Search PubMed⌕ Search

Biomedical subjects

H Yamamura

Publications and source records attributed to H Yamamura.

At least 73 records · Page 4Linked to original sources
PubMed1999

Spatio-temporally regulated expression of receptor tyrosine kinases, mRor1, mRor2, during mouse development: implications in development and function of the nervous system.

BACKGROUND: Drosophila neurospecific receptor tyrosine kinases (RTKs), Dror and Dnrk, as well as Ror1 and Ror2 RTKs, isolated from human neuroblastoma, have been identified as a structurally related novel family of RTKs (Ror-family RTKs). Thus far, little is known about the expression and function of mammalian Ror-family RTKs. RESULTS: We have identified murine Ror-family RTKs, mRor1 and mRor2. Both mRor1 and mRor2 genes are induced upon neuronal differentiation of P19EC cells. During neuronal differentiation in vitro, the expression of mRor2 is transiently induced, although that of mRor1 increases continuously. During embryogenesis, the mRor1 gene is expressed in the developing nervous system within restricted regions and in the developing lens epithelium. The expression of mRor1 is sustained in the nervous system and is also detected in non-neuronal tissues after birth. In contrast, the expression of mRor2 is detected mainly in the developing nervous system within broader regions and declines after birth. Possible relationships of mRor1 and mRor2 genes with previously identified mutants have also been examined. CONCLUSIONS: The developmental expressions of mRor1 and mRor2, in particular in the nervous system, are differentially regulated, reflecting their expression patterns in vitro. mRor1 and mRor2 may thus play differential roles during the development of the nervous system.

Amino Acid Sequence↗
PubMed1999

Protein tyrosine kinase Lyn mediates apoptosis induced by topoisomerase II inhibitors in DT40 cells.

Several sets of non-receptor protein tyrosine kinases (PTK) play important roles in apoptosis induced by various extracellular stresses. Anti-cancer drugs induce cellular DNA damage and cytotoxic events, leading to apoptotic cell death. We utilized the established chicken B cell line, DT40 cells and their derived mutants, lacking the respective PTK [DT40/Syk(-), DT40/Lyn(-) and DT40/Btk(-)], to examine a role of these PTK in apoptotic processes induced by anti-cancer drugs. All anti-cancer drugs examined induced apoptosis of wild-type DT40 cells. Interestingly,DT40/Lyn(-), but not DT40/Syk(-) and DT40/Btk(-) cells, become resistant to apoptosis induced by adriamycin and etoposide, topoisomerase II (Topo II) inhibitory agents, compared to wild-type DT40 cells, as assessed by DNA fragmentation and TUNEL analyses. Ectopic expression of Fyn, another Src family member, in DT40/Lyn(-) cells restores largely the susceptibility of the cells against Topo II inhibitor-induced apoptosis. Furthermore, it was found that Topo II inhibitors activate c-Jun N-terminal kinase (JNK) slightly in both wild-type and DT40/Lyn(-) cells to similar extents. Collectively, these results suggest that Lyn is involved in Topo II inhibitor-induced apoptotic signaling in DT40 cells independent of JNK.

Animals↗
PubMed1999

Does growth hormone augment brain edema caused by brain injury? A study with a freeze brain injury model in the rat.

OBJECTIVE: Because of the known sodium and water retention associated with growth hormone (GH) therapy, it is crucial to evaluate the safety of GH after brain injury. To clarify this issue, we investigated whether GH affects brain edema in a rat brain freeze-injury model. METHODS: Male Wistar rats (n = 29) were divided into four groups according to the substance injected (GH vs. normal saline) and whether the brain was injured or not. The subcutaneous injections of GH (0.8 IU/kg) or saline were given 24 hours apart. In the injury groups, after the second injection, an aluminum rod (4-mm diameter) cooled to -50 degrees C was placed on the exposed dura mater in the right parietal region for 4 minutes, under anesthesia. At 4 hours after the insult, brain and skeletal muscle were excised and their water content was measured by drying. RESULTS: Freeze injury of the brain caused an increase in water and sodium content in skeletal muscle. GH injection augmented this edema in skeletal muscle. Freeze injury of the brain also caused an increase in water and sodium content in the injured hemisphere of the brain. GH injection did not exacerbate this edema in injured brain tissue. Neither freeze injury nor GH injection caused brain edema in the noninjured hemisphere or in the cerebellum. CONCLUSION: GH administration did not augment brain edema caused by brain injury in our model.

