Cloning and functional characterization of a third pituitary adenylate cyclase-activating polypeptide receptor subtype expressed in insulin-secreting cells

VIP as a trophic factor in the CNS and cancer cells

The effects of vasoactive intestinal peptide (VIP) on the proliferation of central nervous system (CNS) and cancer cells were investigated. VIP has important actions during CNS development. During neurogenesis, VIP stimulates the proliferation and differentiation of brain neurons. Addition of VIP to embryonic mouse spinal cord cultures increases neuronal survival and activity dependent neurotrophic factor (ADNF) secretion from astroglial cells. VIP is an integrative regulator of brain growth and development during neurogenesis and embryogenesis. Also, VIP causes increased proliferation of human breast and lung cancer cells in vitro. VIP binds with high affinity to cancer cells, elevates the cAMP and increases gene expression of c-fos, c-jun, c-myc and vascular endothelial cell growth factor. The effects of VIP on cancer cells are reversed by VIPhybrid, a synthetic VPAC(1) receptor antagonist. VIPhyb inhibits the basal growth of lung cancer cells in vitro and tumors in vivo and potentiates the ability of chemotherapeutic drugs to kill cancer cells. Due to the high density of VPAC(1) receptors in cancer cells, VIP has been radiolabeled with 123I, 18F and 99mTc to image tumors. It remains to be determined if radiolabeled VIP analogs will be useful agents for early detection of cancer in patients.

Expression patterns of pituitary adenylate cyclase activating polypeptide and its type I receptor mRNAs in the rat placenta

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated from ovine hypothalamus and is known to act as a tropic factor in various cells. Recent report revealed the expression of PACAP and the PACAP type I (PAC(1)) receptor in human and rat placentas at term. Placenta is a critical organ that synthesizes several growth and angiogenic factors for its own growth as well as fetal development. However, there is little information regarding the expression pattern and cellular localization of PACAP and PAC(1) during pregnancy. The aim of this study was to define the expression and distribution of PACAP and PAC(1) receptor mRNAs in the rat placenta during pregnancy. PACAP and PAC(1) receptor mRNAs were expressed in decidual cells, chorionic vessels, and stromal cells of the chorionic villi. Interestingly, the expression of these genes varied with the day of gestation. For example, PACAP and PAC(1) receptor mRNAs expressed in decidual cells on day 13.5 and 15.5, their expression was strong in chorionic vessels and stromal cells of the chorionic villi within the labyrinth zone on day 17.5, 19.5, and 21.5. In fact, as gestation advanced, the expression of PACAP and PAC(1) receptor mRNAs in the decidua cells disappeared, as their high expression became evident in the chorionic vessels and stromal cells of the chorionic villi. Our finding that PACAP and the PAC(1) receptor are co-localized and their genes seemingly co-regulated within specific placental areas, strongly suggest that this peptide may play an important role, as an autoregulator or pararegulator via its PAC(1) receptor, in physiological functioning of the placenta for gestational maintenance.

Comparative distributions of pituitary adenylyl cyclase-activating polypeptide and its selective type I receptor mRNA in the frog (Xenopus laevis) brain

The detailed mRNA distributions of pituitary adenylyl cyclase-activating polypeptide (PACAP) and its selective type I receptor (PAC(1)) were systematically compared in the brain of the frog Xenopus laevis. PACAP mRNA expression overlapped with that of PAC(1) in many brain areas such as the pallium, hypothalamic preoptic area, ventral hypothalamic nuclei, habenular nucleus, most thalamic nuclei, the cerebellular nucleus, and nuclei of isthmi. In some structures, PACAP and PAC(1) gene transcripts were present in anatomically distinct cell layers. For example, in the olfactory bulb, PACAP mRNA was present in the mitral cell layer, whereas gene transcripts for the receptor were observed in the granule layer. In a number of regions, expression showed no obvious overlap. PAC(1) but not PACAP mRNA was present at moderate levels in the Purkinje cell layer of the cerebellum and distal lobe of the pituitary. Conversely, PAC(1) gene expression was absent in the spinal cord while PACAP mRNA signals were observed in the medial portion of the ventral horn and deep portion of the dorsal horn. The granule and molecular cell layer of the cerebellum, alpha-motor neurons in the spinal cord, and reticular nucleus of isthmi showed neither PACAP nor PAC(1) gene transcripts. These localized patterns of ligand and receptor gene expression suggest possible PACAP projection and target fields in the frog brain.

Up-regulation of the PACAP type-1 receptor (PAC1) promoter by neurotrophins in rat PC12 cells and mouse cerebellar granule cells via the Ras/mitogen-activated protein kinase cascade

The pituitary adenylate cyclase-activating polypeptide type-1 receptor (PAC1) has been involved in the survival and differentiation of neuroblasts during development. This study examined the effects of various neurotrophins on the activity of the mouse PAC1 promoter/luciferase reporter constructs in rat PC12 cells and in 8-day-old mouse cerebellar granule cells. In PC12 cells, both differentiating factors such as nerve growth factor (NGF) and mitogens such as epidermal growth factor (EGF) and insulin growth factor-1 (IGF-1) up-regulated PAC1 promoter activity by 2-4-fold in a concentration-dependent manner. Although PACAP differentiated the PC12 cells, it had no effect on the PAC1 promoter and antagonized the stimulatory effect of NGF. In cerebellar granule cells, IGF-1 and brain-derived neurotrophic factor (BDNF) also stimulated the activity of the PAC1 promoter. NGF and IGF-1 increased endogenous PAC1 mRNA levels, and the NGF-induced up-regulation is the result of an increase in transcription from PAC1 promoter instead of an increase in mRNA stability. The mitogen-activated protein kinase (MAPK) kinase inhibitor, PD98059, prevented the transcriptional effects both in PC12 and cerebellar granule cells. Moreover, expression of dominant-negative Ras protein in PC12 cells also prevented the NGF effect. Our results show that the PAC1 promoter can be up-regulated by diverse neurotrophins via an MAPK-dependent pathway and suggest a role for the Ras protein.

M phase-specific expression and phosphorylation-dependent ubiquitination of the ClC-2 channel

Cl(-) channel activities vary during the cell cycle and are thought to play various roles including regulation of cell volume. We have shown previously that ClC-2 channels are directly phosphorylated and functionally regulated by the M phase-specific cyclin-dependent kinase p34(cdc2)/cyclin B. We investigate here to determine whether the expression levels of ClC-2 channel protein vary during the cell cycle. Immunoblot and immunocytochemical analyses of cells cycle-synchronized by serum depletion/replenishment reveal that ClC-2 channel protein is expressed predominantly at M phase in cells with two nuclei and a clear constriction ring, whereas RNA blot analysis shows that ClC-2 mRNA expression does not change during the cell cycle. Ubiquitin assays reveal that the ClC-2 channels are ubiquitinated at M phase, whereas the magnitude of ubiquitination is suppressed by incubation with olomoucine, an inhibitor of p34(cdc2)/cyclin B, and it is almost completely abolished in ClC-2 channels having an S632A mutation, which cannot be phosphorylated by p34(cdc2)/cyclin B, indicating that ubiquitination of ClC-2 channels requires phosphorylation by M phase-specific p34(cdc2)/cyclin B. Regulation at the post-transcriptional level, including phosphorylation-dependent ubiquitination, may contribute to M phase-specific expression of ClC-2 channels. Cell cycle-dependent regulation of expression at the protein level in addition to the regulation of function suggests that the ClC-2 channel plays a physiological role in the cell cycle.

Differential regulation of pituitary adenylate cyclase-activating peptide receptor variants in the rat suprachiasmatic nucleus

Pituitary adenylate cyclase-activating peptide is densely distributed in the suprachiasmatic nucleus, which functions as the circadian pacemaker. A receptor for pituitary adenylate cyclase-activating peptide, denoted as PAC(1), exists in six variant forms. We used reverse transcriptase-polymerase chain reaction to identify the PAC(1) variants that are expressed in the suprachiasmatic nucleus. Dominant variant forms of PAC(1) in the suprachiasmatic nucleus were PAC(1)short, PAC(1)hip, and PAC(1)hop1. By in situ hybridization, we examined 24-h profiles of mRNAs for the identified receptor variants in the suprachiasmatic nucleus in constant darkness and during the light-dark cycle. In constant darkness there were clear circadian rhythms in PAC(1)short mRNA with a peak at circadian time 4 but no rhythmicity was observed in PAC(1)hip mRNA or PAC(1)hop1 mRNA. In light-dark cycles, on the other hand, PAC(1)hip mRNA displayed a bimodal rhythm with troughs at zeitgeber time 4 and 16 but PAC(1)hop1 mRNA stayed constant during the day. These results suggest that PAC(1) splice variants are differentially regulated in the rat suprachiasmatic nucleus.

