The low affinity neurotrophin receptor p75NTR is expressed in a putative precursor fraction of esophageal squamous cell carcinoma and suppresses lymph node metastasis

Proc Amer Assoc Cancer Res, Volume 46, 2005 2052 Introduction: Several studies reported the existence of celluler hierarchy and a small number of the cells with stem cell property even in solid tumors. We have previously demonstrated that human esophageal keratinocyte stem cells are characterized by the expression of the low affinity neurotrophin receptor (p75NTR) in vitro (Oncogene 2003). We also have proposed that the p75NTR-positive putative stem cell compartment of esophageal epithelium is an initial target cell population for carcinogenesis (AACR 2004). In this study, we investigated the expression of p75NTR and the characteristics of the p75NTR-positive cells in esophageal squamous cell carcinoma (ESCC) to elucidate the possible role of p75NTR-positive cells as cancer stem cells. Methods: We detected the expression of p75NTR and proliferation marker ki67 in 187 resected ESCC specimens by immunohistochemistry. We detected the expression of p75NTR in esophageal squamous cell carcinoma cell lines (KYSEs) by RT-PCR, immunocytochemistry and flow-cytometry. We then fractionated p75NTR-positive and negative cells from a KYSE cell line by magnetic beads and investigated their colony formation. The p75NTR expression and clinicopathological factors or colony size were analyzed by χ2 analysis. The Kaplan-Meier method was used to determine the probability of survival and data was analyzed by the log-rank test. A p value of <0.05 was considered as significant. Results: p75NTR was expressed in the first 1-2 layers from the margin of the tumors in 92 of 187 (49.2%) cancer specimens. ki67staining of the same serial sections indicated that the p75NTR-positive cells are actively proliferating. The p75NTR expression was correlated with the negative lymph node metastasis (p=0.004) and lower TNM staging (p=0.023). The p75NTR positivity was a significant prognostic factor (p=0.029). p75NTR was expressed in all 30 examined KYSEs by RT PCR and immunocytochemistry. Our flow-cytometric analysis revealed that the mean proportion of p75NTR-positive fraction in each KYSE was 30.1% (ranged from 0.5% to 91.8%). p75NTR was expressed in 118 (60.8%) of 194 colonies derived from KYSE150. The mean diameter of p75NTR-positive and negative colonies were 969±513 and 414 ±182μm, respectively (p<0.0001). p75NTR was expressed in 178 (82.0%) of 217 colonies derived from p75NTR-positive fraction isolated from KYSE150, while 65 (30.1%) of 216 colonies derived from p75NTR-negative fraction expressed p75NTR. Conclusion: Our data suggested that p75NTR was expressed in a progenitor cell fraction and suppress lymph node metastasis in ESCC.