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Biomedical subjects

Y Lee

Publications and source records attributed to Y Lee.

At least 271 records · Page 15Linked to original sources
PubMed1998

Resistance to adenovirally induced hyperleptinemia in rats. Comparison of ventromedial hypothalamic lesions and mutated leptin receptors.

Leptin regulates appetite and body weight via hypothalamic targets, but it can act directly on cultured pancreatic islets to regulate their fat metabolism. To obtain in vivo evidence that leptin may act peripherally as well as centrally, we compared the effect of adenovirally induced hyperleptinemia on food intake, body weight, and islet fat content in ventromedial hypothalamic-lesioned (VMHL) rats, sham-lesioned (SL) controls, and Zucker Diabetic Fatty (ZDF) rats in which the leptin receptor is mutated. Infusion with recombinant adenovirus containing the rat leptin cDNA increased plasma leptin by approximately 20 ng/ml in VMHL and ZDF rats but had no effect on their food intake, body weight, or fat tissue weight. Caloric matching of hyperphagic VMHL rats to SL controls did not reduce their resistance to hyperleptinemia. Whereas prediabetic ZDF rats had a fourfold elevation in islet fat, in VMHL rats islet fat was normal and none of them became diabetic. Isolated islets from ZDF rats were completely resistant to the lipopenic action of leptin, while VMHL islets exhibited 50% of the normal response; caloric matching of VMHL rats to SL controls increased leptin responsiveness of their islets to 92% of controls. We conclude that leptin regulation of adipocyte fat requires an intact VMH but that islet fat content is regulated independently of the VMH.

Adenoviridae↗
PubMed1998

Reaffirmation that metabolism of polyamines by bovine plasma amine oxidase occurs strictly at the primary amino termini.

Oxidation of the biologically important polyamines spermine and spermidine by plasma amine oxidase (PAO) was specified many years ago to occur at the terminal primary rather than internal secondary amine positions. However, the finding of sequential enzymatic conversion of spermine to spermidine and then to putrescine (1, 4-butanediamine) is superficially suggestive of metabolism at the secondary amine positions, and a recent publication (Houen, G., Bock, K., and Jensen, A. L. (1994) Acta Chem. Scand. 48, 52-60) claimed that the original interpretation of preferential "terminal" deamination does not stand up to scrutiny with modern methods of analysis. We herein demonstrate that the findings cited in support of secondary amine deamination can arise artifactually from spontaneous elimination/addition reactions following initial metabolism at the terminal positions of 3-(aminopropyl)amines. We further find no evidence for the ability of PAO to metabolize the secondary amine position in homospermidine, which is devoid of such complicating side reactions. Our results support the original claimed specificity of PAO for the primary amino termini of polyamines, all of which are consistent with the general finding that the quinone-dependent copper amine oxidases specifically metabolize primary amines.

Acrolein↗
PubMed1998

Isolation of cDNA clones encoding human histone macroH2A1 subtypes.

cDNA clones encoding two different subtypes of histone macroH2A1, macroH2A1.1 and macroH2A1.2, have been isolated from human liver tissue. The open reading frames in the isolated clones predicted proteins comprising 368 and 371 amino acids respectively. Estimated molecular masses of the two proteins were 39.0 kDa and 39.4 kDa. Human histone macroH2A1.1 and macroH2A1.2 showed about 98% identity with their counterparts isolated from rat. The features of the nucleotide sequences of the two macroH2A1 subtypes in human were the same as in the rat system. Northern blot analysis showed that the macroH2A1.1 and macroH2A1.2 subtypes were expressed as mRNA species with a size of 1.5 and 4.4 kb, respectively. They were expressed in all human tissues examined.

Amino Acid Sequence↗
PubMed1998

Role of peroxisome proliferator-activated receptor alpha in disease of pancreatic beta cells.

Expression of peroxisome proliferator-activated receptor alpha (PPARalpha) and enzymes of fatty acid (FA) oxidation is markedly reduced in the fat-laden, dysfunctional islets of obese, prediabetic Zucker diabetic fatty (fa/fa) rats with mutated leptin receptors (OB-R). Leptin, PPARalpha/retinoid x receptor ligands, and FA all up-regulate PPARalpha and enzymes of FA oxidation and stimulate [3H]-palmitate oxidation in normal islets but not in islets from fa/fa rats. Overexpression of normal OB-R in islets of fa/fa rats corrects all of the foregoing abnormalities and reverses the diabetic phenotype. PPARalpha is a OB-R-dependent factor required for normal fat homeostasis in islet cells.

