Search PubMed⌕ Search

Biomedical subjects

K H Choi

Publications and source records attributed to K H Choi.

At least 55 records · Page 3Linked to original sources
PubMed2000

Lipopolysaccharide-activated kinase, an essential component for the induction of the antimicrobial peptide genes in Drosophila melanogaster cells.

Eukaryotic organisms use a similar Rel/NF-kappaB signaling cascade for the induction of innate immune genes. In Drosophila, lipopolysaccharide (LPS) signal-induced activation of the Rel/NF-kappaB family transcription factors is an essential step in the transcriptional activation of inducible antimicrobial peptide genes. However, the mechanism by which the LPS-induced signaling pathway proceeds remains largely unknown. Here we have cloned a novel Drosophila LPS-activated kinase (DLAK) that is structurally related to mammalian IkappaB kinases. DLAK is expressed and transiently activated in LPS-responsive Drosophila cells following LPS stimulation. Furthermore, DLAK can interact with Cactus, a Drosophila IkappaB and phosphorylate recombinant Cactus, in vitro. Overexpression of dominant-negative mutant DLAK (DLAK(K50A)) blocks LPS-induced Cactus degradation. DLAK-bound Cactus can be degraded in a LPS signal-dependent fashion, whereas the DLAK(K50A) mutant-bound Cactus is completely resistant to degradation in the presence of LPS. The DLAK(K50A) mutant also inhibits nuclear kappaB binding activity and kappaB-dependent diptericin reporter gene activity in a dose-dependent manner, but the kappaB-dependent diptericin reporter gene activity can be rescued by overexpression of wild type DLAK. Moreover, mRNA analysis of various kappaB-dependent antimicrobial peptide genes shows that LPS inducibility of these genes is greatly impaired in cells overexpressing DLAK(K50A). These results establish that DLAK is a novel LPS-activated kinase, which is an essential signaling component for the induction of antimicrobial peptide genes following LPS treatment in Drosophila cells.

Amino Acid Sequence↗
PubMed2000

Evaluation of tTA-mediated gene activation system on human cytomegalovirus and herpes simplex virus type-1 infections.

The tetracycline-controlled transactivator (tTA)-mediated gene activation system was examined in virus infected cells to determine its role in the control of gene expression. In the presence of tTA, the gene expression from the tetO-modified minimal promoter was efficiently activated in the uninfected cells, whereas essentially no activation was observed from the only minimal promoter without the seven direct repeats of 42 bp tetO sequences. However, essentially no activation was observed when only the minimal promoter was used, without the seven direct repetitions of the 42 bp tetO sequences. On the other hand, in the infected cells, a substantial background of beta-glucuronidase expression was detected in the absence of tTA, even though tTA stimulated the gene expression by approximately 7-fold. This background expression indicates that the sequences within or nearby tetO are involved in the background stimulation of the gene expression by HCMV and HSV-1. These results suggest that the application of the tTA-mediated gene activation system may not be extremely useful for studying the biological roles of HCMV and HSV genes in the viral replicative cycles, because of the basal activity of the gene expression.

Cytomegalovirus↗
PubMed2000

Effects of AMPA/kainate receptor blockade on responses to dopamine receptor agonists in the core and shell of the rat nucleus accumbens.

The present experiments were conducted to investigate effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleprionic acid (AMPA)/kainate receptor blockade (CNQX, NBQX) on locomotor responses to D2/3 (7-OH-DPAT) and D1 [(+)-SKF 38393] dopamine receptor agonists in the nucleus accumbens (NAS) core and shell. CNQX (0.25-0.5 microgram) microinjected into the NAS core or shell did not affect baseline locomotor activity. 7-OH-DPAT (2.5-5 micrograms) decreased locomotor activity. Co-administration of CNQX (0.5 microgram) increased the effects of 7-OH-DPAT (5 micrograms) in the NAS core and shell. A similar increase was observed with NBQX (0.5 microgram) in the NAS shell. (+)-SKF 38393 (5 micrograms) into the NAS core and shell increased locomotor activity after 30 min; this effect was not altered by CNQX (0.5 microgram). As the D2/3 dopamine agonist (-)-quinpirole (2 micrograms) increased effects of (+)-SKF 38393 (5 micrograms) in NAS shell but not core, lack of site-selective effects of (+)-SKF-38393 and of 7-OH-DPAT within NAS is not attributable to drug diffusion. The previous observation that glutamate effects on locomotor activity depend on the relative involvement of D1 or D2/3 dopamine receptors in the NAS was based on the dopamine-depletion model. The present results demonstrate differential interactions of AMPA receptor blockade with dopamine agonists in "dopamine-intact" animals.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

