Endocrine Abstracts

Regulatory circuits involving miRNAs and transcription factors (TFs) are prevalent mechanisms of gene expression by which developmental and pathologic processes occur. MiR-146b is one of the most upregulated and abundant oncomiRNAs in papillary thyroid carcinomas (PTCs). We have previously shown that miR-146b and PAX8 regulate each other and share common target genes such as NIS, thus highlighting a miR-146b-3p/PAX8/NIS regulatory circuit that governs the differentiated phenotype of PTC. In this study, we found that DIO2 and IYD (DEHAL1), two thyroid iodide-metabolizing genes essential for thyroid differentiation, are also common targets of miR-146b and PAX8. Our ChIP-Seq characterization showed that DIO2 and IYD (DEHAL1) are downstream target genes that are positively regulated by PAX8 in the rat thyroid cell line PCCl3, and TSH strongly induces the upregulation of both DIO2 and DEHAL1. Our NGS analysis of PTC tumor samples as well as analysis of TCGA data sets, show a significant negative correlation between the expression levels of miR-146b and the levels of DIO2 and DEHAL1 (r= -0.5; FDR<0.05 and r = -0.6; FDR<0.05, respectively). We next analyzed the protein expression of DIO2 and DEHAL1 in a panel of 13 thyroid cancer cell lines finding a general downregulation for DEHAL1 and various levels of expression for DIO2. Bioinformatic prediction analysis shows that there are three and two binding sites for miR-146b-5p and -3p respectively in the 3’UTR of DEHAL1 and one binding site for miR-146b-5p in the 3’UTR of DIO2. Overexpression of miR-146b markedly decreases DIO2 and DEHAL protein expression in NTHY-ORI cell line and we are currently investigating whether miR-146b-5p is specifically targeting the 3’UTR of both genes. In conclusion, we provide further evidence that a TF-miRNA co-regulatory network based on miR-146b and PAX8 modulate genes essential for thyroid differentiation that may be exploited therapeutically in PTC.