scholarly journals Sledgehammer to Scalpel: Broad Challenges to the Heart and Other Tissues Yield Specific Cellular Responses via Transcriptional Regulation of the ER-Stress Master Regulator ATF6α

2020 ◽  
Vol 21 (3) ◽  
pp. 1134 ◽  
Author(s):  
Winston T. Stauffer ◽  
Adrian Arrieta ◽  
Erik A. Blackwood ◽  
Christopher C. Glembotski
Keyword(s):  
Transcription Factor ◽  
Protein Folding ◽  
Er Stress ◽  
Molecular Mechanisms ◽  
Transmembrane Protein ◽  
Fine Tuning ◽  
Cellular Functions ◽  
Similar Mode ◽  
Activating Transcription Factor ◽  
Activating Transcription Factor 6Α

There are more than 2000 transcription factors in eukaryotes, many of which are subject to complex mechanisms fine-tuning their activity and their transcriptional programs to meet the vast array of conditions under which cells must adapt to thrive and survive. For example, conditions that impair protein folding in the endoplasmic reticulum (ER), sometimes called ER stress, elicit the relocation of the ER-transmembrane protein, activating transcription factor 6α (ATF6α), to the Golgi, where it is proteolytically cleaved. This generates a fragment of ATF6α that translocates to the nucleus, where it regulates numerous genes that restore ER protein-folding capacity but is degraded soon after. Thus, upon ER stress, ATF6α is converted from a stable, transmembrane protein, to a rapidly degraded, nuclear protein that is a potent transcription factor. This review focuses on the molecular mechanisms governing ATF6α location, activity, and stability, as well as the transcriptional programs ATF6α regulates, whether canonical genes that restore ER protein-folding or unexpected, non-canonical genes affecting cellular functions beyond the ER. Moreover, we will review fascinating roles for an ATF6α isoform, ATF6β, which has a similar mode of activation but, unlike ATF6α, is a long-lived, weak transcription factor that may moderate the genetic effects of ATF6α.

scholarly journals ER stress signaling has an activating transcription factor 6α (ATF6)-dependent “off-switch”

2018 ◽  
Vol 293 (47) ◽  
pp. 18270-18284 ◽  
Author(s):  
Franziska Walter ◽  
Aisling O'Brien ◽  
Caoimhín G. Concannon ◽  
Heiko Düssmann ◽  
Jochen H. M. Prehn
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Neuroblastoma Cells ◽  
Stress Signaling ◽  
Signaling Proteins ◽  
Protein Levels ◽  
Activating Transcription Factor ◽  
Screening Platform ◽  
The Unfolded Protein Response ◽  
Activating Transcription Factor 6Α

In response to an accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen, three ER transmembrane signaling proteins, inositol-requiring enzyme 1 (IRE1), PRKR-like ER kinase (PERK), and activating transcription factor 6α (ATF6α), are activated. These proteins initiate a signaling and transcriptional network termed the unfolded protein response (UPR), which re-establishes cellular proteostasis. When this restoration fails, however, cells undergo apoptosis. To investigate cross-talk between these different UPR enzymes, here we developed a high-content live cell screening platform to image fluorescent UPR-reporter cell lines derived from human SH-SY5Y neuroblastoma cells in which different ER stress signaling proteins were silenced through lentivirus-delivered shRNA constructs. We observed that loss of ATF6 expression results in uncontrolled IRE1-reporter activity and increases X box–binding protein 1 (XBP1) splicing. Transient increases in both IRE1 mRNA and IRE1 protein levels were observed in response to ER stress, suggesting that IRE1 up-regulation is a general feature of ER stress signaling and was further increased in cells lacking ATF6 expression. Moreover, overexpression of the transcriptionally active N-terminal domain of ATF6 reversed the increases in IRE1 levels. Furthermore, inhibition of IRE1 kinase activity or of downstream JNK activity prevented an increase in IRE1 levels during ER stress, suggesting that IRE1 transcription is regulated through a positive feed-forward loop. Collectively, our results indicate that from the moment of activation, IRE1 signaling during ER stress has an ATF6-dependent “off-switch.”

scholarly journals Designing Novel Therapies to Mend Broken Hearts: ATF6 and Cardiac Proteostasis

Cells ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 602 ◽  
Author(s):  
Erik A. Blackwood ◽  
Alina S. Bilal ◽  
Winston T. Stauffer ◽  
Adrian Arrieta ◽  
Christopher C. Glembotski
Keyword(s):  
Transcription Factor ◽  
Protein Folding ◽  
Cardiac Myocytes ◽  
Cardiac Myocyte ◽  
Genetic Alterations ◽  
Hypertrophic Growth ◽  
Specific Manner ◽  
Activating Transcription Factor ◽  
Activating Transcription Factor 6Α ◽  
Unique Ability

