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Biomedical subjects

K Ryu

Publications and source records attributed to K Ryu.

At least 37 records · Page 2Linked to original sources
PubMed1996

Cloning of the human sodium lodide symporter.

The iodide concentrating activity of the thyroid gland is essential to the production of thyroid hormone and also provides a mechanism for the treatment of thyroid cancer by radioiodine ablation. We report here the nucleotide and amino acid sequence of the human sodium iodide symporter (hNIS), which mediates the iodide uptake activity in the thyroid gland. An open reading frame of 1929 nucleotides encodes a protein of 643 amino acids with 84% identity to the rat NIS (rNIS). Transient expression of the hNIS cDNA conferred perchlorate-sensitive iodide uptake to a nonthyroid cell line, COS-7. The expression of hNIS was detected at variable levels in papillary thyroid carcinoma tissues but not in any of the thyroid carcinoma cell lines that have lost the iodide uptake activity.

Amino Acid Sequence↗
PubMed1996

Progesterone together with estradiol promotes luteinizing hormone beta-subunit mRNA stability in rat pituitary cells cultured in vitro.

The present study examined the role of ovarian steroids, estradiol and/or progesterone in the regulation of luteinizing hormone beta-subunit (LH-beta) mRNA levels and LH release in the rat anterior pituitary cells cultured in vitro. When estradiol (10 nmol/l) and/or progesterone (100 nmol/l) were added to the cultures, neither estradiol or progesterone nor both together altered the basal LH-beta mRNA levels or LH release. Continuous exposure to gonadotropin-releasing hormone (GnRH, 0.2 nmol/l) for 24 h markedly induced LH-beta mRNA accumulation, and in this experimental condition, progesterone alone and progesterone + estradiol further augmented GnRH-induced LH-beta mRNA levels and LH release. Then we explored further the possibility that ovarian steroids are involved in modulating LH-beta mRNA stability in cultured rat pituitary cells where transcription was inhibited by actinomycin D. Anterior pituitary cells were preincubated with GnRH (0.2 nmol/l) for 16 h and, after removing GnRH from culture medium, the cells were incubated further in the presence of actinomycin D (5 mumol/l) for 24 h. The LH-beta mRNA levels gradually declined to about 30% of the control values (zero time point after GnRH removal) in a time-dependent manner. During this period, either progesterone alone or progesterone + estradiol clearly blocked the degradation of LH-beta mRNA species. These results indicate that ovarian steroids promote LH-beta mRNA stability, thereby contributing to the maintenance of GnRH-stimulated LH-beta mRNA levels.

Animals↗
PubMed1995

A 33 kDa Pit-1-like protein binds to the distal region of the human thyrotrophin alpha-subunit gene.

Our previous studies demonstrated that at least two DNA regions with upstream limits between positions -223 to -190 and positions -151 to -135 of the human TSH gene are important for transcriptional regulation by TRH in GH3 rat pituitary cells. The proximal region (-151 to -135 bp) including the cAMP-responsive element (CRE) was required for the induction of the TSH gene by TRH, while the distal region (-223 to -190 bp) containing an element similar to the binding site for the pituitary-specific transcription factor, Pit-1, was necessary to amplify the effects of TRH. To determine whether a pituitary-specific nuclear protein, in addition to the CRE-binding protein, is involved in the molecular mechanism of TRH regulation, a gel retardation assay and Southwestern blot analysis were performed on the distal region with GH3 cell nuclear extracts. GH3 extracts generated a distinct DNA-protein complex that was effectively eliminated in the presence of excess unlabelled DNA fragment, and TRH treatment increased the affinity of protein binding remarkably. Excess Pit-1 DNA-binding sequence from the rat prolactin gene inhibited formation of the complex, but mutation of the Pit-1 consensus sequence in the distal region did not eliminate the complex. In addition, Southwestern experiments showed that a 33 kDa nuclear protein present in GH3 cells bound to this region and its binding affinity was increased slightly 2 h after TRH treatment, with the maximal increase (fivefold) at 3 h, which was similar to the results when using gel retardation. Phosphatase treatment of nuclear protein also resulted in a loss of binding affinity. Taken together, these data indicate that the interaction of a pituitary-specific nuclear protein, identical or closely related to Pit-1, with the distal region may be involved in the TRH stimulation of human TSH gene expression.

