Estrogen-induced epigenetic silencing of myotrophin reduces proliferation and is associated with chemosensitivity in hepatocellular carcinoma cells

Background: Hepatocellular carcinoma (HCC) carries poor survival and limited response to conventional chemotherapy. Epidemiological evidence suggests a lower incidence of HCC in females, implicating estrogen (E2) in tumor suppression. The epigenetic mechanisms underlying estrogen-associated protection remain incompletely defined. Research design and methods: We investigated the relationship between E2 exposure, myotrophin (MTPN) expression, and chemotherapy response using TCGA HCC datasets, human hepatoma cell lines (HepG2, HUH7), zebrafish larvae, and a diethylnitrosamine (DEN)-induced mouse model. Cells were pretreated with E2 (10 nM, 6 h) followed by doxorubicin (DOX; up to 2.0 nM, 24 h). Promoter methylation was assessed by quantitative methylation-specific PCR. Cell viability, apoptosis, DNA damage, liver size, tumor burden, and protein expression were evaluated. Results: MTPN was overexpressed and hypomethylated in human HCC. E2 exposure reduced MTPN expression and increased promoter methylation in vitro and in vivo. MTPN knockdown decreased HCC cell viability and proliferation. E2 pretreatment enhanced DOX-associated apoptotic responses in hepatoma cells. In DEN-induced HCC, E2 reduced liver size, tumor burden, and hepatic MTPN protein levels. Conclusions: Estrogen-associated epigenetic repression of MTPN contributes to growth suppression in HCC and is associated with enhanced cytotoxic responses to DOX. Clinical validation is required to determine prognostic or therapeutic relevance.