PACAP in avians: origin,occurrence, and receptors--pharmacological and functional considerations

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a novel member of the secretin/glucagon/vasoactive intestinal peptide (VIP) superfamily. In vertebrates, including avians, it occurs in two forms: PACAP(38) and PACAP(27). PACAP structure is well conserved during evolution, being identical in mammals, and showing one amino acid dfifference in avians (chick, turkey). PACAP is widely distributed in the central nervous system and peripheral tissues and displays a pleiotropic activity, including functions as a hypophysiotropic hormone, neuromodulator, and neurotrophic factor. PACAP exerts its biological actions through three types of receptors designated PAC(1), VPAC(1) and VPAC(1). This review (1) presents the current knowledge on PACAP origin, distribution and function, (2) compares the avian findings with those found in mammals, and (3) describes receptor-linked mechanisms in avians, including recent data on receptor-related signal transduction pathways, with a special emphasis on receptor pharmacology and function.     

Pituitary adenylate cyclase-activating polypeptide and its receptors: from structure to functions

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide that was first isolated from ovine hypothalamic extracts on the basis of its ability to stimulate cAMP formation in anterior pituitary cells. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-glucagon-growth hormone releasing factor-secretin superfamily. The sequence of PACAP has been remarkably well conserved during the evolution from protochordate to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, and respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide whose activity remains unknown. Two types of PACAP binding sites have been characterized. Type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes, the PACAP-specific PAC1 receptor, which is coupled to several transduction systems, and the two PACAP/VIP-indifferent VPAC1 and VPAC2 receptors, which are primarily coupled to adenylyl cyclase. PAC1 receptors are particularly abundant in the brain and pituitary and adrenal glands whereas VPAC receptors are expressed mainly in the lung, liver, and testis. The wide distribution of PACAP and PACAP receptors has led to an explosion of studies aimed at determining the pharmacological effects and biological functions of the peptide. This report reviews the current knowledge concerning the multiple actions of PACAP in the central nervous system and in various peripheral organs including the endocrine glands, the airways, and the cardiovascular and immune systems, as well as the different effects of PACAP on a number of tumor cell types.     

VIP and PACAP are autocrine factors that protect the androgen-independent prostate cancer cell line PC-3 from apoptosis induced by serum withdrawal

1. In the present study, we describe the expression of the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as well as their receptors in PC-3 cells, a human prostate cancer cell line. In addition, we have investigated their role in apoptosis induced by serum starvation. 2. By RT-PCR and immunocytochemistry assays, we have demonstrated the production of VIP and PACAP in PC-3 cells. 3. We have demonstrated by RT-PCR and binding assays the expression of common PACAP/VIP (VPAC(1) and VPAC(2)) receptors, but not PACAP-specific (PAC(1)) receptors. The pharmacological profile of [(125)I]-VIP binding assays was as follows: VPAC(1) antagonist=VPAC(1) agonist>VIP>VPAC(2) agonist (IC(50)=1.2, 1.5, 2.3 and 30 nM, respectively). In addition, both receptor subtypes are functional since VIP, PACAP-27 or VPAC(1) and VPAC(2) agonists all increased the intracellular levels of cAMP. 4. The expression of both peptides and their receptors is similar in serum-cultured and serum-deprived PC-3 cells. The treatment of serum-deprived PC-3 cells with exogenous VIP or PACAP-27 increases cell number and viability in a dose-dependent manner, as demonstrated by cellular counting and MTT assays. The increased cell survival is exerted through the VPAC(1) receptor, since a VPAC(1), but not VPAC(2), receptor agonist, mimics the effects and a VPAC(1) receptor antagonist blocks it. Moreover, VIP and PACAP-27 inhibit genomic DNA fragmentation in PC-3 cells triggered by serum starvation, and increase the immunoreactivity of the antiapoptotic protein bcl-2. 5. Our results suggest that VIP and PACAP are autocrine/paracrine factors that protect PC-3 cells from apoptosis through VPAC1 receptors.     