Animals↗
PubMed1994

Catalytic properties and potential of an extracellular protease from an extreme halophile.

An extracellular protease has been isolated and partially purified from the extreme halophile Halobacterium halobium (ATCC 43214). The major enzyme component has a M(r) of 66,000 and is highly dependent upon salt concentrations near saturation for catalytic activity and stability. In aqueous solutions, a decrease in the NaCl concentration from 4 to 1 M results in an increase of nearly three orders of magnitude in the first-order rate constant of inactivation at 30 degrees C. Salt effects the stability of the enzyme in a cooperative manner, with a Hill coefficient of 4.1, which is similar to that of other enzymes from extreme halophiles. The enzyme activity is dramatically affected by the salt concentration, with a loss of 2.5 orders of magnitude in kcat/Km in going from 4 to 0 M NaCl. This loss in catalytic efficiency is primarily due to a dramatic increase in the Km for the substrate in low-salt media. Thermodynamic analysis revealed that this Km increase was mainly the result of increased solubility of the synthetic peptide substrate in low-salt media, which dramatically increases the ground-state stability of the substrate. This results in an effectively reduced substrate partitioning from the bulk solution into the enzyme's active site and an increased value of Km. The halophilic protease is also active in DMF/water mixtures, albeit with novel catalytic properties. In 33% (v/v) DMF in aqueous buffer, the esterase activity of the enzyme is ca. 80-fold higher than the corresponding amidase activity. This contrasts to the situation in pure aqueous buffer, in which the esterase activity is only fourfold higher than the amidase activity. The increased esterase activity relative to amidase activity prompted us to investigate the use of the protease in kinetically controlled peptide synthesis. The enzyme has a broad acyl donor substrate specificity and can effectively use amino acid esters of Phe, Tyr, Trp, Ser, Gly, and Ala. The enzyme is significantly more selective for the amino acid amide, preferring Gly in the P'1 site. A series of glycine-containing oligopeptides have been prepared in yields up to 76% without degradation due to secondary hydrolysis.

Amidohydrolases↗
PubMed1994

Effect of adenylate cyclase inhibitor and protein kinase C inhibitor on GnRH-induced LH release and LH beta subunit biosynthesis in rat anterior pituitary cells.

According to our previous studies together with others, GnRH, a hypothalamic decapeptide, has been known to be a major regulator for LH release and its subunit biosynthesis in anterior pituitary gonadotropes. But the precise mechanisms by which GnRH exerts stimulatory effects on LH release and its subunit biosynthesis have not been clearly understood. In the present study we examined the effect of GnRH on protein kinase C (PKC) activity and intracellular cAMP content in cultured anterior pituitary cells of rat to clarify whether PKC or cAMP are involved in GnRH action. Moreover, we examined the effects of staurosporine (ST), a PKC inhibitor and 2',3'-dideoxyadenosine (2',3'-DDA), an adenylate cyclase inhibitor, on LH release and steady state LH beta subunit mRNA levels in cultured anterior pituitary cells of rat. PKC activity was rapidly increased within 30 min after GnRH treatment whereas intracellular cAMP level was elevated 18 h after GnRH treatment. ST significantly inhibited GnRH-induced LH release and LH beta subunit mRNA levels in a dose-dependent manner, showing an half maximal response at 50 nM ST. 2',3'-DDA inhibited GnRH-induced LH release and LH beta subunit mRNA levels in a dose-dependent manner in pituitary cells. From these results, it is suggested that GnRH stimulates LH beta subunit mRNA level as well as LH release in anterior pituitary cells and this GnRH action might be mediated by PKC activation and cAMP stimulation.

Adenylyl Cyclase Inhibitors↗
PubMed1994

[A surgical case of giant mediastinal teratoma].

