Peroxisome proliferator-activated receptor gamma ligands exert antineoplastic effects in hepatocellular carcinoma cells / 대한내과학회지

ABSTRACT

BACKGROUND/AIMS: Thiazolidinediones, which are synthetic insulin sensitizers, are known activators of peroxisome proliferator-activated receptor gamma (PPARgamma). PPARgamma ligands, including endogenous 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2), are thought to elicit antineoplastic effects in various cancer cells. In this study, the antineoplastic effects of PPARgamma ligands against hepatocellular carcinoma (HCC) cells were investigated. METHODS: HepG2, Hep3B, and PLC/PRF5 cells were cultured with troglitazone (TGZ), pioglitazone (PGZ), rosiglitazone (RGZ), or 15d-PGJ2 at concentrations of 20-100 micrometer. Cell viability, cell cycle arrest, apoptosis, and caspase activity were measured using the MTT assay, flow cytometry, enzyme-linked immunosorbent assay (ELISA), and colorimetric assays, respectively. The effects of various caspase inhibitors were also measured using a cell death detection ELISA. RESULTS: All three cell lines expressed the PPARgamma gene. TGZ and 15d-PGJ2 strongly inhibited growth in HepG2, Hep3B, and PLC/PRF5 cells. In contrast, PGZ and RGZ showed a much weaker effect in all cell lines. In terms of cell cycle arrest and apoptosis, TGZ induced G0/G1 arrest in HepG2 cells and increased the apoptotic fraction in Hep3B and PLC/PRF5 cells. In contrast, 15d-PGJ2 induced apoptosis only in HepG2 and Hep3B cells. TGZ and 15d-PGJ2 increased caspase-3 activity significantly and increased caspase-9 activity slightly. TGZ- and 15d-PGJ2-induced apoptoses were inhibited by a pancaspase inhibitor (Z-VAD-FMK) and a caspase-3 specific inhibitor (Z-DEVD-FMK) in a dose-dependent manner. CONCLUSIONS: TGZ and 15d-PGJ2 elicit antineoplastic effects in various HCC cells via caspase-dependent apoptotic induction. Their differential effects on similar cell types suggest that another antineoplastic mechanism, most likely a PPARgamma-independent pathway, is involved.