Self-renewal and chemotherapy resistance of p75NTR positive cells in esophageal squamous cell carcinomas

p75NTR expression in ESCC was assessed by immunohistochemistry. p75NTR+ and p75NTR- cells of 4 ESCC cell lines were separated by fluorescence-activated cell sorting. Differentially expressed genes between p75NTR+ and p75NTR- cells were determined by real-time quantitative reverse transcription-PCR. Sphere formation assay, DDP sensitivity assay, 64copper accumulation assay and tumorigenicity analysis were performed to determine the capacity of self-renewal, chemotherapy resistance and tumorigenicity of p75NTR+ cells.In ESCC specimens, p75NTR was found mainly confined to immature cells and absent in cells undergoing terminal differentiation. The percentage of p75NTR+ cells was 1.6%–3.7% in Eca109 and 3 newly established ESCC cell lines. The expression of Bmi-1, which is associated with self-renewal of stem cells, was significantly higher in p75NTR+ cells. p63, a marker identified in keratinocyte stem cells, was confined mainly to p75NTR+ cells. The expression of CTR1, which is associated with cisplatin (DDP)-resistance, was significantly decreased in p75NTR+ cells. Expression levels of differentiation markers, such as involucrin, cytokeratin 13, β1-integrin and β4-integrin, were lower in p75NTR+ cells. In addition, p75NTR+ cells generated both p75NTR+ and p75NTR- cells, and formed nonadherent spherical clusters in serum-free medium supplemented with growth factors. Furthermore, p75NTR+ cells were found to be more resistant to DDP and exhibited lower 64copper accumulation than p75NTR- cells.Our results demonstrated that p75NTR+ cells possess some characteristics of CSCs, namely, self-renewal and chemotherapy resistance. Chemotherapy resistance of p75NTR+ cells may probably be attributable to decreased expression of CTR1.The "cancer stem cell" theory has aroused increasing interest in the field of oncology [1-4]. According to this theory, cancer stem cells (CSCs), which account for a very small proportion of tumor tissue, have the self-renewal property typical of normal