title: Two distinct pathways for cAMP-mediated down-regulation of the beta 2-adrenergic receptor. Phosphorylation of the receptor and regulation of its mRNA level.
abstract: We have studied cyclic AMP-mediated regulation of the beta 2-adrenergic receptor (beta 2AR). The effects of cAMP were assessed in Chinese hamster fibroblast (CHW) cells expressing either the wild type human beta 2AR receptor (CH-beta 2) or mutated forms of the receptor lacking the consensus sequences for phosphorylation by the cAMP-dependent protein kinase. Treatment of the CH-beta 2 cells with the cAMP analogue dibutyryl cAMP (Bt2cAMP) induces a time-dependent "down-regulation" of the number of beta 2AR. This down-regulation of the receptors is accompanied by a decline in the steady state level of beta 2AR mRNA. Moreover, the treatment with Bt2cAMP induces an increase in the phosphorylation level of the membrane-associated beta 2AR. Both the reduction in beta 2AR mRNA and the enhanced phosphorylation of the receptor are rapid and precede the loss of receptor. The down-regulation of beta 2AR induced by Bt2cAMP is concentration-dependent and mimicked by the other biologically active cyclic nucleotide analogue, 8-Br-cAMP, by forskolin, and by the phosphodiesterase inhibitor, isobutylmethylxanthine. In the CHW cell lines expressing receptors lacking the putative protein kinase A phosphorylation sites, the Bt2cAMP-induced phosphorylation of beta 2AR is completely abolished. In these cells the down-regulation of beta 2AR receptor number produced by cAMP is significantly slowed, whereas the reduction in beta 2AR mRNA level is equivalent to that observed in CH-beta 2 cells. These data indicate that there are at least two pathways by which cAMP may decrease the number of beta 2ARs in cells: one involves phosphorylation of the receptor by the cAMP-dependent protein kinase and the other leads to a reduction in steady state beta 2AR mRNA levels.
authors: Department of Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710.
authors: M
authors: M
authors: Bouvier
authors: S
authors: S
authors: Collins
authors: B F
authors: BF
authors: O'Dowd
authors: P T
authors: PT
authors: Campbell
authors: A
authors: A
authors: de Blasi
authors: B K
authors: BK
authors: Kobilka
authors: C
authors: C
authors: MacGregor
authors: G P
authors: GP
authors: Irons
authors: M G
authors: MG
authors: Caron
authors: R J
authors: RJ
authors: Lefkowitz
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000502:physiology*; D004247:DNA / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005796:Genes; D005822:Genetic Vectors; D006706:Homeostasis; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009154:Mutation; D010766:Phosphorylation; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013806:Theophylline / Q000031:analogs & derivatives*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D003994:Bucladesine; D004247:DNA; D013806:Theophylline; D000242:Cyclic AMP; D007545:Isoproterenol; D015056:1-Methyl-3-isobutylxanthine