A potent and highly selective VPAC2 agonist enhances glucose-induced insulin release and glucose disposal: a potential therapy for type 2 diabetes

Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) activate two shared receptors, VPAC1 and VPAC2. Activation of VPAC1 has been implicated in elevating glucose output, whereas activation of VPAC2 may be involved in insulin secretion. A hypothesis that a VPAC2-selective agonist would enhance glucose disposal by stimulating insulin secretion without causing increased hepatic glucose production was tested using a novel selective agonist of VPAC2. This agonist, BAY 55-9837, was generated through site-directed mutagenesis based on sequence alignments of PACAP, VIP, and related analogs. The peptide bound to VPAC2 with a dissociation constant (K(d)) of 0.65 nmol/l and displayed >100-fold selectivity over VPAC1. BAY 55-9837 stimulated glucose-dependent insulin secretion in isolated rat and human pancreatic islets, increased insulin synthesis in purified rat islets, and caused a dose-dependent increase in plasma insulin levels in fasted rats, with a half-maximal stimulatory concentration of 3 pmol/kg. Continuous intravenous or subcutaneous infusion of the peptide reduced the glucose area under the curve following an intraperitoneal glucose tolerance test. The peptide had effects on intestinal water retention and mean arterial blood pressure in rats, but only at much higher doses. BAY 55-9837 may be a useful therapy for the treatment of type 2 diabetes.

Vasoactive intestinal polypeptide as mediator of asthma

Vasoactive intestinal polypeptide (VIP) is one of the most abundant, biologically active peptides found in the human lung. VIP is a likely neurotransmitter or neuromodulator of the inhibitory non-adrenergic non-cholinergic airway nervous system and influences many aspects of pulmonary biology. In human airways VIP-immunoreactive nerve fibres are present in the tracheobronchial airway smooth muscle layer, the walls of pulmonary and bronchial vessels and around submucosal glands. Next to its prominent bronchodilatory effects, VIP potently relaxes pulmonary vessels. The precise role of VIP in the pathogenesis of asthma is still uncertain. Although a therapy using the strong bronchodilatory effects of VIP would offer potential benefits, the rapid inactivation of the peptide by airway peptidases has prevented effective VIP-based drugs so far and non-peptide VIP-agonists did not reach clinical use.

Differential expression of vasoactive intestinal polypeptide receptor 1 and 2 mRNA in murine intestinal T lymphocyte subtypes

Neuropeptides may exert a variety of effects on the immune cells at both systemic and mucosal immune sites. The immunoregulatory properties refer to the ability of physiological signals and pathways to influence various immune functions. Vasoactive intestinal polypeptide (VIP), a neuropeptide present in high concentration in gut, was studied for its production and receptor expression in intraepithelial and lamina propria T lymphocytes of mouse intestine. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, it was demonstrated that VIP receptor 1 (VIPR1) was constantly expressed in intraepithelial and lamina propria T lymphocytes from both small and large intestine. In contrast, VIPR2 was identified only in T cells from small intestine. Further studies on purified subpopulations of T lymphocytes indicated the existence of VIPR2 in CD8(+) T cells, but not CD4(+) and CD4CD8 double negative T cells, although all these three subpopulations displayed VIPR1. In addition, VIPR1 mRNA was detected in splenic T lymphocytes, but no signal was obtained for VIPR2 mRNA, even after stimulation of the cells with anti-CD3(epsilon)-chain mAb, phorbol 12-myristate 13-acetate (PMA) and/or VIP. The presence of VIP receptor(s) on intestinal T lymphocytes was supported by the detection of VIP on the cell surface using dual colour immunoflowcytometry. In-vitro treatment with VIP resulted in a tendency towards an increased size of the VIP immunoreactive T cell population and significantly enhanced the average immunofluorescence intensity of the surface labelling. This indicates that the receptors are partially occupied by locally produced VIP in vivo and that more peptide molecules can be bound on the lymphocytes when needed, released and accumulated in higher concentration at the action sites. We failed to detect the expression of VIP mRNA in T lymphocytes, from either intestine or spleen. These observations support that VIP may be an important immune modulator in gut acting through specific receptors on T lymphocytes. The differential mRNA expression of VIP receptor subtypes in cells with different phenotypes and in different immune compartments may suggest diverse regulatory roles of the neuropeptide in immune responses.

Impairment of mossy fiber long-term potentiation and associative learning in pituitary adenylate cyclase activating polypeptide type I receptor-deficient mice

The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor (PAC1) is a G-protein-coupled receptor binding the strongly conserved neuropeptide PACAP with 1000-fold higher affinity than the related peptide vasoactive intestinal peptide. PAC1-mediated signaling has been implicated in neuronal differentiation and synaptic plasticity. To gain further insight into the biological significance of PAC1-mediated signaling in vivo, we generated two different mutant mouse strains, harboring either a complete or a forebrain-specific inactivation of PAC1. Mutants from both strains show a deficit in contextual fear conditioning, a hippocampus-dependent associative learning paradigm. In sharp contrast, amygdala-dependent cued fear conditioning remains intact. Interestingly, no deficits in other hippocampus-dependent tasks modeling declarative learning such as the Morris water maze or the social transmission of food preference are observed. At the cellular level, the deficit in hippocampus-dependent associative learning is accompanied by an impairment of mossy fiber long-term potentiation (LTP). Because the hippocampal expression of PAC1 is restricted to mossy fiber terminals, we conclude that presynaptic PAC1-mediated signaling at the mossy fiber synapse is involved in both LTP and hippocampus-dependent associative learning.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Impairment of mossy fiber long-term potentiation and associative learning in pituitary adenylate cyclase activating polypeptide type I receptor-deficient mice

The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor (PAC1) is a G-protein-coupled receptor binding the strongly conserved neuropeptide PACAP with 1000-fold higher affinity than the related peptide vasoactive intestinal peptide. PAC1-mediated signaling has been implicated in neuronal differentiation and synaptic plasticity. To gain further insight into the biological significance of PAC1-mediated signaling in vivo, we generated two different mutant mouse strains, harboring either a complete or a forebrain-specific inactivation of PAC1. Mutants from both strains show a deficit in contextual fear conditioning, a hippocampus-dependent associative learning paradigm. In sharp contrast, amygdala-dependent cued fear conditioning remains intact. Interestingly, no deficits in other hippocampus-dependent tasks modeling declarative learning such as the Morris water maze or the social transmission of food preference are observed. At the cellular level, the deficit in hippocampus-dependent associative learning is accompanied by an impairment of mossy fiber long-term potentiation (LTP). Because the hippocampal expression of PAC1 is restricted to mossy fiber terminals, we conclude that presynaptic PAC1-mediated signaling at the mossy fiber synapse is involved in both LTP and hippocampus-dependent associative learning.

