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S Kato

Publications and source records attributed to S Kato.

At least 487 records · Page 27Linked to original sources
PubMed1998

A new NEDD8-ligating system for cullin-4A.

NEDD8 is a ubiquitin (Ub)-like protein. Here we report a novel ubiquitinylation-related pathway for modification by NEDD8. NEDD8 was activated by an E1 (Ub-activating enzyme)-like complex, consisting of APP-BP1 and hUba3 with high respective homologies to the amino- and carboxy-terminal regions of E1 and then linked to hUbc12 (a human homolog of yeast Ub-conjugating enzyme Ubc12p). The major target protein modified by NEDD8 was found to be Hs-cullin-4A (Cul-4A), a member of the family of human cullin/Cdc53 proteins functioning as an essential component of a multifunctional Ub-protein ligase E3 complex that has a critical role in Ub-mediated proteolysis.

Amino Acid Sequence↗
PubMed1998

Differential interactions of the C terminus and the cytoplasmic I-II loop of neuronal Ca2+ channels with G-protein alpha and beta gamma subunits. I. Molecular determination.

Interactions of G-protein alpha (Galpha) and beta gamma subunits (Gbeta gamma) with N- (alpha1B) and P/Q-type (alpha1A) Ca2+ channels were investigated using the Xenopus oocyte expression system. Gi3alpha was found to inhibit both N- and P/Q-type channels by receptor agonists, whereas Gbeta1 gamma2 was responsible for prepulse facilitation of N-type channels. L-type channels (alpha1C) were not regulated by Galpha or Gbeta gamma. For N-type, prepulse facilitation mediated via Gbeta gamma was impaired when the cytoplasmic I-II loop (loop 1) was deleted or replaced with the alpha1C loop 1. Galpha-mediated inhibitions were also impaired by substitution of the alpha1C loop 1, but only when the C terminus was deleted. For P/Q-type, by contrast, deletion of the C terminus alone diminished Galpha-mediated inhibition. Moreover, a chimera of L-type with the alpha1B loop 1 gained Gbeta gamma-dependent facilitation, whereas an L-type chimera with the N- or P/Q-type C terminus gained Galpha-mediated inhibition. These findings provide evidence that loop 1 of N-type channels is a regulatory site for Gbeta gamma and the C termini of P/Q- and N-types for Galpha.

Animals↗
PubMed1998

Cloning and characterization of kidney-specific promoter of human PTH/PTHrP receptor gene: absence of mutation in patients with pseudohypoparathyroidism type Ib.

Pseudohypoparathyroidism (PHP) is a heterogeneous disease complex characterized by resistance to parathyroid hormone (PTH). PHP type Ib has been thought to be caused by abnormalities in PTH/PTH-related protein (PTHrP) receptor. However, previous studies have shown no mutation in the coding region of PTH/PTHrP receptor gene in patients with PHP type Ib. Because patients with PHP type Ib do not have Albright's hereditary osteodystrophy, and because resistance to PTH is most prominent in proximal tubules of the kidney, PHP Ib may be caused by a kidney-specific abnormality in PTH/PTHrP receptor. Cloning of 5' region of human PTH/PTHrP receptor gene revealed that there are at least three untranslated exons, U1, U2 and U3. Exons U1 and U2 and the upstream promoter of exon U1 are used in kidney, but not in skin fibroblasts and osteoblastic cells. The upstream region of exon U1 was highly AT-rich and exhibited kidney-specific promoter activity. However, there was no mutation in these kidney-specific promoter regions and untranslated exons in eight patients with PHP type Ib. These results demonstrate that PHP type Ib is not caused by mutations in PTH/PTHrP receptor gene, at least in the examined patients. Identification and characterization of nuclear proteins that bind to kidney-specific promoter region of human PTH/PTHrP receptor may be necessary for the elucidation of pathogenesis of PHP type Ib.

5' Untranslated Regions↗
PubMed1998

Nociceptin receptor-mediated Ca2+ channel inhibition and its desensitization in NG108-15 cells.

