Institute of Radiation Medicine, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Tianjin 300192, P.R. China.
Beijing Institute of Hepatology, Beijing Youan Hospital, Capital Medical University, Beijing 100069, P.R. China.
Int J Oncol. 2017 Aug;51(2):545-554. doi: 10.3892/ijo.2017.4042. Epub 2017 Jun 14.
Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a master regulator of antioxidant and detoxification activities that can eliminate reactive oxygen species (ROS) produced via irradiation. However, Nrf2 overexpression in liver cancer cells may cause both radioresistance and chemoresistance. Reducing Nrf2 levels can enhance the radiosensitivity of HepG2 cells. Wingless/int-3A (Wnt3A) is a Wnt family protein that mainly activates the canonical Wnt signaling pathway. Recent studies showed that the Axin1-GSK-3β protein complex, a component of the canonical Wnt signaling pathway, can capture Nrf2 and facilitate its ubiquitination and proteasomal degradation in the cytoplasm. This protein complex is degraded upon activation of the Wnt signaling pathway. In the present study, we treated HepG2 cells with the Wnt3A inhibitor LGK-974, an effective and specific PORCN inhibitor that can prevent the formation of a proper folding of the Wnt protein in the endoplasmic reticulum. We found that HepG2 cells became more sensitive to radiation with increasing LGK-974 concentrations. Upon 2 Gy or 4 Gy irradiation, the cells treated with LGK-974 more frequently underwent apoptosis and grew less rapidly. PCR and western blot results showed that inhibiting the secretion of Wnt3A blocked the Wnt signaling pathway and prevented Nrf2 signaling. Notably, the Wnt inhibitor may serve as a radiosensitizing drug.
核因子（红细胞衍生 2）样 2（NRF2）是抗氧化和解毒活性的主要调节剂，可消除通过辐照产生的活性氧（ROS）。然而，肝癌细胞中 Nrf2 的过度表达可能导致放射抗性和化疗耐药性。降低 Nrf2 水平可以增强 HepG2 细胞的放射敏感性。Wingless/int-3A（Wnt3A）是一种 Wnt 家族蛋白，主要激活经典 Wnt 信号通路。最近的研究表明，经典 Wnt 信号通路的组成部分 Axin1-GSK-3β 蛋白复合物可以捕获 Nrf2，并促进其在细胞质中的泛素化和蛋白酶体降解。该蛋白复合物在 Wnt 信号通路被激活时被降解。在本研究中，我们用 Wnt3A 抑制剂 LGK-974 处理 HepG2 细胞，LGK-974 是一种有效的、特异性的 PORCN 抑制剂，可防止内质网中 Wnt 蛋白的正确折叠形成。我们发现，随着 LGK-974 浓度的增加，HepG2 细胞对辐射变得更加敏感。用 2 Gy 或 4 Gy 照射后，用 LGK-974 处理的细胞更频繁地发生凋亡，生长速度较慢。PCR 和 Western blot 结果表明，抑制 Wnt3A 的分泌阻断了 Wnt 信号通路并阻止了 Nrf2 信号。值得注意的是，Wnt 抑制剂可能作为一种放射增敏药物。
