Park J S, Qiao L, Su Z Z, Hinman D, Willoughby K, McKinstry R, Yacoub A, Duigou G J, Young C S, Grant S, Hagan M P, Ellis E, Fisher P B, Dent P
Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia, VA 23298, USA.
Oncogene. 2001 May 31;20(25):3266-80. doi: 10.1038/sj.onc.1204258.
We investigated the role of radiation-induced mitogen activated protein kinase (MAPK) pathway activity in the regulation of proliferation, cell survival and vascular endothelial growth factor (VEGF) production in primary astrocytes and in T9 and RT2 glioblastoma cells derived from Fisher 344 rats. In these cells, ionizing radiation (2 Gy) caused activation of the MAPK pathway which was blocked by specific inhibitor drugs. Blunting of radiation-induced MAPK activity weakly enhanced radiation-induced apoptosis 24 h after exposure in RT2 cells. Furthermore, blunting of MAPK activation weakly enhanced the ability of radiation to reduce RT2 cell growth in clonogenic growth assays. These findings argue that inhibition of MAPK signaling reduces proliferation and enhances cell killing by ionizing radiation in transformed astrocytes. Proliferation and survival of cancer cells has been linked in vivo to enhanced expression of angiogenic growth factors. Recently we demonstrated that the gene product of a novel rodent radiation-responsive gene, progression elevated gene 3 (PEG-3), could enhance vascular endothelial growth factor (VEGF) promoter activity in rodent fibroblasts, leading to increased VEGF protein levels and tumorigenic behavior in vivo. Thus PEG-3 and VEGF expression could be expected to directly correlate with the oncogenic potential of transformed cells. RT2 cells expressed more PEG-3 and VEGF protein than T9 cells, and were more tumorigenic in vivo than T9 cells. Radiation activated the PEG-3 promoter via MAPK signaling and ectopic over-expression of PEG-3 enhanced both basal MAPK activity and basal VEGF promoter activity. Basal MAPK activity partially correlated with basal VEGF promoter activity and VEGF protein levels in primary astrocytes, T9 and RT2 cells. Radiation increased the activity of the VEGF promoter and VEGF protein levels in primary astrocytes, T9 and RT2 cells which were dependent upon MAPK function. Furthermore, inhibition of AP-1 transcription factor signaling by dominant negative c-Jun (TAM67) also significantly reduced basal, and to a lesser extent radiation-induced, VEGF promoter function in RT2 cells. Collectively, our data demonstrate that radiation-induced MAPK signaling can both protect cells from radiation-induced cell death as well as enhance protein levels of pro-angiogenic factors such as VEGF. Enhanced VEGF expression in RT2 cells may be mediated via MAPK and JNK pathway signaling which converges upon the AP-1 transcription factor complex.
我们研究了辐射诱导的丝裂原活化蛋白激酶（MAPK）信号通路活性在原代星形胶质细胞以及源自Fisher 344大鼠的T9和RT2胶质母细胞瘤细胞的增殖、细胞存活和血管内皮生长因子（VEGF）产生调控中的作用。在这些细胞中，电离辐射（2 Gy）可导致MAPK信号通路激活，而该激活可被特异性抑制剂药物阻断。在RT2细胞中，辐射诱导的MAPK活性减弱在照射24小时后可轻度增强辐射诱导的细胞凋亡。此外，在克隆生长试验中，MAPK激活的减弱可轻度增强辐射抑制RT2细胞生长的能力。这些发现表明，在转化的星形胶质细胞中，抑制MAPK信号传导可减少增殖并增强电离辐射诱导的细胞杀伤作用。癌细胞的增殖和存活在体内与血管生成生长因子的表达增强有关。最近我们证明，一种新型啮齿动物辐射反应基因——进展升高基因3（PEG - 3）的基因产物，可增强啮齿动物成纤维细胞中血管内皮生长因子（VEGF）启动子活性，导致体内VEGF蛋白水平升高和致瘤行为增加。因此，PEG - 3和VEGF表达有望与转化细胞的致癌潜能直接相关。RT2细胞比T9细胞表达更多的PEG - 3和VEGF蛋白，并且在体内比T9细胞更具致瘤性。辐射通过MAPK信号传导激活PEG - 3启动子，PEG - 3的异位过表达可增强基础MAPK活性和基础VEGF启动子活性。在原代星形胶质细胞、T9和RT2细胞中，基础MAPK活性与基础VEGF启动子活性及VEGF蛋白水平部分相关。辐射可增加原代星形胶质细胞、T9和RT2细胞中VEGF启动子活性和VEGF蛋白水平，这依赖于MAPK功能。此外，通过显性负性c - Jun（TAM67）抑制AP - 1转录因子信号传导，也可显著降低RT2细胞中基础的以及在较小程度上辐射诱导的VEGF启动子功能。总体而言,我们的数据表明，辐射诱导的MAPK信号传导既能保护细胞免受辐射诱导的细胞死亡，又能增强促血管生成因子如VEGF的蛋白水平。RT2细胞中VEGF表达的增强可能是通过MAPK和JNK信号通路介导的，这些信号通路汇聚于AP - 1转录因子复合物。
