Effects of Bmi1 gene on endothelial cells promoting glioma stem cell-like phenotype

Abstract

To explore the effects of B-cell specific Maloney leukemia virus integration site 1 (Bmi1) gene on endothelial cells promoting glioma stem cell (GSC)-like phenotype. Glioblastoma cell line GL261 and brain micro-vessel endothelial cell line b.END3 were used. Transwell co-culture system, limit dilution assay, xenograft, real-time polymerase chain reaction (PCR), Western blot, fluorescence activating cell sorter (FACS) and gene knock-down assay were used to determine the GSC-like phenotype and Bmi1 gene expression in glioma cells. Compared with the control of GL261 cell alone, (1) more and larger tumor spheres formed after co-culturing with endothelial cells (62.5% ± 1.5% vs 25.0% ± 4.6% at 40 cells/well, P = 0.000). Xenografts generated by GL261 cells with b.END3 cells appeared earlier and were larger than that by GL261 cells alone ((0.798 ± 0.297) cm(3) vs (0.362 ± 0.123) cm(3), P = 0.000); (2) CD133 positive glioma cells increased after co-culturing with endothelial cells (8.48% ± 0.78% vs 4.81% ± 0.37%, P = 0.000); (3) the expression of Bmi1 in co-cultured glioma cells was up-regulated at mRNA level (2.72 ± 0.18 vs 1.00 ± 0.15, P = 0.000) and at protein level; (4) the above phenomenon was attenuated when Bmi1 gene expression was inhibited by siRNA in glioma cells, CD133 positive portion of Bmi1-knockdown GL261 cells co-culturing with b.END3 cells decreased than that of wildtype GL261 cells (0.34% ± 0.21% vs 1.70% ± 0.69%, P = 0.025). Endothelial cells promote GSC-like phenotype by up-regulating the expression of Bmi1 in glioma cells.