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H Kwon

Publications and source records attributed to H Kwon.

At least 37 records · Page 2Linked to original sources
PubMed2001

Determination of binding constant of transcription factor AP-1 and DNA. Application of inhibitors.

The equilibrium binding and association kinetics of the fos-jun dimer (basic and leucine zipper domain) to the AP-1 DNA were studied using a quantitative assay. The basic-region and leucine zipper (bZip) domain of c-fos was expressed as a fusion protein with glutathione S-transferase, and it was bound to glutathione-agarose. The GST-fused fos bZip region was allowed to form a heterodimer with the bZip domain of c-jun, to which radiolabeled AP-1 nucleotides were added. After thorough washing, the gel-bound radioactivity was counted. The binding and dissociation rate constants (k(1) and k-(1)) of the fos-jun dimer and DNA could be obtained from a time-course experiment. The association binding constant (K(1)) was determined using both a thermodynamic equation and kinetic parameters. Nordihydroguaiaretic acid (NDGA), momordin I, natural product inhibitors of the fos-jun/DNA complex formation, was applied to this jun-GST-fused fos system and it was found to decrease the apparent equilibrium binding of dimer and DNA. The thermodynamic constant of dimer and inhibitor binding was also determined.

Cloning, Molecular↗
PubMed2001

Role of Hck in the pathogenesis of encephalomyocarditis virus-induced diabetes in mice.

Soluble mediators such as interleukin-1beta, tumor necrosis factor alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS) produced from activated macrophages play an important role in the destruction of pancreatic beta cells in mice infected with a low dose of the D variant of encephalomyocarditis (EMC-D) virus. The tyrosine kinase signaling pathway was shown to be involved in EMC-D virus-induced activation of macrophages. This investigation was initiated to determine whether the Src family of kinases plays a role in the activation of macrophages, subsequently resulting in the destruction of beta cells, in mice infected with a low dose of EMC-D virus. We examined the activation of p59/p56(Hck), p55(Fgr), and p56/p53(Lyn) in macrophages from DBA/2 mice infected with the virus. We found that p59/p56(Hck) showed a marked increase in both autophosphorylation and kinase activity at 48 h after infection, whereas p55(Fgr) and p56/p53(Lyn) did not. The p59/p56(Hck) activity was closely correlated with the tyrosine phosphorylation level of Vav. Treatment of EMC-D virus-infected mice with the Src kinase inhibitor, PP2, resulted in the inhibition of p59/p56(Hck) activity and almost complete inhibition of the production of TNF-alpha and iNOS in macrophages and the subsequent prevention of diabetes in mice. On the basis of these observations, we conclude that the Src kinase, p59/p56(Hck), plays an important role in the activation of macrophages and the subsequent production of TNF-alpha and nitric oxide, leading to the destruction of pancreatic beta cells, which results in the development of diabetes in mice infected with a low dose of EMC-D virus.

Animals↗
PubMed2001

Functional neuroanatomy of visuospatial working memory in fragile X syndrome: relation to behavioral and molecular measures.

OBJECTIVE: Fragile X syndrome is a neurogenetic disorder that is the most common known heritable cause of neurodevelopmental disability. This study examined the neural substrates of working memory in female subjects with fragile X syndrome. Possible correlations among behavioral measures, brain activation, and the FMR1 gene product (FMRP expression), as well as between IQ and behavioral measures, were investigated. METHOD: Functional magnetic resonance imaging was used to examine visuospatial working memory in 10 female subjects with fragile X syndrome and 15 typically developing female subjects (ages 10-23 years). Subjects performed standard 1-back and 2-back visuospatial working memory tasks. Brain activation was examined in four regions of the cortex known to play a critical role in visuospatial working memory. Correlations between behavioral, neuroimaging, and molecular measures were examined. RESULTS: Relative to the comparison group, subjects with fragile X syndrome performed significantly worse on the 2-back task but not on the 1-back task. In a region-of-interest analysis focused on the inferior frontal gyrus, middle frontal gyrus, superior parietal lobule, and supramarginal gyrus, comparison subjects showed significantly increased brain activation between the 1-back and 2-back tasks, but subjects with fragile X syndrome showed no change in activation between the two tasks. Significant correlations were found in comparison subjects between activation in the frontal and parietal regions and the rate of correct responses on the 2-back task, but not on the 1-back task. In subjects with fragile X syndrome, significant correlations were found during the 2-back task between FMRP expression and activation in the right inferior and bilateral middle frontal gyri and the bilateral supramarginal gyri. CONCLUSIONS: Subjects with fragile X syndrome are unable to modulate activation in the prefrontal and parietal cortex in response to an increasing working memory load, and these deficits are related to a lower level of FMRP expression in fragile X syndrome subjects than in normal comparison subjects. The observed correlations between biological markers and brain activation provide new evidence for links between gene expression and cognition.

