p53 and MicroRNA-34 Are Suppressors of Canonical Wnt Signaling

The tumor suppressor p53 activates miRNA-34 to inhibit Wnt signaling and colorectal cancer cell invasiveness. p53 Activates MicroRNA-34 to Inhibit Wnt Signaling The tumor suppressor p53 is missing or nonfunctional in many cancers, whereas the canonical Wnt signaling pathway is frequently activated. Here, Kim et al. show that p53 restrained Wnt signaling during Xenopus development, whereas loss of p53 function led to aberrant activation of the canonical Wnt signaling pathway, with microRNA-34 (miR-34) providing the connection between the two. They found that p53 stimulated production of miR-34, which, in turn, targeted key genes in the Wnt signaling pathway. Analyses of gene expression data sets indicated that loss of p53 or miR-34 function was associated with activation of Wnt signaling in human cancers; moreover, loss of p53 function increased Wnt signaling in colon cancer cells in vitro. In p53-mutant colon cancer cells, miR-34 attenuated Wnt signaling and decreased the invasiveness of these cells in vitro. Thus, the p53–miR-34–Wnt pathway appears to be crucial not only during development but also for p53’s tumor suppressor function. Although loss of p53 function and activation of canonical Wnt signaling cascades are frequently coupled in cancer, the links between these two pathways remain unclear. We report that p53 transactivated microRNA-34 (miR-34), which consequently suppressed the transcriptional activity of β-catenin–T cell factor and lymphoid enhancer factor (TCF/LEF) complexes by targeting the untranslated regions (UTRs) of a set of conserved targets in a network of genes encoding elements of the Wnt pathway. Loss of p53 function increased canonical Wnt signaling by alleviating miR-34–specific interactions with target UTRs, and miR-34 depletion relieved p53-mediated Wnt repression. Gene expression signatures reflecting the status of β-catenin–TCF/LEF transcriptional activity in breast cancer and pediatric neuroblastoma patients were correlated with p53 and miR-34 functional status. Loss of p53 or miR-34 contributed to neoplastic progression by triggering the Wnt-dependent, tissue-invasive activity of colorectal cancer cells. Further, during development, miR-34 interactions with the β-catenin UTR affected Xenopus body axis polarity and the expression of Wnt-dependent patterning genes. These data provide insight into the mechanisms by which a p53–miR-34 network restrains canonical Wnt signaling cascades in developing organisms and human cancer.