Search PubMed⌕ Search

Biomedical subjects

B Cho

Publications and source records attributed to B Cho.

At least 19 recordsLinked to original sources
PubMed2004

Quantitative evaluation of spatial coherence of the electron beam from low temperature field emitters.

By using multiwalled carbon nanotubes as an element of a nanobiprism, we evaluated quantitatively the coherence of electrons emitted from tungsten tips at room temperature and 78 K, and found an enhancement of coherence at 78 K. The increase of the transverse coherence length of the electron beam agreed well with that of the inelastic mean free path of electrons in solids, demonstrating the direct relationship between the coherences of the electron beam and the original electronic states. On the basis of this experimental fact, we comment on the interpretation of recent Hanbury Brown-Twiss type experiments for electrons reported by Kiesel et al. [Nature (London) 418, 392 (2002)]].

Journal Article↗
PubMed2003

Self-organized superlattice formation during crystal growth from continuous beam fluxes.

Alloy superlattice structures consisting of alternating Si-rich and C-rich layers form spontaneously during gas-source molecular beam epitaxy of Si(1-y)C(y) on Si(001) from constant Si2H6 and CH3SiH3 precursor fluxes at T(s)=725-750 degrees C. The self-organized patterning is due to a complex interaction among competing surface reactions. During growth of the initial Si-rich layer, strain-driven C segregation to the subsurface results in charge transfer from surface Si atom dangling bonds to C backbonds. This decreases the Si2H6 sticking probability, and, hence, the instantaneous deposition rate, thereby enhancing C segregation. The Si-rich layer continues until a critical C coverage is reached allowing nucleation of a C-rich layer which grows until the excess subsurface C is depleted. The process then repeats with periods tunable through the choice of T(s) and y(avg).

Journal Article↗
PubMed2001

Enhanced IL-18 expression in common skin tumors.

Interleukin-18 (IL-18) has been found to have multiple effects upon various cells involved in inflammatory response. Recently we reported that B16 murine melanoma cells are able to produce IL-18, which is involved in the regulation of intracellular reactive oxygen intermediates (ROI) and Fas-ligand expression, indicating that IL-18 plays key role in the tumor activity of melanoma. In this study, we investigated the pattern of IL-18 expression in the human system. IL-18 production was tested by enzyme linked immunosorbent assay (ELISA) assay in various tumor cell lines, including Raji (Burkitt's lymphoma), IM-9 (B lymphoblast), Jurkat (acute T cell leukemia), SK-MES-1 (squamous cell carcinoma (SCC) cell line), SK-MEL-2, G-361, DM-4, and DX-3 (melanoma cell lines). ELISA tests showed that IL-18 was highly expressed in malignant skin tumors such as SK-MES-1, SK-MEL-2, G-361, DM-4, and DX-3 cell lines, thus suggesting that IL-18 production may be associated with the malignancy of skin tumors. Here, we report that enhanced IL-18 expression is positively correlated with malignant skin tumors such as SCC and melanoma, suggesting the importance role of IL-18 in malignancy of skin tumors. Taken together, expression of IL-18 by tumor cells in human skin tissue may provide an important clue to understand the pathogenesis of malignant skin tumors.

Basal Cell Carcinoma↗
PubMed2001

Identification of a structural motif of 23S rRNA interacting with 5S rRNA.

To identify RNA motifs interacting with 5S rRNA, a systematic evolution of ligands by exponential enrichment experiment was applied. Some of the resulting RNA aptamers contained a consensus sequence similar to the sequence in the loop region of helix 89 of 23S rRNA. We show that the synthetic helix 89 RNA motif indeed interacted with 5S rRNA and that the region around loop B of 5S rRNA was involved in this interaction. These results suggest the presence of a novel RNA-RNA interaction between 23S rRNA and 5S rRNA which may play an important role in the ribosome function.

Base Pairing↗
PubMed2001

Unilateral complete cleft lip and palate repair using lip adhesion and passive alveolar molding appliance.