Animals↗
PubMed1999

Cardiovascular and neuronal responses to head stimulation reflect central sensitization and cutaneous allodynia in a rat model of migraine.

Reduction of the threshold of cardiovascular and neuronal responses to facial and intracranial stimulation reflects central sensitization and cutaneous allodynia in a rat model of migraine. Current theories propose that migraine pain is caused by chemical activation of meningeal perivascular fibers. We previously found that chemical irritation of the dura causes trigeminovascular fibers innervating the dura and central trigeminal neurons receiving convergent input from the dura and skin to respond to low-intensity mechanical and thermal stimuli that previously induced minimal or no responses. One conclusion of these studies was that when low- and high-intensity stimuli induce responses of similar magnitude in nociceptive neurons, low-intensity stimuli must be as painful as the high-intensity stimuli. The present study investigates in anesthetized rats the significance of the changes in the responses of central trigeminal neurons (i.e., in nucleus caudalis) by correlating them with the occurrence and type of the simultaneously recorded cardiovascular responses. Before chemical stimulation of the dura, simultaneous increases in neuronal firing rates and blood pressure were induced by dural indentation with forces >/= 2.35 g and by noxious cutaneous stimuli such as pinching the skin and warming > 46 degrees C. After chemical stimulation, similar neuronal responses and blood pressure increases were evoked by much smaller forces for dural indentation and by innocuous cutaneous stimuli such as brushing the skin and warming it to >/= 43 degrees C. The onsets of neuronal responses preceded the onsets of depressor responses by 1.7 s and pressor responses by 4.0 s. The duration of neuronal responses was 15 s, whereas the duration of depressor responses was shorter (5.8 s) and pressor responses longer (22.7 s) than the neuronal responses. We conclude that the facilitated cardiovascular and central trigeminal neuronal responses to innocuous stimulation of the skin indicate that when dural stimulation induces central sensitization, innocuous stimuli are as nociceptive as noxious stimuli had been before dural stimulation and that a similar process might occur during the development of cutaneous allodynia during migraine.

Animals↗
PubMed1999

Ca2+ spark as a regulator of ion channel activity.

Ca2+ spark is a local and transient Ca2+ release from sarcoplasmic reticulum (SR) through the ryanodine receptor Ca2+-releasing channel (RyR). In cardiac myocytes, Ca2+ spark is an elementary unit of Ca2+-induced Ca2+ release (CICR) by opening of RyR(s) in junctional SR (jSR), which is triggered by Ca2+-influx through L-type Ca2+ channels to the narrow space between a transverse tubule and jSR. Ca2+ spark has, therefore, been described as the evidence for "the local control of excitation-contraction coupling". In contrast, Ca2+ sparks in smooth muscle have been reported in relation to Ca2+-dependent K+ (K(Ca)) channel activation and muscle relaxation. A spontaneous Ca2+ spark in a superficial area activates 10-100 K(Ca) channels nearby and induces membrane hyperpolarization, which reduces Ca2+ channel activity. In several types of smooth muscle cells, which have relatively high membrane excitability, an action potential (AP) elicits 5-20 Ca2+ hot spots (evoked sparks with long life) in the early stage via CICR in discrete superficial SR elements and activates K(Ca)-channel current highly responsible for AP repolarization and afterhyperpolarization. CICR available for contraction may occur more slowly by the propagation of CICR from superficial SR to deeper ones. The regulatory mechanism of ion channel activity on plasma membrane by superficial SR via Ca2+ spark generation in smooth muscle cells may be analogously common in several types of cells including neurons.

Action Potentials↗
PubMed1999

Activation of Ca(2+)-dependent K(+) current by nordihydroguaiaretic acid in porcine coronary arterial smooth muscle cells.