Animals↗
PubMed1998

Activation and stabilization of chymotrypsin in microdomains of poly(ethylenimine) derivatives. A model of in vivo environment.

Both activity and stability of alpha-Chymotrypsin (ChT) are substantially enhanced in the microdomains of laurylated or benzylated derivatives of poly(ethylenimine). EPR data revealed that the enhancement in activity of ChT is due to increase in the polarity of the microenvironment of Ser-195 caused by complexation of ChT to the polymer derivatives.

Benzyl Compounds↗
PubMed1998

Purification and characterization of the nuclear RNase P holoenzyme complex reveals extensive subunit overlap with RNase MRP.

Ribonuclease P (RNase P) is a ribonucleoprotein enzyme that cleaves precursor tRNA transcripts to give mature 5' ends. RNase P in eubacteria has a large, catalytic RNA subunit and a small protein subunit that are required for precursor tRNA cleavage in vivo. Although the eukaryotic holoenzymes have similar, large RNA subunits, previous work in a number of systems has suggested that the eukaryotic enzymes require a greater protein content. We have purified the Saccharomyces cerevisiae nuclear RNase P to apparent homogeneity, allowing the first comprehensive analysis of an unexpectedly complex subunit composition. Peptide sequencing by ion trap mass spectrometry identifies nine proteins that copurify with the nuclear RNase P RNA subunit, totaling 20-fold more protein than in the bacterial enzyme. All of these proteins are encoded by genes essential for RNase P activity and for cell viability. Previous genetic studies suggested that four proteins might be subunits of both RNase P and RNase MRP, the related rRNA processing enzyme. We demonstrate that all four of these proteins, Pop1p, Pop3p, Pop4p, and Rpp1p, are integral subunits of RNase P. In addition, four of the five newly identified protein subunits, Pop5p, Pop6p, Pop7p, and Pop8p, also appear to be shared between RNase P and RNase MRP. Only one polypeptide, Rpr2p, is unique to the RNase P holoenzyme by genetic depletion and immunoprecipitation studies. The large increase in the number of protein subunits over eubacterial RNase P is consistent with an increase in functional complexity in eukaryotes. The degree of structural similarity between nuclear RNase P and RNase MRP suggests that some aspects of their functions in pre-tRNA and pre-rRNA processing pathways might overlap or be coordinated.

Amino Acid Sequence↗
PubMed1998

The human hepatitis B virus transactivator X gene product regulates Sp1 mediated transcription of an insulin-like growth factor II promoter 4.

Human hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma (HCC). The virus encodes a 17 kDa protein, X, which is known to be a causative agent in the formation of HCC. An insulin-like growth factor-II (IGF-II) is expressed during the formation of HCC. Among the four promoters of the IGF-II gene, promoters 2, 3 and 4 become activated during the formation of HCC. The high frequency of detection of hepatitis B virus X (HBV-X) antigen in liver cells from patients with chronic hepatitis, cirrhosis, and liver cancer suggested that the expressions of HBV-X and IGF-II are associated. Studies were carried out to test the relationship between the HBV-X gene product and the activation of IGF-II promoter 4. We demonstrated that the HBV-X protein increases the endogenous IGF-II expression from promoter 3 and 4 of IGF-II gene. Analysis of the fourth promoter of IGF-II gene showed that the HBV-X gene product positively regulates transcription. Two copies of a motif are responsible for conferring HBV-X regulation on the fourth promoter of IGF-II. These motifs have been identified as Sp1 binding sites. Sp1 binding to IGF-II P4 promoter was identified by gel mobility shift assay using purified Sp1. By using a GAL4-Sp1 fusion protein it was demonstrated that HBV-X positively regulates the Spl mediated transcriptional activity of IGF-II in vivo. A protein-affinity chromatography experiment showed that HBV-X protein does not bind directly to Sp1, but HBV-X does augment the DNA binding activity of the phosphorylated form of Sp1 in HepG2 cells. Sp1 was phosphorylated by HBV-X and its DNA-binding activity was up-regulated upon HBV-X transfections. Various HBV-X mutant expression vectors were used for the demonstration of specific interactions between Sp1 and HBV-X. These results indicate that HBV-X functions as a positive regulator of transcription, and that Sp1 is a direct target for the transcriptional regulation of IGF-II. Increasing the DNA binding ability of the phosphorylated form of Sp1 by HBV-X might be an important mechanism for regulating the IGF-II gene expression and possibly promoting cell division during hepatic carcinogenesis. Our experimental results suggest that expression of HBV-X might induce the expression of IGF-II and the IGF-II might play a role in hepatitis B virus pathogenesis during the formation of HCC.

