A noncanonical function of SKP1 regulates the switch between autophagy and unconventional secretion

ABSTRACT: Intracellular degradation of proteins and organelles by the autophagy-lysosome system is essential for cellular quality control and energy homeostasis. Besides degradation, endolysosomal organelles can fuse with the plasma membrane and contribute to unconventional secretion. Here, we identify a function for mammalian SKP1 in endolysosomes that is independent of its established role as an essential component of the family of SCF/CRL1 ubiquitin ligases. We found that, under nutrient poor conditions, SKP1 is phosphorylated on Thr131, allowing its interaction with V1 subunits of the vacuolar ATPase (V-ATPase). This event, in turn, promotes V-ATPase assembly to acidify late endosomes and enhance endolysosomal degradation. Under nutrient rich conditions, SUMOylation of phosphorylated SKP1 allows its binding to and dephosphorylation by the PPM1B phosphatase. Dephosphorylated SKP1 interacts with SEC22B, recently shown to participate in unconventional secretion, to promote secretion of the content of less acidified hybrid endosomal/autophagic compartments. The differences in abundance of specific proteins between ECVs of SKP1WT and SKP1T131A cells motivated us to determine possible changes in extracellular vesicles (ECV) content depending on SKP1 phosphorylation. To this effect, we performed MS analysis and comparative proteomics of ECVs from SKP1WT and SKP1T131A cells (Fig. 5I, Table S7). We found a higher number of proteins displaying increased abundance (greater than 0.321 log2 fold change) in SKP1T131A cells (127 proteins) compared to SKP1WT cells (16 proteins). The mass spectrometric raw files for this analysis are included here. Collectively, our study implicates SKP1 phosphorylation as a switch between autophagy and unconventional secretion in a manner dependent on cellular nutrient status. Corresponding authors: [e-mail] and [e-mail]

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Beatrix Ueberheide  

PROVIDER: MSV000092361 | MassIVE | Thu Jul 06 14:28:00 BST 2023

REPOSITORIES: MassIVE