The effects of nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor and an antioxidant, on membrane currents were examined in single smooth muscle cells isolated from porcine coronary artery. Spontaneous transient outward currents (STOCs) recorded at -30 mV were markedly enhanced by NDGA (>/=10 microM). Pretreatment with caffeine and ryanodine abolished STOCs and reduced NDGA-induced increase in outward current at -30 mV by approximately 60%. NDGA showed dual action on an outward current elicited by step depolarization from -60 to 0 mV: inhibition and enhancement at concentrations of 3 and >/=10 microM, respectively. In the presence of Cd(2+), the inhibition of outward current by NDGA disappeared and the enhancement remained. NDGA inhibited both the voltage-dependent Ca(2+) channel current (IC(50) = 2.5 microM) and the delayed rectifier K(+) current (IC(50) = 9.8 microM). The NDGA-induced enhancement of STOCs and outward currents on depolarization was abolished by 100 nM iberiotoxin but was not affected by glibenclamide or apamin. Under current clamp mode, 30 microM NDGA significantly hyperpolarized myocytes. The application of lipoxygenase inhibitors (caffeic acid and esculetin), a cyclooxygenase inhibitor (indomethacin), antioxidants (ascorbic acid and erythorbic acid), and structural-related compounds of NDGA (catechol and dopamine) did not enhance K(+) currents. These results indicate that the opening of the large conductance Ca(2+)-dependent K(+) channel by NDGA, which is independent of its lipoxygenase inhibition or antioxidant effect, results in membrane hyperpolarization.

Animals↗
PubMed1999

Distribution and intracellular localization of a mouse homologue of Ca2+/calmodulin-dependent protein kinase Ibeta2 in the nervous system.

Ca2+/calmodulin-dependent protein kinases (CaMKs) are believed to play important roles in the development and function of the nervous system. We report here the identification and expression of mouse CaMKIbeta (mCaMKIbeta), in particular mCaMKIbeta2, an isoform of mCaMKIbeta. During embryogenesis, the mCaMKIbeta2 gene is expressed mainly in the nervous system, including brain, spinal cord, trigeminal ganglion, and retina. Within the CNS, the expression of mCaMKIbeta2 is detected in the mantle zone, but not in the ventricular zone, suggesting its possible involvement in the differentiation of neurons. In the adult brain, mCaMKIbeta2 transcripts are detected at high levels in the anterior olfactory nuclei, piriform cortex, septal nuclei, bed nuclei of the stria terminalis, hippocampal pyramidal cells, dentate granule cells, amygdala, hypothalamic nuclei, parabrachial nucleus, and nucleus of the solitary tract. The distinct gene expression pattern suggests that mCaMKIbeta2 may also be involved in different mature neuronal functions from other CaMKs. In addition, mCaMKI/beta2 proteins are localized to the cytoplasm and nuclei, but not to nucleoli, suggesting that mCaMKIbeta2 proteins might be involved in the cytoplasmic and nuclear signal transduction of the nervous system.

Amino Acid Sequence↗
PubMed1999

Ability of teicoplanin and vancomycin to induce contraction of, and histamine release from, pulmonary tissue of humans, monkeys and guinea pigs.

To assess the safety of teicoplanin and vancomycin with respect to airway tissue, we evaluated whether these two antibiotics induce pulmonary tissue contraction and histamine release in human, monkey and guinea pig specimens in vitro. The effects of these drugs on the release of histamine from monkey blood leucocytes and mouse bone marrow-derived mast cells (BMMC) were also studied. Neither teicoplanin nor vancomycin (10(-6)-10(-3) g/mL) induced contractions of guinea pig trachea or lung parenchyma. Similarly, these drugs induced no appreciable change in the resting tonus of cynomolgus monkey bronchus or lung parenchyma. The tonus of monkey trachea was not influenced by teicoplanin, whereas 10(-3) g/mL vancomycin caused contraction. The spontaneous tonus of human lung parenchyma was not altered by teicoplanin or vancomycin, and that of the bronchus was not influenced by teicoplanin; however, 10(-3) g/mL vancomycin elicited obvious contraction of the bronchus. Neither drug promoted the release of significant amounts of histamine from these pulmonary tissues or from monkey blood leucocytes and BMMC. These results suggest that, compared with vancomycin, teicoplanin may be associated with a lower risk of inducing bronchospasm when used for inhalation therapy.

