title: Bombesin receptor in membranes from Swiss 3T3 cells. Binding characteristics, affinity labelling and modulation by guanine nucleotides.
abstract: Bombesin-like neuropeptides, including mammalian gastrin-releasing peptide (GRP), are potent mitogens for Swiss 3T3 cells. In this study, we have characterized the bombesin receptor in membrane preparations from these cells. Addition of Mg2+ during cell homogenization was essential to preserve 125I-GRP binding activity in the resulting membrane preparation. The effect of Mg2+ was concentration dependent, with a maximum at 5 mM. Specific binding of 125I-GRP was saturable; Scatchard analysis indicated a single class of high-affinity sites of Kd = (2.1 +/- 0.3) x 10(-10) M at 15 degrees C and Kd = (1.9 +/- 0.4) x 10(-10) M at 37 degrees C, and a maximum binding capacity of 580 +/- 50 fmol/mg of protein (15 degrees C) or 604 +/- 40 fmol/mg of protein (37 degrees C). The kinetically derived dissociation constant was 1.5 x 10(-10) M. 125I-GRP binding was inhibited in a concentration-dependent manner by various peptides containing the highly conserved C-terminal heptapeptide of the bombesin family, including bombesin, GRP, neuromedin B and the 8-14 fragment of bombesin. In contrast, a variety of structurally unrelated mitogens and neuropeptides had no effect. The cross-linking agent ethyleneglycolbis(succinimidylsuccinate) covalently linked 125I-GRP to a single Mr 75 000-85 000 protein in membrane preparations of 3T3 cells. Affinity labelling of this molecule was specific and dependent on the presence of Mg2+ during membrane preparation. Finally, the non-hydrolysable GTP analogue guanosine-5'-[gamma-thio]triphosphate (GTP[S]) caused a concentration-dependent inhibition of 125I-GRP binding and cross-linking to 3T3 cell membranes [concentration giving half-maximal inhibition (IC50) approximately 0.2 microM]. The inhibitory effect was specific (GMP, ATP or ATP[S] had no effect at 10 microM) and was due to an increase in Kd from (1.7 +/- 0.2) x 10(-10) M to (4.3 +/- 0.6) x 10(-10) M in the presence of 10 microM-GTP[S]. This modulation of ligand affinity and cross-linking implies that the bombesin receptors that mediate mitogenesis in Swiss 3T3 cells are coupled to a guanine-nucleotide-binding-protein signal-transduction pathway.
authors.affiliation: Imperial Cancer Research Fund, Lincoln's Inn Fields, London, U.K.
authors.forename: J
authors.initials: J
authors.lastname: Sinnett-Smith
authors.forename: W
authors.initials: W
authors.lastname: Lehmann
authors.forename: E
authors.initials: E
authors.lastname: Rozengurt
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001839:Bombesin / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D051379:Mice; D008970:Molecular Weight; D018004:Receptors, Bombesin; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D006728:Hormones; D018004:Receptors, Bombesin; D017981:Receptors, Neurotransmitter; D013873:Thionucleotides; D015636:Magnesium Chloride; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D001839:Bombesin