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Biomedical subjects

H J Chung

Publications and source records attributed to H J Chung.

At least 19 recordsLinked to original sources
PubMed2006

Resistance to adefovir dipivoxil in lamivudine resistant chronic hepatitis B patients treated with adefovir dipivoxil.

BACKGROUND: Adefovir dipivoxil (ADV) is a potent nucleotide analogue against both the wild-type and lamivudine (LMV) resistant hepatitis B virus (HBV). The cumulative incidence of ADV resistant mutations in the nucleoside/-tide treatment naive chronic hepatitis B patient (CHB) at weeks 48, 96, and 144 was 0, 0.8-3%, and approximately 5.9%, respectively. AIMS: The aim of this study was to characterise the genotypic and phenotypic mutation profiles to ADV in 67 LMV resistant CHB patients who were treated with ADV. METHODS: Serum HBV DNA was quantified by real time polymerase chain reaction. The ADV mutant was detected using matrix assisted laser desorption/ionisation time of flight mass spectrometry based genotyping assays, termed restriction fragment mass polymorphism (RFMP). RESULTS: RFMP analysis revealed that a total of 11 amino acid substitutions developed in the rt domain of the HBV polymerase in nine patients. The cumulative incidence of genotypic ADV resistance at months 12 and 24 was 6.4% and 25.4%, respectively. The rtA181V, rtN236T, and rtA181T mutations were detected in five, four, and two of the 67 patients at treatment months 12-17, 3-19, and 7-20, respectively. Serial quantification of serum HBV DNA revealed that two patients with the rtA181V mutation, with or without the rtN236T mutation, and one patient with the rtA181T mutation displayed HBV DNA rebound. CONCLUSION: Emergence of the ADV mutation in LMV resistant patients who are treated with ADV appeared to present earlier and more frequently than was reported in previous studies on nucleoside/-tide treatment naive patients.

Adenine↗
PubMed2005

Interaction of beta-giardin with the Bop1 protein in Giardia lamblia.

A cDNA clone encoding a putative Bop1 homologous protein was identified in Giardia lamblia. Since Bop1 is a nucleolar protein involved in rRNA processing, thereby controlling the cell cycle, we investigated components of cell cycle control in G. lamblia by identifying the protein(s) that interact with Bop 1. Through an immunoaffinity column made with polyclonal antibodies specific to the recombinant Bop1 of G. lamblia, a pool of proteins was obtained from the crude extracts of Giardia and then used as antigens to immunize rats. By employing the resultant sera for cDNA library immunoscreening, we isolated cDNA clones encoding an immunopurified protein, which turned out to contain the gene for beta-giardin, a Giardia-specific cytoskeletal protein. The interaction between Bop1 and beta-giardin was confirmed via two different methods, yeast two-hybrid assay and coimmunoprecipitation.

Amino Acid Sequence↗
PubMed2005

Molecular cloning and characterization of bovine PRKAG3 gene: structure, expression and single nucleotide polymorphism detection.

The protein kinase adenosine monophosphate-activated gamma3-subunit (PRKAG3) gene encodes a muscle-specific isoform of the regulatory gamma-subunit of adenosine monophosphate-activated protein kinase, which plays a key role in regulating energy homeostasis in eucaryotes. It is well known that mutations in the PRKAG3 gene affect high glycogen content in the porcine skeletal muscle and, consequently, meat quality. The genomic structure and sequence of the bovine PRKAG3 were analysed from a Korean cattle BAC clone. The bovine PRKAG3 gene comprises 13 exons and spans approximately 6.8 kb on BTA2. From 5' and 3'-rapid amplification of cDNA ends experiments, the full-length cDNA of bovine PRKAG3 has been identified, encoding a deduced protein of 465 amino acids. Two splice isoforms, generated by the alternative splicing of exon 2, were also identified. Northern blot analysis demonstrated that, similar to other species, the bovine PRKAG3 transcript was only expressed in skeletal muscle. Seven single nucleotide polymorphisms, including two previously identified variants, were detected in four Bos taurus cattle breeds. The bovine PRKAG3 gene described in this study may be involved in muscle-related genetic diseases or meat quality traits in cattle.

