Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University School of Medicine, Springfield, IL 62794, USA.
Nucleic Acids Res. 2012 Aug;40(14):6683-92. doi: 10.1093/nar/gks324. Epub 2012 Apr 11.
MicroRNAs are master gene regulators that can also be under the control of transcriptional regulation. We have previously shown that miR-145 is a tumor suppressor capable of silencing c-Myc and the tumor suppressor p53 induces miR-145 by directly binding to the miR-145 promoter, demonstrating the role of miR-145 in p53-mediated c-Myc repression. However, little is known as to why miR-145 is often downregulated in tumors. In this study, we identify CCAAT/enhancer binding protein beta (C/EBP-β) as a negative regulator for miR-145 expression by direct interaction with the putative C/EBP-β binding site in the miR-145 promoter. In the wild-type p53 background, C/EBP-β counteracts the ability of p53 to induce miR-145. Moreover, C/EBP-β is able to suppress miR-145 in the mutant p53 background, suggesting the p53 independent regulation of miR-145. Of interest, both the large isoform (LAP-2) and the small isoform (LIP) of C/EBP-β can exert suppressive function for miR-145. Finally, we further show that, like serum starvation and PI3K inhibitor LY29, the antioxidant resveratrol suppresses pAkt and phosphorylation of C/EBP-β and at the same time, it induces miR-145. Together, these results suggest a miR-145 regulatory system involving the Akt and C/EBP-β, which may contribute to the downregulation of miR-145 in cancer cells.
微小 RNA 是主基因调控因子，也可以受到转录调控的控制。我们之前已经表明，miR-145 是一种肿瘤抑制因子，能够沉默 c-Myc，肿瘤抑制因子 p53 通过直接结合 miR-145 启动子诱导 miR-145 的表达，证明了 miR-145 在 p53 介导的 c-Myc 抑制中的作用。然而，miR-145 在肿瘤中经常下调的原因知之甚少。在这项研究中，我们通过直接与 miR-145 启动子中的假定 C/EBP-β 结合位点相互作用，鉴定出 CCAAT/增强子结合蛋白 β（C/EBP-β）是 miR-145 表达的负调控因子。在野生型 p53 背景下，C/EBP-β 抵消了 p53 诱导 miR-145 的能力。此外，C/EBP-β 能够在突变型 p53 背景下抑制 miR-145，表明 miR-145 的 p53 独立调节。有趣的是，C/EBP-β 的大异构体（LAP-2）和小异构体（LIP）都可以发挥抑制 miR-145 的功能。最后，我们进一步表明，与血清饥饿和 PI3K 抑制剂 LY29 一样，抗氧化剂白藜芦醇抑制 pAkt 和 C/EBP-β 的磷酸化，同时诱导 miR-145。综上所述，这些结果表明存在涉及 Akt 和 C/EBP-β 的 miR-145 调节系统，这可能导致癌细胞中 miR-145 的下调。
