Biomedical subjects

Tae-Hee Lee

Publications and source records attributed to Tae-Hee Lee.

At least 19 recordsLinked to original sources

PubMed2006

Integrin regulation by vascular endothelial growth factor in human brain microvascular endothelial cells: role of alpha6beta1 integrin in angiogenesis.

The precise role of vascular endothelial growth factor (VEGF) in regulating integrins in brain microvascular endothelial cells is unknown. Here, we analyzed VEGF effects on integrin expression and activation in human brain microvascular endothelial cells (HBMECs). Using human cDNA arrays and ribonuclease (RNase) protection assays, we observed that VEGF up-regulated the mRNA expression of alpha(6) integrin in HBMECs. VEGF significantly increased alpha(6)beta(1) integrin expression, but not alpha(6)beta(4) integrin expression in these cells. Specific down-regulation of alpha(6) integrin expression by small interfering RNA (siRNA) oligonucleotides inhibited both the capillary morphogenesis of HBMECs and their adhesion and migration. Additionally, VEGF treatment resulted in activation of alpha(6)beta(1) integrins in HBMECs. Functional blocking of alpha(6) integrin with its specific antibody inhibited the VEGF-induced adhesion and migration as well as in vivo angiogenesis, and markedly suppressed tumor angiogenesis and breast carcinoma growth in vivo. Thus, VEGF can modulate angiogenesis via increased expression and activation of alpha(6)beta(1) integrins, which may promote VEGF-driven tumor angiogenesis in vivo.

Animals↗

PubMed2006

Disruption of hexokinase II (HXK2) partly relieves glucose repression to enhance production of human kringle fragment in gratuitous recombinant Saccharomyces cerevisiae.

The GAL1 gene encoding galactokinase was disrupted in a recombinant Saccharomyces cerevisiae strain in which production of LK8 protein, a kringle fragment of human apolipoprotein, is under the control of GAL1 promoter. Null mutation of the HXK2 gene was introduced further in the gal1Delta strain to relieve glucose repression. A pattern for LK8 expression was compared for the two recombinant S. cerevisiae systems in continuous and fed-batch cultivations. A critical dilution rate in continuous cultivation that repressed LK8 expression was significantly higher for the gal1Deltahxk2Delta strain than that for the gal1Delta strain to sustain the LK8 production even at high glucose consumption rate. Expressed LK8 for the gal1Delta strain was not detectable when the dilution rate exceeded 0.05 h(-1). Maximum LK8 concentration of 57 mgl(-1) was obtained in glucose-limited fed-batch cultivation of the gal1Deltahxk2Delta strain, corresponding to a 13.8-fold enhancement compared with the gal1Delta strain grown under the same conditions.

Bioreactors↗

PubMed2006

Effect of mycelial extract of Clavicorona pyxidata on acetylcholinesterase and beta-secretase activity in vitro.

In a previous study, an extract of Clavicorona pyxidata DGUM 29005 mycelia demonstrated an inhibitory effect against enzyme-associated perceptual disorders. We have attempted to determine whether this mycelial extract is also capable of inhibiting the activities of acetylcholinesterase (AChE) and beta-secretase (BACE) activity. Butanol, ethanol, and water extracts of C. pyxidata DGUM 29005 mycelia were shown to inhibit AChE activity by 99.3%, 93.7%, and 91.7%, respectively. The inhibitory value of the butanol extract was more profound than that of tacrine (95.4%). The ethanol extract also exerted an inhibitory effect against BACE activity; this fraction may harbor the potential for development into a pharmocotherapeutic modality for the treatment of Alzheimer's disease (AD) patients. Rat pheochromocytoma PC12 cells in culture were not determined to be susceptible to the cytotoxic activity evidenced by the mycelial extract. The ethanol extract inhibited endogenous AChE activity in PC12 cellular homogenates, with an IC50 of 67.5 microg/ml, after incubation with intact cells, and also inhibited BACE activity in a dose-dependent fashion. These results suggest that the C. pyxidata mycelial extract has the potential to enhance cholinergic function and, therefore, may perform a function in the amelioration of the cholinergic deficit observed in cases of AD, as well as other types of age-associated memory impairment.

Acetylcholinesterase↗

PubMed2006

Effect of mycelial extract of Clavicorona pyxidata on the production of amyloid beta-peptide and the inhibition of endogenous beta-secretase activity in vitro.

