• The Korean Journal of Physiology and Pharmacology
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• v.19 no.5
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• pp.413-420
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• 2015

Dexmedetomidine is a sedative and analgesic agent that exerts its effects by selectively agonizing ${\alpha}2$ adrenoceptor. Histamine is a pathophysiological amine that activates G protein-coupled receptors, to induce $Ca^{2+}$ release and subsequent mediate or progress inflammation. Dexmedetomidine has been reported to exert inhibitory effect on inflammation both in vitro and in vivo studies. However, it is unclear that dexmedetomidine modulates histamine-induced signaling and pro-inflammatory cytokine expression. This study was carried out to assess how dexmedetomidine modulates histamine-induced $Ca^{2+}$ signaling and regulates the expression of pro-inflammatory cytokine genes encoding interleukin (IL)-6 and -8. To elucidate the regulatory role of dexmedetomidine on histamine signaling, HeLa cells and human salivary gland cells which are endogenously expressed histamine 1 receptor were used. Dexmedetomidine itself did not trigger $Ca^{2+}$ peak or increase in the presence or absence of external $Ca^{2+}$. When cells were stimulated with histamine after pretreatment with various concentrations of dexmedetomidine, we observed inhibited histamine-induced $[Ca^{2+}]_i$ signal in both cell types. Histamine stimulated IL-6 mRNA expression not IL-8 mRNA within 2 hrs, however this effect was attenuated by dexmedetomidine. Collectively, these findings suggest that dexmedetomidine modulates histamine-induced $Ca^{2+}$ signaling and IL-6 expression and will be useful for understanding the antagonistic properties of dexmedetomidine on histamine-induced signaling beyond its sedative effect.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.3
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• pp.139-142
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• 2002

To examine intracellular signaling of human $S1P_3\;(hS1P_3),$ a sphingosine 1-phosphate (S1P) receptor in plasma membrane, $hS1P_3$ DNA was transfected into RH7777 rat hepatoma cell line, and the inhibition of forskolin-induced cAMP accumulation and activation of MAP kinases by S1P were tested. In $hS1P_3$ transformants, S1P inhibited forskolin-induced activation of adenylyl cyclase activity by about 80% and activated MAP kinases in dose-dependent and pertussis-toxin (PTX) sensitive manners. In oocytes expressing $hS1P_3$ receptor, S1P evoked $Cl^-$ conductance. These data suggested that PTX-sensitive G proteins are involved in $hS1P_3-mediated$ signaling, especially the positive action of S1P in cell proliferation. The potential advantages of rat hepatoma cells for the research of sphingosine 1-phosphate receptor are discussed.

• BMB Reports
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• v.52 no.11
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• pp.647-652
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• 2019

G protein-coupled estrogen receptor (GPER) is known to play an important role in hormone-associated cancers. G-1, a novel synthetic GPER agonist, has been reported to exhibit anti-carcinogenic properties. However, the chemotherapeutic mechanism of GPER is yet unclear. Here, we evaluated GPER expression in human gastric cancer tissues and cells. We found that G-1 treatment attenuates GPER expression in gastric cancer. GPER expression increased G-1-induced antitumor effects in mouse xenograft model. We analyzed the effects of knockdown/overexpression of GPER on G-1-induced cell death in cancer cells. Increased GPER expression in human gastric cancer cells increased G-1-induced cell death via increased levels of cleaved caspase-3, -9, and cleaved poly ADP-ribose polymerase. Interestingly, during G-1-induced cell death, GPER mRNA and protein expression was attenuated and associated with ER stress-induced expression of PERK, ATF-4, GRP-78, and CHOP. Furthermore, PERK-dependent induction of ER stress activation increased G-1-induced cell death, whereas PERK silencing decreased cell death and increased drug sensitivity. Taken together, the data suggest that the induction of ER stress via GPER expression may increase G-1-induced cell death in gastric cancer cells. These results may contribute to a new paradigm shift in gastric cancer therapy.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2008.04a
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• pp.89-99
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• 2008

GPCRs are large families of cell surface receptors that transmit signals through conformational changes upon ligand activation and an interaction with the heterotrimeric G-proteins. GPCRs regulate the cell-signaling pathways and participate in the regulation of physiological processes through the G-proteins defined by their ${\alpha}$ subunits. A family of 20 G protein-coupled receptors (GPCRs) that provide a large class of tractable drug targets for new anti-inflammatory drugs and, in certain instances, for the treatment of the inflammatory indications such as atherosclerosis, rhinitis, asthma, pulmonary disease and arthritis. In view of the important findings showing that $G{\alpha}_{12}/G{\alpha}_{13}$ regulate the various cellular processes such as actin-stress fiber formation, neurite retraction, platelet aggregation, gene induction, and apoptosis, we became interested in whether, after coupling to the activated GPCRs, the G-proteins and their downstream molecules might be involved in the pathologic processes of chronic inflammatory diseases (e.g., liver fibrosis). In this symposium, the possible link of the G-proteins with the pathophysiology will be discussed with the aim of finding potential new drug targets.

