• Biomedical Science Letters
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• v.21 no.2
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• pp.126-130
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• 2015

There are several studies that show hypothermia improves cellular ischemia damages on experimental and clinical bases. However, its exact molecular mechanisms are unclear. In this study, we demonstrate that hypothermia induced insulin-like growth factor 1 (IGF1) gene expression, and its expression was dramatically decreased under ischemic insults. It was also demonstrated that hypothermia activated endoplasmic reticulum (ER) stress sensors especially both the phosphorylation of $eIF2{\alpha}$ (eukaryotic translation initiation factor 2 alpha) and ATF6 (activating transcription factor-6) proteolytic cleavage. However, the factors of apoptosis and autophagy were not associated with hypothermia. We suggest that hypothermia-treated IGF1 gene expression after ischemia may show a good possibility for the development of treatments and diagnostic methods in cerebral ischemic damages.

• Biomedical Science Letters
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• v.11 no.2
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• pp.135-141
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• 2005

A Jopock (Jpk), a trans-acting factor associating with the position-specific regulatory element of murine Hoxa-7, has shown to have a toxicity to both prokaryotic and eukaryotic cells when overexpressed. Since Jpk protein harbors a transmembrane domain and a putative endoplasmic reticulum (ER)-retention signal at the N-terminus, a subcellular localization of the protein was analyzed after fusing it into the green fluorescent protein (GFP): Both N-term (Jpk-EGFP) and C-term tagged-Jpk (EGFP-Jpk) showed to be localized in the ER when analyzed under the fluorescence microscopy after staining the cells with ER- and MitoTracker. Since ER stress triggers the ER-stress mediated apoptosis to eliminate the damaged cells, we analyzed the expression pattern of Jpk under ER-stress condition. When MCF7 cells were treated with the ER-stress inducer such as DTT and EGTA, the expression of Jpk was upregulated at the transcriptional level like that of Grp78, a molecular chaperone well known to be overexpressed under ER-stress condition. In the presence of high concentration of ER-sterss inducer (10 mM), about 70 (DTT) to $95\%$ (EGTA) of cells died stronly expressing ($10\~12$ fold) Jpk. Whereas at the low concentration ($0.001\~1.0\;mM$) of the inducer, the expression of Jpk was increased about 2.5 (EGTA) to 5 fold (DTT), which is rather similar to those of ER chaperone protein Grp78. These results altogether indicate that the ER-stress upregulated the expression of Jpk and the excess stress induces the ER-stress induced apoptosis and the concomitant expression of Jpk.

• BMB Reports
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• v.48 no.8
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• pp.445-453
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• 2015

Endoplasmic Reticulum (ER) is an organelle where most secretory and membrane proteins are synthesized, folded, and undergo further maturation. As numerous conditions can perturb such ER function, eukaryotic cells are equipped with responsive signaling pathways, widely referred to as the Unfolded Protein Response (UPR). Chronic conditions of ER stress that cannot be fully resolved by UPR, or conditions that impair UPR signaling itself, are associated with many metabolic and degenerative diseases. In recent years, Drosophila has been actively employed to study such connections between UPR and disease. Notably, the UPR pathways are largely conserved between Drosophila and humans, and the mediating genes are essential for development in both organisms, indicating their requirement to resolve inherent stress. By now, many Drosophila mutations are known to impose stress in the ER, and a number of these appear similar to those that underlie human diseases. In addition, studies have employed the strategy of overexpressing human mutations in Drosophila tissues to perform genetic modifier screens. The fact that the basic UPR pathways are conserved, together with the availability of many human disease models in this organism, makes Drosophila a powerful tool for studying human disease mechanisms. [BMB Reports 2015; 48(8): 445-453]

• Journal of Microbiology and Biotechnology
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• v.16 no.9
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• pp.1453-1458
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• 2006

PKR-like endoplasmic reticulum (ER) kinase (PERK) is a type I transmembrane ER-resident protein containing a cytoplasmic catalytic domain with a Ser/Thr kinase activity, which is most closely related to the eukaryotic translation initiation factor-$2{\alpha}$ ($eIF2{\alpha}$) kinase PKR involved in the antiviral defense pathway by interferon. We cloned and expressed the PERK C-terminal kinase domain (cPERK) in Escherichia coli. Like PERK activation in cells under ER stress, wild-type cPERK underwent autophosphorylation when overexpressed in E. coli, whereas the cPERK(K621M) with a methionine substitution for the lysine at amino acid 621 lost the autophosphorylation activity. The activated form cPERK which was purified to near homogeneity, formed an oligomer and was able to trans-phosphorylate specifically its cellular substrate $eIF2{\alpha}$. Two-dimensional phosphoamino acids analysis revealed that phosphorylation of cPERK occurs at the Ser and Thr residues. The functionally active recombinant cPERK, and its inactive mutant should be useful for the analysis of biochemical functions of PERK and for the determination of their three-dimensional structures.

