CD51 correlates with the TGF-beta pathway and is a functional marker for colorectal cancer stem cells

Colorectal cancer (CRC) is one of the top three most prevalent and deadly cancers. A cancer stem cell (CSC) sub-population that is characterized by the abilities of tumor initiation, self-renewal, metastasis and resistance to chemotherapy can suggest new therapeutic targets. However, no such sub-population has been conclusively identified for CRC, and we lack any marker to identify cells with all of the above characteristics. Here, we report that CD51⁺ CRC cells displayed greater sphere-forming and tumorigenic capacities, increased migratory and invasive potentials, and enhanced chemoresistance compared with CD51^- CRC cells. CD51 knockdown reduced the side population, sphere formation, cell motility and inhibited tumor incidence and metastasis in an in vivo tumor model. Furthermore, CD51 could bind transforming growth factor beta (TGF-β) receptors, and that it upregulated TGF-β/Smad signaling. These results indicate that CD51 is a novel functional marker for colorectal CSCs which may provide an therapeutic target for the efficient elimination of colorectal CSCs.