Estrogen Receptor-α Suppresses Liver Carcinogenesis and Establishes Sex-Specific Gene Expression

SIMPLE SUMMARY: The hormone estrogen is well known for its role in promoting breast and ovarian cancer. Estrogen has the opposite effect on the liver, which it protects from cancer. We show that this protection requires Estrogen Receptor α, but not Estrogen Receptor β, and correlates with a female pattern of liver gene expression. Female expression in the liver requires Estrogen Receptor α expressed in non-liver cells. Surgical removal of the ovaries, which protect females from liver cancer at least in part through their production of estrogen, does not affect the female-specific liver gene expression pattern. Estrogen may therefore influence liver carcinogenesis through multiple independent mechanisms. We identify six genes that are strong candidates for mediating Esr1′s protection against liver cancer. ABSTRACT: Estrogen protects females from hepatocellular carcinoma (HCC). To determine whether this protection is mediated by classic estrogen receptors, we tested HCC susceptibility in estrogen receptor-deficient mice. In contrast to a previous study, we found that diethylnitrosamine induces hepatocarcinogenesis to a significantly greater extent when females lack Esr1, which encodes Estrogen Receptor-α. Relative to wild-type littermates, Esr1 knockout females developed 9-fold more tumors. Deficiency of Esr2, which encodes Estrogen Receptor-β, did not affect liver carcinogenesis in females. Using microarrays and QPCR to examine estrogen receptor effects on hepatic gene expression patterns, we found that germline Esr1 deficiency resulted in the masculinization of gene expression in the female liver. Six of the most dysregulated genes have previously been implicated in HCC. In contrast, Esr1 deletion specifically in hepatocytes of Esr1 conditional null female mice (in which Cre was expressed from the albumin promoter) resulted in the maintenance of female-specific liver gene expression. Wild-type adult females lacking ovarian estrogen due to ovariectomy, which is known to make females susceptible to HCC, also maintained female-specific expression in the liver of females. These studies indicate that Esr1 mediates liver cancer risk, and its control of sex-specific liver gene expression involves cells other than hepatocytes.