Activated Transcription Factor 6 Research Articles

Identification of novel pathogenic roles of BLZF1/ATF6 in tumorigenesis of gastrointestinal stromal tumor showing Golgi-localized mutant KIT.

Gastrointestinal stromal tumors (GISTs) frequently show KIT mutations, accompanied by overexpression and aberrant localization of mutant KIT (MT-KIT). As previously established by multiple studies, including ours, we confirmed that MT-KIT initiates downstream signaling in the Golgi complex. Basic leucine zipper nuclear factor 1 (BLZF1) was identified as a novel MT-KIT-binding partner that tethers MT-KIT to the Golgi complex. Sustained activation of activated transcription factor 6 (ATF6), which belongs to the unfolded protein response (UPR) family, alleviates endoplasmic reticulum (ER) stress by upregulating chaperone expression, including heat shock protein 90 (HSP90), which assists in MT-KIT folding. BLZF1 knockdown and ATF6 inhibition suppressed both imatinib-sensitive and -resistant GIST in vitro. ATF6 inhibitors further showed potent antitumor effects in GIST xenografts, and the effect was enhanced with ER stress-inducing drugs. ATF6 activation was frequently observed in 67% of patients with GIST (n = 42), and was significantly associated with poorer relapse-free survival (P = 0.033). Overall, GIST bypasses ER quality control (QC) and ER stress-mediated cell death via UPR activation and uses the QC-free Golgi to initiate signaling.

Melissa officinalis extract suppresses endoplasmic reticulum stress-induced apoptosis in the brain of hypothyroidism-induced rats exposed to γ-radiation

The purpose of this study was to demonstrate the neuroprotective effect of Melissa officinalis extract (MEE) against brain damage associated with hypothyroidism induced by propylthiouracil (PTU) and/or γ-radiation (IR) in rats. Hypothyroidism induction and/or exposure to IR resulted in a significant decrease in the serum levels of T3 and T4 associated with increased levels of lipid peroxidation end product, malondialdehyde (MDA), and nitrites (NO) in the brain tissue homogenate. Also, hypothyroidism and /or exposure to IR markedly enhance the endoplasmic reticulum stress by upregulating the gene expressions of the protein kinase RNA-like endoplasmic reticulum kinase (PERK), activated transcription factor 6 (ATF6), endoplasmic reticulum-associated degradation (ERAD), and CCAAT/enhancer-binding protein homologous protein (CHOP) in the brain tissue homogenate associated with a proapoptotic state which indicated by the overexpression of Bax, BCl2, and caspase-12 that culminates in brain damage. Meanwhile, the PTU and /or IR-exposed rats treated with MEE reduced oxidative stress and ERAD through ATF6. Also, the MEE treatment prevented the Bax and caspase-12 gene expression from increasing. This treatment in hypothyroid animals was associated with neuronal protection as indicated by the downregulation in the gene expressions of the microtubule-associated protein tau (MAPT) and amyloid precursor protein (APP) in the brain tissue. Furthermore, the administration of MEE ameliorates the histological structure of brain tissue. In conclusion, MEE might prevent hypothyroidism-induced brain damage associated with oxidative stress and endoplasmic reticulum stress.

Effects of Hedyotis diffusa polysaccharide extract on autophagy of endoplasmic reticulum in laryngeal cancer Hep-2 cells

