miRNA-34 intrinsically links p53 tumor suppressor and Wnt signaling

Though tumor suppressor p53 and the canonical Wnt cascade have been extensively studied for the past 30 years, due to their important physiological roles, the two signaling pathways have been largely considered independent. Recently, the miR-34 family was found to directly link p53 and Wnt, revealing the tight connection between loss of tumor suppressor function and activation of oncogenic signaling. These observations demonstrate that miR-34, known to be directly downstream of p53, targets a set of highly conserved sites in the UTR of Wnt and EMT genes, specifically WNT1, WNT3, LRP6, AXIN2, beta-catenin, LEF1 and Snail, resulting in suppression of TCF/LEF transcriptional activity and the EMT program. The loss of p53 function increases Wnt activities and promotes the Snail-dependent EMT program at multiple levels in a miR-34/UTR-specific manner. The TCF/LEF transcriptional signature was closely associated with functionality of p53 and miR-34 in clinical samples, suggesting the pervasive impact of miR-34 loss on the oncogenic pathway in human cancer. Here, we review recent findings on ceRNA in light of novel data to elucidate the physiological relevance of the p53-miR-34-Wnt network, which encompasses sets of genes and directions of signaling. As loss of wt-p53 or hyperactivation of Wnt is critical in maintaining cancer stem cell properties and in establishing the metastatic program, these observations indicate a mechanism of miR-mediated quasi-sufficiency that connects tumor suppressor and oncogenic signaling pathways, supporting a continuum model of human cancer.