PET imaging of oncogene overexpression using 64Cu-vasoactive intestinal peptide (VIP) analog: comparison with 99mTc-VIP analog

The purpose of this study was to assess the feasibility of PET imaging of oncogene VPAC1 receptors overexpressed in human breast cancer cells.

METHODS

Vasoactive intestinal peptide (VIP) analog (TP3982) was synthesized to harbor a carboxy-terminus lysine (Lys) residue separated from VIP-asparagine (Asn(28)) by 4-aminobutyric acid (Aba) as a spacer. Lys was derivatized with diaminopropionic acid coupled to a pair of dibenzoylthioglycolic acid residues as protecting groups. The analog was labeled with (64)Cu at pH 9 ((64)Cu-TP3982) and (99m)Tc at pH 12 ((99m)Tc-TP3982). (99m)Tc-TP3982 and VIP derivatized with Aba-GAGG and labeled with (99m)Tc ((99m)Tc-TP3654) were used as reference agents. Smooth muscle relaxivity assays performed with each derivative and compared with unaltered VIP(28) demonstrated functional integrity. In vitro stability of (64)Cu-TP3982 was determined by challenging the complex with 100-mol excess of diethylenetriaminepentaacetic acid (DTPA), human serum albumin (HSA), and cysteine. In vivo stability was determined in urine and serum for up to 24 h. The mass of the Cu-TP3982 complex was determined by mass spectrometry. Human T47D breast tumor xenografts were grown in athymic nude mice. Planar scintigraphic imaging was performed at 4 and 24 h after the intravenous administration of (99m)Tc-TP3982 and (99m)Tc-TP3654 and PET imaging was performed using a small animal MOSAIC PET scanner, also at 4 and 24 h after injection of (64)Cu-TP3982. Tissue-distribution studies were also performed. In a separate experiment, receptors were blocked by intravenous injection of authentic VIP(28) 30 min before the administration of (64)Cu-TP3982 and tissue distribution was examined.

RESULTS

(64)Cu-TP3982 labeling yields were 98% +/- 1.2% and those for (99m)Tc-TP3982 and (99m)Tc-TP3654 were 98.2% +/- 1.1% and 97% +/- 1.6%, respectively. The biologic activity of both VIP analogs was uncompromised. When (64)Cu-TP3982 was challenged with 100-mol excess of DTPA, HSA, or cysteine, >98% radioactivity remained as (64)Cu-TP3982. In vivo, >98% of (64)Cu circulating in plasma remained as (64)Cu-TP3982. Of the (64)Cu excreted in urine 4, 20, and 24 h after injection, >98%, 89.9% +/- 0.9%, and 85% +/- 3%, respectively, were bound to TP3982. The mass of Cu-TP3982 as determined by surface-enhanced laser desorption/ionization time of flight (SELDI-TOF) was 4,049.7 Da. Four hours after receptor blocking with VIP(28), there was a significant reduction in uptake of all tissues except in the liver. With (64)Cu-TP3982, the 4-h postinjection tumor uptake was 10.8 +/- 2.1 %ID/g versus 0.5 +/- 0.02 %ID/g and 0.24 +/- 0.08 %ID/g for (99m)Tc-TP3982 and (99m)Tc-TP3654, respectively. Twenty-four hours after injection, the corresponding numbers were 17 +/- 0.7 %ID/g, 0.77 +/- 0.1 %ID/g, and 0.23 +/- 0.1 %ID/g. The severalfold greater uptake (21.2-74) of (64)Cu-TP3982 is attributable to the in vivo stability of the agent.

CONCLUSION

The results suggest that the uncompromised biologic activity and the significantly greater tumor uptake of (64)Cu-TP3982, combined with the high sensitivity and enhanced resolution of PET imaging, make (64)Cu-TP3982 highly desirable for further studies in PET imaging of oncogene receptors overexpressed in breast and other types of cancers.

VIP/PACAP preferentially attract Th2 effectors through differential regulation of chemokine production by dendritic cells

The neuropeptides vasoactive intestinal peptide (VIP) and the structurally related pituitary adenylate cyclase-activating polypeptide (PACAP) are potent immunomodulatory agents, acting as general anti-inflammatory factors. VIP, produced and secreted by Th2 cells following antigen stimulation, participates in a Th2 autoregulatory loop, promoting Th2-type responses through several nonexcluding mechanisms. VIP and PACAP affect the differentiation of CD4+ T cells directly and indirectly through antigen-presenting cells and promote the proliferation and/or survival of the Th2 effectors. Th1 and Th2 effectors express different chemokine receptors that control migration in response to various chemokines. In this study, we investigated the effects of VIP/PACAP on the production of CXCL10 (a Th1 chemokine) and of CCL22 (a Th2 chemokine) by bone marrow-derived dendritic cells. We found that VIP and PACAP inhibit CXCL10, while promoting CCL22 production, and that the effects are mediated through the VPAC1 receptor and involve cAMP/PKA as intracellular messengers. The induction of CCL22 and the suppression of CXCL10 in VIP/PACAP-treated dendritic cells results in the preferential chemoattraction of Th2 effectors both in vivo and in vitro. This is in agreement with the general Th2 bias induced by the two neuropeptides and adds an important parameter to their immunomodulatory function. By promoting Th2 migration, and preventing or reducing Th1 infiltration in inflammatory foci and sites of antigen presentation, VIP and PACAP help in resolving acute inflammatory processes and contribute to the prevention of chronic inflammation.

