Dimerization of sortilin regulates its trafficking to extracellular vesicles

Abstract

Extracellular vesicles (EVs) play a critical role in intercellular communication by transferring microRNAs, lipids, and proteins to neighboring cells. Sortilin, a sorting receptor that directs target proteins to the secretory or endocytic compartments of cells, is found in both EVs and cells. In many human diseases, including cancer and cardiovascular disorders, sortilin expression levels are atypically high. To elucidate the relationship between cardiovascular disease, particularly vascular calcification, and sortilin expression levels, we explored the trafficking of sortilin in both the intracellular and extracellular milieu. We previously demonstrated that sortilin promotes vascular calcification via its trafficking of tissue-nonspecific alkaline phosphatase to EVs. Although recent reports have noted that sortilin is regulated by multiple post-translational modifications, the precise mechanisms of sortilin trafficking still need to be determined. Here, we show that sortilin forms homodimers with an intermolecular disulfide bond at the cysteine 783 (Cys783) residue, and because Cys783 can be palmitoylated, it could be shared via palmitoylation and an intermolecular disulfide bond. Formation of this intermolecular disulfide bond leads to trafficking of sortilin to EVs by preventing palmitoylation, which further promotes sortilin trafficking to the Golgi apparatus. Moreover, we found that sortilin-derived propeptide decreased sortilin homodimers within EVs. In conclusion, sortilin is transported to EVs via the formation of homodimers with an intermolecular disulfide bond, which is endogenously regulated by its own propeptide. Therefore, we propose that inhibiting dimerization of sortilin acts as a new therapeutic strategy for the treatment of EV-associated diseases, including vascular calcification and cancer.

Intraviral interactome of Chikungunya virus reveals the homo-oligomerization and palmitoylation of structural protein TF

“…However, the function of oligomeric state of CHIKV TF remains to be studied. Interestingly, palmitoylation of CHIKV TF reduced the homo-oligomerization of TF, which is consistent with previous reports that less palmitoylation of SNAP-25 and sortilin increased disulfide bonds formation [23,24]. CHIKV TF formed homo-oligomer with an intermolecular disulfide bond at the cysteine 43, which could be palmitoylated.…”

Identification of synaptic PPT1 substrates highlight roles of depalmitoylation in disulfide bond formation and synaptic function

“…Strikingly, we find that for all 12 peptides identified as extracellular and carbamidomethylmodified, the modified cysteines form disulfide bonds in the mature protein (Table S8). This suggests that cysteines could be shared for palmitoylation and disulfide bond formation, and that intracellular palmitoylation precedes disulfide bond formation as proposed previously (Bechtel et al, 2020;Itoh et al, 2018;Yu et al, 2017). Many of the proteins containing these extracellular peptides fall into the broad classes of adhesion molecules (NFASC, NRCAM, CADM2, NTRI, THY1, BASI), and channels/transporters (GRIA1, AT1B1, AT1B2; Figure 4B).…”

“…The site we identified, (C323) typically forms a disulfide bond (to C75). AMPA receptor subunit palmitoylation is known to regulate sensitization as well as localization (Hayashi et al, 2005;Itoh et al, 2018). From the recent crystal structure (Herguedas et al, 2019), the PPT1-depalmitoylated cysteine is an exposed loop, so accessibility of the cysteine appears to be a key feature.…”

Conserved and Divergent Modulation of Calcification in Atherosclerosis and Aortic Valve Disease by Tissue Extracellular Vesicles

“…(4) Calcification-prone extracellular vesicles (EVs) offer a possible explanation: recent work has implicated EVs as important drivers and building blocks of mineralization in the vasculature. (5–7, 8) EVs are small lipid membrane-bound structures secreted by all human cell types. (9) Found throughout the body’s tissues and fluids, these particles arise from two regulated paths: exosomes (~50-150 nm in diameter) are secreted when multivesicular bodies of endosomal origin fuse with the plasma membrane, and microvesicles (~100-500 nm in diameter) are produced by budding and fission of the cell membrane (reviewed in (10)).…”