Activity-Dependent Internalization of Smoothened Mediated by β-Arrestin 2 and GRK2.

Binding of Sonic Hedgehog (Shh) to Patched (Ptc) relieves thelatter's tonic inhibition of Smoothened (Smo), a receptor that spans thecell membrane seven times. This initiates signaling which, by unknownmechanisms, regulates vertebrate developmental processes. We find thattwo molecules interact with mammalian Smo in an activation-dependentmanner: C proteincoupled receptor kinase 2 (GRK2) leads tophosphorylation of Smo, and β-arrestin 2 fused to green fluorescentprotein interacts with Smo. These two processes promote endocytosis ofSmo in clathrin-coated pits. Ptc inhibits association of β-arrestin2 with Smo, and this inhibition is relieved in cells treated with Shh. ASmo agonist stimulated and a Smo antagonist (cyclopamine) inhibited bothphosphorylation of Smo by GRK2 and interaction of β-arrestin 2 withSmo. β-Arrestin 2 and GRK2 are thus potential mediators ofsignaling by activated Smo. [ABSTRACT FROM AUTHOR]