• Title/Summary/Keyword: Biological Signal

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Quercetin suppress CCL20 by reducing IκBα/STAT3 phosphorylation in TNF-α/IL-17A induced HaCaT cells (TNF-α/IL-17A 유도된 HaCaT 세포주에서 Quercetin의 IκBα/STAT3 인산화 조절에 의한 CCL20 발현 억제)

  • Kim, Mi Ran;Kim, Min Young;Hwang, Hyung Seo
    • Journal of Applied Biological Chemistry
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    • v.63 no.3
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    • pp.211-219
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    • 2020
  • Quercetin is a polyphenol compound with excellent antioxidant and anti-inflammatory activity. However, little has been reported about the efficacy of quercetin to control psoriasis. Thus, we aimed to investigate the effect of quercetin to regulate psoriatic dermatitis with HaCaT cell lines activated by TNF-α and IL-17A, which are in vitro psoriasis skin models. When quercetin was treated with TNF-α-activated HaCaT cell line, inflammatory cytokine expressions such as IL-1α, IL-1β and IL-6 were reduced by 49.1±7.14, 42.8±8.16, and 34.5±2.52%, respectively. In addition, mRNA expression levels of IL-8 and CCL20 the chemokines that attract immune cells such as Th17 cells and dendritic cells to the inflammatory reaction site, were also reduced by 38.4±5.83 and 52.9±4.59% compared to the TNF-α treatment group. The expression of proteins KRT6A and KRT16, which was nonspecifically increased in psoriatic skin was also significantly suppressed. Moreover, phosphorylation of IκBα and STAT3 proteins activated by TNF-α was also significantly inhibited. After stimulating the HaCaT with IL-17A, known as another psoriasis-inducing cytokine, it was observed that IκBα mRNA expression decreased by 55.8±5.28%, and STAT3 phosphorylation was downregulated by 36.3±6.81%. Finally, after co-activation by TNF-α/IL-17A, quercetin inhibited all of IL-1α, IL-1β, IL-6, TNF-α and CCL20 gene expression. The above results strongly suggest that quercetin is a material that has not only anti-oxidant and anti-inflammatory activities, but also has an activity in improving psoriasis.

Microarray Analysis of Gene Expression in Rat Glioma after Ethanol Treatment (에탄올 처리에 의한 흰쥐 신경아교종(Glioma) 세포에서의 유전자 발현 - DNA 칩을 이용한 분석 -)

  • Lee, So Hee;Oh, Dong-Yul;Han, Jin-Hee;Choi, Ihn-Geun;Jeon, Yang-Whan;Lee, Joon-Noh;Lee, Tae Kyung;Jeong, Jong-Hyun;Jung, Kyung Hwa;Chai, Young-Gyu
    • Korean Journal of Biological Psychiatry
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    • v.14 no.2
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    • pp.115-121
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    • 2007
  • Objetives : Identification of target genes for ethanol in neurons is important for understanding its molecular and cellular mechanism of action and the neuropathological changes seen in alcoholics. The purpose of this study is to identify of altered gene expression after acute treatmet of ethanol in rat gliom cells. Methods : We used high density cDNA microarray chip to measure the expression patterns of multiple genes in cultured rat glioma cells. DNA microarrays allow for the simultaneous measurement of the expression of several hundreds of genes. Results : After comparing hybridized signals between control and ethanol treated groups, we found that treatment with ethanol increased the expression of 15 genes and decreased the expression of 12 genes. Upregulated genes included Orthodenticle(Drosophila) homolog 1, procollagen type II, adenosine A2a receptor, GATA bindning protein 2. Downregulated genes included diacylglycerol kinase beta, PRKC, Protein phosphatase 1, clathrin-associated protein 17, nucleoporin p58, proteasome. Conclusion : The gene changes noted were those related to the regulation of transcription, signal transduction, second messenger systems. modulation of ischemic brain injury, and neurodengeneration. Although some of the genes were previously known to be ethanol responsive, we have for the most part identified novel genes involved in the brain response to ethanol.

