Biomedical subjects

A Yamaguchi

Publications and source records attributed to A Yamaguchi.

At least 217 records · Page 12Linked to original sources

PubMed1998

[Recent advances in researches on bone formation--role of BMP in bone formation].

Recent advances in action of bone morphogenetic protein (BMP), a member of TGF-beta superfamily, in the differentiation process of mesenchymal cells such as osteoblasts, chondrocytes, bone marrow stromal cells and muscle cells have been reviewed. BMPs induce osteoblast differentiation of various types of cells including undifferentiated mesenchymal cells, bone marrow stromal cells and preosteoblasts. BMPs not only inhibit myogenic differentiation but also convert differentiation pathway of some myogenic cells into an osteoblast lineage. The regulatory mechanism of BMP action discovered in the process of early embryogenesis is also reviewed; noggin, chordin and follistatin inhibit BMP action by specifically binding to BMPs.

Bone Morphogenetic Proteins↗

PubMed1998

[Expression of variant CD44 in colorectal cancer and its relationship to liver metastasis].

A number of different isoforms of CD44 generated by alternative splicing have been isolated and sequenced. There have been several reports that CD44v plays a role in the steps of the metastatic process. We examined the role of the variant CD44v8-10 in metastases of human colon cancer cell line HT29m using a monoclonal antibody reactive with the v9 product (mAb 44-1V). Pretreatment with mAb 44-1V prevented the formation of liver metastases. In addition, we found that the attachment of HT29m cells to the basement membrane matrix was inhibited by mAb 44-1V. Several reports have shown correlations between metastatic potential and expression of CD44v in human colorectal cancer. We demonstrated that CD44v8-10 and CD44v6 RNA expression was higher in carcinomas associated with liver metastases than in those without by Northern blotting. We analyzed the expression of the CD44v8-10 product in colorectal cancer immunohistochemically using mAb 44-1V, and evaluated its prognostic significance. There were significant correlations between CD 44v8-10 immunoreactivity and both lymph node and liver metastases. Patients with CD44v8-10-positive tumors had a greater relative risk of death compared with those whose tumors were CD44v8-10 negative. These results suggest that CD44v8-10 may play an important role in the adhesion of tumor cells to the capillaries of distant organs in the metastatic process, and that immunohistochemical detection of CD44v8-10 may be a biologic marker of prognostic significance.

Animals↗

PubMed1998

[Angiographic diagnosis and management of bleeding from the digestive organs].

Gastrointestinal bleeding is recently seen less often by the angiographer. This is mainly due to advances in endoscopy, and nuclear medicine. When patients with gastrointestinal bleeding are referred, endoscopic diagnosis and therapy should be performed at first. However, when it is impossible to diagnose or to control the bleeding, angiography must be considered as soon as possible. Intra-abdominal bleeding should be diagnosed by angiography at first. In both cases, embolization is generally safe and effective depending on the advance of occlusive agents.

Angiography↗

PubMed1997

Second-site suppressor mutations for the Arg70 substitution mutants of the Tn10-encoded metal-tetracycline/H+ antiporter of Escherichia coli.

The positive charge of the Arg70 residue in the cytoplasmic loop of the Tn10-encoded metal-tetracycline/H+ antiporter (Tet(B)) of Escherichia coli is essential for the tetracycline transport function (Y. Someya and A. Yamaguchi, Biochemistry 35, 9385-9391 (1996)). In this study, we found that the R70A mutation was suppressed by the second-site mutation of Thr171 to Ser. The T171S mutation suppressed any mutations at position 70 regardless of the amino acid residue introduced. The R70A and R70C mutations were also suppressed by the T171A or T171C mutations, but not by the T171Y mutation, indicating that the decrease in the side chain volume at position 171 is essential for the suppression. Tetracycline transport activity of the R70C mutant was stimulated by Hg2+ because mercaptide formed between the SH group of Cys70 and Hg2+ worked as a functional positively-charged side chain. The activity of the R70A/R71C/T171S mutant was also stimulated by Hg2+, whereas those of the R70A/R71C, R71C, and R71C/T171S mutants were not, indicating that the T171S mutation causes the switching of the functional positive charge at position 70 to 71. Since Thr171 is in the middle of the transmembrane helix VI, the switching may be based on a remote conformational effect.