Amino Acid Sequence↗
PubMed2004

Taxonomic discrimination of flowering plants by multivariate analysis of Fourier transform infrared spectroscopy data.

Fourier transform infrared spectroscopy (FTIR) provides biochemical profiles containing overlapping signals from a majority of the compounds that are present when whole cells are analyzed. Leaf samples of seven higher plant species and varieties were subjected to FTIR to determine whether plants can be discriminated phylogenetically on the basis of biochemical profiles. A hierarchical dendrogram based on principal component analysis (PCA) of FTIR data showed relationships between plants that were in agreement with known plant taxonomy. Genetic programming (GP) analysis determined the top three to five biomarkers from FTIR data that discriminated plants at each hierarchical level of the dendrogram. Most biomarkers determined by GP analysis at each hierarchical level were specific to the carbohydrate fingerprint region (1,200-800 cm(-1)) of the FTIR spectrum. Our results indicate that differences in cell-wall composition and structure can provide the basis for chemotaxonomy of flowering plants.

Biomarkers↗
PubMed2004

Plant regeneration from hairy-root cultures transformed by infection with Agrobacterium rhizogenes in Catharanthus roseus.

Hypocotyl explants of Catharanthus roseus produced hairy roots when cultured on Murashige and Skoog (MS) basal medium after infection by Agrobacterium rhizogenes. Explants gave rise to adventitious shoots at a frequency of up to 80% when cultured on MS medium supplemented with 31.1 microM 6-benzyladenine and 5.4 microM alpha-naphthaleneacetic acid. There was a significant difference in the frequency of adventitious shoot formation for each hairy-root line derived from a different cultivar. Plants derived from hairy roots exhibited prolific rooting and had shortened internodes. Approximately half of the plants had wrinkled leaves and an abundant root mass with extensive lateral branching, but otherwise appeared morphologically normal. Plants with hairy roots that were derived from the cultivar Cooler Apricot developed flowers with petals that were white in the proximal region, whereas the wild-type flower petals are red. PCR and Southern blot analyses revealed that plants derived from hairy roots retained the Ri TL-DNA.

Adenine↗
PubMed2003

Taxonomic discrimination of higher plants by pyrolysis mass spectrometry.

Pyrolysis mass spectrometry (PyMS) is a rapid, simple, high-resolution analytical method based on thermal degradation of complex material in a vacuum and has been widely applied to the discrimination of closely related microbial strains. Leaf samples of six species and one variety of higher plants (Rosa multiflora, R. multiflora var. platyphylla, Sedum kamtschaticum, S. takesimense, S. sarmentosum, Hepatica insularis, and H. asiatica) were subjected to PyMS for spectral fingerprinting. Principal component analysis of PyMS data was not able to discriminate these plants in discrete clusters. However, canonical variate analysis of PyMS data separated these plants from one another. A hierarchical dendrogram based on canonical variate analysis was in agreement with the known taxonomy of the plants at the variety level. These results indicate that PyMS is able to discriminate higher plants based on taxonomic classification at the family, genus, species, and variety level.

Hot Temperature↗
PubMed2003

Genetic analysis of the VP1 region of human enterovirus 71 strains isolated in Korea during 2000.

We have isolated Human enterovirus 71 (EV71) from stool and CSF samples taken from patients with acute flaccid paralysis, herpangina, or hand, foot and mouth disease in 2000. Both the cell culture-neutralization test and RT-PCR were used to detect enteroviruses. Rhabdomyosarcoma (RD), HEP2c, and BGM cells were used for the isolation of viruses, and serotypes were determined by the neutralization test using EV71-specific antiserum. For genomic analysis, we amplified a 437-bp fragment of the 5'-noncoding region of the enterovirus genome and a 484-bp fragment of the VP3/VP1 region of EV71 by RT-PCR, with positive results. Products amplified using an EV71-specific primer pair were sequenced and compared with other isolates of EV71. Analysis of the nucleotide sequences of the amplified fragments showed that the EV71 isolates from patients were over 98% homologous and belonged to the genotype C.

