Biomedical subjects

Tae-Hee Lee

Publications and source records attributed to Tae-Hee Lee.

At least 19 recordsLinked to original sources

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↗

PubMed2002

Vascular endothelial growth factor modulates the transendothelial migration of MDA-MB-231 breast cancer cells through regulation of brain microvascular endothelial cell permeability.

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), has been shown to increase potently the permeability of endothelium and is highly expressed in breast cancer cells. In this study, we investigated the role of VEGF/VPF in breast cancer metastasis to the brain. Very little is known about the role of endothelial integrity in the extravasation of breast cancer cells to the brain. We hypothesized that VEGF/VPF, having potent vascular permeability activity, may support tumor cell penetration across blood vessels by inducing vascular leakage. To examine this role of VEGF/VPF, we used a Transwell culture system of the human brain microvascular endothelial cell (HBMEC) monolayer as an in vitro model for the blood vessels. We observed that VEGF/VPF significantly increased the penetration of the highly metastatic MDA-MB-231 breast cancer cells across the HBMEC monolayer. We found that the increased transendothelial migration (TM) of MDA-MB-231 cells resulted from the increased adhesion of tumor cells onto the HBMEC monolayer. These effects (TM and adhesion of tumor cells) were inhibited by the pre-treatment of the HBMEC monolayer with the VEGF/VPF receptor (KDR/Flk-1) inhibitor, SU-1498, and the calcium chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl)ester. These treatments of the HBMEC monolayer also inhibited VEGF/VPF-induced permeability and the cytoskeletal rearrangement of the monolayer. These data suggest that VEGF/VPF can modulate the TM of tumor cells by regulating the integrity of the HBMEC monolayer. Taken together, these findings indicate that VEGF/VPF might contribute to breast cancer metastasis by enhancing the TM of tumor cells through the down-regulation of endothelial integrity.

Brain↗

PubMed2002

Strongly enhanced field-dependent single-molecule electroluminescence.

Individual, strongly electroluminescent Ag(n) molecules (n = 2 approximately 8 atoms) have been electrically written within otherwise nonemissive silver oxide films. Exhibiting characteristic single-molecule behavior, these individual room-temperature molecules exhibit extreme electroluminescence enhancements (>10(4) vs. bulk and dc excitation on a per molecule basis) when excited with specific ac frequencies. Occurring through field extraction of electrons with subsequent reinjection and radiative recombination, single-molecule electroluminescence is enhanced by a general mechanism that avoids slow bulk material response. Thus, while we detail strong electroluminescence from single, highly fluorescent Ag(n) molecules, this mechanism also yields strong ac-excited electroluminescence from similarly prepared, but otherwise nonemissive, individual Cu nanoclusters.

Journal Article↗

PubMed2002

Structure of malonamidase E2 reveals a novel Ser-cisSer-Lys catalytic triad in a new serine hydrolase fold that is prevalent in nature.

A large group of hydrolytic enzymes, which contain a conserved stretch of approximately 130 amino acids designated the amidase signature (AS) sequence, constitutes a super family that is distinct from any other known hydrolase family. AS family enzymes are widespread in nature, ranging from bacteria to humans, and exhibit a variety of biological functions. Here we report the first structure of an AS family enzyme provided by the crystal structure of malonamidase E2 from Bradyrhizobium japonicum. The structure, representing a new protein fold, reveals a previously unidentified Ser-cisSer-Lys catalytic machinery that is absolutely conserved throughout the family. This family of enzymes appears to be evolutionarily distinct but has diverged to acquire a wide spectrum of individual substrate specificities, while maintaining a core structure that supports the catalytic function of the unique triad. Based of the structures of the enzyme in two different inhibited states, an unusual action mechanism of the triad is proposed that accounts for the role of the cis conformation in the triad.

Amidohydrolases↗

PubMed2002

A novel tricomplex of BRCA1, Nmi, and c-Myc inhibits c-Myc-induced human telomerase reverse transcriptase gene (hTERT) promoter activity in breast cancer.

Germ-line mutations in BRCA1 predispose individuals to breast and ovarian cancers. We observed a novel endogenous association of BRCA1 with Nmi (N-Myc-interacting protein) in breast cancer cells. Nmi was found to interact specifically with BRCA1, both in vitro and in vivo, by binding to two major domains in BRCA1, amino acid residues 298-683 and 1301-1863. Homodimerization of Nmi enhanced its association with BRCA1. Nmi functioned as an adaptor molecule to recruit c-Myc to a complex containing Nmi.c-Myc.BRCA1. Because c-Myc can activate transcription of the human telomerase reverse transcriptase gene (hTERT), we addressed the role of BRCA1 and Nmi in modulating c-Myc-induced hTERT promoter activity. Although Nmi or BRCA1 alone had no effect on c-Myc induced hTERT promoter activity, BRCA1 together with Nmi significantly inhibited this c-Myc induced hTERT promoter activity ( approximately 75% inhibition). Two mutated forms of BRCA1, a missense (A1708E) and a nonsense (Y1853X) that have been identified in familial breast cancers, associated with Nmi and c-Myc but failed to suppress c-Myc-induced hTERT promoter activity. These results demonstrate a novel pathogenic mechanism whereby mutations in BRCA1, via a novel transcription factor complex containing BRCA1, c-Myc, and Nmi, impair inhibition of c-Myc-induced hTERT promoter activity, which allows sustained activation of telomerase, a key enzyme in carcinogenesis.

Animals↗