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Biomedical subjects

Y Yamamoto

Publications and source records attributed to Y Yamamoto.

At least 145 records · Page 8Linked to original sources
PubMed2001

The tamoxifen-responsive estrogen receptor alpha mutant D351Y shows reduced tamoxifen-dependent interaction with corepressor complexes.

The effects of estrogen and anti-estrogen are mediated through the estrogen receptors ERalpha and beta, which function as ligand-induced transcriptional factors. The nonsteroidal anti-estrogen tamoxifen is the most commonly used endocrine in the treatment of all stages of breast cancer in both pre- and postmenopausal women. Several lines of evidence have indicated that tamoxifen promotes association between ERalpha and corepressors N-CoR or silencing mediator for retinoid and thyroid hormone receptor (SMRT). Our results indicate that N-CoR/SMRT recognize and interact with helices H3 and H5 of the ERalpha ligand-binding domain in a 4-hydroxy tamoxifen-dependent manner. The mutant ERalpha(D351Y), derived from a tamoxifen-stimulated tumor and containing an amino acid substitution at position 351 within H3, showed reduced interaction with N-CoR/SMRT and high tamoxifen-induced activation function-1 (AF-1) activity. While the estradiol-dependent transcriptional activity of ERalpha(D351Y) was almost equal to that of wild-type ERalpha, the mutant exhibited higher levels of transcriptional activity in the presence of both E2 and 4-hydroxy tamoxifen compared with wild-type ERalpha. These results may explain the observation that the growth of tumor cells expressing ERalpha(D351Y) can be stimulated by tamoxifen, E2, or both.

Amino Acid Sequence↗
PubMed2001

Regulation of beta-catenin function by the IkappaB kinases.

Both the beta-catenin and the nuclear factor kappaB (NF-kappaB) proteins are important regulators of gene expression and cellular proliferation. Two kinases, IKKalpha and IKKbeta, are critical activators of the NF-kappaB pathway. Here we present evidence that these kinases are also important in the regulation of beta-catenin function. IKKalpha- and IKKbeta-deficient mouse embryo fibroblasts exhibited different patterns of beta-catenin cellular localization. IKKbeta decreases beta-catenin-dependent transcriptional activation, while IKKalpha increases beta-catenin-dependent transcriptional activity. IKKalpha and IKKbeta interact with and phosphorylate beta-catenin using both in vitro and in vivo assays. Our results suggest that differential interactions of beta-catenin with IKKalpha and IKKbeta may in part be responsible for regulating beta-catenin protein levels and cellular localization and integrating signaling events between the NF-kappaB and Wingless pathways.

Animals↗
PubMed2001

Intercellular electrical communication among smooth muscle and endothelial cells in guinea-pig mesenteric arterioles.

1. Current clamp studies using two patch electrodes and morphological observations have been performed in guinea-pig mesenteric arterioles to evaluate intercellular electrical couplings. 2. In electron micrographs, preparations were found to have a single layer of smooth muscle cells. Typical gap junctions were readily observed between endothelial cells only. 3. While immunoreactivity to connexin 40 was strongly expressed on the membranes of endothelial cells only, that to connexin 43 was expressed on both smooth muscle and endothelial cell membranes. 4. Neurobiotin injected into a smooth muscle cell diffused into several neighbouring smooth muscle cells while that injected into an endothelial cell diffused into many endothelial cells. 5. Acetylcholine-induced hyperpolarizations were conducted from endothelial cells to smooth muscle cells with a relative amplitude of 80.1 %. Ba(2+)-induced action potentials were conducted in the opposite direction with a relative amplitude of 92.4 %. 6. An electrotonic potential produced in a smooth muscle cell by current injection diminished steeply with distance as it spread along the muscle layer, plateauing at distances beyond 25 microm. An electrotonic potential produced in an endothelial cell spread within the intima with virtually no reduction. Electrotonic potentials could conduct through myoendothelial couplings, which seemed to behave as ohmic resistors without rectification. 7. The coupling resistance between adjacent smooth muscle cells was estimated to be at least 90 MOhms and that between a smooth muscle cell and the whole endothelial layer to be 0.9 GOhms. 8. The results indicate that although the resistance of myoendothelial couplings is appreciable, the endothelium may be important as a low resistance path connecting many smooth muscle cells.

Animals↗
PubMed2001

Purification and characterization of N-acetylglucosaminyl sulfotransferase from chick corneas.

