Fenretinide-induced apoptosis of Huh-7 hepatocellular carcinoma is retinoic acid receptor ß dependent

Abstract

BACKGROUND:Retinoids are used to treat several types of cancer; however, their effects on liver cancer have not been fully characterized. To investigate the therapeutic potential of retinoids on hepatocellular carcinoma (HCC), the present study evaluates the apoptotic effect of a panel of natural and synthetic retinoids in three human HCC cell lines as well as explores the underlying mechanisms.METHODS:Apoptosis was determined by caspase-3 cleavage using western blot, DNA double-strand breaks using TUNEL assay, and phosphatidylserine translocation using flow cytometry analysis. Gene expression of nuclear receptors was assessed by real-time PCR. Transactivation assay and chromatin immunoprecipitation (ChIP) were conducted to evaluate the activation of RXRa/RARß pathway by fenretinide. Knockdown of RARß mRNA expression was achieved by siRNA transfection.RESULTS:Our data revealed that fenretinide effectively induces apoptosis in Huh-7 and Hep3B cells. Gene expression analysis of nuclear receptors revealed that the basal and inducibility of retinoic acid receptor ß (RARß) expression positively correlate with the susceptibility of HCC cells to fenretinide treatment. Furthermore, fenretinide transactivates the RXRa/RARß-mediated pathway and directly increases the transcriptional activity of RARß. Knockdown of RARß mRNA expression significantly impairs fenretinide-induced apoptosis in Huh-7 cells.CONCLUSION:Our findings reveal that endogenous expression of retinoids receptor RARß gene determines the susceptibility of HCC cells to fenretinide-induced apoptosis. Our results also demonstrate fenretinide directly activates RARß and induces apoptosis in Huh-7 cells in a RARß-dependent manner. These findings suggest a novel role of RARß as a tumor suppressor by mediating the signals of certain chemotherapeutic agents.