Animals↗
PubMed1998

Functional cooperation of cyclin C and c-Myc in mediating homotypic cell adhesion via very late antigen-4 activation and vascular cell adhesion molecule-1 induction.

Very late antigen-4 (VLA-4)/vascular cell adhesion molecule-1 (VCAM-1) are a pair of adhesion molecules mediating cell-cell interaction. The binding activity of each depends on its surface expression, yet integrin activity can also be modulated through inside-out signaling. However, the specific intracellular molecules involved in modulating integrin VLA-4 activation via inside-out signaling or in regulating VCAM-1 expression are poorly understood. We show here that constitutive coexpression of cyclin C and c-Myc in hematopoietic BAF-B03 cells induces homotypic cell adhesion, which results from enhanced VLA-4 ligand-binding activity and induced expression of VCAM-1. Furthermore, regulation of cell adhesion appears to be a feature unique to cyclin C, but not other G1 cyclins, E and D3, and its regulatory function is independent of CDK8 kinase activity. Our results provide a novel role for cyclin C and c-Myc in the regulation of cell adhesion through distinct mechanisms.

Animals↗
PubMed1998

The Cspg2 gene, disrupted in the hdf mutant, is required for right cardiac chamber and endocardial cushion formation.

The heart defect (hdf) mouse is a recessive lethal that arose from a transgene insertional mutation on chromosome 13. Embryos homozygous for the transgene die in utero by embryonic day 10.5 postcoitus and exhibit specific defects along the anterior-posterior cardiac axis. The future right ventricle and conus/truncus of the single heart tube fail to form and the endocardial cushions in the atrioventricular and conus/truncus regions are absent. Because the hdf mouse mutation provided the opportunity to identify a gene required for endocardial cushion formation and for specification or maintenance of the anterior most segments of the heart, we initiated studies to further characterize the phenotype, clone the insertion site, and identify the gene disrupted. Chromosome mapping studies first identified the gene, Cspg2 (versican), as a candidate hdf gene. In addition, an antibody recognizing a glycosaminoglycan epitope on versican was found to be positive by immunohistochemistry in the extracellular matrix of normal wild-type embryonic hearts, but absent in homozygous hearts. Expression analysis of the Cspg2 gene showed that the 6/8, 6/9, and 7/9 Cspg2 exon boundaries were present in mRNA of normal wild-type embryonic hearts but absent in the homozygous mutant embryos. DNA sequence flanking the transgene was used to isolate from a normal mouse library overlapping genomic DNA segments that span the transgene insertion site. The contiguous genomic DNA segment was found to contain exon 7 of the Cspg2 in a position 3' to the transgene insertion site. These four separate lines of evidence support the hypothesis that Cspg2 is the gene disrupted by the transgene insertion in the hdf mouse line. The findings of this study and our previous studies of the hdf insertional mutant mouse have shown that normal expression of the Cspg2 gene is required for the successful development of the endocardial cushion swellings and the embryonic heart segments that give rise to the right ventricle and conus/truncus in the outlet of the looped heart.

Alternative Splicing↗
PubMed1998

Outside-In signaling of soluble and solid-phase fibrinogen through integrin alphaIIbbeta3 is different and cooperative with each other in a megakaryoblastic leukemia cell line, CMK.

The function and the outside-in signaling pathways of alphaIIbbeta3 were examined in relation to cell adhesion using a megakaryoblastic leukemia cell line, CMK. After 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, the cells adhered to the culture plate and underwent megakaryocytic differentiation with expression of alphaIIbbeta3. Binding of soluble fibrinogen to the cells via alphaIIbbeta3 was dependent on cell adhesion. Cell detaching reduced the affinity of this integrin for soluble fibrinogen, although its surface expression was almost unchanged. In contrast, detached cells became tightly adherent to the fibrinogen-coated plate (solid-phase fibrinogen). The same ligand, fibrinogen, present either in soluble or solid-phase form, triggered differential signaling pathways mediated by alphaIIbbeta3. By the stimulation with soluble fibrinogen, Syk was tyrosine-phosphorylated but FAK was dephosphorylated, whereas solid-phase fibrinogen promptly caused tyrosine phosphorylation of FAK followed by delayed phosphorylation of Syk. In addition, the binding of soluble fibrinogen to the cells adherent to fibrinogen-coated plate resulted in tyrosine phosphorylation of integrin beta3 and a complex formation of integrin beta3 with Syk. This implies the cooperation of both soluble and solid-phase fibrinogen-mediated signaling pathways.