It has been shown that the membrane of hybrid NG108-15 neuroblastoma x glioma cells contains a high-affinity binding site for nociceptin. In the present study, we first demonstrated the expression of nociceptin receptor mRNA in NG108-15 cells. Application of nociceptin to NG108-15 cells produced a concentration-dependent (EC50 = 29 nM) inhibition of Ca2+ channel currents in a pertussis toxin-sensitive fashion. This nociceptin-induced inhibition of Ca2+ channel currents was prevented in the presence of omega-conotoxin GVIA, a blocker of the N-type Ca2+ channel, and had both voltage-dependent and -independent components. Prolonged application of nociceptin elicited homologous desensitization of the inhibition with a time constant of 5.3 min. These results indicate that the nociceptin receptor is coupled to the N-type Ca2+ channel via pertussis toxin-sensitive G proteins in NG108-15 cells and that this coupling is associated with rapid and homologous desensitization.

Animals↗
PubMed1998

Molecular mechanism of human CD38 gene expression by retinoic acid. Identification of retinoic acid response element in the first intron.

CD38 is a nonlineage-restricted type II transmembrane glycoprotein possessing ecto-NAD+ glycohydrolase activity. Because of its unique expression pattern in lymphocyte differentiation, it appears to function as an immunoregulatory molecule. We previously reported that CD38 was specifically induced by all-trans-retinoic acid (RA) in human promyelocytic leukemia HL-60 cells. Here we studied the molecular mechanism of the RA-dependent induction of human CD38. The expression of CD38 mRNA by RA appeared to be caused by the transcriptional stimulation of the gene, since it was blocked by an RNA synthesis inhibitor, but not by a protein synthesis inhibitor. In search of the RA response element (RARE) possibly present in human CD38 gene promoter, we isolated and sequenced the genomic DNA covering the 5'-flanking region, exon 1, and partial intron 1. Transient transfection experiments revealed that the responsiveness to RA was conferred through an RARE consisting of two direct repeat TGACCT-like hexamer motifs with a 5-nucleotide spacer, which was located in the first intron rather than the 5'-flanking region of the CD38 gene. This RARE interacted with heterodimer composed of RA receptor and retinoid X receptor in vitro. Thus, the RA-induced expression of the human CD38 gene was demonstrated to be mediated through the RARE located in the first intron.

ADP-ribosyl Cyclase↗
PubMed1998

Synthesis of N-(1-ethyl-4-methylhexahydro-1,4-diazepin-6-yl)nicotinamides and their affinities for 5-HT3 and dopamine D2 receptors.

A series of N-(1-ethyl-4-methylhexahydro-1,4-diazepin-6-yl)nicotinamide derivatives were prepared and evaluated for their binding to 5-HT3 and dopamine D2 receptors. Among them, the 5-bromo-2-methoxy-6-methylaminonicotinamide 16 and its (R)-isomer were found to have potent affinities for both receptors. The affinities of (R)-16 for 5-HT3 and dopamine D2 receptors are approximately 3-fold higher than those of the corresponding benzamide (R)-1 (IC50: 1.1 and 12 nM vs. 2.9 and 35 nM, respectively).

Animals↗
PubMed1998

1alpha,25-dehydroxyvitamin D3 synergism toward transforming growth factor-beta1-induced AP-1 transcriptional activity in mouse osteoblastic cells via its nuclear receptor.

The present study demonstrates 1alpha,25-dehydroxyvitamin D3 (1alpha-25-(OH)2D3) synergism toward transforming growth factor (TGF)-beta1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1alpha-25-(OH)2D3 synergistically stimulated TGF-beta1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. We actually showed by a gel mobility shift assay 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1alpha-25-(OH)2D3 markedly stimulated the transient activity of TGF-beta1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene. Also, a synergistic increase in TGF-beta1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. However, the synergistic CAT activity was inhibited by pretreatment with VDR antisense oligonucleotides. In addition, in a Northern blot assay, we observed 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and also found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. The present study strongly suggests a novel positive regulation by 1alpha-25-(OH)2D3 of TGF-beta1-induced AP-1 activity in osteoblasts via "genomic action."

