Cancer burdens and death are largely due to metastasis. Much effort has been put in to study how cancer cells metastasize. Emerging evidence implicates cancer cells at the leading edge of a tumour undergo epithelial-mesenchymal transition (EMT) and enhance cell migration and invasion. EMT facilitates the loss of epithelial cell architecture and acquisition of mesenchymal cell characteristics. Understanding this cellular process would probably enable better management of cancer metastasis.
Soluble-secreted proteins in the tumour microenvironment have been shown to facilitated EMT, and in this study we report a further component of the secretome - exosomes during EMT. Exosomes are nanomembranous vesicles (40-100 nm) of endocytic origin released into the extracellular environment which have diverse biological functions including antigen presentation, mRNA/ protein transfer, and cancer cell invasion.
To gain insights into the roles of exosomes in EMT, we conducted an in vitro study to isolate and characterise exosomes from Madin-Darby canine kidney (MDCK) cells as an epithelial model and Ras-transformed MDCK cells (21D1) as a mesenchymal model. Exosomes were isolated using ultracentrifugation and OptiPrepTM-based density fractionation. Proteomic profiling of exosomes using GeLC-MS/MS resulted in the identification of 382 and 400 proteins in MDCK and 21D1-derived exosomes, respectively. Protein classes shown to be dysregulated in exosomes during EMT include various components linked to cancer progression and the pre-metastatic niche including MMPs, annexins, S100 subunits and integrin subunits. These initial findings make exosomes a promising platform for further research to understand EMT.