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MicroRNA-137, an HMGA1 target, suppresses colorectal cancer cell invasion and metastasis in mice by directly targeting FMNL2.

BACKGROUND & AIMS
Formin-like (FMNL)2 is up-regulated in colorectal tumors and has been associated with tumor progression, but little is known about regulatory mechanisms. We investigated whether microRNAs regulate levels of FMNL2 in colorectal cancer (CRC) cells.


METHODS
We used real-time polymerase chain reaction and immunoblot analyses to measure levels of miR-137, high-mobility group AT-hook (HMGA)1, and FMNL2 in CRC cells and tissue samples from patients (n = 50). We used luciferase reporter assays to determine the association between miR-137 and the FMNL2 3' untranslated region, and HMGA1 and the miR-137 promoter. Chromatin immunoprecipitation assays were used to assess direct binding of HMGA1 to the miR-137 promoter.


RESULTS
miR-137 and miR-142-3p were predicted to bind FMNL2 based on bioinformatic data. Only the level of miR-137 had a significant inverse correlation with the level of FMNL2 protein in CRC cell lines and tissues. FMNL2 messenger RNA was targeted by miR-137; expression of miR-137 inhibited proliferation and invasion by CRC cells in vitro, and metastasis to liver and intestine by CRC xenografts in nude mice. HMGA1 bound to the promoter of miR-137 and activated its transcription, which reduced levels of FMNL2 in CRC cells. Ectopic expression of miR-137 in CRC cells inhibited phosphorylation of mitogen-activated protein kinase (MAPK) and Akt, which reduced levels of matrix metalloproteinase 2, matrix metalloproteinase 9, and vascular endothelial growth factor; it also reduced invasiveness of CRC cells, inhibiting signaling via phosphatidylinositol-4,5-bisphosphate 3-kinase, Akt, and MAPK.


CONCLUSIONS
Levels of miR-137 and HMGA1 are reduced, and levels of FMNL2 are increased, in CRC samples compared with adjacent normal mucosa. In CRC cells, miR-137 targets FMNL2 messenger RNA and is regulated by the transcription factor HMGA1. Expression of miR-137 reduces CRC cell invasion in vitro and metastasis of tumor xenografts in mice. FMNL2 appears to activate phosphatidylinositol-4,5-bisphosphate 3-kinase, protein kinase B (Akt), and MAPK signaling pathways.