Arkadia complexes with clathrin adaptor AP2 and regulates EGF signalling.

Arkadia is a positive regulator of transforming growth factor (TGF)-β signalling that induces ubiquitin-dependent degradation of several inhibitory proteins of TGF-β signalling through its C-terminal RING domain. We report here that, through yeast-two-hybrid screening for Arkadia-binding proteins, the µ2 subunit of clathrin-adaptor 2 (AP2) complex was identified as an interacting partner of Arkadia. Arkadia was located in both the nucleus and the cytosol in mammalian cells. The C-terminal YXXΦ-binding domain of the µ2 subunit associated with the N-terminal YALL motif of Arkadia. Arkadia ubiquitylated the µ2 subunit at Lys130. In addition, Arkadia interacted with the AP2 complex, and modified endocytosis of epidermal growth factor receptor (EGFR) induced by EGF. Arkadia thus appears to regulate EGF signalling by modulating endocytosis of EGFR through interaction with AP2 complex.