Background and Aims: The FOXP transcription factor family has been shown to play an important role in multiple cancer types. However, the function of its member FOXP4 in colorectal cancer has not reported yet. This study was conducted to investigate the FOXP4 expression in colorectal cancer and its relationship with clinicopathologic characteristics and prognosis of the patients, as well as its potential mechanism of action. 
Methods: The FOXP4 expressions in the specimens of tumor tissue and tumor adjacent tissue from 50 colorectal cancer patients were determined by immunohistochemical staining and RT-PCR, respectively. Based on the GEIPA database, the FOXP4 expression in colorectal cancer tissues and its relationship with the survival rates of the patients were analyzed. The colorectal cell lines with stable FOXP4 overexpression or knockdown were created, and then, the changes in proliferative and migration abilities of them were examined by CCK8 and Transwell assay. The possible target promoter for FOXP4 was predicted by using AnimalTFDB 3.0 database, the combining ability of FOXP4 to its target promoter and the regulatory effect of FOXP4 on the corresponding target gene were verified by ChIP assay, luciferase reporter assay, RT-PCR and Western blot analysis, respectively. Finally, the function of the target gen was validated.
Results: The results of both analyses of the clinical specimens and GEIPA database showed that the FOXP4 expression in colorectal cancer tissue was significantly elevated, and its expression level was significantly associated with the tumor size, degree of tumor differentiation and TNM stage of the patients, and those with high FOXP4 expression had a significant low overall survival rate (all P<0.05). The results of the CCK8 and Transwell assay showed that the proliferative and migration abilities in colorectal cancer cells with FOXP4 overexpression were significantly increased, while in those with low FOXP4 expression were significantly decreased (all P<0.05). The analysis of AnimalTFDB 3.0 database showed that β-catenin promoter was the target promoter for FOXP4; ChIP assay revealed that FOXP4 recognized the β-catenin promoter region; luciferase reporter assay found that FOXP4 only recognized the wild-type β-catenin sequence; RT-PCR and Western blot analysis demonstrated that FOXP4 overexpression up-regulated both gene and protein expression levels of β-catenin. In colorectal cancer cells after treatment with β-catenin inhibitor, the enhancing effects of FOXP4 overexpression on proliferative and migration abilities were abolished (all P<0.05).
Conclusion: The FOXP4 expression is increased in colorectal cancer, which is closely related to the malignant clinicopathologic features and unfavorable prognosis of the patients. FOXP4 overexpression can promote the proliferation and migration of colorectal cancer cells probably by regulating the transcription of β-catenin. So, this study suggests that FOXP4 play a critical role in the occurrence and development colorectal cancer, and may be served as a potential therapeutic target for colorectal cancer.