The heart exhibits incredible plasticity in response to both environmental and genetic alterations that affect workload. Over the course of development, or in response to physiological or pathological stimuli, the heart responds to fluctuations in workload by hypertrophic growth primarily by individual cardiac myocytes growing in size. Cardiac hypertrophy is associated with an increase in protein synthesis, which must coordinate with protein folding and degradation to allow for homeostatic growth without affecting the functional integrity of cardiac myocytes (i.e., proteostasis). This increase in the protein folding demand in the growing cardiac myocyte activates the transcription factor, ATF6 (activating transcription factor 6α, an inducer of genes that restore proteostasis. Previously, ATF6 has been shown to induce ER-targeted proteins functioning primarily to enhance ER protein folding and degradation. More recent studies, however, have illuminated adaptive roles for ATF6 functioning outside of the ER by inducing non-canonical targets in a stimulus-specific manner. This unique ability of ATF6 to act as an initial adaptive responder has bolstered an enthusiasm for identifying small molecule activators of ATF6 and similar proteostasis-based therapeutics.

scholarly journals Divest Yourself of a Preconceived Idea: Transcription Factor ATF6 Is Not a Soluble Protein!

2010 ◽  
Vol 21 (9) ◽  
pp. 1435-1438 ◽  
Author(s):  
Kazutoshi Mori
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Transcriptional Activation ◽  
Intracellular Signaling ◽  
Leucine Zipper ◽  
Transmembrane Protein ◽  
Basic Leucine Zipper ◽  
Induction Program ◽  
Activating Transcription Factor ◽  
The Unfolded Protein Response

The unfolded protein response (UPR), an evolutionarily conserved transcriptional induction program that is coupled with intracellular signaling from the endoplasmic reticulum (ER) to the nucleus, is activated to cope with ER stress and to maintain the homeostasis of the ER. In 1996, we isolated a basic leucine zipper protein, which had been previously named activating transcription factor (ATF)6, as a candidate transcription factor responsible for the mammalian UPR. Subsequent analysis, however, was confounding. The problem was eventually tracked down to an unusual property of ATF6: rather than being a soluble nuclear protein, as expected for an active transcription factor, ATF6 was instead synthesized as a transmembrane protein embedded in the ER, which was activated by ER stress-induced proteolysis. ATF6 was thus unique: an ER stress sensor/transducer that is involved in all steps of the UPR, from the sensing step in the ER to the transcriptional activation step in the nucleus.

The effect of baicalein on endoplasmic reticulum stress and autophagy on liver damage

2021 ◽  
pp. 096032712110036
Author(s):  
MC Üstüner ◽  
C Tanrikut ◽  
D Üstüner ◽  
UK Kolaç ◽  
Z Özdemir Köroğlu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Er Stress ◽  
Liver Damage ◽  
Albino Rats ◽  
Tem Analysis ◽  
Stress Markers ◽  
Activating Transcription Factor 4 ◽  
Activating Transcription Factor ◽  
Wistar Albino Rats

Carbon tetrachloride (CCl4) is a toxic chemical that causes liver injury. CCl4 triggers endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UPR triggers autophagy to deal with the damage. The aim of this study was to investigate the effect of baicalein, derived from Scutellaria baicalensis, on CCl4-induced liver damage concerning ER stress and autophagy. Two groups of Wistar albino rats (n = 7/groups) were treated with 0.2 ml/kg CCl4 for 10 days with and without baicalein. Histological and transmission electron microscopy (TEM) analysis, autophagy, and ER stress markers measurements were carried out to evaluate the effect of baicalein. Histological examinations showed that baicalein reduced liver damage. TEM analysis indicated that baicalein inhibited ER stress and triggered autophagy. CCl4-induced elevation of C/EBP homologous protein (CHOP), glucose-regulating protein 78 (GRP78), activating transcription factor 4 (ATF4), activating transcription factor 6 (ATF6), inositol requiring enzyme 1 (IRE1), pancreatic ER kinase (PERK), and active/spliced form of X-box-binding protein 1 (XBP1s) ER stress markers were decreased by baicalein. Baicalein also increased the autophagy-related 5 (ATG5), Beclin1, and Microtubule-associated protein 1A/1B-light chain 3-phosphatidylethanolamine-conjugated form (LC3-II) autophagy marker levels. In conclusion, baicalein reduced the CCl4-induced liver damage by inhibiting ER stress and the trigger of autophagy.

scholarly journals Role of Activating Transcription Factor 4 in Murine Choroidal Neovascularization Model

