Sequence of a cDNA encoding chicken vasoactive intestinal peptide (VIP)

Therapeutic potential of vasoactive intestinal peptide and its receptor VPAC2 in type 2 diabetes

Owing to the increasing prevalence of type 2 diabetes, the development of novel hypoglycemic drugs has become a research hotspot, with the ultimate goal of developing therapeutic drugs that stimulate glucose-induced insulin secretion without inducing hypoglycemia. Vasoactive intestinal peptide (VIP), a 28-amino-acid peptide, can stimulate glucose-dependent insulin secretion, particularly by binding to VPAC2 receptors. VIP also promotes islet β-cell proliferation through the forkhead box M1 pathway, but the specific molecular mechanism remains to be studied. The clinical application of VIP is limited because of its short half-life and wide distribution in the human body. Based on the binding properties of VIP and VPAC2 receptors, VPAC2-selective agonists have been developed to serve as novel hypoglycemic drugs. This review summarizes the physiological significance of VIP in glucose homeostasis and the potential therapeutic value of VPAC2-selective agonists in type 2 diabetes.

Molecular characterization and tissue expression profiles of prepro-vasoactive intestinal peptide in the Chinese alligator (Alligator sinensis) during the active and hibernating periods

The Chinese alligator (Alligator sinensis), a freshwater crocodilian endemic to China, is one of the most endangered crocodilian species; up to this date, very little is known about the endocrine regulation of its metabolic activities during different physiological states. In this study, we characterized the structure of the prepro-vasoactive intestinal peptide in Chinese alligator (prepro-caVIP) for the first time and examined its expression profiles in various tissues during the active and hibernating periods. The prepro-caVIP cDNA consists of a 221-bp 5'-untranslated region (UTR), a 606-bp complete coding region (CDS), and a 312-bp 3'-UTR, which encodes the 201-amino acid prepro-caVIP containing a 28-amino acid vasoactive intestinal peptide (VIP) and a 27-amino acid PHI (peptide histidine isoleucine). Multiple alignment analysis showed that VIP shares 100% identity with the given birds, reptiles, and African clawed frog, and 89% identity with mammals, 96% with fishes. Real-time quantitative PCR showed that the prepro-caVIP is widely expressed in all the examined tissues, and the expression level is significantly higher in small intestine, stomach, pancreas, lung, and skeletal muscle, whereas lower in heart, liver, spleen, kidney, ovary, and oviduct. During hibernation, the expression level of caVIP was significantly decreased in small intestine (P < 0.01), pancreas, and skeletal muscle (P < 0.05), whereas significantly increased in liver, spleen, and lung (P < 0.01). The wide distribution of caVIP and its differential expression changes in various tissues during hibernation implicated that it might play multiple effects in Chinese alligator and participate in the physiological adaptation of various organs in a paracrine and/or neurocrine manner.

Molecular cloning, characterisation and tissues expression analysis of the goose (Anser cygnoides) vasoactive intestinal peptide (VIP) gene

1. Vasoactive intestinal peptide (VIP) is involved in the control of prolactin (PRL) release and plays a pivotal role as a regulator of reproductive behaviour and neuroendocrine secretion in birds. 2. In this study, a 941-bp cDNA fragment covering the complete coding region (CDS) of goose VIP gene was identified. The cDNA contains a 32-bp 5'-untranslated region (UTR), a 603-bp CDS and a 306-bp 3'-UTR containing two ATTTA sequence elements, two polyadenylation signals (AATAAA) and a 25-bp poly (A) tail. 3. Seven exons and 6 introns were identified, and both the cDNA and genomic DNA sequences showed high identity with those of other species. 4. The sequence analysis indicated that there were two alternatively spliced transcripts the long transcript (VIP-1) encoded both VIP and peptide histidine isoleucine exons and the short one (VIP-2) only encoded VIP. 5. RT-PCR analysis indicates that the expression level of the VIP-1 is much lower than that of VIP-2, and that VIP-1 is negligible or absent in muscle, abdominal fat, ovary and spleen, whereas VIP-2 is widely distributed in all the examined tissues. 6. A total of 12 single nucleotide polymorphisms (SNPs), including 2 SNPs located in the coding region and 10 variations in intron regions, were identified in goose VIP gene.

