The role of microRNAs in metastasis and epithelial-mesenchymal transition

For a tumour cell to metastasize it must successfully negotiate a number of events, requiring a series of coordinated changes in the expression of many genes. MicroRNAs are small non-coding RNA molecules that post-transcriptionally control gene expression. As microRNAs are now recognised as master regulators of gene networks and play important roles in tumourigenesis, it is no surprise that microRNAs have recently been demonstrated to have central roles during metastasis. Recent work has also demonstrated critical roles for microRNAs in epithelial-mesenchymal transition, a phenotypic change underlain by altered gene expression patterns that is believed to mirror events in metastatic progression. These findings offer new potential for improved prognostics through expression profiling and may represent novel molecular treatment targets for future therapy. In this review, we summarise the multistep processes of metastasis and epithelial-mesenchymal transition and describe the recent discoveries of microRNAs that participate in controlling these processes.