Anti-Bacterial Agents↗

PubMed1997

Roles of acidic residues in the hydrophilic loop regions of metal-tetracycline/H+ antiporter Tet(K) of Staphylococcus aureus.

Three transmembrane glutamic acid residues play essential roles in the metal-tetracycline/H+ antiporter Tet(K) of Staphylococcus aureus [Fujihira et al., FEBS Lett. 391 (1996) 243-246]. In the putative hydrophilic loop region of the Tet(K) and Tet(L) proteins, six acidic residues are conserved. Asp74, Asp200, Asp318 and Glu381 are located on the putative cytoplasmic side, and Asp39 and Glu345 on the putative periplasmic side. These residues were replaced by a neutral amino acid residue or a charge-conserved one. In contrast to the transmembrane glutamic acid residues, the replacement of the two glutamic acid residues (Glu345 and Glu381) did not affect the tetracycline resistance level. Out of the other four aspartic acid residues, the only essential residue is Asp318, any replacement of which resulted in complete loss of the tetracycline resistance and transport activity. Asp318 is located in cytoplasmic loop 10-11 in the putative 14-transmembrane-segment topology of Tet(K). In the case of the tetracycline exporters of Gram-negative bacteria, the only essential acidic residue in the cytoplasmic loop region is located in loop 2-3 [Yamaguchi et al., Biochemistry 31 (1992) 8344-8348]. It may be a general role for tetracycline efflux proteins that three transmembrane and one cytoplasmic acidic residues are mandatory for the tetracycline transport function.

Amino Acid Sequence↗

PubMed1997

An Eps homology (EH) domain protein that binds to the Ral-GTPase target, RalBP1.

Ral proteins constitute a family of small GTPases that can be activated by Ras in cells. In the GTP-bound state, Ral proteins bind to RalBP1, a GTPase-activating protein for CDC42 and Rac GTPases. We have used the two-hybrid system in yeast to clone a cDNA for a novel approximately 85-kDa protein that can bind to an additional site on RalBP1. This newly identified protein contains an Eps homology (EH) domain, which was first detected in the epidermal growth factor (EGF) receptor substrate Eps15. Recently, the EH domain of Eps15 has been shown to bind to proteins containing an asparagine-proline-phenylalanine motif. Moreover, EH domains have been found in proteins involved in endocytosis and/or actin cytoskeleton regulation. The RalBP1 associated Eps-homology domain protein, Reps1, is tyrosine-phosphorylated in response to EGF stimulation of cells. In addition, Reps1 has the capacity to form a complex with the SH3 domains of the adapter proteins Crk and Grb2, which may link Reps1 to an EGF-responsive tyrosine kinase. Thus, Reps1 may coordinate the cellular actions of activated EGF receptors and Ral-GTPases.

Amino Acid Sequence↗

PubMed1997

Induction of osteogenic differentiation by hedgehog proteins.

In this study we asked whether members of the hedgehog gene family are involved in osteogenesis. C3H10T1/2 cells and MC3T3-E1 cells expressed the putative hedgehog receptor patched (Ptc) gene. Medium conditioned by chicken embryo fibroblast cultures expressing either Indian hedgehog or Sonic hedgehog stimulated alkaline phosphatase (APase) activity in cultures of the mouse mesenchymal cell line C3H10T1/2 and the osteoblastic cell line MC3T3-E1. These stimulatory effects were synergistically enhanced by bone morphogenetic protein-2 (BMP-2). Treatment with the amino-terminal portion of recombinant Sonic hedgehog proteins (rShh-N) up-regulated the expression of the Ptc gene within 12 h and increased production of APase in C3H10T1/2. rShh-N and BMP-2 also synergistically stimulated APase activity. rShh-N treatment did not affect the expression levels of Bmp-2, -4, -5, -6 and -7 genes. These findings indicate that hedgehog proteins directly act on osteogenic precursor cells and osteoblasts and stimulate osteogenic differentiation of these cells in co-operation with BMPs.

