Analysis of domain responsible for desensitization of beta(1)-adrenergic receptor

When the wild type beta(1)-adrenergic receptor (WT-beta(1)AR) was expressed in Sf9 cells, the beta(1)AR-stimulated adenylyl cyclase activities were de sensitized by prior treatment with isoproterenol. The extent of beta(1)AR d esensitization was not modified, and the onset was not promoted by the over expression of G protein-coupled receptor kinase 2 (GRK2), GRK5 or GRK6. How ever, overexpression of the dominant negative mutant of GRK2. appeared to i nhibit desensitization of the beta(1)AR. The change of the potential protei n kinase A phosphorylation site located at the intracellular third loop did not affect beta(1)AR desensitization, Desensitization of the truncated mut ant, in which nearly all of the serine and threonine residues from the carb oxyl terminus were eliminated, was the same as that of the WT-beta(1)AR. A deletion mutant that lacked serine and threonine residues of the intracellu lar third loop was also desensitized by isoproterenol stimulation. Furtherm ore, the deletion of serine and threonine residues from both the intracellu lar third loop and carboxyl terminus did not affect desensitization of the beta(1)AR. These results suggested that phosphorylation by endogenous GRKs in Sf9 cells contributed to desensitization of the beta(1)AR and that the r egions other than third intracellular loop and carboxyl terminus may be res ponsible for beta(1)AR desensitization.