Adolescent↗
PubMed2000

Effective gene transfer into regenerating sciatic nerves by adenoviral vectors: potentials for gene therapy of peripheral nerve injury.

Replication defective adenoviral vectors have been demonstrated as an effective method for delivering genes into a variety of cell types and tissues both in vivo and in vitro. Transfecting genes into neuronal cells has proven to be difficult because of their lack of cell division. Since the major problem in neurological disease is the degeneration of the terminally differentiated neuronal cells, the adenoviral vector's ability to transfer genes into differentiated post-mitotic cells makes them advantageous for a gene delivery system for the nervous system. Here we showed that a replication defective recombinant adenovirus carrying the lacZ gene could infect the neuronal stem cells and even the differentiated neuronal cells derived from the central nervous system. The lacZ gene delivered into the neuronal cells was expressed efficiently. In addition, the recombinant virus also infected Schwann cells in intact and injured nerves in vivo. The expression of the lacZ gene lasted for 5 weeks, within which nerve regeneration is accomplished in the rat. Adenoviral vectors might thus be used to modulate Schwann cell gene expression for treating peripheral nerve injury or peripheral neuropathy.

Adenoviridae↗
PubMed2000

Functional brain activation during cognition is related to FMR1 gene expression.

Fragile X syndrome, the most common known cause of inherited mental retardation, is caused by alterations of the FMR1 gene encoding the FMRP protein. We investigated the relation between FMRP protein levels and functional brain activation during a working memory task. Our study provides the first evidence for a relation between FMR1 gene expression and neural activity during higher-order cognition. More broadly, our findings provide the first demonstration of how gene-brain-behavior investigations can help to bridge the gap between molecular and systems neuroscience.

Adolescent↗
PubMed2000

Sustained formation of focal adhesions with paxillin in morphological differentiation of PC12 cells.

Differentiation of PC12 cells triggered by nerve growth factor (NGF) is characterized by several well-defined events including induction of a set of neuron-specific genes, gain of membrane excitability, and morphological changes such as neurite outgrowth. Here we report that K252a, a protein kinase inhibitor, converts the proliferation signal of epidermal growth factor (EGF) into the morphological differentiation signal without inducing the sustained activation of ERK and the expression of neurofilament. Major effects of EGF/K252a, found also in the NGF-treated cells, are the sustained mobility shift of paxillin in SDS-PAGE and the promoted association of Crk-II with paxillin. These effects explain the prominent and robust development of peripheral focal adhesion assembly and stress fiber-like structures observed in the early stages of PC12 cell differentiation. These results suggest a model that cytoskeletal reorganization via focal adhesion assembly triggered by NGF provides a signal required for the morphological differentiation of PC12 cells.

Actin Cytoskeleton↗
PubMed2000

Antioxidant and anti-tumor promoting activities of the methanol extract of heat-processed ginseng.

Heat treatment of Panax ginseng C.A. Meyer at a temperature higher than that applied to the conventional preparation of red ginseng yielded a mixture of saponins with potent antioxidative properties. Thus, the methanol extract of heat-processed neoginseng (designated as 'NGMe') attenuated lipid peroxidation in rat brain homogenates induced by ferric ion or ferric ion plus ascorbic acid. Furthermore, the extract protected against strand scission in phiX174 supercoiled DNA induced by UV photolysis of H2O2, and was also capable of scavenging superoxide generated by xanthine-xanthine oxidase or by 12-O-tetradecanoylphorbol-13-acetate (TPA) in differentiated human promyelocytic leukemia (HL-60) cells. Topical application of NGMe onto shaven backs of female ICR mice 10 min prior to TPA, significantly ameliorated skin papillomagenesis initiated by 7,12-dimethylbenz[a]anthracene. Moreover, TPA-induced enhancement of epidermal ornithine decarboxylase (ODC) activity and ODC mRNA expression was abolished by a topical dose (0.68 mg) of NGMe. Likewise, TPA-induced production of tumor necrosis factor- in mouse skin was inhibited by NGMe pretreatment.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2000

A national survey of sun safety activities at U.S. zoos.

