The functional investigation of a human adenocarcinoma cell line, stably transfected with the neuropeptide Y Y1 receptor

Y(4) receptors mediate the inhibitory responses of pancreatic polypeptide in human and mouse colon mucosa

The antisecretory effects of several Y agonists, including pancreatic polypeptide (PP), indicate the presence of Y(1), Y(2), and Y(4) receptors in mouse and human (h) colon mucosae. Here, we used preparations from human and from wild-type (WT), Y(4), and Y(1) receptor knockout ((-/-)) mice, alongside Y(4) receptor-transfected cells to define the relative functional contribution of the Y(4) receptor. First, rat (r) PP antisecretory responses were lost in murine Y(4)(-/-) preparations, but hPP and Pro(34) peptide YY (PYY) costimulated Y(4) and Y(1) receptors in WT mucosa. The Y(1) antagonist/Y(4) agonist GR231118 [(Ile,Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Try-NH(2))-2-cyclic(2,4'),(2',4)-diamide] elicited small Y(4)-mediated antisecretory responses in human tissues pretreated with the Y(1) antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphenylacetyl)-argininamide trifluoroacetate)], and attenuated Y(4)-mediated hPP responses in mouse and human mucosa. GR231118 and rPP were also antisecretory in hY(4)-transfected epithelial monolayers but were partial agonists compared with hPP at this receptor. In Y(4)-transfected human embryonic kidney (HEK) 293 cells, Y(4) ligands displaced [(125)I]hPP binding with orders of affinity (pK(i)) at human (hPP = rPP > GR231118 > Pro(34)PYY = PYY) and mouse (rPP = hPP > GR231118 > Pro(34)PYY > PYY) Y(4) receptors. GR231118- and rPP-stimulated guanosine 5'-3-O-(thio)triphosphate binding through hY(4) receptors with significantly lower efficacy than hPP. GR231118 marginally increased basal but abolished further PP-induced hY(4) internalization to recycling (transferrin-labeled) pathways in HEK293 cells. Taken together, these findings show that Y(4) receptors play a definitive role in attenuating colonic anion transport and may be useful targets for novel antidiarrheal agents due to their limited peripheral expression.

Control of signalling efficacy by palmitoylation of the rat Y1 receptor

(1) We have investigated the properties of native and haemagglutinin (HA)-tagged neuropeptide Y (NPY) Y(1) receptors after mutation of the palmitoylation site Cys(337) to Ser or Ala. (2) In Chinese hamster ovary cells expressing similar receptor levels, the C337A mutation abolished incorporation of [(3)H]palmitic acid into the HA-Y(1) receptor. (3) Cys(337) substitution did not alter the affinities of Y(1) receptor agonists or antagonists, but it eliminated the ability of guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) to displace [(125)I]PYY-specific binding (compared to approximately 50% inhibition in Y(1) or HA-Y(1) clones). (4) Stimulation of GTPgamma[(35)S] binding by native and HA-Y(1) receptors in standard incubation buffer (100 mM NaCl, 10 micro M GDP) was prevented by Cys(337) mutation. In this assay, the function of Y(1)(C337S) receptors could be partially rescued by reducing the Na(+) concentration, and when overexpressed (B(max): approximately 10 pmol mg(-1)), both HA-Y(1) and HA-Y(1)(C337A) receptors displayed similar responses to NPY and peptide YY (PYY). (5) In stably transfected adenocarcinoma cells expressing Y(1) or Y(1)(C337S) receptors, PYY inhibited anion secretion stimulated by vasoactive intestinal peptide (VIP; measured as short-circuit current, I(SC)) with similar potency (EC(50): 26-53 nM). In contrast to the transient Y(1) receptor-mediated responses observed at maximal PYY concentrations, I(SC) reductions in both Y(1)(C337S) clones were sustained. (6) We conclude that nonpalmitoylation of the Y(1) receptor reduces its coupling efficiency to G proteins, and may also indirectly influence desensitisation processes that depend on the formation of an active agonist-receptor conformation.

Neuropeptides in drug research

Neuropeptides have been a subject of considerable interest in the pharmaceutical industry over the last 20 years or more. Many drug discovery teams have contributed to our understanding of neuropeptide biology but no significant drugs that act selectively upon neuropeptide receptors have yet emerged from the clinic. There are, however, a plethora of clinically useful drugs that act at other classes of neurotransmitter and neuromodulator receptors, many of them discovered over the last 20 years. Nevertheless, we think that the future for the discovery of novel drugs acting at neuropeptide receptors looks bright for two reasons: (1) there has been a substantial increase in our understanding of the function of neuropeptides; and (2) high-throughput screening (HTS) against neuropeptide receptors has now begun to yield many interesting drug-like molecules, rather than peptides, that have the potential to become clinically useful drugs. The objective of this review is to summarise our current understanding of specific areas of neuropeptide biology and pharmacology in the CNS as well as the PNS. We will also speculate on where we think the new generation of neuropeptide agonists and antagonists could emerge from the clinic.

PYY preference is a common characteristic of neuropeptide Y receptors expressed in human, rat, and mouse gastrointestinal epithelia

This investigation describes the relative potencies of four peptide agonists, namely, peptide YY (PYY), [Leu31,Pro34]PYY (Pro34PYY), neuropeptide Y (NPY), and [Leu31,Pro34]NPY (Pro34NPY), as antisecretory agents in human, rat, and mouse gastrointestinal preparations. The inhibition of agonist responses by the Y1-receptor antagonist BIBP 3226 was also tested in each preparation. An unexpectedly pronounced preference for PYY and Pro34PYY was observed in functional studies of two human epithelial lines stably transfected with the rat Y1 receptor (Y1-7 and C1Y1-6). NPY and Pro34NPY were at least an order of magnitude less effective than PYY in these functional studies but were only marginally less potent in displacement binding studies using membrane preparations of the same clonal lines. The orders of agonist potency obtained in Y1-7 and C1Y1-6 epithelia were compared with those obtained from a single human colonic adenocarcinoma cell line (Colony-6, which constitutively expresses Y1 receptors) and also from mucosal preparations of rat and mouse descending colon. Similar peptide orders of potency were obtained in rat and mouse colonic mucosae and Colony-6 epithelia, all of which exhibited PYY preference (although less pronounced than with Y1-7 and C1Y1-6 epithelia) and significant sensitivity to the Y1 receptor antagonist, BIBP 3226. We have compared the pharmacology of these five mammalian epithelial preparations and provide cautionary evidence against the reliance upon agonist concentration-response relationships alone, in the characterization of NPY receptor types.Key words: Y receptors, neuropeptide Y, gastrointestinal epithelia, ion transport.