β-Arrestin-kinase scaffolds: turn them on or turn them off?

G-protein-coupled receptors (GPCRs) can signal through heterotrimeric G-proteins or through beta-arrestins to elicit responses to a plethora of extracellular stimuli. While the mechanisms underlying G-protein signaling is relatively well understood, the mechanisms by which beta-arrestins regulate the diverse set of proteins with which they associate remain unclear. Multi-protein complexes are a common feature of beta-arrestin-dependent signaling. The first two such complexes discovered were the mitogen-activated kinases modules associated with extracellular regulated kinases (ERK1/2) and Jnk3. Subsequently a number of other kinases have been shown to undergo beta-arrestin-dependent regulation, including Akt, phosphatidylinositol-3kinase (PI3K), Lim-domain-containing kinase (LIMK), calcium calmodulin kinase II (CAMKII), and calcium calmodulin kinase kinase beta (CAMKK beta). Some are positively and some negatively regulated by beta-arrestin association. One of the missing links to understanding these pathways is the molecular mechanisms by which the activity of these kinases is regulated. Do beta-arrestins merely serve as scaffolds to bring enzyme and substrate together or do they have a direct effect on the enzymatic activities of target kinases? Recent evidence suggests that both mechanisms are involved and that the mechanisms by which beta-arrestins regulate kinase activity varies with the target kinase. This review discusses recent advances in the field focusing on 5 kinases for which considerable mechanistic detail and specific sites of interaction have been elucidated. WIREs Syst Biol Med 2013, 5:231241. doi: 10.1002/wsbm.1203 For further resources related to this article, please visit the WIREs website.