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

Background: p75(NTR) has been used to isolate esophageal and corneal epithelial stem cells. In the present study, we investigated the expression of p75(NTR) in esophageal squamous cell carcinoma (ESCC) and explored the biological properties of p75(NTR+) cells. Methods: p75(NTR) expression in ESCC was assessed by immunohistochemistry. p75(NTR+) and p75(NTR-) cells of 4 ESCC cell lines were separated by fluorescence-activated cell sorting. Differentially expressed genes between p75(NTR+) and p75(NTR-) cells were determined by real-time quantitative reverse transcription-PCR. Sphere formation assay, DDP sensitivity assay, (64)copper accumulation assay and tumorigenicity analysis were performed to determine the capacity of self-renewal, chemotherapy resistance and tumorigenicity of p75(NTR+) cells. Results: In ESCC specimens, p75(NTR) was found mainly confined to immature cells and absent in cells undergoing terminal differentiation. The percentage of p75(NTR+) 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 p75(NTR+) cells. p63, a marker identified in keratinocyte stem cells, was confined mainly to p75(NTR+) cells. The expression of CTR1, which is associated with cisplatin (DDP)-resistance, was significantly decreased in p75(NTR+) cells. Expression levels of differentiation markers, such as involucrin, cytokeratin 13, beta 1-integrin and beta 4-integrin, were lower in p75(NTR+) cells. In addition, p75(NTR+) cells generated both p75(NTR+) and p75(NTR-) cells, and formed nonadherent spherical clusters in serum-free medium supplemented with growth factors. Furthermore, p75(NTR+) cells were found to be more resistant to DDP and exhibited lower 64copper accumulation than p75(NTR-) cells. Conclusion: Our results demonstrated that p75(NTR+) cells possess some characteristics of CSCs, namely, self-renewal and chemotherapy resistance. Chemotherapy resistance of p75(NTR+) cells may probably be attributable to decreased expression of CTR1.