• Molecules and Cells
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• v.38 no.10
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• pp.836-842
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• 2015

G protein-coupled receptors (GPCRs) constitute the largest and the most physiologically important membrane protein family that recognizes a variety of environmental stimuli, and are drug targets in the treatment of numerous diseases. Recent progress on GPCR structural studies shed light on molecular mechanisms of GPCR ligand recognition, activation and allosteric modulation, as well as structural basis of GPCR dimerization. In this review, we will discuss the structural features of GPCRs and structural insights of different aspects of GPCR biological functions.

• Molecular & Cellular Toxicology
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• v.4 no.4
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• pp.267-277
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• 2008

Benzene and ethylbenzene (BE), the volatile organic compounds (VOCs) are common constituents of cleaning and degreasing agents, paints, pesticides, personal care products, gasoline and solvents. VOCs are evaporated at room temperature and most of them exhibit acute and chronic toxicity to human. Chronic exposure of benzene is responsible for myeloid leukemia and also ethylbenzene is also recognized as a possible carcinogen. To evaluate the BE effect on human, whole human genome 35 K oligonucleotide microarray were screened for the identification of the differential expression profiling. We identified 280 up-regulated and 201 down-regulated genes changed by more than 1.5 fold by BE exposure. Functional analysis was carried out by using DAVID bioinformatics software. Clustering of these differentially expressed genes were associated with immune response, cytokine-cytokine receptor interaction, toll-like signaling pathway, small cell lung cancer, immune response, apoptosis, p53 signaling pathway and MAPKKK cascade possibly constituting alternative or subordinate pathways of hematotoxicity and immune toxicity. Gene ontology analysis methods including biological process, cellular components, molecular function and KEGG pathway thus provide a fundamental basis of the molecular pathways through BEs exposure in human lymphoma cells. This may provides a valuable information to do further analysis to explore the mechanism of BE induced hematotoxicity.

• Biomedical Science Letters
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• v.12 no.4
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• pp.385-391
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• 2006

Heterotrimeric GTP binding proteins (G proteins) mediate signals generated by neurotransmitters and hormones Among G proteins, Go is found in a large quantity in brain and growth cone membranes of neurons. In spite of its abundance in neurons, the role of Go is not fully understood. In our previous study, we identified promyelocytic leukemia zinc finger protein (PLZF) as an interacting partner of alpha subunit of Go ($Go{\alpha}$) and confirmed their interaction employing several biochemical assays. To date, it is reported that PLZF functioned as a cell growth suppressor and a transcription repressor. To determine effect of $Go{\alpha}$ and PLZF interaction on the cellular function of PLZF, we performed luciferase reporter gene assay and BrdU incorporation assay. Co-expression of $Go{\alpha}$ and PLZF synergistically increased the effect of PLZF alone. These results suggest that $Go{\alpha}$ may act as cellular activator of PLZF. This novel feature of Go may provide insights into understanding diverse role of Go-coupled receptor as well as its cellular actions.

• Genomics & Informatics
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• v.7 no.2
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• pp.111-121
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• 2009

Cell membrane proteins play crucial roles in the cell's molecular interaction with its environment and within itself. They consist of membrane-bound proteins and many types of transmembrane (TM) proteins such as receptors, transporters, channel proteins, and enzymes. Membrane proteomes of cellular organisms reveal some characteristics in their global topological distribution according to their evolutionary positions, and show their own information transfer complexity. Predicted transmembrane segments (TMSs) in membrane proteomes with HMMTOP showed near power-law distribution and frequency characteristics in 6-TMS and 7-TMS proteins in prokaryotes and eukaryotes, respectively. This reaffirms the important roles of membrane receptors in cellular communication and biological evolutionary history.

• Proceedings of the KSAR Conference
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• 2001.03a
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• pp.54-54
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• 2001