Amyloid beta-peptide (Abeta), which is a product of the proteolytic effect of beta-secretase (BACE) on an amyloid precursor protein, is closely associated with Alzheimer's disease (AD) pathogenesis. There is sufficient evidence to suggest that a BACE inhibitor may reduce Abeta levels, thus decreasing the risk of AD. In a previous study, an extract of Clavicorona pyxidata DGUM 29005 mycelia was found to inhibit the production of a soluble beta-amyloid precursor protein (sbetaAPP), Abeta, and BACE in neuronal cell lines. We sought to determine whether this mycelial extract exerts the same effect in human rhabdomyosarcoma A-204 and rat pheochromocytoma PC-12 cells. We found that the production of Abeta decreased in a dose-dependent manner in the presence of the mycelial extract and that the concentration of Abeta never exceeded 50 microg/ml. The presence of sAPP was detected in every culture medium to which the mycelial extract had been added and its concentration remained the same, regardless of the concentration of the extract used. Endogenous beta-secretase activity in A-204 and PC-12 cellular homogenates also decreased in the presence of this extract. These cells, in culture, were not susceptible to the cytotoxic activity of the mycelial extract.

Alzheimer Disease↗

PubMed2005

Carboxyl-terminal Src kinase homologous kinase negatively regulates the chemokine receptor CXCR4 through YY1 and impairs CXCR4/CXCL12 (SDF-1alpha)-mediated breast cancer cell migration.

Using microarray gene analysis, we found that carboxyl-terminal Src kinase homologous kinase (CHK) regulated the expression of the chemokine receptor, CXCR4. Northern blot and fluorescence-activated cell-sorting analyses showed that CHK down-regulated CXCR4 mRNA and protein levels, respectively. Mutated CHK, which contains a mutation within the ATP binding site of CHK, failed to inhibit CXCR4 expression, thus suggesting that CHK kinase activity is involved in the regulation of CXCR4. Results from gel shift analysis indicated that CHK regulates CXCR4 transcriptional activity by altering YY1 binding to the CXCR4 promoter. Whereas CHK had no significant effects on the expression of YY1, c-Myc, Max, and other YY1-binding proteins, CHK was found to modulate the YY1/c-Myc association. Furthermore, CHK inhibited CXCR4-positive breast cancer cell migration. Taken together, these studies show a novel mechanism by which CHK down-regulates CXCR4 through the YY1 transcription factor, leading to decreased CXCR4-mediated breast cancer cell motility and migration.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗

PubMed2005

Nanoparticle-free single molecule anti-stokes Raman spectroscopy.

In the absence of large, plasmon-supporting nanoparticles, biocompatible dendrimer- and peptide-encapsulated few-atom Ag nanoclusters produce scaffold-specific single molecule (SM) Stokes and anti-Stokes Raman scattering. The strong SM vibrational signatures are enhanced by the Agn transitions in nanoparticle-free samples and cannot arise from plasmon enhancement. Characteristic SM-Raman intermittency is observed, with antibunching of the underlying Agn emission directly confirming the SM nature of the emissive species.

Coated Materials, Biocompatible↗

PubMed2005

Single-molecule optoelectronics.

With discrete states, several-atom Ag(n) nanoclusters exhibit molecule-like behavior with strong visible fluorescence and robust optical properties. This new class of single-molecule fluorophores has been created and electrically contacted in thin films to produce the first electroluminescent single molecules. A direct reporter of nanoscale charge injection and transport through discrete energy levels, bright Ag(n) electroluminescence has been harnessed to create single-molecule light-emitting diodes (LEDs) and optoelectronic logic gates and even to demonstrate full addition operations. These experiments utilizing the small size and quantum behavior of individual Ag nanoclusters usher in the new field of single-molecule optoelectronics.

Journal Article↗

PubMed2004

HIV-1 Tat-mediated effects on focal adhesion assembly and permeability in brain microvascular endothelial cells.

