Molecular properties of the vasoactive intestinal peptide receptor in aorta and other tissues

Identification of G-proteins coupling to the vasoactive intestinal peptide receptor VPAC(1) using immunoaffinity chromatography: evidence for precoupling

VPAC(1) receptor subtype-specific G-protein interactions were identified using a strategy that exploits an essential initial signaling event, namely the functional and physical association of the receptor with G-protein. An immunoaffinity purification column was constructed using a previously characterized antibody that had been raised against the first extracellular loop of the VPAC(1) receptor. VPAC(1)/G-protein complexes were solubilized from membranes and copurified. Receptor and Galpha-proteins were detected in eluates using (125)I-VIP labeling and immunoblotting, respectively. Human VPAC(1) transfected in HEK293 cells couples to Gs but not Gi3, Gi1/2, or Gq. Rat VPAC(1) in brain membranes is coupled to Gs and Gi3. Rat VPAC(1) in lung membranes couples to Gs, Gi3, and Gq. Pretreatment of membranes with VIP increased the level of all G-proteins copurifying with VPAC(1). Immunoaffinity chromatography also revealed VPAC(1) receptor precoupling to G-protein in the absence of VIP pretreatment. This was confirmed using a cross-linking procedure to capture VIP receptor/G-protein complexes in the native membrane milieu prior to solubilization. Precoupling suggests that there is a significant basal level of VPAC(1) receptor activity especially in cells, such as some human malignant tumor cells, that express high levels of receptor.

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.

VIP activates G(s) and G(i3) in rat alveolar macrophages and G(s) in HEK293 cells transfected with the human VPAC(1) receptor

We have characterized vasoactive intestinal peptide (VIP) receptor/G-protein coupling in rat alveolar macrophage (AM) membranes and find that pertussis toxin treatment and antisera against G(alphai3) and G(alphas) reduce high-affinity (125)I-VIP binding, indicating that both G(alphas) and G(alphai3) couple to the VIP-receptor. The predominant VIP-receptor subtype in AM is VPAC(1) and we examined the G-protein interactions of the human VPAC(1) that had been transfected into HEK293 cells. VPAC(1) has a molecular mass of 56 kDa; GTP analogs reduced (125)I-VIP binding to this protein demonstrating that high-affinity binding of VIP to the receptor requires coupling to G-protein. Functional VIP/VPAC(1)/G-protein complexes were captured by covalent cross-linking and analyzed by Western blotting. The transfected human VPAC(1) receptor in HEK293 was found to be coupled to G(alphas) but not G(alphai) or G(alphaq). Furthermore, pertussis toxin treatment had no effect on VPAC(1)/G-protein coupling in these cells. These observations suggest that the G-proteins activated by VPAC(1) may be dependent upon species and cell type.

Human vascular endothelium heterogeneity. A comparative study of cerebral and peripheral cultured vascular endothelial cells

BACKGROUND AND PURPOSE

Hormones, neurotransmitters, and autacoids play a key role in the regulation of vascular tone as a result of their interaction with the endothelium. The aim of this study was to compare selected properties of three human endothelial cell lines isolated from cerebral pial arteries (PEC) and two peripheral vessels, the superficial temporal (SEC) and omental (OEC) arteries.

METHODS

Intracellular free calcium concentration ([Ca2+]i) and receptor protein expression were measured in characterized primary cultures of human endothelial cells.

RESULTS

All cell lines labeled positively for factor VIII/von Willebrand factor. Growth rate and constitutive release of endothelin-1, expressed as a function of protein, were both significantly lower in cerebral cells (PEC) than in endothelial cells derived from peripheral vessels. Basal [Ca2+]i measured with the fluorescent calcium indicator fura 2-AM (2 mumol/L) did not differ in either of the three cell lines. Although PEC responded to endothelin-1 (0.1 mumol/L) and vasoactive intestinal peptide (1 mumol/L) by a twofold to threefold increase in [Ca2+]i, OEC were unresponsive to these peptides. Moreover, the calcium response to alpha-thrombin (10 nmol/L) was greater in cerebral (PEC) than in peripheral (SEC, OEC) endothelial cells, while bradykinin (100 nmol/L) increased [Ca2+]i to a similar level in all three cell types.

CONCLUSIONS

This study demonstrates that endothelial cells from different sites of the vasculature exhibit different growth rates and vary in their response to agonists.

alpha-Thrombin upregulates G alpha i3 in human vascular endothelial cells

BACKGROUND AND PURPOSE

During thrombosis, alpha-thrombin becomes sequestered by fibrin and the subendothelial basement membrane, and it is available to interact with the vasculature over prolonged periods. In this study, we investigated the long-term effect of alpha-thrombin on G alpha i3 and G alpha s levels in human vascular endothelial cells (EC). Because obesity is associated with changes in receptor signaling in many animal models, we also explored the influence of this clinical risk factor.

METHODS

Primary cultures of human EC were exposed to alpha-thrombin for 16 hours, and immunologically detectable G alpha i3 and G alpha s levels were measured.

RESULTS

alpha-Thrombin (100 nmol/L) increased G alpha i3 levels in EC derived from the cerebral microvasculature and superficial temporal artery (4.2 +/- 1.2-fold and 2.8 +/- 0.32-fold, respectively) but had no significant effect on EC derived from omental artery (P > .6) or from the superficial temporal artery of obese (body mass index > or = 28 kg/m2) patients (P > .4). The expression of G alpha s was unchanged in all cell types (P > or = .1). Two other circulating peptides, vasoactive intestinal peptide and endothelin-1, failed to alter the expression of either G protein in EC from the cerebral microvasculature, further demonstrating the specificity of the alpha-thrombin effect. However, thrombin receptor activating protein-14 mimicked the alpha-thrombin response and increased G alpha i3 in EC derived from the cerebral microvasculature and superficial temporal artery.

