Thyroglobulin induces thyroid cell growth through suppression of miR-16 and miR-195
T. Akama, T. Hara, D. Yan, A. Kawashima, A. Yoshihara, M. Sue, K. Tanigawa, H. Wu, Y. Ishido, N. Ishii & K. Suzuki
Introduction: Thyroglobulin (Tg) is stored in the follicular lumen of the thyroid and serves as a substrate of thyroid hormone biosynthesis. However, it was shown that Tg significantly induces thyrocyte cell growth and suppresses expression of thyroid-functional genes. Despite having such functions, molecular mechanisms of Tg action are largely unclear. We have recently demonstrated that TSH-induced thyroid cell growth is partly mediated by a downregulation of microRNAs (miRNA) and induction of their target genes required for cell growth. In this study, we examined possible role of such miRNAs on Tg-induced thyroid cell growth.
Methods: Rat thyroid FRTL-5 cells maintained without TSH, insulin, and with 0.2% rather than 5% serum were treated with physiological concentrations of Tg. Total RNA was extracted and expression of miRNAs was determined using miRNA microarray and real-time PCR. The effect of miRNAs on cell growth and the expression of their target genes were assessed by bromodeoxyuridine (BrdU) incorporation, cell count, and real-time PCR using specific miRNA agonists.
Results: We have identified 21 miRNAs whose expression was downregulated by Tg. Those included miR-16 and miR-195, which were previously shown as important mediators of TSH action. Overexpression of miR-16 and miR-195 resulted in suppression of Tg-induced BrdU incorporation and cell growth. In that condition, induction of their target genes essential for cell growth, Mapk8, Ccne1 and Cdc6, were attenuated.
Conclusion: Our results indicate that Tg induces thyroid cell growth through suppression of miR-16 and miR-195 and induction of their target genes, which is similar to the mechanism of TSH action. miR-16 and miR-195 might be essential miRNAs for the regulation of thyroid cell growth.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.