MOLECULAR-CLONING AND EXPRESSION OF A PROSTAGLANDIN E(2) RECEPTOR OF THE EP(3-BETA) SUBTYPE FROM RAT HEPATOCYTES

Rat hepatocytes have previously been reported to possess prostaglandin E(2) receptors of the EP(3)-type (EP(3)-receptors) that inhibit glucagon-stimulated glycogenolysis by decreasing cAMP. Here, the isolation of a functional EP(3 beta) receptor cDNA clone from a rat hepatocyte cDNA library is reported. This clone can be translated into a 362-amino-acid protein, that displays over 95% homology to the EP(3 beta) receptor from mouse mastocytoma. The amino- and carboxy-terminal region of the protein are least conserved. Transiently transfected HEK 293 cells expressed a single binding site for PGE(2) with an apparent K-d of 15 nM. PGE(2) > PGF(2 alpha) > PGD(2) competed for [H-3]PGE(2) binding sites as did the EP(3) receptor agonists M&B 28767 = sulprostone > misoprostol but not the EP(1) receptor antagonist SC 19220. In stably transfected CHO cells M&B 28767 > sulprostone = PGE(2) > misoprostol > PGF(3 beta) inhibited the forskolin-elicited cAMP formation. Thus, the characteristics of the EP(3 beta) receptor of rat hepatocytes closely resemble those of the EP(3 beta) receptor of mouse mastocytoma.