Solubilization and hydrodynamic properties of active peptide YY receptor from rat jejunal crypts. Characterization as a Mr 44,000 glycoprotein

The peptide YY-preferring receptor mediating inhibition of small intestinal secretion is a peripheral Y(2) receptor: pharmacological evidence and molecular cloning

A peptide YY (PYY)-preferring receptor [PYY > neuropeptide Y (NPY)] was previously characterized in rat small intestinal crypt cells, where it mediates inhibition of fluid secretion. Here, we investigated the possible status of this receptor as a peripheral Y(2) receptor in rats. Typical Y(2) agonists (PYY(3-36), NPY(3-36), NPY(13-36), C2-NPY) and very short PYY analogs (N-alpha-Ac-PYY(22-36) and N-alpha-Ac-PYY(25-36)) acting at the intestinal PYY receptor were tested for their ability to inhibit the binding of (125)I-PYY to membranes of rat intestinal crypt cells and of CHO cells stably transfected with the rat hippocampal Y(2) receptor cDNA. Similar PYY preference was observed and all analogs exhibited comparable high affinity in both binding assays. The same held true for the specific Y(2) antagonist BIIE0246 with a K(i) value of 6.5 and 9.0 nM, respectively. BIIE0246 completely abolished the inhibition of cAMP production by PYY in crypt cells and transfected CHO cells. Moreover, the antagonist 1) considerably reversed the PYY-induced reduction of short-circuit current in rat jejunum mucosa in Ussing chamber and 2) completely abolished the antisecretory action of PYY on vasoactive intestinal peptide (VIP)-induced fluid secretion in rat jejunum in vivo. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that Y(2) receptor transcripts were present in intestinal crypt cells (3 x 10(2) molecules/100 ng RNA(T)) with no expression in villus cells, in complete agreement with the exclusive binding of PYY in crypt cells. Finally, a full-length Y(2) receptor was cloned by RT-PCR from rat intestinal crypt cells and also from human small intestine. We conclude that the so-called PYY-preferring receptor mediating inhibition of intestinal secretion is a peripheral Y(2) receptor.

Pharmacological profile of the rat intestinal crypt peptide YY receptor vs. the recombinant rat Y5 receptor

Peptide YY and neuropeptide Y have potent antisecretory effects in rat small intestine. Scatchard analysis of [125I]peptide YY binding revealed a 10-fold higher concentration of receptors in rat jejunal crypt cells than in villus cells and no detectable receptors in colonic epithelium. Reverse transcription polymerase chain reaction analysis of neuropeptide Y Y5 receptor mRNA indicated that they are mainly expressed in rat jejunal crypts with very few or no expression in villus cells and colon epithelium, respectively. In order to determine whether neuropeptide Y Y5 receptors could represent the intestinal crypt receptor for peptide YY and neuropeptide Y, the ability of peptide YY, neuropeptide Y, pancreatic polypeptide and analogues to inhibit [125I]peptide YY binding to membrane prepared from rat crypt cells and COS-7 cells (African green monkey kidney cells) transfected with the rat neuropeptide Y Y5 receptor cDNA was tested. It appeared that several analogues displayed different inhibition constants (Ki) in the two binding assays, more especially N-alpha-acetyl-peptide YY-(22-36) which was 1200 x more potent in the crypt cell binding assay than in the recombinant neuropeptide Y Y5 receptor binding assay. These data support that the intestinal crypt peptide YY receptor is not a Y5 receptor. reserved.

Several receptors mediate the antisecretory effect of peptide YY, neuropeptide Y, and pancreatic polypeptide on VIP-induced fluid secretion in the rat jejunum in vivo

Several Y receptor subtypes have been cloned and/or pharmacologically characterized that mediate the effects of the regulatory peptides peptide YY (PYY), neuropeptide Y (NPY), and pancreatic polypeptide (PP). These peptides possess antisecretory properties on the intestine. This effect can be blocked in vivo by neural antagonists, suggesting the intervention of neural receptors, although epithelial PYY-preferring receptors have been evidenced on jejunal crypt cells. The purpose of the present experiments was to compare the antisecretory properties in vivo of a series of PYY and NPY derivatives with various affinities for different Y receptor subtypes, in order to determine which subtypes were involved. A model of VIP-stimulated secretion by rat jejunal loops was used. The results were compared with the binding affinities for PYY-preferring receptors determined on rat jejunal crypt cell membranes. Full-length PYY(1-36) was about three times more potent than NPY(1-36), and 10 times more potent than PP in the low dose range. PP, however, had a low efficacy limited to about 50% inhibition of VIP effect. Both Y1 agonists ([Leu31, Pro34]PYY and [Leu31,Pro34]NPY), and Y2 agonists [C-terminal fragments ranging from PYY (3-36) and NPY(3-36) to PYY(22-36) to NPY(22-36)] displayed potent antisecretory properties. PYY derivatives and fragments were always more potent than their respective NPY counterparts. In contrast, Y1 derivatives and PP had very low affinity for the epithelial PYY receptor as measured in vitro by radioreceptor assay. These data suggest that the antisecretory effect of PYY/NPY/PP peptides in vivo involves the effects of several receptors: a Y2-like, PYY-preferring receptor identical to the epithelial receptor, a Y1-like receptor, and a third receptor with high affinity for PP.

