Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Biochem J. 2010 Feb 24;426(3):293-306. doi: 10.1042/BJ20091459.
MEK-1 [MAPK (mitogen-activated protein kinase) kinase-1] is an important signal transducing enzyme that is implicated in many aspects of cellular functions. In the present paper, we report that cellular polyamines regulate MEK-1 expression at the post-transcriptional level through the RNA-binding protein HuR (Hu-antigen R) in IECs (intestinal epithelial cells). Decreasing the levels of cellular polyamines by inhibiting ODC (ornithine decarboxylase) stabilized MEK-1 mRNA and promoted its translation through enhancement of the interaction between HuR and the 3'-untranslated region of MEK-1 mRNA, whereas increasing polyamine levels by ectopic ODC overexpression destabilized the MEK-1 transcript and repressed its translation by reducing the abundance of HuR-MEK-1 mRNA complex; neither intervention changed MEK-1 gene transcription via its promoter. HuR silencing rendered the MEK-1 mRNA unstable and inhibited its translation, thus preventing increases in MEK-1 mRNA and protein in polyamine-deficient cells. Conversely, HuR overexpression increased MEK-1 mRNA stability and promoted its translation. Inhibition of MEK-1 expression by MEK-1 silencing or HuR silencing prevented the increased resistance of polyamine-deficient cells to apoptosis. Moreover, HuR overexpression did not protect against apoptosis if MEK-1 expression was silenced. These results indicate that polyamines destabilize the MEK-1 mRNA and repress its translation by inhibiting the association between HuR and the MEK-1 transcript. Our findings indicate that MEK-1 is a key effector of the HuR-elicited anti-apoptotic programme in IECs.
MEK-1（丝裂原活化蛋白激酶激酶-1）是一种重要的信号转导酶，涉及细胞功能的许多方面。在本论文中，我们报道细胞多胺通过肠道上皮细胞（IECs）中的 RNA 结合蛋白 HuR（Hu 抗原 R）在转录后水平调节 MEK-1 的表达。通过抑制 ODC（鸟氨酸脱羧酶）降低细胞多胺水平可稳定 MEK-1 mRNA，并通过增强 HuR 与 MEK-1 mRNA 3'-非翻译区的相互作用促进其翻译，而通过过表达 ODC 增加多胺水平则使 MEK-1 转录本不稳定，并通过减少 HuR-MEK-1 mRNA 复合物的丰度抑制其翻译；这两种干预均不通过其启动子改变 MEK-1 基因转录。HuR 沉默使 MEK-1 mRNA 不稳定并抑制其翻译，从而防止在多胺缺乏的细胞中 MEK-1 mRNA 和蛋白增加。相反，HuR 过表达增加了 MEK-1 mRNA 的稳定性并促进了其翻译。通过 MEK-1 沉默或 HuR 沉默抑制 MEK-1 表达可防止多胺缺乏细胞对细胞凋亡的抵抗力增加。此外，如果抑制 MEK-1 表达，则 HuR 过表达不能防止细胞凋亡。这些结果表明，多胺通过抑制 HuR 与 MEK-1 转录本的结合来使 MEK-1 mRNA 不稳定并抑制其翻译。我们的研究结果表明，MEK-1 是 IECs 中 HuR 引发的抗细胞凋亡程序的关键效应因子。
