Quantitative Proteomic Analysis of Small and Large Extracellular Vesicles (EVs) Reveals Enrichment of Adhesion Proteins in Small EVs

Extracellular vesicles (EVs) are
important mediators of cell–cell
communication due to their cargo content of proteins, lipids, and
RNAs. We previously reported that small EVs (SEVs) called exosomes
promote directed and random cell motility, invasion, and serum-independent
growth. In contrast, larger EVs (LEVs) were not active in those assays,
but might have unique functional properties. In order to identify
protein cargos that may contribute to different functions of SEVs
and LEVs, we used isobaric tags for relative and absolute quantitation
(iTRAQ)–liquid chromatography (LC) tandem mass spectrometry
(MS) on EVs isolated from a colon cancer cell line. Bioinformatics
analyses revealed that SEVs are enriched in proteins associated with
cell–cell junctions, cell–matrix adhesion, exosome biogenesis
machinery, and various signaling pathways. In contrast, LEVs are enriched
in proteins associated with ribosome and RNA biogenesis, processing,
and metabolism. Western blot analysis of EVs purified from two different
cancer cell types confirmed the enrichment of cell–matrix and
cell–cell adhesion proteins in SEVs. Consistent with those
data, we found that cells exhibit enhanced adhesion to surfaces coated
with SEVs compared to an equal protein concentration of LEVs. These
data suggest that a major function of SEVs is to promote cellular
adhesion.