BackgroundGlioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioma stem cells (GSCs). Self-renewal is a complex biological process necessary for maintaining the glioma stem cells. Nuclear factor rythroid 2-related factor 2(Nrf2) plays a significant role in protecting cells from endogenous and exogenous stresses. Nrf2 is a key nuclear transcription factor that regulates antioxidant response element (ARE)-containing genes. Previous studies have demonstrated the significant role of Nrf2 in the proliferation of glioblastoma, and in their resistance to radioactive therapies. We examined the effect of knocking down Nrf2 in GSCs.MethodsNrf2 expression was down-regulated by shRNA transinfected with lentivirus. Expression levels of Nestin, Nrf2, BMI-1, Sox2 and Cyclin E were assessed by western blotting, quantitative polymerase chain reaction (qPCR) and immunohistochemistry analysis. The capacity for self-renewal in vitro was assessed by genesis of colonies. The capacity for self-renewal in vivo was analyzed by tumor genesis of xenografts in nude mice.ResultsKnockdown of Nrf2 inhibited the proliferation of GSCs, and significantly reduced the expression of BMI-1, Sox2 and CyclinE. Knocking down of Nrf2 changed the cell cycle distribution of GSCs by causing an uncharacteristic increase in the proportion of cells in the G2 phase and a decrease in the proportion of cells in the S phase of the cell cycle.ConclusionsNrf2 is required to maintain the self-renewal of GSCs, and its down-regulation can attenuate the self-renewal of GSCs significantly.

Concerns were increasingly raised that several types of cancers overexpressed the nuclear factor erythroid 2-related factor 2 (Nrf2), which contributed strikingly to cancer biological capabilities and chemoresistance. However, the role of Nrf2 in the tumor vascular biology had yet to be mechanistically determined. Here, we investigated the involvement of Nrf2 in glioblastoma (GB) angiogenesis in hypoxia. First, we detected the overexpression of Nrf2 and correlated its protein level with microvessel density (MVD) in human GB tissues. Then, we established the stable RNAi-mediated Nrf2-knockdown cells and mimicked hypoxic condition in vitro. The knockdown of Nrf2 inhibited cell proliferation in vitro and suppressed tumor growth in mouse xenografts with a concomitant reduction in VEGF expression and MVD. Similar antiangiogenic effects were documented in endothelial tube formation assays. The downregulation of Nrf2 in glioma cells led to much lower accumulation of HIF-1α protein and limited expression of VEGF and other HIF-1α target genes in mimicking hypoxia. Mechanistic investigations suggested that HIF-1α degradation during hypoxia could be attributed to reduced mitochondrial O2 consumption in Nrf2-inhibited cells. It can be concluded that Nrf2, with its capacity for affecting the protein level of HIF-1α expression, has good reasons to be considered as a critical transcription factor for controlling glioma angiogenesis.

Mutual association between Nrf2 and HIF-1alpha was found in GB: higher Nrf2 expression and poorer outcome of GB patients. Nrf2 would therefore be a new molecular marker for the targeted treatment of GB.