• Proceedings of the Korean Biophysical Society Conference
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• 2003.06a
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• pp.59-59
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• 2003

Serotonin (5-HT; 5-hydroxytryptamine) exerts multiple effects on central nervous system as well as behaviors such as mood and appetite. The signaling of serotonin is mediated by 7 families of serotonin receptors, designated 5-HT$_1$ to 5-HT$_{7}$. Six families of this receptor are G-protein coupled 7TM receptors, and the third intracellular loop of these receptors is proposed to interact with specific types of G-proteins. To investigate the specific interaction between the third intracellular loop of 5-HT$_{6}$ with G$\square$s, we have constructed a chimera protein that represent the third intracellular loop of 5-HT$_{6}$ within a leucine zipper motifs, In addition an alpha subunit of human G-protein that interact with 5-HT$_{6}$ was cloned into a bacterial expression vector. The two proteins were expressed in E. coli and purified in homogeneity. The interaction of the prepared proteins was examined by ELISA assay. The affinity between the two proteins and effect of insertion mutations were discussed.ussed.d.

• Molecules and Cells
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• v.44 no.7
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• pp.458-467
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• 2021

GPR43 (also known as FFAR2 or FFA2) is a G-protein-coupled receptor primarily expressed in immune cells, enteroendocrine cells and adipocytes that recognizes short-chain fatty acids, such as acetate, propionate, and butyrate, likely to be implicated in innate immunity and host energy homeostasis. Activated GPR43 suppresses the cAMP level and induces Ca²⁺ flux via coupling to Gα_i and Gα_q families, respectively. Additionally, GPR43 is reported to facilitate phosphorylation of ERK through G-protein-dependent pathways and interacts with β-arrestin 2 to inhibit NF-κB signaling. However, other G-protein-dependent and independent signaling pathways involving GPR43 remain to be established. Here, we have demonstrated that GPR43 augments Rho GTPase signaling. Acetate and a synthetic agonist effectively activated RhoA and stabilized YAP/TAZ transcriptional coactivators through interactions of GPR43 with Gα_q/11 and Gα_12/13. Acetate-induced nuclear accumulation of YAP was blocked by a GPR43-specific inverse agonist. The target genes induced by YAP/TAZ were further regulated by GPR43. Moreover, in THP-1-derived M1-like macrophage cells, the Rho-YAP/TAZ pathway was activated by acetate and a synthetic agonist. Our collective findings suggest that GPR43 acts as a mediator of the Rho-YAP/TAZ pathway.

• The Korean Journal of Physiology and Pharmacology
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• v.14 no.3
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• pp.145-150
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• 2010

Adenosine (Ado) is an important mediator of the endogenous defense against ischemia-induced injury in the heart. The action of Ado is mediated by activation of G protein-gated inwardly rectifying $K^+$ (GIRK) channels. In turn, GIRK channels are inhibited by reducing phosphatidylinositol 4,5-bisphosphate ($PIP_2$) through Gq protein-coupled receptors (GqPCRs). We previously found that GIRK channels activated by acetylcholine, a muscarinic M2 acetylcholine receptor agonist, are inhibited by GqPCRs in a receptor-specific manner. However, it is not known whether GIRK channels activated by Ado signaling are also regulated by GqPCRs. Presently, this was investigated in mouse atrial myocytes using the patch clamp technique. GIRK channels were activated by $100\;{\mu}M$ Ado. When Ado was repetitively applied at intervals of 5~6 min, the amplitude of second Ado-activated GIRK currents ($I_{K(Ado)}$) was $88.3{\pm}3.7%$ of the first $I_{K(Ado)}$ in the control. Pretreatment of atrial myocytes with phenylephrine, endothelin-1, or bradykinin prior to a second application of Ado reduced the amplitude of the second $I_{K(Ado)}$ to $25.5{\pm}11.6%$, $30.5{\pm}5.6%$, and $96.0{\pm}2.7%$, respectively. The potency of $I_{K(Ado)}$ inhibition by GqPCRs was different with that observed in acetylcholine-activated GIRK currents ($I_{K(ACh)}$) (endothelin-1>phenylephrine>bradykinin). $I_{K(Ado)}$ was almost completely inhibited by $500\;{\mu}M$ of the $PIP_2$ scavenger neomycin, suggesting low $PIP_2$ affinity of $I_{K(Ado)}$. Taken together, these results suggest that the crosstalk between GqPCRs and the Ado-induced signaling pathway is receptor-specific. The differential change in $PIP_2$ affinity of GIRK channels activated by Ado and ACh may underlie, at least in part, their differential responses to GqPCR agonists.

