Abstract
BackgroundRetinoids 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.MethodsApoptosis 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 RXRα/RARβ pathway by fenretinide. Knockdown of RARβ mRNA expression was achieved by siRNA transfection.ResultsOur 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 β (RARβ) expression positively correlate with the susceptibility of HCC cells to fenretinide treatment. Furthermore, fenretinide transactivates the RXRα/RARβ-mediated pathway and directly increases the transcriptional activity of RARβ. Knockdown of RARβ mRNA expression significantly impairs fenretinide-induced apoptosis in Huh-7 cells.ConclusionOur findings reveal that endogenous expression of retinoids receptor RARβ gene determines the susceptibility of HCC cells to fenretinide-induced apoptosis. Our results also demonstrate fenretinide directly activates RARβ and induces apoptosis in Huh-7 cells in a RARβ-dependent manner. These findings suggest a novel role of RARβ as a tumor suppressor by mediating the signals of certain chemotherapeutic agents.
Highlights
Retinoids are used to treat several types of cancer; their effects on liver cancer have not been fully characterized
Reagents The retinoids used in this study are grouped into three categories: (1) carotenoids including β-carotene, lycopene, and lutein; (2) classic retinoids including all-trans retinol palmitate, retinol acetate, 9-cis retinaldehyde, 13-cis retinol, 13-cis retinaldehyde, 13-cis retinoic acid, and fenretinide; (3) receptor-specific retinoids including all-trans retinoic acid, 9-cis retinoic acid, and TTNPB (4-(E-2-[5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl]-1-propenyl) benzoic acid). β-Carotene, lycopene, all-trans retinol palmitate, 9-cis retinaldehyde, 13cis retinol, fenretinide, all-trans retinoic acid, 9-cis retinoic acid, and TTNPB were purchased from Sigma-Aldrich
This finding suggests a role of retinoic acid receptor β (RARβ) in determining the sensitivity of hepatocellular carcinoma (HCC) cells to certain chemotherapeutic agents, which may hold true for other types of tumor cells
Summary
Retinoids are used to treat several types of cancer; their effects on liver cancer have not been fully characterized. The natural and synthetic derivates of vitamin A, has a long history in clinical application in addition to its roles as an essential nutrient. The best example of retinoid anticancer effect is the retinoic acid (RA) differentiation therapy for acute promyelocytic leukemia (APL) [3]. The use of RA has changed the clinical course of APL from a highly lethal to a curable leukemia, establishing the prototype of retinoidbased therapies and the rationale for the use of retinoids in the treatment and prevention of cancer [4]. Retinoids have been used either alone or in combination with other chemotherapeutic agents to treat other types of cancer and precancerous lesions. The anti-proliferative effect of tamoxifen is synergistically enhanced when used in combination with retinoids [5]
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