Binding Sites↗
PubMed1998

Identification of differentially expressed genes in human hepatoblastoma cell line (HepG2) and HBV-X transfected hepatoblastoma cell line (HepG2-4x).

Hepatitis B virus-X protein (HBV-X) is known to be an important factor in the formation of hepatocellular carcinoma by acting as a transcriptional activator on viral or cellular genes. To identify differentially expressed genes between the human hepatoblastoma cell line HepG2 and HBV-X gene transfected hepatoblastoma cell line HepG2-4X, we used a differential display polymerase chain reaction technique. The technique produced numerous up-regulated and down-regulated bands, each representing a partial cDNA fragment. We isolated 23 different kinds of cDNA fragments that showed marked differences in two cell lines. The fragments were used as templates for DNA sequencing analysis and as probes for Northern blot analysis. This analysis revealed that eight cDNA clones were differentially expressed in each cell line but fifteen cDNA clones were not. Among the 8 clones, 3 clones showed sequence similarities with human mitochondrial ATPase subunit 6 (mtATPase 6) and the human amidophosphoribosyl transferase (ATase) precursor, whereas 5 other clones were human novel protein encoding genes. Two genes having similarity with known genes were repressed by HBV-X. These results reflect that complex alterations of the expression of enzymes concerning the energy-generating system in mitochondria and metabolite synthesis are closely associated with the HBV-X function during the formation of hepatocellular carcinoma. These newly obtained genes will be useful for analyzing HBV-X functions. We are in the process of further characterizing these genes.

Blotting, Northern↗
PubMed1998

The importance of postoperative radiation therapy in multimodality management of locally advanced breast cancer: a phase II trial of neoadjuvant MVAC, surgery, and radiation.

PURPOSE: To determine the impact of postoperative radiation on locoregional relapse and overall survival rate in a multimodality protocol for locally advanced breast cancer (LABC). MATERIAL AND METHODS: Of the patients entered in the protocol, 55 were evaluable. Treatment consisted of: neoadjuvant MVAC (methotrexate, vinblastine, adriamycin, and cisplatin) until a maximum response had been achieved; modified radical mastectomy; 6 courses of postoperative adjuvant MVAC chemotherapy, and chest wall irradiation (CWXRT). Multivariate analysis of locoregional response and overall survival was done. RESULTS: Of the total, 42 patients received chest wall radiation; 28 of these also received radiation to regional lymph nodes. Chest wall doses ranged from 45 Gy to 50.4 Gy to the whole chest wall, with 31 patients receiving an additional chest-wall boost. The incidence of locoregional relapse with and without radiation was 7% vs. 31%, respectively (p = 0.026). An overall survival benefit was seen in those receiving radiation, with a mean overall survival of 50 months vs. 20 months, and a 3-year overall survival of 88% vs. 46% with and without radiation, respectively (p = 0.003). Multivariate analysis showed that overall survival was affected by the presence of pathological CR (p = .047), the number of pre-operative chemotherapy cycles (p = .036) and whether or not they received radiation (p = 0.003). Neither the interval between surgery and radiation, technique of radiation, nor radiation modality significantly affected local control. CONCLUSION: The significant improvement in local regional control and overall survival with the addition of radiation suggests that radiation should be an integral part of multimodality management of locally advanced breast cancer.

Adult↗
PubMed1998

Expression of C5 protein, the protein component of Escherichia coli RNase P, from the tac promoter.

The accurate function of C5 protein, the protein component of Escherichia coli RNase P, is uncertain in vivo. A controllable expression system for C5 protein was constructed which can be used to investigate effects of C5 protein on various cellular functions including biosynthesis of RNase P in vivo. The semisynthetic rnpA gene encoding C5 protein was fused to the tac promoter of the pKK223-3 expression vector. This tac promoter expression system produced a high level of C5 protein upon induction with isopropyl-beta-D-thiogalacto-pyranoside. When the overexpressed C5 protein was purified and used for reconstitution of RNase P, the reconstituted enzyme was active. The N-terminal amino acid of the overexpressed C5 protein was leucine specified by the second codon of the rnpA gene. The more controllable expression system was constructed by introducing the lacIq gene into the vector sequence itself.

