Down-regulated expression of complement factor I: A potential suppressive protein for gastric cancer identified by serum proteome analysis

BackgroundScreening tests are needed for gastric cancer. In order to find serologic biomarkers for gastric cancer screening, we used proteomics to search for protein biomarkers that may be detected in serum of gastric cancer patients.MethodsFour groups of serum samples (from 20 gastric cancer patients) included pTNM stages I to IV were compared with two control groups of serum samples. The serum samples were first chromatographed using an immunoaffinity column to selectively remove albumin and IgG. Then serum proteins separated by 2-DE and identified by MALDI–TOF/TOF–MS.ResultsThere were 3 proteins including complement C4-B precursor, complement factor I (CFI) precursor and haptoglobin precursor were found significantly different between the healthy and gastric cancer patients. Further validation study by Western blot showed that the detection of CFI precursor was under-expressed in gastric cancer sera compared to normal sera (p < 0.05), in addition to a declining expression with the advanced pTNM stage from stage I to IV of gastric cancer patients. Area under the receiver operating characteristic (ROC) curve was 0.78 for the expression of CFI precursor (p < 0.01).Conclusions2-DE-based serum proteome analysis may be useful in the screening of serum biomarkers for gastric cancer. CFI precursor could aid in the diagnosis and indicate the advancement of gastric cancer.