A constitutively active pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor shows enhanced photoaffinity labeling of its highly glycosylated form

In the present study, we have analyzed a previously identified constitutively active pituitary adenylate cyclase activating polypeptide (PACAP) type I (PAC1) receptor with a deletion of the single amino acid residue Glu(261) (Y.-J. Cao, G. Gimpl, F. Fahrenholz, A mutation of second intracellular loop of pituitary adenylate cyclase activating polypeptide type I receptor confers constitutive receptor activation, FEBS Lett. 469 (2000)). This glutamic acid residue is highly conserved within the second intracellular loop of class II G protein-coupled receptors and may thus be of importance for many members of this receptor class. To explore the molecular characteristics of this mutant receptor, we performed photoaffinity labeling using previously defined photoreactive PACAP analogues. In COS cells, the PAC1 receptor was expressed in two differently glycosylated forms: a M(r) 75,000 and a M(r) 55,000 form. According to partial deglycosylation, at least three carbohydrate chains may exist in the rat PAC1 receptor expressed in COS cells. The constitutively active PAC1 receptor was expressed at the surface of COS-7 cells at the same density as the wild-type receptor. With respect to the different photoreactive PACAP analogues, the labeling specificity was the same for the wild-type versus mutant receptor: (125)I-[Lys(15)(pBz(2))]-PACAP-27 and (125)I-[Bpa(22)]-PACAP-27 were efficiently incorporated into each of the receptors, whereas (125)I-[Bpa(6)]-PACAP-27 labeled each of the receptors only to a negligible extent. This suggests that both receptors have the same or at least a very similar hormone binding site which is in close contact to Tyr(22) and Lys(15) located in the carboxy-terminal alpha-helical region of the PACAP-27 molecule. However, in comparison with the wild-type PAC1 receptor, the constitutively active receptor showed a markedly (approx. 6--8-fold) enhanced photoaffinity labeling efficiency in particular of the high glycosylated form. The enzymatically deglycosylated rat PAC1 receptor was efficiently labeled by photoreactive PACAP analogues. In contrast, nonglycosylated PAC1 receptors produced by tunicamycin treatment of the transfected COS-7 cells showed a 30-fold lower affinity for PACAP-27 and were capable of signal transduction with 30--50-fold lower potency as compared with the glycosylated PAC1 receptors.

Molecular cloning of chicken vasoactive intestinal polypeptide receptor complementary DNA, tissue distribution and chromosomal localization

Chicken vasoactive intestinal polypeptide receptor (VIPR) cDNA was cloned by the reverse transcription-polymerase chain reaction method using primers designed on the basis of other species of VIPR cDNA. The cDNA obtained was sequenced by the dideoxy-mediated chain-termination method. Of the 2227 nucleotides that were sequenced, 84, 855, and 1338 bases represent the 5'-untranslated region (UTR), the 3'-UTR, and the open reading frame that predicts a peptide of 446 amino acids. The cDNA of the chicken VIPR shows 65% and 60% homologies to human cDNA of VIP1 and VIP2 receptors, respectively. The clone had the expected similarity to highly conserved features of the other G protein-coupled receptors (GPCRs) such as six cysteine residues that are functionally important in the VIPR subfamily. In addition, the seven potential membrane-spanning domains characteristic of the family B group III GPCR superfamily and highly conserved motif within the third cellular loop between transmembrane regions 5 and 6. Northern blot hybridization analysis in this study indicated mRNA expression of VIPRs in the various tissues of the chicken. Strong signal was detected in the brain and anterior pituitary gland. High levels of VIPR mRNA in the brain was consistent with VIP-binding experiments and with the function of VIP in the brain as a neuroendocrine factor or neurotransmitter. Expression of VIPR was detected in the anterior pituitary gland of chick embryos. The expression of VIPR mRNA in the chick anterior pituitary gland may indicate a regulatory function of VIP on prolactin (PRL) production or PRL cell proliferation during embryogenesis. Chicken VIPR shows high homology with mammalian type I VIPR but, in some part, possesses similarity of amino acid sequence. Expression of VIPR in various tissues supports diverse functions for VIP in the chicken.

Expression and distribution of vasoactive intestinal polypeptide receptor VPAC(2) mRNA in human airways

SUMMARY

Vasoactive intestinal polypeptide (VIP) is a putative neurotransmitter of the inhibitory non-adrenergic non-cholinergic nervous system and influences many aspects of mammalian airway function. VIP binds to two G-protein-coupled VPAC receptors that are highly homologous structurally but distinguished by their different affinities for peptide analogues of VIP. As VIP binding sites in the respiratory tract have only been examined by ligand binding and cytochemical techniques, we studied the distribution of the mRNA that encodes the inducible receptor subtype VPAC(2) in the human respiratory tract. Northern blots demonstrated the expression of VPAC(2) mRNA in human airways and other tissues. A human-specific VPAC(2) cRNA probe was used to detect VPAC(2) mRNA expression in human lung by nonradioactive in situ hybridization. In larger airways, positive VPAC(2) mRNA signals were localized to tracheal and bronchial ciliated epithelial cells. There was also marked staining of mucous and serous cells of submucosal glands. No signals were obtained in airway and vascular smooth muscle myocytes and endothelial cells. In peripheral lung tissues, VPAC(2) mRNA expression was localized to epithelial cells of the bronchioles. Specific staining was detected in immune cells and alveolar macrophages. In summary, VPAC(2) is localized in airway epithelial, glandular, and immune cells of the lung but not in airway and vascular smooth muscle. The absence of VPAC(2) mRNA in vascular and airway smooth muscle myocytes may indicate that the effects of VIP on vasodilation and bronchodilation are mediated by VPAC(1) or undefined receptors. However, a paracrine modulation of the two most prominent effects of VIP in the respiratory tract by VPAC(2) cannot be excluded.

Novel alternatively spliced exon in the extracellular ligand-binding domain of the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1R) selectively increases ligand affinity and alters signal transduction coupling during spermatogenesis

The expression of the paracrine signaling hormone pituitary adenylate cyclase-activating polypeptide (PACAP) is regulated in a cyclical fashion during the 12-day spermatogenic cycle of the adult rat testis. The precise functions of PACAP in the development of germ cells are uncertain, but cycle- and stage-specific expression may augment cAMP-regulated gene expression in germ cells and associated Sertoli cells. Here we report the existence of a heretofore unrecognized exon in the extracellular domain of the PACAP type 1 receptor (PAC1R) that is alternatively spliced during the spermatogenic cycle in the rat testis. This splice variant encodes a full-length receptor with the insertion of an additional 72 base pairs encoding 24 amino acids (exon 3a) between coding exons 3 and 4. The PAC1R(3a) mRNA is preferentially detected in seminiferous tubules and is expressed at the highest levels in round spermatids and Sertoli cells. Analyses of ligand binding and signaling functions in stably transfected HEK293 cells expressing the two receptor isoforms reveals a 6-fold increase in the affinity of the PAC1R(3a) to bind PACAP-38, and alterations in its coupling to both cAMP and inositol phosphate signaling pathways relative to the wild type PAC1R. These findings suggest that the extracellular region between coding exons 3 and 6 of PAC1R may play an important role in the regulation of the relative ligand affinities and the relative coupling to G(s) (cAMP) and G(q) (inositol phosphates) signal transduction pathways during spermatogenesis.

Pharmacologically distinct vasoactive intestinal peptide binding sites: CNS localization and role in embryonic growth

In vitro autoradiography with [125I]vasoactive intestinal peptide revealed that the vasoactive intestinal peptide analogue, stearyl-norleucine17 vasoactive intestinal peptide, reported to be inactive at adenylyl cyclase-linked receptors in astrocytes, displaced a subset of vasoactive intestinal peptide binding sites on rat brain sections. These sites were widespread in adult rat brains and enriched in the olfactory bulb and thalamus, and corresponded to previously demonstrated GTP-insensitive vasoactive intestinal peptide binding sites. Stearyl-norleucine17 vasoactive intestinal peptide also identified receptors in rat lung and liver. In the adult brain, the stearyl-norleucine analog displaced only GTP-insensitive vasoactive intestinal peptide binding sites. In contrast, stearyl-norleucine17 vasoactive intestinal peptide-displaceable sites in the embryonic day 9 mouse appeared to include both GTP-sensitive and GTP-insensitive binding sites. This observation suggested the presence of an embryonic vasoactive intestinal peptide receptor with distinct pharmacological properties. Treatment of whole cultured mouse embryos with stearyl-norleucine17 vasoactive intestinal peptide resulted in stimulation of embryonic growth, with the stearyl-norleucine analog equipotent to vasoactive intestinal peptide, but less efficacious at higher concentrations (10(-7) M). Embryonic growth was inhibited by pituitary adenylyl cyclase-activating peptide and 8-bromoadenosine 3',5'-cyclic monophosphate. In addition, 8-bromoadenosine 3',5'-cyclic monophosphate inhibited stearyl-norleucine17 vasoactive intestinal peptide-stimulated growth. The results of the current study support the hypothesis that vasoactive intestinal peptide regulation of early postimplantation embryonic growth occurs, at least in part, independently of adenylyl cyclase stimulation.

