| Co-Investigator(Kenkyū-buntansha) |
HONDA Zenichiro HEALTH CENTER OF THE UNIVERSITY,THE UNIVERSITY OF TOKYO,ASSISTANT, 保健センター, 助手 (70238814)
KUME Kazuhiko DEPARTMENT OF BIOCHEMISTRY,THE UNIVERSITY OF TOKYO,ASSISTANT, 医学部(医), 助手 (30251218)
IZUMI Takashi DEPARTMENT OF BIOCHEMISTRY,THE UNIVERSITY OF TOKYO,ASSISTANT, 医学部(医), 助手 (70232361)
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| Research Abstract |
Following results were obtained on the physiological role and cellular signaling of platelet-activating factor (PAF).
(1)Cellular signaling via PAF receptor
By using transfected receptor in CHO cells, cellular signaling after PAF application was determined. PAF stimulates phosphoinositide turnover, mitogen-activated protein (MAP) kinase, phospholipase A2, and inhibits adenylate cyclase. From the results of PTX-treatment, PAF receptor appears to couple with two types of G-proteins. Ca-independent activation of MAP kinase was inhibited by wortmannin, suggesting a wortmannin-sensitive molecule such as phosphatidylinositol 3-kinase is present between Gi and MAP kinase.
To determine the molecular mechanisms of signal desensitization by PAF,we prepared CHO cells carrying wild-type, C-terminal deletion mutant, and substitution mutant (Ser, Thr to Ala) receptors. We found that C-terminal cytoplasmic tail is not required for forward signal transduction, but it is essential for signal-shut down. A family of GRK (G-protein receptor kinase) may be involved in the phosphorylation of Ser/Thr residues leading to signal shut down.
(2)Genomic structure of PAF receptor.
Human PAF receptor gene is present as a single copy in haploid on the chromosome 1q. The gene consists of three exons, separated each other > 20kb intron. Two5'-noncoding exons has distinct transcriptional start site, and promoters. These exons are alternatively spliced to a common splice acceptor to yield two different mRNAs. Transcript 1 is present in almost all tissues, and up-regulated by PAF or endotoxin through its NF-kB site. Transcript 2 is expressed in more tissue-specific way, and up-regulated by estrogen, and down-regulated by TGF-b. The physiological and pathological significance of these promoters are currently under investigation.
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