A ligand for peroxisome proliferator activated receptor γ inhibits cell growth and induces apoptosis in human liver cancer cells

Background and aims: Induction of apoptosis of cancer cells through ligands of nuclear hormone receptors (NHRs) is a new approach in cancer therapy. Recently, one of the NHRs, peroxisome proliferator activated receptor gamma (PPARgamma), has been shown to influence cell growth in certain cancer cells although its effect on hepatocellular carcinoma (HCC) has not been analysed. Methods: Experiments were conducted using three human liver cancer cell lines, PLC/PRF/5, Hep G2 and HuH-7, in vitro. These cells were exposed to troglitazone, a synthetic ligand for PPARgamma, and the effects on cell growth were analysed. Results: Expression of PPARgamma mRNA was detected in all three liver cancer cell lines. Activation of PPARgamma by troglitazone caused a marked growth inhibition in a dose dependent manner in three hepatoma cell lines. The DNA fragmentation ELISA assay and Hoechst 33258 staining revealed that the growth inhibitory effect by adding troglitazone was due to apoptosis of PLC/PRF/5, which strongly expressed PPARgamma. Troglitazone also induced activation of the cell death protease, caspase 3, but not cospase 8, in PLC/PRF/5 cells, However, expression levels of antiapoptotic factor bcl-2 and apoptosis inducing factor box were not affected. Conclusion: Our study showed that PPARgamma was expressed in human liver cancer cells and that the ligand for PPARgamma, troglitozone, inhibited the growth of these cells by inducing apoptosis through cospase 3 activation, indicating that troglitozone could be potentially useful as an apoptosis inducer for the treatment of HCC.