Introduction: There is emerging concern that several types of cancers overexpress NF-E2-related factor 2 (Nrf2), which is related to tumor cell chemoresistance and proliferation. But the role of Nrf2 in the tumor vascular biology has yet to be mechanistically determined. Here we studied the involvement of NRF2 in gliblastoma angiogenesis in hypoxia.
Methods: Two kinds of stable RNAi-mediated plasmids, pEGFP-Nrf2 and Si-Nrf2, were constructed and transfected into the U251 and U87 glioma cell lines to upregulate or downregulate the Nrf2 expression. The mimicking hypoxic condition was established by hypoxic chamber and CoCl2 treatment in vitro. Protein, mRNA and the DNA binding activity of Nrf2 and HIF-1a were investigated in the transfected cells in hypoxia. The supernatants of glioma cell cultures were collected to assess the VEGF by ELISA and to perform endothelial tube formation assays. Tumor vessel formation were assessed in nude mouse xenografts and chick chorioallantoic membrane(CAM) assays.
Results: In Nrf2-upregulated cell lines in hypoxia, the levels of HO-1 mRNA and protein were higher than the control, and it accumulated more HIF-1a protein, with a higher expression of VEGF. It also promoted the vessel formation in the mouse xenografts, CAM assays and the endothelial tube formation assays, While in Nrf2-downregulated cell lines, the mRNA level of HO-1 and the expression of HO-1 and HIF-1a were much lower than the control, with a concomitant reduction of VEGF expression. The kockdown of Nrf2 suppressed tumor growth and blood vessel formation in mouse xenografts and there was a similar anti-angiogenic effect in CAM assays and endothelial tube formation assays. Yet the mRNA level of HIF-1a was not affected by the different expression of Nrf2.
Conclusions: Nrf2, as a critical transcription factor, plays a candidate role in controlling glioma angiogenesis, probably by affecting the protein level of HIF-1a expression.
Patient Care: We hope these will improve the understanding of the mechanism about glioma vascular biology, provide a thought of new therapeutic target and ameliorate the prognosis of malignant gliomas.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of experimental tumor research in the neuroscience, 2) Discuss, in small groups,the new therapeutic targets in gliomas, 3) Identify an effective treatment on glioma patients.