Endoplasmic Reticulum Stress Induces MUC5AC and MUC5B Expression in Human Nasal Airway Epithelial Cells

OBJECTIVES: Endoplasmic reticulum (ER) stress is known to be associated with inflammatory airway diseases, and three major transmembrane receptors: double-stranded RNA-activated protein kinase-like ER kinase, inositol requiring enzyme 1, and activating transcription factor 6 (ATF6) play important roles in ER stress-related proinflammatory signaling. However, the effects of ER stress and these three major signaling pathways on the regulation of the production of airway mucins in human nasal airway epithelial cells have not been elucidated. METHODS: In primary human nasal epithelial cells, the effect of tunicamycin (an ER stress inducer) and 4-phenylbutyric acid (4-PBA, ER stress inhibitor) on the expression of MUC5AC and MUC5B was investigated by reverse transcriptasepolymerase chain reaction, real-time polymerase chain reaction, enzyme immunoassay, and immunoblot analysis. Small interfering RNA (siRNA) transfection was used to identify the mechanisms involved. RESULTS: Tunicamycin increased the expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules, including spliced X-box binding protein 1 (XBP-1), transcription factor CCAAT-enhancer-binding protein homologous protein (CHOP), and ATF6. In addition, 4-PBA attenuated the tunicamycin-induced expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules. Furthermore, siRNA knockdowns of XBP-1, CHOP, and ATF6 blocked the tunicamycin-induced mRNA expressions and glycoprotein productions of MUC5AC and MUC5B. CONCLUSION.: These results demonstrate that ER stress plays an important role in the regulation of MUC5AC and MUC5B via the activations of XBP-1, CHOP, and ATF6 in human nasal airway epithelial cells.

Coxsackievirus B3 Infection Triggers Autophagy through 3 Pathways of Endoplasmic Reticulum Stress / 生物医学与环境科学（英文）

OBJECTIVE@#Autophagy is a highly conserved intracellular degradation pathway. Many picornaviruses induce autophagy to benefit viral replication, but an understanding of how autophagy occurs remains incomplete. In this study, we explored whether coxsackievirus B3 (CVB3) infection induced autophagy through endoplasmic reticulum (ER) stress.@*METHODS@#In CVB3-infected HeLa cells, the specific molecules of ER stress and autophagy were detected using Western blotting, reverse transcription polymerase chain reaction (RT-PCR), and confocal microscopy. Then PKR-like ER protein kinase (PERK) inhibitor, inositol-requiring protein-1 (IRE1) inhibitor, or activating transcription factor-6 (ATF6) inhibitor worked on CVB3-infected cells, their effect on autophagy was assessed by Western blotting for detecting microtubule-associated protein light chain 3 (LC3).@*RESULTS@#CVB3 infection induced ER stress, and ER stress sensors PERK/eIF2α, IRE1/XBP1, and ATF6 were activated. CVB3 infection increased the accumulation of green fluorescent protein (GFP)-LC3 punctuation and induced the conversion from LC3-I to phosphatidylethanolamine-conjugated LC3-1 (LC3-II). CVB3 infection still decreased the expression of mammalian target of rapamycin (mTOR) and p-mTOR. Inhibition of PERK, IRE1, or ATF6 significantly decreased the ratio of LC3-II to LC3-I in CVB3-infected HeLa cells.@*CONCLUSION@#CVB3 infection induced autophagy through ER stress in HeLa cells, and PERK, IRE1, and ATF6a pathways participated in the regulation of autophagy. Our data suggested that ER stress may inhibit mTOR signaling pathway to induce autophagy during CVB3 infection.

