Recently, cancer stem cells (CSCs), which possess the capacity for self-renewal and generate the progenies of different phenotypes from parental cells, were identified in the solid tumors and maintained in vitro (Al-Haij et al, 2003, Singh et al, 2004, Yuan et al, 2004). In this study, we separated the CSCs from a human esophageal squamous cell carcinoma cell line (KYSE70). KYSE70 cells formed morphologically variable colonies in one dish: a densely mounding type (M-type), a flat, diffusive type (F-type), and a type with mixed mounding and flat cells (M/F-type). Classification of colonies into three types made possible to evaluate the extent of morphological heterogeneity. The proportion of M-type colonies decreased with increasing X-ray dose. In contrast, the proportions of M/F- and F-type colonies increased with increasing dose. X-ray irradiation seemed to stimulate the cells to transform from M-type to F-type. Two clones (EC13M and EC13F) were separated from one clone (clone 13) of the KYSE70 cells. The EC13M cells produced three types of colonies. The EC13F cells mainly produced the F-type colonies, but not M-type colonies. Clustering analysis for gene expression level by oligonucleotide microarray demonstrated that the EC13F cells were less closely related to the parental KYSE70 cells than were the EC13M cells. Gene Ontology analysis demonstrated that ARHE, ARHGDIB, COL5A1, CYR61, DLC1, ESDN, LAMC2, NELL2, OLR1, PCDH11Y, PTPNS1, TGFB1, CDC42EP3 and LCP1 were up-regulated in the EC13F cells. These genes were involved in the regulation of cell adhesion, cell motility and/or cellular morphogenesis. The diffusive EC13F cells may be more active in migrating into other tissues than the mounding cells. The tumor recurred after radiation therapy is usually more malignant than the primary tumor. Our data provide a clue as to why metastatic cells appear in the tissues of tumors that recur after radiotherapy.HUGO\u27s 10th Human Genome Meeting (HGM2005
