Department of Neurosurgery, Jinling Hospital, School of Medicine, Nanjing University, Nanjing, Jiangsu 210002, PR China.
Oncol Rep. 2013 Aug;30(2):715-22. doi: 10.3892/or.2013.2485. Epub 2013 May 23.
The ERK and PI3K signaling cascades are aberrantly activated in human glioblastoma cells, resulting in the dysregulation of numerous downstream transcription factors. The dark side of the transcription factor, NF-E2-related factor 2 (Nrf2) in human cancer has been revealed. It has been accepted that high levels of Nrf2 promote tumor progression. In the present study, we investigated the effect of the ERK and PI3K signaling cascades on Nrf2 in human glioblastoma cells. Immunohistochemical staining for Nrf2 in clinical specimens showed that the expression and nuclear localization of Nrf2 were increased in human glioblastoma tissues when compared to peritumoral normal tissues. In addition, we detected decreased nuclear localization of Nrf2 following combined treatment with ERK and PI3K inhibitors in three human glioblastoma cell lines and selected the cell line (U251) most sensitive to the inhibitors for further study. Our data demonstrated that inhibition of ERK and PI3K not only suppressed the nuclear accumulation of Nrf2 protein but also decreased the expression of the Nrf2 protein. In addition, combined inhibition of ERK and PI3K also decreased the mRNA levels of Nrf2 target genes. Finally, we found that Nrf2 overexpression partly reversed the ERK and PI3K inhibitor-induced inhibition of cell viability. Therefore, the ERK and PI3K signaling cascades regulate the expression and activation of Nrf2 and control cell viability partly through Nrf2 in U251 human glioblastoma cells. Thus, targeting the ERK and PI3K signaling cascades for Nrf2 activation may provide new methods for the treatment of glioblastoma.
丝裂原活化蛋白激酶（ERK）和磷脂酰肌醇 3-激酶（PI3K）信号级联在人类脑胶质瘤细胞中异常激活，导致众多下游转录因子的失调。转录因子 NF-E2 相关因子 2（Nrf2）在人类癌症中的“阴暗面”已经被揭示。人们已经接受了高水平的 Nrf2 促进肿瘤进展的观点。在本研究中，我们研究了 ERK 和 PI3K 信号级联对人类脑胶质瘤细胞中 Nrf2 的影响。临床标本中 Nrf2 的免疫组织化学染色显示，与肿瘤周围正常组织相比，人类脑胶质瘤组织中 Nrf2 的表达和核定位增加。此外，我们在三种人类脑胶质瘤细胞系中检测到 ERK 和 PI3K 抑制剂联合处理后 Nrf2 的核定位减少，并选择对抑制剂最敏感的细胞系（U251）进行进一步研究。我们的数据表明，抑制 ERK 和 PI3K 不仅抑制了 Nrf2 蛋白的核积累，还降低了 Nrf2 蛋白的表达。此外，ERK 和 PI3K 的联合抑制也降低了 Nrf2 靶基因的 mRNA 水平。最后，我们发现 Nrf2 的过表达部分逆转了 ERK 和 PI3K 抑制剂诱导的细胞活力抑制。因此，ERK 和 PI3K 信号级联通过 Nrf2 调节 U251 人类脑胶质瘤细胞中 Nrf2 的表达和激活，并部分控制细胞活力。因此，针对 ERK 和 PI3K 信号级联以激活 Nrf2 可能为治疗脑胶质瘤提供新的方法。
