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Dive into the research topics where Taeyoon Kim is active.

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Featured researches published by Taeyoon Kim.


Cell | 2001

Chromogranin A, an “On/Off” Switch Controlling Dense-Core Secretory Granule Biogenesis

Taeyoon Kim; Jung-Hwa Tao-Cheng; Lee E. Eiden; Y. Peng Loh

We present evidence that regulation of dense-core secretory granule biogenesis and hormone secretion in endocrine cells is dependent on chromogranin A (CGA). Downregulation of CGA expression in a neuroendocrine cell line, PC12, by antisense RNAs led to profound loss of dense-core secretory granules, impairment of regulated secretion of a transfected prohormone, and reduction of secretory granule proteins. Transfection of bovine CGA into a CGA-deficient PC12 clone rescued the regulated secretory phenotype. Stable transfection of CGA into a CGA-deficient pituitary cell line, 6T3, lacking a regulated secretory pathway, restored regulated secretion. Overexpression of CGA induced dense-core granules, immunoreactive for CGA, in nonendocrine fibroblast CV-1 cells. We conclude that CGA is an on/off switch that alone is sufficient to drive dense-core secretory granule biogenesis and hormone sequestration in endocrine cells.


Journal of Biological Chemistry | 2009

Syndecan-2 Regulates the Migratory Potential of Melanoma Cells

Jung-hyun Lee; Haein Park; Heesung Chung; Sojoong Choi; Younghwa Kim; Hyun Yoo; Taeyoon Kim; Hoo-Jae Hann; Ikjoo Seong; Jaesang Kim; Kathleen G. Kang; Inn-Oc Han; Eok-Soo Oh

Syndecan-2, a transmembrane heparan sulfate proteoglycan, is a critical mediator in the tumorigenesis of colon carcinoma cells. We explored the function of syndecan-2 in melanoma, one of the most invasive types of cancers, and found that the expression of this protein was elevated in tissue samples from both nevus and malignant human melanomas but not in melanocytes of the normal human skin tissues. Similarly, elevated syndecan-2 expression was observed in various melanoma cell lines. Overexpression of syndecan-2 enhanced migration and invasion of melanoma cells, whereas the opposite was observed when syndecan-2 levels were knocked down using small inhibitory RNAs. Syndecan-2 expression was enhanced by fibroblast growth factor-2, which is known to stimulate melanoma cell migration; however, α-melanocyte-stimulating hormone decreased syndecan-2 expression and melanoma cell migration and invasion in a melanin synthesis-independent manner. Furthermore, syndecan-2 overexpression rescued the migration defects induced by α-melanocyte-stimulating hormone treatment. Together, these data strongly suggest that syndecan-2 plays a crucial role in the migratory potential of melanoma cells.


Journal of Molecular Neuroscience | 2004

Secretory granule biogenesis and neuropeptide sorting to the regulated secretory pathway in neuroendocrine cells.

Y. Peng Loh; Taeyoon Kim; Yazmin M. Rodriguez; Niamh X. Cawley

Neuropeptide precursors synthesized at the rough endoplasmic reticulum are transported and sorted at the trans-Golgi network (TGN) to the granules of the regulated secretory pathway (RSP) of neuroendocrine cells. They are then processed into active peptides and stored in large dense-core granules (LDCGs) until secreted upon stimulation. We have studied the regulation of biogenesis of the LDCGs and the mechanism by which neuropeptide precursors, such as pro-opiomelanocortin (POMC), are sorted into these LDCGs of the RSP in neuroendocrine and endocrine cells. We provide evidence that chromogranin A (CgA), one of the most abundant acidic glycoproteins ubiquitously present in neuroendocrine/endocrine cells, plays an important role in the regulation of LDCG biogenesis. Specific depletion of CgA expression by antisense RNAs in PC12 cells led to a profound loss of secretory granule formation. Exogenously expressed POMC was neither stored nor secreted in a regulated manner in these CgA-deficient PC12 cells. Overexpression of CgA in a CgA- and LDCG-deficient endocrine cell line, 6T3, restored regulated secretion of transfected POMC and the presence of immunoreactive CgA at the tips of the processes of these cells. Unlike CgA, CgB, another granin protein, could not substitute for the role of CgA in regulating LDCG biogenesis. Thus, we conclude that CgA is a key player in the regulation of the biogenesis of LDCGs in neuroendocrine cells. To examine the mechanism of sorting POMC to the LDCGs, we carried out site-directed mutagenesis, transfected the POMC mutants into PC12 cells, and assayed for regulated secretion. Our previous molecular modeling studies predicted a three-dimensional sorting motif in POMC that can bind to a sorting receptor, membrane carboxypeptidase E (CPE). The sorting signal consists of four conserved residues at the N-terminal loop structure of POMC: two acidic residues and two hydrophobic residues. The two acidic residues were predicted to bind to a domain on CPE (CPE254–273) containing two basic residues (R255 and K260) to effect sorting into immature secretory granules. Site-directed mutagenesis of the motif on POMC resulted in accumulation of the mutant in the Golgi, as well as high basal secretion, indicating that the mutant POMC was inefficiently sorted to the RSP. These results support the model that POMC is actively sorted to the RSP granules for processing and secretion by a sorting signal-mediated mechanism.