Objective: To investigate the effects of Hedyotis diffusa polysaccharide extract (HDPE) on endoplasmic reticulum autophagy in laryngeal cancer Hep-2 cells. Methods: The cells were divided into control group, HDPE 100, 200, 400 mg/L group and 3-MA(autophagy inhibitor) group. MTT assay was used to detect the inhibition rate of cell proliferation after 24, 48 and 72 h of culture, and TUNEL was used to detect the apoptosis of cells in each group. The changes of autophages and autophagic lysosomes were observed by MDC staining, and the formation of autophagic vesicles around endoplasmic reticulum was observed by transmission electron microscopy. Western blot was used to detect the expressions of Beclin-1, microtubule-associated light chain protein 3I (LC3I), microtubule-associated light chain protein 3II (LC3II), glucose regulatory protein 78 (GRP78), activated transcription factor 6 (ATF6) and CCAAT enhancer binding protein homologous protein (CHOP) in each group. Results: Compared with the control group, the inhibition rate of cell proliferation and apoptotic index AI in HDPE 100, 200, 400 mg/L group and blocker group were increased, the positive rate of MDC was decreased, and the autophagic vesicles around endoplasmic reticulum were reduced. The expression levels of GRP78, ATF6 and CHOP and the ratio of LC3I/LC3II were increased, and the expression of Beclin-1 was decreased (P＜0.05). Compared with 3-MA group, the inhibition rate of cell proliferation and apoptotic index AI in HDPE 400 mg/L group were increased, the positive rate of MDC was decreased, the expressions of GRP78, ATF6 and CHOP and LC3I/LC3II ratio were increased, and the expression of Beclin-1 was decreased (P＜0.05). Conclusion: HDPE may inhibit the proliferation of Hep-2 cells by inhibiting endoplasmic reticulum autophagy and promoting the apoptosis of endoplasmic reticulum stress in laryngeal cancer Hep-2 cells.

Ketogenic diet attenuates aging-associated myocardial remodeling and dysfunction in mice.

Cardiac aging is manifested as unfavorable geometric and functional alterations in heart. The current work was to test whether a ketogenic diet (KD) impacted aging-associated myocardial remodeling and dysfunction in mice and investigate the underlying mechanism. The young and aged male mice were fed with KD or standard chow for four months. Echocardiography results revealed that KD decreased left ventricular end systolic diameter (LVESD) and increased fractional shortening in aged mice. With KD feeding, aged mice exhibited reduced cardiomyocyte cross-sectional area, fibrosis, and mRNA expression of atrial natriuretic peptide (ANP), Col1A1 and alpha smooth muscle actin (α-SMA) in myocardium. KD enhanced activities of superoxide dismutase 2 (SOD2), glutathione peroxidase (GPx) and catalase, and reduced the levels of malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) in myocardium of aged mice. KD led to a downregulation of expression of C/EBP homologous protein (CHOP), glucose regulated protein 78 (GRP78), cleaved activated transcription factor 6 (ATF6), and spliced X box-binding protein 1 (XBP-1s) in myocardium of aged mice. KD in aged mice reduced mitochondrial reactive oxygen species (ROS) formation, enhanced mitochondrial ATP production and mitochondrial membrane potential (MMP), and preserved activity of complex III and electron-coupling capacities between complexes I and III and between complexes II and III in myocardium. Importantly, KD in aged mice promoted autophagic flux, evidenced by reduced protein expression of p62 and enhanced protein expression of lysosome-associated membrane protein-2 (Lamp2) in myocardium. In conclusion, long-time KD intake delayed cardiac aging in male mice, possibly through abating oxidative stress, improving mitochondrial function, and promoting autophagic flux.

Hydroxycamptothecin Inhibits Peritendinous Adhesion via the Endoplasmic Reticulum Stress-Dependent Apoptosis.

Traumatic peritendinous fibrosis is a worldwide clinical problem resulting in severe limb disability. Hydroxycamptothecin (HCPT) is an anti-neoplastic drug widely exploited in clinical practice. It has shown potential of anti-fibrosis in recent years. We previously demonstrated that HCPT inhibited the characterization of fibrosis in vitro. However, it is still unclear whether it ameliorates peritendinous adhesion in an in vivo animal tendon injury model. The underlying mechanism is also worth investigating. The present study aims to determine whether HCPT inhibits tendon adhesion and to explore the underlying mechanisms. In a rat tendon injury model, we observed that topical application of HCPT significantly attenuated peritendinous adhesion as revealed by the results of macroscopic observation, biomechanical, histological, immunohistochemical evaluation, western blot, and quantitative PCR (q-PCR) analyses. Furthermore, western blot and q-PCR analyses revealed that this phenomenon is correlated with HCPT activation of endoplasmic reticulum (ER) stress. In addition, in vitro studies show that HCPT significantly inhibits fibroblast proliferation and induces apoptosis by reducing the expression of extracellular matrix (ECM) proteins COL3A1 and α-smooth muscle actin (α-SMA). Finally, we employed small interfering RNA (siRNA) to target inositol requiring kinase 1 (IRE1) and activated transcription factor 6 (ATF-6) to verify that the effect of inhibitory fibrosis of HCPT disappears after knockdown of ATF-6 and IRE1, thereby suggesting that an anti-fibrotic effect of HCPT is mediated by the ER-dependent apoptotic pathway. In conclusion, our results indicate that HCPT inhibits peritendinous fibrosis through the ER-dependent apoptotic pathway and might serve as a potential solution to prevent traumatic peritendinous adhesion.

