title: Apoptosis induced by troglitazone is both peroxisome proliferator-activated receptor-gamma- and ERK-dependent in human non-small lung cancer cells.
abstract: The role of the peroxisome proliferator-activated receptor-gamma (PPARgamma) in cell differentiation, cell-cycle arrest, and apoptosis has attracted increasing attention. We have recently demonstrated that PPARgamma ligands-troglitazone (TGZ) induced apoptosis in lung cancer cells. In this report, we further studied the role of ERK1/2 in lung cancer cells treated by TGZ. The result demonstrated that TGZ induced PPARgamma and ERK1/2 accumulation in the nucleus, in which the co-localization of both proteins was found. The activation of ERK1/2 resulted in apoptosis via a mitochondrial pathway. Both PPARgamma siRNA and U0126, a specific inhibitor of ERK1/2, were able to block these effects of TGZ, suggesting that apoptosis induced by TGZ was PPARgamma and ERK1/2 dependent. Inhibition of ERK1/2 by U0126 also led to a significant decrease in the level of PPARgamma, indicating a positive cross-talk between PPARgamma and ERK1/2 or an auto-regulatory feedback mechanism to amplify the effect of ERK1/2 on cell growth arrest and apoptosis. In addition to ERK1/2, TGZ also activated Akt. Interestingly, inhibition of ERK1/2 prevented the activation of Akt whereas the suppression of Akt had no effect on ERK1/2, suggesting that Akt was not necessary for TGZ-PPARgamma-ERK pathway. However, the inhibition of Akt promoted the release of cytochrome c, suggesting the activation of Akt may have a negative effect on apoptosis induced by TGZ. In conclusion, our study has demonstrated that TGZ, a synthetic PPARgamma ligand, induced apoptosis in NCI-H23 lung cancer cells via a mitochondrial pathway and this pathway was PPARgamma and ERK1/2 dependent.
authors.affiliation: Department of Surgery, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
authors.forename: Mingyue
authors.initials: M
authors.lastname: Li
authors.forename: Tak W
authors.initials: TW
authors.lastname: Lee
authors.forename: Anthony P C
authors.initials: AP
authors.lastname: Yim
authors.forename: Tony S K
authors.initials: TS
authors.lastname: Mok
authors.forename: George G
authors.initials: GG
authors.lastname: Chen
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology*; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000201:enzymology; D002839:Chromans / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D051336:Mitochondrial Membranes / Q000187:drug effects; D008954:Models, Biological; D047495:PPAR gamma / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D045162:Thiazolidinediones / Q000494:pharmacology*; D000077288:Troglitazone; D014407:Tumor Cells, Cultured
chemical_list: D002839:Chromans; D047495:PPAR gamma; D045162:Thiazolidinediones; D045304:Cytochromes c; D019869:Phosphatidylinositol 3-Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020169:Caspases; D000077288:Troglitazone