Regulatory Peptides | 2010

Chromogranin A: A New Proposal for Trafficking, Processing and Induction of Granule Biogenesis

Hisatsugu Koshimizu; Taeyoon Kim; Niamh X. Cawley; Y. Peng Loh

Chromogranin A (CgA), a member of the granin family serves several important cell biological roles in (neuro)endocrine cells which are summarized in this review. CgA is a prohormone that is synthesized at the rough endoplasmic reticulum and transported into the cisternae of this organelle via its signal peptide. It is then trafficked to the Golgi complex and then to the trans-Golgi network (TGN) where CgA aggregates at low pH in the presence of calcium. The CgA aggregates provide the physical driving force to induce budding of the TGN membrane resulting in dense core granule (DCG) formation. Within the granule, a small amount of the CgA is processed to bioactive peptides, including a predicted C-terminal peptide, serpinin. Upon stimulation, DCGs undergo exocytosis and CgA and its derived peptides are released. Serpinin, acting extracellularly is able to signal the increase in transcription of a serine protease inhibitor, protease nexin-1 (PN-1) that protects DCG proteins against degradation in the Golgi complex, which then enhances DCG biogenesis to replenish those that were released. Thus CgA and its derived peptide, serpinin, plays a significant role in granule formation and regulation of granule biogenesis, respectively, in (neuro) endocrine cells.


Journal of Biological Chemistry | 2003

Nerve Growth Factor-dependent Sorting of Synaptotagmin IV Protein to Mature Dense-core Vesicles That Undergo Calcium-dependent Exocytosis in PC12 Cells

Mitsunori Fukuda; Eiko Kanno; Yukie Ogata; Chika Saegusa; Taeyoon Kim; Y. Peng Loh; Akitsugu Yamamoto

Synaptotagmin IV (Syt IV) is a fourth member of the Syt family and has been shown to regulate some forms of memory and learning by analysis of Syt IV null mutant mice (Ferguson, G. D., Anagnostaras, S. G., Silva, A. J., and Herschman, H. R. (2000) Proc. Natl. Acad. Sci. U.u2009S.u2009A. 97, 5598–5603). However, the involvement of Syt IV protein in vesicular trafficking and even its localization in secretory vesicles are still matters of controversy. Here we present several lines of evidence showing that the Syt IV protein in PC12 cells is normally localized in the Golgi or immature vesicles at the cell periphery and is sorted to fusion-competent mature dense-core vesicles in response to short nerve growth factor (NGF) stimulation. (i) In undifferentiated PC12 cells, Syt IV protein is mainly localized in the Golgi and small amounts are also present at the cell periphery, but according to the results of an immunocytochemical analysis, they do not colocalize with conventional secretory vesicle markers (Syt I, Syt IX, Rab3A, Rab27A, vesicle-associated membrane protein 2, and synaptophysin) at all. By contrast, limited colocalization of Syt IV protein with dense-core vesicle markers is found in the distal parts of the neurites of NGF-differentiated PC12 cells. (ii) Immunoelectron microscopy with highly specific anti-Syt IV antibody revealed that the Syt IV protein in undifferentiated PC12 cells is mainly present on the Golgi membranes and immature secretory vesicles, whereas after NGF stimulation Syt IV protein is also present on the mature dense-core vesicles. (iii) An N-terminal antibody-uptake experiment indicated that Syt IV-containing vesicles in the neurites of NGF-differentiated PC12 cells undergo Ca2+-dependent exocytosis, whereas no uptake of the anti-Syt IV-N antibody was observed in undifferentiated PC12 cells. Our results suggest that Syt IV is a stimulus (e.g. NGF)-dependent regulator for exocytosis of dense-core vesicles.