Effects of pituitary adenylate cyclase activating polypeptide on lumbosacral preganglionic neurons in the neonatal rat spinal cord

The effects of PACAP-38 on phasic and tonic preganglionic neurons (PGN) in L6 and S1 spinal cord slices from neonatal rats (5--11 days old) were studied using the whole-cell patch clamp technique. PGN were identified by retrograde axonal transport of a fluorescent dye (Fast Blue, 5 microl of 4% solution) injected into the intraperitoneal space 3--7 days prior to the study. Bath application of pituitary adenylate cyclase activating polypeptide (PACAP) (20 nM) increased the frequency of spontaneous excitatory postsynaptic potentials (EPSPs) and spontaneous firing in both types of PGN. PACAP markedly increased the number (200--800%) and frequency of action potentials elicited by depolarizing current pulses in phasic PGN, but had a smaller effect on tonic PGN. PACAP decreased the threshold for action potential generation by approximately 25% in both types of neurons (e.g. -34.0+/-1.5 to -38.4+/-1.7 mV from a holding potential of -50 mV in phasic PGN, P<0.005). PACAP did not affect the duration of the action potential. The amplitude of the spike after hyperpolarization was not changed but the duration was significantly reduced by PACAP from 204.4+/-12.2 to 106.2+/-8.1 ms in tonic but not in phasic PGN. PACAP suppressed a transient outward current that was also suppressed by 4-aminopyridine (0.5 mM). These results coupled with the immunohistochemical identification of a dense collection of PACAP fibers in the region of the PGN, raises the possibility that PACAP may function as an excitatory transmitter in lumbosacral parasympathetic reflex pathways in the neonatal rat.

Pituitary adenylate cyclase-activating polypeptide activates K(ATP) current in rat atrial myocytes

Because the electrophysiological effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on the heart are little known, we studied the regulation of the atrial ATP-sensitive K(+) (K(ATP)) current by PACAP on primary cultured neonatal rat atrial myocytes. PACAP-38 stimulates cAMP production with EC(50) = 0.28 nmol/l (r = 0.92, P < 0.02). PACAP-38 and PACAP-27 (10 nmol/l) have similar maximal effects, whereas 100 nmol/l vasoactive intestinal polypeptide (VIP) is 2.7 times less effective (P < 0.05). RT-PCR shows the presence of cloned PACAP receptors PAC(1) (> or =2 isoforms), VPAC(1), and VPAC(2). PACAP-38 dose dependently activates the whole cell atrial K(ATP) current with EC(50) = 1-3 nmol/l (n = 44). Maximal effects occur at 10 nmol/l (91 +/- 15 pA/pF, n = 18). Diazoxide further increases the PACAP-activated current by 78% (P < 0.05; n = 6). H(89) (500 nmol/l), a protein kinase A (PKA) inhibitor, reduces the PACAP-activated K(ATP) current to 17.8 +/- 9.6% (n = 5) of the maximal diazoxide-induced current and totally inhibits the cAMP-induced K(ATP) current. A protein kinase C (PKC) inhibitor peptide (50 micromol/l) in the pipette reduces the PACAP-38-induced K(ATP) current to 33 +/- 17 pA/pF (P < 0.05, n = 6) without significantly affecting the currents induced by cAMP or VIP. The results suggest that: 1) PAC(1), VPAC(1), and VPAC(2) are present in atrial myocytes; and 2) PACAP-38 activates the atrial K(ATP) channels through both PKA and PKC pathways.

The effects of PACAP on insulin secretion and glucose disposal are altered by adrenalectomy in mice

We previously showed that pituitary adenylate cyclase-activating polypeptide (PACAP) potently stimulates insulin secretion in vivo in mice without altering glucose disposal. Such a combination of results would be explained if epinephrine released by PACAP counteracts the action of insulin and, therefore, that the glucose disposal after PACAP administration is altered by adrenalectomy. In the study reported in this paper, we examined the influence of PACAP27 (1.3 nmol/kg i.v.) on insulin secretion and glucose disposal during an intravenous glucose (1 g/kg) tolerance test in mice subjected to bilateral adrenalectomy 48 h prior to the tolerance test. We found that in control mice, PACAP potentiated glucose-stimulated insulin secretion threefold without affecting glucose disposal. Adrenalectomy potentiated the augmentation by PACAP27 of glucose-stimulated insulin secretion, and in adrenalectomized mice, PACAP27 simultaneously augmented glucose disposal (elimination rate 2.30 +/- 0.07%/min vs. 2.56 +/- 0.05%/min; p = 0.011). Furthermore, PACAP27 augmented glucose elimination stimulated by i.v. insulin administration only in adrenalectomized, but not in control mice. We, therefore, conclude that under in vivo conditions, epinephrine released by PACAP from the adrenals prevents the marked insulinotropic action of the peptide from augmenting glucose disposal.

Maxadilan specifically interacts with PAC1 receptor, which is a dominant form of PACAP/VIP family receptors in cultured rat cortical neurons

Maxadilan is a potent vasodilator peptide isolated from salivary gland extracts of the hematophagous sand fly. Recently, the possibility was demonstrated that maxadilan binds to PAC1 receptor (PACAP, pituitary adenylate cyclase activating polypeptide type I receptor) in mammals. In the present study, we demonstrated that: (1) maxadilan specifically binds to PAC1 receptor and stimulates cyclic AMP accumulation in a dose-dependent manner in CHO cells stably expressing PAC1 receptor, not VIP (vasoactive intestinal polypeptide) receptors; that (2) the deleted peptide (amino acid #24-42) of maxadilan (termed max.d.4) also specifically binds to PAC1 receptor although max.d.4 inhibits cyclic AMP accumulation stimulated by both maxadilan and PACAP; and that (3) max.d.4 completely blocks the cyclic AMP accumulation induced by VIP in cultured rat cortical neurons. The expression of specific PACAP receptors in cultured rat cortical neurons was further investigated by the reverse transcription-polymerase chain reaction technique, which showed the presence of mRNA coding for PAC1 receptor among PACAP/VIP family receptors. These data indicate that maxadilan and max.d.4 represent important tools for clarifying the physiological role of PAC1 receptor, and that PAC1 receptor plays an important role in the regulation of the functions induced by PACAP in rat cultured cortical neurons.

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.

Pituitary adenylate cyclase-activating polypeptide prevents cytokine-induced cytotoxicity via inhibition of inducible nitric oxide synthase expression in beta TC cells

Type 1 diabetes mellitus is an autoimmune disease resulting from apoptotic destruction of pancreatic beta-cells. The activation of inducible nitric oxide synthase (iNOS) by inflammatory cytokines is considered a mediator of destruction in beta-cells. Recent findings showed that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), whose distribution was identified in pancreatic neurons, inhibited nitric oxide (NO) production in cytokine-activated macrophages. In the present study, we investigated the cytoprotective effect of PACAP in the cytokine-exposed mice beta-cell line, beta TC cells. 1 x 10(-8) M PACAP inhibited the reduction of cell viability, NO production, expression of iNOS mRNA, and iNOS promoter activity caused by the combination of three proinflammatory cytokines. Selective iNOS inhibitor also showed the cytoprotective effect in beta TC cells. These data suggested that PACAP has a cytoprotective effect in cytokine-treated beta-cells through inhibition of iNOS transcription.

The Na+-driven Cl-/HCO3- exchanger. Cloning, tissue distribution, and functional characterization

The Na(+)-driven Cl(-)/HCO(3)(-) exchanger is an important regulator of intracellular pH in various cells, but its molecular basis has not been determined. We show here the primary structure, tissue distribution, and functional characterization of Na(+)-driven chloride/bicarbonate exchanger (designated NCBE) cloned from the insulin-secreting cell line MIN6 cDNA library. The NCBE protein consists of 1088 amino acids having 74, 72, and 55% amino acid identity to the human skeletal muscle, rat smooth muscle, and human kidney sodium bicarbonate cotransporter, respectively. The protein has 10 putative membrane-spanning regions. NCBE mRNA is expressed at high levels in the brain and the mouse insulinoma cell line MIN6 and at low levels in the pituitary, testis, kidney, and ileum. Functional analyses of the NCBE protein expressed in Xenopus laevis oocytes and HEK293 cells demonstrate that it transports extracellular Na(+) and HCO(3)(-) into cells in exchange for intracellular Cl(-) and H(+), thus raising the intracellular pH. Thus, we conclude that NCBE is a Na(+)-driven Cl(-)/HCO(3)(-) exchanger that regulates intracellular pH in native cells.

cAMP-GEFII is a direct target of cAMP in regulated exocytosis

Although cAMP is well known to regulate exocytosis in many secretory cells, its direct target in the exocytotic machinery is not known. Here we show that cAMP-GEFII, a cAMP sensor, binds to Rim (Rab3-interacting molecule, Rab3 being a small G protein) and to a new isoform, Rim2, both of which are putative regulators of fusion of vesicles to the plasma membrane. We also show that cAMP-GEFII, through its interaction with Rim2, mediates cAMP-induced, Ca2+-dependent secretion that is not blocked by an inhibitor of cAMP-dependent protein kinase (PKA). Accordingly, cAMP-GEFII is a direct target of cAMP in regulated exocytosis and is responsible for cAMP-dependent, PKA-independent exocytosis.

