MicroRNA miR-146b-5p regulates signal transduction of TGF-β by repressing SMAD4 in thyroid cancer

Oncogene. 2012 Apr 12;31(15):1910-22. doi: 10.1038/onc.2011.381. Epub 2011 Aug 29.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3' Untranslated Regions
  • Animals
  • Carcinoma, Papillary / genetics*
  • Cell Line, Tumor
  • Cell Transformation, Neoplastic
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MicroRNAs / antagonists & inhibitors
  • MicroRNAs / physiology*
  • Oncogenes*
  • Rats
  • Signal Transduction
  • Smad4 Protein / genetics
  • Smad4 Protein / metabolism*
  • Thyroid Gland / cytology
  • Thyroid Neoplasms / genetics*
  • Transforming Growth Factor beta / metabolism*

Substances

  • 3' Untranslated Regions
  • MIRN146 microRNA, human
  • MicroRNAs
  • SMAD4 protein, human
  • Smad4 Protein
  • Transforming Growth Factor beta