The serendipitous origin of chordate secretin peptide family members

Background

The secretin family is a pleotropic group of brain-gut peptides with affinity for class 2 G-protein coupled receptors (secretin family GPCRs) proposed to have emerged early in the metazoan radiation via gene or genome duplications. In human, 10 members exist and sequence and functional homologues and ligand-receptor pairs have been characterised in representatives of most vertebrate classes. Secretin-like family GPCR homologues have also been isolated in non-vertebrate genomes however their corresponding ligands have not been convincingly identified and their evolution remains enigmatic.

Results

In silico sequence comparisons failed to retrieve a non-vertebrate (porifera, cnidaria, protostome and early deuterostome) secretin family homologue. In contrast, secretin family members were identified in lamprey, several teleosts and tetrapods and comparative studies revealed that sequence and structure is in general maintained. Sequence comparisons and phylogenetic analysis revealed that PACAP, VIP and GCG are the most highly conserved members and two major peptide subfamilies exist; i) PACAP-like which includes PACAP, PRP, VIP, PH, GHRH, SCT and ii) GCG-like which includes GCG, GLP1, GLP2 and GIP. Conserved regions flanking secretin family members were established by comparative analysis of the Takifugu, Xenopus, chicken and human genomes and gene homologues were identified in nematode, Drosophila and Ciona genomes but no gene linkage occurred. However, in Drosophila and nematode genes which flank vertebrate secretin family members were identified in the same chromosome.

Conclusions

Receptors of the secretin-like family GPCRs are present in protostomes but no sequence homologues of the vertebrate cognate ligands have been identified. It has not been possible to determine when the ligands evolved but it seems likely that it was after the protostome-deuterostome divergence from an exon that was part of an existing gene or gene fragment by rounds of gene/genome duplication. The duplicate exon under different evolutionary pressures originated the chordate PACAP-like and GCG-like subfamily groups. This event occurred after the emergence of the metazoan secretin GPCRs and led to the establishment of novel peptide-receptor interactions that contributed to the generation of novel physiological functions in the chordate lineage.

Cloning of PRL and VIP cDNAs of the Java sparrow (Padda oryzivora)

Complementary DNA (cDNA) of prolactin (PRL) and vasoactive intestinal polypeptide (VIP) of the Java sparrow were cloned and sequenced. The proximal region of the PRL promoter was also identified. Java sparrow PRL was found to have 88.3, 88.3, and 89.1% sequence identity at the cDNA level to PRL of chicken, turkey, and duck, respectively. The predicted amino acid sequence had an overall similarity with a comparable region of chicken (91.4%), turkey (88.9%) and duck (92.0%) PRL. Based on the cDNA sequence and genomic structure of the chicken PRL gene, the proximal promoter was characterized. Sequence analysis of the proximal region of Java sparrow PRL promoter revealed a high degree of similarity to that of chicken, turkey and duck PRL promoters. Moreover, cDNA of prepro-VIP was also cloned and sequenced. Java sparrow prepro-VIP shows high similarity to chicken and turkey prepro-VIP. However, the region upstream of the 5' untranslated region of Java sparrow prepro-VIP did not show similarity to that of chicken. These results suggest that the mechanisms, which regulate expression of the VIP gene, may be different between precocial and altricial birds, but expression of the PRL gene may be widely conserved in avian species.

