Angiotensin (1-7) Induces Mas Receptor Internalization

Abstract

Angiotensin (Ang) (1-7) is the endogenous ligand for the G protein–coupled receptor Mas, a receptor associated with cardiac, renal, and cerebral protective responses. Physiological evidence suggests that Mas receptor (MasR) undergoes agonist-dependent desensitization, but the underlying molecular mechanism regulating receptor activity is unknown. We investigated the hypothesis that MasR desensitizes and internalizes on stimulation with Ang-(1-7). For this purpose, we generated a chimera between the MasR and the yellow fluorescent protein (YFP; MasR-YFP). MasR-YFP–transfected HEK 293T cells were incubated with Ang-(1-7), and the relative cellular distribution of MasR-YFP was observed by confocal microscopy. In resting cells, MasR-YFP was mostly localized to the cell membrane. Ang-(1-7) induced a redistribution of MasR-YFP to intracellular vesicles of various sizes after 5 minutes. Following the time course of [125I]Ang-(1-7) endocytosis, we observed that half of MasR-YFP underwent endocytosis after 10 minutes, and this was blocked by a MasR antagonist. MasR-YFP colocalized with Rab5, the early endosome antigen 1, and the adaptor protein complex 2, indicating that the R is internalized through a clathrin-mediated pathway and targeted to early endosomes after Ang-(1-7) stimulation. A fraction of MasR-YFP also colocalized with caveolin 1, suggesting that at some point MasR-YFP traverses caveolin 1–positive compartments. In conclusion, MasR undergoes endocytosis on stimulation with Ang-(1-7), and this event may explain the desensitization of MasR responsiveness. In this way, MasR activity and density may be tightly controlled by the cell.