Absence of CD71 Transferrin Receptor Characterizes Human Gastric Adenosquamous Carcinoma Stem Cells

Background. Although the importance of cancer stem cells (CSCs) in overcoming resistance to therapy and metastasis has recently been reported, the role of CSCs in gastric cancer remains to be elucidated. Methods. MKN-1 cells were used to study markers of CSCs in gastric adenosquamous carcinoma, as these cells are suitable for determining multidifferentiation ability. Changes in expression of CD44, CD49f, CD133, and CD71 following 5-fluorouracil (5-FU) treatment were assessed. Results. After 5-FU treatment, only the CD71(-) fraction was significantly increased. Investigation of CD71 indicated that the CD71(-) cell fraction was present in the G1/G0 cell cycle phase and showed high resistance to the anticancer agent 5-FU. Limiting dilution and serial transplantation assays revealed the CD71(-) cell fraction to have higher tumorigenicity than the CD71(+) cell fraction. The CD71(-) cell fraction showed multipotency to adenocarcinoma and squamous cell carcinoma. A three-dimensional (3D) invasion assay and immunohistochemical analysis showed CD71(-) cells to be highly invasive and to exist in the invasive fronts of cancer foci. Conclusion. The present study suggests that use of CD71(-) as a marker for adenosquamous carcinoma may provide a useful model for studying CSCs.