Abstract

G protein-coupled receptor kinases (GRKs) are thought to be important in mediating the agonist-induced phosphorylation and consequent desensitization of G protein-coupled receptor responses. NG108–15 mouse neuroblastoma X rat glioma cells express a wide range of G protein-coupled receptors and significant levels of GRK2. Therefore, to determine the role of GRK2 in agonist-induced desensitization of various G_s-coupled receptors in NG108–15 cells, we stably transfected cells with a dominant negative mutant GRK2 construct (Lys220Arg). In homogenates prepared from cells overexpressing the dominant negative mutant GRK2, the acute stimulation of adenylyl cyclase by various receptor and nonreceptor agonists was the same as in control cells stably transfected with plasmid only. NG108–15 cells express both A_2a and A_2b adenosine receptors, which mediate activation of adenylyl cyclase, with both of these responses being subject to agonist-induced desensitization with at _1/2 of 15–20 min. In dominant negative mutant GRK2 cells, the rates of desensitization of A_2a and A_2b receptor-stimulated adenylyl cyclase were markedly slower than in plasmid transfected controls, with the latter being similar to wild-type cells. After a 20-min treatment with an adenosine agonist, the desensitization of A_2a and A_2breceptor-stimulated adenylyl cyclase in dominant negative mutant GRK2 cells was less than half that seen in plasmid transfected control cells. On the other hand, the agonist-induced desensitization of secretin and IP-prostanoid receptor-stimulated adenylyl cyclase was the same in dominant negative mutant GRK2 cells as in plasmid transfected control cells. These results indicate that in intact cells, GRK2 may mediate the desensitization of adenosine A₂ receptors. Furthermore, there seems to be selectivity of GRK2 action between G_s-coupled receptors because the agonist-induced desensitization of secretin and IP-prostanoid receptor-stimulated adenylyl cyclase was not affected by dominant negative mutant GRK2 overexpression.