Fenofibrate induced PPAR alpha expression was attenuated by oestrogen receptor alpha overexpression in Hep3B cells

The physiological regulation of Oestrogen receptor (ER) and peroxisome proliferator-activated receptor alpha (PPAR) in Hepatocellular carcinoma (HCC) remains unknown. The present study we first treat the cells with fenofibrate and further investigated the possible mechanisms of 17-estradiol (E-2) and/or ER on regulating PPAR expression. We also found higher PPAR expression in the tumor area than adjacent areas and subsequently compared PPAR expression in four different hepatic cancer cell lines. Hep3B cells were found to express more PPAR than the other cell lines. Using the PPAR agonist fenofibrate, we found that fenofibrate increased Hep3B cell proliferation efficiency by increasing cell cycle proteins, such as cyclin D1 and PCNA, and inhibiting p27 and caspase 3 expressions. Next, we performed transient transfections and immuno-precipitation studies using the pTRE2/ER plasmid to evaluate the interaction between ER and PPAR. ER interacted directly with PPAR and negatively regulated its function. Moreover, in Tet-on ER over-expressed Hep3B cells, E-2 treatment inhibited PPAR, its downstream gene acyl-CoA oxidase (ACO), cyclin D1 and PCNA expression and further increased p27 and caspase 3 expressions. However, over-expressed ER plus 17--estradiol (10(-8) M) reversed the fenofibrate effect and induced apoptosis, which was blocked in ICI/melatonin/fenofibrate-treated cells. This study illustrates that PPAR expression and function were negatively regulated by ER expression in Hep3B cells.