticulum (ER) stress. Using CRISPR-Cas9 gene editing and comparative transcriptome analysis, we identified the ATF4-mediated stress response pathway as a crucial mediator to elicit iDISC-mediated apoptosis following the inhibition of autophagosome closure. Notably, ATF4-mediated iDISC activation occurred independently of the death receptor TNFRSF10B/DR5 upregulation but required the pro-apoptotic transcriptional factor DDIT3/CHOP to enhance the mitochondrial amplification pathway for full-activation of CASP8 in VPS37A-deficient cells stimulated with ER stress inducers. Our analysis also revealed the upregulation of NFKB/NF-kB signaling as a potential mechanism responsible for restraining iDISC activation and promoting cell survival upon VPS37A depletion. These findings have important implications for the future development of new strategies to treat human cancers, especially those with VPS37A loss.
    Keywords:  ATF4-mediated ER stress response; Autophagy; ESCRT-mediated phagophore closure; NFKB/NF-kB signaling; VPS37A-deficient cancer; iDISC-mediated apoptosis
  7. Cell Mol Life Sci. 2023 Sep 16. 80(10): 292
      Phosphatase and tensin homolog (PTEN) loss tightly correlates with prostate cancer (PCa) progression and metastasis. Inactivation of PTEN leads to abnormal activation of PI3K/AKT pathway. However, results from clinical trials with AKT inhibitors in PCa have been largely disappointing. Identification of novel regulators of PTEN in PTEN-dysfunctional PCa is urgently needed. Here we demonstrated that the expression level of PTEN is inversely correlated with the signature score of unfolded protein response (UPR) in PCa. Importantly, PTEN suppresses the activity of ATF6α, via interacting to de-phosphorylate ATF6α and consequently inhibiting its nuclear translocation. Conversely, ATF6α promotes the ubiquitination and degradation of PTEN by inducing CHIP expression. Thus, ATF6α and PTEN forms a negative feedback loop during PCa progression. Combination of ATF6α inhibitor with AKT inhibitor suppresses tumor cell proliferation and xenograft growth. Importantly, this study highlighted ATF6α as a therapeutic vulnerability in PTEN dysfunctional PCa.
    Keywords:  ATF6α; PTEN; Prostate cancer; UPR
  8. mSphere. 2023 Sep 21. e0032123
      A crucial phase in the life cycle of tick-borne pathogens is the time spent colonizing and persisting within the arthropod. Tick immunity is emerging as a key force shaping how transmissible pathogens interact with the vector. How pathogens remain in the tick despite immunological pressure remains unknown. In persistently infected Ixodes scapularis, we found that Borrelia burgdorferi (causative agent of Lyme disease) and Anaplasma phagocytophilum (causative agent of granulocytic anaplasmosis) activate a cellular stress pathway mediated by the endoplasmic reticulum receptor PKR-like ER kinase (PERK) and the central regulatory molecule eIF2α. Disabling the PERK pathway through pharmacological inhibition and RNA interference (RNAi) significantly decreased microbial numbers. In vivo RNAi of the PERK pathway not only reduced the number of A. phagocytophilum and B. burgdorferi colonizing larvae after a bloodmeal but also significantly reduced the number of bacteria that survive the molt. An investigation into PERK pathway-regulated targets revealed that A. phagocytophilum and B. burgdorferi induce activity of the antioxidant response regulator, nuclear factor erythroid 2-related factor 2 (Nrf2). Tick cells deficient for nrf2 expression or PERK signaling showed accumulation of reactive oxygen and nitrogen species in addition to reduced microbial survival. Supplementation with antioxidants rescued the microbicidal phenotype caused by blocking the PERK pathway. Altogether, our study demonstrates that the Ixodes PERK pathway is activated by transmissible microbes and facilitates persistence in the arthropod by potentiating an Nrf2-regulated antioxidant environment. IMPORTANCE Recent advances demonstrate that the tick immune system recognizes and limits the pathogens they transmit. Innate immune mediators such as antimicrobial peptides and reactive oxygen/nitrogen species are produced and restrict microbial survival. It is currently unclear how pathogens remain in the tick, despite this immune assault. We found that an antioxidant response controlled by the PERK branch of the unfolded protein response is activated in ticks that are persistently infected with Borrelia burgdorferi (Lyme disease) or Anaplasma phagocytophilum (granulocytic anaplasmosis). The PERK pathway induces the antioxidant response transcription factor, Nrf2, which coordinates a gene network that ultimately neutralizes reactive oxygen and nitrogen species. Interfering with this signaling cascade in ticks causes a significant decline in pathogen numbers. Given that innate immune products can cause collateral damage to host tissues, we speculate that this is an arthropod-driven response aimed at minimizing damage to "self" that also inadvertently benefits the pathogen. Collectively, our findings shed light on the mechanistic push and pull between tick immunity and pathogen persistence within the arthropod vector.
