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Biomedical subjects

J Choi

Publications and source records attributed to J Choi.

At least 145 records · Page 8Linked to original sources
PubMed1999

Laser prostatectomy: checkup on the promises.

Voiding symptoms caused by benign prostatic hyperplasia are responsible for significant compromise in the quality of life of many men. As our population ages, more men are seeking medical evaluation and treatment for this condition. In addition, with the recognition that this benign condition rarely creates significant life-threatening medical problems, there has been a movement toward less invasive therapies that are associated with the least possible iatrogenic morbidity. Among the currently available, minimally invasive techniques is laser prostatectomy. Is it standing up to its rival, transurethral resection of the prostate, or lagging behind?

Journal Article↗
PubMed1999

Refined structure of the FKBP12-rapamycin-FRB ternary complex at 2.2 A resolution.

The structure of the FKBP12-rapamycin-FRB ternary complex has now been refined at 2.2 A resolution. The cell-cycle arrest agent rapamycin binds FK506-binding protein (FKBP12) and the FKBP12-rapamycin binding (FRB) domain of FKBP12-rapamycin associated protein (FRAP) simultaneously, and the inhibition of FRAP is responsible for rapamycin's biological activity. The conformation of rapamycin in the ternary complex is very similar to that observed in the FKBP12-rapamycin binary complex, with an r.m.s. difference of only 0.30 A. However, a slight (9 degrees ) rotation repositions the FRB-binding face of rapamycin in the ternary complex. There are extensive rapamycin-protein interactions and relatively few interactions between the two protein partners FKBP12 and FRB, these interactions mainly involving residues in the 40s and 80s loops of FKBP12 and alpha1 and alpha4 of FRB. The high-resolution refinement has revealed the crucial role of several buried waters in the formation of the ternary complex.

Amino Acid Sequence↗
PubMed1999

A new member of the Sin3 family of corepressors is essential for cell viability and required for retroelement propagation in fission yeast.

Tf1 is a long terminal repeat (LTR)-containing retrotransposon that propagates within the fission yeast Schizosaccharomyces pombe. LTR-retrotransposons possess significant similarity to retroviruses and therefore serve as retrovirus models. To determine what features of the host cell are important for the proliferation of this class of retroelements, we screened for mutations in host genes that reduced the transposition activity of Tf1. We report here the isolation and characterization of pst1(+), a gene required for Tf1 transposition. The predicted amino acid sequence of Pst1p possessed high sequence homology with the Sin3 family of proteins, known for their interaction with histone deacetylases. However, unlike the SIN3 gene of Saccharomyces cerevisiae, pst1(+) is essential for cell viability. Immunofluorescence microscopy indicated that Pst1p was localized in the nucleus. Consistent with the critical role previously reported for Sin3 proteins in the histone acetylation process, we found that the growth of the strain with the pst1-1 allele was supersensitive to the specific histone deacetylase inhibitor trichostatin A. However, our analysis of strains with the pst1-1 mutation was unable to detect any changes in the acetylation of specific lysines of histones H3 and H4 as measured in bulk chromatin. Interestingly, the pst1-1 mutant strain produced wild-type levels of Tf1-encoded proteins and cDNA, indicating that the defect in transposition occurred after reverse transcription. The results of immunofluorescence microscopy showed that the nuclear localization of the Tf1 capsid protein was disrupted in the strain with the pst1-1 mutation, indicating an important role of pst1(+) in modulating the nuclear import of Tf1 virus-like particles.

Amino Acid Sequence↗
PubMed1999

Inhibition of cPLA2 translocation and leukotriene C4 secretion by fluticasone propionate in exogenously activated human eosinophils.

We examined the effect of the highly lipophilic corticosteroid, fluticasone propionate (FP), in causing (1) inhibition of nuclear translocation of cytosolic phospholipase A2 (cPLA2), and (2) blockade of leukotriene C4 (LTC4) synthesis in isolated human eosinophils in vitro. Eosinophils were isolated from peripheral blood, treated with either buffer or 10(-)10 M to 10(-)6 M FP in the presence of 10 pg/ml human recombinant interleukin-5 (rhIL-5) and activated with formyl-met-leu-phe (FMLP) + cytochalasin B (CB). At 24 h, stimulated LTC4 secretion from eosinophils was unchanged; however, when corrected for cell viability, LTC4 secretion decreased from 1,429 +/- 327 pg/10(6) cells to 762 +/- 113 pg/10(6) cells for eosinophils treated for 48 h with >/= 10(-)8 M FP (p < 0.003). FMLP/CB-stimulated translocation of cPLA2 to the nuclear envelope assessed by specific immunohistochemical staining also was blocked by FP. By contrast, membrane expression of annexin-1, which was not minimal at 30 min, was substantial at 48 h for eosinophils treated with > 10(-)10 M FP, and inhibition of LTC4 synthesis was reversed by exogenous arachidonic acid (AA). We find that FP causes a decrease in stimulated eosinophil secretion of LTC4 that is regulated by phospholipase A2 (PLA2). Inhibition of LTC4 synthesis precedes the global cytotoxic effects of FP as indicated by the simultaneous upregulation of annexin-1 expression. Inhibited stimulated secretion corresponds to inhibited translocation of cPLA2 to the nuclear envelope during cellular activation.

