MicroRNA-141 and MicroRNA-146b-5p Inhibit the pro-Metastatic Mesenchymal Characteristics through the RNA Binding Protein AUF1 Targeting the Transcription Factor ZEB1 and the Protein Kinase AKT [Gene Regulation]

September 26th, 2014 by Al-Khalaf, H. H., Aboussekhra, A.

MMiR-141 and miR-146b-5p are two important tumor suppressor microRNAs, which control several cancer-related genes and processes. In the present report, we have shown that these microRNAs bind specific sites at the 3[prime]-untranslated region (UTR) of the mRNA-binding protein AUF1, leading to its down-regulation. This inverse correlation between the levels of these microRNAs and AUF1 has been identified in various osteosarcoma cell lines. Additionally, we present clear evidence that AUF1 promotes mesenchymal features in osteosarcoma cells, and that miR-141 and miR-146b-5p suppress this pro-metastatic process through AUF1 repression. Indeed, both microRNAs suppressed the invasion/migration and proliferation abilities of osteosarcoma cells through inhibiting the AKT protein kinase in an AUF1-dependent manner. We have also shown that AUF1 binds to and stabilizes the mRNA of the AKT activator phosphoinositide-dependent kinase-1 (PDK1). Furthermore, miR-141 and miR-146b-5p positively regulate the epithelial markers (E-cadherin and Epcam) and represses the mesenchymal markers (N-cadherin, Vimentin, Twist2 and ZEB1). These effects were mediated via the repression of the epithelial-to-mesenchymal (EMT)-inducer ZEB1 through targeting AUF1, which binds the 3[prime]UTR of the ZEB1 mRNA and reduces its turnover. These results indicate that at least some tumor suppressor functions of miR-141 and miR-146b-5p are mediated through the repression of the oncogenic potentials of AUF1. Thereby, these 3[prime]-UTR-directed post-transcriptional gene expression regulators constitute promising new targets for diagnostic and/or therapeutic interventions.
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