Fenofibrate suppresses growth of the human hepatocellular carcinoma cell via PPARα-independent mechanisms

Fenofibrate, a peroxisome proliferator-activated receptor (PPAR) α agonist, is a hypolipidemic drug. Although several studies have explored the fenofibrate-induced antiproliferative effect in cultured human cells, it is not clear which role PPARα plays in this antiproliferative effect. Therefore, we investigated the antiproliferative mechanism of fenofibrate in Huh7 (human hepatoma cell line). Cell viability was measured by the WST-8 assay and cell proliferation was assessed using the BrdU incorporation assay. The cell cycle was analyzed by flow cytometry. The cyclins, tumor suppressor proteins and regulators of the AKT signaling pathway were analyzed by immunoblotting. Using flow cytometry, we showed that fenofibrate blocks entry into the S phase of the cell cycle. We certified that this G1 arrest is caused by the reduction of cyclin A and E2F1 and the accumulation of the cyclin-dependent kinase inhibitor p27. Interestingly, the antiproliferative effect of fenofibrate was not affected by the PPARα antagonist (GW6471) or by PPARα-specific siRNA. These results suggest that fenofibrate suppresses Huh7 cell growth through a PPARα independent mechanism. Furthermore, we showed that treatment of Huh7 cells with fenofibrate leads to suppression of AKT phosphorylation. We also found for the first time that fenofibrate increased the C-terminal modulator protein (CTMP), which inhibits AKT phosphorylation. Our data suggest that fenofibrate inhibits the proliferation of Huh7 cells by blocking Akt activation, and that CTMP is one of the key players for this antiproliferative property of fenofibrate in Huh7 cells.