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MicroRNAs (miRNAs) are small, non-coding RNAs that can function as oncogenes or tumor suppressors in human cancer. Abnormally expressed miR-224 was found to play a fundamental role in several types of cancer. The aim of this study was to investigate the prognostic and biological values of miR-224 in colorectal cancer (CRC).

Quantitative RT-PCR (qRT-PCR) was used to evaluate expression levels of miR-224. The postoperative survival rate was analyzed with Kaplan--Meier method. The roles of miR-224 in cell proliferation, migration and invasion were analyzed with pre-miR-224 transfected cells. In addition, the regulation of SMAD4 by miR-224 was evaluated by qRT-PCR, Western blotting and luciferase reporter assays.

In the present study, we demonstrated that miR-224 was significantly up-regulated in CRC tissue samples and associated with disease relapse and a relative poorer disease-free survival rate. Moreover, ectopic expression of miR-224 potently promoted tumor cell proliferation, migration and invasion in vitro. Furthermore, the over-expression of miR-224 in CRC cell lines decreased SMAD4 expression at the translational level and decreased SMAD4-driven luciferase-reporter activity.

Our data suggest that miR-224 could play an oncogenic role in the cellular processes of CRC and represent a novel biomarker for tumor relapse of CRC patients.

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