A 35-year-old female was admitted with a large abnormal shadow in the left lung field on a chest X-ray. She was examined by chest tomogram, chest CT, MRI and bronchofiberscope. The CT and MRI showed a large tumor mass pressing the left lung and calcified deposits in the central part of the tumor. Bronchofiberscopic findings showed a stenosis of the left main bronchus. The clinical diagnosis was mature teratoma arising from anterior medistinum. She underwent a median sternotomy and the tumor was removed. The size of the resected specimen, filled with sebaceous material, hair and teeth, etc., was 14 x 12 x 10 cm (1,045 g). Histopathological examination of the specimen revealed a mediastinal mature teratoma. She has been well for 16 months postoperatively.

Female↗
PubMed1993

Inhibition of tyrosine phosphorylation prevents IFN-gamma-induced HLA-DR molecule expression.

We have previously demonstrated that HLA-DR molecule expression induced by IFN-gamma is associated with phosphatidylinositide turnover, activation of protein kinase C, and elevation of intracellular calcium. Because phosphorylation of phospholipase C-gamma 1 on tyrosine residues is known to be involved in the activation of phosphatidylinositide turnover, we investigated the role of tyrosine protein kinase (TPK) in the signal transduction for IFN-gamma-inducible DR molecule expression on T98G cells. The effects of three specific TPK inhibitors, genistein, herbimycin A, and tyrphostin, suggest that TPK is involved in the signal transduction. These inhibitors inhibited the IFN-gamma-inducible DR molecule expression in a dose-dependent manner. Being consistent with this, immunoblotting with an anti-phosphotyrosine mAb revealed that IFN-gamma induces a rapid increase in protein tyrosine phosphorylation. Genistein not only abrogated the IFN-gamma-induced enhancement of tyrosine phosphorylation, but also inhibited the IFN-gamma-induced production of inositol-4-5-triphosphate and the elevation of intracellular calcium. However, these three TPK inhibitors failed to inhibit the DR molecule expression induced by PMA and A23187. These findings suggest that the tyrosine phosphorylation is an early and critical event that precedes phosphatidylinositide turnover leading to activation of protein kinase C and elevation of intracellular calcium concentration during IFN-gamma-inducible DR molecule expression.

Benzoquinones↗
PubMed1993

Chemoembolotherapy for recurrent hepatocellular carcinoma in the residual liver after hepatectomy.

The efficacy of transcatheter arterial chemoembolization using Lipiodol (TACE) to treat recurrent hepatocellular carcinoma (r-HCC) in the residual liver after radical hepatic resection was evaluated. During the last 8 years, TACE was performed in 68 patients with r-HCC for an aggregate total of 150 times. Of the 68 patients, 4 had a massive type r-HCC with tumor thrombus in the main portal vein (PVTT) at the time of the first TACE. Among the remaining 64 patients without PVTT, multiple r-HCCs were revealed in 46, and a single r-HCC in 18 by angiography and/or follow-up CT scans after the initial TACE. In 26 of the 68 patients (38.2%), at least one or more r-HCCs were fed not only by the hepatic arteries, but also by the extrahepatic collateral arteries, such as branches of the right inferior phrenic artery. The cumulative survival rates of these patients after hepatectomy and after the initial TACE for r-HCC were 98.6% and 87.1% for one year, 89.7% and 62.9% for 2 years, 74.0% and 34.3% for 3 years, 53.1% and 20.0% for 4 years and 40.3% and 0% for 5 years (mean survival duration: 1,647 days and 947 days), respectively. These results indicate that repeat TACE against r-HCC can help obtain long-term survival in patients with r-HCC. However, during TACE, we must give consideration to the newly developed collateral feeding artery to the r-HCC.

Adult↗
PubMed1992

How do organic solvents affect peroxidase structure and function?

