Abstract

The octapeptide angiotensin II (AngII) exerts a variety of cardiovascular effects through the activation of the AngII type 1 receptor (AT₁), a G protein–coupled receptor. The AT₁ receptor engages and activates several signaling pathways, including heterotrimeric G proteins G_q and G₁₂, as well as the extracellular signal–regulated kinases (ERK) 1/2 pathway. Additionally, following stimulation, βarrestin is recruited to the AT₁ receptor, leading to receptor desensitization. It is increasingly recognized that specific ligands selectively bind and favor the activation of some signaling pathways over others, a concept termed ligand bias or functional selectivity. A better understanding of the molecular basis of functional selectivity may lead to the development of better therapeutics with fewer adverse effects. In the present study, we developed assays allowing the measurement of six different signaling modalities of the AT₁ receptor. Using a series of AngII peptide analogs that were modified in positions 1, 4, and 8, we sought to better characterize the molecular determinants of AngII that underlie functional selectivity of the AT₁ receptor in human embryonic kidney 293 cells. The results reveal that position 1 of AngII does not confer functional selectivity, whereas position 4 confers a bias toward ERK signaling over G_q signaling, and position 8 confers a bias toward βarrestin recruitment over ERK activation and G_q signaling. Interestingly, the analogs modified in position 8 were also partial agonists of the protein kinase C (PKC)–dependent ERK pathway via atypical PKC isoforms PKCζ and PKCι.