Curcumin reactivates epigenetically silenced tumor suppressor gene tissue factor pathway inhibitor-2 in hepatocellular carcinoma cells
Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third most fatal, with a rising incidence in the US as a result of the increase in alcoholic liver disease and obesity. Current therapeutic strategies are unsatisfactory with poor treatment outcomes and efficacious therapies are acutely needed for better management of this deadly disease. Curcumin, a phenolic compound from the rhizome of the plant Curcuma longa has been shown to inhibit growth and induce cell death in various types of cancer cells including HCC. However, the anti-HCC mode of action of curcumin has not yet been elucidated.
In HCC, aberrant promoter methylation and histone deacetylation are implicated in the inactivation of tumor suppressor genes which has a significant impact on carcinogenesis. Tissue factor pathway inhibitor-2 (TFPI-2), a Kunitz-type serine protease inhibitor, is a tumor suppressor gene that is frequently epigenetically silenced in human HCC and HCC cell lines. Restoration of TFPI-2 expression in tumor tissue has been shown to not only inhibit invasion, tumor growth, metastasis and angiogenesis but also induce apoptosis. We examined the effects of curcumin on tumor suppressor genes in HCC and observed robust reactivation of TFPI-2 in HepG2 cells upon curcumin treatment. We confirmed that TFPI-2 was under epigenetic control in HepG2 cells by using demethylating agent 5-Aza-2'deoxycytidine (5-AZA) and histone deacetylase inhibitor trichostatin A (TSA), both of which induced gene expression. Further, we investigated the epigenetic modifications at the TFPI-2 promoter and the alterations induced by curcumin in these epigenetic states. Histone H3 acetylation at the transcription factor binding sites of the TFPI-2 promoter region was increased by curcumin and correlated with the induction of gene expression. The reactivation of TFPI-2 also corresponded with a decrease in cell invasiveness and increase in cell death in HepG2 cells. Overall, our data strongly suggest that curcumin can reverse the epigenetic alterations at the TFPI-2 promoter and thus, reactivate this silenced tumor suppressor gene. These results support a potential therapeutic role for curcumin in the management of HCC.