Lack of PPARβ/δ‐Inactivated SGK‐1 Is Implicated in Liver Carcinogenesis

Objective. The present study examined the role of PPARβ/δ in hepatocellular carcinoma (HCC). Methods. The effect of PPARβ/δ on HCC development was analyzed using PPARβ/δ‐overexpressed liver cancer cells and PPARβ/δ‐knockout mouse models. Results. PPARβ/δ(-/-) mice were susceptible to diethylnitrosamine‐ (DEN‐) induced HCC (87.5% vs. 37.5%, p < 0.05). In addition, PPARβ/δ‐overexpressed HepG2 cells had reduced proliferation, migration, and invasion capabilities accompanied by increased apoptosis and cell cycle arrest at the G0/G1 phase. Moreover, differential gene expression profiling uncovered that the levels of serine/threonine‐protein kinase (SGK‐1) mRNA and its encoded protein were reduced in PPARβ/δ‐overexpressed HepG2 cells. Consistently, elevated SGK‐1 levels were found in PPARβ/δ(-/-) mouse livers as well as PPARβ/δ‐knockdown human SMMC‐7721 HCC cells. Chromatin immunoprecipitation (ChIP) assays followed by real‐time quantitative polymerase chain reaction (qPCR) assays further revealed the binding of PPARβ/δ to the SGK‐1 regulatory region in HepG2 cells. Conclusions. Due to the known tumor‐promoting effect of SGK1, the present data suggest that PPARβ/δ‐deactivated SGK1 is a novel pathway for inhibiting liver carcinogenesis.