Putative functions of the Nedd4 family of ubiquitin ligases and their adaptors in extracellular vesicle budding

N Foot1, K Mackenzie1, K Gembus1, S Mathivanan2 and S Kumar1

  1. Centre for Cancer Biology, University of South Australia, Adelaide
  2. La Trobe Institute for Molecular Science, La Trobe University, Melbourne

Ubiquitination is essential for regulating protein function via degradation, trafficking, sorting and stabilisation. Ubiquitin-protein ligases (E3s) determine the substrate specificity of ubiquitination by binding to their targets directly or through accessory or adaptor proteins. Ndfips (Ndfip1 and Ndfip2) and the arrestin-domain containing proteins (Arrdcs) are two groups of adaptor proteins that facilitate the recruitment of the Nedd4 family of E3s to their substrates. In previous studies we found that Ndfip1 and Ndfip2 act as adaptors to promote the ubiquitination of the iron transporter DMT1 by specific members of Nedd4 family through intracellular degradation pathways, and that this regulation is critical for iron homeostasis in mouse models. Our recent data demonstrate that Arrdc1 and Arrdc4 also interact with and regulate DMT1 function, however, instead of mediating DMT1 endocytosis, DMT1 is released in extracellular vesicles (EVs) derived from plasma membrane. We found that Arrdc1 and Arrdc4 assisted ubiquitination is necessary for DMT1 inclusion into EVs, thus uncovering a potentially novel mechanism of membrane protein turnover, distinct from endocytosis. Based on additional data, we predict that Arrdcs and ubiquitination are required for both the formation of EVs and the targeting of specific proteins to them.