• Biomolecules & Therapeutics
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• v.32 no.3
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• pp.341-348
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• 2024

Endoplasmic reticulum (ER) stress plays a crucial role in liver diseases, affecting various types of hepatic cells. While studies have focused on the link between ER stress and hepatocytes as well as hepatic stellate cells (HSCs), the precise involvement of hepatic macrophages in ER stress-induced liver injury remains poorly understood. Here, we examined the effects of ER stress on hepatic macrophages and their role in liver injury. Acute ER stress led to the accumulation and activation of hepatic macrophages, which preceded hepatocyte apoptosis. Notably, macrophage depletion mitigated liver injury induced by ER stress, underscoring their detrimental role. Mechanistic studies revealed that ER stress stimulates macrophages predominantly via the PERK signaling pathway, regardless of its canonical substrate ATF4. hnRNPA1 has been identified as a crucial mediator of PERK-driven macrophage activation, as the overexpression of hnRNPA1 effectively reduced ER stress and suppressed pro-inflammatory activation. We observed that hnRNPA1 interacts with mRNAs that encode UPR-related proteins, indicating its role in the regulation of ER stress response in macrophages. These findings illuminate the cell type-specific responses to ER stress and the significance of hepatic macrophages in ER stress-induced liver injury. Collectively, the PERK-hnRNPA1 axis has been discovered as a molecular mechanism for macrophage activation, presenting prospective therapeutic targets for inflammatory hepatic diseases such as acute liver injury.

• Journal of Life Science
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• v.28 no.10
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• pp.1186-1192
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• 2018

The purpose of this study was to compare the effects of either aerobic exercise or polyphenols supplementation on mRNA expression of endoplasmic reticulum stress in skeletal muscle of high fat diet-induced obese mice. In the study, mice were divided into five groups: (1) NC (normal diet for 16 weeks as a control, n=10), (2) HC (high fat diet for 16 weeks as a control, n=10), (3) H-Re (high fat diet with resveratrol 25 mg/kg supplementation for 16 weeks, n=10), (4) H-Ch (high fat diet with chrysin 50 mg/kg supplementation for 16 weeks, n=10), and (5) HE (high fat diet with aerobic exercise for 16 weeks, n=10). Aerobic exercise was performed on a treadmill for 40~60 min/day at 10~14 m/min, 0% grade, four days/week for 16 weeks. Endoplasmic reticulum stress related genes were measured by real-time polymerase chain reaction. ATF6, PERK, $IRE1{\alpha}$, and BIP/GRP78 mRNA were significantly decreased in HE compared with those in HC (p<0.05). Also, ATF6, $IRE1{\alpha}$, and BIP/GRP78 mRNA were significantly decreased in H-Re compared with those in HC (p<0.05). ATF6 mRNA was significantly decreased in H-Ch compared with that in HC (p<0.05). These findings suggest that aerobic exercise, resveratrol, and chrysin supplementation changed ER stress markers. However, aerobic exercise was most effective on ameliorating the high fat diet induced ER stress markers. Thus, it seems that aerobic exercise might have a more positive effect on skeletal muscle endoplasmic reticulum stress compared with polyphenol supplementation in high fat diet-induced obese mice.

• Journal of Life Science
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• v.25 no.4
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• pp.473-480
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• 2015

The endoplasmic reticulum (ER) in the eukaryotic cells is the first compartment in the secretory pathway. Almost secretory proteins and membrane proteins are secreted through the ER, in which post-translational modifications occur via diverse signals from the ER lumen to the cytoplasm and nucleus. Only then are correctly-folded proteins secreted to the outside cells. Unfolded proteins that accumulate in the ER cause a kind of intracellular stress, ER stress, and activate an unfolded protein response (UPR) system. The 3 major transducers of the UPR are inositol requiring 1 (IRE1), PKR-like ER kinase (PERK) and activating transcription factor 6 (ATF6), all of which are ER transmembrane proteins. Recently, novel types of a new ATF6 family have been identified. Those commonly have an ER-transmembrane domain, a transcription-activation domain and a basic leucine zipper (bZIP) domain―Luman, OASIS, BBF2H7, CREBH and CREB4. Each factor functions by regulating the UPR in specific organs and tissues. Although the detailed molecular mechanisms of OASIS family members are unknown, in this study we comprehensively introduce these molecular signals.

