Ras stimulates DNA topoisomerase II alpha through MEK: a link between oncogenic signaling and a therapeutic target.
Ras stimulates DNA topoisomerase II alpha through MEK: a link between oncogenic signaling and a therapeutic target.
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Ras 通过 MEK 刺激 DNA 拓扑异构酶 II α：致癌信号传导与治疗靶点之间的联系。
作者：
Chen,G;Templeton,D;Suttle,DP;Stacey,DW
拓扑异构酶IIα（topo IIα）是抗肿瘤治疗的主要靶点。为了确定为什么这种蛋白质在肿瘤细胞中可能是比在正常细胞中更好的靶点，我们试图确定肿瘤细胞中改变的增殖信号是否可能影响topo IIα基因的表达水平。为了支持这一观点，发现在显微注射致癌Ras蛋白后topo IIα升高。致癌ras进一步显示刺激topo IIα启动子。ras的刺激作用不依赖于该启动子的正常细胞周期调节。ras对topo IIα的反式激活需要MEK/ERK通路和应激相关蛋白激酶（SAPK）信号通路。作为ERK和SAPK参与topo IIα调节的直接证实，同时刺激这两种激酶的组成型活性MEKK显示出强烈诱导topo IIα启动子活性。另一方面，单独激活任一途径仅轻微刺激topo IIα启动子。缺失分析表明，启动子5′和3′端的元件都对ras的激活起作用。定点突变进一步证明，5′端附近的Ets样结合位点（− 480至− 475）是响应元件之一。总之，这些研究证明了Ras信号传导在刺激topo IIα表达中的直接作用，从而建立了常见肿瘤突变作用与多种抗肿瘤试剂靶点之间的联系。
Topoisomerase IIα (topo IIα) is a major target of antitumor treatments. In an effort to determine why this protein might be a better target in tumor cells than in normal cells, we attempted to determine if the altered proliferative signaling in a tumor cell might effect the levels of expression of the topo IIα gene. In support of this idea, it was found that topo IIα was elevated following microinjection of oncogenic Ras protein. Oncogenic ras was further shown to stimulate the topo IIα promoter. Stimulation by ras was independent of the normal cell cycle regulation of this promoter. Transactivation of topo IIα by ras required both the MEK/ERK pathway, and the stress-associated protein kinase (SAPK) signaling pathway. As a direct confirmation that both ERK and SAPK were involved in topo IIα regulation, a constitutively active MEKK that stimulates these two kinases simultaneously was shown to strongly induce topo IIα promoter activity. Activation of either pathway alone, on the other hand, only slightly stimulated the topo IIα promoter. Deletion analyses showed that elements near both the 5′ and 3′ ends of the promoter were responsible for the ras stimulation. Site-directed mutagenesis further demonstrated that an Ets-like binding site near the 5′ end (− 480 to− 475) was one of the responsive elements. Taken together, these studies demonstrate the direct role of Ras signaling in stimulation of topo IIα expression, and thereby establish a link between the action of a common tumor mutation and the target of multiple anti-tumor reagents.