Discrimination between neuropeptide Y and peptide YY in the rat tail artery by the neuropeptide Y1-selective antagonist, BIBP 3226

1. The ability of the novel, nonpeptide, neuropeptide Y (NPY) Y1-selective antagonist, BIBP 3226 ¿(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine amide¿, to antagonize the increase in perfusion pressure induced by NPY and peptide Y (PYY) was tested in the perfused rat tail artery, a postjunctional Y1-receptor bioassay, precontracted by 1 microM phenylephrine. 2. NPY and PYY produced a concentration-dependent enhancement of the vasoconstrictor response evoked by 1 microM phenylephrine. Although NPY and PYY are roughly equipotent, the maximal contractile response elicited by PYY was about twice that elicited by NPY. 3. Increasing concentrations of BIBP 3226 caused a parallel and rightward shift in the NPY concentration-response curve without depressing the maximal response. The contractile effect of NPY was potently inhibited in a competitive manner. The pA2 value for BIBP 3226 was 7.01 +/- 0.08, a value equivalent to that observed in the rabbit saphenous vein. Although increasing concentrations of BIBP 3226 shifted the concentration-response curve of PYY to the right without any significant decrease in the maximal vasoconstrictor response, the antagonism appeared non-competitive as the slope of the Schild plot was significantly different from unity (0.58 +/- 0.04). 4. In conclusion, these data confirm that BIBP 3226 is a potent and selective nonpeptide Y1 receptor antagonist. Moreover, they show that complex interactions occur between BIBP 3226 and postjunctional receptors activated by PYY. We postulate that BIBP 3226 might discriminate between the effects of NPY and PYY at the postjunctional level in the rat tail artery. It may be that distinct receptors for NPY and PYY exist; these may or may not allosterically interact with each other. Another working hypothesis would be that there is a single receptor complex with allosterically interacting binding sites for the two peptides.

G alpha i RNA antisense expression demonstrates the exclusive coupling of peptide YY receptors to G(i)2 proteins in renal proximal tubule cells

A clone PKSV-PCT Cl.10 referred to as Cl.10 was selected from the PKSV-PCT renal proximal tubule cell line which expressed peptide YY (PYY) receptors (Voisin, T., Bens, M., Cluzeaud, F., Vandewalle, A., and Laburthe, M. (1993) J. Biol. Chem. 268, 20547-20554). In order to identify G(i) protein(s) coupled to PYY receptors, antisense G alpha i protein RNAs were expressed in Cl.10 cells by transfecting the pcDNA3 vector into which were inserted 39 bases of the 5'-noncoding region of G alpha i2 or G alpha i3 used as specific antisense templates. A Cl.10/alpha i2-clone was selected which displayed a drastic decrease (> 90%) of the expression of G alpha i2 without changes of G alpha i3, G alpha s, and G beta subunits (G alpha i1 is not present in Cl.10 cells) as evidenced by Western blots. When compared to untransfected cells, this clone exhibited: (i) an increase in the dissociation constant of PYY receptors (5.3 versus 0.6 nM) identical to that observed in pertussis toxin-treated untransfected cells; (ii) an absence of inhibition of 125I-PYY binding by guanosine 5'-O-(thiotriphosphate) (GTP gamma S); and (iii) the failure of PYY to inhibit cAMP levels and to stimulate [methyl-3H]thymidine incorporation into DNA. A clone was also selected which exhibited a specific decrease (> 80%) of G alpha i3 as compared to untransfected cells. The sensitivity to GTP gamma S and the dissociation constant of PYY receptors as well as PYY-mediated inhibition of cAMP were identical to those observed in untransfected cells. These findings support an exclusive coupling of PYY receptors to G alpha i2.

