Genetic changes in colon cancer are known to parallel the tissue abnormalities associated with the disease, namely adenoma and adenocarcinoma. The role of microRNA dysregulation in dysplastic progression, however, is not well understood. Here, we show that miR-182 and miR-503 undergo sequential up-regulation and drive the progression of colon adenoma to adenocarcinoma by cooperatively down-regulating the tumour suppressor FBXW7. We identified that increased expression of miR-182 is a feature of adenomas. A subsequent increase in miR-503 expression works cooperatively with miR-182 to induce transformation of an adenoma to adenocarcinoma. We show that introducing miR-503 into AAC1 cells, which are derived from a benign adenoma, confers tumourigenic potential. We also demonstrated that blocking both miR-182 and miR-503 in HCT116 colon cancer cells resulted in increased FBXW7 expression and significantly reduced tumour size in xenograft models. We confirmed relevance of these results in patients by examining the expression levels of miR-182 and miR-503 in over 200 colon cancer patients with 12 year survival outcome data. Decreased patient survival was correlated with elevated expression of both miRNAs, suggesting that elevated levels of both miR-182 and miR-503 define a novel prognostic biomarker for colon cancer patients. In conclusion, we show that a sequential expression of miR-182 and miR-503 in benign adenoma cooperatively regulates the tumour suppressor FBXW7, contributing to the malignant transformation of colon adenoma to adenocarcinoma and miR-182 and miR-503 may prove to be novel therapeutic targets. Array data are available at: http://www.oncomir.umn.edu/

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Progression from adenoma to colon cancer is a multi-step process and the role of microRNAs in this transformation is not completely understood. We used both in vitro and in vivo approaches to demonstrate the role of miRNAs in the transformation of adenoma to adenocarcinoma. Reporter assays were used to show the direct interaction of miRNAs to target gene. A Tet-inducible TripZ system and miRzips constructs were used in the in vitro function and xenograft studies. Kaplan-Meier survival curves and Cox regression were used to analyze the survival data in colon cancer patients. Here, we show that the combination of miR-503 and miR-182 contributes to the transformation of colon adenoma to adenocarcinoma by cooperatively regulating the tumor suppressor gene, FBXW7. We found that miR-182 was upregulated in both colon adenoma and adenocarcinoma, whereas miR-503 was upregulated only in adenocarcinoma, indicating a potential hierarchical and stepwise expression of these miRNAs in the regulation of FBXW7. Furthermore, we showed that colon adenoma derived non-tumorigenic AAC1 cells were transformative and tumorigenic in mice when expressing Tet-inducible miR-503. Finally, the combination of miR-503 and miR-182 transcript levels was predictive of poor outcome in colon cancer patients. We conclude that a step-wise expression of miR-182 and miR-503 in benign adenoma synergistically regulates the driver gene FBXW7, thus contributing to the progression of colon adenoma to adenocarcinoma. Citation Format: Lihua Li, Aaron Sarver, Rohini Khatri, Praveensingh Hajeri, Iris Kamenev, Stephen Thibodeau, Clifford J. Steer, Subbaya Subramanian. MicroRNAs miR-503 and -182 regulate FBXW7 contributing to the malignant transformation to colon adenocarcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4368. doi:10.1158/1538-7445.AM2014-4368