Lipid Raft Endocytosis and Exosomal Transport Facilitate Extracellular Trafficking of Annexin A2

Abstract

Annexin A2 (AnxA2), a Ca 2؉ -dependent phospholipid-binding protein, is known to associate with the plasma membrane and the endosomal system. Within the plasma membrane, AnxA2 associates in a Ca 2؉ dependent manner with cholesterolrich lipid raft microdomains. Here, we show that the association of AnxA2 with the lipid rafts is influenced not only by intracellular levels of Ca 2؉ but also by N-terminal phosphorylation at tyrosine 23. Binding of AnxA2 to the lipid rafts is followed by the transport along the endocytic pathway to be associated with the intralumenal vesicles of the multivesicular endosomes. AnxA2-containing multivesicular endosomes fuse directly with the plasma membrane resulting in the release of the intralumenal vesicles into the extracellular environment, which facilitates the exogenous transfer of AnxA2 from one cell to another. Treatment with Ca 2؉ ionophore triggers the association of AnxA2 with the specialized microdomains in the exosomal membrane that possess raft-like characteristics. Phosphorylation at Tyr-23 is also important for the localization of AnxA2 to the exosomal membranes. These results suggest that AnxA2 is trafficked from the plasma membrane rafts and is selectively incorporated into the lumenal membranes of the endosomes to escape the endosomal degradation pathway. The Ca 2؉ -dependent exosomal transport constitutes a novel pathway of extracellular transport of AnxA2.

STIM1/ORAI1-mediated Ca2+ Influx Regulates Enolase-1 Exteriorization

“…Rebinding of exteriorized ENO-1 to the cell surface closes the cycle of ENO-1 extracellular transport. A similar mechanism has been proposed to explain extracellular localization of annexin A2 (51). Nonetheless, it still remains to be elucidated which part of ENO-1 stays on the cell surface and which one is packed into exosomes and where the decision about ENO-1 sorting is made.…”

Characterization of a Secretory Annexin in Echinococcus granulosus

“…More recent studies showed that annexin A2 was an important component of exosomes in dendritic cells 40 and could be transferred from one cell to another in exosomes in a raft-associated manner. 19,41 More research is required to better understand the secretory annexins.…”

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

“…For example, many phosphorylated proteins appear in exosomes, including the calcium-dependent phospholipid-binding protein Annexin A2, which is enriched in cholesterol-rich lipid raft micro-domains of exosome membranes [101,108,109]. The localization of this protein depends on the phosphorylation of Tyr23, which prevents its endosomal degradation and allows its incorporation into exosomal membranes [109].…”

“…For example, many phosphorylated proteins appear in exosomes, including the calcium-dependent phospholipid-binding protein Annexin A2, which is enriched in cholesterol-rich lipid raft micro-domains of exosome membranes [101,108,109]. The localization of this protein depends on the phosphorylation of Tyr23, which prevents its endosomal degradation and allows its incorporation into exosomal membranes [109]. Other phosphorylated proteins found in exosomes include Tau, type 1 insulin receptor substrate (IRS-1), Crystalline alphaB (CryAB), Epidermal Growth Factor Receptor (EGFR), Na + -Cl − co-transporter (NCC), Aquaporin 2, FasL and proteins implicated in cellular processes such as apoptosis, survival and metabolism [79,101,108,[110][111][112][113][114][115][116][117] (Table 2 and Fig.…”