Poster Sessions

CANCER-24

Neetu Dahiya

N. Dahiya, C.A. Sharman-Baust, T.L. Wang, B. Davidson, I.M. Shih, Y. Zhang, W. Wood III4, K.G. Becker, P.J. Morin

MicroRNA Expression and Identification of Putative miRNA Targets in Ovarian Cancer

MicroRNAs (miRNAs) represent a class of small non-coding RNAs that control gene expression by targeting mRNAs and triggering either translation repression or RNA degradation. Emerging evidence suggests the potential involvement of altered regulation of miRNA in the pathogenesis of cancers, and these genes are thought to function as both tumor suppressors and oncogenes. Using microRNA microarrays, we identify several miRNAs aberrantly expressed in human ovarian cancer tissues and cell lines. miR-221 stands out as a highly elevated miRNA in ovarian cancer, while miR-21 and several members of the let-7 family are found downregulated. Finding targets of miRNA is the most challenging work for understanding the role of miRNAs. In order to experimentally identify transcripts whose stability may be affected by the differentially expressed miRNAs, we transfected precursor miRNAs into human cancer cell lines and used oligonucleotide microarrays to examine changes in the mRNA levels. Members of let-7 family have been reported to have tumor suppressor roles in various cancers. Among various let-7 members, let-7f was highly downregulated in our study. In order to get insight into let-7f function, we used three different approaches to identify possible targets. First, we performed gene expression profiling of cell lines overexpressing let-7f. Second, we investigated the enrichment of mRNA in Biotin-Streptavidin pull down assays using let-7f (and controls) as bait. In a third approach, we overexpressed let-7f in an ovarian cancer cell line expressing HA-tagged Ago2 and isolated mRNA associated with the Ago2 complex using immunoprecipitation. Our results identify several differentially expressed miRNAs in ovarian cancer. Our further studies investigating let-7f, suggest several new targets for this miRNA. Finding the targets of miRNAs and functional analysis of miRNA:mRNA interaction will help in understanding the role of miRNA in ovarian cancer.