Skin cancer incidence in the United States has increased. Exposure to ultraviolet radiation (UVR) is a major risk factor for skin cancer. Every year, millions of children with their families visit outdoor leisure facilities such as zoos where overexposure to UVR may occur. This study was conducted to assess the proportion of U.S. zoos that provided sun safety activities during the summer of 1998 and their willingness to incorporate skin cancer prevention strategies at their facility in the future. A 56 item self-administered questionnaire was mailed to 140 zoos accredited by the American Zoo and Aquarium Association. A follow-up telephone survey was also conducted with 33 mail non-respondents. The response rate was 97% (N = 136). Results revealed that in the summer of 1998, only 5% of zoos provided sun safety recommendations to visitors and 25% of zoos provided recommendations to their employees. The recommendations made most often to visitors and employees were to use sunscreen and wear protective clothing. Eighty-five percent of zoos indicated interest in providing sun safety activities at their facilities in the future. The next step will be to design environmentally appropriate sun safety programs for zoos and to encourage zoos to implement these programs.

Adult↗
PubMed2000

Determination of ethyl carbamate in some fermented Korean foods and beverages.

Ethyl carbamate has been associated with cancer for several decades. It is mainly found in fermented foods and beverages. In view of the importance of fermented foods in the Korean diet and the significant level of ethyl carbamate expected, we determined ethyl carbamate concentrations in some of the staple food items and estimated the daily intake for the Korean population. Ethyl carbamate in commercial samples of kimchi, soy sauce, vinegar, soybean paste, and alcoholic beverages were determined by gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM). Homemade soy sauce and kimchi were also analysed. The maximum ethyl carbamate concentrations observed were 73 micrograms/kg in soy sauce, 7.9 micrograms/kg in soybean paste, 2.5 micrograms/l in vinegar, 16.2 micrograms/kg in kimchi and 15.4 mu/l in Korean traditional alcoholic beverages. Combining these values with the average daily food intake data, we estimated that the maximum daily exposure of Korean population to ethyl carbamate is 2.8 micrograms/day, which is not a negligible amount considering the 'virtually safe dose' derived by animal experiment ranges between 1.2 and 4.8 micrograms/day. It would be desirable to closely monitor ethyl carbamate levels in Korean foods and to find ways to reduce the daily intake.

Alcoholic Beverages↗
PubMed2000

A survey of nonphysician medical screening examinations in academic emergency medicine.

OBJECTIVES: To determine the proportions of U.S. emergency medicine (EM) residency programs that use nonphysicians to perform medical screening examinations (MSEs) in lieu of a physician evaluation. METHODS: This was a cross-sectional observational study consisting of a mail survey of the 109 base hospitals of accredited U.S. EM residency programs. Follow-up letters were sent twice to nonrespondents. Questions regarding ED demographics, the performance and structure of MSEs by physicians and nonphysicians, and the exact nature and purpose of such examinations were included. RESULTS: Ninety of 109 (83%) programs responded. Eighty-seven of the 90 programs (97%) perform MSEs on all patients presenting to the ED prior to discharge. Thirty-seven percent (33/90) perform nonphysician MSEs (NPMSEs) at least some of the time. Fifty percent (16/32) refer patients to an outside facility based on the result of the screening, and in 32% of cases the patient is not offered the choice of an ED evaluation. Seventy percent (19/27) at times refer patients, including uninsured patients, to a same-day clinic within their hospital system. Seven of 27 (26%) programs performing NPMSEs reported occasional adverse events, defined as two to 11 per year. Eight of 22 (36%) reported poorer clinical outcomes than expected from ED care as a result of the NPMSE, and 18 of 25 (72%) reported some degree of patient dissatisfaction. Two programs reported death as a result of NPMSEs. CONCLUSIONS: The use of NPMSEs is common and is frequently used as a basis for referring patients away from the ED without a physician examination. Using NPMSEs may be associated with adverse events, including patient dissatisfaction, morbidity, and possibly, mortality.

