1988 Fiscal Year Final Research Report Summary
The study of the structure and the function of GTP-binding protein which involved in the mechanism of TRH-sensitive phospholipase C activation
| Project/Area Number |
62570529
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
内分泌・代謝学
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| Research Institution | The Tokyo Metroplotan Institute of Medical Science |
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Principal Investigator |
YAJIMA Yukiko The Tokyo Metropolitan Institute of Medical Science, Dept. Tumor Cell Biology, 腫瘍細胞研究室, 主任・研究員 (60090114)
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| Co-Investigator(Kenkyū-buntansha) |
KAWASAKI Hiroshi The Tokyo Metropolitan Institute of Medical Science, Dept. Molecular Biolgy, 遺伝情報研究部, 研究員 (70169704)
AKITA Yoshiko The Tokyo Metropolitan Institute of Medical Science, Dept. Molecular Biolgy, 遺伝情報研究部, 研究員 (40124432)
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| Project Period (FY) |
1987 – 1988
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| Keywords | TRH / TRH-receptor / Guanine nucleotide (GTP)-binding protein / cholera toxin / phospholipase C / adenylate cyclase / ADP-ribosylation / Caチャンネル |
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| Research Abstract |
The hypothalamic tripetide TRH (thyrotropin-releasing hormone) binds to specific high affinity receptors on target cells of the pituitary within seconds, stimulates the degradation of polyphosphoinositides by phospholipase C and the concomitant formation of inositol phosphates and diacylglycerol. Recently, guanine nucleotide-binding protein, G protein has been proposed to coupled cell-surface receptors to phospholipase C-mediated polyphosphoinositide breakdown. In order to determine the structure and the function of G protein coupled TRH-receptor, we have characterized the relationship between TRH-receptor and G protein in GH3 clonal pituitary cells and membranes which are frequently used to study for the mechanism of TRH action.
We found that TRH stimultes the activity of phospholipase C using exogenous substrate [^3H]phosphatidylinositol-4,5 bisphosphate with the dependency of guanine nucleotide in these cell membranes. And also we found that the cholera toxin-treated membranes demonstrated a partial reduction in the activity of TRH-induced low Km GTPase activity and a 10-fold increase in the concentration of guanine nuclerotide required for a half-maxmimal effect in regulating the TRH-receptor affinity for TRH-ligand. These data suggested that cholera toxin may act directly on a G rotein that is associated with TRH-receptors. There have been one report that cholera toxin inhibits secretin-mediated increase in the hydrolysis of polyphosphoinositide by a cAMP-independent mechanism. Recently it was found that Gs, the stimulatory G protein for adenylate cyclase, can stimulete the activity of ca channel. Therefore, cholera toxin-sensitive G protein will be considered about a new role of the signal transduction system and our results will help to study these purpose.
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