Overactivation of the MEK/ERK Pathway in Liver Tumor Cells Confers Resistance to TGF-β-Induced Cell Death through Impairing Up-regulation of the NADPH Oxidase NOX4
Overactivation of the MEK/ERK Pathway in Liver Tumor Cells Confers Resistance to TGF-β-Induced Cell Death through Impairing Up-regulation of the NADPH Oxidase NOX4
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DOI：
10.1158/0008-5472.can-09-1482
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发表时间：
2009-10-01
期刊：
影响因子：
11.2
通讯作者：
Fabregat, Isabel
中科院分区：
文献类型：
--
作者：
Caja, Laia;Sancho, Patricia;Fabregat, Isabel
转化生长因子-β（TGF-β）诱导肝细胞凋亡，被认为是肝肿瘤抑制因子。然而，许多人肝细胞癌（HCC）细胞逃避其促凋亡作用，获得对这种细胞因子的恶性反应。我们最近报道，肝细胞中TGF-β诱导的凋亡需要NADPH氧化酶NOX 4的上调，其介导活性氧（ROS）的产生。TGF-β诱导的N 0X 4表达被抗凋亡信号抑制，例如磷酸二肌醇-3-磷酸激酶或促分裂原活化蛋白激酶（MAPK）/细胞外信号调节激酶（ERK）途径。本研究的目的是分析肝癌细胞对TGF-β诱导的凋亡的抵抗是否与生存信号过度激活导致的NOX 4上调受损有关。结果表明，HepG 2细胞中MAPK/ERK激酶（MEK）/ERK通路的抑制，这是难治性的TGF-β的促凋亡作用，通过细胞依赖性机制，与RIM和BMF的水平增加，BCL-XL和MCL 1的水平降低，BAX/巴克激活一致，使它们对细胞死亡敏感。BMF、BCL-XL和MCL 1的调节发生在mRNA水平，而RIM调节发生在转录后。仅在用TGF-β和PD 98059处理的细胞中观察到ROS产生和谷胱甘肽消耗，这与N 0X 4上调相关。靶向敲除NOX 4通过调节BIM、BMF、BCL-XL和MCL 1水平的上游机制损害ROS增加和所有细胞依赖性凋亡特征。总之，肝肿瘤细胞中MEK/ERK通路的过度活化通过损害NOX 4上调而赋予对TGF-β诱导的细胞死亡的抗性，NOX 4上调是有效的肿瘤依赖性凋亡所需的。[Cancer Res 2009;69（19）：7595-602]
Transforming growth factor-beta (TGF-beta) induces apoptosis in hepatocytes, being considered a liver tumor suppressor. However, many human hepatocellular carcinoma (HCC) cells escape from its proapoptotic effects, gaining response to this cytokine in terms of malignancy. We have recently reported that the apoptosis induced by TGF-beta in hepatocytes requires up-regulation of the NADPH oxidase NOX4, which mediates reactive oxygen species (ROS) production. TGF-beta-induced NOX4 expression is inhibited by antiapoptotic signals, such as the phosphatydilinositol-3-phosphate kinase or the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathways. The aim of the present work was to analyze whether resistance to TGF-beta-induced apoptosis in HCC cells is related to the impairment of NOX4 up-regulation due to overactivation of survival signals. Results indicate that inhibition of the MAPK/ERK kinase (MEK)/ERK pathway in HepG2 cells, which are refractory to the proapoptotic effects of TGF-beta, sensitizes them to cell death through a mitochondrial-dependent mechanism, coincident with increased levels of RIM and BMF, decreased levels of BCL-XL and MCL1, and BAX/BAK activation. Regulation of BMF, BCL-XL, and MCL1 occurs at the mRNA level, whereas RIM regulation occurs post-transcriptionally. ROS production and glutathione depletion are only observed in cells treated with TGF-beta and PD98059, which correlates with NOX4 up-regulation. Targeting knockdown of NOX4 impairs ROS increase and all the mitochondrial-dependent apoptotic features by a mechanism that is upstream from the regulation of BIM, BMF, BCL-XL, and MCL1 levels. In conclusion, overactivation of the MEK/ERK pathway in liver tumor cells confers resistance to TGF-beta-induced cell death through impairing NOX4 up-regulation, which is required for an efficient mitochondrial-dependent apoptosis. [Cancer Res 2009;69(19):7595-602]