title: Mouse beta 3a- and beta 3b-adrenoceptors expressed in Chinese hamster ovary cells display identical pharmacology but utilize distinct signalling pathways.
abstract: 1. This study characterizes the mouse beta(3a)-adrenoceptor (AR) and the splice variant of the beta(3)-AR (beta(3b)-AR) expressed in Chinese hamster ovary cells (CHO-K1). 2. Stable clones with high (approximately 1200), medium (approximately 500) or low receptor expression (approximately 100 fmol mg protein(-1)) were determined by saturation binding with [(125)I]-(-)-cyanopindolol. Competition binding studies showed no significant differences in affinity of beta-AR ligands for either receptor. 3. Several functional responses of each receptor were measured, namely extracellular acidification rate (EAR; cytosensor microphysiometer), cyclic AMP accumulation, and Erk1/2 phosphorylation. The beta(3)-AR agonists BRL37344, CL316243, GR265162X, L755507, SB251023, the non-conventional partial beta-AR agonist CGP12177 and the beta-AR agonist (-)-isoprenaline caused concentration-dependent increases in EAR in cells expressing either splice variant. CL316243 caused concentration-dependent increases in cyclic AMP accumulation and Erk1/2 phosphorylation in cells expressing either receptor. 4. PTX treatment increased maximum EAR and cyclic AMP responses to CL316243 in cells expressing the beta(3b)-AR but not in cells expressing the beta(3a)-AR at all levels of receptor expression. 5. CL316243 increased Erk1/2 phosphorylation with pEC(50) values and maximum responses that were not significantly different in cells expressing either splice variant. Erk1/2 phosphorylation was insensitive to PTX or H89 (PKA inhibitor) but was inhibited by LY294002 (PI3K gamma inhibitor), PP2 (c-Src inhibitor), genistein (tyrosine kinase inhibitor) and PD98059 (MEK inhibitor). 6. The adenylate cyclase activators forskolin or cholera toxin failed to increase Erk1/2 levels although both treatments markedly increased cyclic AMP accumulation in both beta(3a)- or beta(3b)-AR transfected cells. 7. These results suggest that in CHO-K1 cells, the beta(3b)-AR, can couple to both G(s) and G(i) to stimulate and inhibit cyclic AMP production respectively, while the beta(3a)-AR, couples solely to G(s) to increase cyclic AMP levels. However, the increase in Erk1/2 phosphorylation following receptor activation is not dependent upon coupling of the receptors to G(i) or the generation of cyclic AMP.
authors.affiliation: Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia.
authors.forename: Dana S
authors.initials: DS
authors.lastname: Hutchinson
authors.forename: Tore
authors.initials: T
authors.lastname: Bengtsson
authors.forename: Bronwyn A
authors.initials: BA
authors.lastname: Evans
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Summers
mesh_terms: D058667:Adrenergic beta-3 Receptor Agonists; D058673:Adrenergic beta-3 Receptor Antagonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D004149:Dioxoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D022702:Receptors, Adrenergic, beta-3 / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
chemical_list: D058667:Adrenergic beta-3 Receptor Agonists; D058673:Adrenergic beta-3 Receptor Antagonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004149:Dioxoles; D020033:Protein Isoforms; D022702:Receptors, Adrenergic, beta-3; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases