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Z Honda

Publications and source records attributed to Z Honda.

At least 37 records · Page 2Linked to original sources
PubMed1994

Cloning, expression and tissue distribution of rat platelet-activating-factor-receptor cDNA.

The biological functions of platelet-activating factor (PAF) have been extensively studied in the rat. However, the precise structure and distribution of rat PAF receptor has not been reported. To address this question, we isolated a rat PAF-receptor cDNA from a size-fractionated rat spleen cDNA library. The deduced amino acid sequence of the rat PAF receptor showed 80% and 79% identity with guinea pig and human PAF receptors, respectively. Pharmacological properties (ED50, inhibition by WEB2086) of rat PAF receptors expressed in Xenopus oocytes were similar to those for PAF receptors expressed from guinea pig or human cDNAs. Northern blot analysis showed a widespread distribution of PAF-receptor mRNA in almost all organs including spleen, small intestine, kidney, lung, liver and brain. Considerable difference in the PAF-receptor distribution detected among species suggests the existence of a species-specific and tissue-specific regulatory mechanism for PAF-receptor-mRNA expression. Isolation of rat PAF-receptor cDNA should facilitate further analysis of PAF-receptor function and pharmacology in diverse pathophysiological processes.

Amino Acid Sequence↗
PubMed1994

Transfected platelet-activating factor receptor activates mitogen-activated protein (MAP) kinase and MAP kinase kinase in Chinese hamster ovary cells.

The platelet-activating factor (PAF) was seen to potently activate mitogen-activated protein (MAP) kinase and MAP kinase kinase through the cloned guinea pig PAF receptor stably expressed in Chinese hamster ovary (CHO) cells. Both 42- and 44-kDa MAP kinases were activated and tyrosine-phosphorylated in response to PAF. The PAF receptor also triggered the production of inositol phosphates and the release of arachidonic acid and inhibited cyclic AMP accumulation. Differential inhibitory effects of pertussis toxin (PTX) on these signals suggested that the PAF receptor couples to both PTX-sensitive and -insensitive G proteins in CHO cells. MAP kinase and MAP kinase activations were partially regulated by PTX-sensitive G proteins. The PAF receptor did not trigger any detectable increase in the GTP form of Ras under the conditions in which the human insulin receptor expressed in the same parent CHO cells potently increased the level. Since these agonists induced comparable MAP kinase activations through cognate receptors, Ras seems to play different roles in MAP kinase activation by the two different classes of receptors. The activation of MAP kinase by the cloned PAF receptor may explain part of the mechanisms underlying PAF-induced differentiation and proliferation in non-inflammatory cells.

Animals↗
PubMed1993

Two distinct signal transduction pathways for the activation of guinea-pig macrophages and neutrophils by endotoxin.

Lipopolysaccharide (LPS, endotoxin) is a major component of the outer membrane of gram-negative bacteria. Although it interacts with many types of cells and is linked to numerous events associated with sepsis and endotoxic shock, the mechanisms underlying these actions are poorly understood. We found that Ca-signaling induced by endotoxin in guinea-pig neutrophils and macrophages is caused by cross-recognition of LPS with platelet activating factor (PAF) receptors. However, the synthesis of tumor necrosis factor-alpha or the priming effect of O2- production was not affected by PAF antagonists. Thus, at least two distinct pathways are involved in the actions of LPS, one via the PAF receptor, while the other is independent of a PAF receptor and Ca-signaling.

Animals↗
PubMed1993

Two different promoters direct expression of two distinct forms of mRNAs of human platelet-activating factor receptor.

The human platelet-activating factor (PAF) receptor gene exists as a single copy on chromosome 1. We identified two 5'-noncoding exons, each of which has distinct transcriptional initiation sites. These exons are alternatively spliced to a common splice acceptor site on a third exon that contains the total open reading frame to yield two different species of functional mRNA (Transcript 1 and 2). Transcript 1 has consensus sequences for transcription factor NF-kappa B and Sp-1, and the Initiator (Inr) sequence homologous to the murine terminal deoxynucleotidyltransferase gene. Transcript 2 also contains consensus sequences for transcription factor AP-1, AP-2, and Sp-1. Transcripts 1 and 2 were both detected in heart, lung, spleen, and kidney, whereas only Transcript 1 was found in peripheral leukocytes, a differentiated human eosinophilic cell line (EoL-1 cells), and brain. Existence of distinct promoters was thus suggested to play a role in the regulatory control of PAF receptor gene expression in different human tissues and cells.