N-Acetylglucosaminyl(GlcNAc) sulfotransferase, which transfers sulfate from adenosine 3'-phosphate 5'-phosphosulfate to GlcNAc at the nonreducing end of oligosaccharides, was purified 887-fold with a 8.4% yield from 2-day-old chick corneas by chromatography on CM-Sepharose, WGA-agarose, GlcNAc-agarose, and 3',5'-ADP-agarose columns. The purified enzyme has an optimum pH of 6.0 (Mes buffer) and specifically transfers a sulfate to GlcNAc at the nonreducing end but not to internal GlcNAc. The enzyme was stimulated by protamine and Mn(2+). SDS-polyacrylamide gel electrophoresis of the purified enzyme still showed two main bands (66 and 55 kDa) with some minor bands. It appears that this enzyme competes with beta-galactosyltransferase in binding to the nonreducing GlcNAc residue on KS synthesis; this suggests that the sulfation of the GlcNAc residue is coupled with the elongation of the KS chain.

Animals↗
PubMed2001

IKKgamma /NEMO facilitates the recruitment of the IkappaB proteins into the IkappaB kinase complex.

IKKgamma/NEMO is an essential regulatory component of the IkappaB kinase complex that is required for NF-kappaB activation in response to various stimuli including tumor necrosis factor-alpha and interleukin-1beta. To investigate the mechanism by which IKKgamma/NEMO regulates the IKK complex, we examined the ability of IKKgamma/NEMO to recruit the IkappaB proteins into this complex. IKKgamma/NEMO binding to wild-type, but not to a kinase-deficient IKKbeta protein, facilitated the association of IkappaBalpha and IkappaBbeta with the high molecular weight IKK complex. Following tumor necrosis factor-alpha treatment of HeLa cells, the majority of the phosphorylated form of endogenous IkappaBalpha was associated with the high molecular weight IKK complex in HeLa cells and parental mouse embryo fibroblasts but not in IKKgamma/NEMO-deficient cells. Finally, we demonstrate that IKKgamma/NEMO facilitates the association of the IkappaB proteins and IKKbeta and leads to increases in IKKbeta kinase activity. These results suggest that an important function of IKKgamma/NEMO is to facilitate the association of both IKKbeta and IkappaB in the high molecular weight IKK complex to increase IkappaB phosphorylation.

Animals↗
PubMed2001

Characterization of alpha1-adrenoceptor-mediated contraction in the mouse thoracic aorta.

In the mouse thoracic aorta, noradrenaline, adrenaline, phenylephrine and methoxamine behaved as full agonists. The pA(2) values for 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9-dione dihydrochloride (BMY 7378) against each agonist were in good agreement with the generally accepted affinity value of alpha(1D)-adrenoceptors. 5-Methylurapidil, 2-[2,6-dimethoxyphenoxyethyl]aminomethyl-1,4-benzodioxane hydrochloride (WB 4101) and prazosin inhibited the contraction in response to noradrenaline. A significant correlation was obtained between the antagonist affinities in mouse thoracic aorta and those of native alpha(1D)-adrenoceptors in rat thoracic aorta or with those of cloned alpha(1d)-adrenoceptors, but not with those for either alpha(1a)- or alpha(1b)-adrenoceptors. Buspirone behaved as a partial agonist in mouse thoracic aorta, the contraction of which was antagonized by BMY 7378 with a pA(2) value (8.49) consistent with that found against noradrenaline (8.43). Clonidine acted as a partial agonist (pD(2)=5.94). The pK(p) value for clonidine against noradrenaline was similar to the pD(2) value for clonidine. The apparent pK(B) value for BMY 7378 against clonidine was similar to the pA(2) value against other full agonists used in the present study. These results suggest that the alpha(1D)-adrenoceptor subtype exists, and that the full agonists and the partial agonists evoke the contraction mediated through the alpha(1D)-adrenoceptor in mouse thoracic aorta.

Adrenergic alpha-Agonists↗
PubMed2001

Ruthenium(II)-catalyzed isomer-selective cyclization of 1,6-dienes leading to exo-methylenecyclopentanes: unprecedented cycloisomerization mechanism involving ruthenacyclopentane(hydrido) intermediate.

