Analysis of the signal transduction pathway through the thromboxane A_2 receptor using the receptor-G-protein reconstitution system

点击翻译按钮获取中文摘要

Thromboxane (TX) A_2 is a metabolite of arachidonic acid. It induces activation of platelets and constriction of vascular- and bronchial smooth muscles. It is well known that TXA_2 has physiologically and path-physologically important roles in these tissues. On the other hand, we have recently cloned a cDNA of the mouse TXA_2 receptor and have revealed its primary structure. We have also examined the distribution of the mouse TXA_2 receptor mRNA and found its broad and specific expressions in various mouse organs. In this study, we intended to construct the TXA_2 receptor-G-protein reconstitution system and to clarify the signal transduction mechanisms through the receptor using this system.We have purified Gi and Gq proteins and partially purified the TXA_2 receptor from human platelets. We also succeeded in reconstituting these proteins in phospholipid vesicles last year.This year, we examined the ligand binding characteristics of the reconstituted receptor and the agonist-induced activation of the reconstituted G-proteins. We found that the TXA_2 receptor couples to both Gq and Gi proteins. We also evaluated the efficacies and the extent of the receptor-G-protein coupling. These results explained at least partially the multiplicity of signal transduction pathways through the TAX_2 receptor and suggested the participation of the Gi protein in the signal transduction, with which TXA_2 induces cell proliferation.