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Whitening activity of Ficus carica L. fruits extract through inhibition of tyrosinase and MITF expression (무화과(Ficus carica L.) 열매 추출물의 tyrosinase 및 MITF 발현 억제를 통한 미백 활성)

  • Min Ji Kim;Si Eun Park;Geun soo Lee;Jin Hwa Kim;Sunwoo Kwon;Hyung Seo Hwang
    • Journal of Applied Biological Chemistry
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    • v.66
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    • pp.204-212
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    • 2023
  • Whitening is inhibitory activity of the melanin synthesis of melanocytes. Recently, whitening materials have been developed on natural materials because of its side effects on skin. Figs (Ficus Carica L.) is a fruit belonging to the Moraceae family and whitening activity was reported in focusing on the fig's stem and leaf components, but whitening activity of the figs fruit was not known. Thus, in this study, we tried to observe its anti-melanogenesis as well as antioxidant and anti-inflammation. The radical scavenging activity of figs fruits extract (FFE) was observed as the level of 34.52±1.98%/60.71±1.26% compared to the control in the its maximum concentration in the DPPH/ABTS assay. Cytotoxicity of FFE was observed at 10% concentration by CCK8 assay, so the maximum concentration was set at 5% and applied to all experiments. FFE concentration dependently decreased NO production associated with inducible nitric oxide synthase, cyclooxygenase-2, interleukin-6 and tumor necrosis factor-α gene expression, these strongly suggesting anti-inflammatory activity. In melanin contents assay, FFE significantly down-regulated melanin production in α-MSH-stimulated B16F10 cell as well as tyrosinase inhibition in vitro. In addition, FFE decreased the Microphthalmia-associated transcription factor (MITF) mRNA expression about 94.34% compared to the α-MSH treatment group in RT-PCR. Finally, FFE significantly reduced the MITF, cAMP response element-binding protein and tyrosinase protein expression in the α-MSH stimulated B16F10 cell. Through these results, we found that FFE can not only directly inhibit tyrosinase enzyme activity but also suppress melanogenesis through regulation of MITF gene expression in α-MSH signal transduction.

Expression of Phospholipase C Isozymes in Human Lung Cancer Tissues (인체 폐암조직에서 Phospholipase C 동위효소의 발현양상)