Providing services to Asian Americans with developmental disabilities and their families: mainstream service providers' perspective.

This survey investigated the opinions and perceptions of 44 mainstream social service providers regarding barriers to Asian Americans with developmental disabilities and their families receiving appropriate supportive services. Six main barriers were identified: (1) Language and communication difficulties; (2) Lack of knowledge concerning mainstream service delivery system; (3) Perceived cultural differences; (4) Being a "minority within a minority" in the service delivery system; (5) Individual differences within families and differences among Asian ethnic groups; and (6) Lack of resources to meet needs within the family. Implications of the interrelationships among the identified barriers were discussed.

Adolescent↗
PubMed2000

Role of azaamino acid residue in beta-turn formation and stability in designed peptide.

The structural perturbation induced by C(alpha)-->N(alpha) exchange in azaamino acid-containing peptides was predicted by ab initio calculation of the 6-31G* and 3-21G* levels. The global energy-minimum conformations for model compounds, For-azaXaa-NH2 (Xaa=Gly, Ala, Leu) appeared to be the beta-turn motif with a dihedral angle of phi= +/- 90 degrees, psi=0 degrees. This suggests that incorporation of the azaXaa residue into the i+2 position of designed peptides could stabilize the beta-turn structure. The model azaLeu-containing peptide, Boc-Phe-azaLeu-Ala-OMe, which is predicted to adopt a beta-turn conformation was designed and synthesized in order to experimentally elucidate the role of the azaamino acid residue. Its structural preference in organic solvents was investigated using 1H NMR, molecular modelling and IR spectroscopy. The temperature coefficients of amide protons, the characteristic NOE patterns, the restrained molecular dynamics simulation and IR spectroscopy defined the dihedral angles [ (phi i+1, psi i+1) (phi i+2, psi i+2)] of the Phe-azaLeu fragment in the model peptide, Boc-Phe-azaLeu-Ala-OMe, as [(-59 degrees, 127 degrees) (107 degrees, -4 degrees)]. This solution conformation supports a betaII-turn structural preference in azaLeu-containing peptides as predicted by the quantum chemical calculation. Therefore, intercalation of the azaamino acid residue into the i+2 position in synthetic peptides is expected to provide a stable beta-turn formation, and this could be utilized in the design of new peptidomimetics adopting a beta-turn scaffold.

Aza Compounds↗
PubMed2000

Amino-acid sequence and glycan structures of cysteine proteases with proline specificity from ginger rhizome Zingiber officinale.

The ginger proteases (GP-I and GP-II), isolated from the ginger rhizome Zingiber officinale, have an unusual substrate specificity preference for cleaving peptides with a proline residue at the P2 position. The complete amino-acid sequence of GP-II, a glycoprotein containing 221 amino acids, and about 98% that of GP-I have been determined. Both proteases, which are 82% similar, have cysteine residues at positions 27 and histidines at position 161, corresponding to the essential cysteine-histidine diads found in the papain family of cysteine proteases, and six corresponding cysteine residues that form the three invariant disulfide linkages seen in this family of proteins. The sequence homology with other members (papain, bromelain, actinidin, protease omega, etc.) of this family is approximately 50%. GP-II has two predicted glycosylation sites at Asn99 and Asn156. Analyisis by electrospray and collision-induced dissociation MS showed that both sites were occupied by the glycans (Man)3(Xyl)1(Fuc)1(GlcNAc)2 and (Man)3(Xyl)1(Fuc)1(GlcNAc)3, in a ratio of approximately 7 : 1. Both glycans are xylose containing biantennary complex types that share the common core structural unit, Man1-->6(Man1-->3) (Xyl1-->2)Man1-->4GlcNAc1-->4(Fuc1-->3)GlcNAc for the major form, with an additional N-acetylglucosamine residue being linked, in the minor form, to one of the terminal mannose units of the core structure.

