Details of
metastasis, the deadliest aspect of
cancer, are unclear.
Cell surface proteins play central roles in adhesive contacts between the
tumor cell and the stroma during
metastasis. We optimized a fast, small-scale isolation of biotinylated
cell surface proteins to reveal novel
metastasis-associated players from an isogenic pair of human MDA-MB-435
cancer cells with opposite metastatic phenotypes. Isolated
proteins were
trypsin digested and analyzed using LC-MS/MS followed by quantitation with the Progenesis LC-MS software. Sixteen
proteins displayed over twofold expression differences between the metastatic and non-metastatic cells. Interestingly, overexpression of most of them (14/16) in the metastatic cells indicates a gain of novel
surface protein profile as compared to the non-metastatic ones. All five validated, differentially expressed
proteins showed higher expression in the metastatic cells in culture, and four of these were further validated in vivo. Moreover, we analyzed expression of two of the identified
proteins, CD109 and ITGA6 in 3-dimensional cultures of six
melanoma cell lines. Both
proteins marked the surface of cells derived from
melanoma metastasis over cells derived from primary
melanoma. The unbiased identification and validation of both known and novel
metastasis-associated
proteins indicate a reliable approach for the identification of differentially expressed
surface proteins.