INTERPLAY OF 2 FUNCTIONALLY AND STRUCTURALLY DISTINCT DOMAINS OF THE C-FOS AU-RICH ELEMENT SPECIFIES ITS MESSENGER-RNA-DESTABILIZING FUNCTION
INTERPLAY OF 2 FUNCTIONALLY AND STRUCTURALLY DISTINCT DOMAINS OF THE C-FOS AU-RICH ELEMENT SPECIFIES ITS MESSENGER-RNA-DESTABILIZING FUNCTION
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DOI：
10.1128/mcb.14.1.416
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发表时间：
1994-01-01
影响因子：
5.3
通讯作者：
SHYU, AB
中科院分区：
文献类型：
--
作者：
CHEN, CYA;CHEN, TM;SHYU, AB
在许多原癌基因、淋巴因子和细胞因子高度不稳定的mRNAs的3‘非翻译区，富Au元素(ARE)可以起到破坏RNA稳定的作用。由于缺乏对ARE的关键序列和其破坏稳定功能所需的结构特征的清楚了解，因此无法进一步阐明其作用方式和其特异性的基础。结合对c-fos ARE的广泛突变和对mRNA稳定性的体内分析，我们能够识别出表现出与两步机制的两相衰退特征一致的动力学表型的突变：加速的聚(A)缩短和随后的转录部分的衰退。这些影响单个步骤或两个步骤的突变都改变了信使核糖核酸的稳定性。我们的实验进一步揭示了构成c-fos ARE的两个结构不同和功能相互依赖的结构域的存在。结构域I位于ARE的5‘49核苷酸片段内，包含三个AUUUA基序，本身就可以作为RNA去稳定器发挥作用。它构成了反稳定功能所必需的基本核心单元。结构域II是一个20个核苷酸的富含U的序列，位于c-fos ARE的3‘端。虽然它本身不能作为RNA的破坏稳定剂，但这个结构域有两个关键作用：(I)它的存在通过加速去烯化步骤来增强结构域I的去稳定能力，以及(Ii)它具有一种新的能力，可以缓冲结构域I中引入的突变所产生的阻止衰退的效应。我们提出了一个模型来解释这些关键结构特征如何参与c-fos定向的mRNA衰退途径。这些发现对于进一步理解不同ARE介导的差异mRNA衰变的分子基础具有重要意义。
AU-rich elements (ARE) in the 3' untranslated region of many highly labile mRNAs for proto-oncogenes, lymphokines, and cytokines can act as an RNA-destabilizing element. The absence of a clear understanding of the key sequence and structural features of the ARE that are required for its destabilizing function has precluded the further elucidation of its mode of action and the basis of its specificity. Combining extensive mutagenesis of the c-fos ARE with in vivo analysis of mRNA stability, we were able to identify mutations that exhibited kinetic phenotypes consistent with the biphasic decay characteristic of a two-step mechanism: accelerated poly(A) shortening and subsequent decay of the transcribed portion of the mRNA. These mutations, which affected either an individual step or both steps, all changed the mRNA stability. Our experiments further revealed the existence of two structurally distinct and functionally interdependent domains that constitute the c-fos ARE. Domain I, which is located within the 5' 49-nucleotide segment of the ARE and contains the three AUUUA motifs, can function as an RNA destabilizer by itself. It forms the essential core unit necessary for the ARE-destabilizing function. Domain II is a 20-nucleotide U-rich sequence which is located within the 3' part of the c-fos ARE. Although it alone can not act as an RNA destabilizer, this domain serves two critical roles: (i) its presence enhances the destabilizing ability of domain I by accelerating the deadenylation step, and (ii) it has a novel capacity of buffering decay-impeding effects exerted by mutations introduced within domain I. A model is proposed to explain how these critical structural features may be involved in the c-fos ARE-directed mRNA decay pathway. These findings have important implications for furthering our understanding of the molecular basis of differential mRNA decay mediated by different AREs.