Analysis of a porcine EP3-receptor: cloning, expression and signal transduction

A cDNA clone, encoding a complete porcine EP3 receptor, was isolated from a porcine heart cDNA library. The deduced amino acid sequence revealed a protein of 387 amino acid residues with an estimated molecular weight of 43 kD and strongest homology to the human EP3-II receptor (84% identity on protein level). Ligand binding studies with transfected COS-7 cells, expressing the porcine receptor, showed displacement of [3H]PGE1 with the EP3-specific agonist M&B 28.767, the EP1/EP3-agonist sulprostone but not with the EP2-specific agonist butaprost. Stimulation of transfected CHO cells with M&B 28.767 resulted in inhibition of forskolin-induced cAMP formation, suggesting coupling to an inhibitory G protein. Agonist-induced translocation of the transcription factor NFkappaB into the nucleus of transfected CHO cells was demonstrated by Western blot analysis, indicating that these EP3 receptors modulate NFkappaB-dependent cellular signal transduction. Analysis of the genomic organization identified the major transcription initiation site at about 160 bp upstream of the ATG start codon. The 800-bp 5' flanking region contains a variety of putative cis-acting regulatory elements, including binding sites for AP2, SP1 and MyoD (E-box). The present data will now allow further studies on EP3 receptor-mediated signal transduction and its regulation.