Endocrine Abstracts

Objectives: Aberrances in expression and sequence of miR-146a have a well-established role in pathogenesis of papillary thyroid carcinoma (PTC). The G/C heterozygosity in rs2910164 of miR-146a underlies genetic predisposition to PTC and occurs as a somatic mutation in thyroid tumors. Deleterious function of rs2910164 consists in creation of a new variant of microRNA, resulting from the fact that a single microRNA precursor gives rise to −5p and −3p microRNAs. The SNP is located in the seed region (responsible for target gene recognition) of miR-146a-3p, thus its presence generates two isoforms that regulate distinct sets of target genes. As a result, heterozygous carriers of the SNP produce three mature miRs: miR-146a-5p, miR-146a-3p (G) and 146a-3p (C). Interestingly, there is only one gene concertedly targeted by the three isoforms, and its deregulation can underlie the miR-146a-dependent predisposition to PTC.

Aim: The aim of this project was to analyze the synergistic action of isoforms of polymorphic miR-146a on the expression of their shared target gene – NTRK2 - and to determine the role of this process in thyroid carcinogenesis.

Methods and results: In silico analysis revealed that all three isoforms of miR-146a potentially target one gene – NTRK2, coding for a member of the high-affinity neurotrophin receptors with tyrosine kinase activity, that controls differentiation and programmed cell death. Binding of miR-146a to 3′ UTR of NTRK2, analyzed in luciferase assay, resulted in a 30% (P=0.0037) reduction of luciferase activity. NTRK2 expression quantified in 58 pairs of PTC and unaffected tissue samples revealed that NTRK2 levels were significantly, twofold decreased in 93% of tumors (P=4.75×10⁻⁷).

Outcome: This is the first functional study of the synergistic effect exerted by polymorphic miRNAs produced from a single precursor. Results of the analysis may give a strong basis for better understanding of the role of miR-146a and NTRK gene in development of PTC.