Animals↗
PubMed1998

A novel isoform of rat estrogen receptor beta with 18 amino acid insertion in the ligand binding domain as a putative dominant negative regular of estrogen action.

A novel isoform of rat estrogen receptor (ER) beta, ER beta 2, which is a putative alternative splicing product of the reported ER beta (ER beta 1) has been identified. Rat ER beta 2 cDNA contains an additional, in-frame 54 base pair insertion in the ligand binding domain of ER beta 1, which generates an 18 amino acid residue insertion. Northern blot and RT-PCR analyses revealed that ER beta 2 coexists with ER alpha and ER beta 1 in all tissues examined including brain, lung, liver, kidney, fat, bone, uterus, prostate, and ovary. The insertion caused loss of ligand binding activity of ER beta 2, whereas the ability to bind the palindromic estrogen response element (ERE) was retained. In an ERE-containing luciferase reporter gene assay using COS-1 cells, ER beta 2 failed to activate estrogen-dependent transcription. Furthermore, ER beta 2 dose dependently suppressed the ER alpha- and ER beta 1-mediated transcriptional activation. These results suggest that rat ER beta 2 functions as a negative regulator of estrogen action.

Alternative Splicing↗
PubMed1998

Detection of lectins using ligand blotting and polyacrylamide-type glycoconjugate probes.

A sensitive and convenient method for detection of the carbohydrate-binding activity of lectins was established using the combination of blotting of lectins on polyvinylidene difluoride membranes, carbohydrate-conjugated biotinylated polyacrylamide-type probes (carbohydrate-bp probes), horseradish peroxidase-streptavidin, and detection by enhanced chemiluminescence of the enzyme reaction. This method was tested for detection of four plant lectins blotted on the membrane: concanavalin A was detectable down to 100 ng by mannose-bp probe, Ricinus communis agglutinin 120 to as low as 5 ng by N-acetyllactosamine-bp probe, soybean agglutinin to 1 microgram by beta-N-acetyl-D-galactosamine-bp probe, and wheat germ agglutinin to 5 ng by beta-N-acetyl-D-glucosamine-bp probe. All four lectins were detectable on an electroblotted membrane after SDS-polyacrylamide gel electrophoresis. This method was used to detect recombinant human galectin-3 in Escherichia coli cell lysates and mannan-binding protein in human serum. These results indicate that this method is widely applicable to convenient detection and characterization of lectins in crude samples.

Acrylic Resins↗
PubMed1998

A putative tumor suppressor, TSG101, acts as a transcriptional suppressor through its coiled-coil domain.

TSG101 is thought as a putative tumor suppressor gene, and mutations of this gene were recently found in 7 of 15 breast cancer patients, though the physiological function remains to be elucidated. In this report, we showed that TSG101 protein acts as a transcriptional suppressor for estrogen receptor (ER) as well as other members of the nuclear hormone receptor super-family, VP16, and on its own. The basal promoter activity was also inhibited by TSG101. The suppression of transcription by TSG101 protein required its coiled-coil domain, which is also shown to be required for the tumor suppressive function. Expressed TSG101 protein did not have any histone acetylase nor deacetylase activity, which certain transcriptional co-factors have. The requirement of the same domain in the TSG101 protein for transcriptional suppression and in the tumor suppression indicates a possibility that transcriptional suppression of TSG101 is related to its tumor suppression.

Acetyltransferases↗
PubMed1998

Inhibition of gastric acid secretion by galanin in rats. Relation to endogenous histamine release.