Human chorionic gonadotropin (hCG) is a member of the glycoprotein hormone family which includes FSH, hCG, TSH. These hormone family is characterized by a heterodimeric structure composed a common $\alpha$-subunit noncovalently linked to a hormone specific $\beta$-subunit. The correct conformation of the heterodimer is also important for efficient secretion, hormone-specific post-translational modifications, receptor binding and signal transduciton. To determine $\alpha$ and $\beta$-subunits can be synthesized as a single polypeptide chain (tethered-hCG) and also display biological activity, the tethered-hCG molecule by fusing the carboxyl terminus of the hCG $\beta$-subunit to the amino terminus of the $\alpha$-subunit was constructed and transfected into chinese hamster ovary (CHO-K1) cells. We also constructed C-terminal deletion mutants (D9l, D89, D88, D87, D86, D84, D83) of single chain hCG to determine the biological function (secretion, LH-activity, receptor binding, cAMP production) of these mutants. Between six and eight stably transfected pools of cells expressing wild type and mutant hCGs were selected for neomycin resistant. The hCGs secreted by the stably transfected cells into serum-free media were collected and quantified by radioimmunoassay, as described in protocol (DPC(hCG IRMA). LH activity was in terms of testosterone production and aromatase activity in primary cultured rat Leydig cells. The tethered-wthCG was efficiently secreted and showed similar LH-like activity to the dimeric hCG. The D83hCG mutant was not detected in this assay. It is suggest that hCG C-terminal part is very important for hCG secretion. Now, we checking the LH-like activity of these mutant hCGs. These data indicate that the constructs of tethered molecule will be useful in the study of mutants that affect subunit association and/or secretion.

• BMB Reports
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• v.49 no.6
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• pp.305-310
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• 2016

Toll-like receptors (TLRs) play a critical role in the innate immune response against pathogens. Each TLR recognizes specific pathogen-associated molecular patterns, after which they activate the adaptor protein MyD88 or TRIF-assembled signaling complex to produce immune mediators, including inflammatory cytokines and type I IFNs. Although the activation of TLR is important for host defense, its uncontrolled activation can damage the host. During the past decade, numerous studies have demonstrated that GSK3β is a key regulator of inflammatory cytokine production in MyD88-mediated TLR signaling via TLR2 and TLR4. Recently, GSK3β has also been implicated in the TRIF-dependent signaling pathway via TLR3. In this review, we describe current advances on the regulatory role of GSK3β in immune responses associated with various TLRs. A better understanding of the role of GSK3β in TLR signaling might lead to more effective anti-inflammatory interventions.

• Archives of Pharmacal Research
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• v.28 no.3
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• pp.249-268
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• 2005

Drug metabolizing enzymes (DMEs) play central roles in the metabolism, elimination and detoxification of xenobiotics and drugs introduced into the human body. Most of the tissues and organs in our body are well equipped with diverse and various DMEs including phase I, phase II metabolizing enzymes and phase III transporters, which are present in abundance either at the basal unstimulated level, and/or are inducible at elevated level after exposure to xenobiotics. Recently, many important advances have been made in the mechanisms that regulate the expression of these drug metabolism genes. Various nuclear receptors including the aryl hydrocarbon receptor (AhR), orphan nuclear receptors, and nuclear factor-erythoroid 2 p45-related factor 2 (Nrf2) have been shown to be the key mediators of drug-induced changes in phase I, phase II metabolizing enzymes as well as phase III transporters involved in efflux mechanisms. For instance, the expression of CYP1 genes can be induced by AhR, which dimerizes with the AhR nuclear translocator (Arnt) , in response to many polycyclic aromatic hydrocarbon (PAHs). Similarly, the steroid family of orphan nuclear receptors, the constitutive androstane receptor (CAR) and pregnane X receptor (PXR), both heterodimerize with the ret-inoid X receptor (RXR), are shown to transcriptionally activate the promoters of CYP2B and CYP3A gene expression by xenobiotics such as phenobarbital-like compounds (CAR) and dexamethasone and rifampin-type of agents (PXR). The peroxisome proliferator activated receptor (PPAR), which is one of the first characterized members of the nuclear hormone receptor, also dimerizes with RXR and has been shown to be activated by lipid lowering agent fib rate-type of compounds leading to transcriptional activation of the promoters on CYP4A gene. CYP7A was recognized as the first target gene of the liver X receptor (LXR), in which the elimination of cholesterol depends on CYP7A. Farnesoid X receptor (FXR) was identified as a bile acid receptor, and its activation results in the inhibition of hepatic acid biosynthesis and increased transport of bile acids from intestinal lumen to the liver, and CYP7A is one of its target genes. The transcriptional activation by these receptors upon binding to the promoters located at the 5-flanking region of these GYP genes generally leads to the induction of their mRNA gene expression. The physiological and the pharmacological implications of common partner of RXR for CAR, PXR, PPAR, LXR and FXR receptors largely remain unknown and are under intense investigations. For the phase II DMEs, phase II gene inducers such as the phenolic compounds butylated hydroxyanisol (BHA), tert-butylhydroquinone (tBHQ), green tea polyphenol (GTP), (-)-epigallocatechin-3-gallate (EGCG) and the isothiocyanates (PEITC, sul­foraphane) generally appear to be electrophiles. They generally possess electrophilic-medi­ated stress response, resulting in the activation of bZIP transcription factors Nrf2 which dimerizes with Mafs and binds to the antioxidant/electrophile response element (ARE/EpRE) promoter, which is located in many phase II DMEs as well as many cellular defensive enzymes such as heme oxygenase-1 (HO-1), with the subsequent induction of the expression of these genes. Phase III transporters, for example, P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs), and organic anion transporting polypeptide 2 (OATP2) are expressed in many tissues such as the liver, intestine, kidney, and brain, and play crucial roles in drug absorption, distribution, and excretion. The orphan nuclear receptors PXR and GAR have been shown to be involved in the regulation of these transporters. Along with phase I and phase II enzyme induction, pretreatment with several kinds of inducers has been shown to alter the expression of phase III transporters, and alter the excretion of xenobiotics, which implies that phase III transporters may also be similarly regulated in a coordinated fashion, and provides an important mean to protect the body from xenobiotics insults. It appears that in general, exposure to phase I, phase II and phase III gene inducers may trigger cellular 'stress' response leading to the increase in their gene expression, which ultimately enhance the elimination and clearance of these xenobiotics and/or other 'cellular stresses' including harmful reactive intermediates such as reactive oxygen species (ROS), so that the body will remove the 'stress' expeditiously. Consequently, this homeostatic response of the body plays a central role in the protection of the body against 'environmental' insults such as those elicited by exposure to xenobiotics.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.3
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• pp.185-191
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• 2008

