Characterization and proteomic profiling of pancreatic cancer-derived serum exosomes

Pancreatic cancer (PC) is one of the most lethal cancers known worldwide, and its prognosis is poor in most patients. Exosomes are nanosized extracellular vesicles, which are released from various cell types. They are involved in cellular communication. The diagnosis and treatment of PC were improved substantially with exosomes. In this study, we isolated PC-derived exosomes and investigated their proteomic profile. Then, we conducted bioinformatic analysis on proteomic data. Differential ultracentrifugation was performed to isolate exosomes from human serum samples and four PC cell lines. Transmission electron microscopy and Western blot analysis were used to characterize the isolated exosomes. Liquid chromatography coupled with tandem mass spectrometry was conducted to identify the proteome of serum exosomes. Proteomic analysis demonstrated that all the serum exosomes were derived from three cohorts of human subjects; these serum exosomes contained a total of 655 proteins, out of which 315 proteins overlapped with ExoCarta database. Gene oncology and kyoto encyclopedia of genes and genomes analyses provided the functional annotation of the proteome. Interestingly, 18 or 14 proteins were upregulated and 11 or 14 proteins were downregulated in serum exosomes derived from patients with PC as compared with in serum exosomes derived from healthy volunteers or from pancreatitis patients respectively. Annexin A11, a calcium-dependent phospholipid-binding protein, was expressed in a PC cell line (CFPAC-1)-derived exosomes and in tumor tissues of patients with PC, respectively. Our data provided a basic foundation for further studies on the protein composition of PC-derived exosomes and its involvement in PC biology.