In the presence of a catalytic amount of ruthenium(II) complexes, [RuCl(2)(cod)](n)(), RuCl(2)(cod)(MeCN)(2), [RuCl(2)(nbd)](n)(), [RuCl(2)(CO)(3)](2), and Cp*Ru(cod)Cl, 1,6-dienes were effectively converted into the corresponding exo-methylenecyclopentanes in good to excellent yields with good isomer purity in i-PrOH at 90 degrees C. The alcoholic solvent was essential for the present catalytic cyclization, and the efficiency increased in the following order: t-BuOH << EtOH < or = i-PrOH. In contrast, a Ru(0) complex, (C(6)Me(6))Ru(cod), catalyzed the cycloisomerization only in 1,2-dichloroethane. The unusual isomer-selectivity occurred when a 1,7-octadiene was subjected to cyclization to give a similar exo-methylenecyclopentane isomer as the major product. The identical isomer selectivity was observed for the cyclization of unsymmetrical 1,6-dienes having one terminal- and one internal-alkene termini. On the basis of the results from the studies using the known ruthenium hydrides and deuterium-labeling substrates, the novel mechanism via the Ru(II) <--> Ru(IV) system involving a ruthenacyclopentane(hydrido) intermediate was proposed, which better explains the particular regiochemistry of the present cyclization than other previous mechanisms.

Journal Article↗
PubMed2001

Behavioral-independent features of complex heartbeat dynamics.

We test whether the complexity of the cardiac interbeat interval time series is simply a consequence of the wide range of scales characterizing human behavior, especially physical activity, by analyzing data taken from healthy adult subjects under three conditions with controls: (i) a "constant routine" protocol where physical activity and postural changes are kept to a minimum, (ii) sympathetic blockade, and (iii) parasympathetic blockade. We find that when fluctuations in physical activity and other behavioral modifiers are minimized, a remarkable level of complexity of heartbeat dynamics remains, while for neuroautonomic blockade the multifractal complexity decreases.

Activities of Daily Living↗
PubMed2001

Novel, potent, and selective phosphodiesterase 5 inhibitors: synthesis and biological activities of a series of 4-aryl-1-isoquinolinone derivatives.

A novel class of potent and selective phosphodiesterase 5 (PDE5) inhibitors, 4-aryl-1-isoquinolinone derivatives, which have been designed by the comparison of the structure of cGMP and a previously reported 1-arylnaphthalene lignan, was disclosed. Among these compounds, methyl 2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridinylmethoxy)-4-(3,4,5-trimethoxyphenyl)-3-isoquinoline carboxylate dihydrochloride (36a) exhibited potent PDE5 inhibitory activity (IC(50) = 1.0 nM) with high isozyme selectivities (IC(50) ratio: PDE1/PDE5 = 1300, PDE2/PDE5 > 10 000, PDE3/PDE5 > 10 000, PDE4/PDE5 = 4700, PDE6/PDE5 = 28). Compound 36a also showed the most potent relaxant effect on isolated rabbit corpus cavernosum (EC(30) = 7.9 nM). Compound 63 (T-1032), the sulfate form of 36a, was selected for further biological and pharmacological evaluation of erectile dysfunction.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2001

Histamine production by cultured microglial cells of the mouse.

We previously reported that cells other than mast cells or neurons could synthesize histamine in response to lipopolysaccharide (LPS) or interleukin 1beta in the rat brain. To identify the responsible cells, we examined histidine decarboxylase (HDC) activity and the expression of HDC mRNA in GMI 6-3 mouse microglial cells. Both the activity and mRNA for HDC in GMI 6-3 cells were induced by LPS treatment, and the induction was sensitive to calmodulin-dependent kinase II inhibitor, KN62. These findings indicate that microglia is a third cell type producing histamine in the brain.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed2001

Amino acids and peptides. Part 39: a bivalent poly(ethylene glycol) hybrid containing an active site (RGD) and its synergistic site (PHSRN) of fibronectin.

Fibronectin contains the active sequence Arg-Gly-Asp (RGD), along with its synergic site Pro-His-Ser-Arg-Asn (PHSRN). However, the PHSRN peptide does not show synergic activity when it is mixed with the RGD peptide, indicating that a spatial array between RGD and PHSRN in fibronectin may be necessary for synergic activity. Here, we have used an amino acid type poly(ethylene glycol) derivative (aaPEG) to design a bivalent PEG hybrid of fibronectin active peptides. We prepared the aaPEG hybrid peptides PHSRN-aaPEG, aaPEG-RGD, and PHSRN-aaPEG-RGD, and tested their biological activity. Whereas aaPEG-RGD promoted cell spreading activity, PHSRN-aaPEG had no activity. The PHSRN-aaPEG-RGD hybrid strongly promoted cell spreading compared with aaPEG-RGD. These results suggest that the PHSRN sequence in the PHSRN-aaPEG-RGD molecule synergistically enhances the cell spreading activity of the RGD sequence, and that the bivalent aaPEG hybrid method may be useful for conjugating functionally active peptides.

