1. General Information
VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase-activating peptide) belong to a family of structurally related peptides, the secretin/VIP family which includes VIP, secretin, glucagon, PACAP, GRF (growth hormone-releasing factor), GLP-1 (glucagon like peptide-1), GIP (gastric inhibitory peptide) and PHI (peptide histidine isoleucine, a biologically active peptide contained in the VIP precursor). The structure, function and role in the pancreas for VIP and PACAP are reviewed elsewhere in the Pancreapedia (19, 48). VIP and PACAP bind to three VPAC receptors: VPAC1 (originally VIP1), VPAC2 (originally VIP2), and PAC1 (PACAP preferring) which are distinct from receptors for the other members of the family (12). While these receptors were initially defined by ligand binding and second messenger activation, molecular cloning studies in the 1990s showed that their receptors were members of a distinct group of 7-transmembrane, G-protein coupled receptors characterized by a long external amino terminal (N-ted) of around 140 amino acids and termed Class B or Class II GPCRs (9, 21). Overall, the VPAC receptors contain around 540 amino acids. Photoaffinity cross-linking and NMR studies have shown that the alpha helical portion of VIP interacts with the N-ted region of the receptor (7, 28). The remainder of the receptor structure is similar to other GPCR with three intracellular loops and a C terminal intracellular tail.
The two receptors recognizing VIP with high affinity are termed VPAC1 and VPAC2 because they recognize both VIP and PACAP with similar affinity (2, 25, 30, 40, 47). They have 50% homology to each other and 30 to 50% homology to other Class B GPCRs. The PACAP receptor, termed PAC1 specifically binds PACAP and not VIP with high affinity (35). Since VIP is primarily a neuropeptide and is released locally near VPAC receptors, VIP and PACAP can function differently even though their receptors are homologous. VPAC receptors signal primarily through cyclic AMP while PAC1 signals through an increase in intracellular Ca2+. VPAC1 has three glycosylation sites in the N terminal and at least one needs to be glycosylated for the receptor to reach the plasma membrane (8). Some GPCR can interact with additional intracellular proteins such as RAMPS (receptor activity modifying proteins) which VPAC1 but not VPAC2 can interact with through a PDZ domain in the carboxyl terminal of the receptor (6). This does not affect the ligand binding specificity but may mediate the ability of VIP to act through Ca2+ in some circumstances. VPAC1 receptors can homodimerize and heterodimerize with VPAC2 or secretin receptors although the significance of this is not clear (20).
Selective agonists and antagonists, largely mutated peptides, have been developed (28). Ala11,22,28VIP is a selective VPAC1 agonist (33) and PG 97-269 is a VPAC1 antagonist (17). For VPAC2, a cyclic VIP peptide analog termed Ro 25-1392 is a potent and selective agonist (18) but there are not yet well defined antagonists.
VPAC1 receptors are widely distributed in the brain and are located on both neurons and blood vessels particularly in the cerebral cortex and hippocampus (21, 25, 45). In peripheral tissues it is present most abundantly in the liver, lung and intestine. VPAC2 receptors in the brain are most abundant in the thalamus and suprachiasmatic nucleus with lesser amounts in the hippocampus, brainstem and spinal cord (44). VPAC2 is present in peripheral tissues especially smooth muscle in the cardiovascular, gastrointestinal and reproductive system. VIP and its receptors also play a role in the immune response and inflammatory disease (11).
The role of VIP and its receptors has also been augmented by studies of genetically modified mice in which specific receptors have been deleted which affects different physiological actions of VIP. VPAC1 KO mice show growth impairment with small islets and intestinal obstruction (13). These mice also show an abnormal immune response (1). VPAC2 KO mice show growth impairment, decreased fat mass, and increased metabolic rate (3). In a different study the VPAC2 receptor was shown to be essential for circadian function in the suprachiasmatic nucleus (22).
