EP2B protein

The expression pattern of EP2 variants was examined in the rhesus monkey (Macaca mulatta). Using reverse transcriptase-polymerase chain reaction and rapid amplification of complementary cDNA protocols, 11 message variants were identified in rhesus epididymis, only three of which (EP2B, EP2C, and EP2E) have previously been reported. The most abundant variant found in human, EP2A, was not found in rhesus. Seven of the eight new rhesus EP2 variants (EP2J-EP2Q) use previously unidentified 5'-splicing sites in exon 3, and four variants use three previously unidentified exons whose counterparts are present in the human EP2 gene. Overall, 3 of the 11 variants, EP2C, EP2E, and EP2Q, code for beta-defensin-like peptides whose probable physiological role is to protect the male reproductive tract against microbial invasions. Because of the complex splicing pattern that causes some downstream exons to be read in any of the three reading frames, the N-termini of the other eight EP2 peptide variants consist of a partial beta-defensin motif with three cysteines, followed by amino acid sequences that have no recognizable homology to known proteins.

The EP2 gene codes for a family of androgen-dependent, epididymis-specific secretory proteins. Using probes derived from human HE2 cDNA, a chimpanzee epididymal cDNA library was screened. Five variants of chimpanzee EP2 cDNA were identified. Variant 1 (EP2A) is the chimpanzee ortholog of HE2. Variant 2 (EP2B) has an alternative 5' end. Variant 3 (EP2C) has an alternative 3' end. Two additional variants were identified by reverse transcriptase-polymerase chain reaction analysis. Variant 4 (EP2D) and variant 5 (EP2E) appear to lack an exon, resulting in a shift in the open reading frame. Presumably, the 5 variants originate from the same gene and result from alternative promoters and alternative splicing. Each of the putative proteins encoded by these variant messages has a leader sequence characteristic for a secretory protein. After removal of the leader sequence, each of these proteins is predicted to consist of 1 or 2 out of 4 possible peptide modules. Two of these modules have no recognizable homology to known proteins. The other 2 modules have a distribution of cysteine residues characteristic for beta-defensins, a family of proteins with antimicrobial activity.

Prostanoids comprising prostaglandins (PGs) and thromboxanes have been shown to play physiological and pathological roles in zebrafish. However, the molecular basis of zebrafish prostanoid receptors has not been characterized to date. Here, we demonstrate that there exist at least six 'relaxant' (Gs-coupled) prostanoid receptors in zebrafish; one PGI2 receptor IP and five PGE2 receptors comprising two EP2 (EP2a and EP2b), and three EP4 receptors (EP4a, EP4b and EP4c). In contrast, we failed to find a zebrafish PGD2 receptor with any structure and/or character similarities to the mammalian DP1 receptor. [(3)H]iloprost, a stable IP radioligand, specifically bound to the membrane of cells expressing zebrafish IP with a Kd of 42nM, and [(3)H]PGE2 specifically bound to the membranes of cells expressing zebrafish EP2a, EP2b, EP4a, EP4b and EP4c with a Kd of 6.9, 6.0, 1.4, 3.3 and 1.2nM, respectively. Upon agonist stimulation, the 'relaxant' prostanoid receptors showed intracellular cAMP accumulation. The responsiveness of these zebrafish receptors to subtype-specific agonists correlated with their structural conservation to the corresponding receptor in mammals. RT-PCR analysis revealed that the six zebrafish prostanoid receptors show unique tissue distribution patterns; each receptor gene may hence be under unique transcriptional regulation. This work provides further insights into the diverse functions of prostanoids in zebrafish.