ERα36 is an effective target of epigallocatechin-3-gallate in hepatocellular carcinoma

Epigallocatechin-3-gallate (EGCG) is a natural product with potential anti-cancer property whose direct target has not been identified. This study intended to investigate ERα36, a new isoform of estrogen receptor alpha (ERa), as a therapeutic target of EGCG in hepatocellular carcinoma (HCC). In this work, we examined the expression level of ERs in HCC cell lines and a normal human liver cell line, and evaluated inhibition effect of EGCG on these cells , and further on Hep3B . The results showed that ERα36 was the main ER in HCC cells and served as a biomarker of responsiveness to EGCG inhibition, and there was a positive correlation between ERα36 expression level and inhibitory effect of EGCG as indicated by IC . experiments also showed dose-dependent inhibition of EGCG on ERα36 high-expressing Hep3B. EGCG exerted inhibition on Hep3B cells by both anti-proliferation and pro-apoptosis. ERα36-EGFR-Her-2 feedback loop, PI3K/Akt and MAPK/ERK pathways were inhibited, while caspase 3 was activated by EGCG in Hep3B cells, with p-ERK accumulated in cytoplasm. The inhibitory effect of EGCG was significantly attenuated when ERα36 was pre-activated. This is the first evidence that EGCG exerts its anti-cancer effect by inhibiting ERα36, followed with inhibition of the ERα36-EGFR-Her-2 feedback loop and PI3K/Akt, MAPK/ERK pathway, activation of caspase 3, and accumulation of p-ERK in cytoplasm. It suggests that ERα36 might be an efficient target of EGCG in HCC.