Allied Health Personnel↗
PubMed2000

Import of proteins into the trypanosome nucleus and their distribution at karyokinesis.

In all eukaryotic organisms proteins are targeted to the nucleus via a receptor-mediated mechanism that requires a specific nuclear localization sequence (NLS) in the protein. Little is known about this process in trypanosomatid protozoa that are considered amongst the earliest divergent eukaryotes. We have used the green fluorescent protein (gfp) and beta-galactosidase reporters to identify the NLS of two trypanosomal proteins, namely the Trypanosoma brucei La protein homologue and histone H2B of T. cruzi. A monopartite NLS was demonstrated at the C terminus of the La protein, whereas a bipartite NLS was identified within the first 40 amino acids of histone H2B. Treatment of live trypanosomes with poisons of ATP synthesis resulted in exit of the La NLS-gfp fusion from the nucleus. Interestingly, this fusion protein accumulated at several discrete sites in the cytoplasm, rather than equilibrating between the nucleus and the cytoplasm. When ATP levels returned to normal, the protein reentered the nucleus, demonstrating that the process was energy dependent. Finally, using fusion proteins that localize to the nucleoplasm or the nucleolus, we identified a subpopulation of mitotic cells in which the chromosomes have segregated but the daughter nuclei remain connected by a thin thread-like structure. We propose that cells containing this structure represent a late stage in nuclear division that can be placed after chromosome segregation, but before completion of karyokinesis.

Amino Acid Sequence↗
PubMed1999

Promotion of skeletal muscle differentiation by K252a with tyrosine phosphorylation of focal adhesion: a possible involvement of small GTPase Rho.

K252a, a protein kinase inhibitor, acts as a neurotrophic factor in several neuronal cells. In this study we show that K252a enhanced the differentiation of C2C12 myoblasts as well as tyrosine phosphorylation of several focal adhesion-associated proteins including p130(Cas), focal adhesion kinase, and paxillin. The tyrosine phosphorylation of these proteins, reaching a maximum at 30 min after K252a treatment, closely correlated with the colocalization of these proteins in focal adhesion complexes and the coimmunoprecipitation of these proteins with p130(Cas). In addition, K252a stimulated longitudinal development of stress fiber-like structures and cell-matrix interaction in postmitotic myoblasts and eventually formation of well-developed myofibrils in multinucleated myotubes. Herbimycin A, a potent inhibitor of Src family kinases, and cytochalasin D, a selective disrupting-agent of actin filament, completely inhibited K252a-induced tyrosine phosphorylation as well as myoblast differentiation. Similar inhibitory effect was observed in the cells scrape loaded with a Rho inhibitor, C3 transferase, and the treatment of K252a induced a rapid translocation of Rho. These results are consistent with the model that Rho-dependent tyrosine phosphorylation of focal adhesion-associated proteins plays an important role in skeletal muscle differentiation.

Animals↗
PubMed1999

Role of hyperpolarization attained by linoleic acid in chick myoblast fusion.

Our previous report has suggested that hyperpolarization generated by reciprocal activation of calcium-activated potassium (K(Ca)) channels and stretch-activated channels induces calcium influx that triggers myoblast fusion. Here we show that linoleic acid is involved in the process of generating hyperpolarization in cultured chick myoblasts and hence in promotion of the cell fusion. Linoleic acid dramatically hyperpolarized the membrane potential from -14 +/- 3 to -58 +/- 5 mV within 10 min. This effect was partially blocked by 1 mM tetraethylammonium (TEA) or 30 nM charybdotoxin, a selective K(Ca) channel inhibitor, and completely abolished by 10 mM TEA. Single-channel recordings revealed that linoleic acid activates TEA-resistant potassium channels as well as K(Ca) channels. Furthermore, linoleic acid induced calcium influx from extracellular solution, and this effect was partially blocked by 1 mM TEA and completely prevented at 10 mM, similar to the effect of TEA on linoleic acid-mediated hyperpolarization. Since the valinomycin-mediated hyperpolarization promoted calcium influx, hyperpolarization itself appears capable of inducing calcium influx. In addition, gadolinium prevented the valinomycin-mediated increase in intracellular calcium level under hypotonic conditions, revealing the involvement of stretch-activated channels in calcium influx. Furthermore, linoleic acid stimulated myoblast fusion, and this stimulatory effect could completely be prevented by 10 mM TEA. These results suggest that linoleic acid induces hyperpolarization of membrane potential by activation of potassium channels, which induces calcium influx through stretch-activated channels, and thereby triggers myoblast fusion.