Cell Adhesion↗
PubMed1998

Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder.

1. Electrical events and intracellular calcium concentration ([Ca2+]) imaged using fluo-3 and laser scanning confocal microscopy were simultaneously monitored in single smooth muscle cells freshly isolated from guinea-pig vas deferens or urinary bladder. 2. Images obtained every 8 ms, during stepping from -60 to 0 or +10 mV for 50 ms under voltage clamp, showed that a rise in [Ca2+] could be detected within 20 ms of depolarization in five to twenty small (< 2 micrometer diameter) 'hot spots', over 95 % of which were located within 1.5 micrometer of the cell membrane. Depolarization at 30 s intervals activated hot spots at the same places. 3. Cd2+ or verapamil abolished both hot spots and Ca2+-activated K+ current (IK,Ca). Caffeine almost abolished hot spots and markedly reduced IK,Ca. Cyclopiazonic acid, which raised basal global [Ca2+], decreased the rise in hot spot [Ca2+] and IK,Ca amplitude during depolarization. These results suggest that Ca2+ entry caused Ca2+-induced Ca2+ release (CICR). 4. Under voltage clamp, hot spot [Ca2+] closely paralleled the rise in IK,Ca and reached a peak within 20 ms of the start of depolarization, but the rise in global [Ca2+] over the whole cell area was much slower. Step depolarization to potentials positive to -20 mV caused hot spots to grow in size and coalesce, leading to a rise in global [Ca2+] and contraction. Ca2+ hot spots also occurred during the up-stroke of an evoked action potential under current clamp. 5. It is concluded that the entry of Ca2+ in the early stages of an action potential evokes CICR from discrete subplasmalemma Ca2+ storage sites and generates hot spots that spread to initiate a contraction. The activation of Ca2+-dependent K+ channels in the plasmalemma over hot spots initiates IK,Ca and action potential repolarization.

Action Potentials↗
PubMed1998

Expression of the smooth muscle calponin gene in human osteosarcoma and its possible association with prognosis.

The basic calponin gene is a smooth muscle differentiation-specific gene that encodes an actin-binding protein involved in the regulation of smooth muscle contractility. We studied the expression of the calponin gene in 8 human osteosarcoma cell lines and 17 primary human osteosarcoma tissues by RT-PCR analysis. We also analyzed mRNA expression of smooth muscle-specific genes including SM22alpha, caldesmon and alpha-actin, and for neutral and acidic calponin isoforms. The genes were expressed at various levels by osteosarcoma cell lines and tissues of diverse histological subtypes. The basic calponin protein of an expected size was detected in osteosarcoma cell lines by immunoblot analysis and was localized by immunohistochemistry in the cytoplasm of the tumor cells in osteosarcoma tissues. Survival was found to be significantly increased in patients whose tumors exhibited basic calponin expression, compared with those with no expression. Alterations in the expression of other markers examined were not correlated with prognosis. Our results suggest that the basic calponin gene product may be a novel prognostic variable in patients with osteosarcoma.

Adolescent↗
PubMed1998

Involvement of reactive oxygen intermediates in lectin-induced protein-tyrosine phosphorylation of Syk in THP-1 cells.

Oxidative stress (H2O2) has been shown to be associated with tyrosine phosphorylation and activation of protein-tyrosine kinase Syk. In the present study, we examined the possibility that reactive oxygen intermediates (ROI) were involved in concanavalin A (Con A)-induced tyrosine phosphorylation in THP-1 cells. Rapid tyrosine phosphorylations of Syk, Fc gamma receptor(s) and phospholipase C gamma 2 (PLC gamma 2) were induced by Con A treatment in THP-1 cells. Pretreatment of cells with antioxidants N-acetylcysteine (NAC) and glutathione (GSH) almost completely blocked tyrosine phosphorylations of Syk, Fc gamma receptor(s) and PLC gamma 2. In addition, THP-1 cells showed significant levels of ROI from the early period of Con A treatment and the levels of ROI were inhibited by antioxidant treatment. These data suggest that ROI have an important role in Con A-induced protein-tyrosine kinase(s) signaling pathways.