CONCLUSIONS

We conclude that alpha-thrombin increases G alpha i3 expression in some EC through activation of its tethered liganded receptor. Obesity appears to suppress this action of alpha-thrombin.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.

VIP receptor-effector system in rat harderian gland and its coupling to activation of type II thyroxine 5'-deiodinase

Vasoactive intestinal peptide (VIP) receptors were investigated in rat Harderian gland membranes using [125I]VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, temperature, and membrane concentration. At 30 degrees C, the stoichiometric data suggested the presence of two classes of VIP receptors with Kd values of 0.36 +/- 0.06 and 65.37 +/- 8.08 nM and binding capacities of 323 +/- 54 and 39,537 +/- 3100 fmol VIP/mg protein, respectively. The interaction showed a high degree of specificity, as suggested by competitive displacement experiments with several peptides structurally or not structurally related to VIP. The binding of [125I]VIP to membranes was sensitive to guanine nucleotides in a dose-dependent manner. The molecular characterization of VIP receptors was realized by chemical cross-linking; sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the solubilized membrane proteins revealed the presence of two specific [125I]VIP-protein complexes of M(r) 57 and 35 kDa as estimated in denaturing conditions. VIP stimulated adenylate cyclase activity in rat Harderian gland membranes in a dose-dependent manner. Finally, VIP stimulated in vivo the type II thyroxine 5'-deiodinase activity. These results demonstrate the presence of specific and functional VIP receptors in Harderian gland and suggest a role for VIP in the physiology of this gland.

Expression of VIP receptors in mouse peritoneal macrophages: functional and molecular characterization

Receptors for VIP in mouse peritoneal macrophages (MPM) were examined using [125I]labeled VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, pH, temperature and cell concentration. At 15 degrees C, the stoichiometric data suggested the presence of two classes of VIP receptors with Kd values of 1.05 +/- 0.2 and 66.4 +/- 11.0 nM and binding capacities of 19.2 +/- 2.8 and 706.6 +/- 172.0 fmol VIP/10(6) cells. The interaction showed a high degree of specificity, as suggested by competition experiments with various peptides structurally related to VIP as follows: VIP > helodermin > rGRF > PHI >> secretin. Glucagon, pancreastatin, somatostatin, insulin, and octapeptide of cholecystokinin (CCK 26-33) were ineffective at concentrations as high as 1 microM. VIP was a potent and efficient stimulator of cyclic AMP production in MPM. The stimulation was observed at a concentration as low as 0.01 nM VIP. Half-maximal stimulation (ED50) was observed at 1.0 +/- 0.2 nM VIP, and maximal stimulation (three-fold above basal levels) was obtained between 0.1-1 microM. The cyclic AMP system of mouse peritoneal macrophages showed a high specificity for VIP. The order of potency observed in inducing cyclic AMP production was VIP > helodermin > rGRF > PHI >> secretin. Glucagon, insulin, pancreastatin, somatostatin and octapeptide of cholecystokinin did not modify cyclic AMP levels at concentrations as high as 1 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of receptors for VIP in rat peritoneal macrophage membranes

Vasoactive intestinal peptide (VIP) receptors were investigated in rat peritoneal macrophage membranes (RPMM) using [125I]VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, temperature, and membrane concentration. The Scatchard analysis of binding data was consistent with the existence of two classes of VIP binding sites with Kd values of 0.60 +/- 0.08 and 275 +/- 39 nM and binding capacities of 580 +/- 71 and 72,500 +/- 810 fmol VIP/mg protein, respectively. The interaction showed a high degree of specificity, as suggested by competitive displacement experiments with several peptides structurally or not structurally related to VIP. These pharmacological studies showed the following order of potency: VIP (IC50 = 1 nM) > rGRF (IC50 = 13 nM) > PHI (IC50 = 421 nM) >> secretin. Glucagon, somatostatin, insulin octapeptide of cholecystokinin [CCK(26-33)], and pancreastatin were ineffective at concentrations up to 1 microM. Binding of [125I]VIP to membranes is markedly reduced by increasing the ionic strength of incubation medium. Treatment of membranes with dithiothreitol, trypsin, and phospholipases A2 and C resulted in a loss of the ability of these membranes to bind VIP. However, treatment with phospholipase D did not affect binding of VIP by membranes. The molecular characterization of VIP receptors in RPMM was performed after [125I]VIP cross-linking to membranes using the cross-linker dithiobis (succinimidyl propionate). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane proteins revealed specific [125I]VIP-protein complexes of M(r) 55,000 +/- 1700, 35,000 +/- 900, and 22,000 +/- 500.

Characterization of the oligosaccharide moiety of VIP receptor from the human pancreatic cell line BxPC-3

The human pancreatic cell line BxPC-3 displays two classes of binding sites with high and low affinity for VIP. The order of potency of VIP-related peptides in inhibiting either [125I]VIP or [125I]N-AcPACAP27 binding and in stimulating cAMP production was typical of the human VIP receptor. By combining affinity labeling with glycosidase treatments, we have characterized the VIP receptor as a M(r) = 68,200 glycoprotein, consisting of a M(r) = 39,300 polypeptide core with at least three N-linked oligosaccharide chains. In addition, our results revealed the presence of a low amount of sialic acid residues in the carbohydrate moiety of receptor.