3T3 Cells↗

PubMed1997

Early song-deprivation affects the expression of protein kinase C in the song control nuclei of the zebra finch during a sensitive period of song learning.

Male zebra finches learn to imitate a tutor's song through auditory and motor learning during a sensitive period. The molecular aspects of auditory-dependent learning was investigated using protein kinase C (PKC) as a molecular marker for synaptic plasticity. We found a transient increase in the expression of PKC in the robust nucleus of the archistriatum (RA) during a sensitive period. Furthermore, both early deafening by cochlea removal and song deprivation inhibited the increase of PKC enzyme activity. The results strongly suggest that PKC is an important enzyme related to the synaptic plasticity of RA neurons during a sensitive period of song learning in the zebra finch.

Animals↗

PubMed1997

Mechanism of action of E7010, an orally active sulfonamide antitumor agent: inhibition of mitosis by binding to the colchicine site of tubulin.

E7010 (N-[2-[(4-hydroxyphenyl)amino]-3-pyridinyl]-4-methoxybenzenesulfonami de), an orally active sulfonamide antitumor agent that is currently in a Phase I clinical trial, showed rather consistent growth-inhibitory activities against a panel of 26 human tumor cell lines (IC50 = 0.06-0.8 microg/ml), in contrast to vincristine (VCR; IC50 = 0.0002-0.04 microg/ml), 5-fluorouracil (IC50 = 0.2-30 microg/ml), Adriamycin (IC50 = 0.002-0.7 microg/ml), mitomycin C (IC50 = 0.007-3 microg/ml), 1-beta-D-arabinofuranoxylcytosine (IC50 = 0.005 to >30 microg/ml), camptothecin (IC50 = 0.002-0.4 microg/ml), and cisplatin (IC50 = 0.5-20 microg/ml). It caused a dose-dependent increase in the percentage of mitotic cells in parallel with a decrease in cell proliferation, like VCR. It also showed a dose-dependent inhibition of tubulin polymerization, which correlated well with the cell growth-inhibitory activity. 14C-labeled E7010 bound to purified tubulin, and this binding was inhibited by colchicine but not by VCR. However, its binding properties were different from those of colchicine, as well as those of VCR. E7010 was active against two kinds of VCR-resistant P388 cell lines, one of which showed multidrug resistance due to the overexpression of P-glycoprotein (resistant to Taxol), and the other did not show multidrug resistance (sensitive to Taxol). Furthermore, four E7010-resistant P388 cell lines showed no cross-resistance to VCR, a different pattern of resistance to podophyllotoxin, and collateral sensitivity to Taxol. Therefore, E7010 is a novel tubulin-binding agent that has a wider antitumor spectrum than VCR and has different properties from those of VCR or Taxol.

Aminophenols↗

PubMed1997

A novel compound, 1,1-dimethyl-5(1-hydroxypropyl)-4,6,7-trimethylindan, is an effective inhibitor of the tet(K) gene-encoded metal-tetracycline/H+ antiporter of Staphylococcus aureus.

