Raf/MEK/MAPK signaling stimulates the nuclear translocation and transactivating activity of FOXM1c
Raf/MEK/MAPK signaling stimulates the nuclear translocation and transactivating activity of FOXM1c
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DOI：
10.1242/jcs.01657
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发表时间：
2005-02-15
影响因子：
4
通讯作者：
Yao, KM
中科院分区：
文献类型：
--
作者：
Ma, RYM;Tong, THK;Yao, KM
叉头盒（FOX）转录因子FOXM1在增殖细胞中普遍表达。FOXM1的表达在细胞周期的G2/M期达到峰值，其在小鼠体内的功能缺失导致有丝分裂缺陷。为了研究FOXM1在细胞周期中的作用，我们使用同步hTERT-BJ1成纤维细胞来检测FOXM1功能的细胞周期依赖性调节。我们观察到FOXM1主要定位于g1晚期和S期细胞的细胞质中。核易位发生在进入G2/M期之前，与FOXM1的磷酸化有关。与FOXM1功能对有丝分裂信号的依赖性一致，FOXM1的核易位需要Raf/MEK/MAPK信号通路的活性，并通过MAPK激活剂金三羧酸增强。这种激活作用被MEK1/2抑制剂U0126抑制。在瞬时报告基因试验中，组成型活性MEK1增强了FOXM1c对细胞周期蛋白B1启动子的反激活作用，而不是FOXM1b。RT-PCR分析证实不同细胞系和组织主要表达FOXM1c转录物。FOXM1c中两个ERK1/2靶序列的突变完全消除了MEK1增强作用，提示Raf/MEK/MAPK信号传导与FOXM1功能之间存在直接联系。重要的是，U0126抑制Raf/MEK/ MAPK信号传导导致FOXM1靶基因表达抑制，并通过G2/M延迟进展，验证了MEK1激活FOXM1的功能相关性。综上所述，我们首次提供了Raf/MEK/MAPK信号通过FOXM1c发挥G2/M调控作用的证据。
The forkhead box (FOX) transcription factor FOXM1 is ubiquitously expressed in proliferating cells. FOXM1 expression peaks at the G2/M phase of the cell cycle and its functional deficiency in mice leads to defects in mitosis. To investigate the role of FOXM1 in the cell cycle, we used synchronized hTERT-BJ1 fibroblasts to examine the cell cycle-dependent regulation of FOXM1 function. We observed that FOXM1 is localized mainly in the cytoplasm in cells at late-G1 and S phases. Nuclear translocation occurs just before entry into the G2/M phase and is associated with phosphorylation of FOXM1. Consistent with the dependency of FOXM1 function on mitogenic signals, nuclear translocation of FOXM1 requires activity of the Raf/MEK/MAPK signaling pathway and is enhanced by the MAPK activator aurintricarboxylic acid. This activating effect was suppressed by the MEK1/2 inhibitor U0126. In transient reporter assays, constitutively active MEK1 enhances the transactivating effect of FOXM1c, but not FOXM1b, on the cyclin B1 promoter. RT-PCR analysis confirmed that different cell lines and tissues predominantly express the FOXM1c transcript. Mutations of two ERK1/2 target sequences within FOXM1c completely abolish the MEK1 enhancing effect, suggesting a direct link between Raf/MEK/MAPK signaling and FOXM1 function. Importantly, inhibition of Raf/MEK/ MAPK signaling by U0126 led to suppression of FOXM1 target gene expression and delayed progression through G2/M, verifying the functional relevance of FOXM1 activation by MEK1. In summary, we provide the first evidence that Raf/MEK/MAPK signaling exerts its G2/M regulatory effect via FOXM1c.