Profile of the unfolded protein response in rat cerebellar cortical development

The unfolded protein response (UPR) has been reported during normal development of cortical neurons and cerebellar white matter and may also contribute to the pathogenesis of neurological conditions, such as Marinesco-Sjogren syndrome and Borna virus infection, which result in cerebellar defects. The UPR is initiated when the processing capacity of the endoplasmic reticulum (ER) is overwhelmed. Misfolded proteins accumulate and can activate ER stress sensors; PKR-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1), activated transcription factor 6 (ATF6) and their downstream targets glucose-regulated protein 78 (GRP78), glucose-regulated protein 94 (GRP94) and protein disulfide isomerase (PDI). In order to provide a fuller appreciation of the possible importance of ER stress-associated proteins in the context of cerebellar disease, we have profiled the expression of ER stress sensors and their downstream targets in the developing cerebellar cortex in postnatal rat. Activation of PERK and IRE1 stress sensors was observed for the first time in normally developing granule cell precursors. A second proliferative pPERK-positive population was also detected in the internal granular layer (IGL). In general, the density of UPR protein-positive cells was found to decrease significantly when profiles in early and late postnatal ages were compared. These data may be relevant to studies of medulloblastoma and warrant further investigation.

Status of sFlt‐1 in Pregnant Women with Preeclampsia and its Impact on GRP78 in Trophoblast Cells

IntroductionsFlt‐1 is secreted in large amounts by placental trophoblasts, released into maternal circulation and reduces bioavailability of angiogenic molecule, VEGF. Plenty of evidence suggest that production of excess sFlt‐1 is a consequence of placental hypoxia leading to stressed placenta noted in preeclampsia (PE). Placental stress has been categorized into oxidative, immunologic and endoplasmic reticulum (ER) stress. Placental ER stress arises due to failure of unfolded protein response (UPR) affects its central regulator, GRP78, which dissociates from transmembrane sensors, PERK like ER kinase, IRE1 (Inositol‐Requiring Enzyme 1) and ATF6 (Activated Transcription Factor 6). The present study was aimed to unravel whether sFlt‐1 had any correlation with GRP78. Also, in vitro experiments were performed to explore effect of sFlt‐1 on GRP78.MethodsSera from 60 recruited women [(30 PE patients and 30 Normotensive, Non‐proteinuric (NT, NP; controls)] were used to estimate levels of sFlt‐1 and GRP78 proteins (ELISA; R and D system). Trophoblast cells (BeWo cells; human choriocarcinoma cell line) were subjected to various treatments with varying sFlt‐1 concentrations and expression of GRP78 was analysed using immunofluorescence (IF), western blot and qRT‐PCR at 8, 14 and 24 hours. The BeWo cells of group 1 and group 2 were exposed to sera from normotensive pregnant women (low sFlt‐1), and preeclamptic pregnant women (high sFlt‐1). The BeWo cells of group 3 were exposed to normotensive sera with recombinant sFlt‐1 (NT+re‐sFlt‐1). Statistical tests used were Paired t, Pearson correlation coefficient, One‐way ANOVA, Kruskal‐Wallis, Wilcoxon signed‐rank.ResultsSerum sFlt‐1 levels were found to be significantly elevated in women with preeclampsia [11295.25 (2936.2–37818) pg/ml] than in controls [2936.2 (1180.43–6706.6) pg/ml] (p=0.0001). GRP78 levels were also raised significantly in PE patients (1103.26 ± 104.27) ng/ml as compared to controls (1018.61 ± 125.51) ng/ml (p=0.023). Patients with increased sFlt‐1 in their sera had higher GRP78 levels suggesting a positive correlation. Significant expression of GRP78 was observed at 8 h when BeWo cells were treated with PE sera and NT sera with recombinant sFlt‐1 by IF. GRP78 expression was observed as early as 8 h, reached peak at 14 h, started diminishing after 14 h and was significantly upregulated when BeWo cells were treated with PE sera as compared to NT sera at both protein (p<0.0001) and mRNA (p<0.0001) levels. Expression of GRP78 was significantly raised at 8 and 14 h when BeWo cells were treated with NT+re‐sFlt‐1 as compared to NT sera at both protein (p<0.0001) and mRNA (p<0.0001) levels.ConclusionPositive correlation was observed between increased maternal serum levels of sFlt‐1 and GRP78 in preeclamptic patients. Upregulation of GRP78 in trophoblast cells exposed to group 2 and 3 indicate towards an important role which may be played by sFlt‐1 in inducing ER stress in Preeclampsia.Ethical clearance IESC/T‐323Support or Funding InformationA‐159 AIIMS, New DelhiThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