2021 ◽  
Vol 22 (16) ◽  
pp. 8890
Author(s):  
Hiroto Yasuda ◽  
Miruto Tanaka ◽  
Anri Nishinaka ◽  
Shinsuke Nakamura ◽  
Masamitsu Shimazawa ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Transcription Factor ◽  
Er Stress ◽  
Choroidal Neovascularization ◽  
Retinal Pigment ◽  
Age Related Macular Degeneration ◽  
Activating Transcription Factor 4 ◽  
Age Related ◽  
Activating Transcription Factor ◽  
Transcription Factor 4

Neovascular age-related macular degeneration (nAMD) featuring choroidal neovascularization (CNV) is the principal cause of irreversible blindness in elderly people in the world. Integrated stress response (ISR) is one of the intracellular signals to be adapted to various stress conditions including endoplasmic reticulum (ER) stress. ISR signaling results in the upregulation of activating transcription factor 4 (ATF4), which is a mediator of ISR. Although recent studies have suggested ISR contributes to the progression of some age-related disorders, the effects of ATF4 on the development of CNV remain unclear. Here, we performed a murine model of laser-induced CNV and found that ATF4 was highly expressed in endothelial cells of the blood vessels of the CNV lesion site. Exposure to integrated stress inhibitor (ISRIB) reduced CNV formation, vascular leakage, and the upregulation of vascular endothelial growth factor (VEGF) in retinal pigment epithelium (RPE)-choroid-sclera complex. In human retinal microvascular endothelial cells (HRMECs), ISRIB reduced the level of ATF4 and VEGF induced by an ER stress inducer, thapsigargin, and recombinant human VEGF. Moreover, ISRIB decreased the VEGF-induced cell proliferation and migration of HRMECs. Collectively, our findings showed that pro-angiogenic effects of ATF4 in endothelial cells may be a potentially therapeutic target for patients with nAMD.

scholarly journals Unification of Opposites between Two Antioxidant Transcription Factors Nrf1 and Nrf2 in Mediating Distinct Cellular Responses to the Endoplasmic Reticulum Stressor Tunicamycin

Antioxidants ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 4 ◽  
Author(s):  
Yu-ping Zhu ◽  
Ze Zheng ◽  
Shaofan Hu ◽  
Xufang Ru ◽  
Zhuo Fan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Transcription Factors ◽  
Er Stress ◽  
Target Genes ◽  
Cellular Responses ◽  
Water Soluble ◽  
Heme Oxygenase 1 ◽  
Nuclear Factor ◽  
Activating Transcription Factor

The water-soluble Nrf2 (nuclear factor, erythroid 2-like 2, also called Nfe2l2) is accepted as a master regulator of antioxidant responses to cellular stress, and it was also identified as a direct target of the endoplasmic reticulum (ER)-anchored PERK (protein kinase RNA-like endoplasmic reticulum kinase). However, the membrane-bound Nrf1 (nuclear factor, erythroid 2-like 1, also called Nfe2l1) response to ER stress remains elusive. Herein, we report a unity of opposites between these two antioxidant transcription factors, Nrf1 and Nrf2, in coordinating distinct cellular responses to the ER stressor tunicamycin (TU). The TU-inducible transcription of Nrf1 and Nrf2, as well as GCLM (glutamate cysteine ligase modifier subunit) and HO-1 (heme oxygenase 1), was accompanied by activation of ER stress signaling networks. Notably, the unfolded protein response (UPR) mediated by ATF6 (activating transcription factor 6), IRE1 (inositol requiring enzyme 1) and PERK was significantly suppressed by Nrf1α-specific knockout, but hyper-expression of Nrf2 and its target genes GCLM and HO-1 has retained in Nrf1α−/− cells. By contrast, Nrf2−/−ΔTA cells with genomic deletion of its transactivation (TA) domain resulted in significant decreases of GCLM, HO-1 and Nrf1; this was accompanied by partial decreases of IRE1 and ATF6, rather than PERK, but with an increase of ATF4 (activating transcription factor 4). Interestingly, Nrf1 glycosylation and its trans-activity to mediate the transcriptional expression of the 26S proteasomal subunits, were repressed by TU. This inhibitory effect was enhanced by Nrf1α−/− and Nrf2−/−ΔTA, but not by a constitutive activator caNrf2ΔN (that increased abundances of the non-glycosylated and processed Nrf1). Furthermore, caNrf2ΔN also enhanced induction of PERK and IRE1 by TU, but reduced expression of ATF4 and HO-1. Thus, it is inferred that such distinct roles of Nrf1 and Nrf2 are unified to maintain cell homeostasis by a series of coordinated ER-to-nuclear signaling responses to TU. Nrf1α (i.e., a full-length form) acts in a cell-autonomous manner to determine the transcription of most of UPR-target genes, albeit Nrf2 is also partially involved in this process. Consistently, transactivation of ARE (antioxidant response element)-driven BIP (binding immunoglobulin protein)-, PERK- and XBP1 (X-box binding protein 1)-Luc reporter genes was mediated directly by Nrf1 and/or Nrf2. Interestingly, Nrf1α is more potent than Nrf2 at mediating the cytoprotective responses against the cytotoxicity of TU alone or plus tBHQ (tert-butylhydroquinone). This is also further supported by the evidence that the intracellular reactive oxygen species (ROS) levels are increased in Nrf1α−/− cells, but rather are, to our surprise, decreased in Nrf2−/−ΔTA cells.

