Increased expression of PDGFA and RAF1 in tumor-derived exosomes in human colorectal cancer

Background: Overexpression of tumor markers in Extracellular vesicles (EV), especially in tumor-derived exosomes (TDEs), is implicated in metastasis. However, identifying the specific content of Ev's roles in CRC diagnosis or prognosis requires further validation by bioinformatics and clinical investigations. Methods: In the current study, we explored molecular markers shared between TDEs and circulating tumor cells (CTCs) in the blood of cancer patients to identify candidate genes involved in CRC metastasis. Common markers were analyzed in gene expression profiles of two studies (GSE31023 and GSE72577). Results: In blood samples from 20 CRC patients, the expression of candidate genes was assessed by real-time PCR in CTC, TDEs, and microvesicles (MVs), and the expression levels were correlated with clinicopathological features. To further confirm, the expression of candidate genes was investigated in exosomes derived from the parental HT-29 colorectal cancer cell line (HT-29-EXOs), and CSC-enriched spheroids (CSC-EXOs) derived thereof. Gene ontology (GO) analysis suggested platelet-derived growth factor A (PDGFA) and proto-oncogene, Serine/Threonine kinase Raf-1 (RAF1) as new CRC candidate markers in CTCs and TDEs. According to real-time PCR, expression of PDGFA (P=0.0086) and RAF1 (P=0.048) were upregulated in TDEs but significantly decreased (P=0.0001) in MVs. Furthermore, expression in CSC-EXOs (P=0.0004) was increased compared to HT-29-EXOs. Conclusion: PDGFA and RAF1 mRNA are higher in CSC-EXOs than in HT-29-EXOs, which correlates with higher expression in CSC than the primary tumor. Notably, as no increase was observed in MVs, PDGFA and RAF1 mRNA appear to be actively recruited into TDE.