An interplay between the p38 MAPK pathway and AUBPs regulates c-fos mRNA stability during mitogenic stimulation.
An interplay between the p38 MAPK pathway and AUBPs regulates c-fos mRNA stability during mitogenic stimulation.
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DOI：
10.1042/bj20141100
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发表时间：
2015-04-01
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丝裂原活化蛋白激酶（MAPK）通路是连接细胞外刺激和核基因表达的关键调控元件。激活蛋白1（AP-1）家族的立即早期应答基因（IEGs），如fos，在细胞用生长因子刺激后不久达到峰值表达水平，此后急剧下降。几种富含AU的结合蛋白（AUBP），包括HuR（Hu-antigen R，Elav-like protein 1，ELAVL 1）和KSRP（far upstream element-binding protein 2，KHSRP），与fos mRNA 3′-UTR（untranslated region，非翻译区）的富含AU的元件（fos AU rich element，ARE）结合，调节fos mRNA的稳定性。我们在本研究中发现，HuR结合并稳定转录的携带fos 3′-UTR的报告基因mRNA，而KSRP抵消了这种作用。此外，我们发现，fos mRNA的稳定性和HuR磷酸化状态依赖于p38 MAPK的活性在上皮细胞和成纤维细胞增殖刺激后。分析PPI（蛋白质-蛋白质相互作用）网络，我们进行了一个彻底的查询p38 MAPK，HuR和其他AUBP生长因子刺激后的相互作用蛋白。这揭示了新的HuR相互作用物，包括蛋白磷酸酶2（PP 2A）活性的抑制剂。这些相互作用物中的两个，pp 32和APRIL（酸性富亮氨酸核磷蛋白32家族成员B，ANP 32 B）的过表达和PP 2A的药理学抑制稳定了fos报告mRNA。我们的研究结果表明，p38 MAPK调节fos mRNA的衰减，通过影响磷酸化状态的HuR，同时控制尚未完全阐明PP调控网络。
Mitogen-activated protein kinase (MAPK) pathways constitute key regulatory elements linking extracellular stimuli to nuclear gene expression. Immediate-early responsive genes (IEGs) of the activator protein 1 (AP-1) family, such as fos, achieve peak expression levels shortly after cells are stimulated with growth factors and sharply decrease thereafter. Several AU-rich binding proteins (AUBPs), including HuR (Hu-antigen R, Elav-like protein 1, ELAVL1) and KSRP (far upstream element-binding protein 2, KHSRP) bind to a fos AU-rich element (ARE) present in the 3′-UTR (untranslated region) of fos mRNA regulating its stability by a still poorly defined mechanism. We show in the present study that, whereas HuR binds and stabilizes transcribed reporter mRNAs bearing the fos 3′-UTR, KSRP counteracts this effect. Furthermore, we found that fos mRNA stability and HuR phosphorylation status are dependent on the activity of p38 MAPK in both epithelial cells and fibroblasts upon proliferative stimulation. Analysing PPI (protein–protein interaction) networks, we performed a thorough query of interacting proteins for p38 MAPKs, HuR and other AUBPs upon growth factor stimulation. This revealed novel HuR interactors including inhibitors of protein phosphatase 2 (PP2A) activity. Over-expression of two of these interactors, pp32 and APRIL (acidic leucine-rich nuclear phosphoprotein 32 family member B, ANP32B) and pharmacological inhibition of PP2A stabilized a fos reporter mRNA. Our results indicate that p38 MAPK regulates fos mRNA decay by affecting the state of phosphorylation of HuR while controlling yet to be fully elucidated PP regulatory networks.