MiR-30a и lin28b образуют петлю двойной отрицательной связи, регулируемую pik3, способным изменять степень прогрессирования рака щитовидной железы

Abstract

Background . Our recent results showed that tumor supressor miR-30a is firmly downregulated in Thyroid carcinomas. On the other hand, recent studies showed RNA- and DNA- binding proteins LIN28B and HMGA2 induce EMT, thus playing an important role in dedifferentiation and cancer malignification. Finally, latterly several authors agreed on the importance of a robust activation of PI3K for thyroid cancer emergency and progression. Aim : to study the link between the emergency of LIN28B and HMGA2, miR-30a silencing and PI3K hyperactivation, and to determine their effect on thyroid cancer progression. Methors . MiRNA targets computational predictions were performed with MiRanda algorythm. LIN28B and miR-30a expression vectors were transfected in ATC derived and normal thyroid cell lines; mRNA and protein levels were determined by qPCR, Luciferase and Western Blot. Invasion, proliferation and cell cycle assays were performed in Transwell, cell counter, and FACScan respectively. Results . MiRanda algorythm identified multiple miR30a recognition elements in all LIN28B, HMGA2 and PI3K effectors. LIN28B expression correlated with PI3K activating mutations in ATC derived cell lines. Overexpression of miR30a resulted in LIN28B, HMGA2, and several PI3K effectors silencing, and in an increase in p27(Kip) protein levels. Inversely, LIN28B overexpressing cells showed a decrease in miR30a levels and an increased expression of HMGA2 and PI3K effectors. The general outcome was a significant decrease in invasion and proliferation in miR-30a overexpressing cells and, conversely, an increase in these parameters by LIN28B. Conclusions . These data suggest the existence of a PI3K regulated feedback with a double-negative loop between miR-30a and LIN28B. Here, PI3K activation acts to switch the steady states. Initially, high miR-30a levels repress LIN28B expression. After PI3K is activated, LIN28B is produced and miR-30a is repressed. This state reinforces PI3K hyperactivation. Thus, the feedback implements a tumoral gene expression shift, contributing to thyroid cancer progression.