Rhythmic secretion of prolactin in rats: action of oxytocin coordinated by vasoactive intestinal polypeptide of suprachiasmatic nucleus origin

Prolactin (PRL) is secreted from lactotrophs of the anterior pituitary gland of rats in a unique pattern in response to uterine cervical stimulation (CS) during mating. Surges of PRL secretion occur in response to relief from hypothalamic dopaminergic inhibition and stimulation by hypothalamic releasing neurohormones. In this study, we characterized the role of oxytocin (OT) in this system and the involvement of vasoactive intestinal polypeptide (VIP) from the suprachiasmatic nucleus (SCN) in controlling OT and PRL secretion of CS rats. The effect of OT on PRL secretion was demonstrated in cultured lactotrophs showing simultaneous enhanced secretion rate and increased intracellular Ca(2+). Neurosecretory OT cells of the hypothalamic paraventricular nucleus that express VIP receptors were identified by using immunocytochemical techniques in combination with the retrogradely transported neuronal tracer Fluoro-Gold (iv injected). OT measurements of serial blood samples obtained from ovariectomized (OVX) CS rats displayed a prominent increase at the time of the afternoon PRL peak. The injection of VIP antisense oligonucleotides into the SCN abolished the afternoon increase of OT and PRL in CS-OVX animals. These findings suggest that VIP from the SCN contributes to the regulation of OT and PRL secretion in CS rats. We propose that in CS rats the regulatory mechanism(s) for PRL secretion comprise coordinated action of neuroendocrine dopaminergic and OT cells, both governed by the daily rhythm of VIP-ergic output from the SCN. This hypothesis is illustrated with a mathematical model.

Vasoactive intestinal peptide (VIP) stimulates cortisol secretion from the H295 human adrenocortical tumour cell line via VPAC1 receptors

Vasoactive intestinal peptide (VIP) shows a wide tissue distribution and exerts numerous physiological actions. VIP was shown in a dose-dependent manner to increase cortisol secretion in the NCI-H295R human adrenocortical carcinoma (H295) cell line (threshold dose 3.3x10(-10) M, maximal dose 10(-7) M), coupled with a parallel increase in cAMP accumulation. Receptor-specific agonists were employed to determine which of the two known VIP receptor subtypes was involved in cortisol secretion. Treatment with the VPAC1 receptor agonist, [K(15), R(16), L(27)]VIP(1-7)/GRF(8-27), produced a dose-dependent increase in H295 cell cortisol secretion (threshold dose 10(-11) M, maximal dose 10(-7) M) similar to that seen with VIP. Meanwhile, the high-affinity VPAC2 receptor agonist, RO-25-1553, failed to stimulate significantly cortisol or cAMP production from H295 cells. Inhibition of VIP-mediated H295 cell cortisol secretion by PG97-269, a competitive VPAC1-specific antagonist, produced parallel shifts of the dose-response curve and a Schild regression slope of 0.99, indicating competitive inhibition at a single receptor subtype. VIP is known also to interact with the PAC1 receptor, albeit with lower affinity (EC(50) of approximately 200 nM) than the homologous ligand, PACAP (EC(50) of approximately 0.5 nM). PACAP stimulated cortisol secretion from H295 cells (EC(50) of 0.3 nM), suggesting the presence of functional PAC1 receptors. However, stimulation of cortisol secretion by nanomolar concentrations of VIP (EC(50) of 5 nM), coupled with real-time PCR estimation that VPAC1 receptor transcripts appear 1000-fold more abundant than PAC1 transcripts in H295 cells, makes it unlikely that VIP signals via PAC1 receptors. Together, these data suggest that VIP directly stimulates cortisol secretion from H295 cells via activation of the VPAC1 receptor subtype.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [125I]-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a Kd of 0.70 nM and a Bmax of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to turkey cerebrum was: PACAP38 approximately PACAP27 approximately chicken VIP approximately mammalian VIP >>> PHI >> secretin, chicken VIP16-28 (inactive). About 65% of specific [125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [125I]-VIP.

The neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) modulate several biochemical pathways in human leukemic myeloid cells

The neuropeptides Vasoactive-intestinal peptide (VIP) and Pituitary adenylate-cyclase activating protein (PACAP) increased cAMP levels in three out of five human myeloid leukemic cell lines tested while an increased in calcium intracytoplasmic levels was seen only in one cell line (HEL). This increase was phospholipase C, Pertussis toxin dependent and associated with an increase in c-fos and c-jun protein expression together with the formation of functional AP-1 transcriptional factor complex. Cell exposure to VIP or PACAP resulted in a decrease in HEL cell proliferation associated with a down-regulation of the erythroid marker, Glycophorin A. Both peptides were found to increase intra-cytoplasmic calcium levels in blasts isolated from patients with myeloid leukemia. Thus VIP and PACAP are involved in the physiology and pathophysiology of human myeloid cells.

Temporal and spatial distribution of VIP, CGRP and their receptors in the development of airway hyperresponsiveness in the lungs

To explore the role of intrapulmonary neuropeptides in the development of airway hyperresponsiveness, we established an animal model of airway hyperresponsiveness (AHR) in rabbits by using ozone exposure. With the model, after test of the mechanics of respiration and bronchoalveolar lavage assay, the levels of vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) in the lungs were determined by radioimmunoassay, and the expression of mRNA coding receptors of these two neuropeptides was evaluated by reverse transcriptional-polymerase chain reaction (RT-PCR). At the same time, the distribution of VIP receptor-1 (VIPR1) and CGRP receptor-1 (CGRPR1) in lung tissues and its time-course were examined by in situ hybridization. The results showed: (1) in ozone-stressing groups, airway resistance increased significantly and typical inflammatory pathological changes were observed in pulmonary tissue slides, including neutrophil and eosinophil infiltration, mucus exudation and bronchial epithelial cells (BECs) shedding; (2) with elongation of ozone exposure, the levels of VIP and CGRP in the lungs increased at first, reaching a peak on d 2 to 4, then decreased slowly, and CGRP peaked somewhat earlier than VIP; (3) mRNA expression of the two neuropeptide receptors in the lungs changed in a similar manner like VIP and CGRP, but the high level of mRNA expression of VIPR1 lasted longer than that of CGRPR1; and (4) in situ hybridization for neuropeptide receptors demonstrated that, in unstressed control, VIPR1 and CGRPR1 positive cells appeared in the airway epithelium, pulmonary interstitial and focal areas of airway and vascular smooth muscles. With the elongation of ozone exposure, hybridization stained deeper and the majority of positive cells were located around the vessels and bronchus except a few in the alveoli. At 8 d, only a small number of positive cells were seen in the lungs. From the results, it is concluded that ozone-stressing can induce the development of AHR, in which VIP and CGRP may play important roles. That implies, through binding to CGRPR1, CGRP stimulates an early inflammation response which contributes in cleaning up of irritants, while VIP exerts a later dampening of pulmonary inflammation response. These two neuropeptides may play sequential and complementary roles in the development of AHR.

Effect of pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal polypeptide on mouse preantral follicle development in vitro

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a bioactive peptide isolated from ovine hypothalamus. It is transiently expressed in preovulatory follicles and positively affects several parameters correlated with the ovulatory process. It has also been shown to be expressed in the interstitial tissue around primordial and preantral follicles. The aim of the present study was to investigate whether PACAP influences preantral follicle growth and differentiation. Mouse preantral follicles were cultured for 5 d in the presence of FSH and increasing concentrations of PACAP or vasoactive intestinal polypeptide (VIP) (10(-12) to 10(-7) m). In the presence of FSH, follicles increased in diameter and formed an antrum. At the concentrations tested, neither PACAP alone nor VIP alone had any effect on follicle development, but the addition of either peptide to FSH-stimulated follicles caused a dose-dependent inhibition of follicle growth, antrum formation, granulosa cell proliferation, and estradiol production. The effect of PACAP on follicle growth and antrum formation was directly correlated with the length of stimulation and was reversible. Although exposure of follicles to 10(-7) m PACAP and VIP did not affect oocyte growth, it severely impaired completion of meiotic maturation in oocytes isolated from the follicles and cultured for 17 h in medium alone. The cyclic production of PACAP by preovulatory follicles during the estrous cycle in adult rats and its induction by LH in the rat and mouse ovary suggest that this peptide may play a role in the local regulation of preantral follicle growth.

VIP/PACAP oppositely affects immature and mature dendritic cell expression of CD80/CD86 and the stimulatory activity for CD4(+) T cells

The neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) released within lymphoid organs from nerve terminals and/or immune cells play a significant, anti-inflammatory role by inhibiting macrophage-induced inflammatory reactions and promoting T helper cell type 2 (Th2) responses. However, dendritic cells (DC) and not macrophages often are the major antigen-presenting cells and link between innate and adaptive immunity. The role of VIP/PACAP in DC development and function is mostly unknown. Here, we report that bone marrow-derived DC express VIP/PACAP receptors and that VIP and PACAP exert a differential effect on immature DC (iDC) and lipopolysaccharide (LPS)-treated DC. In iDC, VIP/PACAP up-regulates CD86 expression and enables them to stimulate T cell proliferation and differentiation into Th2 effectors in vivo and in vitro. In contrast, VIP/PACAP down-regulates CD80/CD86 expression in LPS-stimulated DC and strongly reduces their capacity to stimulate T cell proliferation and secretion of Th1 and Th2 cytokines. The VIP/PACAP effects on iDC and LPS-stimulated DC are mediated primarily through the VIP receptor 1. These results indicate that neuropeptides such as VIP and PACAP can differentially affect the function of iDC and mature DC. In the absence of an ongoing immune response, VIP/PACAP contributes to the initiation of Th2-type immunity, whereas in the presence of a full-blown, inflammatory reaction, VIP/PACAP act as anti-inflammatory agents.

