Abstract 3537: Suppression of miR-145 by long noncoding RNA RoR in colon cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: The human genome makes a large number of non-coding RNAs including long non-coding RNAs (lncRNAs) and microRNAs. Compared to well-characterized microRNAs, much less is known about lncRNAs. However, emerging evidence has implicated lncRNAs as master gene regulators; and they are often aberrantly expressed in a variety of human diseases including cancer. In particular, several studies suggest that lncRNAs can modulate the concentration and biological functions of microRNAs through a competing endogenous RNA (ceRNA) mechanism. We have previously demonstrated that lncRNA-RoR is a strong negative regulator of p53 in response to DNA damage and miR-145 is a direct transcription target for p53. Therefore, it is important to further characterize this p53 regulatory network involving lncRNA-RoR and miR-145, and to determine their role in tumorigenesis. Methods: To determine cell growth, we performed MTT assays. Protein levels from treated cells were analyzed by western blot. Real-time RT-PCR was used to determine relative expression of genes. Interaction between lncRNA-RoR and the key component (AGO2) of the RNA-induced silencing complex (RISC) was confirmed by RNA co-immunoprecipitation and RNA precipitation. Dual fluorescent in situ hybridization (FISH) was used to determine the relative levels of lncRNA-RoR and miR-145, and their co-localizations in colon cancer specimens. The effect of lncRNA-RoR on tumor growth was determined by a xenograft mouse model. Results: LncRNA-RoR suppressed miR-145 and upregulated c-Myc, one of major miR-145 target genes. In contrast, RoR-siRNA increased miR-145 expression and inhibited c-Myc. Of interest, miR-145 can also repress lncRNA-RoR expression. This reciprocal repression between lncRNA-RoR and miR-145 appeared to work through the CeRNA mechanism. Mechanistically, we showed that lncRNA-RoR directly interacted with AGO2, a key component of RISC complex, by RNA precipitation assays. This interaction was further confirmed by RNA immunoprecipitation with AGO2 antibody. In consistent with these finding, lncRNA-RoR stimulated proliferation in different cancer cells. Moreover, ectopic expression of lncRNA-RoR in HCT-116 cells significantly promoted tumor growth in a xenograft mouse model. Finally, experiments with dual FISH revealed an inverse correlation between lncRNA-RoR and miR-145 in colon cancer specimens. LncRNA-RoR was upregulated in colon cancer whereas miR-145 was downregulated in the same specimens. Conclusion: Taken together, these results suggest that lncRNA-RoR plays an oncogene role in colon cancer in part through suppression of the tumor suppressor miR-145. Thus, a better understanding of the p53-RoR-miR-145 regulatory system will provide new insight of colon cancer therapy. Citation Format: Jianguo Huang, Yin-Yuan Mo. Suppression of miR-145 by long noncoding RNA RoR in colon cancer. [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 3537. doi:10.1158/1538-7445.AM2014-3537