The P4-ATPase TAT-5 Inhibits the Budding of Extracellular Vesicles in C. elegans Embryos

Abstract

Summary Background Cells release extracellular vesicles (ECVs) that can influence differentiation, modulate the immune response, promote coagulation, and induce metastasis. Many ECVs form by budding outwards from the plasma membrane, but the molecules that regulate budding are unknown. In ECVs, the outer leaflet of the membrane bilayer contains aminophospholipids that are normally sequestered to the inner leaflet of the plasma membrane, suggesting a role for lipid asymmetry in ECV budding. Results We show that loss of the conserved P4-ATPase TAT-5 causes the large-scale shedding of ECVs and disrupts cell adhesion and morphogenesis in C. elegans embryos. TAT-5 localizes to the plasma membrane and its loss results in phosphatidylethanolamine exposure on cell surfaces. We show that RAB-11 and the ESCRT complex, which regulate the topologically analogous process of viral budding, are enriched at the plasma membrane in tat-5 embryos and are required for ECV production. Conclusions TAT-5 is the first protein identified to regulate ECV budding. TAT-5 provides a potential molecular link between loss of phosphatidylethanolamine asymmetry and the dynamic budding of vesicles from the plasma membrane, supporting the hypothesis that lipid asymmetry regulates budding. Our results also suggest that viral budding and ECV budding may share common molecular mechanisms.

Lipid flippase modulates olfactory receptor expression and odorant sensitivity in Drosophila

“…In yeast, the major phenotype associated with loss of P4-ATPase function is abnormal transport vesicle budding from the transgolgi network (19,33,34). Similar defects in cargo sorting have been observed in Caenorhabditis elegans Tat-1 mutants (35), and other C. elegans P4-ATPase mutants are defective for phagocytosis of dead cells and regulation of ectosome production (35)(36)(37)(38). Proper lipid localization may be required for vesicle docking or receptor recycling leading to reduced receptor levels in the cilia.…”

Exosomes as Hedgehog carriers in cytoneme-mediated transport and secretion

“…36) supporting an MVB fusion origin. However, we have also observed a decrease in signalling and Hh release when interfering with P4-ATPase (CG31729), the Drosophila orthologue of TAT-5 specifically involved in the formation of ectosomes in C. elegans 24 . Thus, as it is difficult to account for the considerable differences between the two types of vesicles, the result of knocking down Vps22 and P4-ATPase together with the EM data and the in vivo imaging indicate that Hh might be released in both ectosomes/microvesicles and exosome-like vesicles.…”

“…Although shedding vesicles/ectosomes seem to have a different origin 31 , the mechanisms of their sorting process remain obscure and might also be dependent on the ESCRT complex 24 . In addition, studies have shown a crucial role for cholesterol-rich microdomains of the plasma membrane for shedding vesicle formation 32 as well as for biogenesis of exosomes 14 .…”

Formation and release of arrestin domain-containing protein 1-mediated microvesicles (ARMMs) at plasma membrane by recruitment of TSG101 protein

“…Whether ARMMs production also requires ESCRT-III and ALIX which are involved in Gag-mediated HIV budding (46), is not known at present. Recently, the shedding of ESCRT-dependent microvesicles that may prove to be ARMMs has been found to be increased in Caenorhabditis elegans embryos by loss of the evolutionarily conserved P4-ATPase, TAT-5, and consequent exposure of phosphatidylethanolamine at the cell surface (47).…”