Distribution of the VPAC2 receptor in peripheral tissues of the mouse

The neuropeptide vasoactive intestinal peptide (VIP) exerts its actions through two structurally related G protein-coupled receptors (VPAC(1) and VPAC(2)). Pituitary adenylate cyclase-activating polypeptide (PACAP) is also a potent agonist of VPAC(1) and VPAC(2) receptors as well as of a third, PACAP-specific receptor (PAC(1)). We report here the distribution of the VPAC(2) receptor in peripheral tissues of the mouse, determined by receptor autoradiography using [(125)I]VIP and the selective VPAC(2) receptor agonist [(125)I]Ro25-1553 in wild-type and VPAC(2) receptor-null mice. In addition, displacement experiments with the VPAC(2)-selective agonist Ro25-1553 and the VPAC(1)-selective agonist [K(15),R(16),L(27)]VIP(1-7)/GRF(8-27) were performed using the universal radioligand [(125)I]VIP. The VPAC(2) receptor is found predominantly in smooth muscle (in blood vessels and in the smooth muscle layers of the gastrointestinal and reproductive systems), the basal part of the mucosal epithelium in the colon, lung, the vasculature of the kidney, adrenal medulla, and retina. Unexpectedly, the receptor was also present in thyroid follicular cells and acinar cells of the pancreas, tissues that have not been found to express the receptor in other species, and in very large amounts in the lung. Our data suggest novel functions of the VPAC(2) receptor and additional potential therapeutic uses of drugs acting at the receptor (including the treatment of erectile dysfunction), but our results also indicate that caution should be exercised in using the mouse as an animal model for the evaluation of VIP analogs intended for diagnostic or therapeutic use in man.

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.

[Peptide histidine-isoleucine and and its human analogue peptide histidine-methionine: localization, receptors and biological function]

Peptide histidine-isoleucine (PHI) and its human analogue peptide histidine-methionine (PHM) are members of a superfamily of structurally related peptides embracing, among others, pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), peptide histidine-valine (PHV), and helodermin. All the peptides display a pleiotropic biological activity. PHI, PHM, PHV and VIP are co-synthesized from the same precursor and share high levels of structural and functional similarity. These peptides may act through common receptors and are widely distributed throughout the body tissues (the central nervous system, gastrointestinal tract, respiratory system, and reproductive system); however, their role remains largely unknown. Changes in the levels of the peptides in the course of different diseases suggest their possible importance and usefulness in diagnostics. Moreover, the neurotrophic and neuroprotective properties of PHI suggest, by analogy to VIP or PACAP, its therapeutic potential in many neurodegenerative diseases, such as Alzheimer's and Parkinson's disease.

Activation of VPAC1 receptors by VIP and PACAP-27 in human bronchial epithelial cells induces CFTR-dependent chloride secretion

1. In the human airway epithelium, VIP/PACAP receptors are distributed in nerve fibers and in epithelial cells but their role in transepithelial ion transport have not been reported. Here, we show that human bronchial epithelial Calu-3 cells expressed the VPAC(1) receptor subtype which shares similar high affinity for VIP and PACAP-27. 2. The stoichiometric binding parameters characterizing the (125)I-VIP and (125)I-PACAP-27 binding to these receptors were determined. 3. We found that VIP (EC(50) approximately 7.6 nM) and PACAP-27 (EC(50) approximately 10 nM) stimulated glibenclamide-sensitive and DIDS-insensitive iodide efflux in Calu-3 cells. 4. The protein kinase A (PKA) inhibitor, H-89 and the protein kinase C (PKC) inhibitor, chelerythrine chloride prevented activation by both peptides demonstrating that PKA and PKC are part of the signaling pathway. This profile corresponds to the pharmacological signature of CFTR. 5. In the cystic fibrosis airway epithelial IB3-1 cell lacking functional CFTR but expressing VPAC(1) receptors, neither VIP, PACAP-27 nor forskolin stimulated chloride transport. 6. Ussing chamber experiments demonstrated stimulation of CFTR-dependent short-circuit currents by VIP or PACAP-27 applied to the basolateral but not to the apical side of Calu-3 cells monolayers. 7. This study shows the stimulation in human bronchial epithelial cells of CFTR-dependent chloride secretion following activation by VIP and PACAP-27 of basolateral VPAC(1) receptors.

VIP receptor antagonists inhibit mammary carcinogenesis in C3(1)SV40T antigen mice

The effects of a vasoactive intestinal peptide (VIP) receptor antagonist on mammary carcinogenesis were investigated using the C3(1)SV40T antigen (ag) mice. Ten microg/day VIPhybrid (VIPhyb) administered daily subcutaneously increased significantly the survival of C3(1)SV40Tag mice. At 5.2 months, VIPhyb significantly reduced the mammary tumor burden in C3(1)SV40Tag mice relative to control animals. 125I-VIP bound with high affinity to mouse mammary tumor homogenate. Because (Lys15, Arg16, Leu27)VIP1-7GRF8-27 (VPAC1 selective) but not Ro25-1553 (VPAC2 selective) inhibited specific 125I-VIP binding to mammary tumor membranes with high affinity, VPAC1 receptors predominate. By RT-PCR, VPAC1 receptor mRNA was detected in mammary tumors. By Western blot, a major 60 Kdalton band was detected in mammary tumor extracts using VPAC1 receptor antisera. By immunocytochemistry, VPAC1-R immunostaining was detected in the cytosol and plasma membrane but not the nucleus of fixed mammary tumor tissue. Using laser capture microdissected tumor cells and surface enhanced laser desorption/ionization (SELDI) techniques on mammary tumor cells, the proteomic profile was altered in mice treated with VIPhyb. Because VPAC1 receptor antagonists increase the survival and reduce the tumor burden in C3(1)SV40Tag mice, they may function as chemopreventive agents in mammary cancer.

Calcium signal-mediated expression of the vasoactive intestinal polypeptide gene and its small contribution to activity-dependent survival of mouse cerebellar granule cells

We have demonstrated previously in primary cultures of mouse cerebellar granule cells (CGCs) that endogenously synthesized pituitary adenylate cyclase-activating polypeptide (PACAP) contributes at least in part to the activity-dependent survival of CGCs (Tabuchi et al. [2001] Neurosci. Res. 39:85-93). In this study, we have demonstrated that expression of vasoactive intestinal polypeptide (VIP), a member of the same VIP/secretin/glucagon family as PACAP, was activated markedly by Ca(2+) influx through L-type voltage-dependent Ca(2+) channels (L-VDCCs), which could be induced under the depolarizing condition induced by high concentration of potassium (K(+)) in the medium. The activation of VIP mRNA expression, different from that of PACAP, was dependent partly on de novo protein synthesis. On the other hand, mRNA expression of secretin and PACAP/VIP receptors (PAC(1), VPAC(1), and VPAC(2)) was not activated by the Ca(2+) influx; rather, PAC(1) mRNA expression was reduced. Exogenously added VIP prevented apoptosis of CGCs under nondepolarizing conditions, the effect of which was mediated specifically through the VPAC(1) receptor. Furthermore, the survival of CGCs under depolarizing conditions could be mediated partly through VPAC(1), the contribution of which was much less than that of PAC(1). These findings indicate that PACAP and VIP genes are coordinately activated by the Ca(2+) signals in CGCs, but the contribution of VIP to the activity-dependent survival of CGCs is quite small.

Serine 447 in the carboxyl tail of human VPAC1 receptor is crucial for agonist-induced desensitization but not internalization of the receptor

The VPAC1 receptor for vasoactive intestinal peptide (VIP) belongs to the class II family of G protein-coupled receptors and is coupled to Gs protein/adenylyl cyclase. We assessed whether 10 different Ser/Thr residues in human VPAC1 receptor intracellular domains play a role in the process of VIP-induced desensitization/internalization by performing a site-directed mutagenesis study. The Ser/Thr residues mutated to Ala include potential G protein-coupled receptor kinase, protein kinase A and protein kinase C targets that are of particular interest for VPAC1 receptor desensitization. The data show that when Chinese hamster ovary cells expressing wild-type receptors were pretreated for 5 min with VIP (50 nM), receptor desensitization occurred with a 10-fold right shift of the ED50 for adenylyl cyclase activation. When the construct with the widest span of mutations was studied, there was no longer any short-term desensitization. By using constructs with fewer and fewer mutations, we identified Ser447 in the C-terminal tail to be crucial for rapid desensitization. We also showed that Ser447 plays an essential role for VIP-induced VPAC1 phosphorylation in Chinese hamster ovary cells. Furthermore, we demonstrated that none of the mutated Ser/Thr residues was involved in down-regulation after a 12-h treatment of cells with 50 nM VIP. Neither were they involved in VIP and VIP-induced receptor internalization as shown using a novel fluorescein-tagged VIP and VPAC1 receptor bearing a Flag epitope in the N-terminal domain and a green fluorescent protein at the C terminus. We conclude that Ser447, a likely G protein-coupled receptor kinase target, is crucial for VIP-induced phosphorylation and rapid desensitization of VPAC1 receptor.