While indirect targeting strategies using reporter-genes are taking center stage in current molecular imaging research, another vital strategy has long involved direct imaging of specific receptors using radiolabeled ligands. Recently, there is renewal of immense interest in this area with particular attention to the epidermal growth factor receptor (EGFR), a transmembrane glycoprotein critically involved in the regulation of many cellular functions and malignancies. Recently, two novel classes of EGFR-targeting anticancer drugs have entered clinical trials with great expectations. These are monoclonal antibodies such as cetuximab that target the extracellular domain, and small molecule tyrosine kinase inhibitors such as gefitinib (lressa) and erlotinib (Tarceva) that target the catalytic domain of the receptor. However, early results have showed disappointing survival benefits, disclosing a major challenge for this therapeutic strategy; namely, the need to identify tumors that are most likely to respond to the agents. To address this important clinical issue, several noninvasive imaging techniques are under investigation including radiolabeled probes based on small molecule tyrosine kinase inhibitors, anti-EGFR antibodies, and EGF peptides. This review describes the current status, limitations, and future prospects in the development of radiotracer methods for EGFR imaging.

• Molecules and Cells
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• v.24 no.2
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• pp.194-199
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• 2007

GCN4 is a typical eukaryotic transcriptional activator that is implicated in the expression of many genes involved in amino acids and purine biosyntheses under stress conditions. It is degraded by 26S proteasomes following ubiquitination. However, the immediate receptor for ubiquitinated Gcn4p has not yet been identified. We investigated whether ubiquitinated Gcn4p binds directly to Rpn10p as the ubiquitinated substrate receptor of the 26S proteasome. We found that the level of Gcn4p increased in cells deleted for Rpn10p but not in cells deleted for RAD23 and DSK2, the other ubiquitinated substrate receptors and, unlike Rpn10p, neither of these proteins recognized ubiquitinated Gcn4p. These results suggest that Rpn10p is the receptor that binds the polyubiquitin chain during ubiquitin-dependent proteolysis of Gcn4p.

• International Journal of Oral Biology
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• v.42 no.2
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• pp.55-61
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• 2017

Recent studies indicate that mitochondria are an important source of reactive oxygen species (ROS) in the spinal dorsal horn. In our previous study, application of malate, a mitochondrial electron transport complex I substrate, induced a membrane depolarization, which was inhibited by pretreatment with ROS scavengers. In the present study, we used patch clamp recording in the substantia geletinosa (SG) neurons of spinal slices, to investigate the cellular mechanism of mitochondrial ROS on neuronal excitability. DNQX (an AMPA receptor antagonist) and AP5 (an NMDA receptor antagonist) decreased the malate-induced depolarization. In an external calcium free solution and addition of tetrodotoxin (TTX) for blockade of synaptic transmission, the malate-induced depolarization remained unchanged. In the presence of DNQX, AP5 and AP3 (a group I metabotropic glutamate receptor (mGluR) antagonist), glutamate depolarized the membrane potential, which was suppressed by PBN. However, oligomycin (a mitochondrial ATP synthase inhibitor) or PPADS (a P2 receptor inhibitor) did not affect the substrates-induced depolarization. These results suggest that mitochondrial substrate-induced ROS in SG neuron directly acts on the postsynaptic neuron, therefore increasing the ion influx via glutamate receptors.