G protein‐coupled receptor regulation of the alpha‐arrestin ARRDC3

Abstract

Adaptor proteins are an important class of proteins that help to maintain proper spatiotemporal control of cell signaling. One of the best‐studied families of adaptor proteins are the ubiquitously expressed beta‐arrestins, which are known to be key regulators of G protein‐coupled receptor (GPCR) function. Recently another family of arrestins, termed the alpha‐arrestins, were discovered and shown to be expressed in mammalian cells. While alpha‐ and beta‐arrestins share minimal sequence homology, they are predicted to be structurally similar, and therefore may be subject to common regulatory mechanisms. However, while GPCR regulation of beta‐arrestin function has been well characterized, it remains entirely unknown how GPCRs might regulate alpha‐arrestins, such as ARRDC3. We recently showed that ARRDC3 is a multifunctional adaptor that distinctly regulates protease‐activated receptor‐1 (PAR1) signaling and trafficking, but it remains unknown how these distinct ARRDC3 functions may be regulated. PAR1 is a GPCR for the protease thrombin and is known to regulate a diverse array of physiological functions in health and disease, thus, it is important to better understand the molecular mechanisms that control PAR1 function. The objective of this study is to understand the mechanisms that control ARRDC3 multifaceted functions. We hypothesize that GPCRs regulate ARRDC3 function via distinct processes that enable diverse functions. Using biochemical and microscopy‐based techniques, we show that PAR1 may regulate ARRDC3 through modulation of post‐translational modifications, including ubiquitination. We also show that ubiquitin is critical for regulating distinct ARRDC3 functions, including regulation of GPCR signaling and trafficking, through various mechanisms that may include control of protein stability, subcellular localization, and protein‐protein interactions. Additionally, ARRDC3 has previously been shown to act as a tumor suppressor in highly invasive triple‐negative breast cancers. Thus, in future studies we will assess the role of ubiquitination on ARRDC3 tumor suppressor function in vitro in vivo. The results of these studies will advance our understanding of how alpha‐arrestins may contribute to GPCR regulation and may lead to the identification of novel targets for therapeutic development to treat metastatic breast cancer.