ARRDC1

ARRDC1 is a plasma membrane α-arrestin adaptor that couples substrate recognition to ubiquitin-mediated turnover and drives the budding of extracellular vesicles (PMID:23886940, PMID:30035390). It heterodimerizes with β-arrestins and uses its PPxY motifs to directly recruit the Itch E3 ubiquitin ligase, forming a tripartite complex that ubiquitylates substrates and routes them to lysosomal/proteasomal degradation; mutation of the PPxY motifs abolishes this activity (PMID:23886940). Through this PPxY/Itch axis it promotes degradation of non-activated Notch (PMID:23886940) and binds the WW domains of YAP1 to control YAP1 protein stability, with loss of ARRDC1-driven YAP1 turnover relieving suppression of renal cell carcinoma growth, migration, invasion, and EMT (PMID:29416926). Independently of its degradative role, ARRDC1 governs the biogenesis and protein cargo of both exosomes and ectosomes, and its membrane-budding activity can be redirected to actively load defined protein and nucleic-acid cargo into secreted vesicles (PMID:30035390, PMID:38785998, PMID:41392542). The same membrane localization and ubiquitin-ligase-binding motif underlie an antiviral function: ARRDC1 binds alphavirus nonstructural protein nsP4 and promotes its ubiquitination-dependent degradation to restrict Semliki Forest virus replication (PMID:40824091).

1. 2013 High

   Established the core molecular logic of ARRDC1 as an adaptor: how could an α-arrestin direct substrate degradation? It bridges β-arrestins and the Itch E3 ligase via PPxY motifs to ubiquitylate and degrade Notch.

   Evidence Co-IP, PPxY mutant transfection, ubiquitylation and lysosomal degradation assays in β-arrestin-/- and Itch-/- cells

   PMID:23886940

   Open questions at the time

   • Whether Notch is recognized directly by ARRDC1 or via β-arrestin is not resolved
   • Physiological contexts of Notch regulation by ARRDC1 not defined
2. 2018 High

   Extended the adaptor model to a second substrate and a disease context: ARRDC1 binds YAP1 WW domains through its PPXY motifs and drives Itch-mediated YAP1 degradation, positioning ARRDC1 as a tumor suppressor in renal cell carcinoma.

   Evidence AP-MS, reciprocal Co-IP, PPXY/WW domain mapping, shRNA knockdown, proliferation/migration/invasion/EMT assays

   PMID:29416926

   Open questions at the time

   • In vivo tumor evidence not established
   • Relative contribution of proteasomal vs lysosomal degradation unclear
3. 2018 Medium

   Defined a degradation-independent role: how does ARRDC1 shape extracellular vesicle output? Genetic loss alters the protein cargo of both exosomes and ectosomes.

   Evidence Arrdc1-/- MEFs, nanoparticle tracking, proteomic profiling of isolated EVs

   PMID:30035390

   Open questions at the time

   • Mechanism by which ARRDC1 selects specific cargo classes not defined
   • Single cell type (MEF), not confirmed across tissues
4. 2024 Medium

   Demonstrated that ARRDC1 actively loads cargo into vesicles rather than passively associating: ARRDC1-p53 fusion enriches p53 protein and mRNA in small EVs and boosts sEV production.

   Evidence ARRDC1-p53 fusion overexpression in HEK293T, sEV marker Western blots, functional assays in recipient cells

   PMID:38785998

   Open questions at the time

   • Overexpression/fusion strategy may not reflect endogenous cargo loading
   • Mechanism of mRNA recruitment unknown
5. 2025 Medium

   Showed ARRDC1's budding activity is engineerable: ARRDC1-mediated microvesicles carrying protein, mRNA, or CRISPR-Cas9 can be surface-targeted for selective in vivo delivery.

   Evidence Engineered ARMMs with targeting ligands, in vitro and in vivo delivery and gene-editing readouts

   PMID:41392542

   Open questions at the time

   • Engineering proof-of-concept rather than endogenous mechanism
   • Endogenous physiological cargo and triggers of budding not addressed
6. 2025 High

   Connected ARRDC1's degradative adaptor function to host defense: it binds alphavirus nsP4 and promotes its ubiquitination-dependent degradation to restrict viral replication, requiring membrane localization and the PPxY motif.

   Evidence siRNA knockdown, CRISPR/Cas9 KO, trans-complementation, ARRDC1–nsP4 Co-IP, PPxY mutant analysis, viral replication assays

   PMID:40824091

   Open questions at the time

   • Whether the same Itch ligase mediates nsP4 ubiquitination not shown
   • Breadth of antiviral activity against other viruses not defined

• How ARRDC1 selects its diverse substrates and EV cargo, and whether its degradative and vesicle-budding functions are mechanistically linked, remains unresolved.
• No structural model of ARRDC1 substrate or cargo recognition
• Determinants distinguishing degradative targeting from EV cargo loading unknown