The blood-brain barrier (BBB) is a network formed mainly by brain microvascular endothelial cells (BMECs). The integrity of the BBB is critical for brain function. Breakdown of the BBB is commonly seen in AIDS patients with HIV-1-associated dementia despite the lack of productive HIV infection of the brain endothelium. The processes by which HIV causes these pathological conditions are not well understood. In this study we characterized the molecular mechanisms by which Tat mediates its pathogenic effects in vitro on primary human BMECs (HBMECs). Tat treatment of HBMECs stimulated cytoskeletal organization and increased focal adhesion sites compared with control cells or cells treated with heat-inactivated Tat. Pretreatment with Tat Abs or with the specific inhibitor SU-1498, which interferes with vascular endothelial growth factor receptor type 2 (Flk-1/KDR) phosphorylation, blocked the ability of Tat to stimulate focal adhesion assembly and the migration of HBMECs. Focal adhesion kinase (FAK) was tyrosine-phosphorylated by Tat and was found to be an important component of focal adhesion sites. Inhibition of FAK by the dominant interfering mutant form, FAK-related nonkinase, significantly blocked HBMEC migration and disrupted focal adhesions upon Tat activation. Furthermore, HIV-Tat induced permeability changes in HBMECs in a time-dependent manner. Tat also impaired BBB permeability, as observed in HIV-1 Tat transgenic mice. These studies define a mechanism for HIV-1 Tat in focal adhesion complex assembly in HBMECs via activation of FAK, leading to cytoskeletal reorganization and permeability changes.

Adenoviridae↗

PubMed2004

Quantum mechanical single-gold-nanocluster electroluminescent light source at room temperature.

Electrically contacted gold-nanocluster arrays formed within electromigration-induced break junctions exhibit bright, field-dependent electroluminescence in the near infrared (650-800 nm). Intensity autocorrelation of spatially isolated individual nanocluster emission driven at high electrical frequency (f(ac)= approximately 200 MHz) reveals antibunched electroluminescence at room temperature. These results demonstrate the single quantum nature of several-atom gold molecules and suggest their use as room-temperature electrically driven single-photon sources.

Journal Article↗

PubMed2004

Photon antibunching from oriented semiconducting polymer nanostructures.

Fluorescence intensity correlation measurements reveal that z-oriented nanostructures from single chains of a cyano-substituted polyphenylene vinylene (CN-PPV) polymer act as single-quantum emitters. Photon antibunching is observed for the first time on individual polymer nanostructures with a modulation depth exceeding 90%, providing definitive proof that radiative recombination of molecular excitons occurs at a single localized site within the folded polymer chain.

Journal Article↗

PubMed2004

Functional identification of the SecB homologue in Methanococcus jannaschii and direct interaction of SecB with trigger factor.

In this study Mj0357 protein, a hypothetical protein from Methanococcus jannaschii which shows an 18% sequence identity with SecB from E. coli, has been identified as a functional homologue of SecB in M. jannaschii through a number of biochemical and biophysical examinations. It is composed mostly of beta-strands and exists as a homotetramer in solution. Mj0357 protein exhibits in vitro chaperone-like activity, suppressing thermal aggregation of citrate synthase and binding to partially folded maltose-binding protein. Upon binding to a peptide ligand, the protein undergoes a conformational change to expose a hydrophobic patch on the protein surface. All these physicochemical properties are highly similar to those of E. coli SecB. In addition, E. coli trigger factor (TF) has been shown here for the first time to bind E. coli SecB and Mj0357 protein with low micromolar affinities, indicating that the TF could interact directly along the SecB-dependent translocation pathway. These results indicate that the translocation pathway is conserved and functionally homologous in at least one of the archaeal organisms.

Animals↗

PubMed2004

Antinociceptive profiles of platycodin D in the mouse.

Platycodin D (PD), one of several triterpene saponins, was isolated from roots of Platycodon grandiflorum. We previously reported that intracerebroventricular (i.c.v.) administration of PD showed an antinociceptive effect as measured by the tail-flick assay. However, its exact role in the regulation of antinociception in the various types of pain models has not yet been characterized. Thus, we attempted to find antinociceptive profiles of PD in various pain models. PD administered intraperitoneally (i.p.), i.c.v. or intrathecally (i.t.) showed antinociceptive effects in dose-dependent manners as measured by the tail-flick, writhing and formalin tests. In the tail-flick test, PD at the low doses reached the peak after 15 minutes and returned to the control level after 60 minutes. However, higher doses of PD showed a strong antinociception at least for 1 hour. PD administered i.t. showed stronger antinociception than that induced by i.c.v. administration PD in both tail-flick and writhing tests. In the formalin test, PD administered i.p., i.c.v. or i.t. showed antinociceptive effects during both the first (direct nociceptive stimulation) and second (late inflammatory) phases. Pretreatment with naltrexone i.p., i.c.v. or i.t. did not affect PD-induced inhibition of the tail-flick response. Our results suggest that PD shows a strong antinociceptive effect on the tail-flick, writhing and formalin tests, acting on central nervous system. However, PD-induced antinociception may not be mediated by the opioid receptors.