A novel indan derivative, 1,1-dimethyl-5-(1-hydroxypropyl)-4,6,7-trimethylindan (Ro 07-3149), was found to be a strong inhibitor of the tet(K) gene-encoded tetracycline/H+ antiporter of Staphylococcus aureus. One micromole of this compound per mg membrane protein was enough for complete inhibition of the Tet(K)-mediated tetracycline transport and tetracycline-coupled proton transport, without the energy state of the membrane being affected. The mode of inhibition was non-competitive. Although this compound caused membrane de-energization at a high concentration, the IC50 value for de-energization (7.3 micromol/mg membrane protein) was about 17 times and 33 times higher than the values for Tet(K)-mediated proton/tetracycline antiport and [3H]tetracycline transport, respectively, indicating that the inhibitory action of Ro 07-3149 is not due to the uncoupling effect of the inhibitor.

Antiporters↗

PubMed1997

Parathyroid hormone exerts disparate effects on osteoblast differentiation depending on exposure time in rat osteoblastic cells.

It has been reported that PTH exerts bone-forming effects in vivo when administered intermittently. In the present study, the anabolic effects of PTH(1-34) on osteoblast differentiation were examined in vitro. Osteoblastic cells isolated from newborn rat calvaria were cyclically treated with PTH(1-34) for the first few hours of each 48-h incubation cycle. When osteoblastic cells were intermittently exposed to PTH only for the first hour of each 48-h incubation cycle and cultured for the remainder of the cycle without the hormone, osteoblast differentiation was inhibited by suppressing alkaline phosphatase activity, bone nodule formation, and mRNA expression of alkaline phosphatase, osteocalcin, and PTH/PTHrP receptor. Experiments using inhibitors and stimulators of cAMP/protein kinase A (PKA) and Ca2+/PKC demonstrated that cAMP/PKA was the major signal transduction system in the inhibitory action of PTH. In contrast, the intermittent exposure to PTH for the first 6 h of each 48-h cycle stimulated osteoblast differentiation. Both cAMP/ PKA and Ca2+/PKC systems appeared to be involved cooperatively in this anabolic effect. Continuous exposure to PTH during the 48-h incubation cycle strongly inhibited osteoblast differentiation. Although both cAMP/PKA and Ca2+/PKC were involved in the effect of continuous exposure to PTH, they appeared to act independently. A neutralizing antibody against IGF-I blocked the stimulatory effect on alkaline phosphatase activity and the expression of osteocalcin mRNA induced by the 6-h intermittent exposure. The inhibitory effect induced by the 1-h intermittent exposure was not affected by anti-IGF-I antibody. These results suggest that PTH has diverse effects on osteoblast differentiation depending on the exposure time in vitro mediated through different signal transduction systems. These in vitro findings explain at least in part the in vivo action of PTH that varies with the mode of administration.

Alkaline Phosphatase↗

PubMed1997

Remote conformational effects of the Gly-62 --> Leu mutation of the Tn10-encoded metal-tetracycline/H+ antiporter of Escherichia coli and its second-site suppressor mutation.

Substitution of Gly-62 of the Tn10-encoded metal-tetracycline/H+ antiporter caused a functional defect corresponding to the volume of the substituent [Yamaguchi, A., Someya, Y., and Sawai, T. (1992) J. Biol. Chem. 267, 19155-19162]. A spontaneous revertant exhibiting tetracycline resistance was isolated from Escherichia coli cells carrying the tetA(B) gene encoding the G62L mutation. The revertant showed a second-site mutation at codon 30 of TTA (Leu) to TCA (Ser). Site-directed mutagenesis studies revealed that the L30S mutation could suppress the effects of the G62A, G62C, G62N, and G62V mutations as well as the G62L mutation. Positions 62 and 30 are located in hydrophilic loops estimated to be in the cytoplasm and periplasm, respectively. Their sidedness was confirmed by the fact that, in intact cells, the [14C]N-ethylmaleimide (NEM) binding to the G62C mutant was not affected by preincubation with a membrane-impermeant sulfhydryl reagent, whereas the binding to the L30C mutant was blocked by the reagent. The reactivity of the L30C and L29C mutants with [14C]NEM was drastically decreased when Gly-62 was replaced by Leu, indicating that the residues around position 30 became embedded in the intramembrane region due to the remote conformational effect of the G62L mutation across the membrane. Moreover, the reactivity of the L29C/G62L mutant with [14C]NEM was restored with the L30S mutation. These results clearly indicate that the second-site suppression by the L30S mutation was based on the blocking of the remote conformational change around position 30 across the cell membrane caused by the G62L mutation.