To manage a unilateral complete cleft lip and palate, lip adhesion along with the positioning of a passive alveolar molding appliance was performed in infants at 3 to 6 weeks of age. The lip adhesion creates a force acting on the cleft alveolus. There-after, the greater segment of the alveolus is guided by the appliance, while the lesser segment of the alveolus is prevented from collapsing. Definite cheiloplasty was then performed at 5 to 6 months of age and palatoplasty at 12 to 14 months of age. Fifteen patients with a unilateral complete cleft lip and palate were treated using this protocol from April 1995 to October 1998. Nine were female and six were male. The mean follow-up period was 13 months. The lip adhesion failed in one patient and was performed again 1 month later. Thirteen patients developed good or fair symmetrically aligned alveolar segments plus a symmetric platform for the nose. However, two patients developed poor maxillary orthopedics because of the displacement of the appliance by the patient. The resulting lip scar was aesthetically acceptable in most patients.

Alveolar Process↗
PubMed2001

Development of virtual environment for treating acrophobia.

Virtual Reality (VR) is a new technology that makes humans communicate with computer. It allows the user to see, hear, feel and interact in a three-dimensional virtual world created graphically. Virtual Reality Therapy (VRT), based on this sophisticated technology, has been recently used in the treatment of subjects diagnosed with acrophobia, a disorder that is characterized by marked anxiety upon exposure to heights, avoidance of heights, and a resulting interference in functioning. Conventional virtual reality system for the treatment of acrophobia has a limitation in scope that it is based on over-costly devices or somewhat unrealistic graphic scene. The goal of this study was to develop a inexpensive and more realistic virtual environment for the exposure therapy of acrophobia. We constructed two types virtual environment. One is constituted a bungee-jump tower in the middle of a city. It includes the open lift surrounded by props beside tower that allowed the patient to feel sense of heights. Another is composed of diving boards which have various heights. It provides a view of a lower diving board and people swimming in the pool to serve the patient stimuli upon exposure to heights.

Altitude↗
PubMed2000

Pathway for the strain-driven two-dimensional to three-dimensional transition during growth of Ge on Si(001)

The two-dimensional (2D) to three-dimensional (3D) morphological transition in strained Ge layers grown on Si(001) is investigated using scanning tunneling microscopy. The initial step takes place via the formation of 2D islands which evolve into small ( approximately 180 A) 3D islands with a height to base diameter ratio of approximately 0.04, much smaller than the 0.1 aspect ratio of 105-faceted pyramids which had previously been assumed to be the initial 3D islands. The "prepyramid" Ge islands have rounded bases with steps oriented along <110> and exist only over a narrow range of Ge coverages, 3.5-3.9 monolayers.

Journal Article↗
PubMed2000

Expression of functional markers in acute nonlymphoblastic leukemia.

Multidrug resistance parameters, tissue infiltration parameters, receptors for colony-stimulating factors (CSFr) and cell cycle parameters were analyzed using flow cytometry in 145, 109 initial and 36 relapsed or refractory, acute nonlymphoblastic leukemia (ANLL) patients to find out clinically more reliable functional parameters. Lung resistance-associated protein (LRP) was most frequently expressed in ANLL (44.1%) followed by P-glycoprotein (PGP) (35.9%) and multidrug resistance-associated protein (MRP) (8.3%). LRP and PGP were expressed more frequently in relapsed or refractory ANLL than initial ANLL cases. Complete remission rate after standard chemotherapy falls in PGP-positive cases (p = 0.001). CD44-positive ANLL cases relapsed more frequently. The organ tropism is different depending on the infiltration parameters, vascular cell adhesion molecule to splenomegaly, matrix metalloprotease-2 to hepatomegaly and to extramedullary infiltration other than spleen, liver or lymph node. The percentage of the granulocyte-macrophage-CSFr expression was high in M4 and M5, and granulocyte-CSFr-positive ANLL showed less extramedullary infiltration (p = 0.007) and more PGP expression. Ki-67 was expressed significantly less in refractory ANLL than initial ANLL and DNA topisomerase IIalpha was expressed significantly more in the surviving patients group. In conclusion, analysis of these new functional parameters could help to predict and overcome the clinical behavior of each ANLL at the time of diagnosis.

Adolescent↗
PubMed1999

A novel MDMX transcript expressed in a variety of transformed cell lines encodes a truncated protein with potent p53 repressive activity.

