Low Expression of the FoxO4 Gene may Contribute to the Phenomenon of EMT in Non-small Cell Lung Cancer

Abstract

Because of its importance in tumor invasion and metastasis, the epithelial-mesenchymal transition (EMT) has become a research focus in the field of cancer. Recently, evidence has been presented that FoxO4 might be involved in EMT. Our study aimed to detect the expression of FoxO4, E-cadherin and vimentin in non-small cell lung cancers (NSCLCs). We also investigated clinical features and their correlations with the markers. In our study, FoxO4, E-cadherin and vimentin were assessed by immunohistochemistry in a tissue microarray (TMA) containing 150 cases of NSCLC. In addition, the expression level of FoxO4 protein was determined by Western blotting. The percentages of FoxO4, E-cadherin and vimentin positive expression in NSCLCs were 42.7%, 38.7% and 55.3%, respectively. Immunoreactivity of FoxO4 was low in NSCLC when compared with paired normal lung tissues. There were significant correlations between FoxO4 and TNM stage (P<0.001), histological differentiation (P=0.004) and lymph node metastasis (P<0.001), but no significant links with age (P=0.323), gender (P=0.410), tumor size (P=0.084), smoking status (P=0.721) and histological type (P=0.281). Our study showed that low expression of FoxO4 correlated with decreased expression of E-cadherin and elevated expression of vimentin. Cox regression analysis indicated FoxO4 to be an independent prognostic factor in NSCLC (P=0.046). These data suggested that FoxO4 might inhibit the process of EMT in NSCLC, and might therefore be a target for therapy. Particularly, the activation of EMT pathway often precedes cancer metastasis for tumors of the epithelial origin (Wells et al., 2008). Epithelial cells lead to loosen and even loss of cell-cell adhesion throughout EMT. Besides, at the molecular level, EMT is characterized by loss or downregulation of E-cadherin and cytokeratins, with the exception of mesenchymal proteins like Vimentin, fibronectin and N-cadherin, whose expression are often upregulated (Wells et al., 2008;Ivaska 2011; SatelliLi 2011;Vaid et al., 2011). It has been shown that EGF and resultant EGFR activation could promote EMT in HCC cell lines by altered the expression and morphology of EMT-associated markers (E-cadherin/β-catenin complex) (Fan et al., 2014 (Silhan et al., 2009). DBD is characterized by three α helices, three stranded β sheet and two wing-like loops, and is thought to play important roles interacting with other proteins (Boura et al., 2007). The interaction with 14-3-3 proteins affected FoxO4 binding to the target DNA and prevented FoxO4 from entering the nucleus by interfering with the function of nuclear localization sequence (NLS) (Obsilova et al., 2005;Boura et al., 2007). Human FoxO4 gene is located on chromosome Xq13.1 and encodes a protein of 65KD. FoxO4 participates in many cellular processes, including regulation of cell cycle, proliferation, differentiation, apoptosis, ageing, metabolism, response to stress and tumorigenesis (Tran et al., 2002). Another Fox family member-FoxK1, promoted cell proliferation by inhibiting the ...

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