Downregulation of bradykinin B2 receptor in human fibroblasts during prolonged agonist exposure

Abstract

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 B2 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 B2 receptor protein followed by Western blotting using monoclonal antibodies to the B2 receptor. Whereas B2 receptor mRNA levels did not change during 24 h of agonist treatment, B2receptor de novo synthesis was attenuated by 35–50%, indicating translational control of B2 receptor levels. Furthermore, the half-life of B2 receptor protein was shortened by 20–40% as shown by 35S-labeled pulse-chase and immunoprecipitation experiments. This study demonstrates that bradykinin B2 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.