Background: p75NTR has been used to isolate esophageal and corneal epithelial stem cells. In the present study, we investigated the expression of p75NTR in esophageal squamous cell carcinoma (ESCC) and explored the biological properties of p75NTR+ cells.
Methods: 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.
Results: 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, beta1-integrin and beta4-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.
Conclusion: 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.