Cloning, regulation of messenger ribonucleic acid expression, and function of a new isoform of pituitary adenylate cyclase-activating polypeptide in the zebrafish ovary

Increasing evidence suggests that pituitary adenylate cyclase-activating polypeptide (PACAP) acts as a local factor in the ovary of mammals. In nonmammalian vertebrates, although the expression of PACAP has also been demonstrated in the ovary, the information on its functions and regulation is limited. In the present study, we identified a new type of PACAP, zebrafish (zf)PACAP38-2, from the zebrafish ovary. The precursor of GHRH-zfPACAP38-2 consists of 175 amino acids with only 64% homology with another type of zebrafish PACAP, zfPACAP38-1. RT-PCR analysis detected two messengers of zfPACAP38-2 in the zebrafish ovary. The short product was more abundant, and it encodes zfPACAP38-2 only, whereas the long form codes for both zfPACAP38-2 and GHRH. Using a primary culture of zebrafish follicle cells, we demonstrated that gonadotropin (human chorionic gonadotropin and goldfish pituitary extract) significantly stimulated zfPACAP38-2 expression within 2 h; however, the effect decreased to the control level after 8 h of treatment. The stimulation of zfPACAP38-2 expression by gonadotropin could be mimicked by cAMP analogs and forskolin but suppressed by H89 (10 mum), suggesting the involvement of the cAMP-protein kinase A signaling pathway. We also examined the expression of PACAP receptor VPAC2-R in the zebrafish ovary. Unlike zfPACAP38-2, which showed a trend of increase during follicle development, the expression of VPAC2-R mRNA in the follicles showed no significant stage-dependent variation, and its expression in the follicle cells did not respond to gonadotropin treatment. Our studies further demonstrated that synthetic zfPACAP38-2 stimulated oocyte maturation and increased the expression of follistatin in zebrafish ovarian follicle cells. These results suggest that zfPACAP38-2 is a potential ovarian factor that mediates gonadotropin actions in paracrine/autocrine manners, and its functional roles are likely, to some extent, related to the ovarian activin/follistatin system.

VIP receptor 1 (VPAC1) promoter targets the expression of a reporter gene to cerebellum and adrenal medulla in transgenic mice

Vasoactive intestinal peptide (VIP) is a neurotransmitter with neurotropic effects. VIP functions through two distinct G-protein-coupled receptor subtypes (VPAC1 and VPAC2). We have demonstrated expression of VPAC1 in pediatric nervous system tumors, including medulloblastoma arising in the cerebellum and neuroblastoma arising in the adrenal medulla. More recently, we have reported the differentiation of neuroblastoma cells by upregulation of VIP type 1 receptor suggesting a role for VPAC1 in neuronal development. To understand the molecular mechanisms regulating VPAC1 expression in both cerebellum and adrenal medulla, we have cloned the human VPAC1 gene and sequenced 2.6-kb of the 5'-flanking sequence. Expression of the luciferase reporter gene under the control of this 2.6-kb human VPAC1 promoter was induced 35-fold in a human medulloblastoma cell line (DAOY) and 36-fold in a human neuroblastoma cell line (SKNSH). Analysis of 5'-unidirectional deletion derivatives of the 2.6-kb fragment demonstrated that a 241-bp sequence immediately upstream of the VPAC1 coding region retains high activity, suggesting that it contains the core promoter region. Quantitative RT-PCR analysis demonstrated that VPAC1 is expressed in mouse cerebellar and adrenal tissues. The VPAC1 promoter also directed expression of a reporter gene in cerebellum and adrenal medulla in transgenic mice. Along with our previous findings, these results suggest that VPAC1 may play a functional role in development of both cerebellum and adrenal medulla.

Differential involvement of the Ras and Rap1 small GTPases in vasoactive intestinal and pituitary adenylyl cyclase activating polypeptides control of the prolactin gene

In pituitary cells, transcriptional regulation of the prolactin (PRL) gene and prolactin secretion are controlled by multiple transduction pathways through the activation of G protein coupled receptors and receptor tyrosine kinases. In the somatolactotrope GH4C1 cell line, we have previously identified crosstalk between the MAPKinase cascade ERK1/2 and the cAMP/protein kinase A pathway after the activation of the VPAC2 receptor by vasoactive intestinal polypeptide (VIP) or pituitary adenylyl cyclase-activating polypeptide (PACAP38). In the present study, we focus on the involvement of the GTPases Ras and Rap1 as downstream components of signal transmission initiated by activation of the VPAC2 receptor. By using pull-down experiments, we show that VIP and PACAP38 preferentially activate Rap1, whereas thyrotropin releasing hormone (TRH) and epidermal growth factor (EGF) mainly activate Ras GTPase. Experiments involving the expression of the dominant-negative mutants of Ras and Rap1 signaling (RasN17 or Rap1N17) indicate that both GTPases Ras and Rap1 are recruited for the ERK activation by VIP and PACAP38, whereas Rap1 is poorly involved in TRH or EGF-induced ERK activation. The use of U0126, a selective inhibitor of MAPKinase kinase, provides evidence that MAPKinase contributes to the regulation of the PRL gene. Moreover, cotransfection of RasN17 or Rap1N17 with the PRL proximal promoter luciferase reporter construct indicates that Rap1 may be responsible for VIP/PACAP-induced activation of the PRL promoter. Interestingly, Ras would be involved as a negative regulator of VIP/PACAP-induced PRL gene activation, in contrast to its stimulatory role in the regulation of the PRL promoter by TRH and EGF.

