Factors determining the specificity of signal transduction by guanine nucleotide-binding protein-coupled receptors. III. Coupling of alpha 2-adrenergic receptor subtypes in a cell type-specific manner.
A number of diverse signaling pathways can be activated by G-protein coupled receptors. However, the factors involved in selection of a particular transduction pathway by a single receptor are not well understood. We are attempting to address this issue utilizing the alpha 2-adrenergic receptor (alpha 2-AR) subfamily as a representative model system. In this report, we demonstrate that the cellular response mediated by an alpha 2-AR subtype is cell-specific and thus depends on its environment. Receptor coupling to adenylylcyclase was determined following stable expression of the rat alpha 2B- and alpha 2D-AR subtypes in three functionally distinct cell types (NIH-3T3 fibroblasts, DDT1 MF-2 smooth muscle cells, and the pheochromocytoma cell line PC-12). When the receptor subtype gene is expressed in NIH-3T3 and DDT1 MF-2 cells, receptor activation inhibits basal and forskolin-induced increases in cellular cAMP. However, in PC-12 transfectants the same receptor subtype actually increases basal cAMP and augments the effect of forskolin. Potentiation of the forskolin effect in PC-12 cells is insensitive to pertussis toxin but is blocked by loading the cells with BAPTA (bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid) which minimizes changes in Ca2+i by calcium chelation. These data and the functional demonstration of a Ca2+/calmodulin-sensitive adenylylcyclase in PC-12 but not NIH-3T3 and DDT1 MF-2 cells, suggests that the cell-specific effects of epinephrine are due to receptor coupling to both different G-proteins and types of adenylylcyclase.
Department of Pharmacology, Medical University of South Carolina, Charleston 29425.
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D016475:3T3 Cells; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D051379:Mice; D009130:Muscle, Smooth / Q000378:metabolism; D016716:PC12 Cells; D037342:Pertussis Toxin; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008345:Manganese; D000068438:Brimonidine Tartrate; D004533:Egtazic Acid; D004492:Edetic Acid; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D004837:Epinephrine