RT Journal Article
SR Electronic
T1 Guanine Nucleotide Exchange-Independent Activation of G<sub>s</sub> Protein by β<sub>2</sub>-Adrenoceptor
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 720
OP 728
DO 10.1124/mol.104.010306
VO 68
IS 3
A1 Özlem Uğur
A1 Şükrü Sadik Öner
A1 Paola Molinari
A1 Caterina Ambrosio
A1 Kemal Sayar
A1 H. Ongun Onaran
YR 2005
UL http://molpharm.aspetjournals.org/content/68/3/720.abstract
AB β2-Adrenoceptor-mediated activation of Gs and adenylyl cyclase or other receptor-mediated G protein activations is believed to occur by receptor-catalyzed replacement of GDP with GTP on the α-subunit of the G protein. Here we showed that a β2-adrenoceptor-Gs system, heterologously expressed in cyc- or human embryonic kidney (HEK)-293 cells, can be activated in the presence of GDP or its phosphorylation-resistant analog, guanosine 5′-O-(2-thiodiphosphate) (GDPβS). The potency and maximal ability of GDP to activate Gs and adenylyl cyclase were identical to those of GTP. GDP-mediated activation of adenylyl cyclase, similar to that mediated by GTP, was concentration-dependent, required high magnesium concentrations, was inhibited by inverse agonists, and was correlated with the efficacy of receptor ligands used to stimulate the receptor. UDP did not block the GDP-mediated activation, although it completely blocked the formation of a small amount of GTP (∼5% GDP) from GDP. Moreover, the activation of Gs in the presence of GDP was insensitive to cholera toxin treatment of the cells, whereas that observed in the presence of GTP was amplified by the treatment, which showed that the activation observed in the presence of GDP was not mediated by GTP. Therefore, we concluded that GDP itself could mediate β-adrenoceptor-induced activation of Gs-adenylyl cyclase system as much as GTP. We discuss the results in the context of the current paradigm of receptor-mediated G protein activation and propose an additional mode of activation for β2-adrenoceptor-Gs adenylyl cyclase system where nucleotide exchange is not necessary and GDP and GTP play identical roles in receptor-induced Gs protein activation.