PPARγ在非小細胞肺癌(H460)抗藥性(TGFβ)生成過程中所扮演的角色:細胞暨動物實驗層次的探討

Abstract

The primary goal of the study was to understand the molecular mechanism responsible for the development of drug resistance of non-small cell lung cancer (NSCLC) cell, H460, against transforming growth factor β (TGFβ). The role of peroxisome proliferator-activated receptor γ (PPARγ) in disabling the tumor suppressing effect whereas promoting the metastasizing effect of TGFβ on H460 cells were the first two major issues to be approached followed by signaling pathways identification. A novel tumor mouse model using a group of middle aged BALB/c mice implanted with H460 xenograft tumor cells has also been established to further examine the development and metastasis of H460 cells within the animal body and to screen for anti-cancer drug for control of H460 cells in vivo. Our results showed the H460 cells revealed a drug resistance to TGFβ after the short or long term drug exposure. TGFβ-induced PPARγ was able to interact with and prevent the nuclear infiltration of Smad3/p-Smad3 that subsequently disrupt TGFβ-induced mitoinhibition in H460 cells and led to TGFβ resistance. TGFβ was later found can act through P38 and/or β-catenin signaling pathway to trigger the expression of PPARγ, which was also critical for TGFβ-induced epithelial to mesenchymal transition (EMT) and metastasis of H460 cells. PPARγ could activate the epidermal growth factor receptor (EGFR)/c-mesenchymal-epithelial transition factor (c-MET) pathway to decrease the expression of E-cadherin, or interact with β-catenin and promote its nuclear infiltration, either way might contribute to the EMT and metastasis of H460 cells induced by TGFβ. PPARγ was shown to have a positive reciprocal interaction with β-catenin. GW9662 (PPARγ inhibitor) and PPARγ-specific shRNA both revealed a therapeutic value in the control of H460 cells by breaking of PPARγ-protected cell growth and TGFβ-induced/PPARγ-mediated metastasis of H460 cells. The therapeutic value of GW9662 in the control of H460 cells-derived tumor was further confirmed in vivo by using the tumor mouse model has just described above. In addition to the tumor suppressive effect, GW9662 also inhibited the lung inflammation in H460 cells-implanted mice. This anti-inflammatory effect, however, might be due to GW9662-caused tumor inhibition of H460 cells. The novelty of our newly-developed tumor mouse model was that, human H460 cells were able to grow in immunocompetent mice instead of nude or SCID mice (immunodeficient). In brief, the decline of neutrophil activity in middle aged mouse was critical for the development of H460 xenograft in lung whereas the increase of macrophage activity was critical for the growth of murine-derived tumor. H460 xenograft tumor, on the other hand, might further decrease neutrophil activity to favor the tumor growth, and be the reason to cause pulmonary inflammation in H460-bearing mice. In overall, PPARγ was for the first time being addressed in H460 tumorigenesis and its drug resistance to TGFβ. The growth protecting and metastasis promoting effects of PPARγ in H460 cells have suggested that PPARγ may be a good molecule target to be approached in target therapy for many drug resistant-cancer cells such as H460. The therapeutic value of GW9662 in the control of H460 cells both in vitro and in vivo further supported this notion.