Amino Acid Sequence↗
PubMed2000

beta-ketoacyl-acyl carrier protein synthase III (FabH) is a determining factor in branched-chain fatty acid biosynthesis.

A universal set of genes encodes the components of the dissociated, type II, fatty acid synthase system that is responsible for producing the multitude of fatty acid structures found in bacterial membranes. We examined the biochemical basis for the production of branched-chain fatty acids by gram-positive bacteria. Two genes that were predicted to encode homologs of the beta-ketoacyl-acyl carrier protein synthase III of Escherichia coli (eFabH) were identified in the Bacillus subtilis genome. Their protein products were expressed, purified, and biochemically characterized. Both B. subtilis FabH homologs, bFabH1 and bFabH2, carried out the initial condensation reaction of fatty acid biosynthesis with acetyl-coenzyme A (acetyl-CoA) as a primer, although they possessed lower specific activities than eFabH. bFabH1 and bFabH2 also utilized iso- and anteiso-branched-chain acyl-CoA primers as substrates. eFabH was not able to accept these CoA thioesters. Reconstitution of a complete round of fatty acid synthesis in vitro with purified E. coli proteins showed that eFabH was the only E. coli enzyme incapable of using branched-chain substrates. Expression of either bFabH1 or bFabH2 in E. coli resulted in the appearance of a branched-chain 17-carbon fatty acid. Thus, the substrate specificity of FabH is an important determinant of branched-chain fatty acid production.

3-Oxoacyl-(Acyl-Carrier-Protein) Synthase↗
PubMed2000

Incidence and significance of demonstrating the meniscofemoral ligament on MRI.

The aim was to evaluate how often MRI can detect the meniscofemoral ligament and if there is any relationship with the presence of lateral meniscal tears. Sagittal and coronal MR images of 138 patients with arthroscopically proven meniscal tears were included in this study. MR images were retrospectively reviewed for the presence of a meniscofemoral ligament and a lateral meniscal tear. The chi 2 test was used for statistical analysis. Either one or both meniscofemoral ligaments were shown in 114 (83%) of 138 patients on MR images. In 61 cases with a lateral meniscal tear, the meniscofemoral ligament was present in 82% (50/61) and absent in 18% (11/61). In 77 cases without lateral meniscal tear, the meniscofemoral ligament was present in 83% (64/77) and absent in 17% (13/77). A significant correlation was not established between the meniscofemoral ligament and lateral meniscal tear (p = 0.85).

Adolescent↗
PubMed2000

The usefulness of orbital lines in detecting blow-out fracture on plain radiography.

The purpose of this study was to assess the diagnostic value of orbital line changes on plain radiographs in detecting blow-out fracture. 92 cases of surgically confirmed blow-out fracture were retrospectively analysed in regard to plain radiographs and CT. Anterior and posterior lamina papyracea lines (ALPL and PLPL, respectively) of the orbital medial wall as well as the posteromedial floor line (PMFL) were assessed on orbital posteroanterior projections. The inferomedial orbital line (IMOL) and the inferior wall line were assessed on Waters projections. Orbital lines on plain radiographs were compared with CT findings. Of 53 cases of lamina papyracea fracture, 47 cases showed orbital line changes on plain radiographs (sensitivity 88.7%). Changes of PLPL (41/47), IMOL (29/47), ALPL (4/47) and PMFL (2/47) were demonstrated as depression, loss, discontinuity and irregularity. In four cases showing normal radiographs, the fractures measured less than 9 mm in size on CT. All 25 cases with orbital floor fracture accompanying medial wall fracture demonstrated orbital line changes of PMFL (16/25), PLPL (14/25), ALPL (3/25) and IMOL (2/25) (sensitivity 100%). 12 of 14 cases with orbital floor fracture demonstrated changes of inferior wall line (7/12) and PMFL (6/12) (sensitivity 85.7%). Two cases demonstrated asymmetric focal soft tissue density without orbital line changes. Orbital line changes on plain radiographs corresponded well with CT findings, confirming the usefulness of plain radiographs in detecting blow-out fracture.

