Proteomics and liquid biopsy characterization of human EMT-related metastasis in colorectal cancer

Abstract Introduction: Circulating tumor cells (CTCs) undergo epithelial-mesenchymal transition (EMT), and the heterogeneity of EMT possibly affects colorectal cancer metastasis (mCRC) evolution. The aim of this study was to identify novel metastasis-related proteins and EMT-related pathways.Methods: The EMT status of the CTCs derived from CRC patients with liver metastasis was determined on the basis of surface markers. Comparative proteomic analysis was then performed on matched pairs of primary tumors, adjacent para-tumor and liver metastases tissues. An optimized proteomic workflow including data independent acquisition (DIA) and parallel reaction monitoring (PRM) was used to screen for novel EMT-related protein clusters. Results: The proportion of the unstable epithelial/mesenchymal (E/M)-type CTCs correlated significantly with distant metastases. We screened 105 proteins related to EMT from 4,752 proteins identified in all samples, of which 40 proteins were differentially expressed across the different tissues. We identified a novel EMT-related protein cluster (e.g., GNG2, COL6A1, COL6A2, DCN, COL6A3, LAMB2, TNXB, CAVIN1) and found that the expression levels of the core EMT-related proteins KRAS and ERBB2 were altered during metastasis progression. The proteomics data indicated that KRAS, ERBB2, COL6A1 and CAVIN1 are promising EMT-related metastatic biomarkers.Conclusions: The plasticity of EMT phenotypes in the CTCs are key to CRC metastasis, prognosis and treatment outcome. Therapies targeting this aggressive CTC subset and the related proteins may suppress metastatic evolution.