Cloning of a carboxyl-terminal isoform of the prostanoid FP receptor.

An FP prostanoid receptor isoform, which appears to arise from alternative mRNA splicing, has been cloned from a mid-cycle ovine large cell corpus luteum library. The isoform, named the FP(B) receptor, is identical to the original isoform, the FP(A), throughout the seven transmembrane domains, but diverges nine amino acids into the carboxyl terminus. In contrast to FP(A), whose carboxyl terminus continues for another 46 amino acids beyond the nine shared residues, the FP(B) terminates after only one amino acid. The FP(A) isoform appears to arise by the failure to utilize a potential splice site, while a 3.2-kilobase pair intron is spliced out from the FP gene to generate the FP(B) isoform mRNA. The two isoforms have indistinguishable radioligand binding properties, but seem to differ in functional coupling to phosphatidylinositol hydrolysis. Thus, in COS-7 cells transiently transfected with either the FP(A) or the FP(B) receptor cDNAs, prostaglandin F(2alpha) stimulates inositol phosphate accumulation to the same absolute maximum, but the basal level of inositol phosphate accumulation is approximately 1.3-fold higher in cells transfected with the FP(B) as compared with cells transfected with the FP(A) isoform. Using the polymerase chain reaction, mRNA encoding the FP(B) isoform was identified in the ovine corpus luteum.