Abstract 5026: Loss of microRNA-143/145 disturbs cell growth of cancers by impairing the MDM2-p53 feedback loop

Abstract

Abstract BACKGROUND: Dysregulated microRNAs (miRNAs) play an important role in many malignant tumors, including epithelial cancers, but little is known about the molecular mechanisms and clinical significances of miRNAs dysregulation. The aim is to identify and determine the miR-143 and miR-145 how to specifically be involved in controlling MDM2 expression in a tumor tissue-specific manner. METHODS: Using real-time PCR, the expression of miR-143, miR-145 and MDM2 were evaluated and analyzed in epithelial cancer cell lines and oral cancer specimens. The different PCR-derived fragments and mutagenesis from the MDM2 mRNA 3′ UTR were inserted into the pGL3 vector to generate the luciferase reporters and the reporter activities were assayed by luciferase assay kits. The effects of overexpression of miR-143 and miR-145 on MDM2 and p53 levels were analyzed by western blot. The effects of miR-143 and miR-145 on cell proliferation and cell cycle were determined by the EdU assay and flow cytometry analysis. The effects of miR-143 and miR-145 on tumorigenicity in vivo were investigated with HNSCC cell xenograft models and the cell apoptotic rate as well as mechanism were tested by TUNEL and apoptosis-protein expression in the tumor tissues. RESULTS: The results showed that both miR-143 and miR-145, which belong to the same miRNA cluster, can negatively modulate expression of their target gene, MDM2. The miR-143 and miR-145 is post-transcriptionally activated by up-regulated p53, thereby generating a short miRNAs-MDM2-p53 feedback loop. Re-expression of these miRNAs suppresses cellular growth and triggers the apoptosis of epithelial cancer, in vitro and in vivo, by enhancing p53 activity via MDM2 turnover. Moreover, the miRNA-dependent MDM2 turnover contributes to the equilibrium of repeated p53 pulses in response to DNA damage stress. CONCLUSIONS: These findings suggest that MDM2 dysregulation caused by down-regulation of miR-143 and miR-145 contributes to epithelial cancer development and palys a key role in regulating cellular proliferation and apoptosis. Recruitment of miR-143 and miR-145 may be a reasonable strategy for treatment of epithelial cancers. KEYWORDS: miRNA-143, miRNA-145, MDM2, p53, epithelial cancers. ACKNOWLEDGMENTS: This study was supported by the National Natural Science Foundation of China (Grant No. 30973343 and 81101515), Projects of the Shanghai Science and Technology Committee (Grant No. 08JC1414400 and 10XD1402500), the Shanghai Leading Academic Discipline Project (S30206). *The first two authors contributed equally to this work. 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 5026. doi:1538-7445.AM2012-5026