The microRNA-371~373 cluster represses colon cancer initiation and metastatic colonization by inhibiting the TGFBR2/ID1 signaling axis

P. Ullmann, F. Rodriguez, M. Schmitz, S.K. Meurer, K. Qureshi-Baig, P. Felten, A. Ginolhac, L. Antunes, S. Frasquilho, N. Zügel, R. Weiskirchen, S. Haan and E. Letellier.

Cancer Research. May 2018; doi: 10.1158/0008-5472.CAN-17-3003. [Epub ahead of print]


Abstract

The vast majority of colorectal cancer (CRC)-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 CRC cell lines and recently established primary cultures enriched in colon cancer stem cells (CSCs) – also known as tumor-initiating cells (TICs) – to identify genes and microRNAs (miRNAs) with regulatory functions in CRC progression. We show here that metastasis-derived TICs display increased capacity for self-renewal, transforming growth factor beta (TGF-β) signaling activity, and reduced expression of the miR-371~373 cluster compared to non-metastatic cultures. TGF-β 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.

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