Differential expression of nucleostemin, a stem cell marker, and its variants in different types of brain tumors

Nucleostemin (NS) is implicated in the control of stem and cancer cell proliferation. In the present study, we have examined the expression of NS and its spliced variants in various brain tumors. Total RNA was extracted from 59 brain tumor samples, and the expression of different NS spliced variants was measured by semi-quantitative RT-PCR. The subcellular distribution of NS protein in brain tumors was further examined by immunohistochemistry. Furthermore, to decipher the potential involvement of NS in brain tumorogenesis, its expression was knocked-down by means of RNA interference (RNAi) in two malignant glioma (U-87MG and A172), one astrocytoma (1321N1) and one medulloblastoma (DAOY) cell lines. The alterations in cell-cycle progression of the treated cells were then analyzed by flow cytometry. Our data revealed that NS and its variants are widely expressed in different types of brain tumors. Among the NS spliced variants, variant "1" and variant "3" were detected in the majority of tumor samples, whereas variant "2" was only detectable in few samples. Moreover, the intensity of the expression was correlated with the grade of the tumors (P < 0.05). Accordingly, the expression was much higher in glial tumors compared to that of meningiomas. As expected, a nucleolar/nucleoplasmic localization of NS protein was observed in the examined tumor samples. RNAi results revealed a significant reduction of NS expression along with a moderate blockade of the cell cycle in G(2)/M and S phases of NS-siRNA treated cells. All in all, our data suggest a potential role for NS in tumorogenesis of brain cancers.