Amino Acid Sequence↗

PubMed1997

L-aspartate-evoked inhibition of melatonin production in rat pineal glands.

Our previous studies in rat indicated that pinealocytes secrete L-glutamate through microvesicle-mediated exocytosis to regulate negatively melatonin production. Recently, we further found that pinealocytes secrete L-aspartate through microvesicle-mediated exocytosis. In the present study, we investigated the role of L-aspartate in the melatonin production in isolated rat pineal glands. It was found that L-aspartate inhibits norepinephrine-stimulated melatonin production as well as serotonin N-acetyltransferase activity reversibly and dose-dependently, the concentrations required for 50% inhibition being 150 and 175 microM, respectively. L-Asparagine and oxaloacetate, metabolites of L-aspartate, had no effect on the melatonin production. These results suggest that pinealocytes use L-aspartate, as well as L-glutamate, as a negative regulator for melatonin production.

Animals↗

PubMed1997

Targeted disruption of Cbfa1 results in a complete lack of bone formation owing to maturational arrest of osteoblasts.

A transcription factor, Cbfa1, which belongs to the runt-domain gene family, is expressed restrictively in fetal development. To elucidate the function of Cbfa1, we generated mice with a mutated Cbfa1 locus. Mice with a homozygous mutation in Cbfa1 died just after birth without breathing. Examination of their skeletal systems showed a complete lack of ossification. Although immature osteoblasts, which expressed alkaline phophatase weakly but not Osteopontin and Osteocalcin, and a few immature osteoclasts appeared at the perichondrial region, neither vascular nor mesenchymal cell invasion was observed in the cartilage. Therefore, our data suggest that both intramembranous and endochondral ossification were completely blocked, owing to the maturational arrest of osteoblasts in the mutant mice, and demonstrate that Cbfa1 plays an essential role in osteogenesis.

Animals↗

PubMed1997

Petrological evidence for shock melting of carbonates in the martian meteorite ALH84001.

The meteorite ALH84001--a shocked igneous rock of probable martian origin-contains chemically and isotopically heterogeneous carbonate globules, associated with which are organic and inorganic structures that have been interpreted as possible fossil remains of ancient martian biota. A critical assumption underlying this suggestion is that the carbonates formed from low-temperature fluids penetrating the cracks and voids of the host rock. Here we report petrological studies of ALH84001 which investigate the effects of shock on the various mineralogical components of the rock. We find that carbonate, plagioclase and silica were melted and partly redistributed by the same shock event responsible for the intense local crushing of pyroxene in the meteorite. Texture and compositional data show that, during the period of shock decompression, monomineralic melts were injected into pyroxene fractures that were subsequently cooled and resealed within seconds. Our results therefore suggest that the carbonates in ALH84001 could not have formed at low temperatures, but instead crystallized from shock-melted material; this conclusion weakens significantly the arguments that these carbonates could host the fossilized remnants of biogenic activity.

Aluminum Silicates↗

PubMed1997

Interaction between soluble type I receptor for bone morphogenetic protein and bone morphogenetic protein-4.