Inhibitory effect of galanin on basal and secretagogs-stimulated gastric acid secretion was investigated in urethane-anesthetized rats. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and either gastric acid or alkaline secretion was determined by titrating the perfusate. Gastric mucosal blood flow (GMBF) was measured by a laser Doppler flowmeter. Intravenous infusion of galanin dose-dependently inhibited the increase of acid secretion induced by pentagastrin and carbachol but not by histamine, without any influence on the GMBF response. Galanin also reduced basal acid secretion while increasing GMBF, but did not evoke any change in basal gastric alkaline secretion. M15, which is a galanin receptor antagonist in the central nervous system but acts as a full agonist in the gastrointestinal smooth muscle, also suppressed pentagastrin-induced acid secretion, similar to galanin. In addition, pentagastrin increased the release of histamine into the gastric lumen, and this response was significantly inhibited by galanin. These results suggest that the inhibitory effect of galanin on acid secretion is mediated by suppression of endogenous histamine release from enterochromaffin-like cells and that the process may be related to the activation of the same subtype of galanin receptors as in the central nervous system and pancreatic beta-cells.

Animals↗
PubMed1998

Identification and characterization of a novel SH3-domain binding protein, Sab, which preferentially associates with Bruton's tyrosine kinase (BtK).

Protein interaction cloning method was used to identify a novel molecule, Sab, which binds to the SH3 domain of Bruton's tyrosine kinase (Btk), the deficient cytoplasmic tyrosine kinase in human X-linked agammaglobulinemia and murine X-linked immunodeficiency. Immunoprecipitation using the anti-Sab antibody identified the protein product of the gene as a 70 kDa molecule. While Sab does not have a proline-rich sequence, it was shown to bind to Btk through the commonly conserved structure among SH3 domains. Remarkably, Sab exhibited a high preference for binding to Btk rather than to other cytoplasmic tyrosine kinases, which suggests a unique role of Sab in the Btk signal transduction pathway.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Adaptations to chronic agonist exposure of mu-opioid receptor-expressing Chinese hamster ovary cells.

To investigate cellular adaptation responses induced by chronic agonist treatment of the mu-opioid receptor, Chinese hamster ovary (CHO) cells were stably transfected with the rat mu-opioid receptor cDNA. Chronic treatment with agonists selective for the mu-opioid receptor, [D-Ala2, N-MePhe4, Gy-ol5]enkephalin (DAMGO), morphine and fentanyl, time- and dose-dependently induced down-regulation of the mu-opioid receptor. The down-regulation was not significantly affected by pretreatment with pertussis toxin, but was completely blocked by treatment with hypertonic sucrose, suggesting that receptor internalization mediated by clathrin-coated vesicles is an essential step in the mu-opioid receptor down-regulation. On the other hand, forskolin-stimulated cyclic AMP formation was increased by chronic DAMGO treatment, which was inhibited by pertussis toxin pretreatment. These results indicate that two adaptation responses induced by chronic agonist treatment of the mu-opioid receptor-expressing CHO cells, down-regulation of the mu-opioid receptor and supersensitization of adenylate cyclase, are mediated by distinct mechanisms.

Animals↗
PubMed1998

A novel series of N-(hexahydro-1,4-diazepin-6-yl) and N-(hexahydroazepin- 3-yl)benzamides with high affinity for 5-HT3 and dopamine D2 receptors.

A novel series of benzamides with a hexahydro-1,4-diazepine or hexahydroazepine ring in the amine moiety were prepared, and their binding affinities for 5-HT3 and dopamine D2 receptors were evaluated. The R isomer of the 1-ethyl-4-methylhexahydro-1,4-diazepinylbenzamide (R)-22 had potent affinity for both receptors. The R-enantiomer of the corresponding 1-ethylhexahydroazepinylbenzamide 28 showed potent affinity for dopamine D2 receptors with reduced affinity for 5-HT3 receptors, while the S isomer was found to be a potent and selective 5-HT3 receptor antagonist.

Animals↗
PubMed1998

Inactivating mutations in the 25-hydroxyvitamin D3 1alpha-hydroxylase gene in patients with pseudovitamin D-deficiency rickets.

