Abstract 4366: miR-126 reduces the tumorigenicity of melanoma cells in vitro and alters the melanoma microenvironment

Abstract

The microRNA (miRNA) miR-126 is highly expressed in endothelial cells and often reported as down-regulated in cancer. The present study thoroughly examines the functional relevance of miR-126 in melanoma progression and suggests a central role of this miRNA as prognostic marker and modulator of the melanoma microenvironment. Initially, the expression of miR-126 was quantified in two independent, isogenic cell line model series of melanoma progression. To further explore its functional role, two stable over-expression cell lines were generated and subjected to an extensive series of in vitro assays. Subsequently, the prognostic relevance of miR-126 was assessed via in situ hybridization on a large melanoma tissue microarray cohort. In both melanoma cell line systems, miR-126 expression was inversely correlated with the level of tumorigenicity. Over-expression of miR-126 in vitro resulted in a significant decrease in colony formation, both in the presence and absence of anchorage, while cell viability remained unaffected. Using a three-dimensional spheroid invasion assay, over-expression of miR-126 significantly reduced cell invasiveness. In addition, a substantial reduction in tumor cell adhesion to VCAM-1 coated micro-channels was observed when the adhesive capacity of miR-126 over-expressing cells was examined under shear stress using the Cellix's Microfluidic Platform. Using in situ hybridization on tissue microarrays containing melanoma tissue, miR-126 expression was evident in the tumor vasculature whereas melanoma cells did not appear to express miR-126. Analysis of the degree of vascular staining revealed a significant association between lower vascular miR-126 expression and lower T-stage. In addition, high vascular miR-126 scores were significantly associated with prolonged overall survival, in particular in high grade tumors (T-stages 3 and 4). Overall, miR-126 over-expression was shown to trigger a less aggressive phenotype in melanoma cells in vitro. Nonetheless, its clinical relevance in melanoma may primarily be mediated by the tumor vasculature. Depletion of miR-126 has previously been linked to a number of tumor relevant phenotypes, including inflammation. Vascular up-regulation of the miR-126 target protein VCAM-1 may mediate increased tumor infiltration of lymphocytes and macrophages, which are known to play a crucial role in tumor development and prognosis. This renders miR-126 an exciting target for closer investigation with regard to its role in the melanoma microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4366. doi:1538-7445.AM2012-4366