title: Molecular cloning and expression of multiple isoforms of human prostaglandin E receptor EP3 subtype generated by alternative messenger RNA splicing: multiple second messenger systems and tissue-specific distributions.
abstract: Five distinct cDNA clones encoding four different isoforms of human prostaglandin (PG) E receptor EP3 subtype were isolated from a human kidney cDNA library. Two cDNA clones differed only in their 3'-untranslated regions. The four isoforms, tentatively named EP3-I, EP3-II, EP3-III, and EP3-IV, which were generated by alternative mRNA splicing, had identical amino acid sequences except for their different carboxyl-terminal tails. Transfection experiments revealed that all the four isoforms show high binding affinities to PGE2, PGE1, and M&B28767, an EP3-specific agonist, whereas their downstream signaling pathways are divergent. M&B28767 increased cAMP concentrations in cells expressing EP3-II and EP3-IV, whereas it inhibited forskolin-induced cAMP accumulations in cells expressing all EP3 isoforms. M&B28767 also stimulated phosphoinositide turnover in cells expressing EP3-I and EP3-II. Northern blot analysis revealed that the EP3 gene is expressed in a wide variety of human tissues. The human EP3 mRNA was present most abundantly in the kidney, pancreas, and uterus. A substantial expression was also detected in the heart, liver, skeletal muscle, small intestine, colon, prostate, ovary, and testis. Furthermore, reverse transcription-polymerase chain reaction analysis demonstrated tissue-specific expressions of the five different EP3 mRNA species. The present study suggests the presence of the multiple systems of PGE2/EP3 isoforms and leads to the better understanding of its physiological and pathophysiological implications in humans.
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D000242:Cyclic AMP / Q000032:analysis; D015232:Dinoprostone / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D008969:Molecular Sequence Data; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D018078:Receptors, Prostaglandin E / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D015290:Second Messenger Systems / Q000502:physiology*
chemical_list: D018078:Receptors, Prostaglandin E; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D015232:Dinoprostone