The bovine thromboxane A2 receptor: molecular cloning, expression, and functional characterization

Abstract

This study describes the molecular cloning and functional characterization of the bovine thromboxane A₂ (TP) receptor. Two partial nucleotide sequences coding for the bovine TP receptor were isolated from a bovine genomic and a bovine heart cDNA library. The deduced amino acid sequence suggests a heptahelical protein of 343 amino acids. The receptor protein is homologous with that of human placenta and endothelium at 84.0% and 81.4%, respectively. COS-7 cells were transfected with the bovine TP receptor cDNA, and binding affinities were assessed by radioligand binding studies. Specific displacement of [³H]SQ 29548 was demonstrated in COS-7 cell membranes with the unlabeled TP receptor antagonist SQ 29548 (K _d = 12.6 ± 1.1 nM) and the TP receptor agonist U46619 (K _d = 192.1 ± 58.9 nM), but not with other prostaglandins (PGD₂, PGE₁, PGF_2α), or the PGI₂ mimetic cicaprost. Agonist-induced stimulation of adenylyl cyclase in transfected COS-7 cells indicates a linkage to the cAMP signal transduction pathway via coupling to a stimulatory G-protein. Since bovine cells, e.g. vascular smooth muscle cells, are an established model to study the role of eicosanoids in cell signaling, this report on the molecular structure of the bovine TP receptor will allow further studies on receptor regulation.