G protein-coupled estrogen receptor deficiency accelerates liver tumorigenesis by enhancing inflammation and fibrosis.

Abstract G protein-coupled estrogen receptor (GPER) is a novel estrogen-binding receptor involved in many pathological conditions, including cancer. In this study, we investigated the effect of GPER on hepatocellular carcinoma (HCC). Our data show GPER knockout in a diethylnitrosamine (DEN)-induced mouse tumor model significantly accelerated liver tumorigenesis, accompanied by enhanced immune cell infiltration, fibrosis, and the production of inflammatory factors, such as interleukin-6 (IL-6). We further delineated the function of GPER in macrophages and hepatic stellate cells (HSCs). Treatment with the selective GPER agonist, G-1, decreased the expression of IL-6 in bone marrow-derived macrophages, which was abrogated upon deficiency of GPER. In a HSC line (LX2), G-1 treatment downregulated the expression of α-smooth muscle actin. In addition, both GPER mRNA and protein levels were significantly lower in HCC compared with matched non-tumor tissues. However, modulating GPER expression did not affect the viability and proliferation of hepatoma cells in vitro . Together our results indicate that GPER protects against HCC tumorigenesis through regulating inflammatory responses rather than directly acting on tumor cells. Therefore, GPER activation may be a potential strategy for prevention and treatment of HCC.