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Key Event Title
Unfolded Protein Response
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|CYP2E1 activation and formation of protein adducts leading to neurodegeneration||KeyEvent||Jelle Broeders (send email)||Under development: Not open for comment. Do not cite|
|Inhibition of N-linked glycosylation leads to liver injury||KeyEvent||Marvin Martens (send email)||Under development: Not open for comment. Do not cite|
Key Event Description
The endoplasmic reticulum is responsible for the synthesis of proteins that are secreted from the cell. The folding of these proteins inside the endoplasmic reticulum is a precise mechanism, however the folding capacity is limited. Building block for the folding of the proteins are chaperones and foldases. Stress in the endoplasmic reticulum starts when the demand for protein folding increases over the protein folding capacity. Another factor is the accumulation of unfolded proteins in the endoplasmic reticulum which can cause stress. The stress leads to the activation of the UPR. Three effectors are released: ATF6, IRE1 and PERK. During the release chaperone BiP (GRP78) is removed from the effectors which maintain them in inactive state. The role of the unfolded protein response is to maintain the protein homeostasis in the endoplasmic reticulum.
Description from EU-ToxRisk:
Activation of UPR sensors (IRE1/PERK/ATF6) -> activation of transcription factors (XBP1/ATF4/ATF6f) -> activation of downstream targets (CHOP &Bip)
How It Is Measured or Detected
GRP78 can be used as a biomarker for endoplasmic stress and as discussed before this protein is released from the effector when the unfolded protein reaction occurs. The detection of the GRP78 protein is possible with the use of 2D gel electrophoresis in combination with proteomics. Proteins are extracted from cells, which were incubated with a toxicant, and sampled on the 2D gel. Separation is done based on the protein size and the pH value. Because of the low abundance the GRP78 protein can also be made visible with immunohistochemistry and imaging using an anti-GRP78 antibody. The protein of interest form the 2D gel can be purified and cleaned for the identification with mass spectrometry.
Description from EU-ToxRisk:
Activation of the sensors, transcription factors and targets can be measured through several assays (Takayanagi, et al 2013) and fluorescent reporter cell lines (Wink et al., 2014)
Domain of Applicability
Yang, F. & Luo, J. Endoplasmic reticulum stress and ethanol neurotoxicity. Biomolecules 5, 2538–2553 (2015).
Guan, M. et al. MDA-9 and GRP78 as potential diagnostic biomarkers for early detection of melanoma metastasis. Tumour Biol. 36, 2973–82 (2015).
Foufelle, F. & Fromenty, B. Role of endoplasmic reticulum stress in drug-induced toxicity. Pharmacol. Res. Perspect. 4, e00211 (2016).
Takayanagi, S., Fukuda, R., Takeuchi, Y., Tsukada, S., & Yoshida, K. (2013). Gene regulatory network of unfolded protein response genes in endoplasmic reticulum stress. Cell Stress and Chaperones, 18(1), 11–23. https://doi.org/10.1007/s12192-012-0351-5
Wink, S., Hiemstra, S., Huppelschoten, S., Danen, E., Niemeijer, M., Hendriks, G., … Van De Water, B. (2014). Quantitative high content imaging of cellular adaptive stress response pathways in toxicity for chemical safety assessment. Chemical Research in Toxicology, 27(3), 338–355. https://doi.org/10.1021/tx4004038