Animals↗

PubMed2004

Involvement of the chemokine receptor CXCR4 and its ligand stromal cell-derived factor 1alpha in breast cancer cell migration through human brain microvascular endothelial cells.

In this study, we have characterized the signaling pathways mediated by CXCR4 in breast cancer cells and its role in breast cancer cell invasion and migration. Stromal cell-derived factor 1alpha (SDF-1alpha; CXCL12) stimulation of breast cancer cells resulted in phosphoinositide 3-kinase (PI-3K) activation, AKT phosphorylation, and activation of the FKHRL1 transcription factor. In addition, SDF-1alpha induced activation of the focal adhesion kinase (FAK) as well as the migration of breast cancer cells. Expression of SDF-1alpha, the ligand of CXCR4, was about 2-fold higher in microdissected human breast epithelial cancer cells as compared with normal epithelial cells. Immunohistochemical analysis indicated that SDF-1alpha expression is consistently higher in primary breast tumor cells than in normal breast epithelial cells. Furthermore, SDF-1alpha induced blood vessel instability, through increased vascular permeability, resulting in the penetration of breast tumor cells through the human brain microvascular endothelial cells (HBMEC). Notably, the migration of breast cancer cells was inhibited by the PI-3K inhibitor, Wortmannin, and the Ca(2+) inhibitor BAPTA/AM, indicating that transendothelial breast cancer cell migration induced by SDF-1alpha is mediated by activation of the PI-3K/AKT pathway and Ca(2+)-mediated signaling. Blockade of the CXCR4/SDF1 signaling pathway with anti-CXCR4 antibody also decreased transendothelial breast cancer cell migration as well as vascular permeability. This study focuses on novel interactions between highly relevant signaling pathways in breast cancer cells and brain microvascular endothelial cells and may provide insights into the molecular mechanisms of CXCR4/SDF-1alpha-mediated breast cancer metastasis to the brain.

Brain↗

PubMed2003

The inhibitory effect of ginseng saponins on the stress-induced plasma interleukin-6 level in mice.

The effect of ginseng saponins on plasma interleukin-6 (IL-6) in non-stressed and immobilization-stressed mice were investigated. Ginseng total saponins, ginsenosides Rb2, Rg1 and Rd administered intraperitoneally attenuated the immobilization stress-induced increase in plasma IL-6 level. But, intracerebroventricular injection of each ginsenoside did not affect plasma IL-6 level induced by immobilization stress. Ginsenosides Rb2, Rd and Rg1 significantly decreased norepinephrine and/or epinephrine-induced increase of IL-6 level in macrophage cell line (RAW 264.7). Thus, it can be suggested that the inhibitory action of ginseng saponins against the immobilization stress-induced increase of plasma IL-6 level would be in periphery; at least in part, mediated by blocking norepinephrine- and/or epinephrine-induced increase of IL-6 level in macrophage rather than in the brain. Ginseng saponins might be proposed as a possible candidate in the research or therapeutic modulation of stress-related disorders.

Animals↗

PubMed2003

Vascular endothelial growth factor regulates focal adhesion assembly in human brain microvascular endothelial cells through activation of the focal adhesion kinase and related adhesion focal tyrosine kinase.