Adolescent↗
PubMed2000

UVC-induced apoptosis in human epithelial tumor A431 cells: sequence of apoptotic changes and involvement of caspase (-8 and -3) cascade.

Human epidermoid tumor A431 cells underwent apoptosis following exposure to ultraviolet C (UVC). The apoptosis was of the interphase death type, and mostly occurred within one cell cycle, independent of the cell-cycle phases. We further examined the detailed sequential order of apoptotic changes in cells after UVC exposure and the involvement of caspases using six caspase inhibitors. The loss of mitochondrial transmembrane potential (delta psi m) appeared in the earliest phase; subsequently, the chromatin condensation and DNA-fragmentation occurred. Cell shrinkage and loss of the plasma-membrane integrity, judged by propidium iodide (PI) staining, were observed in the later phase. A broad-spectrum caspase inhibitor, z-VAD-fmk, completely prevented all apoptotic changes, except for the depletion of delta psi m. Both Ac-DEVD-CHO and Ac-IETD-CHO, inhibitors of caspase -3 and -8, respectively, effectively inhibited typical chromatin condensation to almost the same extent. However, the nuclei still showed partial condensation. A caspase -9 inhibitor, Ac-LEHD-CHO, did not prevent chromatin condensation, though it partially inhibited cell-size reduction and PI-stainability. None of the caspase inhibitors could inhibit the delta psi m reduction. These results strongly suggest that the collapse of delta psi m is not a part of the central apoptotic machinery, and that caspase cascade(s), especially caspase-8 to -3, play an important role in UVC-induced apoptosis in A431.

Apoptosis↗
PubMed2000

The detection of circulating breast cancer cells in peripheral blood by reverse transcriptase-polymerase chain reaction.

Some circulating cancer cells in the blood play a central role in the metastatic process and may have a major influence on patient progress. Their numbers can be very small and techniques for their detection need to be both sensitive and specific. Polymerase chain reaction (PCR) has been successfully used to detect small numbers of tumor cells in cancer. We used a reverse transcriptase-polymerase chain reaction (RT-PCR) to detect circulating breast cancer cells in venous blood samples before operations and assessed cytokeratin-19 (CK-19) and cytokeratin-20 (CK-20) as target mRNA markers in the blood of healthy donors (n=6) and breast cancer patients (n=30) with American Joint Committee on Cancer stages 0 to IIIa. CK-19 mRNA was expressed in all blood samples of healthy donors and patients. But CK-20 was the only mRNA marker not detected in the blood from healthy donors. Seven of 30 (23%) venous blood isolates of breast cancer patients yielded a CK-20 mRNA with positive results. There was no correlating CK-20 mRNA expression with stage and axillary lymph node status. In conclusion, CK-19 showed no diagnostic value as a mRNA marker in the detection of circulating cancer cells by RT-PCR assay because this was expressed in the blood of healthy donors. CK-20 mRNA was an useful marker to detect circulating cancer cells in breast cancers.

Breast Neoplasms↗
PubMed2000

The prevalence and associated risk factors of renal artery stenosis in patients undergoing cardiac catheterization.

