Exosomes are 40-100 nm sized extracellular membrane vesicles of late endosomal origin that can mediate intercellular communication by transferring RNAs and proteins. Using the primary (SW480) human colorectal cancer (CRC) cell line and its isogenic regional lymph node metastatic (SW620) variant, we previously compared exosome protein profiles (geLC-MS/MS and label-free quantitation) in order to gain insights into metastatic factors and signalling molecules that might contribute to tumour progression. 941 and 796 proteins were identified in exosomes derived from SW480 and SW620 cells, respectively. A major finding was the selective enrichment of protein metastatic factors (MET, S100A8, S100A9, TNC), signal transduction molecules (EFNB2, EGFR, JAG1, SRC, TNIK) and lipid raft and lipid raft-associated components (CAV1, FLOT1, FLOT2, PROM1) in exosomes derived from metastatic SW620 cells (Ji H et al 2013, PMID 23585443).
Here, we report preliminary functional properties of SW620- and SW480-Exos. Using lipophilic dye (DiI) to fluorescently label exosomes, we demonstrated that they are actively taken up by endothelial (2F2B) cells. Uptake also suggests that SW480 and SW620 exosomes could potentially propagate paracrine signalling to the endothelium. To investigate the functional significance of this uptake, we performed an in vitro angiogenesis assay which involves culturing of endothelial cells on a 3-D MatrigelTM matrix system. Our preliminary data suggests that exosomes from SW420 and SW620 cells promote differentiation of 2F2B cells into pre-mature vascular tubules that are morphologically distinct. Such stark differences in 2F2B morphology could be dictated by proteins that are differentially enriched in SW480 and SW620 exosomes. Ongoing transcriptomics and proteomic analysis of 2F2B cells following exosome uptake may potentially unravel the underlying mechanism of uptake and the observed function.