Synthesis, receptor binding, and crosslinking of photoactive analogues of neuropeptide Y

Five photoactive analogues of porcine neuropeptide Y (NPY), a 36 amino acid hormone of the pancreatic polypeptide family, have been synthesized by solid phase peptide synthesis method, Fmoc/tBu strategy and carefully characterized. The analogues contain the photoactivatable amino acid 4'-(3-trifluoromethyl)-3H-diazirine-3-yl-phenyl-alanine ((Tmd)Phe) individually at different positions (1, 20, 21, 27 or 36) instead of tyrosine in the wildtype sequence. Affinity to membranes prepared from SMS-KAN cells, which stably express the Y2 receptor has been investigated by measuring the displacement of 125I-Bolton Hunter-NPY. After incubation of the membranes with different concentrations of the crosslinker and subsequent photolysis, the specific binding of 125I-Bolton Hunter-NPY at those membranes was tested in order to quantify the crosslinking efficiency. Whereas [(Tmd)Phe20] NPY, [(Tmd)Phe21] NPY and [(Tmd)Phe27] NPY revealed highest affinity to the Y2 receptor, crosslinking was most efficient when Tyr36 was replaced by (Tmd)Phe. This is in good agreement with the previously suggested C-terminal binding site of neuropeptide Y.

Subtypes of receptors for neuropeptide Y: implications for the targeting of therapeutics

Neuropeptide Y is a 36 amino acid peptide that was originally discovered in extracts of porcine brain. The peptide has a broad distribution in the central or peripheral nervous system. Receptors for this peptide were originally subdivided into postsynaptic Y-1 receptors and presynaptic Y-2 receptors. The Y-1 receptor has recently been cloned and appears to mediate several effects of NPY including vasoconstriction and an anxiolytic effect in animal models of anxiety. The Y-2 receptor inhibits the release of neurotransmitters in the CNS by the inhibition of the mobilization of intracellular calcium. Additional receptors have been proposed including a Y-3 receptor that recognizes NPY but not the related endocrine peptide, PYY. The functional importance of these newer receptors remains to be established. The absence of useful antagonists has made the study of NPY a challenge for investigators in the field. The potential utility of such molecules is discussed.

Receptors for gut regulatory peptides

Receptors for regulatory peptides (hormones or neurotransmitters) play a pivotal role in the ability of cells to taste the rich neuroendocrine environment of the gut. Recognition of low concentration of peptides with a high specificity and translation of the peptide-receptor interaction into a biological response through different signalling pathways (adenylyl cyclase-cAMP or phospholipase C-phosphatidylinositol) are crucial properties of receptors. While many new receptors have been identified and thereafter characterized functionally during the 1980s, molecular biology now emerges as the privileged way for the structural characterization and discovery of receptors. Different strategies of receptor cloning have been developed which may or may not require prior receptor purification. Among cloning strategies that do not require receptor purification, homology screening of cDNA libraries, expression of receptor cDNA or mRNA in Xenopus laevis oocytes or in COS cells, and the polymerase chain reaction method achieved great success, e.g. cloning of receptors for cholecystokinin, gastrin, glucagon-like peptide 1, gastrin-releasing peptide/bombesin, neuromedin K, neuropeptide Y, neurotensin, opioids, secretin, somatostatin, substance K, substance P and vasoactive intestinal peptide. All these receptors belong to the superfamily of G-protein-coupled receptors which consist of a single polypeptide chain (350-450 amino acids) with seven transmembrane segments, an N-terminal extracellular domain and a C-terminal cytoplasmic domain. In this chapter, we have detailed the properties of three receptors which play an important role in digestive tract physiology and illustrate various signal transduction pathways: pancreatic beta-cell galanin receptors which mediate inhibition of insulin release and intestinal epithelial receptors for vasoactive intestinal peptide and peptide YY, which mediate the stimulation and inhibition of water and electrolyte secretion, respectively.

Structure-activity studies of peptide YY(22-36): N-alpha-Ac-[Phe27]PYY(22-36), a potent antisecretory peptide in rat jejunum

Peptide YY (PYY) and its homologous peptide, neuropeptide Y (NPY), are known to exhibit potent antisecretory effects in the intestine. To determine the structural requirements to elicit antisecretory effects, we have synthesized several analogs of the PYY active site, PYY(22-36), and compared their binding affinities and antisecretory potencies in rat jejunum. These investigations revealed that the hydroxyl groups of Ser23 and Thr32, as well as the imidazole group of His26, are important for activity in the intestine. N-alpha-acetylation of PYY(22-36) increased both the binding affinity and antisecretory potency. Structure-activity studies with N-alpha-Ac-PYY(22-36) showed that substitution of His26 with parachlorophenylalanine (pCl-Phe) or Tyr36 with N-Me-Tyr reduced receptor affinity, while replacement of Tyr27 with Phe increased the activity substantially. Furthermore, acylation of the alpha-NH2 group with hydrophobic groups, myristic and naphthaleneacetic acids, substantially reduced the antisecretory potencies but not the binding affinities. Further modification of N-alpha-Ac-[Phe27]PYY(22-36) may lead to the development of more potent agonist compounds, which may provide a framework for the design of a new class of antidiarrheal drugs.