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Foxm1 transcription factor is required for lung fibrosis and epithelial-to-mesenchymal transition.

ABSTRACT: Alveolar epithelial cells (AECs) participate in the pathogenesis of pulmonary fibrosis, producing pro-inflammatory mediators and undergoing epithelial-to-mesenchymal transition (EMT). Herein, we demonstrated the critical role of Forkhead Box M1 (Foxm1) transcription factor in radiation-induced pulmonary fibrosis. Foxm1 was induced in AECs following lung irradiation. Transgenic expression of an activated Foxm1 transcript in AECs enhanced radiation-induced pneumonitis and pulmonary fibrosis, and increased the expression of IL-1β, Ccl2, Cxcl5, Snail1, Zeb1, Zeb2 and Foxf1. Conditional deletion of Foxm1 from respiratory epithelial cells decreased radiation-induced pulmonary fibrosis and prevented the increase in EMT-associated gene expression. siRNA-mediated inhibition of Foxm1 prevented TGF-β-induced EMT in vitro. Foxm1 bound to and increased promoter activity of the Snail1 gene, a critical transcriptional regulator of EMT. Expression of Snail1 restored TGF-β-induced loss of E-cadherin in Foxm1-deficient cells in vitro. Lineage-tracing studies demonstrated that Foxm1 increased EMT during radiation-induced pulmonary fibrosis in vivo. Foxm1 is required for radiation-induced pulmonary fibrosis by enhancing the expression of genes critical for lung inflammation and EMT.

SUBMITTER: Balli D

PROVIDER: S-EPMC3553386 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Macrophages have a key role in tumor-associated pulmonary inflammation that supports the proliferation of tumor cells and promotes lung tumor growth. Although increased numbers of tumor-associated macrophages are linked to poor prognosis in lung cancer patients, little is known regarding the transcriptional mechanisms controlling recruitment of macrophages during lung tumorigenesis. Forkhead Box m1 (Foxm1) transcription factor is induced in multiple cell types within tumor lesions and its increased expression is associated with poor prognosis in patients with lung adenocarcinomas. To determine the role of Foxm1 in recruitment of tumor-associated macrophages, a mouse line with macrophage-specific Foxm1 deletion was generated (macFoxm1(-/-)). Lung tumorigenesis was induced using a 3-methylcholanthrene/butylated hydroxytoluene (BHT; 3,5-di-t-butyl-4-hydroxytoluene) tumor initiation/promotion protocol. Ablation of Foxm1 in macrophages reduced the number and size of lung tumors in macFoxm1(-/-) mice. Decreased tumorigenesis was associated with diminished proliferation of tumor cells and decreased recruitment of macrophages during the early stages of tumor formation. The expression levels of the pro-inflammatory genes iNOS, Cox-2, interleukin-1b (IL-1b) and IL-6, as well as the migration-related genes macrophage inflammatory protein-1 (MIP-1?), MIP-2 and MMP-12, were decreased in macrophages isolated from macFoxm1(-/-) mice. Migration of Foxm1-deficient macrophages was reduced in vitro. The chemokine receptors responsible for monocyte recruitment to the lung, CX(3)CR1 and CXCR4, were decreased in Foxm1-deficient monocytes. In co-transfection experiments, Foxm1 directly bound to and transcriptionally activated the CX(3)CR1 promoter. Adoptive transfer of wild-type monocytes to macFoxm1(-/-) mice restored BHT-induced pulmonary inflammation to the levels observed in control mice. Expression of Foxm1 in macrophages is required for pulmonary inflammation, recruitment of macrophages into tumor sites and lung tumor growth.

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Foxm1 transcription factor is required for lung fibrosis and epithelial-to-mesenchymal transition.

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