Comparative proteomic analysis identifies exosomal Eps8 protein as a potential metastatic biomarker for pancreatic cancer

Abstract

Exosomes are small vesicles found in extracellular environments including blood, urine, and cell culture medium. Their contents are cell-type specific, and molecules embedded in exosomes can be useful fluid-based clinical biomarkers. To identify proteins with metastatic marker potential, we conducted a comparative exosomal proteome analysis using human pancreatic cancer cell lines derived from metastasis, ascites, and primary tumors. Metastatic potential of cell lines was assessed by migratory and invasive activities. A pancreatic cancer cell line from metastasis (SU.86.86) revealed 23-fold and 20-fold increases in cell migratory and invasive activities, respectively, compared to the MIA PaCa-2 cell line derived from primary tumor cells. Liquid chromatography-mass spectrometry-based proteome analysis and subsequent validation by immunoblot analysis revealed that epidermal growth factor receptor pathway substrate 8 (Eps8) was highly abundant in exosomes from metastasis-derived SU.86.86 cells. Comparison of 12 pancreatic cancer cell lines derived from different stages of malignancy revealed a strong relationship between exosomal Eps8 protein levels and cell motile activities (migration: r=0.85, P=4.2x10-4; invasion: r=0.60, P=3.2x10-2). Conversely, relationships between intracellular Eps8 protein levels and cell motile activities were moderate (migration: r=0.65, P=2.0x10-2; invasion: r=0.51, P=9.2x10-2). It was therefore concluded that exosomal Eps8 protein levels were correlated with the migratory cell potential of human pancreatic cancer cells, indicating that exosomal Eps8 has the potential to be a metastatic biomarker for human pancreatic cancer.