Identification of the Differentially Expressed Proteins in the PBMC of Colorectal Cancer by DIA-MS

The colorectal cancer (CRC) is one of the most common malignant tumors of digestive system, and has a complex process of development and progression. Its development is a complex and multistep process so the occurrence of CRC may influence organism immune and cause change of immunity. There are lots of researches demonstrating the immune system’s reaction during the occurrence or development of the malignancy. Peripheral blood mononuclear cell (PBMC) is an ideal sample to study the immune functions, which is main part of the immune system and easily available. In this study, a novel MS method, data independent acquision (DIA) was utilized, which has high specificity and coverage, to perform protein quantitation and find out differentially expressed proteins between the peripheral blood mononuclear cells (PBMC) of CRC and benign intestines disease. Based on the quantified results, 113 differentially expressed proteins (p<0.05) were identified, including 23 up-regulated proteins and 90 down-regulated proteins. The gene ontology (GO) and reactome pathway enrichment analyses of the up-regulated proteins and the down-regulated proteins were performed separately. GO analysis results showed that down-regulated proteins were significantly enriched in platelet degranulation, regulated exocytosis, exocytosis, vesicle-mediated transport and secretion by cell and secretion biological processes (BP). For molecular function (MF) analysis, the down-regulated proteins were enriched in cell adhesion molecule binding, cadherin binding involved in cell-cell adhesion, protein binding involved in cell-cell adhesion, protein binding involved in cell adhesion, cadherin binding. And GO cell component (CC) analysis showed that the downregulated proteins were significantly enriched in the membrane-bounded vesicle, extracellular exosome, extracellular vesicle, extracellular organelle, extracellular region part, extracellular region, while up-regulated proteins were not enriched in any cell component. The reactome pathway analysis showed the down-regulated proteins were enriched in Platelet degranulation, MAP2K and MAPK activation, P130Cas linkage to MAPK signaling for integrins, GRB2: SOS provides linkage to MAPK signaling for integrins, integrin alphaIIb beta3 signaling, common pathway of fibrin clot formation, integrin cell surface interactions, RHO GTPases activate PAKs, RHO GTPases activate PKNs pathway. The up-regulated proteins were enriched in SRP-dependent cotranslational protein targeting to membrane pathways. Especially, the up-regulated protein Galectin-1 and the downregulated ones Dok-2, AHNAK1 are expected to be biomarkers of CRC in PBMC, which are closely related to immune function. They all involve in kinds of immune activities of macrophage, T cell and dendritic cell and are expected to be biomarkers of CRC in PBMC.