UPR Induction Prevents Iron Accumulation and Oligodendrocyte Loss in ex vivo Cultured Hippocampal Slices.

The accumulation of iron within the brain occurs in many chronic disorders including Alzheimer’s and Parkinson’s disease and multiple sclerosis. Outside the CNS, a link between levels of iron and the unfolded protein response has already been established. To determine if such a relationship operates in within the brain, we used our ex vivo hippocampal slice-based model of iron accumulation. Ferrocene addition caused accumulation of iron within slices and loss of oligodendrocytes, an effect that was partially inhibited when ferrocene and ER stressor tunicamycin (Tm) were added together. An upward trend (not found to be statistically significant) in the expression of UPR transcripts in response to ferrocene was demonstrated using real-time PCR, while a significant upregulation of mRNA for B cell immunoglobulin-binding protein (BiP) and C/EBP homologous binding protein (CHOP) occurred following exposure to Tm. In silico analysis revealed consensus DNA-binding sequences for UPR-associated transcription factors within the promoter regions of eight iron-regulatory genes. In addition, dual-staining for CHOP and oligodendrocyte transcription factor 2 (OLIG2) or Ionized calcium binding adaptor molecule 1 (Iba1) showed nuclear expression of CHOP in some oligodendrocyte-lineage cells in response to Tm or Tm+ferrocene, but CHOP was rarely found in microglia. Co-expression of UPR-associated activated transcription factor 6 (ATF6) was detected in the nuclei of some oligodendrocyte-lineage cells exposed to Tm alone, or to Tm and ferrocene, but rarely in microglia. These data highlight the therapeutic potential of targeting UPR-associated proteins when developing novel treatments for chronic brain disorders that are affected by dysregulated iron.

Long noncoding RNA MEG3 inhibits breast cancer growth via upregulating endoplasmic reticulum stress and activating NF-κB and p53.