Bone morphogenetic proteins (BMPs) are multifunctional proteins that comprise the largest subfamily of the transforming growth factor-beta. These proteins bind to types I and II serine/threonine kinase receptors. Ligand-induced heteromeric dimerization of these receptors is the key event in initiation of biological responses. We report here large-scale expression and purification of extracellular domain of the type I receptor for BMP-2/4, using a silkworm expression system. This soluble form of BMP receptor (sBMPR) was in monomer form in solution and bound to BMP-4 but not to activin or transforming growth factor-beta1. Surface plasmon resonance studies showed that kinetic parameters of sBMPR for BMP-4 consisted of a relatively rapid association rate constant (ka = 3.81 +/- 0.19 x 10(4) s-1 M-1) and an extremely slow dissociation rate constant (kd = 3.69 +/- 0.26 x 10(-4) s-1). From these two kinetic parameters, affinity was determined to be similar to that of the intact membrane-associated receptor expressed on COS cells. sBMPR inhibited the alkaline phosphatase activity in BMP responsive cell lines such as mouse osteoblastic cell MC3T3-E1 and bone marrow stromal cell ST2. These data indicate that the extracellular domain of type I receptor for BMP-2 and BMP-4 is sufficient for high-affinity binding to its ligands and should prove useful in understanding the role of BMP-2/4 in vivo, because a suitable high-affinity anti-BMP antibody has yet to be developed.

Amino Acid Sequence↗

PubMed1997

Fibroblasts expressing Sonic hedgehog induce osteoblast differentiation and ectopic bone formation.

We investigated the role of Sonic hedgehog (SHH) in osteoblast differentiation and bone formation. The numbers of ALP-positive cells in the mouse fibroblastic cell line C3H10T1/2 and the mouse osteoblastic cell line MC3T3-E1 were increased by co-culture with chicken fibroblasts transfected with chicken Shh cDNA encoding amino-terminal peptide (Shh-N). The conditioned medium of Shh-N-RCAS-transfected chicken fibroblast cultures also significantly increased ALP activity in both C3H10T1/2 and MC3T3-E1 cells. Intramuscular transplantation of Shh-N-RCAS-transfected chicken fibroblasts into athymic mice induced ectopic bone formation. These results indicate that SHH induces osteoblast differentiation and ectopic bone formation.

3T3 Cells↗

PubMed1997

Bone morphogenetic protein-2 inhibits terminal differentiation of myogenic cells by suppressing the transcriptional activity of MyoD and myogenin.

Bone morphogenetic protein (BMP) is a family of cytokines that induce ectopic bone formation when implanted into muscular tissues. We reported that BMP-2 inhibits the terminal differentiation of C2C12 myoblasts and converts them into osteoblast lineage cells (Katagiri, T., Yamaguchi, A., Komaki, M., Abe, E., Takahashi, N., Ikeda, T., Rosen, V., Wozney, J. M., Fujisawa-Sehara, A., and Suda, T. (1994) J. Cell Biol. 127, 1755-1766). In the present study, we examined the molecular mechanism of the inhibitory effect of BMP-2 on terminal differentiation of myogenic cells. When either MyoD or myogenin cDNA was introduced into C3H10T1/2 (10T1/2) cells with a muscle-specific CAT reporter containing four copies of the right E-box of muscle creatine kinase (MCK) enhancer, the CAT activity was dose-dependently suppressed by BMP-2. Furthermore, BMP-2 inhibited the terminal differentiation of these subclonal 10T1/2 cells that stably expressed MyoD or myogenin into mature myotubes that expressed myosin heavy chain and troponin T. The differentiation of a subclone of the MyoD-transfected NIH3T3 cells into mature muscle cells was also inhibited by BMP-2. BMP-2 induced alkaline phosphatase activity in 10T1/2-derived, but not in NIH3T3-derived MyoD-transfected cells. These cells constitutively expressed exogenous MyoD and myogenin, which were localized exclusively in the nuclei irrespective of the presence and the absence of BMP-2. However, these cells failed to express the mRNAs of endogenous myogenic factors and MCK when cultured with BMP-2. In the electrophoresis mobility shift assay using nuclear extracts of the myogenic cells, MyoD and myogenin bound to the right E-box in the enhancer region of the MCK gene even in the presence of BMP-2. These results suggest that BMP-2 inhibits the terminal differentiation of myogenic cells by suppressing the transcriptional activity of the myogenic factors.

3T3 Cells↗