Peroxisome proliferator-activated receptor gamma ligand troglitazone induces cell cycle arrest and apoptosis of hepatocellular carcinoma cell lines.
BACKGROUND
Ligand activation of peroxisome proliferator-activated receptor gamma (PPARgamma) results in the inhibition of proliferation of various cancer cells. The aim of this study is to investigate the mechanisms of cell growth inhibition of hepatocellular carcinoma (HCC) cell lines by the PPARgamma ligand, troglitazone.


METHODS
Six HCC cell lines were used to study the effects of troglitazone on cell growth by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, on cell cycle by flow cytometry, and on the cell cycle-regulating factors of late G1 phase by Western blotting. Apoptosis assays were performed by flow cytometry using membrane, nuclear, cytoplasmic, and mitochondrial markers. Caspase inhibitors were used to analyze the mechanisms of apoptosis induced by troglitazone.


RESULTS
Troglitazone showed a potent dose-dependent effect on the growth inhibition of all six HCC cell lines, which were suppressed to under 50% of control at the concentration of 10 micromol/L. The growth inhibition was linked to the G1 phase cell cycle arrest through the up-expression of the cyclin-dependent kinase inhibitors, p21 and p27 proteins, and the hypophosphorylation of retinoblastoma protein. Troglitazone induced apoptosis by caspase-dependent (mitchondrial transmembrane potential decrease, cleavage of poly [adenosine diphosphate ribose] polymerase, 7A6 antigen exposure, Bcl-2 decrease, and activation of caspase 3) and caspase-independent (phosphatidylserine externalization) mechanisms.


CONCLUSIONS
Our data suggest that ligand activation of PPARgamma by troglitazone or modified analogs of the thiazolidinedione class of drugs is a novel target for effective therapy against HCC, because of the significant antiproliferative and programmed cell death induction capabilities demonstrated by troglitazone.
Yoshizawa
Kaname
K
The Second Department of Internal Medicine, Shinshu University School of Medicine, Matsumoto, Japan. kanamey@hsp.md.shinshu-u.ac.jp
Cioca
Daniel P
DP
Kawa
Shigeyuki
S
Tanaka
Eiji
E
Kiyosawa
Kendo
K
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects*; D002839:Chromans / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006801:Humans; D008024:Ligands; D008113:Liver Neoplasms / Q000473:pathology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects*; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones; D014157:Transcription Factors / Q000187:drug effects*; D000077288:Troglitazone; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000970:Antineoplastic Agents; D002839:Chromans; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D013844:Thiazoles; D045162:Thiazolidinediones; D014157:Transcription Factors; D000077288:Troglitazone