Discovery of potential colorectal cancer serum biomarkers through quantitative proteomics on the colonic tissue interstitial fluids from the AOM-DSS mouse model

Quantitative proteomic analysis was performed using iTRAQ to discover colorectal cancer (CRC)-related proteins in tissue interstitial fluids (TIFs). A typical inflammation-related CRC mouse model was generated using azoxymethane-dextran sodium sulfate (AOM-DSS), and TIFs were collected from these mice in four stages during CRC development. Using stringent criteria, a total of 144 proteins displayed changes in their abundances during tumor growth, including 45 that consecutively increased, 17 that consecutively decreased and 82 that changed irregularly. Of these 144 proteins, 24 of the consecutively changed proteins were measured using MRM in individual TIF samples, and 18 were verified. Twelve proteins verified to be consecutively increased in TIFs were examined using MRM to evaluate changes in their abundance in individual mouse serum samples. The abundances of leucine-rich alpha-2-glycoprotein 1 (LRG1), tubulin beta-5 chain (TUBB5) and immunoglobulin J chain (IGJ) were significantly higher in CRC mice than in control mice. Using clinical samples and MRM, we further verified that LRG1 and TUBB5 are potential CRC serum biomarkers. These data demonstrate that coupling dynamic TIF proteomics with targeted serum proteomics in an animal model is a promising avenue for pursuing the discovery of tumor serum biomarkers.

Biological significance: Colorectal cancer (CRC) is one of the most dangerous diseases worldwide. However, few of CRC biomarkers possess satisfied specificity and sensitivity in clinical practices. Exploration of more CRC biomarkers, especially in serum, is an urgent and also a time-consuming campaign in the CRC study. Our study demonstrates that quantitatively evaluating the phase-dependent proteins in colonic tissue interstitial fluids from AOM-DSS mice is a feasible and effective way for exploration of the CRC-related proteins and the potential serum biomarkers. We identified two proteins, LRG1 and TUBB5, which may be practicable in human clinical samples as CRC serum biomarkers. To sum up, this study provides a novel angle to explore the critical factors in tumorigenesis and a new pipeline for potential serum biomarker discovery and verification.