Quantitative analysis of caveolin-rich lipid raft proteins from primary and metastatic colorectal cancer clones

Caveolin-rich lipid rafts (CLRs) are thickened sections of the cell membrane that are composed of the integral membrane proteins caveolins together with saturated long chain fatty acids, cholesterol and lipids. Membrane proteins - lipid raft proteins in particular - may play important roles in cell signaling and cell-cell interaction. Due to their unique structure, CLRs seem to be the preferred docking site for specific proteins involved in focal adhesion and cancer metastasis. Our objective was thus to identify and quantify CLR proteins from primary and metastatic colorectal cancer (CRC) clones. We found differential expression of nine CLR proteins from primary and metastatic CRC clones. Among the identified proteins, an immune system inhibiting protein was significantly overexpressed in the metastatic clone, while cell adhesion and transport molecules were among the overexpressed proteins in the primary clone. All the identified CRL proteins are involved in tumorigenesis, specifically metastasis, and may thus serve as therapeutic targets. A novel concept for identification and quantification of CLR proteins with label-free mass spectrometry method was specifically examined in this study. Validation of the method against immunoblotting and FACS analysis indicates that it can be applied for the identification of novel biomarkers for cancer and metastasis.