title: Heterodimerization of type A and B cholecystokinin receptors enhance signaling and promote cell growth.
abstract: Dimerization of several G protein-coupled receptors has recently been described, but little is known about its clinical and functional relevance. Cholecystokinin (CCK) and gastrin are structurally related gastrointestinal and neuronal peptides whose functions are mediated by two structurally related receptors in this superfamily, the type A and B CCK receptors. We previously demonstrated spontaneous homodimerization of type A CCK receptors and the dissociation of those complexes by agonist occupation (Cheng, Z. J., and Miller, L. J. (2001) J. Biol. Chem. 276, 48040-48047). Here, for the first time, we also demonstrate spontaneous homodimerization of type B CCK receptors, as well as heterodimerization of that receptor with the type A CCK receptor. Unlike type A CCK receptor dimers, the homodimerization of type B CCK receptors was not affected by ligand occupation. However, although heterodimers of type A and B CCK receptors bound natural agonists normally, they exhibited unusual functional and regulatory characteristics. Such complexes demonstrated enhanced agonist-stimulated cellular signaling and delayed agonist-induced receptor internalization. As a likely consequence, agonist-stimulated cell growth was markedly enhanced in cells simultaneously expressing both of these receptors. Our results provide the first evidence that heterodimerization of G protein-coupled receptors can form a more "powerful" signaling unit, which has potential clinical significance in promoting cell growth.
authors.affiliation: Mayo Clinic Scottsdale, Cancer Center and, Department of Molecular Pharmacology and Experimental Therapeutics, Scottsdale, Arizona 85259, USA.
authors.forename: Zhi-Jie
authors.initials: ZJ
authors.lastname: Cheng
authors.forename: Kaleeckal G
authors.initials: KG
authors.lastname: Harikumar
authors.forename: Eileen L
authors.initials: EL
authors.lastname: Holicky
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Miller
mesh_terms: D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D019556:COS Cells; D002455:Cell Division; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008024:Ligands; D018613:Microscopy, Confocal; D011485:Protein Binding; D043886:Receptor, Cholecystokinin A / Q000737:chemistry*; D043887:Receptor, Cholecystokinin B / Q000737:chemistry*; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D018076:DNA, Complementary; D005456:Fluorescent Dyes; D008024:Ligands; D043886:Receptor, Cholecystokinin A; D043887:Receptor, Cholecystokinin B