Administration, Topical↗
PubMed1999

Changes in the evolution of the antigenic profiles and morphology during coccoid conversion of Helicobacter pylori.

OBJECTIVES: The significance of the coccoid forms of H. pylori is still controversial and the questions of whether these forms are viable and infective or degenerative are still open. We induced conversion from rod to coccoid forms and studied morphological changes and antigenic evolutions during this conversion and, thereby, elucidated the viability of coccoid forms. METHODS: The H. pylori strain (C001) used for Western blotting was isolated from the patient with gastric cancer. The antigenic evolution during coccoid conversion of H. pylori was studied by Western blotting, using different sera from thirty patients known to be culture positive. These sera were used to reveal the total antigens of the strain cultured for 2 days (100% rod) and 15 days (> 99% coccoid). After SDS-PAGE, with 10% separating gel of total antigens (rod and coccoid), transblotting (Trans-Blot electrophoretic cell, Bio-Rad) was taken onto a nitrocellulose membrane (Bio-Rad). Then, the blots, with human sera diluted at 1/100, were developed with color reaction by goat serum anti-human IgG with alkaline phosphatase and BCIP. RESULTS: The antigenic profiles were not changed in 46.7% (14/30 cases) and were changed in 53.3% (16/30 cases) during coccoid conversion. Antigenic fractions changed during coccoid conversion were protein band at 120 kDa and band at 35 kDa, and were not detected in coccus forms. The rest of the profiles were identical between rod and coccoid forms. The protein which disappeared include CagA (120 kDa) and porin, or adhesin (35 kDa). The morphological changes during coccoid conversion were U shaped at day 7, doughnut shaped at day 9 and full coccoid at day 15. CONCLUSIONS: The results showed that coccoid forms of H. pylori retain cellular structures similar to rod form, and some of the antigens (CagA and porin) disappeared during coccoid conversion. Therefore, coccoid form might be viable and represent one of the stages of H. pylori biological cycle.

Adaptation, Physiological↗
PubMed1998

Human gamma-aminobutyric acid B receptor gene: complementary DNA cloning, expression, chromosomal location, and genomic organization.

BACKGROUND: The 6p21.3 region of human chromosome 6 is a genetic locus for schizophrenia, juvenile myoclonic epilepsy, and dyslexia. METHODS: Due to our interest in these disorders we performed complementary DNA (cDNA) hybridization selection on genomic DNA clones spanning this region to identify potential positional-candidate genes. RESULTS: We identified a full-length cDNA with an open reading frame of 2883 bp corresponding to a predicted protein of 961 amino acids that shares greater than 95% homology with the rat gamma-aminobutyric acid B (GABAB) receptor. Northern blot hybridization identified a 4.4-kb transcript in human brain. The human gene mapped to two sites on 6p21.3 separated by 2 Mb. Sequence analysis of both sites showed that the centromeric gene is transcribed, whereas the telomeric site is likely a pseudogene. The transcribed gene is distributed over 22 exons spanning 18 kb of genomic DNA. CONCLUSIONS: The genomic location, tissue expression, and function of the human GABAB receptor gene suggest that it is an important positional-candidate for the neurobehavioral disorders with a genetic locus on 6p21.3. In addition, delineation of the genomic organization will now permit it to be integrated as part of pharmacogenetic studies in trials of anxiolytic, narcotic, antiepileptic, and fluoxetine therapies.

Blotting, Northern↗
PubMed1998

Dispensability of the actin-binding site and spectrin repeats for targeting sarcomeric alpha-actinin into maturing Z bands in vivo: implications for in vitro binding studies.

