miR-493 induction during carcinogenesis blocks metastatic settlement of colon cancer cells in liver.

Liver metastasis is a major lethal complication associated with colon cancer, and post-intravasation steps of the metastasis are important for its clinical intervention. In order to identify inhibitory microRNAs (miRNAs) for these steps, we performed 'dropout' screens of a miRNA library in a mouse model of liver metastasis. Functional analyses showed that miR-493 and to a lesser extent miR-493(*) were capable of inhibiting liver metastasis. miR-493 inhibited retention of metastasized cells in liver parenchyma and induced their cell death. IGF1R was identified as a direct target of miR-493, and its inhibition partially phenocopied the anti-metastatic effects. High levels of miR-493 and miR-493(*), but not pri-miR-493, in primary colon cancer were inversely related to the presence of liver metastasis, and attributed to an increase of miR-493 expression during carcinogenesis. We propose that, in a subset of colon cancer, upregulation of miR-493 during carcinogenesis prevents liver metastasis via the induction of cell death of metastasized cells.