THE BOVINE THROMBOXANE A(2) RECEPTOR - MOLECULAR-CLONING, EXPRESSION,AND FUNCTIONAL-CHARACTERIZATION

This study describes the molecular cloning and functional characteriza tion of the bovine thromboxane A(2) (TP) receptor. Two partial nucleot ide sequences coding for the bovine TP receptor were isolated from a b ovine genomic and a bovine heart cDNA library. The deduced amino acid sequence suggests a heptahelical protein of 343 amino acids. The recep tor protein is homologous with that of human placenta and endothelium at 84.0% and 81.4%, respectively. COS-7 cells were transfected with th e bovine TP receptor cDNA, and binding affinities were assessed by rad ioligand binding studies. Specific displacement of [H-3]SQ 29548 was d emonstrated in COS-7 cell membranes with the unlabeled TP receptor ant agonist SQ 29548 (K-d = 12.6 +/- 1.1 nM) and the TP receptor agonist U 46619 (K-d = 192.1 +/- 58.9 nM), but not with other prostaglandins (PG D(2), PGE(1), PGF(2 alpha)), or the PGI(2) mimetic cicaprost. Agonist- induced stimulation of adenylyl cyclase in transfected COS-7 cells ind icates a linkage to the cAMP signal transduction pathway via coupling to a stimulatory G-protein. Since bovine cells, e.g. vascular smooth m uscle cells, are an established model to study the role of eicosanoids in cell signaling, this report on the molecular structure of the bovi ne TP receptor will allow further studies on receptor regulation.