Stoecklin Georg, Lu Min, Rattenbacher Bernd, Moroni Christoph
Institute of Medical Microbiology, University of Basel, Petersplatz 10, CH-4003 Basel, Switzerland.
Mol Cell Biol. 2003 May;23(10):3506-15. doi: 10.1128/MCB.23.10.3506-3515.2003.
Tumor necrosis factor alpha (TNF-alpha) expression is regulated by transcriptional as well as posttranscriptional mechanisms, the latter including the control of mRNA decay through an AU-rich element (ARE) in the 3' untranslated region (UTR). Using two mutant cell lines deficient for ARE-mediated mRNA decay, we provide evidence for a second element, the constitutive decay element (CDE), which is also located in the 3' UTR of TNF-alpha. In stably transfected RAW 264.7 macrophages stimulated with lipopolysaccharide (LPS), the CDE continues to target a reporter transcript for rapid decay, whereas ARE-mediated decay is blocked. Similarly, the activation of p38 kinase and phosphatidylinositol 3-kinase in NIH 3T3 cells inhibits ARE-mediated but not CDE-mediated mRNA decay. The CDE was mapped to an 80-nucleotide (nt) segment downstream of the ARE, and point mutation analysis identified within the CDE a conserved sequence of 15 nt that is required for decay activity. We propose that the CDE represses TNF-alpha expression by maintaining the mRNA short-lived, thereby preventing excessive induction of TNF-alpha after LPS stimulation. Thus, CDE-mediated mRNA decay is likely to be an important mechanism limiting LPS-induced pathologic processes.
肿瘤坏死因子α（TNF-α）的表达受转录及转录后机制调控，后者包括通过3'非翻译区（UTR）中的富含AU元件（ARE）来控制mRNA降解。利用两个缺乏ARE介导的mRNA降解的突变细胞系，我们为另一个元件——组成性降解元件（CDE）提供了证据，该元件也位于TNF-α的3'UTR中。在用脂多糖（LPS）刺激的稳定转染的RAW 264.7巨噬细胞中，CDE继续靶向报告转录本进行快速降解，而ARE介导的降解被阻断。同样，NIH 3T3细胞中p38激酶和磷脂酰肌醇3激酶的激活抑制ARE介导的但不抑制CDE介导的mRNA降解。CDE被定位到ARE下游的一个80个核苷酸（nt）的片段，点突变分析在CDE内鉴定出一个15 nt的保守序列，该序列是降解活性所必需的。我们提出，CDE通过维持mRNA的短寿命来抑制TNF-α的表达，从而防止LPS刺激后TNF-α的过度诱导。因此，CDE介导的mRNA降解可能是限制LPS诱导的病理过程的重要机制。
