beta-arrestin1 interacts with the catalytic domain of the tyrosine kinase c-SRC - Role of beta-arrestin1-dependent targeting of c-SRC in receptor endocytosis

beta-Arrestins can act as adapter molecules, coupling G-protein-coupled rec eptors to proteins involved in mitogenic as well as endocytic pathways. We have previously identified c-SRC as a molecule that is rapidly recruited to the beta 2-adrenergic receptor in a beta-arrestin1-dependent manner, Recru itment of c-SRC to the receptor appears to be involved in pathways leading to receptor internalization and mitogen-activated protein kinase activation . This recruitment of c-SRC to the receptor involves an interaction between the amino-terminal proline-rich region of beta-arrestin1 and the Src homol ogy 3 (SH3) domain of c-SRC, but deletion of the proline-rich domain does n ot totally ablate the interaction. We have found that a major interaction a lso exists between beta-arrestin1 and the catalytic or kinase domain (SH1) of c-SRC, We therefore hypothesized that a catalytically inactive mutant of the isolated catalytic subunit, SH1 (kinase dead) (SH1(KD)), would specifi cally block those cellular actions of c-SRC that are mediated by beta-arres tin1 recruitment to the G-protein-coupled receptor. In contrast, the majori ty of cellular phosphorylations catalyzed by c-SRC, which do not involve in teraction with the SH1 domain, would be predicted to be unaffected. The SH1 (KD) mutant did indeed block beta 2-adrenergic receptor internalization and receptor-stimulated tyrosine phosphorylation of dynamin, actions previousl y shown to be c-SRC-dependent, In contrast, SAM-68 and whole cell tyrosine phosphorylation by c-SRC was unaffected, indicating that the SH1(KD) mutant did not inhibit c-SRC tyrosine kinase activity in general. These results n ot only clarify the nature of the beta-arrestin1/c-SRC interaction but also implicate beta-arrestin1 as an important mediator of receptor internalizat ion by recruiting tyrosine kinase activity to the cell surface to phosphory late key endocytic intermediates, such as dynamin.