Characterization of the extra-large G protein alpha-subunit XLalphas. I. Tissue distribution and subcellular localization

Our group previously described a new type of G protein, the 78-kDa XLalphas (extra large alphas) (Kehlenbach, R. H., Matthey, J., and Huttner, W. B. (1994) Nature 372, 804-809 and (1995) Nature 375, 253). Upon subcellular fractionation, XLalphas labeled by ADP-ribosylation with cholera toxin was previously mainly detected in the bottom fractions of a velocity sucrose gradient that contained trans-Golgi network and was differentially distributed to Galphas, which also peaked in the top fractions containing plasma membrane. Here, we investigate, using a new antibody specific for the XL domain, the tissue distribution and subcellular localization of XLalphas and novel splice variants referred to as XLN1. Upon immunoblotting and immunofluorescence analysis of various adult rat tissues, XLalphas and XLN1 were found to be enriched in neuroendocrine tissues, with a particularly high level of expression in the pituitary. By both immunofluorescence and immunogold electron microscopy, endogenous as well as transfected XLalphas and XLN1 were found to be predominantly associated with the plasma membrane, with only little immunoreactivity on internal, perinuclear membranes. Upon subcellular fractionation, immunoreactive XLalphas behaved similarly to Galphas but was differentially distributed to ADP-ribosylated XLalphas. Moreover, the bottom fractions of the velocity sucrose gradient were found to contain not only trans-Golgi network membranes but also certain subdomains of the plasma membrane, which reconciles the present with the previous observations. To further investigate the molecular basis of the association of XLalphas with the plasma membrane, chimeric proteins consisting of the XL domain or portions thereof fused to green fluorescent protein were analyzed by fluorescence and subcellular fractionation. In both neuroendocrine and non-neuroendocrine cells, a fusion protein containing the entire XL domain, in contrast to one containing only the proline-rich and cysteine-rich regions, was exclusively localized at the plasma membrane. We conclude that the physiological role of XLalphas is at the plasma membrane, where it presumably is involved in signal transduction processes characteristic of neuroendocrine cells.

Progesterone receptor activation mediates LH-induced type-I pituitary adenylate cyclase activating polypeptide receptor (PAC(1)) gene expression in rat granulosa cells

We have previously reported that the pituitary adenylate cyclase activating polypeptide (PACAP) gene is regulated in ovarian granulosa cells by the autocrine and/or paracrine interaction between progesterone and its nuclear receptor progesterone receptor (PR). To initiate studies on the functional significance of the progesterone-induced PACAP production in luteinizing granulosa cells, we sought to determine the expression and hormonal regulation of PACAP receptors in the rat ovary. The relative mRNA levels of three known PACAP receptor subtypes (PAC(1), VPAC(1), and VPAC(2)) were determined in ovaries of immature rats treated with gonadotropins, by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. Results show that all PAC(1), VPAC(1), and VPAC(2) transcripts are expressed at a detectable level in immature rat ovaries. Importantly, the ovarian level of PAC(1), but not VPAC(1) or VPAC(2), mRNA notably changes during gonadotropin challenges. Ovarian PAC(1) mRNA expression decreases during the pregnant mare's serum gonadotropin (PMSG)-induced follicular phase but substantially increases during the human chorionic gonadotropin (hCG)-induced periovulatory period. Because the hCG-induced increase in ovarian PAC(1) mRNA expression is attributable to the hormone-induced PAC(1) mRNA expression in granulosa cells of the preovulatory follicles, we next examined whether hCG regulates PAC(1) mRNA expression by directly acting on granulosa cells. When granulosa cells isolated from PMSG (40 h)-primed immature rats were challenged with hCG (or forskolin), PAC(1), but not VPAC(1) or VPAC(2), mRNA expression significantly increased within 6 h. Because the LH-induced PAC(1) mRNA expression (6 h) proceeds PR activation (3 h) in granulosa cells as the LH-induced PACAP mRNA expression (6 h) does, we further determined the cause-effect relationship among LH, PR activation and PAC(1) receptor gene expression, by examining the effect of PR antagonist, ZK98299, on the ability of LH to increase PAC(1) mRNA levels in luteinizing granulosa cells. Results show that ZK98299 inhibited the stimulatory effect of hCG (or forskolin) on PAC(1) mRNA expression, at the level of all known splice variants of PAC(1) mRNA in granulosa cells. In summary, our results demonstrating that PR activation is critical for the LH-induced PAC(1) gene expression in luteinizing granulosa cells suggest that PR activation regulates the finely tuned expression of the PACAP/PACAP receptor genes in luteinizing granulosa cells and thus dictates the timing of the autocrine and/or paracrine function of PACAP in preovulatory follicles.

New members of the parathyroid hormone/parathyroid hormone receptor family: the parathyroid hormone 2 receptor and tuberoinfundibular peptide of 39 residues

The parathyroid hormone (PTH) family currently includes three peptides and three receptors. PTH regulates calcium homeostasis through bone and kidney PTH1 receptors. PTH-related peptide, probably also through PTH1 receptors, regulates skeletal, pancreatic, epidermal, and mammary gland differentiation and bladder and vascular smooth muscle relaxation and has a CNS role that is under investigation. Tuberoinfundibular peptide of 39 residues (TIP39) was recently purified from bovine hypothalamus based on selective PTH2 receptor activation. PTH2 receptor expression is greatest in the CNS, where it is concentrated in limbic, hypothalamic, and sensory areas, especially hypothalamic periventricular neurons, nerve terminals in the median eminence, superficial layers of the spinal cord dorsal horn, and the caudal part of the sensory trigeminal nucleus. It is also present in a number of endocrine cells. Thus TIP39 and PTH2 receptor-influenced functions may range from pituitary and pancreatic hormone release to pain perception. A third PTH-recognizing receptor has been found in zebrafish.

Cloning, characterization and tissue distribution of the rat ATP-binding cassette (ABC) transporter ABC2/ABCA2

The ABC1 (ABCA) subfamily of the ATP-binding cassette (ABC) transporter superfamily has a structural feature that distinguishes it from other ABC transporters. Here we report the cloning, molecular characterization and tissue distribution of ABC2/ABCA2, which belongs to the ABC1 subfamily. Rat ABC2 is a protein of 2434 amino acids that has 44.5%, 40.0% and 40.8% identity with mouse ABC1/ABCA1, human ABC3/ABCA3 and human ABCR/ABCA4 respectively. Immunoblot analysis showed that proteins of 260 and 250 kDa were detected in COS-1 cells transfected with ABC2 having a haemagglutinin tag, while no band was detected in mock-transfected cells. After incubation with N-glycosidase F, the mobilities of the two proteins increased and a single band was detected, suggesting that ABC2 is a glycoprotein. Photoaffinity labelling with 8-azido-[alpha-(32)P]ATP confirmed that ATP binds to the ABC2 protein in the presence of Mg(2+). RNA blot analysis showed that ABC2 mRNA is most abundant in rat brain. Examination of brain by in situ hybridization determined that ABC2 is expressed at high levels in the white matter, indicating that it is expressed in the oligodendrocytes. ABC2, therefore, is a glycosylated ABC transporter protein, and may play an especially important role in the brain. In addition, the N-terminal 60-amino-acid sequence of the human ABC1, which was missing from previous reports, has been determined.

