Abstract 5025: Regulation of miR-145 expression by Foxo3a, C/EBP-β and p53 in cancer cells

Abstract Background: MicroRNAs are master gene regulators that control gene expression through the posttranscriptional repression mechanism. Accumulating evidence indicates that microRNAs are often dysregulated in human cancers, and they may function as oncogenes or tumor suppressors. Our laboratory and other groups have previously shown that miR-145 is a tumor suppressor that is downregulated in a variety of tumors. However, it is not fully understood about the underlying mechanism of miR-145 regulation. In this study, we characterized miR-145 regulation involving transcription factors FoxO3a, C/EBP-β and p53 in cancer cells. Methods: We previously constructed the miR-145 promoter luciferase reporter in pGL3-basic, which was used in this study to determine the effect of FoxO3a, C/EBP-β or p53 on miR-145 promoter activity. p53 expression vector was constructed in pEGFP; C/EBP-β and FoxO3a were cloned into pCDH lentiviral vector carrying copGFP. Western blot and fluorescence microscope were used to determine expression of exogenous genes. Endogenous miR-145 levels were determined by TaqMan real time PCR after reverse transcription as well as by in situ hybridization. The expression vectors or luciferase reporter were introduced into cells by either transfection or infection. Results: We showed that miR-145 functions a downstream effector of Akt, and impacts tumor growth and invasion. For example, suppression of Akt by serum starvation or PI3K inhibitor LY29 significantly activates p53, which in turn binds to the miR-145 promoter and induces miR-145 expression. Furthermore, we showed that in addition to p53, FoxO3a also functions a positive regulator of miR-145. Of considerable interest, FoxO3a induces miR-145 expression in the mutant p53 background; however, in the wild type p53 background, p53 suppresses the ability of FoxO3a to induce miR-145. On the other hand, C/EBP-β serves as a negative regulator of miR-145 in both wild type p53 and mutant p53 backgrounds, which is likely in part through regulation of Akt activity. Experiments are underway to further dissect the regulation of miR-145. Conclusion: Together, these results suggest a sophisticated regulatory system controlling miR-145 expression in cancer cells. Thus, a better understanding of this regulatory network will aid in the identification of novel cancer biomarkers and therapeutic targets, and improve cancer diagnosis and treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5025. doi:1538-7445.AM2012-5025