Passage of VIP/PACAP/secretin family across the blood-brain barrier: therapeutic effects

In recent years, VIP/PACAP/secretin family has special interest. Family members are vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), secretin, glucagon, glucagon like peptide-1 (GLP(1)), GLP(2), gastric inhibitory peptide (GIP), growth hormone releasing hormone (GHRH or GRF), and peptide histidine methionine (PHM). Most of the family members present both in central nervous system (CNS) and in various peripheral tissues. The family members that are released into blood from periphery, especially gut, circulate the brain and they can cross the blood brain barrier. On the other hand, some of the members of this family that present in the brain, can cross from brain to blood and reach the peripheral targets. VIP, secretin, GLP(1), and PACAP 27 are transported into the brain by transmembrane diffusion, a non-saturable mechanism. However, uptake of PACAP 38 into the brain is saturable mechanism. While there is no report for the passage of GIP, GLP(2), and PHM, there is only one report that shows, glucagon and GHRH can cross the BBB. The passage of VIP/PACAP/secretin family members opens up new horizon for understanding of CNS effects of peripherally administrated peptides. There is much hope that those peptides may prove to be useful in the treatment of serious neurological diseases such as Alzheimer's disease, amyotropic lateral sclerosis, Parkinson's disease, AIDS related neuropathy, diabetic neuropathy, autism, stroke and nerve injury. Their benefits in various pathophysiologic conditions undoubtly motivate the development of a novel drug design for future therapeutics.     

Cardioprotective role of the VIP signaling system

Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide that belongs to a family of structurally related peptide hormones including pituitary adenylate cyclase-activating peptide (PACAP). These hormones are widely distributed in the nervous system, where they act as neurotransmitters. Their biological effects are mediated by specific receptors, VPAC1 and VPAC2, which have comparable affinity for VIP and PACAP, and PAC1, which binds VIP with 1,000-fold lower affinity than PACAP. Both peptides are involved in autonomic regulation of the cardiovascular system, where they exert positive inotropic and chronotropic effects, and cause coronary vasodilatation. Additionally, PACAP inhibits proliferation of cardiac fibroblasts. Several cardiovascular diseases, such as myocardial fibrosis, heart failure, cardiomyopathy and pulmonary hypertension, have been found to be associated with changes in myocardial VIP concentration or with alteration of affinity, density and physiological responsiveness of VIP/PACAP receptors. Application of the peptides or their agonists has beneficial effect in hypertension, heart failure and myocardial fibrosis. Taken together, VIP and PACAP have beneficial effects in various pathological conditions.     

The role of VIP/PACAP receptor subtypes in spinal somatosensory processing in rats with an experimental peripheral mononeuropathy

Peripheral nerve damage often results in the development of chronic pain states, resistant to classical analgesics. Since vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are up-regulated in dorsal root ganglion cells following peripheral nerve injury, we investigated the expression and influence of VPAC1, VPAC2 and PAC1 receptors in rat spinal dorsal horn following a chronic constriction injury (CCI). Electrophysiological studies revealed that selective antagonists of VPAC1, VPAC2 and PAC1 receptors inhibit mustard oil-, but not brush-induced activity of dorsal horn neurones in CCI animals, while cold-induced neuronal activity was attenuated by VPAC1 and PAC1, but not VPAC2 receptor antagonists. Ionophoresis of selective agonists for the receptor subtypes revealed that the VPAC2 receptor agonist excited twice as many cells in CCI compared to normal animals, while the number of cells excited by the VPAC1 receptor agonist decreased and responses to PACAP-38 remained unchanged. In situ hybridisation histochemistry (ISHH) confirmed an increase in the expression of VPAC2 receptor mRNA within the ipsilateral dorsal horn following neuropathy, while VPAC1 receptor mRNA was seen to decrease and that for PAC1 receptors remained unchanged. These data indicate that VIP/PACAP receptors may be important regulatory factors in neuropathic pain states.     

