Colorectal cancer (CRC) is one of the most prevalent cancers worldwide. The discovery of non-invasive biomarker candidates for diagnosis and prognosis is important for the management of CRC. In this study, we performed proteomic profiling of serum from patients with different stages of CRC using a 2D-LC-MS/MS based approach combined with the APEX quantitative method. 917 proteins were identified and 93 were differentially expressed in normal and three patient groups (stages I, II and III). These proteins were predominantly involved in cell adhesion, immune response, coagulation process and metabolism. Importantly, we found collagen I dynamically changed from stages I to IV, with maximum expression in stage II, as detected in serum by MS analysis. Expression of collagen I was also validated in tumor tissues from the same group of CRC patients by real-time PCR and western blotting. Furthermore, we demonstrate that serum levels of collagen I degradation telopeptide (CTx) are correlated with staging and poor disease-free survival of CRC patients by ELISA analysis. These results suggest (1) serum proteomics may reflect biological changes in colorectal tumor tissues and (2) altered collagen I expression may be an early event in CRC tumorigenesis and CTx may provide additional information for prognosis of CRC.
Biological significance: In this work, we performed a systematic characterization of serum proteomic alterations in colorectal cancer (CRC) with different stages using a LC-MS based approach combined with the APEX quantitative method, attempting to gain overview of relevant proteins in tumorigenesis and discover non-invasive CRC-derived markers. We found a significant up-regulation of collagen I based on the proteomics data, and confirmed its expression in tissue and serum of the same group of patients. In addition, we also demonstrated that serum levels of collagen I degradation telopeptide (CTx) are correlated with the staging and poor survival rate of CRC. Those findings imply that alternation of collagen I might be an early event during tumorigenesis of CRC, and might contribute to the metastasis of CRC under the degradation regulated by some specific proteases. This work provides evidence for the clinical application of serum proteomics, and would aid the understanding of the role of the ECM in the clinical progression of CRC.
Keywords: 2D-LC–MS/MS; APEX; AUC; C-terminal telopeptide of type I collagen; CEA; COL1A1; COL1A2; CRC; CRC tumorigenesis; CTx; Collagen I; Colorectal cancer; ECM; EMT; MMPs; PICP; ROC; UICC; Union Internationale Contre Le Cancer; absolute protein expression; area under the curve; carboxyterminal propeptide of type I collagen; carcinoembryonic antigen; colorectal cancer; epithelial-mesenchymal transition; equal to type I collagen in this study; extracellular matrix; matrix metalloproteinases; receiver operating characteristic; two-dimensional liquid chromatography with tandem mass spectrometry; α1 chain of type I collagen; α2 chain of type I collagen.