title: Modulation of agonist binding to human dopamine receptor subtypes by L-prolyl-L-leucyl-glycinamide and a peptidomimetic analog.
abstract: The present study was undertaken to investigate the role of the hypothalamic tripeptide L-prolyl-L-leucyl-glycinamide (PLG) and its conformationally constrained analog 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) in modulating agonist binding to human dopamine (DA) receptor subtypes using human neuroblastoma SH-SY5Y cells stably transfected with respective cDNAs. Both PLG and PAOPA enhanced agonist [3H]N-propylnorapomorphine (NPA) and [3H]quinpirole binding in a dose-dependent manner to the DA D2L,D2S, and D4 receptors. However, agonist binding to the D1 and D3 receptors and antagonist binding to the D2L receptors by PLG were not significantly affected. Scatchard analysis of [3H]NPA binding to membranes in the presence of PLG revealed a significant increase in affinity of the agonist binding sites for the D2L, D2S, and D4 receptors. Analysis of agonist/antagonist competition curves revealed that PLG and PAOPA increased the population and affinity of the high-affinity form of the D2L receptor and attenuated guanosine 5'-(beta,gamma-imido)-triphosphate-induced inhibition of high-affinity agonist binding sites for the DA D2L receptor. Furthermore, direct NPA binding with D2L cell membranes pretreated with suramin, a compound that can uncouple receptor/G protein complexes, and incubated with and without DA showed that both PLG and PAOPA had only increased agonist binding in membranes pretreated with both suramin and DA, suggesting that PLG requires the D2L receptor/G protein complex to increase agonist binding. These results suggest that PLG possibly modulates DA D2S, D2L, and D4 receptors in an allosteric manner and that the coupling of D2 receptors to the G protein is essential for this modulation to occur.
authors.affiliation: Department of Psychiatry and Behavioural Neuroscience, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Vaneeta
authors.initials: V
authors.lastname: Verma
authors.forename: Amandeep
authors.initials: A
authors.lastname: Mann
authors.forename: Willard
authors.initials: W
authors.lastname: Costain
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pontoriero
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Castellano
authors.forename: Kevin
authors.initials: K
authors.lastname: Skoblenick
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Gupta
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Pristupa
authors.forename: Hyman B
authors.initials: HB
authors.lastname: Niznik
authors.forename: Rodney L
authors.initials: RL
authors.lastname: Johnson
authors.forename: Venugopalan D
authors.initials: VD
authors.lastname: Nair
authors.forename: Ram K
authors.initials: RK
authors.lastname: Mishra
mesh_terms: D001667:Binding, Competitive / Q000187:drug effects; D045744:Cell Line, Tumor; D018491:Dopamine Agonists / Q000378:metabolism / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D009075:MSH Release-Inhibiting Hormone / Q000494:pharmacology*; D008956:Models, Chemical; D015394:Molecular Structure; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology*; D011954:Receptors, Dopamine / Q000145:classification* / Q000187:drug effects*; D013498:Suramin / Q000494:pharmacology
chemical_list: D018491:Dopamine Agonists; D010455:Peptides; D011954:Receptors, Dopamine; D013498:Suramin; D009075:MSH Release-Inhibiting Hormone; D019204:GTP-Binding Proteins