The thyroid hormone 3,3 0 ,5-triiodo-L-thyronine (T 3 ) regulates growth, development, and differentiation processes in animals. These activities are mediated by the nuclear thyroid hormone receptors (TRs). Microarray analyses were performed previously to study the mechanism of regulation triggered by T 3 treatment in hepatoma cell lines. The results showed that spondin 2 was regulated positively by T 3 . However, the underlying mechanism and the physiological role of T 3 in the regulation of spondin 2 are not clear. To verify the microarray results, spondin 2 was further investigated using semi-quantitative reverse transcription-PCR and western blotting. After 48 h of T 3 treatment in the HepG2-TRa1#1 cell line, spondin 2 mRNA and protein levels increased by 3.9-to 5.7-fold. Similar results were observed in thyroidectomized rats. To localize the regulatory region in spondin 2, we performed serial deletions of the promoter and chromatin immunoprecipitation assays. The T 3 response element on the spondin 2 promoter was localized in the K1104/K1034 or K984/K925 regions. To explore the effect of spondin 2 on cellular function, spondin 2 knockdown cell lines were established from Huh7 cells. Knockdown cells had higher migration ability and invasiveness compared with control cells. Conversely, spondin 2 overexpression in J7 cells led to lower migration ability and invasiveness compared with control cells. Furthermore, this study demonstrated that spondin 2 overexpression in some types of hepatocellular carcinomas is TR dependent. Together, these experimental findings suggest that spondin 2, which is regulated by T 3 , has an important role in cell invasion, cell migration, and tumor progression.

Thyroid hormone (T 3 ) signaling through the thyroid hormone receptor (TRa1) 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 T 3 through a native T 3 response element in the primary miR-21 promoter. Overexpression of miR-21 promoted hepatoma cell migration and invasion, similar to that observed with T 3 stimulation in hepatoma cells. In addition, anti-miR-21-induced suppression of cell migration was rescued by T 3 . 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 T 3 . 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 b-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 ¼ 0.005) between the tumor/nontumor ratios of TRa1 and miR-21 expression, whereas a negative correlation (P ¼ 0.019) was seen between miR-21 and TIAM1 expression in patients with hepatoma. Our findings collectively indicate that miR-21 stimulation by T 3 and subsequent TIAM1 suppression promotes hepatoma cell migration and invasion. Cancer Res; 73(8); 2505-17. Ó2013 AACR.