• Animal Bioscience
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• v.35 no.1
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• pp.22-28
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• 2022

Objective: Endoplasmic reticulum (ER) stress engages the unfolded protein response (UPR) that serves as an important mechanism for modulating hepatic fatty acid oxidation and lipogenesis. Chronic fasting in mice induced the UPR activation to regulate lipid metabolism. However, there is no direct evidence of whether negative energy balance (NEB) induces ER stress in the liver of cows. This study aimed to elucidate the relationship between the NEB attributed to feed deprivation and ER stress in bovine hepatocytes. Methods: Blood samples and liver biopsy tissues were collected from 6 non-lactating cows before and after their starvation for 48 h. The blood non-esterified fatty acids (NEFA), β-hydroxybutyric acid (BHBA) and glucose level were analyzed. Real-time quantitative polymerase chain reaction and Western blotting were used to explore the regulation of genes associated with UPR and lipid metabolism. Results: The starvation increased the plasma BHBA and NEFA levels and decreased the glucose level. Additionally, the starvation caused significant increases in the mRNA expression level of spliced X-box binding protein 1 (XBP1s) and the protein level of phosphorylated inositol-requiring kinase 1 alpha (p-IRE1α; an upstream protein of XBP1) in the liver. The mRNA expression levels of peroxisome proliferator-activated receptor alpha and its target fatty acid oxidation- and ketogenesis-related genes were significantly upregulated by the starvation-mediated NEB. Furthermore, we found that the mRNA expression levels of lipogenic genes were not significantly changed after starvation. Conclusion: These findings suggest that in the initial stage of NEB in dairy cows, the liver coordinates an adaptive response by activating the IRE1 arm of the UPR to enhance ketogenesis, thereby avoiding a fatty liver status.

• The Korean Journal of Pain
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• v.35 no.4
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• pp.383-390
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• 2022

Background: The treatment of trigeminal neuralgia remains a challenging issue. Stem cells from human exfoliated deciduous teeth (SHED) provide optimized therapy for chronic pain. This study aimed to investigate the mechanisms underlying the attenuation of trigeminal neuralgia by SHED. Methods: Trigeminal neuralgia was induced by chronic constriction injury of the infraorbital nerve. The mechanical threshold was assessed after model establishment and local SHED transplantation. Endoplasmic reticulum (ER) morphology and Caspase12 expression in trigeminal ganglion (TG) was evaluated as well. BiP expression was observed in PC12 cells induced by tunicamycin. Results: The local transplantation of SHED could relieve trigeminal neuralgia in rats. Further, transmission electron microscopy revealed swelling of the ER in rats with trigeminal neuralgia. Moreover, SHED inhibited the tunicamycin-induced up-regulated expression of BiP mRNA and protein in vitro. Additionally, SHED decreased the up-regulated expression of Caspase12 mRNA and protein in the TG of rats caused by trigeminal neuralgia after chronic constriction injury of the infraorbital nerve mode. Conclusions: This findings demonstrated that SHED could alleviate pain by relieving ER stress which provide potential basic evidence for clinical pain treatment.

• Molecules and Cells
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• v.19 no.2
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• pp.268-278
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• 2005

We investigated the effect of cytosolic and extracellular $Ca^{2+}$ on $Ca^{2+}$ signals in pancreatic acinar cells by measuring $Ca^{2+}$ concentration in the cytosol($[Ca^{2+}]_c$) and in the lumen of the ER($[Ca^{2+}]_{Lu}$). To control buffers and dye in the cytosol, a patch-clamp microelectrode was employed. Acetylcholine released $Ca^{2+}$ mainly from the basolateral ER-rich part of the cell. The rate of $Ca^{2+}$ release from the ER was highly sensitive to the buffering of $[Ca^{2+}]_c$ whereas ER $Ca^{2+}$ refilling was enhanced by supplying free $Ca^{2+}$ to the cytosol with $[Ca^{2+}]_c$ clamped at resting levels with a patch pipette containing 10 mM BAPTA and 2 mM $Ca^{2+}$. Elevation of extracellular $Ca^{2+}$ to 10 mM from 1 mM raised resting $[Ca^{2+}]_c$ slightly and often generated $[Ca^{2+}]_c$ oscillations in single or clustered cells. Although pancreatic acinar cells are reported to have extracellular $Ca^{2+}$-sensing receptors linked to phospholipase C that mobilize $Ca^{2+}$ from the ER, exposure of cells to 10 mM $Ca^{2+}$ did not decrease $[Ca^{2+}]_{Lu}$ but rather raised it. From these findings we conclude that 1) ER $Ca^{2+}$ release is strictly regulated by feedback inhibition of $[Ca^{2+}]_c$, 2) ER $Ca^{2+}$ refilling is determined by the rate of $Ca^{2+}$ influx and occurs mainly in the tiny subplasmalemmal spaces, 3) extracellular $Ca^{2+}$-induced $[Ca^{2+}]_c$ oscillations appear to be triggered not by activation of extracellular $Ca^{2+}$-sensing receptors but by the ER sensitised by elevated $[Ca^{2+}]_c$ and $[Ca^{2+}]_{Lu}$.