Effects of pituitary adenylate cyclase activating polypeptide27 on cyclic AMP efflux and atrial dynamics in perfused beating atria

Although pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to increase cardiac force of contraction and to change the heart rate, the effect of PACAP on cyclic (c) AMP production in the atrium still has to be defined. In the present experiments, a simple protocol was developed for the evaluation of cAMP production in real-time base in the perfused beating left atria. The PACAP27-induced cAMP efflux in the atrial perfusate reflected changes in the production of cAMP in the atrial tissue. cAMP efflux was measured as an indicator of cAMP production in beating perfused rabbit atria. PACAP27 increased cAMP production in a dose- and time-dependent manner with a minor effect on atrial dynamics. These results suggest that PACAP27 has other roles besides control of force of contraction through cAMP production in the atrium.

Central administration of an antisense oligodeoxynucleotide against type I pituitary adenylate cyclase-activating polypeptide receptor suppresses synthetic activities of LHRH-LH axis during the pubertal process

Central administration of an antisense oligodeoxynucleotide against type I pituitary adenylate cyclase-activating polypeptide receptor suppresses synthetic activities of LHRH-LH axis during the pubertal process In the present study, we determined the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP receptor type I (PAC1) genes during juvenile development and the pubertal process. Female rats were assigned--based on uterine weights, the presence and abundance of uterine fluid, and their vaginal patency--to one of the following: anestrus (AE), early proestrus (EP), late proestrus (LP) or first estrus (E). The hypothalami from 22-, 24- and 26-day-old animals and from those in the peripubertal phases of AE, EP, LP and E were collected, and the content of PACAP and PAC1 mRNA was assessed. These levels were found to decrease in EP and LP. To determine the effect of PACAP on prepubertal luteinizing hormone-releasing hormone (LHRH) and LH synthesis through PAC1, a PAC1 antisense oligodeoxynucleotide (ODN) was i.c.v.-administered, and mRNA levels of LHRH, LH beta, and LHRH receptor (LHRH-R) were determined. Prepubertal increases in LHRH, LH beta, and LHRH-R mRNA levels were markedly suppressed, and the onset of puberty was delayed by the i.c.v. injection of the antisense PAC1 ODN. These data suggest that PACAP may play a role in the regulation of hypothalamic LHRH neurons, through which it regulates synthetic machinery of pituitary LH, during the pubertal process.

Pituitary adelylate cyclase-activating peptide is an activator of vasoactive intestinal polypeptide gene transcription in human neuroblastoma cells

In many ganglia, the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) innervates nerve cell bodies containing the homologous neuropeptide vasoactive intestinal polypeptide (VIP). We therefore investigated whether PACAP affected the VIP gene expression and elucidated the molecular mechanisms using the human neuroblastoma cell line NB-1. A concentration dependent induction of the VIP mRNA level was found upon PACAP stimulation. Five nM PACAP mediated transient elevation of the VIP mRNA being evident after 2 h, the maximal 65-fold induction was reached after 6-8 h and hereafter the level decreased rapidly. In cell extracts, the concentration of immunoreactive VIP was elevated four-fold upon PACAP stimulation for 8 h, and it remained elevated during the next 40 h. In conditioned medium, a stable 20-fold VIP increase was seen after 8-24 h. Experiments with the translational inhibitor cycloheximide showed a direct effect of PACAP on the VIP mRNA level, and nuclear run-on assays revealed a three- to four-fold enhancement of the VIP gene transcription rate after PACAP stimulation. The VIP mRNA induction was abolished by transcriptional inhibition with the actinomycin D, and PACAP did not seem to mediate any changes in the VIP mRNA half-life. However, the VIP mRNA level seemed very stable during the transcriptional cessation. Reporter gene constructs were used to evaluate involvement of the VIP CRE site in the PACAP mediated induction of the VIP gene transcription. Mutation of the CRE site did not abolish the induction suggesting it to be of minor if any importance for the induction. In conclusion, the PACAP mediated induction of the VIP gene expression suggests that PACAP released from nerve terminals could influence the function of VIP'ergic neurons in target tissues.

Characterization of a novel VPAC(1) selective agonist and identification of the receptor domains implicated in the carboxyl-terminal peptide recognition

Vasoactive Intestinal Polypeptide (VIP) interacts with a high affinity to two subclasses of G protein coupled receptors named VPAC(1) and VPAC(2), and has a 3 - 10 fold preference for VPAC(1) over VPAC(2) receptors. Selective ligands for each receptor subclass were recently described. [R(16)]-PACAP (1 - 23) and [L(22)]-VIP are two selective VPAC(1) agonists. Chimaeric human VPAC(2)-VPAC(1) recombinant receptors expressed in CHO cells were used to identify the receptor domains implicated in these two selective ligands recognition. The VPAC(2) preference for [R(16)]-PACAP (1 - 27) over [R(16)]-PACAP (1 - 23) did not require the receptor's NH(2)-terminus domain but involved the whole transmembrane domain. In contrast, the selectivity of [L(22)]-VIP depended only on the presence of the NH(2) terminus and EC(2) domains of the VPAC(1) receptor. The present data support the idea that in the GPCR-B family of receptors the different selective ligands require different domains for their selectivity, and that the peptides carboxyl terminal sequence (amino acids 24 - 27) folds back on the transmembrane receptor domain, close to the peptides, aminoterminus.

Pituitary adenylate cyclase activating peptide mediates inhibitory nonadrenergic noncholinergic relaxation

We investigated the contribution of pituitary adenylate cyclase activating peptide (PACAP) to inhibitory nonadrenergic noncholinergic (inhibitory-NANC) relaxation of tracheal smooth muscle in cats. We also investigated the roles of vasoactive intestinal peptide (VIP) and nitric oxide (NO) on this function. Smooth muscle strips prepared from feline trachea were precontracted with 1 microM serotonin, and inhibitory-NANC relaxation was induced by electrical-field stimulation in the presence of atropine and propranolol. PACAP-(6-38) (a selective antagonist of PACAP; 1, 3 and 10 microM), VIP-(10-28) (a selective antagonist of VIP; 1, 3 and 10 microM) and N(omega)-nitro-L-arginine methyl ester (L-NAME, a selective NO synthase inhibitor; 3, 10 and 30 microM) each partially but significantly attenuated the amplitude of inhibitory-NANC relaxation. The effects of PACAP-(6-38) and VIP-(10-28) were additive. Addition of PACAP-(6-38) and/or VIP-(10-28) further attenuated relaxation in the presence of L-NAME. These results suggest that PACAP, VIP and NO contribute to the relaxation induced by inhibitory-NANC in tracheal smooth muscle in cats, and that they mediate this relaxation via different pathways.

Pituitary adenylate cyclase activating polypeptide as a novel hypophysiotropic factor in fish

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel member of the secretin-glucagon peptide family. In mammals, this peptide has been located in a wide range of tissues and is involved in a variety of biological functions. In lower vertebrates, especially fish, increasing evidence suggests that PACAP may function as a hypophysiotropic factor regulating pituitary hormone secretion. PACAP has been identified in the brain-pituitary axis of representative fish species. The molecular structure of fish PACAP is highly homologous to mammalian PACAP. The prepro-PACAP in fish, however, is distinct from that of mammals as it also contains the sequence of fish GHRH. In teleosts, the anterior pituitary is under direct innervation of the hypothalamus and PACAP nerve fibers have been identified in the pars distalis. Using the goldfish as a fish model, mRNA transcripts of PACAP receptors, namely the PAC1 and VPAC1 receptors, have been identified in the pituitary as well as in various brain areas. Consistent with the pituitary expression of PACAP receptors, PACAP analogs are effective in stimulating growth hormone (GH) and gonadotropin (GTH)-II secretion in the goldfish both in vivo and in vitro. The GH-releasing action of PACAP is mediated via pituitary PAC1 receptors coupled to the adenylate cyclase-cAMP-protein kinase A and phospholipase C-IP3-protein kinase C pathways. Subsequent stimulation of Ca2+ entry through voltage-sensitive Ca2+ channels followed by activation of Ca2+-calmodulin protein kinase II is likely the downstream mechanism mediating PACAP-stimulated GH release in goldfish. Although the PACAP receptor subtype(s) and the associated post-receptor signaling events responsible for PACAP-stimulated GTH-II release have not been characterized in goldfish, these findings support the hypothesis that PACAP is produced in the hypothalamus and delivered to the anterior pituitary to regulate GH and GTH-II release in fish.Key words: PACAP, VIP, PAC1 receptor, VPAC1 receptor, VPAC2 receptor, growth hormone, gonadotropin-II, cAMP, protein kinase A, protein kinase C, calcium, pituitary cells, goldfish, and teleost.

