p53-Induced miR-15a/16-1 and AP4 Form a Double-Negative Feedback Loop to Regulate Epithelial–Mesenchymal Transition and Metastasis in Colorectal Cancer

The transcription factor AP4 mediates epithelial–mesenchymal transition (EMT) in colorectal cancer but its control in this setting is not fully understood. Here, we report the definition of a double-negative feedback loop involving AP4 and miR-15a/16-1 that regulates EMT and metastatic progression. In colorectal cancer cells, AP4 was downregulated by DNA damage in a p53-dependent manner. AP4 downregulation by p53 was mediated indirectly by the tumor-suppressive microRNAs miR-15a and miR-16-1, which targeted the 3′ untranslated region (3′-UTR) of AP4 mRNA, induced mesenchymal–epithelial transition (MET), and inhibited colorectal cancer cell migration and invasion. The downregulation of AP4 was necessary for induction of MET and cell cycle arrest by miR-15a/16-1. In tumor xenoplants, ectopic miR-15a/16-1 suppressed formation of lung metastases. Furthermore, AP4 directly suppressed expression of miR-15a/16-1. In clinical specimens of colorectal cancer, miR-15a levels inversely correlated with AP4 protein levels shown previously to correlate with distant metastasis and poor survival. In summary, our results define a double-negative feedback loop involving miR-15a/16-1 and AP4 that stabilizes epithelial and mesenchymal states, respectively, which may determine metastatic prowess. Cancer Res; 74(2); 532–42. ©2013 AACR .