c-Src Regulates Clathrin Adapter Protein 2 Interaction with β-Arrestin and the Angiotensin II Type 1 Receptor during Clathrin- Mediated Internalization

Abstract

Abstractβ-Arrestins are multifunctional adapters involved in the internalization and signaling of G protein-coupled receptors (GPCRs). They target receptors to clathrin-coated pits (CCPs) through binding with clathrin and clathrin adapter 2 (AP-2) complex. They also act as transducers of signaling by recruiting c-Src kinase to certain GPCRs. Here we sought to determine whether c-Src regulates the recruitment of AP-2 to β-arrestin and the angiotensin II (Ang II) type 1 receptor (AT1R) during internalization. We show that the agonist stimulation of native AT1R in vascular smooth muscle cells (VSMCs) induces the formation of an endogenous complex containing c-Src, β-arrestins and AP-2. In vitro studies using coimmunoprecipitation experiments and a yeast three-hybrid assay reveal that c-Src stabilizes the agonist-independent association between β-arrestin2 and the β-subunit of AP-2 independently of the kinase activity of c-Src. However, although c-Src expression promoted the rapid dissociation of AP-2 from both β-arrestin and AT1R after receptor stimulation, a kinase-inactive mutant of c-Src failed to induce the dissociation of AP-2 from the agonist-occupied receptor. Thus, the consequence of c-Src in regulating the dissociation of AP-2 from the receptor was also examined on the internalization of AT1R by depleting c-Src in human embryonic kidney (HEK) 293 cells using a small interfering RNA strategy. Experiments in c-Src depleted cells reveal that AT1R remained mostly colocalized with AP-2 at the plasma membrane after Ang II stimulation, consistent with the observed delay in receptor internalization. Moreover, coimmunoprecipitation experiments in c-Src depleted HEK 293 cells and VSMCs showed an increased association of AP-2 to the agonist-occupied AT1R and β-arrestin, respectively. Together, our results support a role for c-Src in regulating the dissociation of AP-2 from agonist-occupied AT1R and β-arrestin during the clathrin-mediated internalization of receptors and suggest a novel function for c-Src kinase in the internalization of AT1R.