Abstract B24: New views on microRNAs involvement in melanoma
Authors: Greenberg Eyal , Eyal Eran , Rechavi Gideon , Shomron Noam , Schachter Jacob , Markel Gal , Nemlich Yael , Hajdu Steven , Itzhaki Orit , Edry Liat , Solomon Oz , Amariglio Ninette , Besser Michal J. , Keisari Yona 
Published: April 2013

MicroRNAs (miRNAs) are small non-coding RNAs with regulatory roles, which are involved in a broad spectrum of physiological and pathological processes, including cancer. Most published data is focused on miRNAs that are differentially expressed between melanocytes and melanoma cells. These experiments lead to the discovery of a plurality of new miRNA-based mechanisms. However, this widely common approach fails to address at least two important issues: a) the effect of genomic mutations on target gene regulation by miRNAs; b) the role of miRNAs in shaping the phenotypic heterogeneous nature of metastatic disease. Here we address these issues to provide new insights on the pathogenesis of melanoma and facilitate the development of innovative diagnostic and therapeutic implementations.

Melanoma cells acquire tens of thousands of genomic mutations, most of which are defined as “passengers” and few as “drivers”. We analyzed a fully sequenced genome of melanoma tumor and found that &gt;200 mutations hit the 3′UTR of genes, the main target area of miRNAs (out of 499 that hit transcribed genes). Three different computational algorithms (PITA, miRanda and our in-house tool, MirHB) concur and predict that these somatic mutations globally reduce the binding of miRNAs to the mutated 3′UTRs. This phenomenon is not genome-specific and proved to reflects the nature of the characteristic UV-induced mutation, C-to-T. Accordingly, mutation patterns in other malignancies, which are not primarily induced by UV-radiation, such as lung cancer and AML, do not yield similar predictions. This indicates that miRNA-based regulation can progressively perturb even with no apparent alterations in the expression of miRNAs. We define these mutations as “dormant drivers”, as each mutation is expected to have a moderate effect, but the cumulative effect is significant.

We next identified miRNAs that regulate the aggressive phenotype of established melanoma cells. For that purpose, we tested two isogenic human melanoma cell lines (derived from the same patient) that dramatically differ in net proliferation, invasion, tube formation and tumorigenicity in vivo. Comparative screening revealed a large cohort of differentially expressed miRNAs. Molecular manipulation of highly ranked miRNAs (miR-31, -34a, -184, -185 and -204 and miR-17-5p) resulted in significant changes of the aggressive phenotype in vitro and in vivo. Remarkably, none of these miRNAs has been studied in cutaneous melanoma before. In conclusion, this study might lead to the development of novel lines of therapy.

Citation Format: Eyal Greenberg, Eran Eyal, Gideon Rechavi, Noam Shomron, Jacob Schachter, Gal Markel, Yael Nemlich, Steven Hajdu, Orit Itzhaki, Liat Edry, Oz Solomon, Ninette Amariglio, Michal J. Besser, Yona Keisari. New views on microRNAs involvement in melanoma [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr B24.