Mice lacking PACAP: a mini-review focussing on brain function

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the vasoactive intestinal peptide (VIP)/ secretin/ glucagon superfamily and functions as a hormone, neurohormone, and neurotransmitter in the central nervous system as well as in several peripheral tissues. Recently, several groups including ours have independently produced lines of mice lacking PACAP (PACAP(-/-)). These mutant mice have not only led to a better understanding of the physiologic roles of endogenous PACAP, but have also revealed some unexpected roles of PACAP. In this paper, phenotypic changes in several brain functions in PACAP(-/-) mice, including light-induced phase-resetting of the circadian activity rhythm, hippocampal long-term potentiation, and psychomotor behaviors, are reviewed based on the results obtained in our laboratory.     

Neuronal and smooth muscle receptors involved in the PACAP- and VIP-induced relaxations of the pig urinary bladder neck

BACKGROUND AND PURPOSE: As pituitary adenylate cyclase-activating polypeptide 38 (PACAP 38)- and vasoactive intestinal peptide (VIP) are widely distributed in the urinary tract, the current study investigated the receptors and mechanisms involved in relaxations induced by these peptides in the pig bladder neck. EXPERIMENTAL APPROACH: Urothelium-denuded strips were suspended in organ baths for isometric force recordings and the relaxations to VIP and PACAP analogues were investigated. KEY RESULTS: VIP, PACAP 38, PACAP 27 and [Ala(11,22,28)]-VIP produced similar relaxations. Inhibition of neuronal voltage-gated Ca(2+) channels reduced relaxations to PACAP 38 and increased those induced by VIP. Blockade of capsaicin-sensitive primary afferents (CSPA), nitric oxide (NO)-synthase or guanylate cyclase reduced the PACAP 38 relaxations but failed to modify the VIP responses. Inhibition of VIP/PACAP receptors and of voltage-gated K(+) channels reduced PACAP 38 and VIP relaxations, which were not modified by the K(+) channel blockers iberiotoxin, charybdotoxin, apamin or glibenclamide. The phosphodiesterase 4 inhibitor rolipram and the adenylate cyclase activator forskolin produced potent relaxations. Blockade of protein kinase A (PKA) reduced PACAP 38- and VIP-induced relaxations. CONCLUSIONS AND IMPLICATIONS: PACAP 38 and VIP relax the pig urinary bladder neck through muscle VPAC(2) receptors linked to the cAMP-PKA pathway and involve activation of voltage-gated K(+) channels. Facilitatory PAC(1) receptors located at CSPA and coupled to NO release, and inhibitory VPAC receptors at motor endings are also involved in the relaxations to PACAP 38 and VIP, respectively. VIP/PACAP receptor antagonists could be useful in the therapy of urinary incontinence produced by intrinsic sphincter deficiency.     

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in the goose cerebral cortex

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in the goose cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [(125)I]-VIP, and (2) effects of peptides from the VIP/PACAP/secretin family on cyclic AMP formation. The binding of [(125)I]-VIP to goose cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding sites with a high affinity (K(d)=0.76 +/- 0.13 nM) and high capacity (B(max)=70 +/- 7 fmol/mg of protein). Various peptides displaced the specific binding of 0.12 nM [(125)I]-VIP to the goose cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [(125)I]-VIP binding to the goose cerebrum was: PACAP(38) asymptotically equal to mammalian VIP > or = PACAP(27) asymptotically equal to chicken VIP > PHI (peptide histidine-isoleucine) > secretin (inactive). About 52% of specific [(125)I]-VIP binding sites in the goose cerebral cortex was sensitive to 5'-guanylimidodiphosphate [Gpp(NH)p], a nonhydrolyzable analogue of GTP. PACAP(38) and PACAP(27) potently stimulated cyclic AMP formation in the goose cerebral cortical slices in a concentration-dependent manner, displaying EC(50) values of 45.5 nM and 51.5 nM, respectively. Chicken VIP was markedly less potent than both forms of PACAP, mammalian VIP only weakly affected the nucleotide production, while effects evoked by PHI were negligible. It is concluded that the cerebral cortex of goose contains VPAC type receptors that are labeled with [(125)I]-VIP and are positively linked to cyclic AMP formation. In addition, the observed stronger action of PACAP, when compared to VIP, on cyclic AMP production in this tissue suggests its interaction with both PAC(1) and VPAC receptors.     