Vascular endothelial growth factor (VEGF) plays a significant role in blood-brain barrier breakdown and angiogenesis after brain injury. VEGF-induced endothelial cell migration is a key step in the angiogenic response and is mediated by an accelerated rate of focal adhesion complex assembly and disassembly. In this study, we identified the signaling mechanisms by which VEGF regulates human brain microvascular endothelial cell (HBMEC) integrity and assembly of focal adhesions, complexes comprised of scaffolding and signaling proteins organized by adhesion to the extracellular matrix. We found that VEGF treatment of HBMECs plated on laminin or fibronectin stimulated cytoskeletal organization and increased focal adhesion sites. Pretreating cells with VEGF antibodies or with the specific inhibitor SU-1498, which inhibits Flk-1/KDR receptor phosphorylation, blocked the ability of VEGF to stimulate focal adhesion assembly. VEGF induced the coupling of focal adhesion kinase (FAK) to integrin alphavbeta5 and tyrosine phosphorylation of the cytoskeletal components paxillin and p130cas. Additionally, FAK and related adhesion focal tyrosine kinase (RAFTK)/Pyk2 kinases were tyrosine-phosphorylated by VEGF and found to be important for focal adhesion sites. Overexpression of wild type RAFTK/Pyk2 increased cell spreading and the migration of HBMECs, whereas overexpression of catalytically inactive mutant RAFTK/Pyk2 markedly suppressed HBMEC spreading ( approximately 70%), adhesion ( approximately 82%), and migration ( approximately 65%). Furthermore, blocking of FAK by the dominant-interfering mutant FRNK (FAK-related non-kinase) significantly inhibited HBMEC spreading and migration and also disrupted focal adhesions. Thus, these studies define a mechanism for the regulatory role of VEGF in focal adhesion complex assembly in HBMECs via activation of FAK and RAFTK/Pyk2.

Adenoviridae↗

PubMed2003

Origin of the different pH activity profile in two homologous ketosteroid isomerases.

Two homologous Delta5-3-ketosteroid isomerases from Comamonas testosteroni (TI-WT) and Pseudomonas putida biotype B (PI-WT) exhibit different pH activity profiles. TI-WT loses activity below pH 5.0 due to the protonation of the conserved catalytic base, Asp-38, while PI-WT does not. Based on the structural analysis of PI-WT, the critical catalytic base, Asp-38, was found to form a hydrogen bond with the indole ring NH of Trp-116, which is homologously replaced with Phe-116 in TI-WT. To investigate the role of Trp-116, we prepared the F116W mutant of TI-WT (TI-F116W) and the W116F mutant of PI-WT (PI-W116F) and compared kinetic parameters of those mutants at different pH levels. PI-W116F exhibited significantly decreased catalytic activity at acidic pH like TI-WT, whereas TI-F116W maintained catalytic activity at acidic pH like PI-WT and increased the kcat/Km value by 2.5- to 4.7-fold compared with TI-WT at pH 3.8. The crystal structure of TI-F116W clearly showed that the indole ring NH of Trp-116 could form a hydrogen bond with the carboxyl oxygen of Asp-38 like that of PI-WT. The present results demonstrate that the activities of both PI-WT and TI-F116W at low pH were maintained by a tryptophan, which was able not only to lower the pKa value of the catalytic base but also to increase the substrate affinity. This is one example of the strategy nature can adopt to evolve the diversity of the catalytic function in the enzymes. Our results provide insight into deciphering the molecular evolution of the enzyme and creating novel enzymes by protein engineering.

Aspartic Acid↗

PubMed2003

Discrete two-terminal single nanocluster quantum optoelectronic logic operations at room temperature.

Readily formed at nanoscale break junctions, arrays of individual spatially isolated, strongly electroluminescent Ag(2)-Ag(8) nanoclusters perform complex logic operations within individual two-terminal nanoscale optoelectronics devices. Simultaneous electrical excitation of discrete room-temperature nanocluster energy levels directly yields AND, OR, NOT, XOR, and even full addition logic operations with either individual nanoclusters or nanocluster pairs as the active medium between only two electrodes. Imaged in parallel, noncontact electroluminescent readout obviates the need for electrically isolating individual features. This gated, pulsed, two-terminal device operation will likely drive future nano and molecular electronics advances without complicated nanofabrication.

Journal Article↗

PubMed2003

Acupuncture modulates expressions of nitric oxide synthase and c-Fos in hippocampus after transient global ischemia in gerbils.

The effects of acupuncture on the expressions of nitric oxide synthase (NOS) and c-Fos in the hippocampus of gerbils after transient ischemia were investigated via nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and Fos immunohistochemistry. In animals of the ischemia-induction groups, both common carotid arteries were occluded for 5 minutes. Animals of the acupunctued groups were given acupunctural treatment at Zusanli twice daily for 9 consecutive days. Acupuncture was shown to decrease NADPH-d and c-Fos levels in both the sham-operation group and the ischemia-induction group. These results suggest that acupuncture modulates the expressions of NOS and c-Fos in the hippocampus.

Acupuncture↗