2. VIP Receptors in Pancreas
The initial studies characterizing VIP receptors on pancreatic acini were carried out using radioiodinated VIP (125I-VIP) and isolated guinea pig acinar cells prepared using collagenase digestion (5). Binding was reversible, saturable and could be displaced with unlabeled VIP or secretin but not CCK or glucagon. Displacement curves suggested two separate classes of binding sites one with high affinity for VIP and low affinity for secretin and the other with a high affinity for secretin and low affinity for VIP. Subsequent studies on rat acini also revealed a high affinity VIP receptor whose occupancy correlated with an increase in cyclic AMP and amylase secretion induced by VIP (4, 39). Studies with a variety of VIP and secretin analogues as well as using 125I-secretin as ligand confirmed the presence of distinct VIP and secretin receptors (14, 15, 43, 50, 51). VIP receptors on acini also bind helodermin, a peptide from Gila monster venom (10, 37), PHI (50), and GRF (50) with high affinity and stimulate adenylyl cyclase in the plasma membrane (15, 29). Using ligand binding assays, [4Cl-D-Phe6, Leu17] VIP and [N-Ac-Tyr1, D-Phe2] GRF-1-29 NH2 were developed as antagonists for VIP binding to acini (34, 46). Covalent cross-linking studies suggested that the VIP receptor on guinea pig acini was a single protein with an apparent molecular mass of 45,000 (31). However, Svoboda et al concluded that the receptor was a 77,000 molecular mass protein which is similar to other tissues (41). Le Meuth et al labelled a glycoprotein of 55 kDa in calf pancreas membranes (29). These numbers are less important after molecular cloning but also reflect additional glycosylation that may differ between cell types and species. These binding studies have been summarized by Gardner and Jensen (15, 16).
Following the cloning and description of VPAC1 and VPAC2 receptors, Northern blotting has been used to show the presence of mRNA for both receptors in pancreas and isolated acini of guinea pig, mouse, and rat (23, 26). Earlier studies had also shown both receptor mRNAs in the human pancreas but primarily localized to blood vessels and islets (47). Ito et al then used [Lys15, Arg16, Leu27] VIP(1-7)-GRF(8-27), a VPAC1 selective agonist (17) and Ro-25-1553 a VPAC2 selective agonist (45) to show that both receptors on acini would bind VIP resulting in stimulation of amylase release and that 85-90% of the effects of VIP on rat and guinea pig acini were mediated by the VPAC1 receptor. However, based on adenylyl cyclase activation, VPAC2 was the predominate VIP receptor in calf pancreas (32). On rat acini, 125I-VIP also bound to VIP and PACAP receptors (39). At another level, both VPAC1 and VPAC2 receptor activation increased pancreatic blood flow (24).
VPAC2 has been shown to play a role in the embryonic development of the pancreas. The presence of VPAC2 was shown by Northern blot in rat pancreas between E12 and E16. In vitro, VIP and Ro25-1553 increased cyclic AMP, cellular proliferation and survival in pancreatic organ culture (36). VIP receptors are present in most pancreatic ductal adenocarcinoma tissue and in tumor derived cell lines where VIP stimulates cyclic AMP formation (27). In addition, VPAC2 receptors are present in islets (44) and on normal beta cells (49) and a VPAC2 specific peptide (BAY 55-9837) stimulates insulin secretion (42).
Considering the importance of VIP to stimulate ductal fluid secretion, there is unfortunately less information on the type of VIP receptors on normal pancreatic ductal cells. In a autoradiographic study of human pancreatic tumors and surrounding normal tissue VIP binding to a normal duct was displaced by a VPAC1 specific ligand (38).
3. Tools for the Study of VIP Receptors
a. Peptides – Synthetic agonist and antagonist peptides against the two VPAC receptors are available from Sigma, Calbiochem, and Tocris
b. Antibodies – Antibodies to VPAC1 (ab138260) and VPAC2 (ab 194383) are available from Abcam but have not been tested by us. Other polyclonal rabbit antibodies from MyBioSource.
c. Knockout mice – Whole body genetic deletions of VPAC1 and VPAC2 have been reported (13, 22).
- Abad C, and Tan YV. Immunomodulatory Roles of PACAP and VIP: Lessons from Knockout Mice. J Mol Neurosci 66: 102-113, 2018. PMID: 30105629.
- Adamou JE, Aiyar N, Van Horn S, and Elshourbagy NA. Cloning and functional characterization of the human vasoactive intestinal peptide (VIP)-2 receptor. Biochem Biophys Res Commun 209: 385-392, 1995. PMID: 7733904.
- Asnicar MA, Koster A, Heiman ML, Tinsley F, Smith DP, Galbreath E, Fox N, Ma YL, Blum WF, and Hsiung HM. Vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide receptor 2 deficiency in mice results in growth retardation and increased basal metabolic rate. Endocrinology 143: 3994-4006, 2002. PMID: 12239111.
- Bissonnette BM, Collen MJ, Adachi H, Jensen RT, and Gardner JD. Receptors for vasoactive intestinal peptide and secretin on rat pancreatic acini. Am J Physiol Gastrointest Liver Physiol 246: G710-G717, 1984. PMID: 6204536.
