Arrestins (arr) comprise a small family of cytosolicproteins that regulate signaling of G protein-coupledreceptors (GPCRs) at the eukaryotic cell membrane.Arrestins bind to active and phosphorylated GPCRsto induce receptor desensitization and trafficking viaclathrin-coated vesicles. At the same time, they functionas scaffolds for protein kinases [1–5] and activatorsof protein kinase pathways [6], such as theextracellular signal-regulated kinase 1 and 2 (ERK1/2)and mitogen-activated protein kinase (MAPK) cascade