Long noncoding RNA (lncRNA) maternally expressed 3 (MEG3) has been implicated as a tumor suppressor gene in several human cancer types. However, little is known regarding its involvement and potential mechanism in human breast cancer. In this study, we explored the effect of MEG3 on the growth of human breast cancer cell line MDA-MB-231 in vitro and in vivo, and sought to elucidate the potential signaling mechanisms. Ectopic overexpression of MEG3 using a lentiviral vector Lv-MEG3 significantly inhibited breast cancer cell growth in vitro and a cancer xenograft growth in vivo. MEG3 overexpression led to marked increase of apoptosis in breast cancer cells as determined using flow cytometry and fragmented DNA labeling. Moreover, ectopic expression of MEG3 increased the expression of endoplasmic reticulum (ER) stress-related proteins required for unfolded protein response, including glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1 (IRE1), protein kinase RNA (PKR)-like ER kinase (PERK), and activated transcription factor 6 (ATF6), as well as proapoptotic proteins CCAAT/enhancer binding protein homologous protein (CHOP) and caspase-3. Finally, MEG3 overexpression markedly increased nuclear factor κB (NF-κB) expression, NF-κB translocation to the nucleus, and p53 expression, whereas pharmacological inhibition of NF-κB completely abolished MEG3-induced activation of p53. Together, these results suggest that MEG3 inhibits breast cancer growth and induces breast cancer apoptosis, partially via the activation of the ER stress, NF-κB and p53 pathways, and that NF-κB signaling is required for MEG3-induced p53 activation in breast cancer cells. Our results indicate targeting lncRNA MEG3 may represent a novel strategy for breast cancer therapy.

Opposite Roles of RNase and Kinase Activities of Inositol-Requiring Enzyme 1 (IRE1) on HSV-1 Replication.

In response to the endoplasmic reticulum (ER) stress induced by herpes simplex virus type 1 (HSV-1) infection, host cells activate the unfolded protein response (UPR) to reduce the protein-folding burden in the ER. The regulation of UPR upon HSV-1 infection is complex, and the downstream effectors can be detrimental to viral replication. Therefore, HSV-1 copes with the UPR to create a beneficial environment for its replication. UPR has three branches, including protein kinase RNA (PKR)-like ER kinase (PERK), inositol-requiring enzyme 1 (IRE1), and activated transcription factor 6 (ATF6). IRE1α is the most conserved branch of UPR which has both RNase and kinase activities. Previous studies have shown that IRE1α RNase activity was inactivated during HSV-1 infection. However, the effect of the two activities of IRE1α on HSV-1 replication remains unknown. Results in this study showed that IRE1α expression was up-regulated during HSV-1 infection. We found that in HEC-1-A cells, increasing RNase activity, or inhibiting kinase activity of IRE1α led to viral suppression, indicating that the kinase activity of IRE1α was beneficial, while the RNase activity was detrimental to viral replication. Further evidence showed that the kinase activity of IRE1α leads to the activation of the JNK (c-Jun N-terminal kinases) pathway, which enhances viral replication. Taken together, our evidence suggests that IRE1α is involved in HSV-1 replication, and its RNase and kinase activities play differential roles during viral infection.

Netrin-1 Protects Hepatocytes Against Cell Death Through Sustained Translation During the Unfolded Protein Response.

Background & AimsNetrin-1, a multifunctional secreted protein, is up-regulated in cancer and inflammation. Netrin-1 blocks apoptosis induced by the prototypical dependence receptors deleted in colorectal carcinoma and uncoordinated phenotype-5. Although the unfolded protein response (UPR) triggers apoptosis on exposure to stress, it first attempts to restore endoplasmic reticulum homeostasis to foster cell survival. Importantly, UPR is implicated in chronic liver conditions including hepatic oncogenesis. Netrin-1's implication in cell survival on UPR in this context is unknown.MethodsIsolation of translational complexes, determination of RNA secondary structures by selective 2’-hydroxyl acylation and primer extension/dimethyl sulfate, bicistronic constructs, as well as conventional cell biology and biochemistry approaches were used on in vitro–grown hepatocytic cells, wild-type, and netrin-1 transgenic mice.ResultsHepaRG cells constitute a bona fide model for UPR studies in vitro through adequate activation of the 3 sensors of the UPR (protein kinase RNA–like endoplasmic reticulum kinase (PERK)), inositol requiring enzyme 1α (IRE1α), and activated transcription factor 6 (ATF6). The netrin-1 messenger RNA 5'-end was shown to fold into a complex double pseudoknot and bear E-loop motifs, both of which are representative hallmarks of related internal ribosome entry site regions. Cap-independent translation of netrin 5' untranslated region–driven luciferase was observed on UPR in vitro. Unlike several structurally related oncogenic transcripts (l-myc, c-myc, c-myb), netrin-1 messenger RNA was selected for translation during UPR both in human hepatocytes and in mice livers. Depletion of netrin-1 during UPR induces apoptosis, leading to cell death through an uncoordinated phenotype-5A/C–mediated involvement of protein phosphatase 2A and death-associated protein kinase 1 in vitro and in netrin transgenic mice.ConclusionsUPR-resistant, internal ribosome entry site–driven netrin-1 translation leads to the inhibition of uncoordinated phenotype-5/death-associated protein kinase 1–mediated apoptosis in the hepatic context during UPR, a hallmark of chronic liver disease.

