Regulation of cardiovascular signaling by kinins and products of similar converting enzyme systems -: Downregulation of bradykinin B2 receptor in human fibroblasts during prolonged agonist exposure

Sustained activation of G protein-coupled receptors results in an attenuation of cellular responses, a phenomenon termed desensitization. Whereas mechanisms for rapid desensitization of ligand-receptor-G protein-effector systems are relatively well characterized, much less is known about long-term adaptation processes that occur in the continuous presence of an agonist. Here we have studied the fate of endogenously expressed bradykinin B-2 receptors on human fibroblasts during prolonged agonist treatment. Stimulation with bradykinin for up to 24 h resulted in a 50% reduction of surface binding sites that was paralleled by a similar decrease of total B-2 receptor protein followed by Western blotting using monoclonal antibodies to the B-2 receptor. Whereas B-2 receptor mRNA levels did not change during 24 h of agonist treatment, B-2 receptor de novo synthesis was attenuated by 35-50%, indicating translational control of B-2 receptor levels. Furthermore, the half-life of B-2 receptor protein was shortened by 20-40% as shown by S-35-labeled pulse-chase and immunoprecipitation experiments. This study demonstrates that bradykinin B-2 receptor expression during long-term agonist treatment is primarily regulated on the (post) translational level, i.e., by attenuation of de novo synthesis and by reduction of receptor stability.