Renal artery stenosis may be a cause of hypertension and a potential contributor to progressive renal insufficiency. However, the prevalence of renal artery disease in a general population is poorly defined. The purposes of this study were to evaluate the prevalence of angiographically-determined renal artery narrowing in a patient population undergoing routine cardiac catheterization, and to identify the risk factors for renal artery stenosis. After left ventriculography, abdominal aortography was performed to screen for the presence of renal artery stenosis. A total of 427 patients (274 males, 153 females) were studied and the mean age was 59 years. Renal artery narrowing was identified in 10.5% of patients. Significant (> or = 50% diameter narrowing) renal artery stenosis was found in 24 patients (5.6%) and insignificant stenosis was found in 21 patients (4.9%). Significant unilateral stenosis was present in 4.2% of patients and bilateral stenosis was present in 1.4%. The stem of the renal artery was a more common site of stenosis in 62.2% of patients than in the ostium (37.8%), but the severity of stenosis was not significantly different according to the site of stenosis. By univariate and multivariate logistic regression analysis, the association of clinical variables with renal artery stenosis was assessed. Multivariable predictors included age, hypertension and peripheral vascular disease (p < 0.05). The variables such as sex, smoking history, hyperlipidemia, renal insufficiency, as well as the presence of obesity, severity of coronary heart disease and D.M., were not associated. In conclusion, the prevalence of angiographically-determined renal artery narrowing in a patient population undergoing cardiac catheterization is 10.5%. Old age, hypertension and evidence of peripheral vascular disease represent the predictors of renal artery stenosis.

Adult↗
PubMed2000

Gentamicin induced apoptosis of renal tubular epithelial (LLC-PK1) cells.

Nephrotoxicity is a major limiting factor in the use of aminoglycoside antibiotics, the mechanisms for which are still speculative. To clarify the mechanisms of renal tubular cell death induced by aminoglycosides, we examined the renal proximal tubule-like cell line, LLC-PK1, after inducing apoptosis through a chronic treatment with gentamicin (GM). Changes in the expression of the Fas were also investigated. On flow cytometric analysis, 5.7 +/- 3.3% of the control cells appeared in a region of decreased forward light scatter and increased side light scatter, where both indices represent the characteristics of apoptotic cell death. Compared to the control, treatment with 10 mM of GM for 15 days significantly increased the proportion of cells in the apoptotic region to 23.9 +/- 8.5%. This finding was supported by electrophoretic analysis of the DNA extracted from the GM-treated cells, where a series of bands corresponding to integer multiples of 180 to 200 base pairs was visualized. However, the 15-day GM treatment did not cause a significant elevation in the expression of the 45 kD Fas protein, the cell surface molecule that stimulates apoptosis, by Western blot analysis. In conclusion, long-term exposure to GM induces apoptosis of the renal tubular epithelial cells, and this process may contribute to some of the aminoglycoside nephrotoxicities. Further studies are needed on the mechanism(s) of apoptosis induced by GM.

Animals↗
PubMed2000

Induction of p53-independent p21 during ceramide-induced G1 arrest in human hepatocarcinoma cells.

Ceramide is known to induce pRb (retinoblastoma gene product) dephosphorylation through the activation of ceramide-activated protein phosphatase (CAPP) during G1 arrest, but other molecular mechanisms linked to regulation of pRb dephosphorylation during ceramide-induced G1 arrest are poorly understood. In this paper, we investigated whether p21, a cdk (cyclin-dependent kinase) inhibitor, is involved in the induction of pRb dephosphorylation during ceramide-induced G1 arrest. In SK-Hep-1 cells, the addition of ceramide resulted in pRb dephosphorylation and G1 arrest. The activity of cdk2 was inhibited in response to ceramide during this process. p21 protein and mRNA were remarkably induced, while the protein level of p53, known as a transcriptional activator of p21, was not elevated at the same condition. p21 induction was also observed in the Hep3B cells lacking a functional p53 after exposure to ceramide. Although p21 is induced in ceramide-treated Hep3B cells, Hep3B cells do not induce G1 arrest, because Hep3B cells are deficient in a functional pRb protein. To confirm that pRb is a critical target for the induction of G1 arrest by inhibiting cdk2 activity through p53-independent p21, pRb-expressing vector was transfected into Hep3B cells. After treatment with ceramide, pRb-expressing cells (pRb+/+), but not pRb-/- cells, were arrested in G1 phase. In pRb+/+ cells, ceramide-mediated G1 arrest was accompanied by the accumulation of hypophosphorylated pRb and p21 associated with cdk2. Together, these results suggest that p21, induced through p53-independent pathway, participates in the induction of pRb dephosphorylation by inhibiting cdk2 activity during ceramide-mediated G1 arrest in hepatocarcinoma cells.

Blotting, Northern↗