Endocrine Abstracts

The oncofoetal miRNA-binding protein LIN28B plays an important role in differentiation and cancer progression. Lin28B induces epithelial-mesenchymal transition, and it is considered as a bad prognostic marker in several tumours. The aim of this work was to study the effect and regulation of LIN28B on the thyroid cancer progression process. In a first approximation a miRNA targets computational predictions were performed with miRanda algorithm and we found that among others the miR-30a binds to the 3′ UTR of LIN28B. As previous results, obtained by next-generation sequencing expression analysis, performed in our laboratory showed that miR-30a is one of the most significantly miR subexpressed in thyroid cancer, we decided to focus on its role over LIN28B. miR-30a expression vector was transfected in 8505c and Cal62 cells; LIN28B in NThy-ori thyroid cells; and reporter construct containing LIN28B 3′ UTR in HeLa cells. The levels of mRNA and protein were determined by RT-qPCR and western blot. Invasion and proliferation assays were performed in Transwell^® and TC20 cell counter, respectively, Lin28B protein expression was determined in 16 thyroid cancer cell lines and was correlated with RAS and BRAF mutations in ATC derived cells. Overexpression of miR-30a resulted in LIN28B, HMGA2, H-RAS, PI3Kβ, BCL2, and CDK6 mRNA and protein silencing, and in an increase in p27(Kip) protein levels in the nucleus. Inversely, LIN28B overexpressing cells showed a decrease in miR-30a levels and an increased expression of HMGA2 and H-RAS oncogenes. Furthermore, we observed that the LIN28B inhibition by miR-30a is specifically elicited through a direct binding to its 3′ UTR. The general outcome was a significant decrease in invasion and proliferation in miR-30a overexpressing cells and, conversely, an increase in these parameters in LIN28B overexpressing cells. These data suggest the existence of a LIN28B/30a axis, with a double negative feedback regulation, whose tumoural shift, leading to overexpression of LIN28B and silencing of miR-30a, widely contributes to thyroid cancer progression.

Disclosure: This work was supported by the Ministerio de Economia y Competitividad (SAF2013-44709R) and by the Comunidad de Madrid (S2011/BMD-2328-Tironet).