Differential kinetic and spatial patterns of β-arrestin and G protein-mediated ERK activation by the angiotensin II receptor

The seven-membrane-spanning angiotensin II type 1A receptor activates the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2) by distinct pathways dependent on either G protein (likely G _q/G₁₁) or β-arrestin2. Here we sought to distinguish the kinetic and spatial patterns that characterize ERK1/2 activated by these two mechanisms. We utilized β-arrestin RNA interference, the protein kinase C inhibitor Ro-31-8425, a mutant angiotensin II receptor (DRY/AAY), and a mutant angiotensin II peptide (SII-angiotensin), which are incapable of activating G proteins, to isolate the two pathways in HEK-293 cells. G protein-dependent activation was rapid (peak <2 min), quite transient (t_1/2 ∼2 min), and led to nuclear translocation of the activated ERK1/2 as assessed by confocal microscopy. In contrast, β-arrestin2-dependent activation was slower (peak 5-10 min), quite persistent with little decrement noted out to 90 min, and entirely confined to the cytoplasm. Moreover, ERK1/2 activated via β-arrestin2 accumulated in a pool of cytoplasmic endosomal vesicles that also contained the internalized receptors and β-arrestin. Such differential regulation of the temporal and spatial patterns of ERK1/2 activation via these two pathways strongly implies the existence of distinct physiological endpoints.