Extracellular vesicle sorting of α-Synuclein is regulated by sumoylation

Abstract

Extracellular α-Synuclein has been implicated in interneuronal propagation of disease pathology in Parkinson’s Disease. How α-Synuclein is released into the extracellular space is still unclear. Here, we show that α-Synuclein is present in extracellular vesicles in the central nervous system. We find that sorting of α-Synuclein in extracellular vesicles is regulated by sumoylation and that sumoylation acts as a sorting factor for targeting of both, cytosolic and transmembrane proteins, to extracellular vesicles. We provide evidence that the SUMO-dependent sorting utilizes the endosomal sorting complex required for transport (ESCRT) by interaction with phosphoinositols. Ubiquitination of cargo proteins is so far the only known determinant for ESCRT-dependent sorting into the extracellular vesicle pathway. Our study reveals a function of SUMO protein modification as a Ubiquitin-independent ESCRT sorting signal, regulating the extracellular vesicle release of α-Synuclein. We deciphered in detail the molecular mechanism which directs α-Synuclein into extracellular vesicles which is of highest relevance for the understanding of Parkinson’s disease pathogenesis and progression at the molecular level. We furthermore propose that sumo-dependent sorting constitutes a mechanism with more general implications for cell biology.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-015-1408-1) contains supplementary material, which is available to authorized users.

Post-translational add-ons mark the path in exosomal protein sorting

“…In the same way, we propose the use of known PTMs motifs, such as the myristoylation sequence MGCINSKRKD, in the N-t of the protein of interest to drive it specifically into exosomes, as other authors have described for Tya [124]. Moreover, addition of a C-t ubiquitin or SUMO tag could deliver proteins into exosomes, including targeting-peptides-LAMP2 with glycosylated motifs for specific tissue delivery [106,137,142]. Besides, protein glycosylation has improved the efficacy of therapeutic proteins [143].…”

“…In the case of acetylated-GRP78 and ISGylated-TSG101, these PTMs act as cellular retention tags, promoting their degradation in lysosomes [128,129]. However, Ub-HSP70, SUMOylated-hnRNPA2B1, SUMOylated-α-synuclein, ph-AKT, oxidized and phosphorylated γ-synuclein and citrullinated vimentin are loaded into ILVs and driven to EVs [80,104,106,108,118,154]. Besides, unmodified TSG101 and GRP78 proteins can also be present in EVs [128,129].…”

“…Besides, EVs can contribute to disseminate neurotoxic proteins, which favours the development of PD pathogenesis. Hence, sumoylated α-synuclein is incorporated into exosomes by a mechanism dependent on the ESCRT complex and phospholipids [106] (Table 2 and Fig. 1).…”

“…Similar to ubiquitin, the UBL SUMO also plays an important role in protein sorting to EVs. For example, SUMOylation is necessary for α-synuclein sorting into exosomes in an ESCRT-dependent manner [106] (Table 2). A recent study showed that other UBL called autophagy-related protein 12 (ATG12) and its E3 ligase ATG3 interact with ALIX, regulating diverse functions carried out by ALIX, for example, viral budding and MVBs biogenesis [126].…”

“…However, although exosome-based vaccines could trigger antigenspecific immune responses, they also contain other proteins that could trigger side-or off-target effects. In addition to ubiquitin, GFP SUMOylation drives it into exosomes, suggesting that SUMO could work as a specific sorting tool for antigen incorporation into exosomes for vaccination schemes [106] (Fig. 3).…”