Identification of cytoplasmic domains of hVPAC1 receptor required for activation of adenylyl cyclase. Crucial role of two charged amino acids strictly conserved in class II G protein-coupled receptors

The VPAC1 receptor mediates the action of two neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide. It is a class II G protein-coupled receptor-activating adenylyl cyclase (AC). The role of the N-terminal extracellular domain of hVPAC1 receptor for VIP binding is now established (Laburthe, M., Couvineau, A. and Marie, J. C. (2002) Recept. Channels 8, 137-153), but nothing is known regarding the cytoplasmic domains responsible for AC activation. Here, we constructed a large series of mutants by substituting amino acids with alanine in the intracellular loops (IL) 1, 2, and 3 and proximal C-terminal tail of the receptor. The mutation of 40 amino acids followed by expression of mutants in chinese hamster ovary cells showed the following. (i) Mutations IL1 result in the absence of expression of mutants, suggesting a role of this loop in receptor folding. (ii) All residues of IL2 can be mutated without alteration of receptor expression and AC response to VIP. (iii) Mutation of residues IL3 points to the specific role of lysine 322 in the efficacy of the stimulation of AC activity by VIP. This efficacy is reduced by 50% in the K322A mutant. (iv) The proximal C-terminal tail is equipped with another important amino acid since mutation of glutamic acid 394 reduces AC response by 50%. The double mutant K322A/E394A exhibits a drastic reduction of >85% in the efficacy of VIP in stimulating AC activity in membranes and cAMP response in intact cells without alteration of receptor expression or affinity for VIP. These data highlight the role of charged residues in IL3 and the proximal C-terminal tail of hVPAC1 receptor for agonist-induced AC activation. Because these charged residues are absolutely conserved in class II receptors for peptides, which are all mediating AC activation, they may play a general role in coupling of class II receptors with the Gs protein.

Localisation of VIP-binding sites exhibiting properties of VPAC receptors in chromaffin cells of rainbow trout (Oncorhynchus mykiss)

The current model for the neuronal control of catecholamine release from piscine chromaffin cells advocates that the neurotransmitters vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are co-released with acetylcholine from preganglionic fibres upon nerve stimulation. Both VIP and PACAP elicit the secretion of exclusively adrenaline from rainbow trout chromaffin cells, which presumably arises from the activation of VPAC type receptors. Thus, the goals of the present study were (1) to localise VPAC receptors in the chromaffin cell fraction of the posterior cardinal vein (PCV) of trout and (2) to test the hypothesis that the selective secretion of adrenaline elicited by VIP could be explained by the absence of the VPAC receptors from the noradrenaline-containing cells. Fluorescent labelling of chromaffin cells using aldehyde-induced fluorescence of catecholamines and antisera raised against dopamine beta-hydroxylase (DbetaH) revealed a distinct layer of chromaffin cells lining the walls of the PCV. Furthermore, specific VIP-binding sites were demonstrated on chromaffin cells using a biotinylated VIP that was previously established as being bioactive. Although multiple labelling experiments revealed that a number of DbetaH-positive cells were immunonegative for phenylethanolamine N-methyl transferase (PNMT; noradrenaline-containing cells versus adrenaline-containing cells, respectively), labelling of VIP-binding sites was similar to that of DbetaH labelling, suggesting that all chromaffin cells possess VIP-binding sites. Pharmacological assessment of the VIP-binding sites indicated that they exhibited characteristics of VPAC receptors. Specifically, the labelling of VIP-binding sites was prevented after pre-treatment of PCV tissue sections with unlabelled VIP, PACAP or the specific VPAC receptor antagonist VIP 6-28. By contrast, sections pre-treated with the PAC(1) receptor blocker PACAP 6-27 displayed normal labelling of VIP-binding sites. Finally, partial cDNA clones for the trout VPAC(1) and VPAC(2) receptor were obtained and sequenced. Tissue distribution experiments using RT-PCR revealed the presence of VPAC(1) receptor mRNA but not that of the VPAC(2) receptor in the PCV tissue. The results provide direct evidence that VIP and PACAP can elicit the secretion of adrenaline from the chromaffin tissue via specific VIP-binding sites that exhibit properties of VPAC receptors. However, the selective secretion of adrenaline by VIP or PACAP cannot be explained by a lack of VIP-binding sites on the noradrenaline-containing cells.

