Differential coupling of beta(3A)- and beta(3B)-adrenergic receptors to endogenous and chimeric G(alpha)s and G(alpha)i

作者：Lenard Natalie R; Prpic Veronica; Adamson Aaron W; Rogers Richard C; Gettys Thomas W^*

来源：American Journal of Physiology - Endocrinology And Metabolism, 2006, 291(4): E704-E715.

DOI：10.1152/ajpendo.00048.2006

• beta-adrenergic receptor
• G proteins
• cyclic adenosine monophosphate
• signaling plasticity

Chimeric G proteins made by replacing the COOH-terminal heptapeptide of G(alpha)q with the COOH-terminal heptapeptide of G(alpha)s or G(alpha)i were used to assess the relative coupling of beta(3)-adrenergic receptor (beta(3)-AR) splice variants (beta(3A) and beta(3B)) to G(alpha)s and G(alpha)i. The G(alpha)q/s and G(alpha)q/i chimeras transformed the response to receptor activation from regulation of adenylyl cyclase to mobilization of intracellular calcium (Ca-i(2+)). Complementary high-throughput and single-cell approaches were used to evaluate agonist-induced coupling of the receptor to the G protein chimeras. In cells stably transformed with rat beta(3)-AR, transfected with the G protein chimeras, and evaluated using a scanning fluorometer, beta(3)-AR-induced coupling to G(alpha)q/s produced a rapid eightfold increase in Ca-i(2+) followed by a slow decay to levels 25% above baseline. G(alpha)q/i also linked rat beta(3)-AR to mobilization of Ca-i(2+) in a similar time- and agonist-dependent manner, but the net 2.5-fold increase in Ca-i(2+) was only 30% of the response obtained with G(alpha)q/s. Activation of the rat beta(3)-AR also increased GTP binding to endogenous G(alpha)i threefold in membranes from CHO cells stably transformed with the receptor. A complementary single-cell imaging approach was used to assess the relative coupling of mouse beta(3A)- and beta(3B)-AR to G(alpha)i under conditions established to produce equivalent agonist-dependent coupling of the receptor splice variants to G(alpha)q/s and to increases in intracellular cAMP through endogenous G(alpha)s. The beta(3A)- and beta(3B)-AR coupled equivalently to G(alpha)q/i, but the temporal patterns of Ca-i(2+) mobilization indicated that coupling was significantly less efficient than coupling to G(alpha)q/s. Collectively, these findings indicate less efficient but equivalent coupling of beta(3A)- and beta(3B)-AR to G(alpha)i vs. G(alpha)s and suggest that differential expression of the splice variants would not produce local differences in signaling networks linked to beta(3)-AR activation.

• 出版日期2006-10