Fibronectin on the Surface of Myeloma Cell-derived Exosomes Mediates Exosome-Cell Interactions

Abstract

Exosomes regulate cell behavior by binding to and delivering their cargo to target cells; however, the mechanisms mediating exosome-cell interactions are poorly understood. Heparan sulfates on target cell surfaces can act as receptors for exosome uptake, but the ligand for heparan sulfate on exosomes has not been identified. Using exosomes isolated from myeloma cell lines and from myeloma patients, we identify exosomal fibronectin as a key heparan sulfate-binding ligand and mediator of exosome-cell interactions. We discovered that heparan sulfate plays a dual role in exosome-cell interaction; heparan sulfate on exosomes captures fibronectin, and on target cells it acts as a receptor for fibronectin. Removal of heparan sulfate from the exosome surface releases fibronectin and dramatically inhibits exosome-target cell interaction. Antibody specific for the Hep-II heparin-binding domain of fibronectin blocks exosome interaction with tumor cells or with marrow stromal cells. Regarding exosome function, fibronectin-mediated binding of exosomes to myeloma cells activated p38 and pERK signaling and expression of downstream target genes DKK1 and MMP-9, two molecules that promote myeloma progression. Antibody against fibronectin inhibited the ability of myeloma-derived exosomes to stimulate endothelial cell invasion. Heparin or heparin mimetics including Roneparstat, a modified heparin in phase I trials in myeloma patients, significantly inhibited exosome-cell interactions. These studies provide the first evidence that fibronectin binding to heparan sulfate mediates exosomecell interactions, revealing a fundamental mechanism important for exosome-mediated cross-talk within tumor microenvironments. Moreover, these results imply that therapeutic disruption of fibronectin-heparan sulfate interactions will negatively impact myeloma tumor growth and progression.

Genotoxic stress modulates the release of exosomes from multiple myeloma cells capable of activating NK cell cytokine production: Role of HSP70/TLR2/NF-kB axis

“…48,49 Our findings also show that both resting or IL-15 activated primary NK cells internalize, and not only bind MM cell-derived exosomes with a rapid kinetics. Interestingly, we found that NK cell exosome uptake is an active process that mainly depends on endocytic route/s requiring dynamin and caveolae/raft endocytosis ( Fig.…”

Cancer-derived extracellular vesicles: the ‘soil conditioner’ in breast cancer metastasis?

“…These EVs have an outer coating of fibronectin which is bound to the EVs through integrin α5. This fibronectin coat facilitates the interaction between the EVs and target cells through heparan sulfate (Purushothaman, Bandari et al 2016). These fibronectin-containing EVs may anchor themselves to both the cancer cell and the endothelial wall, allowing for the cancer cell to undergo directional migration on the inner surface of blood vessels (Fig.…”

Glycosylated extracellular vesicles released by glioblastoma cells are decorated by CCL18 allowing for cellular uptake via chemokine receptor CCR8

“…Integrins have also been shown to act as EV receptors by binding lysophosphatidic acid from the EV surface [32]. Furthermore, heparan sulphate proteoglycans (HSPGs) on the plasma membrane were reported to function as EV receptors, in a mechanism in which fibronectin acts as a bridging molecule that interacts with both cellular and exosomal HSPGs [33,34]. …”