ERN1_HUMAN = Inositol-requiring enzyme 1-

Inositol-requiring enzyme 1-mediated endoplasmic reticulum stress triggers apoptosis and fibrosis formation in liver cirrhosis rat models. 2015

  • Long‑term and advanced cirrhosis is usually irreversible and often coincides with variceal hemorrhage or development of hepatocellular carcinoma; therefore, liver cirrhosis is a major cause of morbidity and mortality globally. The aim of the present study was to investigate the specific mechanism behind the formation of fibrosis or cirrhosis using rat models of hepatic fibrosis. The cirrhosis model was established by intraperitoneally administering dimethylnitrosamine to the rats. Hematoxylin and eosin staining was performed on the hepatic tissues of the rats to observe the fibrosis or cirrhosis, and western blot analysis was employed to detect α‑smooth muscle actin and desmin protein expression. Flow cytometric analysis was used to examine early and late apoptosis, and the protein and mRNA expression of endoplasmic reticulum (ER) stress-associated unfolded protein response (UPR) pathway proteins and apoptotic proteins [C/EBP homologous protein (CHOP) and caspase‑12] was detected by western blotting and the reverse-transcription polymerase chain reaction, respectively. The results indicated that the cirrhosis model was established successfully and that fibrosis was significantly increased in the cirrhosis model group compared with that in the normal control group. Flow cytometric analysis showed that early and late apoptosis in the cirrhosis model was significantly higher compared with that in the control group. The expression of the UPR pathway protein inositol-requiring enzyme (IRE) 1, as well as the expression of CHOP, was increased significantly in the cirrhotic rat tissues compared with that in the control group tissues (P<0.05). In conclusion, apoptosis was clearly observed in the hepatic tissue of cirrhotic rats, and the apoptosis was caused by activation of the ER stress-mediated IRE1 and CHOP.

Liraglutide alleviates diabetic cardiomyopathy by blocking CHOP-triggered apoptosis via the inhibition of the IRE-α pathway. 2014

  • Clinically, diabetes mellitus is closely associated with and induces certain cardiovascular diseases. The aim of this study was to investigate endoplasmic reticulum (ER) stress-associated apoptosis of diabetic cardiomyopathy (DCM), and explore the protective mechanism of liraglutide. The DCM model was established with a high-fat diet and streptozotocin (STZ). Cardiac function was detected by echocardiogram examination and hematoxylin-eosin staining. ER stress unfolded protein response (UPR) hallmarks [inositol-requiring enzyme-α (IRE-α), p-Perk and ATF6] and transcription factors were detected with western blotting. Apoptosis inducers CHOP, c-Jun amino terminal kinase (JNK) and casapse-12 were also examined with western blotting. The results indicated that liraglutide is capable of improving cardiac function in DCM rats (P<0.05). IRE-α expression was significantly increased in the DCM group compared with the control group (P<0.05), and liraglutide is capable of decreasing IRE-α expression. X-box transcription factor-1 (XBP-1) was significantly spliced in the model group, and downregulated in the liraglutide-treated group. CHOP protein was upregulated in the DCM group, but inactivated by liraglutide treatment. In conclusion, liraglutide is capable of protecting DCM and blocking CHOP-mediated ER stress by inhibiting the IREUPR pathway.


Melittin protein inhibits the proliferation of MG63 cells by activating inositol‑requiring protein‑1α and X‑box binding protein 1‑mediated apoptosis, 2014

Membrane aberrancy and unfolded proteins activate the endoplasmic reticulum stress sensor Ire1 in different ways, 2011

Eukaryotic cells activate the unfolded-protein response (UPR) upon endoplasmic reticulum (ER) stress, where the stress is assumed to be the accumulation of unfolded proteins in the ER. Consistent with previous in vitro studies of the ER-luminal domain of the mutant UPR initiator Ire1, our study show its association with a model unfolded protein in yeast cells. An Ire1 luminal domain mutation that compromises Ire1's unfolded-protein–associating ability weakens its ability to respond to stress stimuli, likely resulting in the accumulation of unfolded proteins in the ER. In contrast, this mutant was activated like wild-type Ire1 by depletion of the membrane lipid component inositol or by deletion of genes involved in lipid homeostasis. Another Ire1 mutant lacking the authentic luminal domain was up-regulated by inositol depletion as strongly as wild-type Ire1. We therefore conclude that the cytosolic (or transmembrane) domain of Ire1 senses membrane aberrancy, while, as proposed previously, unfolded proteins accumulating in the ER interact with and activate Ire1.

Ubiquitination of inositol-requiring enzyme 1 (IRE1) by the E3 ligase CHIP mediates the IRE1/TRAF2/JNK pathway.2014

  • Deciphering the inositol-requiring enzyme 1 (IRE1) signaling pathway is fundamentally important for understanding the unfolded protein response (UPR). The ubiquitination of proteins residing on the endoplasmic reticulum (ER) membrane has been reported to be involved in the UPR, although the mechanism has yet to be fully elucidated. Using immunoprecipitation and mass spectrometry, IRE1 was identified as a substrate of the E3 ligase CHIP (carboxyl terminus of HSC70-interacting protein) in HEK293 cells under geldanamycin-induced ER stress. Two residues of IRE1, Lys(545) and Lys(828), were targeted for Lys(63)-linked ubiquitination. Moreover, in CHIP knockdown cells, IRE1 phosphorylation and the IRE1-TRAF2 interaction were nearly abolished under ER stress, which may be due to lacking ubiquitination of IRE1 on Lys(545) and Lys(828), respectively. The cellular responses were evaluated, and the data indicated that CHIP-regulated IRE1/TRAF2/JNK signaling antagonized the senescence process. Therefore, our findings suggest that CHIP-mediated ubiquitination of IRE1 contributes to the dynamic regulation of the UPR.
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