  • Hwang, Sung-Chul;Mah, Kyung-Ae;Choi, So-Yeon;Oh, Yoon-Jung;Choi, Young-In;Kim, Deog-Ki;Lee, Hyung-Noh;Choi, Young-Hwa;Park, Kwang-Ju;Lee, Yi-Hyeong;Lee, Kyi-Beom;Ha, Mahn-Joon;Bae, Yoon-Su
    • Tuberculosis and Respiratory Diseases
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    • v.49 no.3
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    • pp.310-322
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    • 2000
  • Background : Phospholipase C(PLC) plays an important role in cellular signal transduction and is thought to be critical in cellular growth, differentiation and transformation of certain malignancies. Two second messengers produced from the enzymatic action of PLC are diacylglycerol (DAG) and inositol 1, 4, 5-trisphosphate (IP3). These two second messengers are important in down stream signal activation of protein kinase C and intracellular calcium elevation. In addition, functional domains of the PLC isozymes, such as Src homology 2 (SH2) domain, Src homology 3 (SH3) domain, and pleckstrin homology (PH) domain play crucial roles in protein translocation, lipid membrane modificailon and intracellular memrane trafficking which occur during various mitogenic processes. We have previously reported the presence of PLC-${\gamma}1$, ${\gamma}2$, ${\beta}1$, ${\beta}3$, and ${\delta}1$ isozymes in normal human lung tissue and tyrosine-kinase-independent activation of phospholipase C-${\gamma}$ isozymes by tau protein and AHNAK. We had also found that the expression of AHNAK protein was markedly increased in various mstologic types of lung can∞r tissues as compared to the normallungs. However, the report concerning expression of various PLC isozymes in lung canærs and other lung diseases is lacking. Therefore, in this study we examined the expression of PLC isozymes in the paired surgical specimens taken from lung cancer patients. Methods : Surgically resected lung cancer tissue samples taken from thirty seven patients and their paired normal control lungs from the same patients, The expression of various PLC isozymes were studied. Western blot analysis of the tissue extracts for the PLC isozymes and immunohistochemistry was performed on typical samples for localization of the isozyme. Results : In 16 of 18 squamous cell carcinomas, the expression of PLC-${\gamma}1$ was increased. PLC-${\gamma}1$ was also found to be increased in all of 15 adenocarcinoma patients. In most of the non-small cell lung cancer tissues we had examined, expression of PLC-${\delta}1$ was decreased. However, the expression of PLC-${\delta}1$ was markedly increased in 3 adenocarcinomas and 3 squamous carcinomas. Although the numbers were small, in all 4 cases of small cell lung cancer tissues, the expression of PLC-${\delta}1$ was nearly absent. Conclusion : We found increased expression of PLC-${\gamma}1$ isozyme in lung cancer tissues. Results of this study, taken together with our earlier findings of AHNAK protein-a putative PLD-${\gamma}$, activator-over-expression, and the changes observed in PLC-${\delta}1$ in primary human lung cancers may provide a possible insight into the derranged calcium-inositol signaling pathways leading to the lung malignancies.

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Biological Functions of N- and O-linked Oligosaccharides of Equine Chorionic Gonadotropin and Lutropin/Chorionicgonadotropin Receptor

  • Min, K. S.
    • Proceedings of the KSAR Conference
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    • 2000.10a
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    • pp.10-12
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    • 2000
  • Members of the glycoprotein family, which includes CG, LH, FSH and TSH, comprise two noncovalently linked $\alpha$- and $\beta$-subunits. Equine chorionic gonadotropin (eCG), known as PMSG, has a number of interesting and unique characteristics since it appears to be a single molecule that possesses both LH- and FSH-like activities in other species than the horse. This dual activity of eCG in heterologous species is of fundamental interest to the study of the structure-function relationships of gonadotropins and their receptors. CG and LH $\beta$ genes are different in primates. In horse, however, a single gene encodes both eCG and eLH $\beta$-subunits. The subunit mRNA levels seem to be independently regulated and their imbalance may account for differences in the quantities of $\alpha$ - and $\beta$ -subunits in the placenta and pituitary. The dual activities of eCG could be separated by removal of the N-linked oligosaccharide on the $\alpha$-subunit Asn 56 or CTP-associated O-linked oligosaccharides. The tethered-eCG was. efficiently secreted and showed similar LH-like activity to the dimeric eCG. Interestingly, the FSH-like activity of the tethered-eCG was increased markedly in comparison with the native and wild type eCG. These results also suggest that this molecular can implay particular models of FSH-like activity not LH-like activity in the eCG/indicate that the constructs of tethered molecule will be useful in the study of mutants that affect subunit association and/or secretion. A single-chain analog can also be constructed to include additional hormone-specific bioactive generating potentially efficacious compounds that have only FSH-like activity. The LH/CG receptor (LH/CGR), a membrane glycoprotein that is present on testicular Leydig cells and ovarian theca, granulosa, luteal, and interstitial cells, plays a pivotal role in the regulation of gonadal development and function in males as well as in nonpregnant and pregnant females. The LH/CGR is a member of the family of G protein-coupled receptors and its structure is predicted to consist of a large extracellular domain connected to a bundle of seven membrane-spanning a-helices. The LH/CGR phosphorylation can be induced with a phorbol ester, but not with a calcium ionophore. The truncated form of LHR also was down-regulated normally in response to hCG stimulation. In contrast, the cell lines expressing LHR-t63I or LHR-628, the two phosphorylation-negative receptor mutant, showed a delay in the early phase of hCG-induced desensitization, a complete loss of PMA-induced desensitization, and an increase in the rate of hCG-induced receptor down-regulation. These results clearly show that residues 632-653 in the C-terminal tail of the LHR are involved in PMA-induced desensitization, hCG-induced desensitization, and hCG-induced down-regulation. Recently, constitutively activating mutations of the receptor have been identified that are associated with familial male-precocious puberty. Cells expressing LHR-D556Y bind hCG with normal affinity, exhibit a 25-fold increase in basal cAMP and respond to hCG with a normal increase in cAMP accumulation. This mutation enhances the internalization of the free and agonist-occupied receptors ~2- and ~17-fold, respectively. We conclude that the state of activation of the LHR can modulate its basal and/or agonist-stimulated internalization. Since the internalization of hCG is involved in the termination of hCG actions, we suggest that the lack of responsiveness detected in cells expressing LHR-L435R is due to the fast rate of internalization of the bound hCG. This statement is supported by the finding that hCG responsiveness is restored when the cells are lysed and signal transduction is measured in a subcellular fraction (membranes) that cannot internalize the bound hormone.

