Functional characterization of an oncogenic role for the miRNA-506-514 cluster in initiating melanocyte transformation and promoting melanoma growth.

Abstract 8514 Background: Malignant melanoma is the most aggressive form of skin cancer and its incidence has doubled in the last two decades. It represents only 4% of skin cancer cases per year, but encompasses as many as 74% of skin cancer deaths. If diagnosed early, the 5-year survival rates are encouraging-90% at Stage I and 60% at Stage II; however, this decreases substantially to 10% at stage III and nearly 0% at stage IV. Dysregulation of microRNA (miRNA) expression has been linked to tumor progression by functioning either as a tumor suppressor, an oncogene, or a metastasis regulator in multiple cancer types. To understand the role of miRNA in the pathogenesis of melanoma and identify putative biomarkers, miRNA expression profiles in skin punches from 36 melanoma patients and 15 healthy donors were compared. Mutational status of B-RAF and N-RAS was also determined. Primary melanocytes and multiple melanoma cell lines were transfected with miRNA mimics or hairpin inhibitors to manipulate levels of miRNAs of interest and determine the functional consequences. From the miRNA analysis, we identified a novel miRNA cluster (comprised of miRs-506-510, -513, and -514) on the X chromosome, termed the miR-506-514 cluster, that is uniformly over-expressed in nearly all melanomas tested, regardless of mutational status. Inhibiting the expression of this cluster as a whole, or one of its sub-clusters (Sub-cluster A, containing miRs-506-508, and -513), led to significant functional alterations, including reduced cell growth, increased apoptosis, decreased invasiveness, and decreased colony formation in soft agar across multiple melanoma cell lines. Sub-cluster A was critical for maintaining the cancer phenotype, but the over-expression of the full miR-506-514 cluster was required for melanocyte transformation and cancer initiation. To our knowledge, this is the first report on the functional role of the miR-506-514 cluster in melanoma. Further work is needed to evaluate this cluster as a therapeutic target or a potential diagnostic marker; however, these results significantly impact our understanding of the critical role of miRNAs in oncogenesis.