Review on the protective effects of PACAP in models of neurodegenerative diseases in vitro and in vivo

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic and multifunctional peptide exerting its effects via 3 main receptors (PAC1, VPAC1 and VPAC2). PACAP is now considered to be a potent neurotrophic and neuroprotective peptide. It plays an important role during the embryonic development of the nervous system. PACAP also protects neurons against various toxic insults in neuronal cultures of diverse origins. In vivo, PACAP shows neuroprotection in models of ischemic and traumatic brain injuries, and those of neurodegenerative diseases. The present review summarizes the findings on the neuroprotective potential of PACAP in models of neurodegenerative diseases, with special focus on in vitro and in vivo models of Parkinson`s disease, Huntington chorea and Alzheimer`s disease. Based on these observations, both endogenous and exogenously administered PACAP or its novel analogs, fragments offer a novel therapeutic approach in treatment of neurodegenerative diseases.     

Effects of neuropeptides of the secretin/VIP/PACAP family on cyclic AMP formation in the chick hypothalamus and cerebral cortex

Six neuropeptides: short and long form of the pituitary adenylate cyclase activating polypeptide (PACAP), i.e. PACAP27 and PACAP38, vasoactive intestinal peptide (VIP), peptide histidine-isoleucine (PHI), secretin and glucagon, members of the secretin/VIP/PACAP superfamily ofpolypeptides, were tested for their ability to stimulate cyclic AMP formation in [3H]adenine-prelabeled slices of the chick hypothalamus and cerebral cortex. Of the tested peptides, only PACAP evoked pronounced and significant responses in the two analyzed brain structures. Although magnitude of the responses varied in different experiments, the effects of both forms of PACAP were usually larger in the cerebral cortex than in the hypothalamus. Glucagon, PHI (both used at concentrations 0.01-1 microM) and VIP (0.1-3 microM) induced concentration-dependent yet comparatively small effects that did not reach statistical significance, while secretin (0.1-3 microM) had no effect.     

Comparative effects of PACAP and VIP on pancreatic endocrine secretions and vascular resistance in rat.

1. The effects of pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and secretin on pancreatic endocrine secretions and vascular resistance were investigated and compared in the isolated perfused pancreas of the rat. The PACAP/VIP receptor types involved have been characterized. 2. On insulin secretion, in the range 10(-11) to 10(-8) M, PACAP and VIP elicited a concentration-dependent biphasic response from pancreas perfused with 8.3 mM glucose; the peptides were equipotent. In contrast, secretin was ineffective in the range 10(-11) to 10(-9) M; at 10(-8) and 10(-7) M, it induced only low and transient insulin responses. On the other hand, the peptides did not modify the basal insulin release in the presence of a non stimulating glucose concentration (2.8 mM). 3. On glucagon secretion, PACAP and VIP (10(-11) to 10(-8) M) but also secretin (10(-9) to 10(-7) M) caused a concentration-dependent peak shaped response from pancreas perfused with 2.8 mM glucose; PACAP and VIP were equipotent and 20 times more potent then secretin. On the other hand, the peptides did not affect the glucagon release in the presence of 8.3 mM glucose. 4. On pancreatic vessels, in the range 10(-11) to 10(-9) M, the three peptides were equipotent in inducing a concentration-dependent sustained increase in pancreatic flow rate. On the other hand, at the high concentration of 10(-7) M PACAP but not VIP provoked a transient decrease of flow rate. 5. This study provides evidence for PACAP/VIP type II receptors mediating insulin and glucagon secretion as well as vasodilatation in rat pancreas. In addition, the different efficacies of secretin suggest that these effects are mediated by different PACAP/VIP type II receptor subtypes.     