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Analysis of Global Gene Expression Profile of Human Adipose Tissue Derived Mesenchymal Stem Cell Cultured with Cancer Cells (암세포주와 공동 배양된 인간 지방 조직 유래 중간엽 줄기 세포의 유전자 발현 분석)

  • Kim, Jong-Myung;Yu, Ji-Min;Bae, Yong-Chan;Jung, Jin-Sup
    • Journal of Life Science
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    • v.21 no.5
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    • pp.631-646
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    • 2011
  • Mesenchymal stem cells (MSC) are multipotent and can be isolated from diverse human tissues including bone marrow, fat, placenta, dental pulp, synovium, tonsil, and the thymus. They function as regulators of tissue homeostasis. Because of their various advantages such as plasticity, easy isolation and manipulation, chemotaxis to cancer, and immune regulatory function, MSCs have been considered to be a potent cell source for regenerative medicine, cancer treatment and other cell based therapy such as GVHD. However, relating to its supportive feature for surrounding cell and tissue, it has been frequently reported that MSCs accelerate tumor growth by modulating cancer microenvironment through promoting angiogenesis, secreting growth factors, and suppressing anti-tumorigenic immune reaction. Thus, clinical application of MSCs has been limited. To understand the underlying mechanism which modulates MSCs to function as tumor supportive cells, we co-cultured human adipose tissue derived mesenchymal stem cells (ASC) with cancer cell lines H460 and U87MG. Then, expression data of ASCs co-cultured with cancer cells and cultured alone were obtained via microarray. Comparative expression analysis was carried out using DAVID (Database for Annotation, Visualization and Integrated Discovery) and PANTHER (Protein ANalysis THrough Evolutionary Relationships) in divers aspects including biological process, molecular function, cellular component, protein class, disease, tissue expression, and signal pathway. We found that cancer cells alter the expression profile of MSCs to cancer associated fibroblast like cells by modulating its energy metabolism, stemness, cell structure components, and paracrine effect in a variety of levels. These findings will improve the clinical efficacy and safety of MSCs based cell therapy.