• Genomics & Informatics
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• v.10 no.3
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• pp.153-166
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• 2012

A variety of ligands differ in their capacity to bind the receptor, elicit gene expression, and modulate physiological responses. Such receptors include Toll-like receptors (TLRs), which recognize various patterns of pathogens and lead to primary innate immune activation against invaders, and G-protein coupled receptors (GPCRs), whose interaction with their cognate ligands activates heterotrimeric G proteins and regulates specific downstream effectors, including immuno-stimulating molecules. Once TLRs are activated, they lead to the expression of hundreds of genes together and bridge the arm of innate and adaptive immune responses. We characterized the gene expression profile of Toll-like receptor 4 (TLR4) in RAW 264.7 cells when it bound with its ligand, 2-keto-3-deoxyoctonate (KDO), the active part of lipopolysaccharide. In addition, to determine the network communications among the TLR, Janus kinase (JAK)/signal transducer and activator of transcription (STAT), and GPCR, we tested RAW 264.7 cells with KDO, interferon-${\beta}$, or cAMP analog 8-Br. The ligands were also administered as a pair of double and triple combinations.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.39-42
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• 2008

G protein-coupled receptor(GPCR) family is a cell membrane protein, and plays an important role in a signaling mechanism which transmits external signals through cell membranes into cells. Now, it is estimated that there may be about 800-1000 GPCRs in a human genome. But, GPCRs each are known to have various complex control mechanisms and very unique signaling mechanisms. GPCRs are involved in maintaining homeostasis of various human systems including an endocrine system or a neural system and thus, disorders in activity control of GPCRs are thought to be the major source of cardiovascular disorders, metabolic disorders, degenerative disorders, carcinogenesis and the like. As more than 60% of currently marketed therapeutic agents target GPCRs, the GPCR field has been actively explored in the pharmaceutical industry. Structural features, and class and subfamily of GPCRs are well known by function, and accordingly, the most fundamental work in studies identifying the previous GPCRs is to classify the GPCRs with given protein sequences. Studies for classifying previously identified GPCRs more easily with mathematical models have been mainly going on. Considering that secondary sequences of proteins, namely, secondary binding structures of amino acids constituting proteins are closely related to functions, the present paper does not place the focus on primary sequences of proteins as previously practiced, but instead, proposes a method to transform primary sequences into secondary structures and compare the secondary structures, and then detect an unknown GPCR assumed to have a same function in databases of previously identified GPCRs.

• Tuberculosis and Respiratory Diseases
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• v.55 no.1
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• pp.21-30
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• 2003

Background : Mucin synthesis in airways has been reported to be regulated by the epidermal growth factor receptor (EGFR) system. Epidermal growth factor receptor transactivation was identified as a critical element in G-protein-coupled receptors (GPCRs)-induced mitogenic signaling. EGF receptor transactivation by G-protein-coupled receptors requires metalloproteinase cleavage of proHB-EGF. This study was hypothesized that lipopolysaccharide (LPS)-induced mucin production associates with epidermal growth factor receptor transactivation, and MUC5AC production associates with epidermal growth factor receptor transactivation by G-protein-coupled receptors that regulates by metalloproteinase. Method : MUC5AC mucin production was examined in NCI-H292 cells and MUC5AC protein synthesis was assessed using ELISA. For the evaluation of mechanism of LPS-induced MUC5AC production, $TNF{\alpha}$ was measured using ELISA with or without pretreatment of heterotrimeric G-protein inhibitor, mastoparan. MUC5AC protein was measure with pretreatment of polyclonal $TNF{\alpha}$ antibody or mastoparan on LPS-induced MUC5AC production. For the evaluation of relation of G-protein and MUC5AC production, G-protein stimulant, mastopara-7, or matrix metalloproteinase, ADAM10, was added to NCI-H292 cells. MUC5AC protein was measure with pretreatment of polyclonal EGF antibody on mastoparan-7-induced MUC5AC production. Results : LPS alone did not increase significantly MUC5AC production. LPS with $TNF{\alpha}$ induced dose-dependently MUC5AC production in NCI-H292 cells. LPS increased dose-dependently $TNF{\alpha}$ secretion, which was inhibited by mastoparan. LPS with $TNF{\alpha}$-induced MUC5AC production was inhibited by neutralizing polyclonal $TNF{\alpha}$ antibody, mastoparan or AG 1472. Mastoparan-7 or ADAM10 increased dose-dependently MUC5AC production, which was inhibited by polyclonal neutralizing EGF antibody. Conclusion : In LPS-induced MUC5AC synthesis, LPS causes $TNF{\alpha}$ secretion, which induces EGFR expression. EGFR tyrosine kinase phosphorylation result in MUC5AC production. EGF-R transactivation by G-protein-coupled receptors requires matrix metalloproteinase cleavage of proHB-EGF.