PAC1 receptor-mediated relaxation of longitudinal muscle of the mouse proximal colon

Since pituitary adenylate cyclase-activating polypeptide (PACAP) was shown to partially mediate nonadrenergic, noncholinergic (NANC) relaxation of longitudinal muscle of the proximal colon of ICR mice, we further studied the receptor subtype activated by PACAP by using a mutant mouse whose PAC1 receptors are markedly reduced. In wild-type mice, the PACAP-mediated component of NANC relaxation was 33%, but it was absent in the mutant mice. The potency of exogenous PACAP in inducing relaxation in the mutant mice was one hundredth of that in wild-type mice. VPAC1 and VPAC2 receptors were not suggested to have any role in the relaxation. These results suggest that PACAP mediates NANC relaxation of longitudinal muscle of mouse proximal colon via PAC1 receptors.     

Heterogeneity of neuronal and smooth muscle receptors involved in the VIP- and PACAP-induced relaxations of the pig intravesical ureter

1. The mechanisms and receptors involved in the vasoactive intestinal peptide (VIP)- and pituitary adenylate cyclase-activating polypeptide (PACAP)-induced relaxations of the pig intravesical ureter were investigated. 2. VIP, PACAP 38 and PACAP 27 concentration-dependently relaxed U46619-contracted ureteral strips with a similar potency. [Ala(11,22,28)]-VIP, a VPAC(1) agonist, showed inconsistent relaxations. 3. The neuronal voltage-gated Ca(2+) channel inhibitor, omega-conotoxin GVIA (omega-CgTX, 1 microm), reduced the VIP relaxations. Urothelium removal or blockade of capsaicin-sensitive primary afferents, nitric oxide (NO) synthase and guanylate cyclase with capsaicin (10 microm), N(G)-nitro-l-arginine (l-NOARG, 100 microm) and 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 microm), respectively, did not change the VIP relaxations. However, the PACAP 38 relaxations were reduced by omega-CgTX, capsaicin, l-NOARG and ODQ. 4. The VIP and VIP/PACAP receptor antagonists, [Lys(1), Pro(2,5), Arg(3,4), Tyr(6)]-VIP (1 microm) and PACAP (6-38) (0.4 microm), inhibited VIP and VIP and PACAP 38, respectively, relaxations. 5. The nonselective and large-conductance Ca(2)-activated K(+) channel blockers, tetraethylammonium (3 mm) and charybdotoxin (0.1 microm), respectively, and neuropeptide Y (0.1 microm) did not modify the VIP relaxations. The small-conductance Ca(2)-activated K(+) channel blocker apamin (1 microm) did not change the PACAP 27 relaxations. 6. The cAMP-dependent protein kinase A (PKA) blocker, 8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate (Rp-8-CPT-cAMPS, 100 microm), reduced VIP relaxations. The phosphodiesterase 4 inhibitor rolipram and the adenylate cyclase activator forskolin relaxed ureteral preparations. The rolipram relaxations were reduced by Rp-8-CPT-cAMPS. Forskolin (30 nm) evoked a potentiation of VIP relaxations. 7. These results suggest that VIP and PACAP relax the pig ureter through smooth muscle receptors, probably of the VPAC(2) subtype, linked to a cAMP-PKA pathway. Neuronal VPAC receptors localized at motor nerves and PAC(1) receptors placed at sensory nerves and coupled to NO release, seem also to be involved in the VIP and PACAP 38 relaxations.     

Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, gastric inhibitory peptide (GIP) and growth hormone-releasing hormone (GHRH). VIP and PACAP exert their actions through three GPCRs – PAC₁, VPAC₁ and VPAC₂– belonging to class B (also referred to as class II, or secretin receptor-like GPCRs). This family comprises receptors for all peptides structurally related to VIP and PACAP, and also receptors for parathyroid hormone, corticotropin-releasing factor, calcitonin and related peptides. PAC₁ receptors are selective for PACAP, whereas VPAC₁ and VPAC₂ respond to both VIP and PACAP with high affinity. VIP and PACAP play diverse and important roles in the CNS, with functions in the control of circadian rhythms, learning and memory, anxiety and responses to stress and brain injury. Recent genetic studies also implicate the VPAC₂ receptor in susceptibility to schizophrenia and the PAC₁ receptor in post-traumatic stress disorder. In the periphery, VIP and PACAP play important roles in the control of immunity and inflammation, the control of pancreatic insulin secretion, the release of catecholamines from the adrenal medulla and as co-transmitters in autonomic and sensory neurons. This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee on receptors for VIP and PACAP, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More detailed information has been incorporated into newly revised pages in the IUPHAR database (http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=67).