Iron chelating agent, deferoxamine, induced apoptosis in Saos-2 osteosarcoma cancer cells (Saos-2 골육종 세포에서 iron chelating agent, deferoxamine에 의한 apoptosis 유도)

  • Park, Eun Hye;Lee, Hyo Jung;Lee, Soo Yeon;Kim, Sun Young;Yi, Ho Keun;Lee, Dae Yeol;Hwang, Pyoung Han
    • Clinical and Experimental Pediatrics
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    • v.52 no.2
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    • pp.213-219
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    • 2009
  • Purpose:Iron is a critical nutritional element that is essential for a variety of important biological processes, including cell growth and differentiation, electron transfer reactions, and oxygen transport, activation, and detoxification. Iron is also required for neoplastic cell growth due to its catalytic effects on the formation of hydroxyl radicals, suppression of host defense cell activities, and promotion of cancer cell multiplication. Chronic transfusion-dependent patients receiving chemotherapy may have iron overload, which requires iron-chelating therapy. We performed this study to demonstrate whether the iron chelating agent deferoxamine induces apoptosis in Saos-2 osteosarcoma cells, and to investigate the underlying apoptotic mechanism. Methods:To analyze the apoptotic effects of an iron chelator, cultured Saos-2 cells were treated with deferoxamine. We analyzed cell survival by trypan blue and crystal violet analysis, apoptosis by nuclear condensation, DNA fragmentation, and cell cycle analysis, and the expression of apoptotic related proteins by Western immunoblot analysis. Results:Deferoxamine inhibited the growth of Saos-2 cell in a time- and dose-dependent manner. The major mechanism for growth inhibition with the deferoxamine treatment was by the induction of apoptosis, which was supported by nuclear staining, DNA fragmentation analysis, and flow cytometric analysis. Furthermore, bcl-2 expression decreased, while bax, caspase-3, caspase-9, and PARP expression increased in Saos-2 cells treated with deferoxamine. Conclusion:These results demonstrated that the iron chelating agent deferoxamine induced growth inhibition and mitochondrial-dependent apoptosis in osteosarcoma Saos-2 cells, suggesting that iron chelating agents used in controlling neoplastic cell fate can be potentially developed as an adjuvant agent enhancing the anti-tumor effect for the treatment of osteosarcoma.

