Members of the miR-34 family are induced by the tumor suppressor p53 and are known to inhibit epithelial-to-mesenchymal transition (EMT) and therefore presumably suppress the early phases of metastasis. Here, we determined that exposure of human colorectal cancer (CRC) cells to the cytokine IL-6 activates the oncogenic STAT3 transcription factor, which directly represses the MIR34A gene via a conserved STAT3-binding site in the first intron. Repression of MIR34A was required for IL-6–induced EMT and invasion. Furthermore, we identified the IL-6 receptor (IL-6R), which mediates IL-6–dependent STAT3 activation, as a conserved, direct miR-34a target. The resulting IL-6R/STAT3/miR-34a feedback loop was present in primary colorectal tumors as well as CRC, breast, and prostate cancer cell lines and associated with a mesenchymal phenotype. An active IL-6R/STAT3/miR-34a loop was necessary for EMT, invasion, and metastasis of CRC cell lines and was associated with nodal and distant metastasis in CRC patient samples. p53 activation in CRC cells interfered with IL-6–induced invasion and migration via miR-34a–dependent downregulation of IL6R expression. In Mir34a-deficient mice, colitis-associated intestinal tumors displayed upregulation of p-STAT3, IL-6R, and SNAIL and progressed to invasive carcinomas, which was not observed in WT animals. Collectively, our data indicate that p53-dependent expression of miR-34a suppresses tumor progression by inhibiting a IL-6R/STAT3/miR-34a feedback loop.

The tumor suppressor p53 is one of the most frequently mutated genes in human cancers. MicroRNAs (miRNAs) are small non-protein coding RNAs that regulate gene expression on the post-transcriptional level. Recently, it was shown that p53 regulates the expression of several miRNAs, thereby representing an important mechanism of p53 signaling. Several independent studies identified the members of the miR-34 family as the most prevalent p53-induced miRNAs. miR-34s are frequently silenced in variety of tumor entities, suggesting that they are important tumor suppressors. Indeed, ectopic expression of miR-34s inhibits proliferation, epithelial to mesenchymal transition, migration, invasion, and metastasis of various cancer cell entities. Moreover, delivery or re-expression of miR-34 leads to notable repression of tumor growth and metastasis in cancer mouse models, and may therefore represent an efficient strategy for future cancer therapeutics. Besides their crucial functions in cancer, members of the miR-34 family also play important roles in spermatogenesis, stem cell differentiation, neuronal development, aging, and cardiovascular functions. Consequently, miR-34 has also been implicated in various non-cancerous diseases, such as brain disorders, osteoporosis, and cardiovascular complications.

Here, we developed and comprehensively characterized a cellular model of colon cancer progression consisting of four defined derivatives of a colon cancer cell line that resulted from consecutive epithelial–mesenchymal and mesenchymal–epithelial transitions (EMT/MET) and phenotypically recapitulate the metastatic cascade. Initial EMT was induced by prolonged exposure to IL6, a cytokine also generated by the tumor-stroma. Genome-wide characterization of transcriptional (mRNA, miRNA, and lncRNA) and epigenetic (DNA methylation, H3K4me3, H3K79me3, and H3K27me3 histone modifications) profiles of the cell derivatives, combined with correlative analyses of expression, methylation, and clinical data from the TCGA-COAD database gave insights into the molecular basis of their phenotypic changes. The signatures characterizing invasive, mesenchymal-like cell states as well as the metastases-derived epithelial-like state showed significant association with metastasis, positive nodal status, and poor survival of colon cancer patients. Global hypomethylation of gene-regulatory regions was observed during tumor progression, with the lowest degree of methylation present in cells isolated from metastases. Upregulation of an axon-guidance–related gene signature was the most significant feature of metastatic tumor cells and was also found in primary tumors from colon cancer patients with distant metastases. Furthermore, the microRNAs miR-99a, miR-100, and miR-125b showed elevated expression in mesenchymal-like cells, associated with poor survival, and promoted migration and invasion. Finally, elevated expression of H19 lncRNA due to promoter demethylation was observed in cells isolated from metastases and was associated with poor survival of colon cancer patients. In the future, our results may be further exploited for the discovery and evaluation of novel metastasis-associated mechanisms and biomarkers. Cancer Res; 77(8); 1854–67. ©2017 AACR.

Epithelial-mesenchymal transition (EMT) plays an important role in tumor invasion and metastasis. A comprehensive, bioinformatics analysis of CCLE and TCGA datasets of seven tumor types allowed us to identify a novel pan-cancer EMT-associated gene expression signature consisting of 16 epithelial and 4 mesenchymal state-associated mRNAs. Among the identified epithelial cell state-associated factors, down-regulation of the RBM47 (RNA binding motif protein 47) mRNA displayed the most significant association with metastasis and poor survival in multiple cohorts of colorectal cancer (CRC) patients. Moreover, decreased RBM47 protein expression was associated with metastasis in a cohort of primary CRCs. RBM47 was directly suppressed during EMT induced by IL6-activated STAT3 or ectopic SNAIL and SLUG expression via conserved binding motifs of these factors within the RBM47 promoter. Moreover, RNAi-mediated down-regulation of RBM47 in CRC lines resulted in increased cell migration, invasion and metastases formation. As demonstrated by the example of RBM47, the EMT-associated signature characterized here allows to identify biomarkers for predicting clinical outcome of CRC and presumably other cancer entities. In addition, our functional analysis of RBM47 shows that the down-regulation of RBM47 during CRC progression may promote EMT and metastasis.