Animals↗
PubMed1999

Interferon regulatory factors: the next generation.

Interferons are a large family of multifunctional secreted proteins involved in antiviral defense, cell growth regulation and immune activation. Viral infection induces transcription of multiple IFN genes, a response that is in part mediated by the interferon regulatory factors (IRFs). The initially characterized members IRF-1 and IRF-2 are now part of a growing family of transcriptional regulators that has expanded to nine members. The functions of the IRFs have also expanded to include distinct roles in biological processes such as pathogen response, cytokine signaling, cell growth regulation and hematopoietic development. The aim of this review is to provide an update on the novel discoveries in the area of IRF transcription factors and the important roles of the new generation of IRFs--particularly IRF-3, IRF-4 and IRF-7.

Amino Acid Sequence↗
PubMed1999

Differential regulation of CC chemokine gene expression in human immunodeficiency virus-infected myeloid cells.

The importance of chemokine expression on HIV infection has been emphasized by the discovery that infection of CD4(+) T cells by M-tropic strains of HIV-1 is antagonized by the chemokines RANTES, MIP-1alpha, and MIP-1beta, which are natural ligands of CCR5, a major coreceptor for macrophagetropic (M-tropic) isolates of HIV-1. Similarly, the CCR2b ligands MCP-1 and MCP-3 inhibit productive infection of PBMCs by both CCR5- and CXCR4-dependent strains of HIV-1, suggesting that expression of the MCP-1 chemokine may affect HIV infection via signaling through the CCR2 receptor and subsequent desensitization of the CCR5 and/or CXCR4 signaling pathway. Given the major role played by chemokine receptors in HIV-1 fusion/entry and the regulatory effects of chemokines on HIV-1 infection, we examined the pattern of chemokine gene expression in HIV-1-infected myeloid cells and in primary monocyte/macrophages. Chronic HIV-1 infection of U937 monocytic cells increased the expression of RANTES, MIP-1alpha, MIP-1beta, and IL-8 chemokine genes, but strongly inhibited PMA/PHA- and TNFalpha-induced MCP-1 gene transcription. HIV-1-mediated inhibition of MCP-1 transcription and secretion was further confirmed in de novo HIV-1-infected U937 cells and correlated with a delay in HIV- and signal-induced NF-kappaB binding to the MCP-1 promoter. The inhibition of MCP-1 gene expression may provide a mechanism by which HIV-1 escapes the early influence of chemokine expression in monocytic cells.

Cells, Cultured↗
PubMed1999

Neuregulin stimulates myogenic differentiation in an autocrine manner.

During myogenesis, mononucleated myoblasts form multinucleated myotubes by membrane fusion. Efficiency of this intercellular process can be maximized by a simultaneous progress, with a time window, of other neighboring myoblasts in the differentiation program. This phenomenon has been described as the community effect. It proposes the existence of a molecule that acts as a differentiation-inducing signal to a group of identical cells. Here, we show that neuregulin is a strong candidate for this molecule in myoblast differentiation. The expression of neuregulin increased rapidly but transiently at early stage of differentiation of rat L6 cells. Neuregulin showed a potent differentiation-promoting activity in membrane fusion and expression of myosin heavy chain. The antibodies raised against neuregulin and its cognate receptor ErbB3, which were capable of neutralizing the signal pathway, inhibited myotube formation and expression of myosin heavy chain in both L6 cells and primary rat myoblasts. The progress of differentiation was mostly halted after the expression of myogenin and cell cycle arrest. These results suggest that the activation of an autocrine signaling of neuregulin may provide a basic mechanism for the community effect observed in the differentiation of the embryonic muscle cells.

Animals↗