PS1017 MICRO RNA SIGNATURE OF ONCOGENIC MUSASHI RNA BINDING PROTEINS MSI1 AND MSI2

Background: MSI1 and MSI2 are two paralogous RNA binding proteins (RBPs) which are frequently dysregulated in multiple cancers ranging from breast cancer, gliomas, medullobalstoma to acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). RBPs along with MicroRNAs are key form of regulatory molecules working post‐transcriptionally. The interplay between miRNAs and Musashi proteins on target 3’UTRs can rapidly modulate their target mRNA expression. Therefore, identification of mRNA and miRNA interactome is essential for defining the roles of these proteins. We previously identified the mRNAs that are bound and regulated by MSI proteins, next we chose to identify the microRNAs that are regulated by MSI1/2 Aims: The overall objective of the study is to identify the microRNAs that are regulating and regulated by MSI1 and MSI2 to increase our understanding on the function of these oncogenic proteins. Methods: AGO2 PAR‐CLIP experiments aid in identifying the miRNAs that bind to the MSI1/2 mRNA sequence. We will also bioinformatically identify the seed sequence regions on mRNAs that are preferentially bound by miRNAs. Next, we silenced the expression of MSI1 and MSI2 and sequenced the resulting small RNAs using Truseq small RNA sequencing on Illumina platform to identify the miRNAs that are differentially expressed. We carried out functional validation of some of the most promising leukemic miRNA candidates of MSI1/2 using microRNA mimics which will help us uncover new biomarkers and potential therapeutic targets. Results: We have performed AGO2 PAR‐CLIPs on AML and CML cell lines THP‐1 and K562 along with a control and found several interesting oncogenic microRNAs binding MSI1/2. Additionally, we knocked down the expression of MSI1/2 using siRNA cocktail and isolated the microRNAs. We sequenced these microRNAs and are currently in the process of identifying the differentially regulated miRNAs. Also, miR‐143 was identified as top microRNA that bind to MSI2, therefore using miR143 mimics, we validated its binding and effect of its binding on MSI2 expression. We noted a decreased expression of MSI2 upon transfection of cells with miR143 mimics compared to controls. Other top microRNA targets like miR128, miR137, miR320 and miR181 as currently being validated. Summary/Conclusion: We identified transcriptome wide microRNAs that bind and regulate the expression of MSI1 and MSI2. We are also evaluating the miRNAs that are differentially regulated by MSI1/2. We validated the binding and regulation of miR143 on MSI2 expression. Combining the data from AGO‐CLIPs and TruSeq small RNA sequencing data, we will be able to establish the microRNA interactome of Musashi family of RBPs. Data from this study can help us to design therapeutic RNA‐decoys that can target the expression of oncogenic musashi proteins.