To explore the roles of specific domains of sarcomeric alpha-actinin (s-alpha-actinin) in the assembly and maintenance of striated myofibrils, myogenic cultures were transfected with four MYC-tagged s-alpha-actinin peptides. They were: (1) full-length sarcomeric alpha-actinin, (2) an N-terminal deletion that removed the actin-binding site only (MYC/A-), (3) a peptide that consisted of the actin-binding site only (MYC/A+), and (4) an N-terminal deletion that removed the EF-hands and titin-binding domains (MYC/EFT-). While cytotoxic in replicating myogenic cells, as they were in PtK2 cells, the four MYC peptides were not cytotoxic in postmitotic myotubes. In myotubes each of the four different MYC peptides were promptly and selectively incorporated into normal Z bands. The incorporation of MYC/A-, MYC/A+, and MYC/EFT- into Z bands suggests that (a) the actin-binding site, (b) the spectrin-repeats believed to be responsible for anti-parallel dimerization, and (c) the C-terminal EF-hands and titin-binding domains are each dispensable for targeting s-alpha-actinin/MYC peptides into Z bands. These findings could not have been predicted from the behavior of alpha-actinin (a) in binding assays in cell-free systems or (b) when expressed in transfected nonmuscle cells.

Actinin↗
PubMed1998

Immunological analysis of methamphetamine antibody and its use for the detection of methamphetamine by capillary electrophoresis with laser-induced fluorescence.

An accurate, simple and rapid immunoassay is demonstrated for the detection of methamphetamine in urine by capillary electrophoresis (CE) with laser-induced fluorescence (LIF). An aminobutyl derivative of methamphetamine was conjugated with proteins, and used as an immunogen to produce antibodies for the assay. The methamphetamine derivative was also labeled with fluorescein isothiocyanate (FITC) to compete with free methamphetamine in the sample for the antibody binding site. Levels of free and antibody-bound FITC-labeled methamphetamine were monitored by performing CE-LIF using an untreated fused-silica column. This competitive immunoassay used antiserum instead of purified antibody or antibody fragment, yet was found to have good precision with a sensitivity of lower than 20 ng/ml. Various antibodies were also screened, and cross-reactivity of anti-MA antibody with methamphetamine analogues were also investigated. The results indicate that CE-LIF-based immunoassay is a powerful tool for the screening and characterization of antibody and may have possible applications in the detection of abused drugs in urine.

Animals↗
PubMed1998

Role of protein kinase C in basal and hydrogen peroxide-stimulated NF-kappa B activation in the murine macrophage J774A.1 cell line.

In macrophages, hydrogen peroxide appears to be a physiological activator of the transcription factor, nuclear factor kappa B (NF-kappa B); however, the molecular basis of H2O2-stimulated NF-kappa B activation is not well defined. The observations that NF-kappa B can be activated in cells by phorbol 12-myristate 13-acetate and in vitro by addition of protein kinase C (PKC) are suggestive of a role of PKC in NF-kappa B activation, which was investigated in the J774A.1 murine macrophage cell line. Basal NF-kappa B DNA-binding activity and nuclear localization were decreased by PKC inhibitors. Although PKC activity was modified by H2O2 with a similar time course as H2O2 activation of NF-kappa B, the H2O2-stimulated increase in NF-kappa B DNA binding and translocation to the nucleus was unaffected by PKC inhibitors. Furthermore, PKC down-regulation (through preincubation with phorbol esters) also affected only baseline NF-kappa B DNA binding but not H2O2-stimulated NF-kappa B activation. Buffering of changes in intracellular free calcium concentration also had no effect upon H2O2-stimulated NF-kappa B activation. Thus, classical PKC activity may modulate basal NF-kappa B activity but does not participate in H2O2-stimulated NF-kappa B activation.

Animals↗
PubMed1998

Transmembrane redox signaling activates NF-kappaB in macrophages.

In macrophages, NF-kappaB can be activated by H2O2 generated by the respiratory burst or added exogenously. The mechanism of H2O2 signaling may involve changes in the cellular redox state or a redox reaction at the plasma membrane; however, the site of H2O2 action cannot be readily ascertained because of its membrane permeability. Ferricyanide, a nonpermeable redox active anion, activated NF-kappaB in the macrophage cell line, J774A.1. In contrast with exogenous H2O2, activation by ferricyanide did not correlate with net oxidation of NAD(P)H or glutathione, suggesting that a transplasma membrane redox reaction itself was the first signaling process in NF-kappaB activation.

Animals↗
PubMed1998

Determination of four anabolic steroid metabolites by gas chromatography/mass spectrometry with negative ion chemical ionization and tandem mass spectrometry.

