Suppression of Calcium Entry Modulates the Expression of TRβ1 and Runx2 in Thyroid Cancer Cells, Two Transcription Factors That Regulate Invasion, Proliferation and Thyroid-Specific Protein Levels

SIMPLE SUMMARY: Thyroid cancer is the most common endocrine cancer and the treatment for such hostile tumors remains a complex challenge. Thus, new insights and mechanisms need to be explored, to design a most suitable therapy for thyroid cancer patients. In this study, we found that the expression of thyroid hormone receptor beta 1 (TRβ1) and Runt-related transcription factor 2 (Runx2) is calcium dependent. The expression of TRβ1 was downregulated but Runx2 upregulated in all investigated thyroid cancer cell lines compared to normal primary thyroid cells. The restoration of TRβ1 expression in thyroid cancer cells inhibited proliferation, invasion and restored thyroid specific proteins expression. Conversely, inhibiting Runx2 decreased proliferation and invasion but had no effect on expression of thyroid specific proteins. We present a novel strategy where inhibiting calcium entry, restoration of TRβ1 and blocking Runx2 can serve as potential therapeutic targets. ABSTRACT: The thyroid hormone receptor beta 1 (TRβ1) is downregulated in several human cancer cell types, which has been associated with development of an aggressive tumor phenotype and the upregulation of Runt-related transcription factor 2 (Runx2). In this study, we show that the expression of TRβ1 protein is downregulated in human thyroid cancer tissues and cell lines compared with the normal thyroid tissues and primary cell line, whilst Runx2 is upregulated under the same conditions. In contrast, the expression of TRβ1 is upregulated, whereas Runx2 is downregulated, in STIM1, Orai1 and TRPC1 knockdown cells, compared to mock transfected cells. To study the functional significance of Runx2 in follicular thyroid cancer ML-1 cells, we downregulated it by siRNA. This increased store-operated calcium entry (SOCE), but decreased cell proliferation and invasion. Moreover, restoring TRβ1 expression in ML-1 cells decreased SOCE, basal and sphingosine 1-phosphate (S1P)-evoked invasion, the expression of the promigratory S1P3 receptor and pERK1/2, and at the same time increased the expression of the thyroid specific proteins thyroglobulin, thyroperoxidase, and thyroid transcription factor-1. In conclusion, we show that TRβ1 is downregulated in thyroid cancer cells and that restoration of its expression can reverse the cancer cell phenotype towards a normal thyroid cell phenotype.