Abstract
ABSTRACTRetromer 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.
Highlights
On arriving in the endosomal network, internalized transmembrane protein cargos have two principal fates – either they are sorted from the limiting membrane of the endosome into intraluminal vesicles for delivery to the lysosome for degradation or, alternatively, they are exported from the endosome for recycling to the plasma membrane or to the trans-Golgi network (TGN) (Huotari and Helenius, 2011)
Retromer is composed of two subcomplexes – a membrane remodeling heterodimer of the SNX-BAR [sorting nexins (SNX) that possess Bin/Amphiphysin/Rvs (BAR) domains] proteins Vps5 and Vps17, and a heterotrimer, classically termed the cargoselective complex (CSC), that is composed of Vps26, Vps29 and Vps35 and has been shown to recognize cargo including Vps10 (Seaman et al, 1998)
Through comparative analysis of four functionally distinct SNX27–retromer cargos – the glucose transporter GLUT1, the monocarboxylate transporter MCT1, the TNF-receptor super-family member TRAILR1 and the adhesion receptor CD97 – we reveal underlying mechanistic heterogeneity in retromer-mediated endosome-toplasma-membrane transport and provide a molecular framework to aid the further analysis of retromer function
Summary
On arriving in the endosomal network, internalized transmembrane protein cargos have two principal fates – either they are sorted from the limiting membrane of the endosome into intraluminal vesicles for delivery to the lysosome for degradation or, alternatively, they are exported from the endosome for recycling to the plasma membrane or to the trans-Golgi network (TGN) (Huotari and Helenius, 2011). Retromer is composed of two subcomplexes – a membrane remodeling heterodimer of the SNX-BAR [sorting nexins (SNX) that possess Bin/Amphiphysin/Rvs (BAR) domains] proteins Vps and Vps, and a heterotrimer, classically termed the cargoselective complex (CSC), that is composed of Vps, Vps and Vps and has been shown to recognize cargo including Vps (Seaman et al, 1998). Retromer in yeast serves as a coat complex for co-ordinating cargo selection and cargo enrichment with membrane remodeling to generate cargo-enriched transport carriers for endosome-to-TGN transport (Burd and Cullen, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
