Expression of NANOG in human gliomas and its relationship with undifferentiated glioma cells

Stemness genes, including NANOG, which have been reported to play a significant role in embryonic stem cells (ESCs), are purported to be expressed in specific human tumor types. In the present study, we explored the expression of NANOG in gliomas to demonstrate its key roles in maintaining the undifferentiated state of glioma cells. Brain tumor stem cells (BTSCs) were isolated from the human glioma cell line U87 and cultured in simplified serum-free medium. Significantly higher NANOG mRNA and protein expression levels were demonstrated in U87 parental attached cells and suspended BTSCs as well as in 69 glioma specimens of different pathological grades. The relative levels of NANOG mRNA and protein expression were higher in the BTSCs as compared to those in the U87 parental attached cells and were significantly positively correlated with pathological grade. The coexpression and relationship of NANOG, CD133 and GFAP in situ in the cellular levels was determined through double-label immunohistochemical staining in the gliomas. A positive correlation of NANOG and CD133 expression with pathological grade of the samples was noted, while NANOG and GFAP expression correlated negatively with the pathological grade (P<0.01). Overexpression of NANOG in gliomas and its close relationship with the undifferentiated state of glioma cells in vivo and in vitro indicated that NANOG may contribute to the existence of BTSCs and may be related to tumorigenesis of the cerebrum by maintaining the undifferentiated state of glioma cells, which provides a foundation to further explore its role in the biological behavior of gliomas.