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.

scholarly journals Mammalian Transcription Factor ATF6 Is Synthesized as a Transmembrane Protein and Activated by Proteolysis in Response to Endoplasmic Reticulum Stress

1999 ◽  
Vol 10 (11) ◽  
pp. 3787-3799 ◽  
Author(s):  
Kyosuke Haze ◽  
Hiderou Yoshida ◽  
Hideki Yanagi ◽  
Takashi Yura ◽  
Kazutoshi Mori
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Leucine Zipper ◽  
Transmembrane Domain ◽  
Transmembrane Protein ◽  
Cholesterol Homeostasis ◽  
Basic Leucine Zipper ◽  
Transmembrane Glycoprotein ◽  
Stressed Cells ◽  
The Unfolded Protein Response

The unfolded protein response (UPR) controls the levels of molecular chaperones and enzymes involved in protein folding in the endoplasmic reticulum (ER). We recently isolated ATF6 as a candidate for mammalian UPR-specific transcription factor. We report here that ATF6 constitutively expressed as a 90-kDa protein (p90ATF6) is directly converted to a 50-kDa protein (p50ATF6) in ER-stressed cells. Furthermore, we showed that the most important consequence of this conversion was altered subcellular localization; p90ATF6 is embedded in the ER, whereas p50ATF6 is a nuclear protein. p90ATF6 is a type II transmembrane glycoprotein with a hydrophobic stretch in the middle of the molecule. Thus, the N-terminal half containing a basic leucine zipper motif is oriented facing the cytoplasm. Full-length ATF6 as well as its C-terminal deletion mutant carrying the transmembrane domain is localized in the ER when transfected. In contrast, mutant ATF6 representing the cytoplasmic region translocates into the nucleus and activates transcription of the endogenous GRP78/BiP gene. We propose that ER stress-induced proteolysis of membrane-bound p90ATF6 releases soluble p50ATF6, leading to induced transcription in the nucleus. Unlike yeast UPR, mammalian UPR appears to use a system similar to that reported for cholesterol homeostasis.

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 Molecular Symbiosis of CHOP and C/EBPβ Isoform LIP Contributes to Endoplasmic Reticulum Stress-Induced Apoptosis

2010 ◽  
Vol 30 (14) ◽  
pp. 3722-3731 ◽  
Author(s):  
Calin-Bogdan Chiribau ◽  
Francesca Gaccioli ◽  
Charlie C. Huang ◽  
Celvie L. Yuan ◽  
Maria Hatzoglou
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Er Stress ◽  
Transcriptional Activation ◽  
Nuclear Import ◽  
Cellular Response ◽  
Transcriptional Control ◽  
Nuclear Translocation ◽  
Basic Leucine Zipper ◽  
Induced Apoptosis

ABSTRACT Induction of the transcription factor CHOP (CCAAT-binding homologous protein; GADD 153) is a critical cellular response for the transcriptional control of endoplasmic reticulum (ER) stress-induced apoptosis. Upon nuclear translocation, CHOP upregulates the transcription of proapoptotic factors and downregulates antiapoptotic genes. Transcriptional activation by CHOP involves heterodimerization with other members of the basic leucine zipper transcription factor (bZIP) family. We show that the bZIP protein C/EBPβ isoform LIP is required for nuclear translocation of CHOP during ER stress. In early ER stress, LIP undergoes proteasomal degradation in the cytoplasmic compartment. During later ER stress, LIP binds CHOP in both cytoplasmic and nuclear compartments and contributes to its nuclear import. By using CHOP-deficient cells and transfections of LIP-expressing vectors in C/EBPβ−/− mouse embryonic fibroblasts (MEFs), we show that the LIP-CHOP interaction has a stabilizing role for LIP. At the same time, CHOP uses LIP as a vehicle for nuclear import. LIP-expressing C/EBPβ−/− MEFs showed enhanced ER stress-induced apoptosis compared to C/EBPβ-null cells, a finding in agreement with the decreased levels of Bcl-2, a known transcriptional control target of CHOP. In view of the positive effect of CHOP-LIP interaction in mediating their proapoptotic functions, we propose this functional cooperativity as molecular symbiosis between proteins.

scholarly journals Endoplasmic Reticulum Stress-induced mRNA Splicing Permits Synthesis of Transcription Factor Hac1p/Ern4p That Activates the Unfolded Protein Response

1997 ◽  
Vol 8 (10) ◽  
pp. 1845-1862 ◽  
Author(s):  
Tetsushi Kawahara ◽  
Hideki Yanagi ◽  
Takashi Yura ◽  
Kazutoshi Mori
Keyword(s):  
Endoplasmic Reticulum ◽  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Intracellular Signaling ◽  
Mrna Splicing ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Precursor Mrna

