Constitutively Active Mutant N111G of Angiotensin II Type 1 (AT1) Receptor Induces Homologous Internalization Through Mediation of AT1-Receptor Antagonist

Abstract

The present study investigated the internalization behavior of the constitutively active mutant (CAM) N111G of angiotensin II type 1 (AT1) receptor and correlated the result with the mechanism of the constitutive activity of the mutant. The inverse agonist activity of valsartan, losartan, candesartan, and telmisartan was also examined by inositol phosphate (IP) accumulation study as well as receptor-internalization assay. Both wild-type (WT) and N111G mutant receptors were transiently expressed in COS-7 cells and the binding affinities towards the agonist and these four AT1 antagonists were determined. Production of total IP was measured in the presence and absence of the compounds. The agonist-induced receptor internalization of both WT and N111G mutant receptors was also investigated. Although the mutant showed similar binding characteristics with agonist and the antagonists used as WT, the internalization of the mutant was much lower (19.56 ± 2.87%) than that of the WT receptor (74.63 ± 1.00%). Internalization of the mutant significantly increased (63.22 ± 0.03%) in the presence of valsartan, which also showed significant inverse agonist activity in the N111G mutant. The results indicate that internalization of CAM N111G of the AT1 receptor is induced by the use of valsartan, which may be an important characteristic of inverse agonist activities of AT1 antagonists in N111G. Keywords:: angiotensin II type 1 (AT1) receptor, internalization, constitutive activity, inverse agonist activity, binding affinity