NUCLEAR ORPHAN RECEPTOR COUP-TF2 INCREASED THE RESISTANCE TO ANIKOISIS AND THE METASTATIC POTENTIAL IN HEPATOCELLULAR CARCINOMA

Background and aim: Hepatocellular carcinoma (HCC) is the second cause of cancer-related death worldwide. In the last few years, the role of nuclear receptors in hepatocarcinogenesis has received great attention. The orphan nuclear receptor COUP-TF2 regulates important biological processes such as glucose and lipid metabolic homeostasis. Recent studies indicate that COUP-TF2 is a prooncogenic factor but its role in HCC is still controversial. Aim of this study was to evaluate the role of COUP-TF2 in hepatocarcinogenesis and in HCC progression. Material and methods: COUP-TFII expression on primary HCC samples was evaluated by immunohistochemistry. Overexpressing COUP-TFII HCC cells lines were created through stable transfection with pcR3.1/COUP-TF2 (Hepa1–6/COUP-TF2, HuH7/COUP-TF2, HepG2/COUP-TF2). The migration and the ability to colonize sites at a distance from the growth front were evaluated by Time-Laps microscopy. Finally, we studied the role of COUP-TFII in an in vivo model of mouse carcinogenesis (TgN(Alb1HBV)44Bri) realizing a triple transgenic animal where the liver-specific Cre expression deletes COUP-TF2 in hepatocytes. Results: COUP-TFII was over-expressed in primary HCC samples and Kaplan-Meier and Cox regression analysis showed that it may be an independent prognostic factor of worse outcome. Overexpression of COUP-TF2 has no significant effect on cell proliferation, but induces a pro-metastatic phenotype characterized by an increased resistance to anikoisis. Live cell imaging experiments showed that COUP-TF2 over-expressing cells had increased cell motility, higher shape plasticity and increase tendency to form colonies distant from the cellular growth front. Moreover, we found that several proteins involved in the organization of the cytoskeleton, cell-cell or cell-substrate adhesion (i.e. FAK, P-FAK, T-cadherin, β-catenin, αV-integrin, VCAM and α-tubulin), were differently modulated in COUP-TF2 overexpressing vs control cells. Finally, COUP-TF2 deletion in hepatocytes of HBV-transgenic mice (Tg[HBV]COUP-TF2-KO) reduced tumor growth and pulmonary metastasis compared to control animals. Conclusions: In the light of our data, COUP-TFII appears to play a role in the metastatic progression of HCC. Ongoing research will help clarifying the molecular mechanisms regulated by and the clinical significance of COUP-TF2 expression in HCC cancer cells.