Comparative rates of desensitization of beta-adrenergic receptors by the beta-adrenergic receptor kinase and the cyclic AMP-dependent protein kinase.
Three separate processes may contribute to rapid beta-adrenergic receptor desensitization: functional uncoupling from the stimulatory guanine nucleotide-binding protein Gs, mediated by phosphorylation of the receptors by two distinct kinases, the specific beta-adrenergic receptor kinase (beta ARK) and the cyclic AMP-dependent protein kinase A (PKA), as well as a spatial uncoupling via sequestration of the receptors away from the cell surface. To evaluate the relative importance and potential role of the various processes in different physiological situations, a kinetic analysis of these three mechanisms was performed in permeabilized A431 epidermoid carcinoma cells. To allow a separate analysis of each mechanism, inhibitors of the various desensitization mechanisms were used: heparin to inhibit beta ARK, the PKA inhibitor peptide PKI to inhibit PKA, and concanavalin A treatment to prevent sequestration. Isoproterenol-induced phosphorylation of beta 2 receptors in these cells by beta ARK occurred with a t1/2 of less than 20 sec, whereas phosphorylation by PKA had a t1/2 of about 2 min. Similarly, beta ARK-mediated desensitization of the receptors proceeded with a t1/2 of less than 15 sec, and PKA-mediated desensitization with a t1/2 of about 3.5 min. Maximal desensitization mediated by the two kinases corresponded to a reduction of the signal-transduction capacity of the receptor/adenylyl cyclase system by about 60% in the case of beta ARK and by about 40% in the case of PKA. Receptor sequestration was much slower (t1/2 of about 10 min) and involved no more than 30% of the cell surface receptors. It is concluded that beta ARK-mediated phosphorylation is the most rapid and quantitatively most important factor contributing to the rapid desensitization. This rapidity of the beta ARK-mediated mechanism makes it particularly well suited to regulate beta-adrenergic receptor function in rapidly changing environments such as the synaptic cleft.
Roth
N S
NS
Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710.
Campbell
P T
PT
Caron
M G
MG
Lefkowitz
R J
RJ
Lohse
M J
MJ
D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D002463:Cell Membrane Permeability; D003208:Concanavalin A / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D011494:Protein Kinases / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D051552:beta-Adrenergic Receptor Kinases
D011943:Receptors, Adrenergic, beta; D003208:Concanavalin A; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins; D007545:Isoproterenol