Department of Medicine, Division of Hematology/Oncology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.
J Biol Chem. 2010 Nov 5;285(45):34439-46. doi: 10.1074/jbc.M110.152306. Epub 2010 Sep 7.
F-box and WD-40 domain protein 7 (Fbw7) provides substrate specificity for the Skp1-Cullin1-F-box protein (SCF) ubiquitin ligase complex that targets multiple oncoproteins for degradation, including cyclin E, c-Myc, c-Jun, Notch, and mammalian target of rapamycin (mTOR). Fbw7 is a bona fide tumor suppressor, and loss-of-function mutations in FBXW7 have been identified in diverse human tumors. Although much is known about targets of the Fbw7 ubiquitin ligase pathway, relatively little is known about the regulation of Fbw7 expression. We identified a panel of candidate microRNA regulators of Fbw7 expression within a study of gene expression alterations in primary erythroblasts obtained from cyclin E(T74A T393A) knock-in mice, which have markedly dysregulated cyclin E expression. We found that overexpression of miR-223, in particular, significantly reduces FBXW7 mRNA levels, increases endogenous cyclin E protein and activity levels, and increases genomic instability. We next confirmed that miR-223 targets the FBXW7 3'-untranslated region. We then found that reduced miR-223 expression in primary mouse embryonic fibroblasts leads to increased Fbw7 expression and decreased cyclin E activity. Finally, we found that miR-223 expression is responsive to acute alterations in cyclin E regulation by the Fbw7 pathway. Together, our data indicate that miR-223 regulates Fbw7 expression and provide the first evidence that activity of the SCF(Fbw7) ubiquitin ligase can be modulated directly by the microRNA pathway.
F-box 和 WD-40 结构域蛋白 7（Fbw7）为 Skp1-Cullin1-F-box 蛋白（SCF）泛素连接酶复合物提供底物特异性，该复合物可靶向多种癌蛋白进行降解，包括细胞周期蛋白 E、c-Myc、c-Jun、Notch 和哺乳动物雷帕霉素靶蛋白（mTOR）。Fbw7 是一种真正的肿瘤抑制因子，FBXW7 的功能丧失突变已在多种人类肿瘤中被发现。尽管人们对 Fbw7 泛素连接酶途径的靶标了解很多，但对 Fbw7 表达的调节相对了解较少。我们在一项研究中鉴定了一组候选 microRNA 调节物，该研究是对 cyclin E(T74A T393A) 敲入小鼠中获得的原红细胞基因表达改变进行的研究，该研究中 cyclin E 的表达明显失调。我们发现，miR-223 的过表达，特别是，显著降低 FBXW7 mRNA 水平，增加内源性 cyclin E 蛋白和活性水平，并增加基因组不稳定性。我们接下来证实 miR-223 靶向 FBXW7 的 3'-非翻译区。然后，我们发现原代小鼠胚胎成纤维细胞中 miR-223 表达减少会导致 Fbw7 表达增加和 cyclin E 活性降低。最后，我们发现 miR-223 表达对 Fbw7 途径中 cyclin E 调节的急性改变有反应。总之，我们的数据表明 miR-223 调节 Fbw7 表达，并提供了第一个证据表明 SCF（Fbw7）泛素连接酶的活性可以直接被 microRNA 途径调节。
