In-Depth Proteomic\nAnalysis of Paraffin-Embedded Tissue\nSamples from Colorectal Cancer Patients Revealed TXNDC17 and SLC8A1\nas Key Proteins Associated with the Disease

A deeper understanding of colorectal cancer (CRC) biology\nwould\nhelp to identify specific early diagnostic markers. Here, we conducted\nquantitative proteomics on FFPE healthy, adenoma, and adenocarcinoma\ntissue samples from six stage I sporadic CRC patients to identify\ndysregulated proteins during early CRC development. Two independent\nquantitative 10-plex TMT experiments were separately performed. After\nprotein extraction, trypsin digestion, and labeling, proteins were\nidentified and quantified by using a Q Exactive mass spectrometer.\nA total of 2681 proteins were identified and quantified after data\nanalysis and bioinformatics with MaxQuant and the R program. Among\nthem, 284 and 280 proteins showed significant upregulation and downregulation\n(expression ratio ≥1.5 or ≤0.67, <i>p</i>-value\n≤0.05), respectively, in adenoma and/or adenocarcinoma compared\nto healthy tissue. Ten dysregulated proteins were selected to study\ntheir role in CRC by WB, IHC, TMA, and ELISA using tissue and plasma\nsamples from CRC patients, individuals with premalignant colorectal\nlesions (adenomas), and healthy individuals. <i>In vitro</i> loss-of-function cell-based assays and <i>in vivo</i> experiments\nusing three CRC cell lines with different metastatic properties assessed\nthe important roles of SLC8A1 and TXNDC17 in CRC and liver metastasis.\nAdditionally, SLC8A1 and TXNDC17 protein levels in plasma possessed\nthe diagnostic ability of early CRC stages.