A gas chromatography/mass spectrometry method is described which uses negative ion chemical ionization and tandem mass spectrometry for the determination of anabolic steroid metabolites. Four anabolic steroid metabolites to be derivatized by Pentafluoropropionic anhydride (PFPA) were determined using gas chromatography/mass spectrometry (GC/MS) with negative chemical ionization (NCI) and NCI/MS/MS. The repeatability and reproducibility of this procedure were in the range of 5.3-9.7% and 6.1-10.2%, respectively. This method of derivatization with PFPA for NCI and NCI/MS/MS was useful to determine four metabolites of nandrolone, dromostanolone, methenolone and boldenone. The derivatized metabolites of boldenone could be detected to 2 ppb and the other three steroids could be detected to 25 ppb in urine at a signal-to-noise ratio of S/N = 3.

Anabolic Agents↗
PubMed1998

Comparison of capillary electrophoresis-based immunoassay with fluorescence polarization immunoassay for the immunodetermination of methamphetamine using various methamphetamine antibodies.

An accurate and simple immunoassay using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) was performed for the detection of methamphetamine (MA) in urine. The CE-LIF was conducted with an untreated fused-silica column using antiserum and a tracer of fluorescein isothiocyanate (FITC)-labeled MA. This CE-LIF system was compared with fluorescence polarization immunoassay (FPIA) in a TDx analyzer in the photo-check mode using the same FITC-labeled tracer and the same antiserum. Various antibodies, not only those prepared by our own immunogens but also those from commercial sources, were screened and characterized in both assay systems with regard to sensitivity, precision, and cross-reactivity. Both systems satisfied analytical precision and gave similar cross-reactivity patterns. However, the CE-LIF-based immunoassay was approximately one order superior to FPIA in sensitivity, requiring less volume of sample, antiserum, and tracer for the assay. Considering that the FPIA system is well known to be a useful tool for screening antibodies and detecting drugs, the CE-LIF-based immunoassay system, which is seemingly more advantageous than the FPIA system, appears to have great power for the characterization of antibodies and for the detection of MA in urine.

Antibodies↗
PubMed1998

Biliary cystadenoma of the liver.

Hepatobiliary cystadenoma is an uncommon lesion that is difficult to diagnose preoperatively. Here we report a 34-year-old woman who presented with enlargement of a cyst that had been observed for the previous 6 months. Diagnostic imaging revealed a 7-cm diameter cystic mass with irregular multiple septation in her liver. All laboratory test results were normal except for serum carbohydrate antigen (CA) 19-9 (62.5 U/ml). Because of the malignant potential and the history of enlargement, a complete surgical excision was performed. The patient was discharged after a good recovery; 2 months after surgery her serum CA19-9 level had returned to normal (32.9 U/ml). Regardless of the diagnostic modalities used, cystadenoma and cystadenocarcinoma cannot be differentiated with accuracy. Therefore complete surgical resection is the recommended therapy.

Adenoma, Bile Duct↗
PubMed1998

Learning upregulates brain-derived neurotrophic factor messenger ribonucleic acid: a mechanism to facilitate encoding and circuit maintenance?

Brain-derived neurotrophic factor (BDNF) promotes neuron survival, enhances sprouting, protects neurons against insult, and may be involved in several aspects of learning and memory. In this study, rats trained to locate a submerged platform in a water maze had elevated levels of BDNF messenger ribonucleic acid (mRNA) in the hippocampus (p < .05), a structure associated with spatial memory. BDNF mRNA expression increased after 3 and 6 days but not after 1 day of training in the water maze. A yoked control group that swam without the platform present, to control for physical activity, showed a trend for elevated BDNF mRNA at an intermediate level between the learning and sedentary groups. Other cortical and subcortical areas did not show a significant increase in BDNF mRNA after learning or activity (p > .05). These findings suggest that learning can impact BDNF mRNA expression localized to the brain areas involved in the processing of spatial information. Furthermore, behaviors such as physical activity and learning may help maintain and protect neurons at risk in aging and neurodegenerative disease via increased BDNF expression.

Analysis of Variance↗
PubMed1998

Charged beads enhance cutaneous wound healing in rhesus non-human primates.