LINKED ARTICLES

This article is part of a themed section on Secretin Family (Class B) G Protein-Coupled Receptors. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-1     

Design and in vitro characterization of PAC1/VPAC1-selective agonists with potent neuroprotective effects

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide that exerts a large array of actions in the central nervous system and periphery. Through the activation of PAC1 and VPAC1, PACAP is able to exert neuroprotective, as well as anti-inflammatory effects, two phenomena involved in the pathogenesis and the progression of neurodegenerative diseases. The aim of the current study was to provide insights into the molecular arrangement of the amino terminus of PACAP and to develop new potent and selective PAC1/VPAC1 agonists promoting neuronal survival. We have synthesized a series of PACAP derivatives and measured their binding affinity and their ability to induce intracellular calcium mobilization for each receptor, i.e. PAC1, VPAC1, and VPAC2. Ultimately, analogs with an improved pharmacological profile were evaluated in an in vitro model of neuronal loss. Results showed that introduction of a hydroxyproline or an alanine moiety, respectively, at position 2 or 7 generated derivatives without significant VPAC2 agonistic activity. Moreover, the structure–activity relationship study suggests the presence of common (Asx-turn like) and distinct (different N-capping type) secondary structures that might be responsible for receptor recognition, selectivity and activation. Finally, evaluation of the neuroprotective activity of [Ala⁷]PACAP27 and [Hyp²]PACAP27 demonstrated their ability to protect potently human dopaminergic SH-SY5Y neuroblasts against the toxicity of MPP⁺, in pre- and co-treatment experiments. These new pharmacological and structural data should prove useful for the rational design of PACAP-derived compounds that could be putative therapeutic agents for the treatment of neurodegenerative diseases.     

Therapeutical approaches of vasoactive intestinal peptide as a pleiotropic immunomodulator

The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two neuropeptides belonging to the VIP/secretin/glucagon family of peptides. VIP/PACAP are present and released from both innervation and immune cells, particularly Th2 cells, and exert a wide spectrum of immunological functions controlling the homeostasis of immune system through different receptors expressed in various immunocompetent cells. VIP/PACAP have a general anti-inflammatory effect, both in innate and adaptive immunity. In innate immunity, VIP/PACAP inhibit the production of pro-inflammatory cytokines and chemokines from macrophages, microglia and dendritic cells. In addition, VIP/PACAP reduce the expression of costimulatory molecules (particularly CD80 and CD86) on the antigen-presenting cells, and therefore reduce stimulation of antigen-specific CD4(+) T cells. In terms of adaptive immunity, VIP/PACAP promote Th2-type responses, and reduce the pro-inflammatory Th1-type responses. Several of the molecular mechanisms involved in the inhibition of cytokine and chemokine expression, and in the preferential development and/or survival of Th2 effectors, are perfectly known. Therefore, VIP/PACAP and analogues have been recently proposed as very promising candidates, alternative to other existing treatments, for treating acute and chronic inflammatory and autoimmune diseases, such as septic shock, rheumatoid arthritis, multiple sclerosis, Parkinson's disease, Crohn disease, or autoimmune diabetes. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system; and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as an exciting new candidate for therapeutic intervention and drug development.     

