Biomedical subjects

Young Han Lee

Publications and source records attributed to Young Han Lee.

At least 19 recordsLinked to original sources

PubMed2007

Role of human LZIP in differential activation of the NF-kappaB pathway that is induced by CCR1-dependent chemokines.

Human leucine zipper protein (LZIP) associates with CC chemokine receptor 1 (CCR1) and this protein-protein interaction should play an important role in leukocyte cell mobility. LZIP is known to regulate leukotactin-1 (Lkn-1)-dependent cell migration without affecting the chemotactic activities of other CC chemokines that bind to CCR1. Since Lkn-1 is engaged in the transcriptional activation of nuclear factor kappaB (NF-kappaB) and subsequent activation of the chemoattractant ability of leukocytes, we investigated the regulatory role of LZIP in the NF-kappaB pathway that is induced by CCR1-dependent chemokines. LZIP increased NF-kappaB-dependent luciferase activity in response to Lkn-1 in HOS/CCR1 cells and THP-1 cells. However, the NF-kappaB-dependent luciferase activities induced by other CCR1-dependent chemokines were not affected by LZIP overexpression. LZIP also increased Lkn-1-induced chemotactic activity through activation of the NF-kappaB pathway, whereas LZIP did not affect either the transactivation of NF-kappaB or the chemotactic activities induced by other CCR1-dependent chemokines. Western blot analysis showed that LZIP increased the degradation of IkappaBalpha induced by Lkn-1 but not by other CCR1-dependent chemokines. Results from electrophoretic mobility shift assay (EMSA) showed that LZIP enhanced the Lkn-1-induced DNA-binding activity of NF-kappaB. These data indicate that LZIP functions as a positive regulator in the NF-kappaB activation pathway that is triggered by Lkn-1 without affecting the transcriptional activation of NF-kappaB induced by other CCR1-dependent chemokines.

Cell Line, Tumor↗

PubMed2006

The translation inhibitor anisomycin induces Elk-1-mediated transcriptional activation of egr-1 through multiple mitogen-activated protein kinase pathways.

The early growth response-1 gene (egr-1) encodes a zinc-finger transcription factor Egr-1 and is rapidly inducible by a variety of extracellular stimuli. Anisomycin (ANX), a protein synthesis inhibitor, stimulates mitogen-activated protein kinase (MAPK) pathways and thereby causes a rapid induction of immediate-early response genes. We found that anisomycin treatment of U87MG glioma cells resulted in a marked, time-dependent increase in levels of Egr-1 protein. The results of Northern blot analysis and reporter gene assay of egr-1 gene promoter (Pegr-1) activity indicate that the ANX- induced increase in Egr-1 occurs at the transcriptional level. Deletion of the serum response element (SRE) in the 5'-flanking region of egr-1 gene abolished ANX-induced Pegr-1 activity. ANX induced the phosphorylation of the ERK1/2, JNK, and p38 MAPKs in a time-dependent manner and also induced transactivation of Gal4-Elk-1, suggesting that Elk-1 is involved in SRE-mediated egr-1 transcription. Transient transfection of dominant-negative constructs of MAPK pathways blocked ANX-induced Pegr-1 activity. Furthermore, pretreatment with specific MAPK pathway inhibitors, including the MEK inhibitor U0126, the JNK inhibitor SP600125, and the p38 kinase inhibitor SB202190, completely inhibited ANX-inducible expression of Egr-1. Taken together, these results suggest that all three MAPK pathways play a crucial role in ANX-induced transcriptional activation of Pegr-1 through SRE-mediated transactivation of Elk-1.

Anisomycin↗

PubMed2006

Phospholipase Cgamma1 stimulates transcriptional activation of the matrix metalloproteinase-3 gene via the protein kinase C/Raf/ERK cascade.

The phospholipid hydrolase phospholipase Cgamma1 (PLCgamma1) plays a major role in regulation of cell proliferation, development, and cell motility. Overexpression of PLCgamma1 is associated with tumor development, and it is overexpressed in some tumors. Matrix metalloproteinase-3 (MMP-3) is a protein involved in tumor invasion and metastasis. Here, we demonstrate that overexpression of PLCgamma1 stimulates MMP-3 expression at the transcriptional level via the PKC-mediated Raf/MEK1/ERK signaling cascade. We propose that modulation of PLCgamma1 activity might be of value in controlling the activity of MMPs, which are important regulators of invasion and metastasis in malignant tumors.

Animals↗

PubMed2006

In vitro assay of neurofilament light chain self-assembly using truncated mutants.