An intracellular signaling from the endoplasmic reticulum (ER) to the nucleus, called the unfolded protein response (UPR), is activated when unfolded proteins are accumulated in the ER under a variety of stress conditions (“ER stress”). We and others recently identified Hac1p/Ern4p as a transcription factor responsible for the UPR inSaccharomyces cerevisiae. It was further reported that Hac1p (238 aa) is detected only in ER-stressed cells, and its expression is mediated by unconventional splicing ofHAC1 precursor mRNA. The splicing replaces the C-terminal portion of Hac1p; it was proposed that precursor mRNA is also translated but the putative product of 230 aa is rapidly degraded by the ubiquitin–proteasome pathway. We have identified and characterized the same regulated splicing and confirmed its essential features. Contrary to the above proposal, however, we find that the 238-aa product of mature mRNA and the 230-aa-type protein tested are highly unstable with little or no difference in stability. Furthermore, we demonstrate that the absence of Hac1p in unstressed cells is due to the lack of translation of precursor mRNA. We conclude that Hac1p is synthesized as the result of ER stress-induced mRNA splicing, leading to activation of the UPR.

scholarly journals ATF6 Activated by Proteolysis Binds in the Presence of NF-Y (CBF) Directly to the cis-Acting Element Responsible for the Mammalian Unfolded Protein Response

2000 ◽  
Vol 20 (18) ◽  
pp. 6755-6767 ◽  
Author(s):  
Hiderou Yoshida ◽  
Tetsuya Okada ◽  
Kyosuke Haze ◽  
Hideki Yanagi ◽  
Takashi Yura ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Intracellular Signaling ◽  
Transmembrane Protein ◽  
Consensus Sequence ◽  
Soluble Form ◽  
Dominant Negative Mutant ◽  
Unfolded Protein ◽  
Protein Response

ABSTRACT Transcription of genes encoding molecular chaperones and folding enzymes in the endoplasmic reticulum (ER) is induced by accumulation of unfolded proteins in the ER. This intracellular signaling, known as the unfolded protein response (UPR), is mediated by thecis-acting ER stress response element (ERSE) in mammals. In addition to ER chaperones, the mammalian transcription factor CHOP (also called GADD153) is induced by ER stress. We report here that the transcription factor XBP-1 (also called TREB5) is also induced by ER stress and that induction of CHOP and XBP-1 is mediated by ERSE. The ERSE consensus sequence is CCAAT-N9-CCACG. As the general transcription factor NF-Y (also known as CBF) binds to CCAAT, CCACG is considered to provide specificity in the mammalian UPR. We recently found that the basic leucine zipper protein ATF6 isolated as a CCACG-binding protein is synthesized as a transmembrane protein in the ER, and ER stress-induced proteolysis produces a soluble form of ATF6 that translocates into the nucleus. We report here that overexpression of soluble ATF6 activates transcription of the CHOP and XBP-1 genes as well as of ER chaperone genes constitutively, whereas overexpression of a dominant negative mutant of ATF6 blocks the induction by ER stress. Furthermore, we demonstrated that soluble ATF6 binds directly to CCACG only when CCAAT exactly 9 bp upstream of CCACG is bound to NF-Y. Based on these and other findings, we concluded that specific and direct interactions between ATF6 and ERSE are critical for transcriptional induction not only of ER chaperones but also of CHOP and XBP-1.

Regulation of Gene Transcription by a Constitutively Active Mutant of Activating Transcription Factor 2 (ATF2)

2003 ◽  
Vol 384 (4) ◽  
pp. 667-672 ◽  
Author(s):  
L. Steinmüller ◽  
G. Thiel
Keyword(s):  
Transcription Factor ◽  
Transcriptional Activation ◽  
Leucine Zipper ◽  
Fas Ligand ◽  
Activation Domain ◽  
Transcriptional Targets ◽  
Transcriptional Activation Domain ◽  
Activating Transcription Factor ◽  
Bzip Proteins ◽  
Constitutively Active

AbstractActivating transcription factor 2 (ATF2) belongs to the family ofbasic region leucinezipper (bZIP) proteins that are characterized by the presence of a basic domain that functions as the DNAbinding domain and a leucine zipper domain that is required for dimerization. Together with bZIP proteins of the Fos and Jun families, ATF2 constitutes the AP-1 transcription factor complex. The biological activity of ATF2 is controlled by phosphorylation of two threonine residues within the N-terminal activation domain. Unphosphorylated ATF2 is trancriptionally silent, excluding simple overexpression studies to identify transcriptional targets of ATF2. We therefore decided to construct a constitutively active ATF2 mutant that would allow us to uncouple the investigation of transcriptional targets and biological functions of ATF2 from the variety of signaling pathways that lead to an activation of ATF2. We exchanged the phosphorylationdependent activation domain of ATF2 with the constitutively active transcriptional activation domain of the transcription factor CREB2. In transient transfection experiments, this constitutively active ATF2 mutant stimulated c-jun, tumor necrosis factor α, and Fas ligand promoter activities. The transcriptional activity of the constitutively active ATF2 mutant could be impaired by dominantnegative forms of ATF2 or c-jun, indicating that ATF2 and c-jun utilize a similar dimerization code. In contrast, a dominantnegative CREB2 mutant did not impair ATF2-mediated transcriptional activation, suggesting that CREB2 exhibits a different dimerization specificity than ATF2 or c-jun.

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.

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