Amino Acid Motifs↗
PubMed2001

Heat shock restores insulin secretion after injury by nitric oxide by maintaining glucokinase activity in rat islets.

Heat shock protein (hsp), including hsp70, has been reported to restore the glucose-induced insulin release suppressed by nitric oxide (NO). However, the mechanism underlying this recovery remains unclear. In the present study, we examine the effects, in rat islets, of heat shock on insulin secretion inhibited by a small amount of NO and also on glucose metabolism, the crucial factor in insulin release. Exposure to a higher dose (15 U/ml) of interleukin-1beta (IL-1beta) abolished the insulin release by stimulation of glucose or KCl in both control and heat shocked islets. In rat islets exposed to a lower dose (1.5 U/ml) of IL-1beta, insulin secretion in response to glucose, but not to glyceraldehydes (GA), ketoisocaproate (KIC), or KCl, was selectively impaired, concomitantly with lower ATP concentrations in the presence of 16.7 mM glucose, while such suppression of insulin secretion and ATP content was not observed in heat shock-treated islets. NO production in islets exposed to 1.5 U/ml IL-1beta was significantly, but only partly, decreased by heat shock treatment. The glucose utilization rate measurement using [5-3H]-glucose and [2-3H]-glucose and the glucokinase activity in vitro were reduced in islets treated with 1.5 U/ml IL-1beta. In heat shock-treated islets, glucose utilization and glucokinase activity were not affected by 1.5 U/ml IL-1beta. These data suggest that heat shock restores glucose-induced insulin release inhibited by NO by maintaining glucokinase activity and the glucose utilization rate in islets in addition to reducing endogenous NO production.

Animals↗
PubMed2001

Diastereoselective inter- and intramolecular pinacol coupling of aldehydes promoted by monomeric titanocene(II) complex Cp(2)TiPh.

A monomeric titanocene(III) derivative, Cp(2)TiPh, effectively promoted the pinacol coupling of both an aromatic aldehyde, benzaldehyde, and an aliphatic aldehyde, 3-phenylpropionaldehyde. The same reactive complex was successfully generated by a catalytic amount of a precursor, Cp(2)Ti(Ph)Cl, and its stoichiometric amount of Zn. The Cp(2)TiPh-catalyzed pinacol coupling of benzaldehyde derivatives and aliphatic aldehydes afforded the corresponding 1,2-diols in high yields with moderate to good threo-selectivity. On the other hand, Cp(2)TiPh-catalyzed pinacol cyclization of dials gave cyclic 1,2-diols with excellent diastereoselectivity. The extension of this protocol to chiral dials demonstrated that the phenyltitanium complex catalytically transmitted an axial chirality or a central chirality of the starting dials to the central chirality of the resultant 1,2-diols.

Journal Article↗
PubMed2001

Radiolytic and thermal dechlorination of organic chlorides adsorbed on molecular sieve 13X.

Reductive dechlorination of chlorobenzene (PhCl), trichloroethylene (TCE), tetrachloroethylene (PCE), 1- and 2-chlorobutanes, chloroform, carbon tetrachloride, and 1,1,1- and 1,1,2-trichloroethanes adsorbed on molecular sieve 13X was investigated. The molecular sieve adsorbing the organic chlorides was irradiated with gamma-rays, heated, or allowed to stand at room temperature in a sealed ampule and was then soaked in water. The dechlorination yields were determined from the Cl- concentrations of the supernatant aqueous solutions. It was found that the chlorinated alkanes adsorbed on the molecular sieve are readily dechlorinated on standing at room temperature. The dechlorination at room temperature was limited for TCE and PCE. PhCl was quite stable even at 200 degrees C. gamma-Radiolysis was examined for PhCl, TCE, and PCE at room temperature. The radiation chemical yields of the dechlorination, G(Cl-), were 1.9, 40, and 30 for PhCl, TCE, and PCE, respectively. After 5 h of heating at 200 degrees C, the dechlorination yields for TCE and PCE were 24.5 and 4.3%, respectively. TCE is much more reactive than PCE in the thermal dechlorination, whereas their radiolytic dechlorination yields are comparable. The pH of the supernatant solutions decreased along with the dechlorination.

Adsorption↗