Expression of Death Receptor 4 Is Positively Regulated by MEK/ERK/AP-1 Signaling and Suppressed upon MEK Inhibition
Expression of Death Receptor 4 Is Positively Regulated by MEK/ERK/AP-1 Signaling and Suppressed upon MEK Inhibition
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DOI：
10.1074/jbc.m116.738302
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发表时间：
2016-10-07
影响因子：
4.8
通讯作者：
Sun, Shi-Yong
中科院分区：
文献类型：
--
作者：
Yao, Weilong;Oh, You-Take;Sun, Shi-Yong
死亡受体4(Death Receptor 4，DR4)是肿瘤坏死因子相关的凋亡诱导配体(TRAIL)的细胞表面受体，与TRAIL或TRAIL结合或聚集后可触发细胞凋亡。MEK/ERK信号通路是RAS和Raf下游一个广为人知、研究最深入的效应通路。本研究旨在确定药物抑制MEK对DR4表达的影响，并阐明其可能的作用机制。我们发现包括MEK162、AZD6244和PD0325901在内的几种MEK抑制剂有效地降低了不同癌细胞系中包括细胞表面DR4在内的DR4蛋白水平。因此，用MEK抑制剂对TRAIL敏感的癌细胞株进行预处理会使它们对TRAIL诱导的细胞凋亡不敏感。这些结果表明，MEK抑制负向调节DR4的表达和细胞对TRAIL诱导的细胞凋亡的反应。MEK抑制剂并没有改变DR4蛋白的稳定性，而是降低了它的mRNA水平，这表明它是一种转录调控。相反，通过表达异位B-Raf(V600E)或组成性激活的MEK1(MEK1-CA)或MEK2(MEK2-CA)来强制激活MEK/ERK信号，可激活ERK并增加DR4的表达；当存在MEK抑制剂时，这些作用被抑制。通过缺失和突变的启动子分析，确定AP-1结合位点是MEK1-CA增强DR4反式激活所必需的反应元件。此外，通过c-jun基因敲除抑制AP-1的表达，可使MEK1-CA增强DR4启动子活性和DR4表达的能力减弱。这些结果提示AP-1在介导MEK/ERK激活诱导的DR4表达中起重要作用。我们的发现共同强调了一个以前未发现的机制，即通过激活MEK/ERK/AP-1信号通路来积极调节DR4的表达。
Death receptor 4 (DR4) is a cell surface receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and triggers apoptosis upon ligation with TRAIL or aggregation. MEK/ERK signaling is a well known and the best-studied effector pathway downstream of Ras and Raf. This study focuses on determining the impact of pharmacological MEK inhibition on DR4 expression and elucidating the underlying mechanism. We found that several MEK inhibitors including MEK162, AZD6244, and PD0325901 effectively decreased DR4 protein levels including cell surface DR4 in different cancer cell lines. Accordingly, pre-treatment of TRAIL-sensitive cancer cell lines with a MEK inhibitor desensitized them to TRAIL-induced apoptosis. These results indicate that MEK inhibition negatively regulates DR4 expression and cell response to TRAIL-induced apoptosis. MEK inhibitors did not alter DR4 protein stability, rather decreased its mRNA levels, suggesting a transcriptional regulation. In contrast, enforced activation of MEK/ERK signaling by expressing ectopic B-Raf (V600E) or constitutively activated MEK1 (MEK1-CA) or MEK2 (MEK2-CA) activated ERK and increased DR4 expression; these effects were inhibited when a MEK inhibitor was present. Promoter analysis through deletion and mutation identified the AP-1 binding site as an essential response element for enhancing DR4 transactivation by MEK1-CA. Furthermore, inhibition of AP-1 by c-Jun knockdown abrogated the ability of MEK1-CA to increase DR4 promoter activity and DR4 expression. These results suggest an essential role of AP-1 in mediating MEK/ERK activation-induced DR4 expression. Our findings together highlight a previously undiscovered mechanism that positively regulates DR4 expression through activation of the MEK/ERK/AP-1 signaling pathway.