Macrophage mannose receptor 1 and S100A9 were identified as serum diagnostic biomarkers for colorectal cancer through a label-free quantitative proteomic analysis

BACKGROUND: Simple blood tests that could be used for early detection are crucial for the ultimate control and prevention of colorectal cancer (CRC). In this study, we performed a serum proteomic analysis of CRC and health volunteers to identify the novel biomarkers involved in CRC. METHOD: A shotgun proteomic method was applied to identify serum proteins in the serum samples of three CRC and three health volunteers using a combination of high-performance liquid chromatography and mass spectrometry. Label-free protein profiling was conducted to quantify the proteins and compare the profiles of the CRC and health volunteers. Two differentially expressed proteins were further validated by western blot analysis. Quantity analysis was performed through enzyme linked immunosorbent assay (ELISA) in serum from 96 healthy and 118 CRC volunteers. RESULTS: Among of the 373 identified proteins, 69 were linked to CRC (33 upregulated and 36 downregulated). The Gene Ontology and DAVID databases were used to identify the location and function of the different proteins. Among the 69 proteins linked to CRC, two proteins, namely, macrophage mannose receptor 1 (MRC1) and S100A9, were verified to be upregulated in CRC by western blot analysis and could be used to identify CRC from healthy volunteers with high accuracy through ELISA analysis. CONCLUSION: MRC1 and S100A9 may contribute to the determination of the mechanisms and screening involved in CRC.