• Biomolecules & Therapeutics
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• v.6 no.4
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• pp.337-344
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• 1998

The objective of the present study was to investigate the effect of senescence on the binding properties of muscarinic receptors in the neostriatum of young (3 months), middle-aged (18 months) and aged (33 months) male Fischer 344 x Brown Norway hybrid rats by employing direct binding of selective radiolabeled antagonists. Using the selective M, muscarinic receptor antagonist, $[^3H]$AF-DX384, as the ligand, no significant difference in the maximal receptor density (Bmax) was observed in the neostriatum among any age-groups. In contrast, with the selective M, receptor antagonist, $[^3H]$4-DAMP, a significant increase in the number of muscarinic receptors was observed in neostriatal membrane fractions prepared from the aged animals relative to that observed in the young rats. For each ligand there was no age-related change in its affinity (Kd) for the muscarinic receptors. These results indicate that the observed age-related changes in the muscarinic receptor density may not be necessarily decremuntal and depend upon the muscarinic receptor subtype examined.

• BMB Reports
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• v.44 no.3
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• pp.182-186
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• 2011

Exogenous stimuli such as nerve growth factor (NGF) exert their effects on neurite outgrowth via Trk neurotrophin receptors. TrkA receptors are known to be ubiquitinated via proteasome inhibition in the presence of NGF. However, the effect of proteasome inhibition on neurite outgrowth has not been studied extensively. To clarify these issues, we investigated signaling events in PC12 cells treated with NGF and the proteasome inhibitor MG132. We found that MG132 facilitated NGF-induced neurite outgrowth and potentiated the phosphorylation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol-3-kinase (PI3K)/AKT pathways and TrkA receptors. MG132 stimulated internalization of surface TrkA receptor and stabilized intracellular TrkA receptor, and the $Ub^{K63}$ chain was found to be essential for stability. These results indicate that the ubiquitin-proteasome system potentiated neurite formation by regulating the stability of TrkA receptors.

• BMB Reports
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• v.38 no.3
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• pp.314-319
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• 2005

Adenosine, as a ubiquitous metabolite, mediates many physiological functions via activation of plasma membrane receptors. Mechanisms of most of its physiological roles have been studied extensively, but research on adenosine-induced apoptosis (AIA) has only started recently. In this study we demonstrate that adenosine dose-dependently triggered apoptosis of cultured baby hamster kidney (BHK) cells. Adenosine-induced apoptotic cell death was characterized by DNA laddering, changes in nuclear chromatin morphology and phosphatidylserine staining. Apoptosis was also quantified by flow cytometry. Results suggest the involvement of adenosine $A_1$ and $A_3$ receptors as well as equilibrative nucleoside transporters in apoptosis induced by adenosine. These results indicate a receptor-transporter co-signaling mechanism in AIA in BHK cells. The involvement of $A_1$ and $A_3$ receptors also implies a possible apoptotic pathway mediated by G protein-coupled receptors.

• Genomics & Informatics
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• v.11 no.4
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• pp.282-288
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• 2013

The molecular vibration-activity relationship in the receptor-ligand interaction of adenosine receptors was investigated by structure similarity, molecular vibration, and hierarchical clustering in a dataset of 46 ligands of adenosine receptors. The resulting dendrogram was compared with those of another kind of fingerprint or descriptor. The dendrogram result produced by corralled intensity of molecular vibrational frequency outperformed four other analyses in the current study of adenosine receptor agonism and antagonism. The tree that was produced by clustering analysis of molecular vibration patterns showed its potential for the functional classification of adenosine receptor ligands.

• Korean Journal of Clinical Pharmacy
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• v.28 no.4
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• pp.273-278
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• 2018

Bile acids are major constituents of bile and known to help absorb dietary fat and fat-soluble vitamins in the gastrointestinal tract. In the past few decades, many studies have shown that bile acids not only play a role in fat digestion but also function as broad range of signal transduction hormones by binding to various receptors present in cell membranes or nuclei. Bile acid receptors are distributed in a wide range of organs and tissues in the human body. They perform multitudes of physiological functions with complex mechanisms. When bile acids bind to their receptors, they regulate fat and glucose metabolism in a tissue-specific way. In addition, bile acids are shown to inhibit inflammation and fibrosis in the liver. Considering the roles of bile acids as metabolic regulators, bile acids and their receptors can be very attractive targets in treating metabolic disorders. In the future, if roles of bile acids and their receptors are further clarified, they will be the novel target of drugs in the treatment of various metabolic diseases.

• Biomedical Science Letters
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• v.12 no.2
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• pp.113-118
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• 2006

Major pelvic ganglia (MPG) in rats are an unique autonomic ganglia, containing both sympathetic and parasympathetic neurons related with the function of bladder, penis and bowel. It has been widely known that ionotropic $GABA_A$ receptors are the molecular target of $\gamma$-aminobutric acid (GABA), a major inhibitory neurotransmitter in central nervous system. However, their functions and regulations of $GABA_A$ receptors expressed in autonomic ganglia have been poorly understood. 1 examined the modulatory role of adenylyl cyclase (AC) and protein kinase A(PKA) on $GABA_A$-induced inward currents in the neurons of rat MPG. $GABA_A$ receptors were identified using immunofluorescent labeling in the rat major pelvic ganglion. Electrophysiological experiments were performed to record the activities of $GABA_A$ receptors. $GABA_A$ receptors were expressed only in sympathetic neurons. GABA induced marked inward currents in a concentration-dependent manner. Mucimol ($5{\mu}M$), a $GABA_A$ receptor agonist induced inward currents were significantly reduced in the presence of SQ 225361 $20{\mu}M$, a AC inhibitor and myristoylated PKA inhibitor 100 nM. In addition, forskolin ($1{\mu}M$), AC activator, augmented the GABA induced currents. The activation of AC/PKA-dependent pathway could involve in the regulation $GABA_A$ receptors, expressed only in sympathetic neurons of rat MPG. These findings are helpful for the better understanding the function of various pelvic organs innervated by MPG.