Neurofilaments (NFs) are heteropolymers composed of light (NF-L), middle (NF-M), and heavy (NF-H) subunits, present in most neurons. NF-L polymerizes on its own to provide a scaffold on which regular NFs form via the cross-bridging of NF-M or NF-H. To clarify the mechanism of regulation of NF-L self-assembly, we developed an assay using truncated mutant NF-L fused to glutathione-S transferase (GST). Western immunoblotting data show that the GST-fused head-rod domains of NF-L are necessary and sufficient for detecting assembled NF-L. The levels of self-assembled NF-L subunits detected using GST fusion proteins were consistent with those detected by electron microscopy and turbidity assay. Our results collectively imply that GST-fused head-rod domains of NF-L are critical tools for analyzing NF-L self-assembly in vitro.

Adenocarcinoma↗

PubMed2006

Suppression of PTEN expression during aggregation with retinoic acid in P19 mouse embryonal carcinoma cells.

Apoptosis is thought to be involved in the maintenance of cellular homeostasis, as well as various pathological processes. However, little information is available about the regulation of apoptosis during the aggregation stage of P19 embryonal carcinoma (EC) cells. Here we report that aggregation-induced apoptosis is markedly attenuated by treatment with retinoic acid (RA). PTEN (phosphatase and tensin homolog deleted on chromosome 10) expression was down-regulated during the aggregation phase of P19 EC cells in the presence, but not in the absence, of RA. Suppression of PTEN expression during the aggregation was accompanied by increased phosphorylation of serine/threonine kinase Akt and glycogen synthase kinase-3beta (GSK-3beta). Our results suggest that RA attenuates the induction of apoptosis during the aggregation phase of P19 EC cells, probably by suppressing PTEN expression.

Animals↗

PubMed2006

The effectiveness of embolotherapy for treatment of hemoptysis in patients with varying severity of tuberculosis by assessment of chest radiography.

The effectiveness of percutaneous embolotherapy in cases of hemoptysis due to pulmonary tuberculosis from increasing severity of lung parenchymal injury was compared. The pattern of pleural involvement, as seen on chest radiography and angiography, were comparatively analyzed in 230 patients who were available for follow-ups from March 1992 to December 2003. Chest radiography findings were classified into 4 types based on levels of complicated lesions and pleural involvement. Angiography findings were divided into 4 groups based on the level of blood supply to lesions. Early hemostasis with respect to radiographic group were as follows: Type I- 92% (73/79), Type II- 80% (52/65), Type III- 70% (42/60), and Type IV- 56% (52/92); there was an average success rate of 73% (219/296), and continued hemostasis was found in 80% of Type I patients (62/77), 77% of Type II patients (41/53), 62% of Type III patients (25/40), and 45% of Type IV patients (27/60), with an average long- term hemostatic rate of 67% (155/230). Increasing severity of pleural involvement and associated complications correlated with increasing development of systemic collateral arteries other than the bronchial artery. The severely increased circulation in systemic collateral arteries makes it difficult to predict good hemostatic results following embolization. Therefore, we recommend aggressive treatment, such as surgical intervention, after embolization in such instances.

Adolescent↗

PubMed2006

Suppression of P-glycoprotein expression by antipsychotics trifluoperazine in adriamycin-resistant L1210 mouse leukemia cells.

Multidrug resistance (MDR) to unrelated chemotherapeutic drugs can be mediated by overexpression of P-glycoprotein (P-gp), the mdr gene product. Trifluoperazine (TFP), a phenothiazine derivative antipsychotics, is known to reverse MDR of tumor cell lines by blocking P-gp efflux function. In the present study, we evaluated the effect of TFP on the expression of P-gp in multidrug-resistant L1210/Adr mouse leukemic cell lines, which are characterized by overexpession of P-gp. We found that TFP induced the downregulation of P-gp protein and mdr1b mRNA in a dose- and time-dependent manner in L1210/Adr cells. TFP reduction of mdr1b mRNA was paralleled by transcriptional suppression of the mdr1b promoter. Moreover, TFP restored the adriamycin-induced apoptosis in L1210/Adr cells. These results suggest that TFP may have utility as an adjuvant in the therapy of leukemia for the reversal of P-gp-dependent MDR as well as for the management of psychological symptoms in the cancer patients.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2006

Clozapine, a neuroleptic agent, inhibits Akt by counteracting Ca2+/calmodulin in PTEN-negative U-87MG human glioblastoma cells.

