Abstract 2068: Profile, target genes and regulation of microRNAs in ovarian carcinoma tumor progression

MicroRNAs (miRNAs) are small non-coding RNAs, that exert their regulatory effect post-transcriptionally by binding the 3’-UTR of their target mRNA and inhibiting gene translation to protein. Depending on whether miRNAs target oncogenes or tumor suppressor genes, they may be referred to as tumor suppressors or oncogenes respectively. Cellular miRNA expression is tightly regulated. One of the post-transcriptional regulatory mechanisms involves changes in expression of miRNA machinery proteins, i.e., Dicer, and miRISC components such as the Argonaute (Ago) family members. Numerous studies, using different profiling approaches, have unraveled that miRNA expression is deregulated in various human cancers. Ovarian cancer is the leading cause of death from gynecological cancers in western countries. The disease is asymptomatic in the early stages, and is usually diagnosed at an advance stage. Primary solid tumors, solid metastases, and effusions to the peritoneal and (ascites) pleural cavities characterize the tumor as it progresses. The aim of the study was to characterize the difference in miRNA expression pattern between primary ovarian solid carcinomas and effusion-derived cells, using fresh-frozen samples. We also assessed changes in regulation of miRNA by evaluating the expression of the machinery proteins at these two sites. Using microRNA-array platforms, we identified three sets of miRNAs: one set is highly expressed in both primary solid carcinomas and effusions. The second set is relatively elevated in effusions, and the third set is relatively reduced in effusions. The most significant miRNAs were validated by real-time PCR. Our results show concordance between the training and the independent test cohorts for the reduced miR-145 and miR-214 and for the elevated let-7f, miR-182, miR-210, miR-200c, miR-222 and miR-23a in effusions. Using in-silico target prediction programs we identified potential target genes for the miRNAs of interest listed above, we investigated the changes of those genes in our cohort. We analyzed the expression levels of Zeb1, a confirmed target of miR-200c as well as c-Myc, that was found to be a predicted target of miR-200c. In addition, we analyzed Pak1 and PTEN, both predicted targets of miR-222. We found inverse correlations between the expression levels of the indicated miRNAs and of the predicted target genes. We further analyzed the miRNA processing machinery genes that regulate miRNA generation and action. We found significantly higher expression of Ago1, Ago2 and Dicer in effusion-derived cells compared to primary carcinoma tumors. These alterations in expression levels indicate on difference in miRNA regulation between the two sites. In summary, miRNA expression profiles and the changes in miRNA processing machinery genes reveal a new level of regulatory elements in ovarian carcinoma tumor progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2068.