• Journal of Microbiology and Biotechnology
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• v.19 no.2
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• pp.208-214
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• 2009

Steroid hormones have long been known to have a profound influence on the immune system. Although the functions of the nuclear receptors in the development of T cells are fairly well studied, the differential expression of these receptors in T helper cells is poorly understood. Here, we investigated the differential expression of nuclear receptors and coregulators in Th1 and Th2 cells by genome-wide micro array analysis. The result showed that several nuclear receptors and coregulators are differentially expressed in these cells. The result was confirmed by RT-PCR. The result showed that $RXR{\alpha}$ is highly expressed in Th2 cells. Overexpression of $RXR{\alpha}$ in a Jurkat human T cell line induced IL4 but not IFN-${\gamma}$ gene expression, suggesting that $RXR{\alpha}$ plays a selective role in Th1 and Th2 differentiation. In summary, these results suggest that Th1/Th2 differentiation is influenced by differential regulation of nuclear receptors and coregulators.

• IMMUNE NETWORK
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• v.10 no.4
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• pp.120-125
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• 2010

Dysfunction of the virus-specific T cells is a cardinal feature in chronic persistent viral infections such as one caused by hepatitis C virus (HCV). In chronic HCV infection, virus-specific dysfunctional CD8 T cells often overexpress various inhibitory receptors. Programmed cell death 1 (PD-1) was the first among these inhibitory receptors that were identified to be overexpressed in functionally impaired T cells. The roles of other inhibitory receptors such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and T cell immunoglobulin and mucin domain-containing molecule 3 (Tim-3) have also been demonstrated in T-cell dysfunctions that occur in chronic HCV patients. Blocking these inhibitory receptors in vitro restores the functions of HCV-specific CD8 T cells and allows enhanced proliferation, cytolytic activity and cytokine production. Therefore, the blockade of the inhibitory receptors is considered as a novel strategy for the treatment of chronic HCV infection.

• Molecules and Cells
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• v.24 no.1
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• pp.1-8
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• 2007

Natural killer (NK) cells play a crucial role in innate immune system and tumor surveillance. NK cells are derived from $CD34^+$hematopoietic stem cells and undergo differentiation via precursor NK cells in bone marrow (BM) through sequential acquisition of functional surface receptors. During differentiation of NK cells, many factors are involved including cytokines, membrane factors and transcription factors as well as microenvironment of BM. NK cells express their own repertoire of receptors including activating and inhibitory receptors that bind to major histocompatibility complex (MHC) class I or class I-related molecules. The balance between activating and inhibitory receptors determines the function of NK cells to kill targets. Binding of NK cell inhibitory receptors to their MHC class I-ligand renders the target cells to be protected from NK cell-mediated cytotoxicity. Thus, NK cells are able to discriminate self from non-self through MHC class I-binding inhibitory receptor. Using intrinsic properties of NK cells, NK cells are emerging to apply as therapeutic agents against many types of cancers. Recently, NK cell alloactivity has also been exploited in killer cell immunoglobulin-like receptor mismatched haploidentical stem cell transplantation to reduce the rate of relapse and graft versus host disease. In this review, we discuss the basic mechanisms of NK cell differentiation, diversity of NK cell receptors, and clinical applications of NK cells for anti-cancer immunotherapy.

• Biomolecules & Therapeutics
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• v.3 no.3
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• pp.192-198
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• 1995

The affinity of mequitazine, a non-sedating antihistamine, for muscarinic receptors was evaluated in the guinea-pig ventricle and ileum by in vitro binding techniques and functional studies. In binding studies, [$^3$H]quinuclidinyl benzilate (QNB) identified a single class of muscarinic receptors with similar apparent $K_{D}$ value of about 100 pM in two tissues. Mequitazine inhibited [$^3$H]QNB binding to muscarinic receptors competitively. Analysis of the mequitazine inhibition curve of [$^3$H]QNB binding to ventricular microsome and ileal homogenate indicated the presence of a single homogeneous binding site with Ki value of 25 nM and 18 nM, respectively. In functional studies, mequitazine caused parallel rightward shifts of concentration-response curves for carbachol and histamine in the isolated guinea-pig ileum. The slope values obtained from Schild plot analysis for the antagonistic action of mequitazine on muscarinic and histamine $H_1$-receptors were not significantly different from unity. The p $A_2$values of mequitazine for muscarinic and histamine $H_1$-receptors were about 7.6 ( $K_{M}$= 25.1 nM) and 8.88 ( $K_{H}$= 1.32 nM), respectively. These results indicate that the muscarinic receptor blocking action of mequitazine is 15 times less potent than the $H_1$receptor blocking action, but high concentration of this drug may cause the peripheral muscarinic receptor blocking effect.t.t.t.