KLF4 is downregulated but not mutated during human esophageal squamous cell carcinogenesis and has tumor stage-specific functions.

The transcriptional regulator Krüppel-like factor 4 (KLF4) is decreased in human esophageal squamous cell cancer (ESCC), and Klf4 deletion in mice produces squamous cell dysplasia. Nonetheless the mechanisms of KLF4 downregulation in ESCC and the functions of KLF4 during ESCC development and progression are not well understood. Here, we sought to define the regulation of KLF4 and delineate the stage-specific effects of KLF4 in ESCC. We found that KLF4 expression was decreased in human ESCC and in 8 of 9 human ESCC cell lines. However, by genomic sequencing, we observed no KLF4 mutations or copy number changes in any of 52 human ESCC, suggesting other mechanisms for KLF4 silencing. In fact, KLF4 expression in human ESCC cell lines was increased by the DNA methylation inhibitor 5-azacytidine, suggesting an epigenetic mechanism for KLF4 silencing. Surprisingly, while KLF4 decreased in high-grade dysplasia and early stage tumors, KLF4 increased with advanced cancer stage, and KLF4 expression in ESCC was inversely correlated with survival. Interestingly, KLF4 promoted invasion of human ESCC cells, providing a functional link to the stage-specific expression of KLF4. Taken together, these findings suggest that KLF4 loss is necessary for esophageal tumorigenesis but that restored KLF4 expression in ESCC promotes tumor spread. Thus, the use of KLF4 as a diagnostic and therapeutic target in cancer requires careful consideration of context.