FOXP3 promotes tumor growth and metastasis by activating Wnt/β-catenin signaling pathway and EMT in non-small cell lung cancer

Background: The role of cancer cell FOXP3 in tumorigenesis is conflicting. We aimed to study FOXP3 expression and regulation, function and clinical implication in human non-small cell lung cancer (NSCLC). Methods: One hundred and six patients with histologically-confirmed NSCLC who underwent surgery were recruited for the study. Tumor samples and NSCLC cell lines were used to examine FOXP3 and its related molecules. Various cell functions related to tumorigenesis were performed. In vivo mouse tumor xenograft was used to confirm the in vitro results. Results: NSCLC patients with the high level of FOXP3 had a significant decrease in overall survival and recurrencefree survival. FOXP3 overexpression significantly induced cell proliferation, migration, and invasion, whereas its inhibition impaired its oncogenic function. In vivo studies confirmed that FOXP3 promoted tumor growth and metastasis. The ectopic expression of FOXP3 induced epithelial-mesenchymal transition (EMT) with downregulation of E-cadherin and upregulation of N-cadherin, vimentin, snail, slug, and MMP9. The oncogenic effects by FOXP3 could be attributed to FOX3-mediated activation of Wnt/beta-catenin signaling, as FOXP3 increased luciferase activity of Topflash reporter and upregulated Wnt signaling target genes including c-Myc and Cyclin D1 in NSCLC cells. Coimmunoprecipitation results further indicated that FOXP3 could physically interacted with beta-catenin and TCF4 to enhance the functions of beta-catenin and TCF4, inducing transcription of Wnt target genes to promote cell proliferation, invasion and EMT induction. Conclusions: FOXP3 can act as a co-activator to facilitate the Wnt-b-catenin signaling pathway, inducing EMT and tumor growth and metastasis in NSCLC.