A mutation in the second intracellular loop of the pituitary adenylate cyclase activating polypeptide type I receptor confers constitutive receptor activation

The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor belongs to the glucagon/secretin/vasoactive intestinal polypeptide (VIP) receptor family. We mutated and deleted an amino acid residue (E261) which is located within the second intracellular loop of the rat PACAP type I receptor and which is highly conserved among the receptor family. The wild-type receptor and the mutant receptors were efficiently expressed at the surface of COS-7 cells at nearly the same level and revealed the same high affinity for the agonist PACAP-27. The cAMP contents of COS cells transfected with the E261A, E261Q, and the deletion mutant receptor were 4.6-, 5.7-, and 6.7-fold higher as compared with COS cells transfected with the wild-type receptor. Thus, all the mutant PACAP receptors were constitutively active. The data suggest that the glutamic acid in the second intracellular loop of the PACAP receptor may be a key residue to constrain the receptor in the inactive conformation with respect to its coupling to G(s) proteins.

Cellular distribution of the splice variants of the receptor for pituitary adenylate cyclase-activating polypeptide (PAC(1)-R) in the rat brain by in situ RT-PCR

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide and its specific receptor (the PAC(1) receptor) is widely distributed in the rat brain. It has been reported that alternative splicing of the region encoding the third intracellular loop of the PAC(1) receptor generates six isoforms which are differentially coupled to signal transduction pathways, but the precise distribution and localization of these splice isoforms in the brain remain to be determined. Using the initial specific primer pairs which correspond to the 'hip' or 'hop' types of receptors for the solution-phase reverse transcription-polymerase chain reaction (RT-PCR), we demonstrated that the major splice variants of the PAC(1) receptor in various regions of the rat brain are the short splice isoform 'PAC(1)-R-s' which does not contain either the 'hip' or 'hop' cassette and the another splice isoform, 'PAC(1)-R-hop', which contains the 'hop' cassette. With an innovative molecular histochemical technique, in situ RT-PCR, we determined that these two splice isoforms are both intensely expressed in the mitral cells of the olfactory bulb, the Purkinje cells of the cerebellum, the pyramidal cells of the hippocampus and neocortex, and many neurons in the nuclei of hypothalamus and thalamus as well as other regions. The initial mapping of the cell type-specific expression of these two splice variants of the PAC(1) receptor provides the basis for a better understanding of the functional significance of the PAC(1)-R and its ligand PACAP in various brain regions.

Rat and guinea pig pancreatic acini possess both VIP(1) and VIP(2) receptors, which mediate enzyme secretion

Pancreatic acini from most species possess vasoactive intestinal peptide (VIP) receptors. Recently, two subtypes of VIP receptors, VIP(1)-R and VIP(2)-R, were cloned. Which subtype exists on pancreatic acini or mediates secretion is unclear. To address this, we examined pancreatic acini from both rat and guinea pig. VIP(1)-R and VIP(2)-R mRNA were identified in dispersed acini from both species by Northern blot analysis and in rat by Southern blot analysis. With the use of the VIP(2)-R-selective ligand Ro-25-1553 in both species, inhibition of binding of (125)I-labeled VIP to acini showed a biphasic pattern with a high-affinity component (10%) and a second representing 90%. The VIP(1)-R-selective ligand, [Lys(15),Arg(16),Leu(27)]VIP-(1-7)-GRF-(8-27), gave a monophasic pattern. Binding of Ro-25-1553 was better fit by a two-site model. In both rat and guinea pig acini, the dose-response curve of Ro-25-1553 for stimulation of enzyme secretion was biphasic, with a high-affinity component of 10-15% of the maximal secretion and a low-affinity component accounting for 85-90%. At low concentrations (10 nM) of Ro-25-1553 and [Lys(15),Arg(16), Leu(27)]VIP-(1-7)-GRF(8-27), which only occupy VIP receptors, a 4-fold and a 56-fold increase in cAMP occurred, respectively. These results show that both VIP(1)-R and VIP(2)-R subtypes exist on pancreatic acini of rat and guinea pig, their activation stimulates enzyme secretion by a cAMP-mediated mechanism, and the effects of VIP are mediated 90% by activation of VIP(1)-R and 10% by VIP(2)-R. Because VIP has a high affinity for both VIP-R subtypes, its effect on pancreatic acini is mediated by two receptor subtypes, which will need to be considered in future studies of the action of VIP in the pancreas.

N-terminal splice variants of the type I PACAP receptor: isolation, characterization and ligand binding/selectivity determinants

Three full-length cDNAs encoding functional splice variants of the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1) were isolated from Y-79 retinoblastoma cells and human cerebellum. Although the third intracellular loops of the three splice variants were identical, their N-terminal extracellular domains differed. The first full-length PAC1 variant, PAC1normal (PAC1n), encoded the entire N-terminus, whereas the second variant named PAC1short (PAC1s) was deleted by 21 amino acids (residues 89-109). Finally, the third variant, named PAC1very short (PAC1vs), was deleted by 57 amino acids (residues 53-109). Using semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis, it was established that all three variants were expressed in neuronal tissues. Binding- and cAMP studies using human embryonic kidney 293 (HEK293) cells stably transfected with PAC1n, PAC1s and PAC1vs showed significant differences in the affinities and selectivities towards PACAP38, PACAP27 and VIP. PAC1n bound PACAP38 and PACAP27 with affinities in the low nanomolar range whereas VIP was bound with up to 400-fold lower affinity. PAC1vs preferentially bound PACAP38 (Ki=121 nM) and PACAP27 (Ki=129 nM) over VIP (Ki>1000 nM) but with 100-fold lower affinity than PAC1n. Surprisingly, PAC1s unselectively bound all three ligands with high affinity. These data indicate that residues 53-88 within the N-terminal domain of the PAC1 are important for high affinity ligand binding, whereas residues 89-109 determine the receptor's ligand selectivity.

Biological relevance of pituitary adenylate cyclase-activating polypeptide (PACAP) in the gastrointestinal tract

Since its initial discovery in 1989, pituitary adenylate cyclase activating peptide (PACAP) has been noted to distribute widely in the brain, the respiratory and the gastrointestinal system. It occurs in two bioactive molecules, PACAP-27 and the C-terminally extended PACAP-38, which evoke activity by binding to three distinct types of high-affinity, G-protein coupled membrane receptors. It is present throughout the entirety of the gut but is rare in certain areas such as the intestinal mucosa and islets of Langerhans. PACAP-induced biological effects are protean and include alterations of motility in the bowel and the gallbladder, stimulation of gastric acid and intestinal secretion, hormone/enzyme release from the exocrine and endocrine pancreas, and the induction as well as inhibition of proliferation in neuroendocrine cells and tumors. Its hepatic activity has to date not been elucidated in detail. One of the interesting features of PACAP is the species and organ dependent variation of its biological effects. Of particular note is its superior potency when compared with other neuropeptides identified in the gut, and the involvement of a number of different second messenger systems upon PACAP receptor activation.

Vasoactive intestinal peptide inhibits cytokine production in T lymphocytes through cAMP-dependent and cAMP-independent mechanisms

Previous reports indicate that VIP and the structurally related peptide PACAP, inhibit IL-2 and IL-10 production in antigen-stimulated T lymphocytes. Intracellular cAMP elevation appears to be the primary transduction pathway involved. However, in the lower concentration range, an additional, cAMP-independent transduction pathway appears to mediate the VIP inhibition of cytokine production. Here, we address this question by using VIP agonists and antagonists which act through cAMP-dependent and -independent pathways. The antagonists based on the neurotensin-VIP hybrid molecule did not affect the inhibitory effect of VIP/PACAP on IL-2 and IL-10 production, confirming that astrocytes and T lymphocytes express different receptors. A lipophilic antagonist with increased membrane permeability, partially reversed the inhibitory effect of VIP/PACAP, forskolin, prostaglandin E2, and 8-bromo-cAMP without significantly affecting cAMP levels, suggesting that it acts downstream of cAMP. Two VIP agonists inhibit IL-2 and IL-10 production. One of the agonists increases cAMP, whereas the second one does not induce cAMP/cGMP. Our results indicate that VIP inhibits cytokine production in stimulated CD4+ T cells through two separate mechanisms, which involve both cAMP-dependent and cAMP-independent transduction pathways.

