Structural and functional identification of the pituitary adenylate cyclase-activating polypeptide receptor VPAC(2) from the frog Rana tigrina rugulosa

Recently, a frog pituitary adenylate cyclase-activating polypeptide (PACAP) /vasoactive intestinal peptide (VIP) receptor (fPVR) has been characterized , and interestingly, this receptor exhibits characteristics of both mammali an PACAP type II receptors VPAC(1)R and VPAC(2)R. In order to investigate t he receptors responsible for mediating the actions of VIP and PACAP in amph ibians, in this report, a frog VPAC(2) receptor (fVPAC(2)R) cDNA was isolat ed. fVPAC(2)R shares 47.7, 46.9 and 62.5% amino acid sequence identity with fPVR, human VPAC(1)R and human VPAC(2)R respectively. Functionally, fVPAC( 2)R, when expressed in CHO cells, was responsive to both frog peptides incl uding VIP, PACAP38 and PACAP27 where the EC50 values of these peptides in i ntracellular cAMP production were 0.15, 0.18 and 0.16 muM respectively. The pharmacological profiles of human peptides (VIP, PACAP38 and peptide histi dine methionine) to stimulate frog and human VPAC(2)Rs were compared, and i t was found that these peptides could only activate the frog receptor at mi cromolar concentrations. fVPAC(2)R was found to be widely distributed in va rious peripheral tissues as well as several regions of the brain. The prese nce of the receptor transcripts suggests the functional roles of the recept or in mediating the actions of PACAP and/or VIP in these tissues. As VIP an d particularly PACAP27 are highly conserved peptides in vertebrate evolutio n, comparative studies of these peptides and their receptors in non-mammali an vertebrates should provide clues to better understand the physiology of these important peptides in human and other vertebrates.