Retromer is a protein assembly that orchestrates the sorting of transmembrane cargo proteins into endosome-to-Golgi and endosome-to-plasma-membrane transport pathways. Here, we have employed quantitative proteomics to define the interactome of human VPS35, the core retromer component. This has identified a number of new interacting proteins, including ankyrin-repeat domain 50 (ANKRD50), seriologically defined colon cancer antigen 3 (SDCCAG3) and VPS9-ankyrin-repeat protein (VARP, also known as ANKRD27). Depletion of these proteins resulted in trafficking defects of retromer-dependent cargo, but differential and cargo-specific effects suggested a surprising degree of functional heterogeneity in retromer-mediated endosome-to-plasma-membrane sorting. Extending this, suppression of the retromer-associated WASH complex did not uniformly affect retromer cargo, thereby confirming cargo-specific functions for retromer-interacting proteins. Further analysis of the retromer–VARP interaction identified a role for retromer in endosome-to-melanosome transport. Suppression of VPS35 led to mistrafficking of the melanogenic enzymes, tyrosinase and tryrosine-related protein 1 (Tyrp1), establishing that retromer acts in concert with VARP in this trafficking pathway. Overall, these data reveal hidden complexities in retromer-mediated sorting and open up new directions in our molecular understanding of this essential sorting complex.
Mcgough, I. J., Steinberg, F., Gallon, M. J., Yatsu, A., Ohbayashi, N., Heesom, K. J., Fukuda, M., & Cullen, P. J. (2014). Identification of molecular heterogeneity in SNX27-retromer-mediated endosome-to-plasma-membrane recycling. Journal of Cell Science, 127(22), 4940-4953. https://doi.org/10.1242/jcs.156299