Amino Acid Sequence↗
PubMed2003

Identification of an encystation-specific transcription factor, Myb protein in Giardia lamblia.

The life cycle of Giardia lamblia contains two differentiation processes, encystation and excystation. We performed an experiment to identify the genes induced during encystation using the differential display reverse transcriptase-polymerase chain reaction. Three of twelve isolated cDNA clones that showed increased transcription during encystation were identified to be of the myb2, which encodes a well-known transcriptional factor involved in cellular development and differentiation. The amino acid sequences of the Myb2 protein deduced from the isolated gene revealed that this Myb2 has a DNA binding domain comprising two imperfect repeats at its carboxyl-terminus. The nuclear localization of Myb2 protein during encystation was observed in vivo by expressing a Myb2-GFP fusion protein. In a random site selection experiment, the oligonucleotides bound by rMyb2 contained a conserved sequence of GTTT(G/T)(G/T). Two promoters of the encystation-induced genes, myb2, and cwp1, were also found to bind to rMyb2, whereas gap1, one of the constitutive genes did not.

Animals↗
PubMed2003

Differences in embryonic development in sensitive and resistant matings to pregnancy block stimuli in mice.

Pregnancy block from exposure to foreign male mouse pheromones is sensitive to both male and female mating strain, as well as the foreign male pheromone-producing strain. Incidence of pregnancy block by male pheromones in mice is different depending on the combination of females, stud males and stimulus males. BALB/cA females mated with BALB/cA males showed a 100% pregnancy block when exposed to males of the DDK strain (Chung et al., 1997). In contrast, BALB/cA females mated with males of dissimilar strain show high rates of pregnancy even if they are exposed to DDK males; this difference is thought to be due to the difference in viability of embryos (Chung et al., 1999). The present study investigated how development of BALB/cA and F1 embryos differ under the influence of pregnancy block stimuli. F1 embryos had significantly higher numbers of cells than did the BALB/cA embryos (P<0.05) at day 3 of pregnancy after exposure to DDK males or after bromocriptine (dopamine agonist, 4 mg kg(-1), i.p.) treatment. Histological observation after bromocriptine treatment revealed that: (i) on day 4 of pregnancy, BALB/cA embryos tended to form a large blastocoel, but showed abnormalities such as degeneration of primitive endoderm and depression of the outer trophoblast-distal endoderm layer at the periphery of the inner cell mass (ICM) or detachment of the ICM from the outer layer. In contrast, 60-70% of F1 embryos were normal late blastocysts and incipient egg cylinders, but 28-40% of early blastocysts were degenerating; and (ii) day 5 BALB/cA embryos were in the range from incipient egg cylinder with a large proamniotic cavity to ectoplacental cone only, but their proximal endoderm and trophoblast-distal endoderm layer were degenerating. In contrast, the F1 embryos were mostly at the egg cylinder stage and maintained normal structure except for occasional enlargement of the developing yolk sac cavity. These results indicate that the lining of the inner surface of trophoblast by distal endoderm layer may be more firmly established and that the inner environment for development of F1 embryos may be more effectively maintained, thereby making them more resistant to deleterious influences due to pregnancy block stimuli than are BALB/cA embryos.

Animals↗
PubMed2002

Time course of expression of mRNA of inducible nitric oxide synthase and generation of nitric oxide by ultraviolet B in keratinocyte cell lines.