THE CURRENT STATUS OF BIOMEDICAL ENGINEERING IN THE USA

  • Webster, John G.
    • Proceedings of the KOSOMBE Conference
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    • v.1992 no.05
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    • pp.27-47
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    • 1992
  • Engineers have developed new instruments that aid in diagnosis and therapy Ultrasonic imaging has provided a nondamaging method of imaging internal organs. A complex transducer emits ultrasonic waves at many angles and reconstructs a map of internal anatomy and also velocities of blood in vessels. Fast computed tomography permits reconstruction of the 3-dimensional anatomy and perfusion of the heart at 20-Hz rates. Positron emission tomography uses certain isotopes that produce positrons that react with electrons to simultaneously emit two gamma rays in opposite directions. It locates the region of origin by using a ring of discrete scintillation detectors, each in electronic coincidence with an opposing detector. In magnetic resonance imaging, the patient is placed in a very strong magnetic field. The precessing of the hydrogen atoms is perturbed by an interrogating field to yield two-dimensional images of soft tissue having exceptional clarity. As an alternative to radiology image processing, film archiving, and retrieval, picture archiving and communication systems (PACS) are being implemented. Images from computed radiography, magnetic resonance imaging (MRI), nuclear medicine, and ultrasound are digitized, transmitted, and stored in computers for retrieval at distributed work stations. In electrical impedance tomography, electrodes are placed around the thorax. 50-kHz current is injected between two electrodes and voltages are measured on all other electrodes. A computer processes the data to yield an image of the resistivity of a 2-dimensional slice of the thorax. During fetal monitoring, a corkscrew electrode is screwed into the fetal scalp to measure the fetal electrocardiogram. Correlations with uterine contractions yield information on the status of the fetus during delivery To measure cardiac output by thermodilution, cold saline is injected into the right atrium. A thermistor in the right pulmonary artery yields temperature measurements, from which we can calculate cardiac output. In impedance cardiography, we measure the changes in electrical impedance as the heart ejects blood into the arteries. Motion artifacts are large, so signal averaging is useful during monitoring. An intraarterial blood gas monitoring system permits monitoring in real time. Light is sent down optical fibers inserted into the radial artery, where it is absorbed by dyes, which reemit the light at a different wavelength. The emitted light travels up optical fibers where an external instrument determines O2, CO2, and pH. Therapeutic devices include the electrosurgical unit. A high-frequency electric arc is drawn between the knife and the tissue. The arc cuts and the heat coagulates, thus preventing blood loss. Hyperthermia has demonstrated antitumor effects in patients in whom all conventional modes of therapy have failed. Methods of raising tumor temperature include focused ultrasound, radio-frequency power through needles, or microwaves. When the heart stops pumping, we use the defibrillator to restore normal pumping. A brief, high-current pulse through the heart synchronizes all cardiac fibers to restore normal rhythm. When the cardiac rhythm is too slow, we implant the cardiac pacemaker. An electrode within the heart stimulates the cardiac muscle to contract at the normal rate. When the cardiac valves are narrowed or leak, we implant an artificial valve. Silicone rubber and Teflon are used for biocompatibility. Artificial hearts powered by pneumatic hoses have been implanted in humans. However, the quality of life gradually degrades, and death ensues. When kidney stones develop, lithotripsy is used. A spark creates a pressure wave, which is focused on the stone and fragments it. The pieces pass out normally. When kidneys fail, the blood is cleansed during hemodialysis. Urea passes through a porous membrane to a dialysate bath to lower its concentration in the blood. The blind are able to read by scanning the Optacon with their fingertips. A camera scans letters and converts them to an array of vibrating pins. The deaf are able to hear using a cochlear implant. A microphone detects sound and divides it into frequency bands. 22 electrodes within the cochlea stimulate the acoustic the acoustic nerve to provide sound patterns. For those who have lost muscle function in the limbs, researchers are implanting electrodes to stimulate the muscle. Sensors in the legs and arms feed back signals to a computer that coordinates the stimulators to provide limb motion. For those with high spinal cord injury, a puff and sip switch can control a computer and permit the disabled person operate the computer and communicate with the outside world.

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Evaluation of Antidepressant Drug Effect in a Depressive Animal Model by Proton MR Spectroscopy (양성자 자기공명분광법을 이용한 우울증 동물모델에서의 항우울제 약물 효능 평가)

  • Kim, Sang-Young;Choi, Chi-Bong;Lee, Sung-Ho;Woo, Dong-Cheol;Yoon, Seong-Ik;Hong, Kwan-Soo;Lee, Hyun-Sung;Cheong, Chae-Joon;Jee, Bo-Keun;Hong, Sung-Tak;Kim, Hwi-Yool;Choe, Bo-Young
    • Progress in Medical Physics
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    • v.19 no.2
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    • pp.95-101
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    • 2008
  • In this study, we observed the alteration of choline signal intensity in hippocampus region of the depressive rat model induced by forced swimming test (FST). The purpose of this study was to evaluate the antidepressant efficacy in the depressive animal model using MR spectroscopy. Fourteen experimentally naive male Sprague-Dawley rats weighting $160{\sim}180\;g$ were used as subjects. Drug injection group was exposed to the FST except for control group. The drugs were administered subcutaneously (SC) in a volume equivalent to 2ml/kg. And three injections were administered 23, 5, and 1h before beginning the given test. 1H MR spectra were obtained with use of a point resolved spectroscopy (PRESS) localization sequence performed according to the following parameters: repetition time, 2500 ms; echo time, 144 ms; 512 average; 2048 complex data points; voxel dimensions, $1.5{\times}2.5{\times}2.5\;mm^3$ ; acquisition time, 25min. There were no differences in NAA/Cr and Cho/Cr ratio between the right and the left hippocampus both normal control rats and antidepressant-injected rats. Also, no differences were observed in NAA/Cr and Cho/Cr ratio between the normal control rats and the antidepressant-injected rats both the right and the left hippocampus. In this study, we found the recovery of choline signals in the depressive animal model similar to normal control groups as injecting desipramine-HCl which was antidepressant causing anti-immobility effects. Thus, we demonstrated that MR spectroscopy was able to aid in evaluating the antidepressant effect of desipramine-HCl.