Clozapine (CZP), a dibenzodiazepine derivative with a piperazinyl side chain, is in clinical use as an antipsychotic drug. This study investigated the effect of CZP on the modulation of the PI3K/Akt/GSK-3beta pathway in PTEN-negative U-87MG glioblastoma cells. Treatment with CZP rapidly inhibited the basal and EGF-induced phosphorylation of Akt. The inhibition of Akt resulted in the dephosphorylation of GSK-3beta and increased GSK-3beta kinase activity. A voltage-sensitive Ca(2+) channel blocker and calmodulin (CaM) antagonists inhibited Akt phosphorylation, whereas elevation of the intracellular Ca(2+) concentration prevented CZP-induced dephosphorylation of Akt and GSK-3beta, suggesting that Ca(2+)/CaM participates in the inhibition of Akt by CZP in U-87MG cells. In addition, similar to LY294002, CZP arrested cell cycle progression at G0/G1 phase, which was accompanied by decreased expression of cyclin D1. The reduction in the cyclin D1 level induced by CZP was abrogated by the inhibition of GSK-3beta, the inhibition of proteasome-dependent proteolysis, or an increase in the intracellular Ca(2+) concentration. These results suggest that the antipsychotic drug CZP modulates the PI3K/Akt/GSK-3beta pathway by counteracting Ca(2+)/CaM in PTEN-negative U-87MG glioblastoma cells.

Antipsychotic Agents↗

PubMed2006

Suppression of Egr-1 transcription through targeting of the serum response factor by oncogenic H-Ras.

The transcription factor Egr-1 functions as a key regulator in cellular growth, differentiation, and apoptosis. The loss of Egr-1 expression is closely associated with tumor development, although the molecular mechanism behind the suppression of Egr-1 is largely unknown. In this report, we show that growth factor-induced transcriptional activation of Egr-1 gene is downregulated by chronic expression of oncogenic H-Ras in NIH3T3 fibroblasts. Our results demonstrate that phosphoinositide 3-kinase (PI3K) signaling is necessary for oncogenic H-Ras-mediated reduction of Egr-1 gene expression. Aberrant activation of PI3K signaling by oncogenic Ras decreased the level of serum response factor (SRF) protein through the acceleration of proteolysis, which resulted in decreased SRF binding to the serum response element (SRE) sites within the Egr-1 promoter, leading to the suppression of Egr-1 transcription. Inhibition of PI3K signaling restored the downregulation of SRF and Egr-1 expression caused by oncogenic Ras. Our findings suggest a novel signaling mechanism by which prolonged activation of oncogenic H-Ras can trigger the loss of tumor suppressor Egr-1 through the PI3K pathway in NIH3T3 fibroblast model cell lines.

3T3 Cells↗

PubMed2006

Phospholipase D prevents etoposide-induced apoptosis by inhibiting the expression of early growth response-1 and phosphatase and tensin homologue deleted on chromosome 10.

Phospholipase D (PLD) has emerged as a critical regulator of cell proliferation and survival signaling. We show for the first time that elevated expression of PLD isozymes attenuates expression of the tumor suppressors early growth response-1 (Egr-1) and the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) tumor suppressor and apoptosis during etoposide treatment. When formation of phosphatidic acid was inhibited by overexpression of catalytically inactive PLD during etoposide treatment, expression of Egr-1 and PTEN and the apoptotic effect of etoposide were not inhibited. This suggests that PLD inhibits expression of these tumor suppressors and inhibits apoptosis. Deletion of a specific Egr-1-binding site present in the PTEN promoter blocked etoposide-induced PTEN activity and elevated expression of PLD decreased the sensitivity to apoptosis induced by ectopic expression of Egr-1. Etoposide-induced activation of Akt was potentiated by overexpression of PLD and PLD-stimulated suppression of Egr-1 was blocked by inhibition of phosphatidylinositol 3-kinase/Akt survival pathway at the both transcriptional and posttranscriptional levels. These results show that survival signals generated by PLD attenuate expression of Egr-1 by activation of phosphatidylinositol 3-kinase signaling pathway and induction of PTEN by Egr-1, which confers resistance to apoptosis.

Animals↗

PubMed2006

Self-test software for PowerPoint: a tool for self-learning.

RATIONALE AND OBJECTIVES: We developed self-test software to improve self-learning efficiency using Microsoft PowerPoint data files. CONCLUSION: This tool can be run on IBM-compatible computer under Microsoft Windows. It is a new useful and interactive tool for self-learning. This tool allows users to do view the cases in the PowerPoint data files by random or sequentially. Goal-oriented effective self-learning is possible from methods that conjecture the possible differential diagnosis without promptly seeing correct diagnosis. Thus effective and interactive self-learning is possible.