BACKGROUND: Pseudovitamin D-deficiency rickets is characterized by the early onset of rickets with hypocalcemia and is thought to be caused by a deficit in renal 25-hydroxyvitamin D3 1alpha-hydroxylase, the key enzyme for the synthesis of 1alpha,25-dihydroxyvitamin D3. METHODS: We cloned human 25-hydroxyvitamin D3 1alpha-hydroxylase complementary DNA (cDNA) using a mouse 1alpha-hydroxylase cDNA fragment as a probe. Its genomic structure was determined, and its chromosomal location was mapped by fluorescence in situ hybridization. We then identified mutations in the 1alpha-hydroxylase gene in four unrelated patients with pseudovitamin D-deficiency rickets by DNA-sequence analysis. Both the normal and the mutant 1alpha-hydroxylase proteins were expressed in COS-1 cells and were assayed for 1alpha-hydroxylase activity. RESULTS: The gene for 25-hydroxyvitamin D3 1alpha-hydroxylase was mapped to chromosome 12q13.3, which had previously been reported to be the locus for pseudovitamin D-deficiency rickets by linkage analysis. Four different homozygous missense mutations were detected in this gene in the four patients with pseudovitamin D-deficiency rickets. The unaffected parents and one sibling tested were heterozygous for the mutations. Functional analysis of the mutant 1alpha-hydroxylase protein revealed that all four mutations abolished 1alpha-hydroxylase activity. CONCLUSIONS: Inactivating mutations in the 25-hydroxyvitamin D3 1alpha-hydroxylase gene are a cause of pseudovitamin D-deficiency rickets.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1998

Possible involvement of protein kinase C in apoptotic cell death of macrophages infected with Actinobacillus actinomycetemcomitans.

We have previously reported the evidence for apoptosis in the mouse macrophage cell line J774.1 by the periodontopathic bacterium Actinobacillus actinomycetemcomitans. In this study, we examined the role of protein kinases in the induction of apoptosis in A. actinomycetemcomitans-infected J774.1 cells by the MTT assay, fluorescence microscopy and flow cytometric analysis. After J774.1 cells were precultured with protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), J774.1 cells infected with A. actinomycetemcomitans showed the increased percentage of apoptotic cells. On the contrary, protein kinase A (PKA) activators, such as forskolin and dibutyryl cAMP, do not mimic the effect of PMA. PKC inhibitors, such as staurosporine, calphostin C, chelerythrine chloride, and H7 were found to suppress apoptotic cell death in J774.1 cells infected with A. actinomycetemcomitans. However, HA1004, known as PKA inhibitor, had no effect on apoptosis in infected macrophages. The results presented here suggest that the signals through PKC may play crucial roles in the modulation of apoptosis in macrophages infected with A. actinomycetemcomitans.

Aggregatibacter actinomycetemcomitans↗
PubMed1998

Necessity of endogenous GTP derived from glucose-6-phosphate for insulin secretion augmented by glucose under protein kinase A activation.

To investigate the possible involvement of some intracellular metabolic signaling other than the ATP derived from glucose metabolism under protein kinase A (PKA) activation, we measured the insulin secretory capacity stimulated by glucose and other fuel secretagogues using diazoxide-treated pancreatic islets. Under these conditions, we found a signal from a site proximal to glyceraldehyde-3-phosphate (GA-3-P) in the glycolysis to be necessary for glucose-induced insulin secretion. By using several different glycolytic enzyme inhibitors, we found that this proximal signal is derived from glucose-6-phosphate (G-6-P), and that metabolic signaling distal to GA-3-P also is necessary. Mycophenolic acid completely inhibited the augmented glucose-induced insulin secretion, which guanosine could reverse, indicating that the proximal signaling is coupling with endogenous GTP production. In this novel system of metabolic signaling, endogenous GTP derived from G-6-P in the glycolysis elicits the augmentation of glucose-induced insulin secretion under PKA activation in diazoxide-treated pancreatic islets.

Animals↗