Thyroid hormone regulation of mir-21 enhances migration and invasion of hepatoma

Thyroid hormone (T₃) signaling through the thyroid hormone receptor (TRα1) regulates hepatoma cell growth and pathophysiology, but the underlying mechanisms are unclear at present. Here, we have shown that the oncomir microRNA-21 (miR-21) is activated by T₃ through a native T₃ response element in the primary miR-21 promoter. Overexpression of miR-21 promoted hepatoma cell migration and invasion, similar to that observed with T₃ stimulation in hepatoma cells. In addition, anti-miR-21-induced suppression of cell migration was rescued by T₃. The Rac-controlled regulator of invasion and metastasis, T-cell lymphoma invasion and metastasis 1 (TIAM1), was identified as a miR-21 target additionally downregulated by T₃. Attenuation and overexpression of miR-21 induced upregulation and downregulation of TIAM1, respectively. TIAM1 attenuation, in turn, enhanced migration and invasion via the upregulation of β-catenin, vimentin, and matrix metalloproteinase-2 in hepatoma cells. Notably, correlations between TRa1, miR-21, and TIAM1 expression patterns in animal models paralleled those observed in vitro. In the clinic, we observed a positive correlation (P=0.005) between the tumor/nontumor ratios of TRa1 and miR-21 expression, whereas a negative correlation (P = 0.019) was seen between miR-21 and TIAM1 expression in patients with hepatoma. Our findings collectively indicate that miR-21 stimulation by T3 and subsequent TIAM1 suppression promotes hepatoma cell migration and invasion. Cancer Res; 73(8); 2505-17.