Antioxidants↗
PubMed1998

Induction of calponin-h1 by transforming growth factor-beta1 in cultured human ito cells, LI90.

We investigated the effect of transforming growth factor-beta1 (TGF-beta1) on the expression of calponin-h1, alpha-smooth muscle actin (alpha-SMA), and extracellular matrix (ECM) components in a cultured human Ito cell line, LI90. The TGF-beta1 treatment stimulated productions of hyaluronic acid and laminin, and significantly decreased the secretion of hepatocyte growth factor in LI90 cells. The functional characteristics of LI90 cells were compatible with those of human-activated Ito cells that are known as pericyte-like mesenchymal liver cells. TGF-beta1 induced a slight growth-inhibition of LI90 cells. TGF-beta1 enhanced the expressions of both alpha-SMA and calponin-h1 at the protein level, while tumor necrosis factor-alpha and interleukin-1alpha did not affect the expressions of these cytoskeletal proteins on LI90 cells. The addition of TGF-beta1 to LI90 cells resulted in a significant increase of calponin-h1 mRNA levels, but not calponin-h2. These data suggest that the expression of calponin-h1 is controlled at the level of mRNA under the coordinate regulation together with alpha-SMA as the process of perpetuation of activated Ito cells promoted by TGF-beta1. The identification of smooth muscle features promoted by TGF-beta1 support the hypothesis that the activation of Ito cells coincides with their contractile behavior, indicating that these cells may be important in vasoregulation during liver injury and fibrosis.

Actins↗
PubMed1998

A deficiency in Syk enhances ceramide-induced apoptosis in DT40 lymphoma B cells.

Syk deficiency significantly enhanced ceramide-induced apoptosis. Ectopic expression of wild-type or kinase-inactive Syk rendered Syk-negative cells resistant to ceramide-induced apoptosis. Furthermore, ceramide could not activate Syk, indicating that Syk protected DT40 cells from ceramide-induced apoptosis, via a mechanism independent of its activity. In addition, a deficiency in Lyn also resulted in the cells becoming susceptible to ceramide-induced apoptosis. However, no difference of Ara-C-induced apoptosis between wild-type and mutant cells was observed. c-Jun N-terminal kinases appeared not to be important in mediating the enhanced apoptosis, as they were still activated in mutant cells following ceramide treatment.

Apoptosis↗
PubMed1998

Differential regulation of oxidative and osmotic stress induced Syk activation by both autophosphorylation and SH2 domains.

Syk, a nonreceptor protein-tyrosine kinase, is activated by both oxidative and osmotic stress and plays different roles in the transduction of stress signals. In this study, the regulation of oxidative and osmotic stress induced Syk activation was investigated utilizing Syk-negative DT40 cells, expressing various Syk mutants. Phosphorylation of Y518Y519 was demonstrated to be required for both oxidative and osmotic stress induced Syk activation. Syk activation by these two types of stress stimuli was a combination of both autophosphorylation and the activities of additional tyrosine kinases. Oxidative stress induced Syk tyrosine phosphorylation was almost completely attributed to autophosphorylation, whereas other tyrosine kinases were largely responsible for osmotic stress induced Syk tyrosine phosphorylation. Moreover, the Src homology 2 (SH2) domains of Syk differentially regulated Syk activation. Both mSH2(N) Syk and mSH2(C) Syk, in which the phosphotyrosine-dependent binding motif within the SH2 domains contained point mutations, showed a significantly higher activity than that observed in wild-type Syk, following osmotic stress treatment. In comparison, in response to oxidative stress, only mSH2(N) Syk demonstrated a stronger activation than wild-type Syk. Therefore, differential activation and regulation of Syk may give an insight into the distinctive functions of Syk in oxidative and osmotic stress signaling.

Animals↗