👤 Irina Kufareva

Mammalian α-arrestins are members of the same arrestin family as the ubiquitously expressed and extensively studied β-arrestins. Arrestins share common structural elements, including the conserved N- and C-arrestin-fold domains, polar core, finger loop, and C-terminal tail, all of which mediate protein-protein interactions. In β-arrestins, these domains enable the control of G protein-coupled receptor (GPCR) signaling and scaffolding interactions with various signaling proteins including c-Src. By contrast, the repertoire of α-arrestin scaffolding partners and regulatory mechanisms that control their interactions are not well-understood. α-arrestins differ considerably from β-arrestins in the C-terminal region; β-arrestins contain clathrin adaptor β-adaptin-binding sites, whereas α-arrestins harbor PPxY motifs, demonstrated to interact with WW domains of E3 ubiquitin ligases such as WWP2. Here we report the identification of a novel phosphorylation site, tyrosine (Y) 394, embedded in the C-terminal PPxY motif of α-arrestin ARRDC3. The Y394 site functions as a phospho-regulatory switch to enable distinct ARRDC3 binding partners and scaffolding functions. We found that ARRDC3 Y394 phosphorylation promotes interaction with c-Src via its SH2 domain, whereas the non-phosphorylated form binds to WWP2. Our results further show that ARRDC3 Y394 phosphorylation and c-Src SH2 domain-dependent interaction enables regulation of c-Src activity, whereas ARRDC3 Y394 phosphorylation disrupts WWP2 interaction and perturbs ARRDC3-dependent lysosomal trafficking of the GPCR, protease-activated receptor-1. Together, these findings indicate that ARRDC3 Y394 functions as a phospho-regulatory switch to enable selective binding to different partners that impact distinct scaffolding functions. Show less

The α-arrestin ARRDC3 is a recently discovered tumor suppressor in invasive breast cancer that functions as a multifaceted adaptor protein to control protein trafficking and cellular signaling. However, the molecular mechanisms that control ARRDC3 function are unknown. Other arrestins are known to be regulated by posttranslational modifications, suggesting that ARRDC3 may be subject to similar regulatory mechanisms. Here we report that ubiquitination is a key regulator of ARRDC3 function and is mediated primarily by two proline-rich PPXY motifs in the ARRDC3 C-tail domain. Ubiquitination and the PPXY motifs are essential for ARRDC3 function in regulating GPCR trafficking and signaling. Additionally, ubiquitination and the PPXY motifs mediate ARRDC3 protein degradation, dictate ARRDC3 subcellular localization, and are required for interaction with the NEDD4-family E3 ubiquitin ligase WWP2. These studies demonstrate a role for ubiquitination in regulating ARRDC3 function and reveal a mechanism by which ARRDC3 divergent functions are controlled. Show less