Exendin-4 Inhibits the Expression of SEPP1 and Fetuin-A via Improvement of Palmitic Acid-Induced Endoplasmic Reticulum Stress by AMPK

BACKGROUND: Selenoprotein P (SEPP1) and fetuin-A, both circulating liver-derived glycoproteins, are novel biomarkers for insulin resistance and nonalcoholic fatty liver disease. However, the effect of exendin-4 (Ex-4), a glucagon-like peptide-1 receptor agonist, on the expression of hepatokines, SEPP1, and fetuin-A, is unknown. METHODS: The human hepatoma cell line HepG2 was treated with palmitic acid (PA; 0.4 mM) and tunicamycin (tuni; 2ug/ml) with or without exendin-4 (100 nM) for 24 hours. The change in expression of PA-induced SEPP1, fetuin-A, and endoplasmic reticulum (ER) stress markers by exendin-4 treatment were evaluated using quantitative real-time reverse transcription polymerase chain reaction and Western blotting. Transfection of cells with AMP-activated protein kinase (AMPK) small interfering RNA (siRNA) was performed to establish the effect of exendin-4-mediated AMPK in the regulation of SEPP1 and fetuin-A expression. RESULTS: Exendin-4 reduced the expression of SEPP1, fetuin-A, and ER stress markers including PKR-like ER kinase, inositol-requiring kinase 1alpha, activating transcription factor 6, and C/EBP homologous protein in HepG2 cells. Exendin-4 also reduced the expression of SEPP1 and fetuin-A in cells treated with tunicamycin, an ER stress inducer. In cells treated with the AMPK activator 5-aminoidazole-4-carboxamide ribonucleotide (AICAR), the expression of hepatic SEPP1 and fetuin-A were negatively related by AMPK, which is the target of exendin-4. In addition, exendin-4 treatment did not decrease SEPP1 and fetuin-A expression in cells transfected with AMPK siRNA. CONCLUSION: These data suggest that exendin-4 can attenuate the expression of hepatic SEPP1 and fetuin-A via improvement of PA-induced ER stress by AMPK.

Preliminary investigation into the mechanism of cardiomyocyte hypertrophy induced by visfatin / 生物医学工程学杂志

The aim of the current study is to investigate the effect of visfatin on cardiomyocyte hypertrophy. Cultured H9c2 cardiomyocytes were exposed to visfatin at different concentrations for different periods of time, and the markers of cardiomyocyte hypertrophy were detected. Moreover, pravastatin, the inhibitor of endoplasmic reticulum stress (ERS) or thapsigargin, an ERS agonist was used respectively to pre-treat the cells before visfatin stimulation. F-actin staining was performed to measure the cell surface change. The mRNA expressions of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and ERS markers including glucose-regulated protein 78(GRP78), C/EPB homologous protein (CHOP) and activating transcription factor 6 (ATF6) were assessed by real time RT-PCR. The change of protein level of GRP78 and CHOP was detected by Western blot. The experimental data demonstrated that exposure to 100 or 150 ng/mL concentrations of visfatin for 24 h, or 100 ng/mL of visfatin for 24 or 48 h, significantly increased the expression of markers for cardiomyocyte hypertrophy. Visfatin stimulation provoked ERS in H9c2 cells. Furthermore, pre-treatment with pravastatin partially inhibited the visfatin-induced mRNA expression of ANP and BNP in H9c2 cells, whereas thapsigargin promoted the visfatin-induced expression of cardiomyocyte hypertrophy markers. The results suggest that visfatin might induce cardiomyocyte hypertrophy via ERS -dependent pathways.

Ophiopogonin D protects cardiomyocytes against doxorubicin-induced injury through suppressing endoplasmic reticulum stress / 药学学报

This study aimed to examine whether ophiopogonin D (OP-D) is capable of protecting cardiomyocytes against DOX-induced injury and the mechanisms involved. H9c2 cells were cultured. MTT assay was used to evaluate cell viability and toxicity. Mito-tracker as fluorescence probe was used to measure ROS content raised from mitochondria. The mRNA and protein expression of ATF6alpha, GRP78 and CHOP were analyzed using real-time PCR and Western blotting, respectively. The results showed that a significant endoplasmic reticulum stress (ERS) was induced upon exposure of H9c2 cells to DOX as indicated by the increase in the expression of ERS related proteins, which was paralleled with the accumulation of reactive oxygen species (ROS) and decrease in the viability of H9c2 cells. Whereas, DOX-induced ROS accumulation and up-regulation of ERS related proteins were partially abolished by pretreatment with OP-D. Consequently, a DOX-induced ERS was mitigated by application of OP-D. Similarly, DOX-induced decrease in cell viability was partially attenuated by either inhibiting CHOP or pretreatment with N-acetylcysteine (NAC), an antioxidant. Moreover, cardiac ultrastructural abnormalities seen in mouse receiving DOX injections were obviously ameliorated by pretreatment of OP-D. Taken together, the present study proved that OP-D protects cardiomyocytes against DOX-induced injury, at least in part, through reducing ROS accumulation and alleviating ERS.

