Epigallocatechin gallate induces apoptosis in human hepatocellular carcinoma HepG2 cells via TGF/Smad signaling pathway

Abstract

To investigate the cytotoxic effect of epigallocatechin gallate (EGCG) on human hepatocellular carcinoma cell line HepG2 cells and corresponding changes of TGF-beta1-Smad pathway. The cytotoxic effect of EGCG on HepG2 cells was determined by MTT assay. Cell cycle and apoptosis rate were detected by flow cytometry. RT-PCR and luciferase assay were used to verify whether TGF-beta1-Smad signaling pathway is intact in HepG2. The mRNA expression of Smad 2, Smad3, Smad4 and Smad7 was detected by real-time PCR. EGCG induced apoptosis in the HepG2 cells in a time- and concentration-dependent manner. The proportion of G(1) phase cells was increased gradually as the concentration increased. However, the percentage of cells in S phase was decreased gradually. Annexin V/PI assay demonstrated that early apoptosis increased as the concentration increased, and late apoptosis also increased, when treated with high-concentration EGCG. The intact TGF-beta1-Smad pathway was verified by luciferase assay and RT-PCR. There was no significant effect of EGCG on mRNA level of Smad 2, Smad 3, and Smad 4 in HepG2 cells, but downregulated mRNA level of Smad 7. EGCG can reduce apoptosis in human hepatocellular carcinoma cell line HepG2 cells. The activation of TGF-beta1-Smad signaling pathway may be involved in its cytotoxicity mechanisms.