To investigate the clinicopathologic significance, role and mechanism of action of miR-224 in colorectal cancer (CRC).

Real-time PCR was used to quantify miR-224 expression. The association of miR-224 with the clinicopathologic features and survival was evaluated in 107 CRC patients. The role of miR-224 in CRC was investigated using in vitro and in vivo assays. Luciferase reporter assays were conducted to confirm target gene associations.

MiR-224 was overexpressed in CRC. High level expression of miR-224 was significantly associated with an aggressive phenotype and poor prognosis. Overexpression of miR-224 promoted CRC cell proliferation in vitro and tumor growth in vivo. Specifically, miR-224 accelerated the G1/S-phase transition through activation of AKT/FOXO3a signaling, downregulation of p21Cip1 and p27Kip1, and upregulation of cyclin D1. Moreover, both PHLPP1 and PHLPP2, antagonists of PI3K/AKT signaling, were confirmed as bona fide targets of miR-224. MiR-224 directly targeted the 3' untranslated regions (3'-UTR) of the PHLPP1 and PHLPP2 mRNAs and repressed their expression.

This study reveals functional and mechanistic links between miRNA-224 and the tumor suppressors PHLPP1 and PHLPP2 in the pathogenesis of CRC. MiR-224 not only plays important roles in the regulation of cell proliferation and tumor growth in CRC, but also has potential as a prognostic marker or therapeutic target for CRC.