Switching of the coupling of the β2-adrenergic receptor to different G proteins by protein kinase A

Abstract

Many of the G-protein-coupled receptors for hormones that bind to the cell surface can signal to the interior of the cell through several different classes of G protein. For example, although most of the actions of the prototype beta2-adrenergic receptor are mediated through Gs proteins and the cyclic-AMP-dependent protein kinase (PKA) system, beta-adrenergic receptors can also couple to Gi proteins. Here we investigate the mechanism that controls the specificity of this coupling. We show that in HEK293 cells, stimulation of mitogen-activated protein (MAP) kinase by the beta2-adrenergic receptor is mediated by the betagamma subunits of pertussis-toxin-sensitive G proteins through a pathway involving the non-receptor tyrosine kinase c-Src and the G protein Ras. Activation of this pathway by the beta2-adrenergic receptor requires that the receptor be phosphorylated by PKA because it is blocked by H-89, an inhibitor of PKA. Additionally, a mutant of the receptor, which lacks the sites normally phosphorylated by PKA, can activate adenylyl cyclase, the enzyme that generates cAMP, but not MAP kinase. Our results demonstrate that a mechanism previously shown to mediate uncoupling of the beta2-adrenergic receptor from Gs and thus heterologous desensitization (PKA-mediated receptor phosphorylation), also serves to 'switch' coupling of this receptor from Gs to Gi and initiate a new set of signalling events.

Cyclic AMP activates Ras

“…Similarly, in HEK293 cells, stimulation of b-adrenergic receptors resulted in Gbg-, Src-and Rasdependent activation of MAPK. In this case, PKAmediated phosphorylation altered receptor coupling from Gas to Gai (Daaka et al, 1997). Activation of the Gs-coupled A 2A -adenosine receptor activated Ras and MAPK, however these e ects were shown to be independent of Gas and cAMP (Seidel et al, 1999).…”

Orally applied doxazosin disturbed testosterone homeostasis and changed the transcriptional profile of steroidogenic machinery, cAMP/cGMP signalling and adrenergic receptors in Leydig cells of adult rats

“…In the same cells, increased transcription for the cAMP 'remover' in Leydig cell (Pde4d) was registered. By this transcriptional signalling scenario, it is possible that the Leydig cell is trying to 'accelerate' cAMP-signalling and to switch off the adrenalin-occupied receptors from Gs to Gi (Daaka et al, 1997) to control both the intracellular bursts of cAMP (through the adrenalin-b2ADR activation of Gs and increased Adcy) and the basal cAMP (through the adrenalin-b2ADR/PDE4d Gi-mediated braking effect). Thus, results present in this article provide new molecular/transcriptional base for the Leydig cells response to the systemic blockade of a1-ADRs and could be of possible interest to further investigation in light of post-traumatic stress disorders, hypertension, obesity, metabolic syndrome, LUTS/BHP, ED and disrupted sexual health.…”

“…In addition, increased catalytic subunit (Prkac1) and decreased regulatory subunit (Prkar2b) of PRKA (cAMP effector) were registered. By this transcriptional signalling scenario, it is possible that the Leydig cell is trying to 'accelerate' cAMP-signalling and to switch off the adrenalin-occupied receptors from Gs to Gi (Daaka et al, 1997) to control both the intracellular bursts of cAMP (through the adrenalin-b2ADRs activation of Gs and increased Adcy) and the basal cAMP (through the adrenalin-b2ADR/PDE4d Gi-mediated braking effect). In the same cells, cGMP signalling up-regulation was registered with the increase of transcripts for Nos1/Nos3 (constitutive NO 'providers'), Gucy1 (soluble cGMP 'provider'), Pde6a (cGMP 'remover') and PRKG1 (cGMP effector) transcript/protein.…”

Catechol- O -methyltransferase inhibition increases pain sensitivity through activation of both β2- and β3-adrenergic receptors

“…Both β 2 -and β 3 ARs belong to the superfamily of G protein-coupled receptors and couple to G s to stimulate adenylyl cyclase (Dixon et al 1986;Strosberg 1997) or to G i/s to stimulate the mitogen-activated protein kinase (MAPK) cascade (Daaka et al 1997;Schmitt and Stork 2000;Soeder et al 1999). Recent studies have also identified a novel G i/s -independent mechanism whereby β 2 -and β 3 ARs activation can stimulate extracellular signal-regulated kinase (ERK; a type of MAPK) through a novel G i/s -independent mechanism (Azzi et al 2003;Cao et al 2000).…”