Suppression of prostaglandin E receptor signaling by the variant form of EP(1) subtype

A cDNA clone of prostaglandin (PG) E receptor EP(1) subtype (rEP(1)) was isolated from a rat uterus cDNA library, It encodes 405 amino acid residues with seven transmembrane spanning domains and couples to Ca2+ mobilization, In addition, three cDNA clones encoding a variant form of rEP(1) were isolated, The open reading frame can code a 366-amino acid protein carrying a specific change of 49 amino acids from the middle of transmembrane segment VI to COOK terminus; it possesses a transmembrane segment VII-like structure lacking an intracellular COOK-terminal tail, Southern blot analysis of rat genomic DNA and genomic polymerase chain reaction demonstrated that these cDNAs were derived from a single copy gene, Northern blot analysis and ribonuclease protection assay revealed that both rEP(1) and rEP(1)-variant receptor mRNAs were highly expressed in the kidney, Immunoblot with an antibody directed toward the specific region of rEP(1)-variant receptor showed that rEP(1)-variant receptor protein was expressed in the membrane of the kidney and Chinese hamster ovary (CHO) cells transfected with rEP(1)-variant cDNA, Thus, the rEP(1)-variant receptor is translated from mRNA which is not spliced at nucleotide position 952 in the segment VI transmembrane region, rEP(1)-variant receptor retained the ligand binding activity with affinity and specificity similar to rEP(1) receptor, but lost the coupling of signal transduction systems by itself, However, when rEP(1)-variant receptor was stably co-expressed with rEP(1) receptor in CHO cells, the Ca2+ mobilization mediated by EP(1) receptor was significantly suppressed, Furthermore, when rEP(1)-variant receptor was expressed in CHO cells, cAMP formation by activation of endogenous EP(4) receptor was strongly blocked, These results suggest that the rEP(1)-variant receptor may affect the efficiency of signal coupling of PGE receptors and attenuate the action of PGE(2) on tissues.