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DDX3 regulates endoplasmic reticulum stress-induced ATF4 expression.

ABSTRACT: Accumulation of unfolded and potentially toxic proteins in the endoplasmic reticulum (ER) activates a cell stress adaptive response, which involves a reprogramming of general gene expression. ATF4 is a master stress-induced transcription factor that orchestrates gene expression in cells treated with various ER stress inducers including those used to treat cancers. ER stress-induced ATF4 expression occurs mainly at the translational level involving the activity of the phosphorylated (P) translation initiation factor (eIF) eIF2α. While it is well established that under ER stress PeIF2α drives ATF4 expression through a specialised mode of translation re-initiation, factors (e.g. RNA-binding proteins and specific eIFs) involved in PeIF2α-mediated ATF4 translation remain unknown. Here we identified the RNA-binding protein named DDX3 as a promotor of ATF4 expression in cancer cells treated with sorafenib, an ER stress inducer used as a chemotherapeutic. Depletion experiments showed that DDX3 is required for PeIF2α-mediated ATF4 expression. Luciferase and polyribosomes assays showed that DDX3 drives ER stress-induced ATF4 mRNA expression at the translational level. Protein-interaction assays showed that DDX3 binds the eIF4F complex, which we found to be required for ER stress-induced ATF4 expression. This study thus showed that PeIF2α-mediated ATF4 mRNA translation requires DDX3 as a part of the eIF4F complex.

SUBMITTER: Adjibade P

PROVIDER: S-EPMC5653821 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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DDX3 regulates endoplasmic reticulum stress-induced ATF4 expression.

Adjibade Pauline P Grenier St-Sauveur Valérie V Bergeman Jonathan J Huot Marc-Etienne ME Khandjian Edouard W EW Mazroui Rachid R

Scientific reports 20171023 1

Accumulation of unfolded and potentially toxic proteins in the endoplasmic reticulum (ER) activates a cell stress adaptive response, which involves a reprogramming of general gene expression. ATF4 is a master stress-induced transcription factor that orchestrates gene expression in cells treated with various ER stress inducers including those used to treat cancers. ER stress-induced ATF4 expression occurs mainly at the translational level involving the activity of the phosphorylated (P) translati ...[more]

PMID: 29062139

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Project description:It has been reported that ginsenoside Rg1 (G‑Rg1) can alleviate alcoholic liver injury, cardiac hypertrophy and myocardial ischemia, as well as reperfusion injury. Therefore, the present study aimed to investigate the role of G‑Rg1 in alcohol‑induced myocardial injury, as well as to elucidate its underlying mechanisms of action. For this purpose, H9c2 cells were stimulated with ethanol. Subsequently, H9c2 cell viability and apoptosis were determined using a Cell Counting Kit‑8 assay and flow cytometric analysis, respectively. The levels of lactate dehydrogenase and caspase‑3 in the H9c2 cell culture supernatant were detected using corresponding assay kits. In addition, the expression of green fluorescent protein (GFP)‑light chain 3 (LC3) and that of C/EBP homologous protein (CHOP) were evaluated using GFP‑LC3 assay and immunofluorescence staining, respectively. The expression levels of apoptosis‑, autophagy‑, endoplasmic reticulum stress (ERS)‑ and adenosine 5'‑monophosphate‑activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway‑related proteins were detected using western blot analysis. The results revealed that treatment with G‑Rg1 enhanced the viability and suppressed the apoptosis of ethanol‑stimulated H9c2 cells. G‑Rg1 also attenuated autophagy and ERS in ethanol‑stimulated H9c2 cells. In addition, the levels of phosphorylated (p)‑protein kinase R (PKR)‑like ER kinase (PERK), p‑eukaryotic translation initiation factor 2a, activating transcription factor 4 (ATF4), CHOP, caspase‑12 and p‑AMPK were downregulated, while the p‑mTOR level was upregulated in ethanol‑stimulated H9c2 cells treated with G‑Rg1. Furthermore, the co‑treatment of G‑Rg1‑treated ethanol‑stimulated H9c2 cells with AICAR, an AMPK agonist, or CCT020312, a PERK agonist, inhibited cell viability and promoted cell apoptosis, autophagy and ERS. Overall, the results of the present study suggest that G‑Rg1 suppresses autophagy and ERS via inhibiting the AMPK/mTOR and PERK/ATF4/CHOP pathways to alleviate ethanol‑induced H9c2 cell injury.

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DDX3 regulates endoplasmic reticulum stress-induced ATF4 expression.

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DDX3 regulates endoplasmic reticulum stress-induced ATF4 expression.

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