A hVIPR transgene as a novel tool for the analysis of circadian function in the mouse suprachiasmatic nucleus

A mouse bearing a novel transgene encoding the human VPAC2 receptor (hVIPR; Shen et al. (2000) PNAS, 97, 11575-11580) was used to investigate circadian function in the hypothalamic suprachiasmatic nuclei (SCN). Neurons expressing hVPAC2R, detected by a beta-galactosidase (beta-GAL) tag, have a distinct distribution within the SCN, closely matching that of neurophysin (NP) neurons and extending into the region of peptide histidine isoleucine (PHI) cells. In common with NP and PHI cells, neurons expressing hVPAC2R are circadian in nature, as revealed by synchronous rhythmic expression of mPERIOD (mPER) proteins. A population of SCN cells not expressing PHI, NP or hVPAC2R exhibited circadian PER expression antiphasic with the rest of the SCN. Nocturnal light exposure induced mPER1 in the ventral SCN and mPER2 widely across the nucleus. Induction of nuclear mPER2 in hVPAC2R cells confirmed their photic responsiveness. Having established their circadian properties, we tested the utility of SCN neurons expressing the hVIPR transgene as functionally and anatomically explicit markers for SCN tissue grafts. Prenatal SCN tissue from hVIPR transgenic pups survived transplantation into adult CD1 mice, and expressed beta-GAL, PER and PHI. Over a series of studies, hVIPR transgenic SCN grafts restored circadian activity rhythms to 17 of 72 arrhythmic SCN lesioned recipients (23.6%). By using heterozygous hVIPR transgenic grafts on a heterozygous Clock mutant background we confirmed that restored activity rhythms were conferred by the donor tissue. We conclude that the hVIPR transgene is a powerful and flexible tool for examination of circadian function in the mouse SCN.

Expression of functional PACAP/VIP receptors in human prostate cancer and healthy tissue

Vasoactive intestinal peptide (VIP) is involved in prostate cell proliferation and function. VIP and pituitary adenylate cyclase-activating peptide (PACAP) are similarly recognized by VPAC(1)/VPAC(2) receptors whereas PACAP binds with higher affinity than VIP to PAC(1) receptor. Here we systematically studied the presence and distribution of functional PAC(1), VPAC(1) and VPAC(2) receptors in human normal and malignant prostate tissue. Functional PACAP/VIP receptors were detected in normal and malignant prostate by adenylyl cyclase stimulation with PACAP-27/38 and VIP. RT-PCR experiments showed PAC(1) (various isoforms due to alternative splicing), VPAC(1) and VPAC(2) receptor expression at the mRNA level, whereas Western blots found the three receptor protein classes in normal and pathological conditions. No conclusive differences could be established when comparing control and cancer tissue samples. Immunohistochemistry showed a weaker immunostaining in tumoral than in normal epithelial cells for the three receptor subtypes. In conclusion, we demonstrate the expression of functional PAC(1), VPAC(1) and VPAC(2) receptors in human prostate as well as its maintenance after malignant transformation.

VPAC receptors for VIP and PACAP

VIP and PACAP are two prominent neuropeptides that share two common G protein-coupled receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. This article reviews the present knowledge regarding various aspects of VPAC receptors including: 1) receptor specificity toward natural VIP-related peptides and pharmacology of synthetic agonists or antagonists; 2) genomic organization and chromosomal localization; 3) signaling and established or putative interactions with G proteins or accessory proteins such as RAMPs or PDZ-containing proteins; 4) molecular basis of ligand-receptor interaction as determined by site-directed mutagenesis, construction of receptor chimeras, and structural modeling; 5) constitutively active receptor mutants; 6) short-term (desensitization, internalization, phosphorylation) and long-term (transcription) regulations and transgenic models; 7) receptor polymorphisms.

Vasoactive intestinal peptide as a new drug for treatment of primary pulmonary hypertension

Primary pulmonary hypertension is a fatal disease causing progressive right heart failure within 3 years after diagnosis. We describe a new concept for treatment of the disease using vasoactive intestinal peptide, a neuropeptide primarily functioning as a neurotransmitter that acts as a potent systemic and pulmonary vasodilator. Our rationale is based on the finding of a deficiency of the peptide in serum and lung tissue of patients with primary pulmonary hypertension, as evidenced by radioimmunoassay and immunohistochemistry. The relevance of this finding is underlined by an upregulation of corresponding receptor sites as shown by Northern blot analysis, Western blot analysis, and immunological techniques. Consequently, the substitution with the hormone results in substantial improvement of hemodynamic and prognostic parameters of the disease without side effects. It decreased the mean pulmonary artery pressure in our eight study patients, increased cardiac output, and mixed venous oxygen saturation. Our data provide enough proof for further investigation of vasoactive intestinal peptide and its role in primary pulmonary hypertension.