Enhanced cutaneous wound healing by positively charged cross-linked diethylaminoethyl dextran beads (CLDD) was studied in a standardized incisional wound model in 20 adult and 20 geriatric Macaca mulatta (rhesus) partitioned equally over five time periods. Physiologic saline served as a control. Soft-tissue linear incisions were prepared between and 1 cm inferior to the scapulae. There were four incisions per rhesus; each incision was 1.5 cm long with 1 cm of undisturbed tissue between incisions, and both the experimental CLDD and physiologic saline treatments were administered to each rhesus. The incision treatments were either CLDD and soft-tissue closure with 4-0 BioSyn sutures or sterile physiologic saline and closure with 4-0 BioSyn sutures. The hypothesis was CLDD would enhance cutaneous wound repair. Verification of the hypothesis consisted of clinical examinations and histologic and tensiometric evaluations on biopsy specimens at 10 and 15 days, whereas 5-day and 2- and 4-month groups were assessed clinically and biopsy specimens were assessed histologically. The clinical course of healing for all groups was unremarkable. At 10 days, incisions in adult rhesus treated with CLDD had a 30-percent greater tensile strength compared with the physiologic saline-treated incisions (p = 0.01), whereas for geriatric rhesus, the CLDD treatment proved to be 15 percent greater in tensile strength compared with the physiologic saline cohort (p = 0.11). By day 15, incisions in adult rhesus were 26 percent stronger than the saline treatment group (p = 0.07), and the difference was 36 percent (p = 0.02) for the geriatric rhesus. From 5 through 15 days, histologic observations revealed a gradual decrease in quantity and integrity of CLDD, with no remnants of CLDD at either 2 or 4 months. Macrophages and multinucleated giant cells were localized in the dermis and were associated with the CLDD. These cells decreased commensurately with the decrease of CLDD beads. The data suggest that CLDD can enhance significantly the tensile properties of healing cutaneous wounds in both adult and geriatric rhesus. Moreover, if the wound healing is enhanced in geriatric patients, this finding may be clinically germane to conditions where wound healing is compromised, such as in diabetics and patients on steroids.

Animals↗
PubMed1998

The application of a homologous recombination assay revealed amino acid residues in an LTR-retrotransposon that were critical for integration.

Retroviruses and their relatives, the LTR-retrotransposons, possess an integrase protein (IN) that is required for the insertion of reverse transcripts into the genome of host cells. Schizosaccharomyces pombe is the host of Tf1, an LTR-retrotransposon with integration activity that can be studied by using techniques of yeast genetics. In this study, we sought to identify amino acid substitutions in Tf1 that specifically affected the integration step of transposition. In addition to seeking amino acid substitutions in IN, we also explored the possibility that other Tf1 proteins contributed to integration. By comparing the results of genetic assays that monitored both transposition and reverse transcription, we were able to seek point mutations throughout Tf1 that blocked transposition but not the synthesis of reverse transcripts. These mutant versions of Tf1 were candidates of elements that possessed defects in the integration step of transposition. Five mutations in Tf1 that resulted in low levels of integration were found to be located in the IN protein: two substitutions in the N-terminal Zn domain, two in the catalytic core, and one in the C-terminal domain. These results suggested that each of the three IN domains was required for Tf1 transposition. The potential role of these five amino acid residues in the function of IN is discussed. Two of the mutations that reduced integration mapped to the RNase H (RH) domain of Tf1 reverse transcriptase. The Tf1 elements with the RH mutations produced high levels of reverse transcripts, as determined by recombination and DNA blot analysis. These results indicated that the RH of Tf1 possesses a function critical for transposition that is independent of the accumulation of reverse transcripts.

Amino Acids↗
PubMed1998

gamma-glutamylcysteine synthetase: mRNA stabilization and independent subunit transcription by 4-hydroxy-2-nonenal.

gamma-Glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo glutathione (GSH) synthesis, is composed of one catalytic (heavy) and one regulatory (light) subunit. Although both subunits are increased at the mRNA level by oxidants, it is not clear whether they are regulated through the same mechanism. 4-Hydroxy-2-nonenal (4HNE), a lipid peroxidation product, may act as a mediator for the induction of gene expression by oxidants. In the present study, 4HNE was used to study the mechanism of induction of the two GCS subunits in rat lung epithelial L2 cells. 4HNE increased both the transcription rates and the stability of mRNA for both GCS subunits, resulting in an increased mRNA content for both subunits. Both GCS subunit proteins and enzymatic activities also increased. Emetine, a protein synthesis inhibitor, blocked the increase in GCS light subunit mRNA but not the increase in GCS heavy subunit mRNA. This suggested that although 4HNE increased transcription and stabilization of both GCS subunit mRNAs, the signaling pathways involved in the induction of the two GCS subunits differed.

Aldehydes↗