Molecular Endocrinology | 2011

Serpinin: A Novel Chromogranin A-Derived, Secreted Peptide Up-Regulates Protease Nexin-1 Expression and Granule Biogenesis in Endocrine Cells

Hisatsugu Koshimizu; Niamh X. Cawley; Taeyoon Kim; Alfred L. Yergey; Y. Peng Loh

Previously we demonstrated that chromogranin A (CgA) promoted secretory granule biogenesis in endocrine cells by stabilizing and preventing granule protein degradation in the Golgi, through up-regulation of expression of the protease inhibitor, protease nexin-1 (PN-1). However, the mechanism by which CgA signals the increase of PN-1 expression is unknown. Here we identified a 2.9-kDa CgA-C-terminus peptide, which we named serpinin, in conditioned media from AtT-20 cells, a corticotroph cell line, which up-regulated PN-1 mRNA expression. Serpinin was secreted from AtT-20 cells upon high potassium stimulation and increased PN-1 mRNA transcription in these cells, in an actinomycin D-inhibitable manner. CgA itself and other CgA-derived peptides, when added to AtT-20 cell media, had no effect on PN-1 expression. Treatment of AtT-20 cells with 10 nm serpinin elevated cAMP levels and PN-1 mRNA expression, and this effect was inhibited by a protein kinase A inhibitor, 6-22 amide. Serpinin and a cAMP analog, 8-bromo-cAMP, promoted the translocation of the transcription factor Sp1 into the nucleus, which is known to drive PN-1 expression. Additionally, an Sp1 inhibitor, mithramycin A inhibited the serpinin-induced PN-1 mRNA up-regulation. Furthermore, a luciferase reporter assay demonstrated serpinin-induced up-regulation of PN-1 promoter activity in an Sp1-dependent manner. When added to CgB-transfected 6T3 cells, a mutant AtT20 cell line, serpinin induced granule biogenesis as evidenced by the presence of CgB puncta accumulation in the processes and tips. Our findings taken together show that serpinin, a novel CgA-derived peptide, is secreted upon stimulation of corticotrophs and plays an important autocrine role in up-regulating PN-1-dependent granule biogenesis via a cAMP-protein kinase A-Sp1 pathway to replenish released granules.


Trends in Endocrinology and Metabolism | 2003

The role of chromogranin A and the control of secretory granule genesis and maturation

Taeyoon Kim; Jung-Hwa Tao-Cheng; Lee E. Eiden; Y. Peng Loh

chicken:noveltargetorgansforprogesteroneandestrogenaction.Mol.Cell. Endocrinol. 135, 79–917 Straub, S.G. et al. (2001) Progesterone inhibits insulin secretion by amembrane delimited, non-genomic action. Biosci. Rep. 21, 653–6668 Magnaterra, R. et al.(1997) The effects of pregnancy steroids onadaptationofbcellstopregnancyinvolvethepancreaticglucosesensorglucokinase. J. Endocrinol. 155, 247–2539 Nieuwenhuizen, A.G. et al. (1999) Progesterone stimulates pancreaticcell proliferation in vivo. Eur. J. Endocrinol. 140, 256–26310 Kawai, M. and Kishi, K. (1999) Adaptation of pancreatic islet b-cellsduring the last third of pregnancy: regulation of b-cell function andproliferation by lactogenic hormones in rats. Eur. J. Endocrinol. 141,419–42511 Hamann, A. and Matthaei, S. (1996) Regulation of energy balance byleptin. Exp Clin. Endocrinol. Diabetes 104, 293–30012 Chu, J.W. (2001) Successful long-term treatment of refractoryCushing’s disease with high-dose mifepristone (RU 486). J. Clin.Endocrinol. Metab. 86, 3568–357313 Medina, D. et al. (2001) Mechanisms of hormonal prevention of breastcancer. Ann. New York Acad. Sci. 952, 23–35


Antioxidants & Redox Signaling | 2012

Superoxide Dismutase 3 Suppresses Hyaluronic Acid Fragments Mediated Skin Inflammation by Inhibition of Toll-Like Receptor 4 Signaling Pathway: Superoxide Dismutase 3 Inhibits Reactive Oxygen Species-Induced Trafficking of Toll-Like Receptor 4 to Lipid Rafts

Myung-Ja Kwon; Jihye Han; Byung Hak Kim; Yun Sang Lee; Taeyoon Kim

AIMSnHyaluronic acid (HA) is a component of the extracellular matrix and has been extensively applied for cosmetic, therapeutic, and antiaging purposes. However, HA fragments (HAFs) cause adverse effects. Considering that UV-exposure produces HAF that accumulated on the skin, the role of HAF in skin inflammation and its precise mechanism needs to be clarified, and strategies for the prevention of skin inflammation are necessary.nnnRESULTSnWe found that extracellular superoxide dismutase (SOD), SOD3, suppresses HAF-mediated skin inflammation, while HAF mediated skin inflammation, macrophages and dendritic cells (DCs) dominantly infiltrate, up-regulating inflammatory cytokines and chemokines receptors. However, keratinocytes indirectly responded to HAF. Instead, epidermis containing keratinocytes were stimulated by secreted molecules from HAF-treated macrophages or DC and produced inflammatory molecules including chemokines, which, in turn, led to skin inflammation. This orchestrated inflammatory response was inhibited by SOD3. In addition, SOD3 inhibited DC maturation by suppressing the expression of major histocompatibility complex II, CD80, and CD86. Interestingly, these responses did not occur in Toll-like receptor 4 (TLR4) deficient mice. Similar to lipopolysaccharide (LPS), HAF promoted TLR4 translocation into the lipid rafts to initiate signaling. This trafficking was mediated, at least in part, by NAPDH oxidase-dependent reactive oxygen species (ROS) generation. Subsequently, nuclear factor kappa B (NFκB) subunit, p65, was recruited the promoters of genes encoding inflammatory molecules. This inflammatory machinery was blocked by SOD3.nnnINNOVATION AND CONCLUSIONnThus, we propose that SOD3 might provide an effective strategy for the treatment of HAF-mediated skin inflammation.


