FOXD1 Promotes Cell Growth and Metastasis by Activation of Vimentin in NSCLC

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Abstract
Background/Aims: Forkhead box D1 (FOXD1) has a well-established role in early embryonic development and organogenesis and functions as an oncogene in several cancers. However, the clinical significance and biological roles of FOXD1 in non-small cell lung cancer (NSCLC) remain largely unknown. Methods: A total of 264 primary NSCLC tissue samples were collected. The expression levels of FOXD1 in these samples were examined by immunohistochemical staining. The expression of FOXD1 was knocked down by lentiviral shRNA. The relative expression of FOXD1 was determined by qRT-PCR, Western blotting and immunofluorescence image. The functional roles of FOXD1 in NSCLC were demonstrated cell viability CCK-8 assay, colony formation, cell invasion and migration assays, and cell apoptosis assay in vitro. In vivo mouse xenograft and metastasis models were used to assess tumorigenicity and metastatic ability. The Chi-square test was used to assess the correlation between FOXD1 expression and the clinicopathological characteristics. Survival curves were estimated by Kaplan-Meier method and compared using the log-rank test. The Cox proportional hazards model was used for univariate and multivariate analyses. Results: We determined that higher levels of FOXD1 were present in NSCLC tissues, especially in metastatic NSCLC tissues. FOXD1 was also higher in all NSCLC cells compared with normal human bronchial epithelial cells. A higher expression level of FOXD1 was associated with malignant behavior and poor prognosis in NSCLC patients. Knockdown of FOXD1 significantly inhibited proliferation, migration, and invasion in vitro and tumor growth and metastasis in vivo, and it increased the apoptosis rates of NSCLC cells. Mechanistic analyses revealed that FOXD1 expressed its oncogenic characteristics through activating Vimentin in NSCLC. Multivariate Cox regression analysis indicated that FOXD1 was an independent prognostic factor both for overall survival (OS) and disease-free survival (DFS) in NSCLC patients. Conclusion: Our results indicated that FOXD1 might be involved in the development and progression of NSCLC as an oncogene, and thereby might be a potential therapeutic target for NSCLC patients.

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