Characterization of VIP-and helodermin-preferring receptors on rat platelets

Vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating peptide receptor subtypes in mouse calvarial osteoblasts: presence of VIP-2 receptors and differentiation-induced expression of VIP-1 receptors

Three distinct complementary DNAs for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) receptors have been cloned and designated VIP-1 receptor (VIP-1R), VIP-2 receptor (VIP-2R), and PACAP receptor (PACAP-R). In the present study, we have characterized the binding sites on primary mouse calvarial osteoblasts for VIP and related peptides. By analyzing the cAMP response, the rank order of response observed was PACAP 38 > PACAP 27 > helodermin > VIP > helospectin > glucagon > PHI >>> secretin. The VIP-2R/PACAP-R antagonist, PACAP 6-38, inhibited both VIP- and PACAP-stimulated cAMP formation. Binding studies using an atomic force microscopy (AFM) technique showed high affinity binding for VIP and PACAP 38, but not for secretin. Radioligand binding studies using (125)I-VIP and (125)I-PACAP 38 demonstrated a more specific and higher affinity binding for PACAP 38 than for VIP. Secretin failed to inhibit both (125)I-VIP and (125)I-PACAP 38 binding. RT-PCR demonstrated that undifferentiated mouse calvarial osteoblasts express messenger RNA for VIP-2R, but not for VIP-1R or PACAP-R. When the osteoblasts were cultured for 20 days to induce bone noduli formation, VIP-1R, in addition to VIP-2R, were expressed when the nodules started to mineralize at 12 days. Taken together, these data demonstrate that mouse calvarial osteoblasts express functional VIP-2R with higher affinity binding for PACAP than for VIP and that the VIP-1R expression is induced during osteoblastic differentiation.

Molecular cloning of the helodermin and exendin-4 cDNAs in the lizard. Relationship to vasoactive intestinal polypeptide/pituitary adenylate cyclase activating polypeptide and glucagon-like peptide 1 and evidence against the existence of mammalian homologues

Helodermin and exendin-4, two peptides isolated from the salivary gland of the Gila monster, Heloderma suspectum, are approximately 50% homologous to vasoactive intestinal peptide (VIP) and glucagon-like peptide-1 (GLP-1), respectively, and interact with the mammalian receptors for VIP and GLP-1 with equal or higher affinity and efficacy. Immunohistochemical studies suggested the presence of helodermin-like peptides in mammals. To determine whether helodermin and exendin-4 are present in mammals and their evolutionary relationship to VIP and GLP-1, their cDNAs were first cloned from Gila monster salivary gland. Northern blots and reverse transcription-polymerase chain reaction of multiple Gila monster tissues identified approximately 500-base pair transcripts only from salivary gland. Both helodermin and exendin-4 full-length cDNAs were approximately 500 base pairs long, and they encoded precursor proteins containing the entire amino acid sequence of helodermin and exendin-4, as well as a 44- or 45-amino acid N-terminal extension peptide, respectively, having approximately 60% homology. The size and structural organization of these cDNAs indicated that they were closely related to one another but markedly different from known cDNAs for the VIP/GLP-1 peptide family previously identified in both lower and higher evolved species. Cloning of the Gila monster VIP/peptide histidine isoleucine, pituitary adenylate cyclase activating polypeptide, and glucagon/GLP-1 cDNAs and Southern blotting of Gila monster DNA demonstrate the coexistence of separate genes for these peptides and suggests, along with the restricted salivary gland expression, that helodermin and exendin-4 coevolved to serve a separate specialized function. Probing of a variety of rat and human tissues on Northern blots, human and rat Southern blots, and genomic and cDNA libraries with either helodermin- or exendin-4-specific cDNAs failed to identify evidence for mammalian homologues. These data indicate that helodermin and exendin-4 are not the precursors to VIP and GLP-1 and that they belong to a separate peptide family encoded by separate genes. Furthermore, the existence of as yet undiscovered mammalian homologues to helodermin and exendin-4 seems unlikely.