title: MicroRNA miR-146b-5p regulates signal transduction of TGF-β by repressing SMAD4 in thyroid cancer.
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.
authors.affiliation: Department of Cell and Developmental Biology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: M V
authors.initials: MV
authors.lastname: Geraldo
authors.forename: A S
authors.initials: AS
authors.lastname: Yamashita
authors.forename: E T
authors.initials: ET
authors.lastname: Kimura
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D002291:Carcinoma, Papillary / Q000235:genetics*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000502:physiology*; D009857:Oncogenes; D051381:Rats; D015398:Signal Transduction; D051901:Smad4 Protein / Q000235:genetics / Q000378:metabolism*; D013961:Thyroid Gland / Q000166:cytology; D013964:Thyroid Neoplasms / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D020413:3' Untranslated Regions; C542542:MIRN146 microRNA, human; D035683:MicroRNAs; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D016212:Transforming Growth Factor beta