BACKGROUND: Nitric oxide (NO), the ubiquitous free radical, has been implicated in the pathogenesis of various inflammatory diseases, including sunburn and ultraviolet (UV) radiation-induced pigmentation, and it also seems to play an important part in host defence against bacterial infection. OBJECTIVES: The purpose of this study was to determine the time course of production of NO and time course of expression of inducible NO synthase (iNOS) by UVB irradiation and lipopolysaccharide (LPS) stimulation in keratinocyte cell lines. Furthermore, we intended to elucidate the relationship between iNOS and NO in various stimulated conditions. METHODS: Normal human keratinocytes (NHK), HaCaT cells and PAM212 cells were irradiated with UVB at a dose of 50 mJ cm-2 and 100 mJ cm-2. Separately, the cell lines were stimulated with 20 micro g of LPS. NO was measured by the Griess assay and iNOS mRNA was isolated by reverse transcriptase-polymerase chain reaction at 12, 24, 48 and 72 h after stimulation. RESULTS: The generation of NO was induced by UVB irradiation and LPS stimulation. NO production was significantly increased at 72 h after irradiation of UVB 100 mJ cm-2 in NHK, and at 48 and 72 h in HaCaT cells. In PAM212 cells, NO production was significantly increased at 12, 24, 48 and 72 h by UVB 100 mJ cm-2 and at 72 h by LPS. Induction of iNOS mRNA peaked at 48 h and then decreased to basal level at 72 h when treated with UVB irradiation. The time course of production of NO was approximately correlated with the timing of induction of iNOS mRNA. CONCLUSIONS: These results suggest that the expression of iNOS mRNA is upregulated by UVB irradiation, and that NO produced by this inducible enzyme may play a part as a mediator or an immunomodulator in UV-induced skin reactions such as sunburn reaction and photo-induced immune alterations.

Cell Culture Techniques↗
PubMed2001

A new reverse PET chemosensor and its chelatoselective aromatic cadmiation.

[reaction: see text]. A new fluorescent chemosensor, anthryl tetra acid, was synthesized and showed large fluorescence quenching effects in 100% aqueous solution with metal ions via photoinduced electron transfer (PET). Chelatoselective fluorescence perturbation was observed with Cd(II) and resulted from electrophilic aromatic cadmiation.

Journal Article↗
PubMed2001

Interaction of the AMPA receptor subunit GluR2/3 with PDZ domains regulates hippocampal long-term depression.

The interaction of PDZ domain-containing proteins with the C termini of alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA) receptors has been suggested to be important in the regulation of receptor targeting to excitatory synapses. Recent studies have shown that the rapid internalization of AMPA receptors at synapses may mediate, at least in part, the expression of long-term depression (LTD). We have previously shown that phosphorylation of Ser-880 on the AMPA receptor GluR2 subunit differentially regulated the interaction of GluR2 with the PDZ domain-containing proteins GRIP1 and PICK1. Here, we show that induction of LTD in hippocampal slices increases phosphorylation of Ser-880 within the GluR2 C-terminal PDZ ligand, suggesting that the modulation of GluR2 interaction with GRIP1 and PICK1 may regulate AMPA receptor internalization during LTD. Moreover, postsynaptic intracellular perfusion of GluR2 C-terminal peptides that disrupt GluR2 interaction with PICK1 inhibit the expression of hippocampal LTD. These results suggest that the interaction of GluR2 with PICK1 may play a regulatory role in the expression of LTD in the hippocampus.

2-Amino-5-phosphonovalerate↗
PubMed2001

Characterization of a novel allele of glucose oxidase from a Korean wild type strain of Aspergillus niger.

We have identified a novel allele of the glucose oxidase (GO, EC1.1.3.4) gene (GO) from a Korean wild type strain of Aspergillus niger, ACMO4, with an increased GO activity in culture filtrate. Southern blot analyses of GO from ACMO4 (GO-ACMO4) revealed that the gene was present as a single copy in the genome of A. niger. However, its sequence differs from that of GO from A. niger ATCC 9029 (GO-ATCC9029). GO-ACMO4 appears to be a functional gene based on the fact that it is enzymatically active when heterologously expressed in yeast. Sequence comparisons of the coding region of GO-ACMO4 revealed 16 nucleotide changes that resulted in four amino acid substitutions; T432D, G517D, G530S, and Q542R. The GO proteins from both ATCC 9029 and ACMO4 were heterologously expressed, purified, and compared biochemically. The two enzymes showed no difference in their apparent Km value for glucose (30 mM), but the Vmax of GO-ACMO4 (515.6 unit/mg) was 10% higher than that of GO-ATCC 9029, resulting in a 10% higher specific activity.