- Christophe JP, Conlon TP, and Gardner JD. Interaction of porcine vasoactive intestinal peptide with dispersed pancreatic acinar cells from the guinea pig. Binding of radioiodinated peptide. J Biol Chem 251: 4629-4634, 1976. PMID: 947900.
- Christopoulos A, Christopoulos G, Morfis M, Udawela M, Laburthe M, Couvineau A, Kuwasako K, Tilakaratne N, and Sexton PM. Novel receptor partners and function of receptor activity-modifying proteins. J Biol Chem 278: 3293-3297, 2003. PMID: 12446722.
- Couvineau A, Ceraudo E, Tan YV, and Laburthe M. VPAC1 receptor binding site: contribution of photoaffinity labeling approach. Neuropeptides 44: 127-132, 2010. PMID: 20031208.
- Couvineau A, Fabre C, Gaudin P, Maoret JJ, and Laburthe M. Mutagenesis of N-glycosylation sites in the human vasoactive intestinal peptide 1 receptor. Evidence that asparagine 58 or 69 is crucial for correct delivery of the receptor to plasma membrane. Biochemistry 35: 1745-1752, 1996. PMID: 8639654.
- Couvineau A, and Laburthe M. VPAC receptors: structure, molecular pharmacology and interaction with accessory proteins. Br J Pharmacol 166: 42-50, 2012. PMID: 21951273.
- Dehaye JP, Winand J, Damien C, Gomez F, Poloczek P, Robberecht P, Vandermeers A, Vandermeers-Piret MC, Stievenart M, and Christophe J. Receptors involved in helodermin action on rat pancreatic acini. Am J Physiol Gastrointest Liver Physiol 251: G602-G610, 1986. PMID: 2430470.
- Delgado M, Pozo D, and Ganea D. The significance of vasoactive intestinal peptide in immunomodulation. Pharmacol Rev 56: 249-290, 2004. PMID: 15169929.
- Dickson L, and Finlayson K. VPAC and PAC receptors: From ligands to function. Pharmacol Ther 121: 294-316, 2009. PMID: 19109992.
- Fabricius D, Karacay B, Shutt D, Leverich W, Schafer B, Takle E, Thedens D, Khanna G, Raikwar S, Yang B, Desmond ME, and O'Dorisio MS. Characterization of intestinal and pancreatic dysfunction in VPAC1-null mutant mouse. Pancreas 40: 861-871, 2011. PMID: 21697765.
- Gardner JD, Conlon TP, Fink ML, and Bodanszky M. Interaction of peptides related to secretin with hormone receptors on pancreatic acinar cells. Gastroenterology 71: 965-970, 1976. PMID: 186350.
- Gardner JD, and Jensen RT. Receptors for gut peptides and other secretagogues on pancreatic acinar cells. In: Handbook of Physiology - The Gastrointestinal System II, edited by Makhlouf GM. Oxford University Press, 1989, p. 171-192.
- Gardner JD, and Jensen RT. Receptors for Secretagogues on pancreatic acinar cells. In: The Pancreas: Bioogy, Pathobiology, and Disease, edited by Go VLW, DiMagno, E.P, Gardner, J.D., Lebenthal, E., Reber, H.A., Scheele, G.A. New York: Raven Press, 1993, p. 151-166.
- Gourlet P, Vandermeers A, Vertongen P, Rathe J, De Neef P, Cnudde J, Waelbroeck M, and Robberecht P. Development of high affinity selective VIP1 receptor agonists. Peptides 18: 1539-1545, 1997. PMID: 9437714.
- Gourlet P, Vertongen P, Vandermeers A, Vandermeers-Piret MC, Rathe J, De Neef P, Waelbroeck M, and Robberecht P. The long-acting vasoactive intestinal polypeptide agonist RO 25-1553 is highly selective of the VIP2 receptor subclass. Peptides 18: 403-408, 1997. PMID: 9145428.
- Goyal D. and Pisegna JR. Pituitary Adenylated Cyclase Activating Polypeptide (PACAP). In: Pancreapedia; Exocrine Pancreas Knowledge Base. 2014. DOI: 10.3998/panc.2014.12.
- Harikumar KG, Morfis MM, Lisenbee CS, Sexton PM, and Miller LJ. Constitutive formation of oligomeric complexes between family B G protein-coupled vasoactive intestinal polypeptide and secretin receptors. Mol Pharmacol 69: 363-373, 2006. PMID: 16244179.