The effect of organic solvents on horseradish peroxidase structure and function has been studied. Some, but not complete, enzyme denaturation occurs even in low volumes of water-miscible organic solvents (e.g., greater than 30% v/v dioxane, greater than 50% v/v methanol, and greater than 20% v/v acetonitrile) as determined by the decreased difference between the fluorescence of peroxidase's sole tryptophan residue and free L-tryptophan in solution. Absorbance and electron paramagnetic resonance spectroscopies indicate exposure of peroxidase's active site to the organic solvent. This reduces the local polarity in the enzyme's active site and results in stronger hydrogen bonding of phenolic substrates to the enzyme. In extreme cases (e.g., 95% v/v dioxane, 90% v/v acetonitrile, and ethyl and butyl acetate containing 2 and 1% v/v aqueous buffer, respectively), the transition state of the enzymic reaction is sufficiently perturbed so as to alter the magnitude of the Hammett rho value. This is most likely the result of the increased strength of hydrogen bonding between electron-donating alkoxyphenols (negative sigma values) and an electrophilic group in the enzyme's active site, thereby reducing catalytic efficiencies for such substrates relative to alkyl- and chlorophenols. Perhaps the most important effect of the organic solvent, however, is the significant ground-state stabilization of phenolic substrates in organic media as opposed to aqueous buffer. This stabilization can account for nearly 4 orders of magnitude in reduction of catalytic efficiency and is manifested in increased Km's. This study indicates that enzymes can maintain much of their native active-site structure in organic media and that the effect of solvent on substrate thermodynamics must be considered.

Acetonitriles↗
PubMed1992

[The signal transduction mechanism responsible for interferon-gamma-inducible indoleamine 2,3-dioxygenase (IDO) gene expression in T98G cells].

The interferon (IFN)-gamma-induced indoleamine 2,3-dioxygenase (IDO) is implicated in the inhibition of intracellular pathogens, e.g. Chlamydia psittaci and Toxoplasma gondii. The intracellular signaling molecules responsible for the induction of IDO gene expression were investigated by the quantitative polymerase chain reaction. The gene expression was inhibited by a tyrosine kinase inhibitor, genistein. Being consistent with this, IFN-gamma induced increased tyrosine phosphorylation and this was inhibited by genistein. The transcription of IDO gene was not inhibited by protein kinase C (PKC) inhibitors, H-7 and staurosporine, or a calmodulin inhibitor, W-7. Irrelevance of PKC in IDO gene expression was supported by the failure of PMA or PMA + A23187 to induce IDO gene expression. These results all suggest that the tyrosine phosphorylation is a critical event in IFN-gamma-inducible IDO gene expression and PKC is not involved in the gene expression.

Gene Expression Regulation, Enzymologic↗
PubMed1990

Regulation of HLA class II molecule expressions by IFN-gamma. The signal transduction mechanism in glioblastoma cell lines.

We examined the signal transduction mechanism responsible for the IFN-gamma-induced HLA class II molecule expressions on glioblastoma cell lines, T98G and A172. A series of experiments demonstrated that the activation of protein kinase C (PKC) is involved in the DR and DP molecule expressions on T98G cells. In addition to the activation of PKC, calcium influx appeared to be involved in the DR and DP molecule expressions on T98G. Northern blot analyses with actinomycin D or cycloheximide revealed that these second messengers induce the transcription of DRA and B and DPA and B genes without de novo protein synthesis. Furthermore, we examined the region of the DPB gene that is responsible for IFN-gamma-induced gene transcription by gene transfer of a series of 5' and 3' deletion mutants in which the upstream region of the DPB was linked to a reporter gene, chloramphenicol acetyltransferase. By using these deletion mutants, it appeared that the region between -152 and -126 bp contains a critical IFN-gamma-responsive element. Taken together, these results suggest that IFN-gamma activates PKC and stimulates calcium influx, resulting in the induction of transcription of DRA and B and DPA and B genes without de novo protein synthesis. In DPB gene, we speculate that preexiting protein(s) phosphorylated by PKC in the presence of Ca2+ might directly bind or indirectly interact with the region between -152 and -126 bp of the upstream sequence, leading to the induction of the transcription (possibly in concert with other nuclear protein(s) bound to the promoter sequences).

Biological Transport↗
PubMed1989

Radiographic findings and hypotensive reactions in excretory urography.

