Differential β-Arrestin-Dependent Conformational Signaling and Cellular Responses Revealed by Angiotensin Analogs

The angiotensin type 1 receptor (AT1R) and its octapeptide ligand, angiotensin II (AngII), engage multiple downstream signaling pathways, including those mediated by heterotrimeric guanosine triphosphate-binding proteins (G proteins) and those mediated by beta-arrestin. Here, we examined AT1R-mediated G alpha(q) and beta-arrestin signaling with multiple AngII analogs bearing substitutions at position 8, which is critical for binding to the AT1R and its activation of G proteins. Using assays that discriminated between ligand-promoted recruitment of beta-arrestin to the AT1R and its resulting conformational rearrangement, we extend the concept of biased signaling to include the analog's propensity to differentially promote conformational changes in beta-arrestin, two responses that were differentially affected by distinct G protein-coupled receptor kinases. The efficacy of AngII analogs in activating extracellular signal-regulated kinases 1 and 2 correlated with the stability of the complexes between beta-arrestin and AT1R in endosomes, rather than with the extent of beta-arrestin recruitment to the receptor. In vascular smooth muscle cells, the ligand-induced conformational changes in beta-arrestin correlated with whether the ligand promoted beta-arrestin-dependent migration or proliferation. Our data indicate that biased signaling not only occurs between G protein-and beta-arrestin-mediated pathways but also occurred at the level of the AT1R and beta-arrestin, such that different AngII analogs selectively engaged distinct beta-arrestin conformations, which led to specific signaling events and cell responses.