- Harmar AJ, Fahrenkrug J, Gozes I, Laburthe M, May V, Pisegna JR, Vaudry D, Vaudry H, Waschek JA, and Said SI. Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1. Br J Pharmacol 166: 4-17, 2012. PMID: 22289055.
- Harmar AJ, Marston HM, Shen S, Spratt C, West KM, Sheward WJ, Morrison CF, Dorin JR, Piggins HD, Reubi JC, Kelly JS, Maywood ES, and Hastings MH. The VPAC2 receptor is essential for circadian function in the mouse suprachiasmatic nuclei. Cell 109: 497-508, 2002. PMID: 12086606.
- Harmar AJ, Sheward WJ, Morrison CF, Waser B, Gugger M, and Reubi JC. Distribution of the VPAC2 receptor in peripheral tissues of the mouse. Endocrinology 145: 1203-1210, 2004. PMID: 14617572.
- Igarashi H, Ito T, Kuwano-Kojima M, Takayanagi R, Coy DH, and Jensen RT. Involvement of VPAC1 and VPAC2 receptors in increasing local pancreatic blood flow in anesthetized rats. Pancreas 37: 236-238, 2008. PMID: 18665096.
- Ishihara T, Shigemoto R, Mori K, Takahashi K, and Nagata S. Functional expression and tissue distribution of a novel receptor for vasoactive intestinal polypeptide. Neuron 8: 811-819, 1992. PMID: 1314625.
- Ito T, Hou W, Katsuno T, Igarashi H, Pradhan TK, Mantey SA, Coy DH, and Jensen RT. Rat and guinea pig pancreatic acini possess both VIP1 and VIP2 receptors, which mediate enzyme secretion. Am J Physiol Gastrointest Liver Physiol 278: G64-G74, 2000. PMID: 10644563.
- Jiang S, Kopras E, McMichael M, Bell RH, Jr., and Ulrich CD, 2nd. Vasoactive intestinal peptide (VIP) stimulates in vitro growth of VIP-1 receptor-bearing human pancreatic adenocarcinoma-derived cells. Cancer Res 57: 1475-1480, 1997. PMID: 9108448.
- Laburthe M, Couvineau A, and Tan V. Class II G protein-coupled receptors for VIP and PACAP: structure, models of activation and pharmacology. Peptides 28: 1631-1639, 2007. PMID: 17574305.
- Le Meuth V, Farjaudon N, Bawab W, Chastre E, Rosselin G, Guilloteau P, and Gespach C. Characterization of binding sites for VIP-related peptides and activation of adenylate cyclase in developing pancreas. Am J Physiol Gastrointest Liver Physiol 260: G265-G274, 1991. PMID: 1847591.
- Lutz EM, Sheward WJ, West KM, Morrow JA, Fink G, and Harmar AJ. The VIP2 receptor: molecular characterisation of a cDNA encoding a novel receptor for vasoactive intestinal peptide. FEBS Lett 334: 3-8, 1993. PMID: 8224221.
- McArthur KE, Wood CL, O'Dorisio MS, Zhou ZC, Gardner JD, and Jensen RT. Characterization of receptors for VIP on pancreatic acinar cell plasma membranes using covalent cross-linking. Am J Physiol Gastrointest Liver Physiol 252: G404-G412, 1987. PMID: 2435170.
- Meuth-Metzinger VL, Philouze-Rome V, Metzinger L, Gespach C, and Guilloteau P. Differential activation of adenylate cyclase by secretin and VIP receptors in the calf pancreas. Pancreas 31: 174-181, 2005. PMID: 16025005.
- Nicole P, Lins L, Rouyer-Fessard C, Drouot C, Fulcrand P, Thomas A, Couvineau A, Martinez J, Brasseur R, and Laburthe M. Identification of key residues for interaction of vasoactive intestinal peptide with human VPAC1 and VPAC2 receptors and development of a highly selective VPAC1 receptor agonist. Alanine scanning and molecular modeling of the peptide. J Biol Chem 275: 24003-24012, 2000. PMID: 10801840.
- Pandol SJ, Dharmsathaphorn K, Schoeffield MS, Vale W, and Rivier J. Vasoactive intestinal peptide receptor antagonist [4Cl-D-Phe6, Leu17] VIP. Am J Physiol Gastrointest Liver Physiol 250: G553-G557, 1986. PMID: 2421587.
- Pisegna JR, and Wank SA. Molecular cloning and functional expression of the pituitary adenylate cyclase-activating polypeptide type I receptor. Proc Natl Acad Sci U S A 90: 6345-6349, 1993. PMID: 8392197.