Inhibitory effect of quercetin preconditioning on tunicamycin-induced apoptosis in macrophages and its mechanism / 生理学报

The purposes of the present study were to investigate the inhibitory effect of quercetin (QUE) preconditioning on endoplasmic reticulum stress (ERS) inducer tunicamycin (TM)-induced apoptosis in RAW264.7 macrophages and the underlying molecular mechanisms. RAW264.7 cells were pretreated with different concentrations (20, 40, and 80 μmol/L) of QUE for 30 min and then treated with TM (5 mg/L) for 12 h. Cell viability and apoptosis were determined using MTT assay and Annexin V-FITC apoptosis detection kit, respectively. The nuclear translocation of activating transcription factor 6 (ATF6) in cells was detected by immunofluorescence analysis and Western blot. Protein and mRNA expressions of C/EBP homologous protein (CHOP) and Bcl-2 were examined by Western blot and real-time PCR, respectively. The results showed that TM reduced cell viability and induced apoptosis in RAW264.7 macrophages. The cytotoxic effects of TM were significantly inhibited by QUE pretreatment at the concentrations of 40 and 80 μmol/L. Interestingly, we found that QUE also significantly suppressed the TM-induced translocation of ATF6, an ERS sensor, from the cytoplasm to the nucleus. In addition, exposure of RAW264.7 macrophages to TM resulted in a significant increase of the expression of CHOP, a transcription factor regulated by ATF6 under conditions of ERS, as well as a decrease of Bcl-2 at transcript and protein levels. QUE blocked these effects in a dose-dependent manner. These data indicate that QUE can protect RAW264.7 cells from TM-induced apoptosis and that the mechanism at least partially involves its ability to inhibit the ATF6-CHOP signaling pathway.

Human Leptin Protein Induces Proliferation of A549 Cells via Inhibition of PKR-Like ER Kinase and Activating Transcription Factor-6 Mediated Apoptosis

PURPOSE: To investigate the anti-apoptotic mechanism of leptin in non-small cell lung cancer. MATERIALS AND METHODS: The influences of leptin on apoptosis were investigated, analyzing the mechanism that triggers growth of A549 cells. The effects of leptin on cell proliferation were examined by XTT analysis. Leptin, C/EBP homologous protein (CHOP), phosphorylated-PKR-like ER kinase (p-Perk), inositol requiring proteins-1, spliced X-box transcription factor-1 (XBP1), cleaved activating transcription factor-6 (ATF6), eukaryotic translation initiation factor-2alpha, caspase-12 and CHOP protein were detected in four groups by western blot, and endoplasmic reticulum (ER) stress related mRNA were detected by reverse transcription PCR. RESULTS: The expression of leptin in A549 and leptin transfected cells inhibited cisplatin activated ER stress-associated mRNA transcription and protein activation. Two ER stress unfolded protein response pathways, PERK and ATF6, were involved, and XBP1 and tumor necrosis factor receptor-associated factor 2 (TRAF2) were increased significantly when treated with cisplatin in A549-siRNA against leptin cells. Furthermore, CHOP expression was inhibited upon leptin expression in A549, LPT-PeP and LPT-EX cells. CONCLUSION: Leptin serves as an important factor that promotes the growth of A549 cells through blocking ER stress-mediated pathways. This blocking is triggered by p-Perk and ATF6 via inhibition of CHOP expression.