Department of Cell and Developmental Biology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
Oncogene. 2012 Apr 12;31(15):1910-22. doi: 10.1038/onc.2011.381. Epub 2011 Aug 29.
MicroRNAs (miRNA) are small non-coding RNAs involved in post-transcriptional gene regulation that have crucial roles in several types of tumors, including papillary thyroid carcinoma (PTC). miR-146b-5p is overexpressed in PTCs and is regarded as a relevant diagnostic marker for this type of cancer. A computational search revealed that miR-146b-5p putatively binds to the 3' untranslated region (UTR) of SMAD4, an important member of the transforming growth factor β (TGF-β) signaling pathway. The TGF-β pathway is a negative regulator of thyroid follicular cell growth, and the mechanism by which thyroid cancer cells evade its inhibitory signal remains unclear. We questioned whether the modulation of the TGF-β pathway by miR-146b-5p can contribute to thyroid tumorigenesis. Luciferase reporter assay confirmed the direct binding of miR-146b-5p on the SMAD4 3'UTR. Specific inhibition of miR-146b-5p with a locked nucleic acid-modified anti-miR-146b oligonucleotide significantly increased SMAD4 levels in the human papillary carcinoma cell lines, TPC-1 and BCPAP. Moreover, suppression of miR-146b-5p increased the cellular response to the TGF-β anti-proliferative signal, significantly decreasing the proliferation rate. The overexpression of miR-146b-5p in normal rat follicular PCCL3 cells decreased SMAD4 levels and disrupted TGF-β signal transduction. MiR-146b-5p overexpression in PCCL3 cells also significantly increased cell proliferation in the absence of thyroid-stimulating hormone and conferred resistance to TGF-β-mediated cell-cycle arrest. Additionally, the activation of thyroid most common oncogenes RET/PTC3 and BRAF in PCCL3 cells upregulated miR-146b-5p expression. Our results confirm the oncogenic role of miR-146b-5p in thyroid follicular cells and contribute to knowledge regarding the modulation of TGF-β signal transduction by miRNAs in PTCs.
微小 RNA（miRNA）是参与转录后基因调控的小非编码 RNA，在包括甲状腺乳头状癌（PTC）在内的几种类型的肿瘤中具有关键作用。miR-146b-5p 在 PTC 中过度表达，被认为是这种癌症的相关诊断标志物。计算机搜索显示，miR-146b-5p 可能与 SMAD4 的 3'非翻译区（UTR）结合，SMAD4 是转化生长因子 β（TGF-β）信号通路的重要成员。TGF-β 途径是甲状腺滤泡细胞生长的负调节剂，甲状腺癌细胞逃避其抑制信号的机制尚不清楚。我们质疑 miR-146b-5p 对 TGF-β 途径的调节是否有助于甲状腺肿瘤的发生。荧光素酶报告基因检测证实了 miR-146b-5p 对 SMAD4 3'UTR 的直接结合。用锁核酸修饰的抗 miR-146b-5p 寡核苷酸特异性抑制 miR-146b-5p 可显著增加人甲状腺乳头状癌细胞系 TPC-1 和 BCPAP 中的 SMAD4 水平。此外，抑制 miR-146b-5p 可增强细胞对 TGF-β 抗增殖信号的反应，显著降低增殖率。miR-146b-5p 在正常大鼠滤泡 PCCL3 细胞中的过表达降低了 SMAD4 水平并破坏了 TGF-β 信号转导。PCCL3 细胞中 miR-146b-5p 的过表达也显著增加了甲状腺刺激激素缺乏时的细胞增殖，并赋予了对 TGF-β 介导的细胞周期阻滞的抗性。此外，在 PCCL3 细胞中激活甲状腺最常见的致癌基因 RET/PTC3 和 BRAF 可上调 miR-146b-5p 的表达。我们的结果证实了 miR-146b-5p 在甲状腺滤泡细胞中的致癌作用，并有助于了解 miRNA 对 PTC 中 TGF-β 信号转导的调节。