High-fat diet leads to elevated lipid accumulation and endoplasmic reticulum stress in oocytes, causing poor embryo development

2020 ◽  
Vol 32 (14) ◽  
pp. 1169
Author(s):  
Arpitha Rao ◽  
Aparna Satheesh ◽  
Guruprasad Nayak ◽  
Pooja Suresh Poojary ◽  
Sandhya Kumari ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Er Stress ◽  
Lipid Accumulation ◽  
High Fat Diet ◽  
High Fat ◽  
Developmental Potential ◽  
Diet Induced Obesity ◽  
Activating Transcription Factor ◽  
Elevated Lipid

The present study was designed to investigate the effect of diet-induced obesity on endoplasmic reticulum (ER) stress in oocytes. Swiss albino mice (3 weeks old) were fed with a high-fat diet (HFD) for 8 weeks. Oocytes were assessed for lipid droplet accumulation, oxidative stress, ER stress and their developmental potential invitro. High lipid accumulation (P<0.01) and elevated intracellular levels of reactive oxygen species were observed in both germinal vesicle and MII oocytes of HFD-fed mice (P<0.05 and P<0.01 respectively compared with control). Further, expression of the ER stress markers X-box binding protein 1 (XBP1), glucose-regulated protein 78 (GRP78), activating transcription factor 4 (ATF4) and activating transcription factor 6 (ATF6) was significantly (P<0.001) higher in oocytes of the HFD than control group. Oocytes from HFD-fed mice exhibited poor fertilisation and blastocyst rates, a decrease in total cell number and high levels of DNA damage (P<0.01) compared with controls. In conclusion, diet-induced obesity resulted in elevated lipid levels and higher oxidative and ER stress in oocytes, which contributed to the compromised developmental potential of embryos.

scholarly journals XBP1 negatively regulates CENPF expression via recruiting ATF6α to the promoter during ER stress

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Tao Shen ◽  
Yan Li ◽  
Shuang Liang ◽  
Zhiguang Chen
Keyword(s):  
Er Stress ◽  
Cell Apoptosis ◽  
Cellular Response ◽  
Luciferase Activity ◽  
Brefeldin A ◽  
Activity Analysis ◽  
Binding Affinities ◽  
Promoter Regions ◽  
Activating Transcription Factor ◽  
Activating Transcription Factor 6Α

Abstract Background Centromere protein F (CENPF) is a key component of the kinetochore complex involved in mitosis, cell differentiation and cellular response to stresses. However, the alteration of CENPF in response to endoplasmic reticulum (ER) stress has not been well described. In the present study, we investigate CENPF regulation in response to ER stress. Methods Quantitative real-time polymerase chain reaction and western blotting were used to determine CENPF expression under ER stress. Luciferase activity analysis was performed to investigate the promoter regions contributing to CENPF transcription in response to TG. Chromatin immunoprecipitation (ChIP) and ChIP Re-IP assays were used to determine if X-box binding protein 1 (XBP1) and/or activating transcription factor 6α (ATF6α) bind in the CENPF promoter region. Cell apoptosis and proliferation were analyzed using TUNEL, cell growth and clonogenic assays. Results CENPF expression is dramatically reduced under ER stress induced by thapsigargin (TG), brefeldin A (BFA), or tunicamycin (TM) and this downregulation of CENPF expression was dependent on XBP1 and ATF6α. Luciferase activity analysis of the truncated CENPF promoter indicates that regions from bases − 679 to − 488 and from − 241 to − 78 in the CENPF promoter were sensitive to TG treatment. Additionally, ChIP and ChIP Re-IP assays reveal that XBP1 and ATF6α were assembled on the same regions of CENPF promoter. Notably, we identify two XBP1 binding sequences at positions − 567 and − 192, to which XBP1 binding was enhanced by TG. Finally, CENPF overexpression inhibits cell apoptosis and promotes cell proliferation in response to ER stress. Conclusion In summary, these results demonstrate that ER stress plays a crucial role in CENPF expression, and XBP1 may up-regulate DNA-binding affinities after TG treatment to the promoter of CENPF. These findings may contribute to the understanding of the molecular mechanism of CENPF regulation.

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