Decoding the Apical–Basal Surfaceome of Colon Epithelial Cells via Side-Selective Biotinylation

Colorectal cancer (CRC) is the third most common malignancy worldwide. Detailed characterization of cell surface proteins (CSPs) is essential for the identification of prognostic biomarkers and the development of novel therapeutic strategies. Cancer progression and epithelial cell polarity influence the expression levels and subcellular localization of these proteins. However, quantitative information on the distribution of CSPs between the apical and basolateral membranes remains limited, particularly in CRC cells. Here, we developed a rapid, high-throughput method based on the enrichment of biotinylated peptides and proteins from the apical and basolateral surfaces of polarized CRC epithelial cells (HT29 and HCT116), followed by LC-MS/MS analysis. This approach enables the simultaneous identification of the side-specific distribution of ~1200 CSPs. In addition, almost 500 potential N-glycosylation sites with the canonical consensus sequence of these proteins were identified, which may serve as targets for future site-specific glycosylation analyses. To evaluate the sensitivity of the method, we altered the surface proteome by generating TKS4-knockout cells and identified several surface markers whose expression levels differed significantly from those of wild-type cells. Overall, our findings provide new insights into the role of CSPs in CRC cells and gene-edited models, particularly in the context of TKS4-dependent epithelial-to-mesenchymal transition (EMT)-like phenotypes that model cancer metastasis.