The MDMX gene product is related to the MDM2 oncoprotein, both of which interact with the p53 tumor suppressor. We have identified a novel transcript of the MDMX gene that is expressed in a variety of cell lines, and in particular, in growing and transformed cells. This transcript is identical to the published sequence yet it has a short internal deletion of 68 base pairs. This deletion produces a shift in the reading frame after codon 114, resulting in the inclusion of a stop codon at amino acid residue 127 (full-length MDMX is 489 residues). This truncated MDMX protein is termed MDMX-S ("short form"), represents only the p53-binding domain, and appears to bind p53 better than full-length MDMX. The MDMX-S protein can be detected in cell extracts and when overexpressed is much more effective than MDMX at inhibiting p53-mediated transcriptional activation and induction of apoptosis. Since MDMX-S lacks the central and carboxyl-terminal regions contained within full-length MDMX, it is likely to play a key role in the regulation of cell proliferation and apoptosis in a way distinct from MDMX.

3T3 Cells↗
PubMed1998

Acute lymphoblastic leukemia with maturation--a new entity with clinical significance.

The diagnosis of 'ALL with maturation' (ALLm) is proposed. One hundred and one patients with untreated ALL were entered into this study. The diagnosis of ALLm was made when more than 20% of all nucleated elements in the bone marrow showed maturation beyond prolymphocytes by light microscopic examination. The mature-appearing leukemic cells showed the same immunophenotype to remaining lymphoblasts. The number of ALLm cases was 19 (18.8%). The mean age at presentation of ALLm was 29 +/- 18, older than that of 18 +/- 16 of the remaining typical ALL (ALLt) (P = 0.015). Remission was induced with daunorubicin, vincristine, prednisone and L-asparaginase. Only two of 19 ALLm patients achieved CR after 4 weeks induction chemotherapy. In contrast, 57 of 82 (69.5%) ALLt patients achieved CR after the same induction chemotherapy. There was no significant difference in immunophenotype of ALLm compared with ALLt. Labeling index of DNA topoisomerase IIalpha (TopoLI) was studied by immunohistochemistry. Initial TopoLI of ALLm (221 +/- 147) was much lower than that of ALLt (609 +/- 262, P = 0.005). Furthermore, the remaining leukemic cells after chemotherapy were not labeled with anti-DNA topoisomerase IIalpha. The P53 protein was expressed in nine of 18 ALLm cases (50.0%) and P-glycoprotein was not expressed in ALLm cases. Twelve of 19 ALLm cases were studied for carrying bcr/abl fusion by karyotyping and/or fluorescent in situ hybridization. Only two cases revealed bcr/abl fusion. In conclusion, ALLm is a separate entity of ALL which has a very poor clinical course and is independent of other prognostic factors. The morphologically mature leukemic cells are in resting GO phase.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Information system for a periodic examination and health promotion center.

The periodic examination and health promotion center (PEHPC) in Seoul National University Hospital has developed and adopted an information system supported by computers which use an electronic medical record to improve the quality of patient care, advance the science of medicine, lower health care costs, and enhance the education of health care professionals. This information system adopted the concept of incomplete and evolutionary systems to conduct the pursuit of practicalness and efficacy. It has increased efficiency to save costs and to enhance the quality of the medical service. It has also activated clinical research due to ease of managing data. We are also preparing for telecare. Telecare and WWW-using information system is postponed because the protection of a patients privacy is not established.

Ambulatory Care Facilities↗
PubMed1997

Interacting RNA species identified by combinatorial selection.

RNA molecules were selected from a random sequence library for their ability to bind to an RNA stem-loop target. Oligonucleotides with extensive Watson-Crick complementarity to the RNA ligand were selected against by inclusion of a blocking oligodeoxynucleotide in the binding phase of the selection protocol. After 18 generations of SELEX (systematic evolution of ligands by exponential enrichment) a single RNA family was predominant in the binding population. The winning aptamer RNA bound the target RNA with an apparent Kd = 70 nM. Structural mapping and Fe(II)-EDTA protection indicated that the target RNA interacted with small unpaired loops in the aptamer structure.

Base Composition↗
PubMed1996

RNA libraries and RNA recognition.

