Molecular evolution of vertebrate VIP receptors and functional characterization of a VIP receptor from goldfish Carassius auratus

Vasoactive intestinal polypeptide (VIP) is a neuropeptide that has numerous physiological actions and is widely distributed in the body. However, as yet, there is no sequence information about VIP receptors in lower vertebrates. Partial cDNA fragments spanning transmembrane domains 2 to 6 of VIP receptors were isolated from six nonmammalian vertebrate species, including chicken, pigeon, frog, lizard, salmon, and goldfish. Sequence comparison of these receptors revealed essential structural motifs responsible for receptor function. In addition, the first nonmammalian full-length VIP receptor cDNA was obtained by screening a goldfish brain and pituitary cDNA library. Functional expression of this receptor in mammalian COS-7 cells showed that it is coupled to cAMP production in a VIP and PACAP concentration-dependent manner; the EC(50) of VIP was determined to be 1 nM. At 100 nM peptide, the relative potency of various peptides in stimulating cAMP in the transfected cells was VIP > PACAP > GHRH = secretin > PHM > PTH > glucagon > GLP-1 > GIP. Characterization of the VIP receptors in lower vertebrates should enhance our understanding of the molecular evolution and physiology of VIP in vertebrates. (C) 1997 Academic Press.