The radiographic findings and the hypotension patterns were reviewed in 19 patients having hypotensive reactions in routine excretory urography using ionic contrast medium. The lowest systolic blood pressure was above 80 mmHg in 10 patients while below 80 mmHg in remaining 9 patients. The urogram was unremarkable as long as the systolic blood pressure was preserved above 80 mmHg. In 2 patients, whose systolic blood pressure decreased quickly beyond 80 mmHg immediately after injection of contrast medium, the pyelogram was faint or non-visualized. On the other hand, in 4 patients, whose systolic blood pressure decreased beyond 80 mmHg in several minutes after injection of contrast medium and remained under 80 mmHg for more than 20 minutes, the nephrogram was dense and the pyelogram was faint or non-visualized. Although systolic blood pressure decreased beyond 80 mmHg, the urogram was unremarkable in 3 patients. This was due to the delayed hypotension or the short duration of hypotension.

Adolescent↗
PubMed1985

Mesencephalic root fibers of the trigeminal nerve in the cat.

The trigeminal nerve has three motor roots and one sensory root in the cat. One of the motor roots can be divided into two bundles: the larger and the smaller. These motor roots form the common root with the sensory root at the exit from the pons, sometimes being separated partially by the subarachnoidal space between the medial and the ventral part of the common root. The mesencephalic root fibers are observed numerously in all the motor roots. Some degenerated fibers are observed in the sensory root. The transitional zone of the trigeminal nerve root between central and peripheral nervous system is occupied by interlocking processes of the fibrous astrocyte.

Animals↗
PubMed1984

Cholesterol dynamics in rats fed cis- and trans-octadecenoate in the form of triglyceride.

The cholesterol dynamics were compared in rats fed diets containing either camellia oil or partially hydrogenated corn oil as a source of cis- and trans-octadecenoate, respectively. The diets contained approximately the same amount of octadecenoic acid, and an equivalent amount of linoleic acid. In rats fed the trans-fat for about 30 days, liver cholesterol levels were clearly low relative to levels in rats fed the cis-fat, while the concentration of serum cholesterol and the distribution of cholesterol in serum lipoproteins were comparable. The activity of hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase and the incorporation of [I-14C]acetate into digitonin-precipitable sterols in the liver homogenate tended to increase in rats fed the trans-fat diet. Cholesterol 7 alpha-hydroxylase activity increased significantly. Cholesterol absorption measured by the dual isotope serum ratio method was markedly lower, and much more radioactivity both from orally and intravenously administered cholesterol was excreted quickly into feces in the trans-fat group, with relatively more excretion in the neutral than in the acidic steroids. Apparent absorption of dietary fat was slightly lower in the trans-fat group. Cholesterol turnover as analyzed according to the two-pool model was much faster in rats fed trans-fat and the pool A size was reduced mainly as a consequence of stimulation of the removal rate from this pool. The intestinal epithelial cells contained relatively more trans-octadecenoate compared to the serum and liver and trans-fat modified the lipid composition specifically. These observations suggest that the changes in cholesterol metabolism due to the ingestion of trans-fat, compared to cis-fat, are as a result of metabolic events in the intestine.

Absorption↗
PubMed1983

Effects of combined oral contraceptive steroids on pituitary-ovarian function during the menstrual cycle of lactating women.

The object of this study was to investigate the effects of combined oral contraceptives on pituitary-ovarian function during the menstrual cycle of lactating women whose prolactin levels were usually elevated. Five of six lactating women studied were considered to have the normal menstrual cycle which was comparable to the presumptive ovulatory cycle of non-puerperal women. The patterns of serum LH and FSH as well as estradiol and progesterone during the menstrual cycle of lactating women were quantitatively and qualitatively, similar to those of non-puerperal women. Prolactin levels, however, were elevated throughout the cycle of lactating women as compared with those of non-puerperal women. Treatment with combined oral contraceptive steroids abolished a midcycle surge of LH and decreased ovarian steroids during the menstrual cycle of lactating women. Serum prolactin levels were also decreased throughout the cycle treated with contraceptives in lactating women.

Adult↗