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Biological Functions of N- and O-linked Oligosaccharides of Equine Chorionic Gonadotropin and Lutropin/Chorionic Gonadotropin Receptor

  • Min, K.S.
    • Korean Journal of Animal Reproduction
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    • v.24 no.4
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    • pp.357-364
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    • 2000
  • Members of the glycoprotein family, which includes CG, LH, FSH and TSH, comprise two noncovalently linked $\alpha$- and $\beta$-subunits. Equine chorionic gonadotropin (eCG), known as PMSG, has a number of interesting and unique characteristics since it appears to be a single molecule that possesses both LH- and FSH-like activities in other species than the horse. This dual activity of eCG in heterologous species is of fundamental interest to the study of the structure-function relationships of gonadotropins and their receptors. CG and LH $\beta$ genes are different in primates. In horse, however, a single gene encodes both eCG and eLH $\beta$ -subunits. The subunit mRNA levels seem to be independently regulated and their imbalance may account for differences in the quantities of $\alpha$ - and $\beta$-subunits in the placenta and pituitary. The dual activities of eCG could be separated by removal of the N-linked oligosaccharide on the $\alpha$-subunit Asn 56 or CTP-associated O-linked oligosaccharides. The tethered-eCG was efficiently secreted and showed similar LH-like activity to the dimeric eCG. Interestingly, the FSH-like activity of the tethered-eCG was increased markedly in comparison with the native and wild type eCG. These results also suggest that this molecular can implay particular models of FSH-like activity not LH-like activity in the eCG/indicate that the constructs of tethered molecule will be useful in the study of mutants that affect subunit association and/or secretion. A single-chain analog can also be constructed to include additional hormone-specific bioactive generating potentially efficacious compounds that have only FSH-like activity. The LH/CG receptor (LH/CGR), a membrane glycoprotein that is present on testicular Leydig cells and ovarian theca, granulosa, luteal, and interstitial cells, plays a pivotal role in the regulation of gonadal development and function in males as well as in nonpregnant and pregnant females. The LH/CGR is a member of the family of G protein-coupled receptors and its structure is predicted to of a large extracellular domain connected to a bundle of seven membrane-spanning a-helices. The LH/CGR phosphorylation can be induced with a phorbol ester, but not with a calcium ionophore. The truncated form of LHR also was down-regulated normally in response to hCG stimulation. In contrast, the cell lines expressing LHR-t631 or LHR-628, the two phosphorylation-negative receptor mutant, showed a delay in the early phase of hCG-induced desensitization, a complete loss of PMA-induced desensitization, and an increase in the rate of hCG-induced receptor down-regulation. These results clearly show that residues 632~653 in the C-terminal tail of the LHR are involved in PMA-induced desensitization, hCG-induced desensitization, and hCG-induced down-regulation. Recently, constitutively activating mutations of the receptor have been identified that are associated with familial male-precocious puberty. Cells expressing LHR-D556Y bind hCG with normal affinity, exhibit a 25-fold increase in basal cAMP and respond to hCG with a normal increase in cAMP accumulation. This mutation enhances the internalization of the free and agoinst-occupied receptors ~2- and ~17- fold, respectively. We conclude that the state of activation of the LHR can modulate its basal and/or agonist-stimulated internalization. Since the internalization of hCG is involved in the termination of hCG actions, we suggest that the lack of responsiveness detected in cells expressing LHR-L435R is due to the fast rate of internalization of the bound hCG. This statement is supported by the finding that hCG responsiveness is restored when the cells are lysed and signal transduction is measured in a subcellular fraction (membranes) that cannot internalize the bound hormone.

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