Alleles↗
PubMed2001

Regulation of starch accumulation by granule-associated plant 14-3-3 proteins.

In higher plants the production of starch is orchestrated by chloroplast-localized biosynthetic enzymes, namely starch synthases, ADP-glucose pyrophosphorylase, and starch branching and debranching enzymes. Diurnal regulation of these enzymes, as well as starch-degrading enzymes, influences both the levels and composition of starch, and is dependent in some instances upon phosphorylation-linked regulation. The phosphoserine/threonine-binding 14-3-3 proteins participate in environmentally responsive phosphorylation-related regulatory functions in plants, and as such are potentially involved in starch regulation. We report here that reduction of the epsilon subgroup of Arabidopsis 14-3-3 proteins by antisense technology resulted in a 2- to 4-fold increase in leaf starch accumulation. Dark-governed starch breakdown was unaffected in these "antisense plants," indicating an unaltered starch-degradation pathway and suggesting a role for 14-3-3 proteins in regulation of starch synthesis. Absorption spectra and gelatinization properties indicate that the starch from the antisense plants has an altered branched glucan composition. Biochemical characterization of protease-treated starch granules from both Arabidopsis leaves and maize endosperm showed that 14-3-3 proteins are internal intrinsic granule proteins. These data suggest a direct role for 14-3-3 proteins in starch accumulation. The starch synthase III family is a possible target for 14-3-3 protein regulation because, uniquely among plastid-localized starch metabolic enzymes, all members of the family contain the conserved 14-3-3 protein phosphoserine/threonine-binding consensus motif. This possibility is strengthened by immunocapture using antibodies to DU1, a maize starch synthase III family member, and direct interaction with biotinylated 14-3-3 protein, both of which demonstrated an association between 14-3-3 proteins and DU1 or DU1-like proteins.

14-3-3 Proteins↗
PubMed2001

Identification of protein kinase C phosphorylation sites within the AMPA receptor GluR2 subunit.

Phosphorylation of AMPA receptor subunits is believed to regulate channel function and synaptic plasticity. Extensive biochemical and molecular studies have identified sites of PKA, PKC and CamKII phosphorylation in the C-termini of the GluR1 and 4 subunits. Recent studies have shown GluR1 phosphorylation to be bidirectionally altered during long-term potentiation (LTP) and long-term depression (LTD) in the hippocampus. The majority of AMPA receptors in the brain are believed to contain the GluR2 subunit that also contains potential sites for protein phosphorylation. Here we characterize PKC phosphorylation on the GluR2 subunit using biochemical and molecular techniques. Site-directed mutagenesis confirmed that this phosphorylation occurs on Serine 863 and Serine 880 of the GluR2 subunit C-terminus. Site identification allowed the generation of phosphorylation site-specific antibodies to facilitate the examination of GluR2 modification in primary neuronal culture. These studies confirmed that GluR2 is modified in response to the activation of PKC and suggests that phosphorylation of the ubiquitous GluR2 subunit may be important in the regulation of excitatory synaptic transmission.

Amino Acid Sequence↗
PubMed2001

Enterocin P selectively dissipates the membrane potential of Enterococcus faecium T136.

Enterocin P is a pediocin-like, broad-spectrum bacteriocin which displays a strong inhibitory activity against Listeria monocytogenes. The bacteriocin was purified from the culture supernatant of Enterococcus faecium P13, and its molecular mechanism of action against the sensitive strain E. faecium T136 was evaluated. Although enterocin P caused significant reduction of the membrane potential (DeltaPsi) and the intracellular ATP pool of the indicator organism, the pH gradient (DeltapH) component of the proton motive force (Deltap) was not dissipated. By contrast, enterocin P caused carboxyfluorescein efflux from E. faecium T136-derived liposomes.

Adenosine Triphosphate↗