Dickkopf 4 positively regulated by the thyroid hormone receptor suppresses cell invasion in human hepatoma cells

Abstract

Thyroid hormone (T 3 ) mediates cellular growth, development, and differentiation by binding to the nuclear thyroid hormone receptor (TR). Recent studies suggest that long-term hypothyroidism is associated with human hepatocellular carcinoma (HCC) independent from other major HCC risk factors. Dickkopf (DKK) 4, a secreted protein, antagonizes the Wnt signal pathway. In this study, we demonstrate that T 3 may play a suppressor role by inducing DKK4 expression in HCC cells at both the messenger RNA (mRNA) and protein levels. DKK4 was down-regulated in 67.5% of HCC cancerous tissues. The decrease in DKK4 levels was accompanied by a concomitant decrease in TR protein levels in the matched cancerous tissues in 31% of tissues compared by immunoblotting with the adjacent noncancerous tissues. Further, TR and DKK4 expression levels were positively correlated in both normal and cancerous specimens by tissue array analysis. In function assays, stable DKK4 transfected into J7 or HepG2 cells decreased cell invasion in vitro. Conversely, knocking down DKK4 restores cell invasiveness. DKK4-expressing J7 clones showed increased degradation of b-catenin, but down-regulation of CD44, cyclin D1, and c-Jun. To investigate the effect of DKK4 and TR on tumor growth in vivo, we established a xenograft of J7 cells in nude mice. J7-DKK4 and J7-TRa1 overexpressing mice, which displayed growth arrest, lower lung colony formation index, and smaller tumor size than in control mice, supporting an inhibitory role of DKK4 in tumor progression. Conclusion: Taken together, these data suggest that the TR/DKK4/Wnt/b-catenin cascade influences the proliferation and migration of hepatoma cells during the metastasis process and support a tumor suppressor role of the TR. (HEPATOLOGY 2012;55:910-920) T hyroid hormone, 3,3 0 -5-triiodo-l-thyronine (T 3 ), is a potent mediator of many physiological processes including embryonic development, cell differentiation, metabolism, and the regulation of cell proliferation.1,2 The actions of T 3 are mediated by nuclear thyroid hormone receptors (TRs). TRs are ligand-dependent transcription factors that comprise modular functional domains that mediate hormone binding (ligands), DNA binding, receptor homo-and heterodimerization, and interaction with other transcription factors and cofactors.3 TRs are derived from two genes, TRa and TRb, located on human chromosomes 17 and 3, respectively. Transcripts of each of these genes undergo alternative promoter choice to generate TRa1 and TRa2 as well as TRb1 and TRb2 receptor isoforms. 2-4Using a complementary DNA (cDNA) microarray technique, we previously identified 148 genes that are positively regulated by T 3 in a TRa1-overexpressing

Thyroid Hormone Regulation of miR-21 Enhances Migration and Invasion of Hepatoma

“…A pilot study additionally revealed miR-21 upregulation by T 3 in HepG2-TRa1 cells. Interestingly, T 3 /thyroid hormone receptor signaling may exert both oncogenic (10) and tumor suppressor effects (21,22). The findings that miR-21 is increased in hepatoma tissue and potentially upregulated as a target of T 3 in HepG2 cells imply that T 3 functions as an oncogene in this case.…”

Role of thyroid hormones in the neoplastic process: an overview

“…Notably, these animals displayed greater tumor sizes and metastasis rates than euthyroid animals, supporting the metastasis-promoting effect of T 3 in HCC (Chen et al 2008). Several members of the MMP family, including MMP-2, MMP-9 and MMP-7, are upregulated upon r-TRAIL stimulation in hepatoma cells, an effect confirmed by increased invasiveness in both in vitro and in vivo models (Chi et al 2012). Cathepsin H, a protease involved in the degradation of ECM components, leading to cancer cell migration and metastasis, is induced by T 3 in HCC cells, enhancing the invasion potential of hepatoma cells in vitro and in vivo (Wu et al 2011).…”

“…Inversely, other studies have demonstrated that T 3 treatment of the same cells leads to spondin 2 overexpression, which inhibits cell invasion and migration (Liao et al 2010). T 3 treatment also upregulates the expression of DKK4 protein, an antagonist of Wnt, in HepG2 TR-expressing cells (Chi et al 2013), suggesting that the T 3 upregulation of the TR/DKK4/Wnt/β-catenin cascade inhibits the metastasis of hepatoma cells (Liao et al 2012).…”

“…T 3 has a suppressive effect on the growth of specific liver tumors such as hepatoma, where the proliferative inhibitory effect of T 3 is mediated by TGF-β upregulation (Yen et al 2006). T 3 /TR signaling mediates Dickkopf 4 (DKK4) expression that inhibits the proliferation and migration of hepatoma cells via blockade of the Wnt signaling pathway (Liao et al 2012). Similarly, THs inhibit cell proliferation by promoting p21 stability through endoglin upregulation (Lin et al 2013a).…”

“…TNFrelated apoptosis-inducing ligand (TRAIL/Apo2L) is a potent effector of tumorigenesis that not only promotes apoptosis but also triggers non-apoptotic pathways (Johnstone et al 2008). T 3 upregulates TRAIL expression at the transcriptional level in TR-overexpressing hepatoma cells, which in turn promotes cell migration and invasion (Chi et al 2012).…”