Computer Graphics↗

PubMed2005

Identification and functional characterization of an alternative splice variant within the fourth exon of human nanog.

Nanog, a homeodomain (HD) transcription factor, plays a critical role in the maintenance of embryonic stem (ES) cell self-renewal. Here, we report the identification of an alternatively-spliced variant of nanog. This variant lacked a stretch of amino acids (residues 168-183) located between the HD and tryptophan-repeat (WR) of the previously-reported full length sequence, suggesting that the deleted sequence functions as a linker and possibly affects the flexibility of the C-terminal transactivation domain relative to the DNA binding domain. Expression of mRNA encoding the splice variant, designated as nanog-delta 48, was much lower than that of the full length version in human ES cells. The ratio of nanog-delta 48 transcript to full length transcript increased, however, in multipotent adult progenitor cells. EMSA analysis revealed that both forms of Nanog were able to bind a nanog binding sequence with roughly the same affinity. A reporter plasmid assay also showed that both variants of nanog modestly repressed transactivation of gata-4, whose expression is proposed to be inhibited by nanog, with comparable potency. We conclude that, despite the difference in primary structure and expression pattern in various stem cells, the alternatively-spliced variant of Nanog has similar activity to that of the full length version.

Alternative Splicing↗

PubMed2005

Involvement of glycogen synthase kinase-3beta in hydrogen peroxide-induced suppression of Tcf/Lef-dependent transcriptional activity.

Hydrogen peroxide (H(2)O(2)) mediates induction of cytotoxicity in various cell types. GSK-3beta has been found to participate in a number of signaling pathways, including cell proliferation and cell death. In the present study, we show that GSK-3beta is rapidly dephosphorylated and activated in response to H(2)O(2) treatment. H(2)O(2) also dephosphorylates Akt/PKB in a dose- and time-dependent manner. Overexpression of Akt/PKB attenuates H(2)O(2)-induced dephosphorylation of GSK-3beta. Ectopic expression of Dvl-1, a component of Wnt signaling, stimulates Akt/PKB and inhibits dephosphorylation of GSK-3beta by H(2)O(2). Furthermore, H(2)O(2) causes the reduction of beta-catenin level and LiCl-mediated activation of Tcf/Lef-dependent transcription activity. These findings suggest that GSK-3beta is involved in H(2)O(2)-mediated inhibition of Tcf/Lef-dependent transcriptional activity.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Eosinophilic differentiation is promoted by blockage of Notch signaling with a gamma-secretase inhibitor.

Although increasing evidence supports the inhibitory role of Notch in granulocyte differentiation, the direct effects of Notch on the differentiation and maturation of eosinophils, one type of granulocyte, have not yet been studied. We investigated whether a blockage of Notch signaling promoted the differentiation of eosinophils from umbilical cord blood (UCB) cells. Freshly isolated UCB cells were cultured with IL-3, IL-5 and GM-CSF in the presence or absence of a gamma-secretase inhibitor L-685,458, and examined for the expression of major basic protein (MBP). Freshly isolated UCB cells expressed mRNA and proteins for Notch 1, Notch 2, Delta 1, and Jagged 1. MBP expression in cultures with the inhibitor was significantly increased, as compared with the cultures in the absence of the inhibitor. Treatment with the inhibitor was accompanied by a decrease in Hes 1 mRNA expression, indicative of Notch-mediated signaling for the inhibitor effect. UCB cells cultured with the inhibitor for 28 days displayed similar levels of CCR3, a late marker of eosinophil development, as compared with the cells cultured without the inhibitor, but almost completely lost chemotaxis response to eotaxin. Our data suggest that Notch signaling may modulate eosinophil migration at the mature stage as well as inhibit eosinophil differentiation.

Amyloid Precursor Protein Secretases↗

PubMed2004

Pleckstrin homology domains of phospholipase C-gamma1 directly interact with beta-tubulin for activation of phospholipase C-gamma1 and reciprocal modulation of beta-tubulin function in microtubule assembly.