Random RNA libraries, consisting of > 10(13) unique sequences, contain molecules capable of specifically binding small molecule and protein ligands by noncovalent interaction. Successive steps of affinity purification and amplification allow the propagation and eventual isolation of specific binding molecules, called aptamers. Although protein- and small-molecule-binding aptamers have been characterized previously, selection of RNA aptamers capable of binding nucleic acids has previously yielded only molecules capable of Watson-Crick base pairing to the nucleic acid ligand used for selection. On the other hand, it is known from studies on catalytic and other RNAs that both inter- and intramolecular RNA-RNA interaction can occur by non-Watson-Crick means. We have therefore incorporated a strategy to obviate the possibility of Watson-Crick interaction into a selection scheme for the isolation of RNA-recognizing aptamers. The aptamers so isolated do not show extensive Watson-Crick complementarity with the RNA ligand used for the selection, thereby validating the selection strategy. Curiously, all of the aptamers characterized contain several oligo-G stretches bounded by U residues. This sequence motif, which occurs as DNA in telomeres (chromosome ends) may therefore be a general RNA-RNA interaction motif. An additional sequence motif is apparently superimposed on this background structure.

Bacillus subtilis↗
PubMed1994

The carboxy-terminal serine 392 phosphorylation site of human p53 is not required for wild-type activities.

Wild-type p53 functions in the G1 DNA damage checkpoint pathway by activating gene transcription and preventing cell cycle progression. Others reported that mutation of the serine 386 codon in mouse p53 abolished its ability to suppress growth. Serine 386 of murine p53 and the homologous residue of human p53, serine 392, are phosphorylated in vivo and can be phosphorylated in vitro by casein kinase II (CKII). We constructed mutants that changed serine 392 of human p53 to alanine (p53-S392A) or aspartic acid (p53-S392D); cotransfection of both these mutants with a reporter gene carrying a p53-responsive element into the p53-null Saos-2 cell line activated transcription as well as did wild-type p53. Furthermore, both mutants blocked cell cycle progression after transient transfection in these cells. A stable derivative of the T98G human glioblastoma cell line was established that expressed p53-S392A in response to dexamethasone. Overexpression of this mutant activated transcription of the endogenous waf1 (also called cip1) and mdm2 genes to the same extent as wild-type p53 and also produced growth arrest. Finally, p53-S392A and p53-S392D suppressed foci formation by activated ras and adenovirus E1A oncogenes as efficiently as did wild-type p53. Thus, unlike mutants that altered the serine 15 phosphorylation site, elimination of the serine 392 phosphorylation site had no discernible effect on p53 function. We conclude that neither phosphorylation nor RNA attachment to serine 392 are required for human p53's ability to suppress cell growth or to activate transcription in vivo.

Adenovirus E1A Proteins↗
PubMed1990

Relative tumor initiating activity of benzo[a]fluoranthene, benzo[b]fluoranthene, naphtho[1,2-b]fluoranthene and naphtho[2,1-a]fluoranthene on mouse skin.

The tumor-initiating activities of benzo[a]fluoranthene (BaF), benzo[b]fluoranthene (BbF), naphtho[1,2-b]fluoranthene (NbF) and naphtho[2,1-a]fluoranthene (NaF) were evaluated on the skin of female CD-1 mice. Each of these polycyclic aromatic hydrocarbons was assayed at total initiation doses of 1.0 and 4.0 mumol/mouse. These hydrocarbons were applied in 10 subdoses administered every other day. Promotion commenced 10 days after the last initiator dose and consisted of thrice weekly application of 2.5 micrograms of tetradecanoylphorbol acetate for 20 weeks. BbF was the most potent tumor initiator inducing a 100% incidence of tumor-bearing mice with an average of 8.5 tumors per mouse at a total initiator dose of 1.0 mumol. NaF was slightly more active as a tumor initiator than either NbF or BaF. NaF induced a 90% incidence of tumor-bearing mice with an average of 5.9 tumors per mouse at a total initiator dose of 1.0 mumol. BaF and NbF at a total initiator dose of 4.0 mumol exhibited similar tumor-initiating activity with both inducing a 90% incidence of tumor-bearing mice with an average of 4.3 and 6.6 tumors per mouse, respectively. However, at a total initiator dose of 1.0 mumol, BaF and NbF induced a 95% and 65% incidence of tumor-bearing mice with an average of 3.3 and 2.5 tumors per mouse, respectively.

Animals↗