The miR-371∼373 Cluster Represses Colon Cancer Initiation and Metastatic Colonization by Inhibiting the TGFBR2/ID1 Signaling Axis

Abstract The vast majority of colorectal cancer–related deaths can be attributed to metastatic spreading of the disease. Therefore, deciphering molecular mechanisms of metastatic dissemination is a key prerequisite to improve future treatment options. With this aim, we took advantage of different colorectal cancer cell lines and recently established primary cultures enriched in colon cancer stem cells, also known as tumor-initiating cells (TIC), to identify genes and miRNAs with regulatory functions in colorectal cancer progression. We show here that metastasis-derived TICs display increased capacity for self-renewal, TGFβ signaling activity, and reduced expression of the miR-371∼373 cluster compared with nonmetastatic cultures. TGFβ receptor 2 (TGFBR2) and aldehyde dehydrogenase A1 (ALDH1A1) were identified as important target genes of the miR-371∼373 cluster. In addition, TGFBR2 repression, either by direct knockdown or indirectly via overexpression of the entire miR-371∼373 cluster, decreased tumor-initiating potential of TICs. We observed significantly reduced in vitro self-renewal activity as well as lowered tumor initiation and metastatic outgrowth capacity in vivo following stable overexpression of the miR-371∼373 cluster in different colon TIC cultures. Inhibitor of DNA binding 1 (ID1) was affected by both TGFBR2 and miR-371∼373 cluster alterations. Functional sphere and tumor formation as well as metastatic dissemination assays validated the link between miR-371∼373 and ID1. Altogether, our results establish the miR-371∼373/TGFBR2/ID1 signaling axis as a novel regulatory mechanism of TIC self-renewal and metastatic colonization. Significance: These findings establish the miR-371∼373/TGFBR2/ID1 signaling axis as a novel mechanism regulating self-renewal of tumor-initiating cell and metastatic colonization, potentially opening new concepts for therapeutic targeting of cancer metastasis. Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/14/3793/F1.large.jpg. Cancer Res; 78(14); 3793–808. ©2018 AACR.