Pituitary adenylate cyclase-activating polypeptides directly stimulate sympathetic neuron neuropeptide Y release through PAC(1) receptor isoform activation of specific intracellular signaling pathways

Pituitary adenylate cyclase-activating polypeptides (PACAP) have potent regulatory and neurotrophic activities on superior cervical ganglion (SCG) sympathetic neurons with pharmacological profiles consistent for the PACAP-selective PAC(1) receptor. Multiple PAC(1) receptor isoforms are suggested to determine differential peptide potency and receptor coupling to multiple intracellular signaling pathways. The current studies examined rat SCG PAC(1) receptor splice variant expression and coupling to intracellular signaling pathways mediating PACAP-stimulated peptide release. PAC(1) receptor mRNA was localized in over 90% of SCG neurons, which correlated with the cells expressing receptor protein. The neurons expressed the PAC(1)(short)HOP1 receptor but not VIP/PACAP-nonselective VPAC(1) receptors; low VPAC(2) receptor mRNA levels were restricted to ganglionic nonneuronal cells. PACAP27 and PACAP38 potently and efficaciously stimulated both cAMP and inositol phosphate production; inhibition of phospholipase C augmented PACAP-stimulated cAMP production, but inhibition of adenylyl cyclase did not alter stimulated inositol phosphate production. Phospholipase C inhibition blunted neuron peptide release, suggesting that the phosphatidylinositol pathway was a prominent component of the secretory response. These studies demonstrate preferential sympathetic neuron expression of PACAP-selective receptor variants contributing to regulation of autonomic function.

Structure of the human VIPR2 gene for vasoactive intestinal peptide receptor type 2

The VPAC(2) (vasoactive intestinal peptide (VIP)(2)) receptor is a seven-transmembrane spanning G protein-coupled receptor which responds similarly to VIP and pituitary adenylate cyclase activating polypeptide (PACAP) in stimulating cAMP production. Recently, we reported the localisation of the human VPAC(2) receptor gene (VIPR2) to chromosome 7q36.3 (Mackay, M. et al. (1996) Genomics 37, 345-353). Here, we describe the characterisation of the VIPR2 gene structure and promoter region. The VIPR2 gene is encoded by 13 exons, the initiator codon of the 438 amino acid open reading frame is located in exon 1 and the termination signal and a poly-adenylation signal sequence are located in exon 13. The 5' untranslated region extends 187 bp upstream of the initiator codon and is extremely GC-rich (80%). The poly-adenylation signal is located 2416 bp downstream of the stop codon. Intron sizes range from 68 bp (intron 11) to 45 kb (intron 4) and the human gene spans 117 kb.

Functional characterization of structural alterations in the sequence of the vasodilatory peptide maxadilan yields a pituitary adenylate cyclase-activating peptide type 1 receptor-specific antagonist

Maxadilan is a vasodilatory peptide derived from sand flies that is an agonist at the pituitary adenylate cyclase-activating peptide (PACAP) type 1 receptor. Surprisingly, maxadilan does not share significant sequence homology with PACAP. To examine the relationship between structure and activity of maxadilan, several amino acid substitutions and deletions were made in the peptide. These peptides were examined in vitro for binding to crude membranes derived from rabbit brain, a tissue that expresses PACAP type 1 receptors; and induction of cAMP was determined in PC12 cells, a line that expresses these receptors. The peptides were examined in vivo for their ability to induce erythema in rabbit skin. Substitution of the individual cysteines at positions 1 and 5 or deletion of this ring structure had little effect on activity. Substitution of either cysteine at position 14 or 51 eliminated activity. Deletion of the 19 amino acids between positions 24 and 42 resulted in a peptide with binding, but no functional activity. The capacity of this deletion mutant to interact with COS cells transfected with the PACAP type 1 receptor revealed that this peptide was a specific antagonist to the PACAP type 1 receptor.

VIP and PACAP: very important in pain?

Neuropathic pain arising from direct trauma to, or compression injury of, peripheral nerves is a common clinical problem. It is characterized by the development of abnormal pain states (spontaneous pain, hyperalgesia, allodynia), which can persist long after the initial injury has resolved. The underlying mechanisms are poorly understood and, as a consequence, treatment is often unsatisfactory. Some of the main contributing factors are thought to be the morphological and phenotypic changes that occur centrally, including alterations in the expression of neurotransmitters and their associated receptors, both in the dorsal root ganglia and in the spinal dorsal horn. This article focuses on the functional role of the two structurally related peptides VIP and PACAP within the spinal cord, and their possible contribution to the altered transmission of sensory information in neuropathic conditions.

Functional and molecular diversity of PACAP/VIP receptors in cortical neurons and type I astrocytes

In the present study we determined the mRNA-expression of pituitary adenylate cyclase activating polypeptide (PACAP)/vasoactive intestinal peptide (VIP) receptors in primary cultures of rat cortical neurons and type I astrocytes, and investigated the effects of PACAP38 on adenylyl cyclase, inositol phospholipid hydrolysis and intracellular calcium homeostasis. PACAP38 elicited a concentration-dependent (1 nM-100 nM) increase in inositol phosphate levels and [Ca2+]i in neurons but not in type I astrocytes. The PACAP-induced increase of intracellular calcium concentration, [Ca2+]i, was characterized by a spike, compatible with inositol trisphosphate (IP3) -induced calcium mobilization from intracellular stores, and a plateau phase, sustained by activation of capacitative calcium entry triggered by depletion of IP3-sensitive calcium stores. In the absence of extracellular calcium, only the spike phase was present while the plateau phase was clearly reduced. In addition, thapsigargin pretreatment abolished the PACAP38-induced [Ca2+]i rise. Treatment with 1 microM VIP did not affect [Ca2+]i in either neurons or type I astrocytes, clearly indicating the coupling of PAC1-HOP subtype to phospholipase-C in neurons. In addition, as previously reported, PACAP38 stimulated cAMP formation in both neurons and type I astrocytes. Using the reverse transcription polymerase chain reaction, we found mRNA-expression of PAC1 (PACAP - HOP variant) and VPAC2 in neurons, PAC1 (PACAP - R variant), VPAC1 and VPAC2 in astrocytes. These data indicate both a functional and molecular diversity of PACAP and VIP receptors in these cell types and support the view that the PAC1-HOP variant may be responsible for phospholipase-C activation and [Ca2+]i elevation in cortical neurons.

A cloned frog vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide receptor exhibits pharmacological and tissue distribution characteristics of both VPAC1 and VPAC2 receptors in mammals

Three receptor subtypes for the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been identified in mammals: the PAC1 receptor (PAC1-R) which is selectively activated by PACAP, and two VPAC receptors (VPAC1-R and VPAC2-R), which are equally stimulated by PACAP and VIP. The structures of PACAP and VIP have been well conserved during evolution, but little is known about VIP/PACAP receptors in nonmammalian species. An amphibian VIP/PACAP receptor complementary DNA (cDNA) has been cloned and characterized from a frog (Rana ridibunda) pituitary cDNA library. The predicted protein contains seven putative transmembrane domains and exhibits the highest sequence identity (65%) with the human VPAC1-R. The cloned cDNA was transiently expressed in LLC-PK1 cells, and its pharmacological profile was determined in comparison with the human VPAC1-R. Both PACAP and VIP stimulated cAMP accumulation through the cloned receptor with an EC50 of about 30 nM. In contrast, secretin, at concentrations that stimulate the human VPAC1-R, had no effect on cAMP production. RT-PCR analysis revealed the widespread distribution of this frog VIP/PACAP receptor in peripheral tissues. In situ hybridization histochemistry using a complementary RNA probe showed that the receptor gene is highly expressed in several hypothalamic and thalamic nuclei and to a lesser extent in the pallium and striatum. In the pituitary, the highest messenger RNA levels were detected in the distal lobe. Taken together, these data show that the cloned frog receptor shares several common features with both the VPAC1-R and VPAC2-R of mammals; the frog receptor exhibits the highest sequence identity with mammalian VPAC1-R, but the lack of effect of secretin and the brain distribution of the receptor are reminiscent of the characteristics of the mammalian VPAC2-R. The sequence of the frog receptor should thus prove useful to decipher the structure-activity relationships of the VIP/PACAP receptor family.