Phosphoinositide-specific phospholipase C-gamma1 (PLC-gamma1) has two pleckstrin homology (PH) domains, an N-terminal domain and a split PH domain. Here we show that pull down of NIH3T3 cell extracts with PLC-gamma1 PH domain-glutathione S-transferase fusion proteins, followed by matrix-assisted laser desorption ionization-time of flight-mass spectrometry, identified beta-tubulin as a binding protein of both PLC-gamma1 PH domains. Tubulin is a main component of microtubules and mitotic spindle fibers, which are composed of alpha- and beta-tubulin heterodimers in all eukaryotic cells. PLC-gamma1 and beta-tubulin colocalized in the perinuclear region in COS-7 cells and cotranslocated to the plasma membrane upon agonist stimulation. Membrane-targeted translocation of depolymerized tubulin by agonist stimulation was also supported by immunoprecipitation analyses. The phosphatidylinositol 4,5-bisphosphate (PIP(2)) hydrolyzing activity of PLC-gamma1 was substantially increased in the presence of purified tubulin in vitro, whereas the activity was not promoted by bovine serum albumin, suggesting that beta-tubulin activates PLC-gamma1. Furthermore, indirect immunofluorescent microscopy showed that PLC-gamma1 was highly concentrated in mitotic spindle fibers, suggesting that PLC-gamma1 is involved in spindle fiber formation. The effect of PLC-gamma1 in microtubule formation was assessed by overexpression and silencing PLC-gamma1 in COS-7 cells, which resulted in altered microtubule dynamics in vivo. Cells overexpressing PLC-gamma1 showed higher microtubule densities than controls, whereas PLC-gamma1 silencing with small interfering RNAs led to decreased microtubule network densities as compared with control cells. Taken together, our results suggest that PLC-gamma1 and beta-tubulin transmodulate each other, i.e. that PLC-gamma1 modulates microtubule assembly by beta-tubulin, and beta-tubulin promotes PLC-gamma1 activity.

Animals↗

PubMed2004

Point mutations in the split PLC-gamma1 PH domain modulate phosphoinositide binding.

A number of signaling molecules contain small pleckstrin homology (PH) domains capable of binding phosphoinositides or proteins. Phospholipase C (PLC)-gamma1 has two putative PH domains, an NH(2)-terminal (PH(1)) and a split PH domain (nPH(2) and cPH(2)). We previously reported that the split PH domain of PLC-gamma1 binds to phosphatidylinositol 4-phosphate (PI(4)P) and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) (Chang et al., 2002). To identify the amino acid residues responsible for binding with PI(4)P and PI(4,5)P(2), we used site-directed mutagenesis to replace each amino acid in the variable loop-1 (VL-1) region of the PLC-gamma1 nPH(2) domain with alanine (a neutral amino acid). The phosphoinositide-binding affinity of these mutant molecules was analyzed by Dot-blot assay followed by ECL detection. We found that two PLC-gamma1 nPH2 domain mutants, P500A and H503A, showed reduced affinities for phosphoinositide binding. Furthermore, these mutant PLC-gamma1 molecules showed reduced PI(4,5)P(2) hydrolysis. Using green fluorescent protein (GFP) fusion protein system, we showed that both PH(1) and nPH(2) domains are responsible for membrane-targeted translocation of PLC-gamma1 upon serum stimulation. Together, our data reveal that the amino acid residues Pro(500) and His(503) are critical for binding of PLC-gamma1 to one of its substrates, PI(4,5)P(2) in the membrane.

Amino Acid Sequence↗

PubMed2004

Implication of Egr-1 in trifluoperazine-induced growth inhibition in human U87MG glioma cells.

The early growth response gene-1 (Egr-1) is a tumor suppressor which plays an important role in cell growth, differentiation and apoptosis. Egr-1 has been shown to be down-regulated in many types of tumor tissues. Trifluoperazine (TFP), a phenothiazine class of antipsychotics, restored serum-induced Egr-1 expression in several cancer cell lines. We investigated the effect of Egr-1 expression on the TFP-induced inhibition of cell growth. Ectopic expression of Egr-1 enhanced the TFP-induced antiproliferative activity and downregulated cyclin D1 level in U87MG glioma cells. Our results suggest that antipsychotics TFP exhibits antiproliferative activity through up-regulation of Egr-1.

Cell Cycle↗

PubMed2004

Hydrogen peroxide negatively modulates Wnt signaling through downregulation of beta-catenin.

The Wnt signal transduction pathway plays an important role in organogenesis and carcinogenesis. In an effort to better understand the action of oxidative stress-induced cellular signaling, we investigate the effect of exogenous H2O2 on the Wnt signal pathway. H2O2 decreases the amount of nuclear beta-catenin and Tcf/Lef-dependent transcription. Overexpression of Dvl-1 abrogated H2O2-induced downregulation of beta-catenin. Pretreatment with LiCl or Wnt-3a conditioned medium completely inhibited H2O2-induced release of mitochondrial cytochrome c and DNA fragmentation. These results suggest that H2O2 negatively modulates the Wnt signal pathway through downregulation of beta-catenin.

Adaptor Proteins, Signal Transducing↗