- Rachdi L, Marie JC, and Scharfmann R. Role for VPAC2 receptor-mediated signals in pancreas development. Diabetes 52: 85-92, 2003. PMID: 12502497.
- Raufman JP, Jensen RT, Sutliff VE, Pisano JJ, and Gardner JD. Actions of Gila monster venom on dispersed acini from guinea pig pancreas. Am J Physiol Gastrointest Liver Physiol 242: G470-G474, 1982. PMID: 6177252.
- Reubi JC, Laderach U, Waser B, Gebbers JO, Robberecht P, and Laissue JA. Vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor subtypes in human tumors and their tissues of origin. Cancer Res 60: 3105-3112, 2000. PMID: 10850463.
- Schmidt WE, Seebeck J, Hocker M, Schwarzhoff R, Schafer H, Fornefeld H, Morys-Wortmann C, Folsch UR, and Creutzfeldt W. PACAP and VIP stimulate enzyme secretion in rat pancreatic acini via interaction with VIP/PACAP-2 receptors: additive augmentation of CCK/carbachol-induced enzyme release. Pancreas 8: 476-487, 1993. PMID: 8103217.
- Sreedharan SP, Huang JX, Cheung MC, and Goetzl EJ. Structure, expression, and chromosomal localization of the type I human vasoactive intestinal peptide receptor gene. Proc Natl Acad Sci U S A 92: 2939-2943, 1995. PMID: 7708752.
- Svoboda M, Poloczek P, Winand J, Robberecht P, and Christophe J. Species differences in the molecular characteristics of vasoactive-intestinal-peptide receptors in the pancreas from rat and guinea-pig. Eur J Biochem 174: 59-66, 1988. PMID: 2836201.
- Tsutsumi M, Claus TH, Liang Y, Li Y, Yang L, Zhu J, Dela Cruz F, Peng X, Chen H, Yung SL, Hamren S, Livingston JN, and Pan CQ. A potent and highly selective VPAC2 agonist enhances glucose-induced insulin release and glucose disposal: a potential therapy for type 2 diabetes. Diabetes 51: 1453-1460, 2002. PMID: 11978642.
- Ulrich CD, 2nd, Holtmann M, and Miller LJ. Secretin and vasoactive intestinal peptide receptors: members of a unique family of G protein-coupled receptors. Gastroenterology 114: 382-397, 1998. PMID: 9453500.
- Usdin TB, Bonner TI, and Mezey E. Two receptors for vasoactive intestinal polypeptide with similar specificity and complementary distributions. Endocrinology 135: 2662-2680, 1994. PMID: 7988457.
- Vertongen P, Schiffmann SN, Gourlet P, and Robberecht P. Autoradiographic visualization of the receptor subclasses for vasoactive intestinal polypeptide (VIP) in rat brain. Peptides 18: 1547-1554, 1997. PMID: 9437715.
- Waelbroeck M, Robberecht P, Coy DH, Camus JC, De Neef P, and Christophe J. Interaction of growth hormone-releasing factor (GRF) and 14 GRF analogs with vasoactive intestinal peptide (VIP) receptors of rat pancreas. Discovery of (N-Ac-Tyr1,D-Phe2)-GRF(1-29)-NH2 as a VIP antagonist. Endocrinology 116: 2643-2649, 1985. PMID: 2859987.
- Wei Y, and Mojsov S. Tissue specific expression of different human receptor types for pituitary adenylate cyclase activating polypeptide and vasoactive intestinal polypeptide: implications for their role in human physiology. J Neuroendocrinol 8: 811-817, 1996. PMID: 8933357.
- Williams JA. Vasoactive Intestinal Polypeptide or VIP. In: Pancreapedia; Exocrine Pancreas Knowledge Base. 2020. DOI: 10.3998/panc.2020.03.
- Yamada H, Watanabe M, and Yada T. Cytosolic Ca2+ responses to sub-picomolar and nanomolar PACAP in pancreatic beta-cells are mediated by VPAC2 and PAC1 receptors. Regul Pept 123: 147-153, 2004. PMID: 15518905.
- Zhou ZC, Gardner JD, and Jensen RT. Interaction of peptides related to VIP and secretin with guinea pig pancreatic acini. Am J Physiol Gastrointest Liver Physiol 256: G283-G290, 1989. PMID: 2465694.
- Zhou ZC, Gardner JD, and Jensen RT. Receptors for vasoactive intestinal peptide and secretin on guinea pig pancreatic acini. Peptides 8: 633-637, 1987. PMID: 2819833.