Molecular Endocrinology | 2008

Aquaporin 1 Is Important for Maintaining Secretory Granule Biogenesis in Endocrine Cells

Irina Arnaoutova; Niamh X. Cawley; Nimesh Patel; Taeyoon Kim; Trushar Rathod; Y. Peng Loh

Aquaporins (AQPs), a family of water channels expressed in epithelial cells, function to transport water in a bidirectional manner to facilitate transepithelial fluid absorption and secretion. Additionally, AQP1 and AQP5 are found in pancreatic zymogen granules and synaptic vesicles and are involved in vesicle swelling and exocytosis in exocrine cells and neurons. Here, we show AQP1 is in dense-core secretory granule (DCSG) membranes of endocrine tissue: pituitary and adrenal medulla. The need for AQP1 in endocrine cell function was examined by stable transfection of AQP1 antisense RNA into AtT20 cells, a pituitary cell line, to down-regulate AQP1 expression. These AQP1-deficient cells showed more than 60% depletion of DCSGs and significantly decreased DCSG protein levels, including proopiomelanocotin/pro-ATCH and prohormone convertase 1/3, but not non-DCSG proteins. Pulse-chase studies revealed that whereas DCSG protein synthesis was unaffected, approximately 50% of the newly synthesized proopiomelanocortin was degraded within 1 h. Low levels of ACTH were released upon stimulation, indicating that the small number of DCSGs that were made in the presence of the residual AQP1 were functionally competent for exocytosis. Analysis of anterior pituitaries from AQP1 knockout mice showed reduced prohormone convertase 1/3, carboxypeptidase E, and ACTH levels compared to wild-type mice demonstrating that our results observed in AtT20 cells can be extended to the animal model. Thus, AQP1 is important for maintaining DCSG biogenesis and normal levels of hormone secretion in pituitary endocrine cells.


Experimental and Molecular Medicine | 2014

Anti-inflammatory activity of compounds isolated from Astragalus sinicus L. in cytokine-induced keratinocytes and skin.

Byung-Hak Kim; Ikhoon Oh; Jung-Ho Kim; Ju-eun Jeon; Byeongwook Jeon; Jongheon Shin; Taeyoon Kim

Inflammation is a part of the complex biological responses of a tissue to injury that protect the organ by removing injurious stimuli and initiating the healing process, and is considered as a mechanism of innate immunity. To identify biologically active compounds against pathogenic inflammatory and immune responses, we fractionated water, aqueous methanol and n-hexane layers from nine kinds of leguminosae and examined anti-inflammatory activity of the fractions in human keratinocytes and mouse skin. Among the fractions, rf3 and rf4, isolated from the aqueous methanol layer of Astragalus sinicus L., exhibited the strongest reactive oxygen species (ROS)-scavenging and anti-inflammatory activities as measured by inhibition of the intracellular ROS production, nuclear factor-kappaB (NF-κB), janus kinase (JAK)/signal transducer and activator of transcription (STAT), and phosphatidylinositol 3-kinase/Akt signaling in cytokine-stimulated human keratinocytes, as well as by effects on T-cell differentiation in mouse CD4+ T cells. In addition, topical application of rf3 and rf4 suppressed the progression of psoriasis-like dermatitis and expression of pro-inflammatory mediators in interleukin (IL)-23-injected mouse ears. Our results suggest that Astragalus sinicus L. may ameliorate chronic inflammatory skin diseases due to its antioxidant and anti-inflammatory activities via regulation of the intracellular ROS production, NF-κB, JAK/STAT and PI3/Akt signaling cascades as well as immune responses, and these results are the first report that Astragalus sinicus L. exhibits pharmacological activity.

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Y. Peng Loh

National Institutes of Health

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Niamh X. Cawley

National Institutes of Health

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Yoon-Jae Jeon

Catholic University of Korea

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Byung-Hak Kim

Seoul National University

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Hisatsugu Koshimizu

National Institutes of Health

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Jung-Hwa Tao-Cheng

National Institutes of Health

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Lee E. Eiden

National Institutes of Health

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Byeongwook Jeon

Catholic University of Korea

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Byung Hak Kim

Chungbuk National University

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Jongheon Shin

Seoul National University

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