The family B1 GPCR: structural aspects and interaction with accessory proteins

G protein coupled receptors (GPCRs) play a crucial role in physiology and pathophysiology in humans. Beside the large family A (rhodopsin-like receptors) and family C GPCR (metabotropic glutamate receptors), the small family B1 GPCR (secretin-like receptors) includes important receptors such as vasoactive intestinal peptide receptors (VPAC), pituitary adenylyl cyclase activating peptide receptor (PAC1R), secretin receptor (SECR), growth hormone releasing factor receptor (GRFR), glucagon receptor (GCGR), glucagon like-peptide 1 and 2 receptors (GLPR), gastric inhibitory peptide receptor (GIPR), parathyroid hormone receptors (PTHR), calcitonin receptors (CTR) and corticotropin-releasing factor receptors (CRFR). They represent very promising targets for the development of drugs having therapeutical impact on many diseases such as chronic inflammation, neurodegeneration, diabetes, stress and osteoporosis. Over the past decade, structure-function relationship studies have demonstrated that the N-terminal ectodomain (N-ted) of family B1 receptors plays a pivotal role in natural ligand recognition. Structural analysis of some family B1 GPCR N-teds revealed the existence of a Sushi domain fold consisting of two antiparallel β sheets stabilized by three disulfide bonds and a salt bridge. The family B1 GPCRs promote cellular responses through a signaling pathway including predominantly the Gsadenylyl cyclase-cAMP pathway activation. Family B1 GPCRs also interact with a few accessory proteins which play a role in cell signaling, receptor expression and/or pharmacological profiles of receptors. These accessory proteins may represent new targets for the design of new drugs. Here, we review the current knowledge regarding: i) the structure of family B1 GPCR binding domain for natural ligands and ii) the interaction of family B1 GPCRs with accessory proteins.     

Domains determining agonist selectivity in chimaeric VIP2 (VPAC2)/PACAP (PAC1) receptors

1 The VPAC2 and PAC1 receptors are closely related members of the Group II G protein-coupled receptor family. At the VPAC2 receptor, VIP is equipotent to PACAP-38 in stimulating cyclic AMP production, whereas at the PAC1 receptor PACAP-38 is many fold more potent than VIP. In this study, domains which confer this selectivity were investigated by constructing four chimaeric receptors in which segments of the VPAC2 receptor were exchanged with the corresponding segment from the PAC1 receptor. 2 When expressed in COS 7 cells all the chimaeric receptors bound the common ligand [125I]PACAP-27 and produced cyclic AMP in response to agonists. 3 Relative selectivity for agonists was determined primarily by the amino terminal extracellular domain of the PAC1 receptor and the VPAC2 receptor. The interchange of other domains had little effect on the potency of PACAP-38 or PACAP-27. 4 For chimaeric constructs with a PAC1 receptor amino terminal domain, the substitution of increasing portions of the VPAC2 receptor decreased the potency of VIP yet increased that of helodermin. 5 This suggests that the interaction of VIP/helodermin but not PACAP with the PAC1 receptor may be influenced (and differentially so) by additional receptor domains.     

Effect of vasoactive intestinal peptide (VIP)-related peptides on cholinergic neurogenic and direct mucus secretion in ferret trachea in vitro

1 We investigated whether vasoactive intestinal peptide (VIP) and its related peptides, pituitary adenylate cyclase activating peptide (PACAP) and secretin, regulate cholinergic neural mucus secretion in ferret trachea in vitro, using 35SO4 as a mucus marker. We also studied the interaction between VIP and secretin on cholinergic mucus output. 2 VIP (1 and 10 microM) increased secretion, whereas neither PACAP1 - 27, PACAP1 - 38 nor secretin (up to 10 microM) increased mucus output. In contrast, VIP, PACAP1 - 27 and PACAP1 - 38 concentration-dependently inhibited cholinergic neural secretion, with an order of potency of VIP>PACAP 1 - 38>PACAP1 - 27. Neither PACAP1 - 27 nor PACAP1 - 38 altered the secretion induced by acetylcholine (ACh). 3 Secretin increased cholinergic neural secretion with a maximal increase of 190% at 1 microM. This potentiation was blocked by VIP or atropine. Similarly, secretin (1 microM) potentiated VIP (1 microM)-induced mucus output by 160%. Secretin did not alter exogenous ACh-induced secretion. VIP vs secretin competition curves suggested these two peptides were competing reversibly for the same receptor. 4 We conclude that, in ferret trachea in vitro, VIP and PACAPs inhibit cholinergic neural secretion via pre-junctional modulation of cholinergic neurotransmission. VIP and secretin compete for the same receptor, possibly a VIP1 receptor, at which secretin may be a receptor antagonist.