Alternative Splicing↗
PubMed1993

Characterization of prostaglandin F2 alpha receptor of mouse 3T3 fibroblasts and its functional expression in Xenopus laevis oocytes.

Prostaglandin (PG) F2 alpha increased [3H]thymidine incorporation into quiescent NIH 3T3 cells, stimulated phosphoinositide breakdown, and raised intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner with ED50 values of 2.0 x 10(-8) M, 4.6 x 10(-8) M, and 7.5 x 10(-8) M, respectively. The increase in [3H]thymidine incorporation with PGF2 alpha was additive with that seen with epidermal growth factor (EGF) or insulin. The peak [Ca2+]i increase with PGF2 alpha was still obvious in the absence of extracellular Ca2+ and was insensitive to islet activating protein (IAP) pretreatment. Membranes prepared from NIH 3T3 cells exhibited a specific binding for PGF2 alpha, which was sensitive to GTP gamma S but not sensitive to IAP pretreatment. Xenopus laevis oocytes injected with NIH 3T3 cell mRNA between 18S and 28S rRNA fractionated by sucrose gradient, expressed a PGF2 alpha-specific Cl- current when examined by voltage clamp. This Cl- current was also insensitive to IAP pretreatment and not affected by extracellular Ca2+ concentration ([Ca2+]o). These results indicate 1) that the NIH 3T3 cells expressed a specific PGF2 alpha receptor which is linked to phosphoinositide-specific phospholipase C (PLC) activation and to mobilization of Ca2+ via an IAP-insensitive G-protein(s), 2) that this PGF2 alpha receptor may play an active role in the proliferation of NIH 3T3 cells, and 3) that this PGF2 alpha receptor can be expressed in the oocyte system.

3T3 Cells↗
PubMed1992

Three types of Gi alpha protein of the guinea-pig lung: cDNA cloning and analysis of their tissue distribution.

cDNA clones encoding three types of Gi alpha, the alpha subunit of GTP-binding protein (Gi1 alpha, Gi2 alpha, and Gi3 alpha), were isolated from a cDNA library of the guinea-pig lung. Nucleotide sequence analysis revealed a high degree of homology with other mammalian Gi alpha cDNAs. By RNA blot analysis, the expression pattern of Gi1 alpha was more tissue-specific than those of other types of Gi alphas in the guinea-pig tissues examined. While Gi2 alpha and Gi3 alpha mRNAs were ubiquitously expressed in all tissues examined, Gi1 alpha mRNA was mainly expressed in the brain, lung and kidney. These results suggest that each Gi alpha protein may have a different role.

Amino Acid Sequence↗
PubMed1992

Endotoxin transduces Ca2+ signaling via platelet-activating factor receptor.

Lipopolysaccharide (LPS) is a pathogenic substance causing severe multiple organ failures and high mortality. Although several LPS binding proteins have been identified, the molecular mechanism underlying the LPS signaling pathway still remains obscure. We have found that the LPS-induced Ca2+ increase in platelets and platelet aggregation is blocked by selective platelet-activating factor (PAF) receptor antagonists, thus suggesting a cross-talk between LPS and the PAF receptor. Next, we confirmed this hypothesis using the cloned PAF receptors [(1991) Nature 349, 342-346; (1991) J. Biol. Chem. 266, 20400-20405] expressed in Xenopus oocytes and Chinese hamster ovary (CHO) cells. In both systems, cells responded to LPS only when PAF receptors were expressed, and specific PAF binding was successfully displaced and reversibly dissociated by LPS. PAF receptor activation by LPS may represent a novel important pathway in the pathogenesis of circulatory collapse and systemic thrombosis caused by endotoxin.

Animals↗
PubMed1992

Expression of platelet activating factor receptor in renal tubular cell line (LLC-PK1).

Northern blot analyses of poly(A)+ RNA extracted from cloned renal tubule cells, LLC-PK1, MDCK and JTC-12 cells, were performed using an isolated cDNA of guinea pig platelet activating factor (PAF) receptor as a probe. The results showed the expression of single entity of PAF receptor mRNA in LLC-PK1, but not in MDCK or JTC-12 cells. PAF also induced a dose-dependent elevation of intracellular calcium in LLC-PK1 cells as assessed by Fura-2 fluorescence signals, which was completely blocked by a PAF receptor antagonist, WEB 2170. These results indicate a PAF receptor-effector system in a renal tubular cell line LLC-PK1, providing a possible model system for studying physiological roles of PAF receptors in renal tubules.

Animals↗
PubMed1992

Platelet-activating factor (PAF) receptor in rat brain: PAF mobilizes intracellular Ca2+ in hippocampal neurons.

Platelet-activating factor (PAF), an alkylether phospholipid, is produced in the brain when it is subjected to various stimuli. Using a Xenopus oocyte expression system, we obtained evidence for functional PAF receptor mRNA expression in rat brain. The presence of the PAF receptor was confirmed and shown to be quite ubiquitous in the CNS by RNA blot and radioligand binding studies. To investigate the neuronal functions of PAF, intracellular Ca2+ increase elicited by nanomolar PAF application was analyzed in cultured rat hippocampal cells. Fractions of NMDA-responsive cells and non-NMDA-responsive cells were shown to respond to PAF, suggesting a potential role for PAF in the Ca2+ signaling pathway in the hippocampus.

Animals↗
PubMed1991

Molecular cloning and expression of platelet-activating factor receptor from human leukocytes.

The cDNA for a platelet-activating factor (PAF) receptor was cloned from a human leukocyte cDNA library using a 0.8-kilobase pair fragment of the guinea pig lung PAF receptor cDNA (Honda, Z., Nakamura, M., Miki, I., Minami, M., Watanabe, T., Seyama, Y., Okado, H., Toh, H., Ito, K., Miyamoto, T., and Shimizu, T. (1991) Nature 349, 342-346). The cDNA (1.8-kilobase pairs) had an open reading frame encoding 342 amino acid residues with a calculated Mr of 39,203. The clone was shown to code for a PAF receptor based on the following criteria: 1) the amino acid sequence possesses seven putative membrane spanning domains with 83% identity to the guinea pig lung PAF receptor, 2) Xenopus laevis oocytes injected with the transcript of the clone showed an electrophysiological response to PAF, and 3) COS-7 cells expressing the encoded receptor showed ligand binding with the pharmacological properties of the PAF receptor. Activation of the PAF receptor yielded inositol 1,4,5-trisphosphate production in both COS-7 cells and oocytes, and guanosine 5'-O-(2-thio)bisphosphate injection into the oocytes inhibited PAF-induced Cl- current, providing an evidence that PAF stimulates phosphoinositide turnover via G-protein(s). PAF receptor mRNA was abundant in leukocytes and less so in an undifferentiated human eosinophilic cell line (EoL-1 cells) or human erythroleukemia cells (HEL cells). The production of the mRNA was prominently increased when EoL-1 cells were treated with granulocyte macrophage colony stimulating factor, interleukin-5, and n-butyrate.

Amino Acid Sequence↗
PubMed1991

Demonstration of platelet activating factor receptor in guinea pig kidney.

Distribution of platelet activating factor (PAF) receptor was examined in the guinea pig kidney. Northern blot analysis showed a single band electrophoresed just below the 28S rRNA, and the mRNA was richest in the cortex with lesser amounts in the outer and then inner medulla. Scatchard analysis of membrane fraction using [3H]WEB 2086, a specific PAF receptor antagonist, revealed a single binding site with Bmax of 522, 228, 58 fmol/mg protein for the cortex, outer medulla and inner medulla, respectively. Kd values were in the same order of magnitude (10(-8) M). These results indicate the presence of a single class of PAF receptor in the guinea pig kidney which is most abundant in the cortex.

Animals↗
PubMed1991

Cloning by functional expression of platelet-activating factor receptor from guinea-pig lung.

Platelet-activating factor (PAF), a unique phospholipid mediator, possesses potent proinflammatory, smooth-muscle contractile and hypotensive activities, and appears to be crucial in the pathogenesis of bronchial asthma and in the lethality of endotoxin and anaphylactic shock. Despite this, little is known of the molecular properties of the PAF receptor and related signal transduction systems. Although several lines of evidence suggest that activation of the PAF receptor stimulates phospholipase C and subsequent inositol trisphosphate formation through G protein(s), the PAF receptor and calcium channel are reported to show a close relation. As a first approach to cloning lipid autacoid receptors, we have isolated complementary DNA for the PAF receptors. Our strategy involved gene expression in Xenopus laevis oocytes and electrophysiological detection of PAF-induced responses. Sequence analysis indicates that the receptor belongs to the superfamily of G protein-coupled receptors.

Amino Acid Sequence↗
PubMed1990

Characterization of the guinea pig lung membrane leukotriene D4 receptor solubilized in an active form. Association and dissociation with an islet-activating protein-sensitive guanine nucleotide-binding protein.

Membrane fractions from the guinea pig lung had high- and low-affinity binding sites for LTD4 with Kd values of 0.016 and 9.1 nM, respectively. In the presence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or by prior treatment of the membrane with islet-activating protein (IAP), the high-affinity site shifted to a low-affinity state. Consistently, a 41-kDa protein was ADP-ribosylated by treatment of the lung membranes with IAP, and this event was inhibited by the addition of GTP gamma S. We solubilized the LTD4 receptor from the lung membranes in an active form with 5 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and 10% glycerol. On a gel filtration column, the binding activity was eluted at the volume corresponding to a Mr of 70,000 or over 500,000 in the presence or absence of Mg2+ (5-20 mM), respectively, in solubilizing buffers. The Kd value of [3H]LTD4 binding to the 70-kDa protein was similar to the low-affinity binding constant of the membrane and was insensitive to GTP gamma S. The preparation solubilized in the absence of Mg2+ showed both high- and low-affinity binding sites for LTD4, and the addition of GTP gamma S shifted the high-affinity site to a low-affinity one. Thus, 1) the LTD4 receptor is coupled to an IAP-sensitive GTP-binding protein, 2) this GTP-binding protein is dissociable from the receptor by solubilizing the lung membrane with CHAPS and Mg2+, and 3) the receptor associated to or dissociated from a GTP-binding protein exhibited a high- or low-affinity state, respectively. These data provide an insight into the molecular mechanism of regulation of the LTD4 receptor signaling process by association and dissociation with an IAP-sensitive GTP-binding protein.

Animals↗
PubMed1990

Biosynthesis and functions of leukotriene C4.

1. The LTC4 synthase activity is rich in the microsomal fraction of the guinea pig spleen and lung. The enzyme was partially purified from the guinea pig lung and separated from the microsomal glutathione S-transferase (GST), by column chromatograpy. The enzyme has a specific activity of 40 nmol/min.mg, and acts preferentially on 5, 6-LTA4. Various types of cytosolic GSTs utilize all types of LTA4 isomers (5,6-, 11,12- and 14,15-LTA4) almost to the same extent, and methyl ester forms are better substrates for GST. 2. Two different types of GSTs (Yn1n1 and P) were purified from rat brain cytosol, to homogeneity. Because both types have a high LTC4 synthase activity, they may participate in the LTC4 production in the rat brain. 3. LTC4, produced in the guinea pig atrium, stimulates pertussis toxin (IAP)-sensitive muscarinic K+ channel (IK.ACh). The negative chronotropic action of alpha 1-adrenergic agonist might relate to the production of arachidonate lipoxygenase metabolites. These results together with the findings in Aplysia sensory neurons, suggest a novel mode of eicosanoid actions.

Animals↗