Regulation of cancer stem cell activity by thyroid hormone receptor β.

Increasing numbers of cancer stem cell markers have been recently identified. It is not known, however, whether a member of the nuclear receptor superfamily, thyroid hormone receptor β (TRβ), can function to regulate cancer stem cell (CSC) activity. Using anaplastic thyroid cancer cells (ATC) as a model, we highlight the role of TRβ in CSC activity. ATC is one of the most aggressive solid cancers in humans and is resistant to currently available therapeutics. Recent studies provide evidence that CSC activity underlies aggressiveness and therapeutic resistance of ATC. Here we show that TRβ inhibits CSC activity by suppressing tumor-sphere formation of human ATC cells and their tumor-initiating capacity. TRβ suppresses the expression of CSC regulators, including ALDH, KLF2, SOX2, b-catenin, and ABCG2, in ATC cell-induced xenograft tumors. Single-cell transcriptomic analysis shows that TRβ reduces CSC population in ATC-induced xenograft tumors. Analysis of The Cancer Genome Atlas (TCGA) database demonstrates that the inhibition of CSC capacity by TRβ contributes to favorable clinical outcomes in human cancer. Our studies show that TRβ is a newly identified transcription regulator that acts to suppress CSC activity and that TRβ could be considered as a molecular target for therapeutic intervention of ATC.