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.

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, ⁶⁴copper accumulation assay and tumorigenicity analysis were performed to determine the capacity of self-renewal, chemotherapy resistance and tumorigenicity of p75^NTR+ cells.

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, β1-integrin and β4-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.

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.