In conclusion, our study has demonstrated that TGZ, a synthetic PPARgamma ligand, inhibits lung cancer cells growth through cell-cycle arrest, increased cell differentiation and induction of apoptosis. In this pathway, the activation of ERK by TGZ plays a central role in promoting apoptosis, which appears to be mediated via a mitochondria-related mechanism and functions in a PPARgamma-dependent manner. The interaction between PPARgamma and ERK may create an auto-regulatory and positive feedback loop to enhance the effect of ERK whereas the activation of Akt may generate a negative regulation to control the degree of apoptosis occurred in lung cancer cells. TGZ may counteract NNK function to inhibit lung cancer cell growth in the PPARgamma-dependent manner. / Lung cancer is the world's leading cause of cancer death. Currently there is not an acceptable adjuvant or palliative treatment modalities that have been conclusively shown to prolong survival in lung cancer. Therefore, translational research to improve outcomes with this disease is critical. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription. PPARgamma ligands have been demonstrated to inhibit growth of cancer cells. The role of the PPARgamma in cell differentiation, cell cycle arrest and apoptosis has attracted increasing attention. Our study focused on the role of PPARgamma and its ligand troglitazone (TGZ) in the cell death of human lung cancer and the interaction between PPARgamma system and 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major tobacco-specific carcinogen. / The epidemic of lung cancer is directly attributable to cigarette. However, it is still not completely known the molecular pathway of cigarette smoking in the pathogenesis of lung cancer. Among the carcinogenoic chemicals of cigarette smoking, 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the most potent, which induces lung cancer in all animal species tested. Unlike PPARgamma ligands, NNK can promote cell proliferationa and growth. It is interesting to know whether PPARgamma ligands can inhibit the growth-promoting function of NNK. To address this question, we used NCI-H23 lung cancer cells as the model to study how TGZ influenced the function of NNK. Results showed that NNK stimulated cell proliferation, induced the DNA binding activity of nuclear factor-kappaB (NF-kappaB), down-regulated Bad expression, and up-regulated PPARgamma protein expressions. Inhibition of NF-kappaB nuclear translocation led to the suppression of NNK-mediated Bad expression, indicating that NNK may regulate Bad expression through the activation of NF-kappaB. TGZ significantly inhibited cell proliferation induced by NNK. Though TGZ did not affect nuclear factor-kappaB (NF-kappaB) activity, it up-regulated Bad expression. Taken together, TGZ can efficiently inhibit the proliferation of lung cancer cells induced by NNK via Bad- and PPARgamma- related pathways, which may not be directly relevant to the activity of NF-kappaB. / To elucidate the mechanism responsible for the effect of PPARgamma and TGZ on lung cancer cells, we further studied the PPARgamma molecular pathway in NCIH23 treated by TGZ. The result demonstrated that TGZ induced PPARgamma and ERK1/2 accumulation in the nucleus, where the co-localization of both proteins was found. It showed that the activation of ERK1/2 resulted in apoptosis via the mitochondrial pathway, reflecting by reduction of mitochondria membrane potential, change in Bcl-2 family members, release of cytochrome c into cytosol, and activation of caspase 9. 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 that there was probably a positive cross-talk between PPARgamma and ERK 1/2 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 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. Thus, the activation of Akt may have a negative effect on apoptosis induced by TGZ. Wortmannin, a PI3K inhibitor, inhibited TGZ-induced ERK1/2 and Akt activation, indicating that PI3K may function at the up-stream of ERK and Akt. In conclusion, our study has demonstrated that TGZ induced apoptosis in NCI-H23 lung cancer cells via a mitochondrial pathway and this pathway was PPARgamma-and ERK1/2-dependent. / We first investigated the effect of PPARgamma ligand TGZ on two human lung cancer cells (NCI-H23 and CRL-2066) and one human lung normal cell (CCL-202). The results showed that in consistence with the loss of cell viability, TGZ induced apoptosis in CRL-2066 and NCI-H23 cells but not in CCL-202 cells. TGZ up-regulated PPARgamma expression in all these three lung cell lines, especially in the cancer cells. In association of the time-dependent inhibition of the cell proliferation, TGZ down-regulated the expression of Bcl-w and Bcl-2 but activated ERK1/2 and p38, suggesting that the growth-inhibitory effect of TGZ is associated with the reduction of Bcl-w and Bcl-2 and the increase of ERK1/2 and p38 activation. SAPK/JNK activation assay showed a decreased activity in all these three cell lines treated by TGZ. It was also demonstrated that TGZ was able to activate PPARgamma transcriptionally. We conclude that TGZ inhibits the growth of human lung cancer cells via the induction of apoptosis, at least in part, in a PPARgamma-relevant manner. / Li Mingyue. / "June 2006." / Advisers: George Gong Chen; Anthony Ping Chuen Yim. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6202. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 174-207). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_343750 |
| Date | January 2006 |
| Contributors | Li, Mingyue., Chinese University of Hong Kong Graduate School. Division of Surgery. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (xxiii, 207 p. : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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