Abstract 768: Molecular Mechanism Of Inverse Agonism In Mechanical Stress-induced Activation Of Angiotensin II Type 1 Receptor
The angiotensin II (AngII) type 1 (AT1) receptor is a G protein-coupled receptor that plays a crucial role in the development of load-induced cardiac hypertrophy. We previously reported that mechanical stress, the most important stimulus for cardiac hypertrophy, activates the AT1 receptor through an AngII-independent mechanism, and that this activation is inhibited by an inverse agonist candesartan. However, it remains unclear how mechanical stress activates AT1 receptor and how candesartan exerts inverse agonism. By serial studies using substituted cysteine accessibility mapping, we demonstrated that mechanical stress directly activates AT1 receptor by changing the conformation of AT1 receptor. Transmembrane (TM) VII of AT1 receptor showed a counterclockwise rotation and shift into the ligand-binding pocket in response to mechanical stretch, and candesartan suppressed this helical movement induced by stretch. Comparison of the inverse agonist activities of several AT1 receptor blockers (ARBs) identified the carboxyl group at the imidazole ring as a critical chemical pharmacophore that is responsible for potent inverse agonism. In addition, CV-7H, a candesartan’s derivative lacking the carboxyl group, showed no inhibitory effect on stretch-induced conformational change of the AT1 receptor. Furthermore, the binding affinities of candesartan were 10-fold reduced in Q257A and T287A mutants compared with wild-type receptor, and the inverse agonist activity of candesartan was abolished in these mutants. These results suggest that candesartan suppressed a stretch-induced helical movement of TM VII via the bindings of the carboxyl group of candesartan to Gln257 in TM VI and Thr287 in TM VII of AT1 receptor. In conclusion, ARBs with potent inverse agonism prevent the conformational change of AT1 receptor via tight drug-receptor interactions, and thereby, inhibit receptor activation induced by not only AngII but also mechanical stretch.