Third isoform of the prostaglandin-E-receptor EP3 subtype with different C-terminal tail coupling to both stimulation and inhibition of adenylate cyclase.

A functional cDNA clone for a third isoform of the mouse prostaglandin-E-receptor EP3 subtype, derived by alternative RNA splicing, named the EP3 gamma receptor, was obtained in addition to those for the two other isoforms, EP3 alpha and EP3 beta. The three isoforms are only different in the amino acid sequence of the putative cytoplasmic carboxy-terminal tail. When expressed, EP3 gamma shows identical ligand-binding properties to these of the other isoforms. The EP3-selective agonist, M&B 28767, increased the basal cAMP level and inhibited the forskolin-induced increase in the cAMP level in EP3 gamma, while it decreased both the basal and forskolin-elevated cAMP levels in EP3 alpha and EP3 beta. The M&B 28767-stimulated GTPase activity consisted of pertussis-toxin-sensitive and cholera-toxin-sensitive portions in the EP3 gamma-expressing cell membrane, suggested that EP3 gamma is coupled to both guanine nucleotide-binding inhibitory and stimulatory proteins. These results indicate that EP3 gamma is coupled to both stimulation and inhibition of adenylate cyclase, but that EP3 alpha and EP3 beta are exclusively coupled to inhibition of adenylate cyclase. Thus, alternative splicing produces a third isoform with a different carboxy-terminal tail, which differs from the other two isoforms in the specificity of coupling to a signal-transduction pathway.