Regulation of alpha‐Arrestin Function in G Protein‐Coupled Receptor Signaling and Trafficking

The ubiquitously expressed β‐arrestins are known to play key roles in regulating G protein‐coupled receptor (GPCR) desensitization, internalization, and signaling. Humans also express a newly discovered family of arrestins, termed α‐arrestins, whose function remains poorly understood. While β‐ and α‐arrestins share minimal sequence homology, they are predicted to be structurally similar, except that β‐arrestins contain clathrin motifs within their C‐tails, which are known to be important in facilitating receptor internalization, and α‐arrestins contain PPxY motifs in their C‐tails, which are known to recruit WW‐domain containing proteins, such as Nedd4‐family E3 ubiquitin ligases. This suggests a separate role for α‐arrestins, although they may be subject to similar regulatory mechanisms, including phosphorylation, ubiquitination, and conformational change. Additionally, yeast, which do not express β‐arrestins, express arrestin‐related trafficking adaptors (ARTs), which are predicted to be structurally similar to human arrestins and contain PPxY motifs. ARTs have been well‐characterized as key regulators of receptor trafficking in yeast and are also regulated through post‐translational modification. Recently, we demonstrated a role for arrestin domain‐containing protein‐3 (ARRDC3), a mammalian α‐arrestin, in regulating trafficking of protease‐activated receptor‐1, a GPCR for thrombin. However, while GPCR regulation of β‐arrestin function has been well characterized, it remains entirely unknown how GPCRs regulate α‐arrestins, such as ARRDC3, or how such regulatory mechanisms might impact α‐arrestin function. Here, we examine how PAR1 signaling regulates ARRDC3 function in facilitating PAR1 trafficking. Using a variety of biochemical and microscopy‐based techniques, we show that PAR1 may regulate ARRDC3 through modulation of post‐translational modifications, and that identified ARRDC3 regulatory domains may play a role in regulating ARRDC3 function through controlling its subcellular localization and recruitment of interaction partners. We additionally will use a variety of approaches to elucidate the role of ARRDC3 regulatory mechanisms in PAR1 trafficking and signaling. Additionally, ARRDC3 has been identified to be a tumor suppressor in invasive breast cancer, functioning at least partially through its role in controlling PAR1 signaling and trafficking. Therefore, the results of these studies will not only advance our understating of how α‐arrestins are regulated but may also lead to the identification of novel therapeutic targets to prevent or treat invasive breast cancer. Support or Funding Information UCSD Graduate Training Program in Cellular and Molecular Pharmacology through NIH General Medical Sciences, T32 GM007752 and by National Institute of Health NIGMS R01 GM090689 and R35 GM127121 (JoAnn Trejo)