title: Desensitization of alpha 2A-adrenoceptor signalling by modest levels of adrenaline is facilitated by beta 2-adrenoceptor-dependent GRK3 up-regulation.
abstract: (1) Adrenaline (ADR) and noradrenaline (NA) can simultaneously activate inhibitory alpha(2)- and stimulatory beta-adrenoceptors (AR). However, ADR and NA differ significantly in that ADR is a potent beta(2)-AR agonist while NA is not. Only recently has the interaction resulting from the simultaneous activation of alpha(2)- and beta(2)-AR been examined at the cellular level to determine the mechanisms of alpha(2)-AR regulation following concomitant activation of both alpha(2)- and beta(2)-ARs by chronic ADR. (2) This study evaluates beta(2)-AR regulation of alpha(2A)-AR signalling following chronic ADR (300 nM) and NA (1 and 30 micro M) treatments of BE(2)-C human neuroblastoma cells that natively express both beta(2)- and alpha(2A)-ARs. (3) Chronic (24 h) treatment with ADR (300 nM) desensitized the response to the alpha(2A)-AR agonist, brimonidine, in BE(2)-C cells. Addition of the beta-AR antagonist, propranolol, blocked the ADR-induced alpha(2A)-AR desensitization. Unlike ADR, chronic NA (1 micro M) treatment had no effect on the alpha(2A)-AR response. However if NA was increased to 30 micro M for 24 h, alpha(2A)-AR desensitization was observed; this desensitization was partially reversed by propranolol. (4) Chronic ADR (300 nM) treatment reduced alpha(2A)-AR binding levels, contributing to the alpha(2A)-AR desensitization. This decrease was prevented by addition of propranolol during ADR treatment. Chronic NA (30 micro M), like ADR, treatment lowered specific binding, whereas 1 micro M NA treatment was without effect. (5) Chronic ADR treatment produced a significant increase in GRK3 levels and this was blocked by propranolol or GRK2/3 antisense DNA treatment. This antisense DNA, common to both GRK2 and GRK3, also blocked chronic ADR-induced alpha(2A)-AR desensitization and down-regulation. (6) Acute (1 h) ADR (300 nM) or NA treatment (1 micro M) produced alpha(2A)-AR desensitization. The desensitization produced by acute treatment was beta-AR independent, as it was not blocked by propranolol. (7) We conclude that chronic treatment with modest levels of ADR produces alpha(2A)-AR desensitization by mechanisms that involve up-regulation of GRK3 and down-regulation of alpha(2A)-AR levels through interactions with the beta(2)-AR.
authors.affiliation: Department of Pharmacological and Pharmaceutical Sciences, Room 521, Science and Research Building 2, University of Houston, Houston, TX 77204-5037, USA.
authors.forename: Tasneem
authors.initials: T
authors.lastname: Bawa
authors.forename: Ghazi F
authors.initials: GF
authors.lastname: Altememi
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eikenburg
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Standifer
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D058666:Adrenergic beta-2 Receptor Agonists; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000008:administration & dosage*; D054770:G-Protein-Coupled Receptor Kinase 3; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis*; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D058666:Adrenergic beta-2 Receptor Agonists; D018341:Receptors, Adrenergic, alpha-2; D018343:Receptors, Adrenergic, beta-2; D017346:Protein Serine-Threonine Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517848:GRK3 protein, human; D004837:Epinephrine