Bacterial Proteins↗
PubMed1998

Troglitazone lowers islet fat and restores beta cell function of Zucker diabetic fatty rats.

The thiazolidinedione compound troglitazone, which is used to treat non-insulin-dependent diabetes mellitus (NIDDM) in man, is also effective in the adipogenic NIDDM of Zucker diabetic fatty (ZDF) rats. To test the "lipotoxicity hypothesis," which attributes the beta cell dysfunction of adipogenic NIDDM to an excessive accumulation of fat in the pancreatic islets, we sought to determine if troglitazone-mediated amelioration of beta cell function in islets of ZDF rats might be associated with a reduction in their elevated triglyceride (TG) content. Troglitazone (10 microM) in the culture medium reduced the TG content of ZDF rats by 52%; this was reflected by decreased esterification and increased oxidation of [3H]palmitate. Glycerol-3-phosphate acyltransferase mRNA fell by 57% and acyl-CoA synthetase mRNA by 67% (brain isoform) and 38% (liver isoform), all consistent with the effects of troglitazone on TG metabolism. The 52% decrease in islet TG was accompanied by >30- and 2-fold improvements in glucose- and arginine-stimulated insulin secretion, respectively. We conclude that troglitazone exerts direct lipopenic activity in normal islets and in islets of obese prediabetic ZDF rats; in the latter, this correlated with improvement in beta cell function. The results are consistent with the lipotoxicity hypothesis for adipogenic diabetes.

Adipose Tissue↗
PubMed1998

Establishment and characterization of cell lines constitutively expressing hepatitis B virus X-protein.

We prepared human hepatoma cell lines, which expressed the human hepatitis B virus-X gene product. The plasmid pMAMneo-X, containing an HBV-X gene promoter, an enhancer and a structural gene was constructed. Transfected HBV-X gene integration and expression were detected by Southern and Northern blotting, as well as by chloramphenicol acetylase transferase (CAT) assay using various kinds of promoter-CAT reporter systems. HBV-X protein expression in stable transfectants was confirmed by immunofluorescence microscopy. Transfected cell lines showed permanent expression of HBV-X proteins. The HBV-X transfectant activated its target promoters in promoter-CAT constructs as reporters. The HBV-X transfectant enhanced AP-1 transcription factor binding to its target DNA. Therefore, X-transfectants are not only stable, but also have specific biological functions. Cell cycle analysis by flow cytometry showed that the majority of the transfectant cells are arrested in the G1 or G2 phase of the cell cycle. These cell lines may be useful in analyzing the biological functions of HBV-X and its functional role in the formation of hepatocellular carcinomas.

Carcinoma, Hepatocellular↗
PubMed1998

Genomic structure and expression of murine poly(A) binding protein II gene.

The genomic structure and expression of the murine poly(A) binding protein II (mPABII) gene were analyzed by using genomic DNA and cDNA clones. The expression level of the mPABII gene varied among tissues. Besides two transcripts detected in all tissues, an additional transcript was detected in testis. The mPAB gene has pseudogenes or related genes in its genome.

Amino Acid Sequence↗
PubMed1998

Pharmacokinetics and tolerability of intravenous rizatriptan in healthy females.

The pharmacokinetics and tolerability of intravenous (i.v.) rizatriptan (MK-0462), a novel 5-HT1D/1B receptor agonist for the acute oral treatment of migraine, were examined in an open, single-dose, four-period, randomized crossover study in healthy females. Results of this study indicated that i.v. rizatriptan (0.5-5 mg) was well tolerated. The disposition kinetics of rizatriptan were linear for i.v. doses up to and including 2.5 mg. Relative to the 0.5 mg dose, geometric mean dose-adjusted AUC ratios were 1.04, 1.09, and 1.18 for 1, 2.5, and 5 mg doses, respectively. Apparent plasma clearance (Cl) ranged between 859 and 941 mL min(-1) from 0.5 to 2.5 mg, but dropped to slightly below 800 mL min(-1) for the 5 mg dose. Therefore, the elimination of rizatriptan appears somewhat dose dependent at the high end of this dose range. Mean plasma half-life (t1/2) was 1.5-2.2 h across all doses while mean residence time in the body (MRT) and steady state volume of distribution (Vss) of rizatriptan remained relatively invariant across doses. Urinary excretion of rizatriptan (Ue) ranged from 14.5 to 34.6% of dose.

Adult↗
PubMed1998

Vertebrate homologs of tinman and bagpipe: roles of the homeobox genes in cardiovascular development.

In Drosophila, dorsal mesodermal specification is regulated by the homeobox genes tinman and bagpipe. Vertebrate homologs of tinman and bagpipe have been isolated in various species. Moreover, there are at least four different genes related to tinman in the vertebrate, which indicates that this gene has been duplicated during evolution. One of the murine homologs of tinman is the cardiac homeobox gene Csx or Nkx2.5. Gene targeting of Csx/Nkx2.5 showed that this gene is required for completion of the looping morphogenesis of the heart. However, it is not essential for the specification of the heart cell lineage. Early cardiac development might therefore be regulated by other genes, which may act either independently or in concert with Csx/Nkx2.5. Possible candidates might be other members of the NK2 class of homeobox proteins like Tix/Nkx2.6, Nkx2.3, nkx2.7, or cNkx2.8. Murine Tix/Nkx2.6 mRNA has been detected in the heart and pharyngeal endoderm (this study). Xenopus XNkx2.3 and chicken cNkx2.3 are expressed in the heart as well as in pharyngeal and gut endoderm. In contrast, murine Nkx2.3 is expressed in the gut and pharyngeal arches but not the heart. In zebrafish and chicken, two new NK-2 class homeoproteins, nkx2.7 and cNkx2.8, have been identified. Zebrafish nkx2.7 is expressed in both, the heart and pharyngeal endoderm. In the chicken, cNkx2.8 is expressed in the heart primordia and the primitive heart tube and becomes undetectable after looping. No murine homologs of nkx2.7 or cNkx2.8 have been found so far. The overlapping expression pattern of NK2 class homeobox genes in the heart and the pharynx may suggest a common origin of these two organs. In the Drosophila genome, the tinman gene is linked to another NK family gene named bagpipe. A murine homolog of bagpipe, Bax/Nkx3.1, is expressed in somites, blood vessels, and the male reproductive system during embryogenesis (this study), suggesting that this gene's function may be relevant for the development of these organs. A bagpipe homolog in Xenopus, Xbap, is expressed in the gut masculature and a region of the facial cartilage during development. In this paper, we discuss molecular mechanisms of cardiovascular development with particular emphasis on roles of transcription factors.

Amino Acid Sequence↗
PubMed1998

Structure-activity relationship of fluoroquinolone in Escherichia coli.

Structure-activity relationship of 20 fluoroquinolones was studied using the susceptible and 4 resistant Escherichia coli which were developed against 4 fluoroquinolones [ciprofloxacin (1), KR-10755 (6), norfloxacin (2), and ofloxacin (3)] in our laboratory. The C-7 and C-8 substituents of fluoroquinolone were important in various functions such as the inhibitory activity on DNA gyrase, permeability, and efflux. Among 20 fluoroquinolones, compounds with a 3-methyl-3,7-diazabicyclo[3.3.0]octan-1(5)-ene-7-yl substituent at the C-7 position or a chlorine substituent at the C-8 position showed a good inhibitory activity on DNA gyrase (especially a mutated DNA gyrase). Compounds with a 3,7-diazabicyclo [3.3.0]octan-1(5)-ene-7-yl substituent at the C-7 position showed good permeability in the susceptible and resistant strains, while compounds with a fluorine substituent at the C-8 position were less effluxed from cells.

Anti-Infective Agents↗
PubMed1998

Ofloxacin resistance mechanism in PA150 and PA300-clinical isolates of Pseudomonas aeruginosa in Korea.

Five hundred and seventy clinical strains of Pseudomonas aeruginosa were isolated from August 1993 to August 1994 in Korea and screened for their resistance to ciprofloxacin, norfloxacin, and ofloxacin. Among these, two P. aeruginosa strains (PA150 and PA300) were selected based on their strong resistance (MICs > 50 micrograms/ml) to all three quinolones. The susceptible strain as well as two resistant strains had proton gradient-dependent efflux system. Efflux system in PA300 showed different specificities to ofloxacin and ciprofloxacin while PA 150 had less permeability for ofloxacin. Ofloxacin had a less inhibitory action on DNA synthesis in permeabilized cells of PA150 and PA300 than 1771M. When quinolone resistance determining region (QRDR) in gyrA was sequenced, PA300 had one missense mutation, Asn 116Tyr, which was newly reported in this work. The results showed that PA150 became ofloxacin resistant by reduced ofloxacin accumulation due to the existence of efflux system and low permeability, while resistance of PA300 was due to the efflux system and a mutation in QRDR of gyrA-the target site of quinolone.

Base Sequence↗