TR₄ nuclear receptor suppresses HCC cell invasion via downregulating the EphA2 expression

Early studies indicated that testicular nuclear receptor 4 (TR₄) could function as a suppressor in the transcriptional regulation of the HBV core gene expression, which might then influence the development of hepatocellular carcinoma (HCC). The direct linkage between TR₄ and HCC progression, however, remained unclear. Here, via a human clinical sample survey, we found that 13 of the 18 HCC patients studied had lower TR₄ expression in metastatic lesions than in matched primary HCC lesions, suggesting that TR₄ may play a negative role in HCC metastasis. Results from in vitro cell migration/invasion studied confirmed that TR₄ could suppress HCC cell migration/invasion. Mechanism dissection revealed that TR₄ might function through downregulating ephrin type-A receptor 2 (EphA2) expression at the transcriptional level via direct binding to the TR₄REs located on the 5' promoter of EphA2 to suppress HCC cell migration/invasion. Targeting the EphA2 via EphA2-siRNA partially reversed the enhanced HCC cell migration/invasion with confirmed TR₄ knockdown. Notably, results from preclinical studies using in vivo mouse model with orthotopic xenograft of HCC LM3 cells also confirmed the in vitro findings. Taking these findings together, preclinical studies using multiple in vitro HCC cell lines and an in vivo mouse model all led to the conclusion that TR₄ may function as a suppressor of HCC metastasis and that targeting this newly identified TR₄-EphA2 signaling may improve our ability to suppress HCC metastasis.