VPAC and PAC receptors: From ligands to function

Vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptides (PACAPs) share 68% identity at the amino acid level and belong to the secretin peptide family. Following the initial discovery of VIP almost four decades ago a substantial amount of knowledge has been presented describing the mechanisms of action, distribution and pleiotropic functions of these related peptides. It is now known that the physiological actions of these widely distributed peptides are produced through activation of three common G-protein coupled receptors (VPAC(1), VPAC(2) and PAC(1)R) which preferentially stimulate adenylate cyclase and increase intracellular cAMP, although stimulation of other intracellular messengers, including calcium and phospholipase D, has been reported. Using a range of in vitro and in vivo approaches, including cell-based functional assays, transgenic animals and rodent models of disease, VPAC/PAC receptor activation has been associated with numerous physiological processes (e.g. control of circadian rhythms) and clinical conditions (e.g. pulmonary hypertension), which underlies on-going research efforts and makes these peptides and their cognate receptors attractive targets for the pharmaceutical industry. However, despite the considerable interest in VPAC/PAC receptors and the processes which they mediate, there is still a paucity of selective and available, non-peptide ligands, which has hindered further advances in this field both at the basic research and clinical level. This review summarises the current knowledge of VIP/PACAP and the VPAC/PAC receptors with regard to their distribution, pharmacology, signalling pathways, splice variants and finally, the utility of animal models in exploring their physiological roles.

PACAP, VIP and their receptors in the metazoa: insights about the origin and evolution of the ligand-receptor pair

The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions.

Inhibitory effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) on food intake in the goldfish, Carassius auratus

Pituitary adenylate cyclase-activating polypeptide (PACAP) has a similar structure to that of vasoactive intestinal peptide (VIP) and both the polypeptides belong to the same molecular group, the secretin-glucagon superfamily. PACAP and VIP have possible potency as hypothalamic factors mediating the release of pituitary hormones in the fish pituitary. However, the roles of PACAP and VIP in the central nervous systems of fish have not yet been made clear. Recently, it was reported that PACAP and/or VIP are involved in the feeding behavior of the mouse and chick. Therefore, we investigated the effects of intracerebroventricular (ICV) and intraperitoneal (IP) administration of synthetic PACAP and VIP on food intake in the goldfish, Carassius auratus. Cumulative food intake was significantly decreased by ICV injection of PACAP (11 or 22 pmol/g body weight) or VIP (11 or 22 pmol/g) during a 60-min observation period after treatment. IP administration of PACAP (44 or 88 pmol/g) or VIP (22 or 44 pmol/g) induced a significant decrease in food intake during a 60-min observation period after treatment. These results suggest that PACAP and VIP may be involved as feeding regulators in goldfish.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

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.

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Sites of gene expression for vasoactive intestinal polypeptide throughout the brain of the chick (Gallus domesticus)

The peptide neurotransmitter vasoactive intestinal polypeptide (VIP) has several important functions in vertebrates, particularly, influencing the neuroendocrine and autonomic nervous systems both in developing and in adult animals. To document potential brain areas that might play significant functional roles, the distribution of VIP mRNA was examined throughout the entire chick brain by using in situ hybridization histochemistry (ISHH). In addition, a VIP binding-site study was completed that focused on the lateral septal organ (LSO), a circumventricular organ of potential significance in avian species. The areas where VIP message was found included the olfactory bulbs, posterior hippocampus, parahippocampal area, hyperstriatum, archistriatum/nucleus (n.) taenia (amygdala), medial part of the LSO, organum vasculosum of the lamina terminalis, medial preoptic region, bed n. of the pallial commissure, anterior hypothalamic (hypo.) n., lateral hypo. area (most extensive and dense message), periventricular hypo. n., lateral to the paraventricular n., ventromedial hypo. n., stratum cellulare externum, inferior hypo. n., infundibular hypo. n., median eminence, three layers within the stratum griseum et fibrosum superficiale, area ventralis of Tsai, n. tegmenti pedunculopontinus pars compacta (substantia nigra), intercollicular n., central gray, locus ceruleus, parabrachial n., ventrolateral medulla, reticular pontine area, in and about the n. vestibularis descendens. When compared with immunocytochemistry that detected the presence of the peptide product VIP, more areas of the brain were found to contain perikarya expressing VIP by using ISHH, particularly in the telencephalon and the mesencephalon. VIP binding sites were found in the lateral portion of the LSO where the blood-brain barrier is not fully developed. Hence, the LSO was found to contain neural elements that synthesize as well as bind VIP. VIP appears to be a useful peptide for defining major components of the visceral forebrain system in birds.