FOXM1 Drives Epithelial-Mesenchymal Transition Program Through E-Cadherin Promoter Biding Ability in Non-Small-Cell Lung Cancer Cells

Abstract Background: Forkhead box (FOX) gene family plays a critical role in regulating Epithelial-mesenchymal transition (EMT) program, and in which, FOXM1 can mediate multiple malignant process in many type of tumor cells. However, the modulate functions of FOXM1 on EMT in non-small-cell lung cancer (NSCLC) cells, especially the transcriptional function on E-cadherin coding gene CDH1 remains unclear. This article mainly focuses on FOXM1, exploring its mechanism in regulating EMT of NSCLC cells, and FOXM1 inhibitor thiostrepton’s effects in EMT intervention. Methods: Morphological changes of overexpressed cells were observed by HE staining. The effects of scratch test, Transwell chamber test and Western-blot analysis on cell migration and invasion ability and the expression of EMT-related markers were analyzed. Dual luciferin reporter enzyme assay and nuclear transcription factor immunoprecipitation assay (ChIP, immunofluorescence) revealed the transcriptional regulation of FOXM1 on EMT markers. MTT assay and clone formation assay were used to determine the effect of thiomycin on the viability of NSCLC cells and the ability of cell clone formation.Rusults: After overexpression of FOXM1, the cells showed intermediate epithelial-mesenchymal morphology, but not complete mesenchymal morphology, and their migration and invasion abilities were enhanced. The protein expression levels of N-cadherin,Snail1 and Vimentin were increased, while the expression levels of E-cadherin were decreased. On the contrary, knockdown of FOXM1 expression showed the opposite result. The double luciferin reporter enzyme assay showed that FOXM1 inhibited the luciferin reporter vector CDH1-2000-promoter. ChIP results confirmed that FOXM1 could bind endogenous to CDH1 gene promoter. In cells overexpressing FOXM1, knockdown of Snail further promotes FOXM1-mediated CDH1 transcription. MTT results and clone formation experiments showed that thiomycin had inhibitory effect on the proliferation of NSCLC cells. Morphological observation, cell migration assay and Transwell chamber assay showed that streptotin inhibited TGF-β1-induced enhanced cell migration and invasion. Western-blot analysis showed that thiomycin down-regulated the expression of FOXM1, N-cadherin, Snail, and Vimentin induced by TGF-β1, while blocking the expression of E-cadherin induced by TGF-β1 decreased.Conclusion: FOXM1 can directly bind to the promoter of E-cadherin encoding gene, and can indirectly inhibit E-cadherin expression by stimulating Snail. Overexpression of FOXM1 can promote EMT progression in NSCLC cells. Therefore, down-regulation of FOXM1 can inhibit this process. In addition, thiostrepton, a FOXM1 inhibitor, blocked proliferation, colony formation, and EMT progression in NSCLC cells.