KLF4-Mediated Negative Regulation of IFITM3 Expression Plays a Critical Role in Colon Cancer Pathogenesis

Abstract

IFITM3, an IFN-inducible gene, is overexpressed in human colorectal cancer. In this study, we sought to determine the clinical significance and underlying mechanisms of its dysregulated expression in human colon tumor specimens and murine models of this disease. IFITM3 expression in a tissue microarray of tumor and matched normal colon tissue specimens and lymph node metastasis specimens obtained from 203 patients with colon cancer was measured immunohistochemically. IFITM3 was expressed at higher levels in colon tumors and, particularly, nodal metastases than in normal colon tissue. A Cox proportional hazards model showed that IFITM3 expression was an independent prognostic factor for disease-free survival in patients with colon cancer. Knockdown of IFITM3 expression by a specific siRNA significantly suppressed the proliferation, colony formation, migration, and invasion of colon cancer cells in vitro and tumor growth and metastasis in a xenograft model. Restored expression of KLF4, a putative tumor suppressor, downregulated IFITM3 expression in colon cancer cells in vitro. Two KLF4-binding sites in the IFITM3 promoter bound specifically to KLF4 protein in a chromatin immunoprecipitation assay and promoter mutagenesis analyses. Specific deletion of KLF4 led to IFITM3 overexpression in colon mucosa in Villin-Cre(+);Klf4(fl/fl) mice. An inverse correlation between loss of KLF4 expression and IFITM3 overexpression was evident in human colon tumors. These clinical and mechanistic findings indicate that IFITM3 is a direct transcriptional target of KLF4 and that dysregulated KLF4 expression leads to aberrant IFITM3 expression, thus contributing to colon cancer progression and metastasis.