    Keywords:  ATF4; Anaplasma phagocytophilum; Borrelia burgdorferi; Ixodes scapularis; Nrf2; PERK; antioxidant response; eIF2α; tick-borne disease; vector competence
  9. J Gastrointest Oncol. 2023 Aug 31. 14(4): 1669-1693
      Background: Due to the abnormal angiogenesis, cancer stem cells (CSCs) in esophageal cancer (EC) have the characteristics of a hypoxic microenvironment. However, they can resist hypoxia-induced apoptosis. the molecular mechanism underlying the resistance of esophageal CSCs to hypoxia-induced apoptosis is currently unclear. Therefore, this study will investigate the molecular mechanism based on CHOP-mediated endoplasmic reticulum stress.Methods: CD44+CD24- cells in EC9706 cells were screened by fluorescence-activated cell sorting (FACS). To clarify which apoptosis pathway esophageal CSCs resist hypoxia-induced cell apoptosis through, the effects of hypoxia on apoptosis were detected by nuclear staining, flow cytometry, and JC-1 reagent, the effects of hypoxia on the expression of apoptosis-related proteins were detected by western blotting (WB) assay and quantitative polymerase chain reaction (qPCR) assay. To clarify the mechanisms of CD44+CD24- cells resistance to hypoxia-induced apoptosis is achieved by inhibiting the activation of endoplasmic reticulum stress (ERS) pathway, silenced CHOP and PERK cell lines of EC9706 cells and overexpressed CHOP and PERK cell lines of CD44+CD24- cells were constructed, the effects of hypoxia on apoptosis, cell cycle, and mitochondrial membrane potential were detected by flow cytometry and JC-1 reagent. WB assay and qPCR assay were used to detect the expressions of apoptosis-related proteins and ERS-related proteins.
    Results: Hypoxia significantly induce apoptosis and cycle arrest of EC9706 cells (P<0.05), but did not affect apoptosis and cycle of CD44+CD24- cells (P>0.05). Hypoxia considerably induced the activation of mitochondrial and ERS apoptosis pathways in EC9706 cells (P<0.05), but did not affect Fas receptor apoptosis pathways (P>0.05). The three apoptosis pathways were not affected by hypoxia in CD44+CD24- cells (P>0.05). Silencing the CHOP and PERK gene inhibited hypoxia-induced apoptosis of EC9706 cells (P<0.05). CHOP and PERK overexpression promoted hypoxia-induced apoptosis of CD44+CD24- cells (P<0.05), whereas mitochondrial membrane permeability inhibitors inhibited hypoxia-induced apoptosis of CD44+CD24- cells overexpressed CHOP gene.
    Conclusions: CD44+CD24- tumor stem cells in EC resist to hypoxia-induced apoptosis by the inhibition of ERS-mediated mitochondrial apoptosis pathway, which suggested that ERS pathway can serve as a potential target for reducing EC treatment resistance in clinical treatment.
    Keywords:  Esophageal cancer (EC); apoptosis; endoplasmic reticulum stress (ERS); hypoxia; tumor stem cells