Inositol-requiring Enzyme 1 Inhibits Respiratory Syncytial Virus Replication

Despite being a major health problem, respiratory syncytial virus (RSV) infections remain without specific therapy. Identification of novel host cellular responses that play a role in the pathogenesis of RSV infection is needed for therapeutic development. The endoplasmic reticulum (ER) stress response is an evolutionarily conserved cellular signaling cascade that has been implicated in multiple biological phenomena, including the pathogenesis of some viral infections. In this study, we investigate the role of the ER stress response in RSV infection using an in vitro A549 cell culture model. We found that RSV infection induces a non-canonical ER stress response with preferential activation of the inositol-requiring enzyme 1 (IRE1) and activated transcription factor 6 (ATF6) pathways with no concomitant significant activation of the protein kinase R-like ER kinase (PERK) pathway. Furthermore, we discovered that IRE1 has an inhibitory effect on RSV replication. Our data characterize, for the first time, the nature of the ER stress response in the setting of RSV infection and identify the IRE1 stress pathway as a novel cellular anti-RSV defense mechanism.

Increased Body Mass Index After Kidney Transplantation in Activating Transcription Factor 6 Single Polymorphism Gene Carriers

Objectives Endoplasmic reticulum stress has been implicated in the pathogenesis of new-onset diabetes after transplantation (NODAT) and of metabolic disorders. Activated Transcription Factor 6 (ATF6), which is activated during endoplasmic reticulum stress, is involved in lipogenesis and gluconeogenesis. Tacrolimus may induce endoplasmic reticulum stress in pancreatic beta cells. Since studies have demonstrated that single nucleotide polymorphisms (SNPs) of ATF6 are associated with type 2 diabetes, we sought to determine whether their mutations were associated with NODAT among renal transplant recipients treated with tacrolimus. Methods We genotyped 269 renal transplant recipients using TaqMan assays for allelic discrimination for 6 ATF6 gene polymorphisms: rs10918215, rs7514053, rs1058405, rs4479731, rs2340721, and rs13401. All patients received an immunosuppressive regimen including tacrolimus. We analyzed all previously known risk factors for NODAT. Results We could not confirm are association between ATF6 SNP and NODAT. We observed a significant association between ATF6 SNP rs2340721 and increased body weight and body mass index (BMI) both upon univariate and multivariate analyses. The average BMI was higher among patients with 2 mutant SNP2 (rs2340721) alleles (CC) than those with 2 wild-type alleles (AA): 23.8 ± 3.7 versus 25.5 ± 4.4 kg/m2 ( P = .02). The odds ratio (95% confidence interval [CI]) for BMI associated with the CC genotype was 2.43 (1.16–5.09; P = .02). Conclusion ATF6 polymorphisms were not associated with NODAT among our population of renal transplant recipients treated with tacrolimus. However, these data underscore the role of ATF6 and endoplasmic reticulum stress in the regulation of metabolic flux among patients treated with tacrolimus, suggesting that inherited disturbances of endoplasmic reticulum stress signaling could predispose people to obesity.

CS11-7. IFN-autophagy and tumor suppression: a novel IFN- γ induced signaling cascade involving Activated transcription factor-6 (ATF-6) that collaborates with C/EBP-beta and promotes tumor suppression

CS11-7. IFN-autophagy and tumor suppression: a novel IFN- γ induced signaling cascade involving Activated transcription factor-6 (ATF-6) that collaborates with C/EBP-beta and promotes tumor suppression