RESUMO
Wnt/ß-catenin signaling plays an important role in melanocyte biology, especially in the early stages of melanocyte transformation and melanomagenesis. ß-catenin, encoded by the gene CTNNB1, is an intracellular signal transducer of Wnt signaling and activates transcription of genes important for cell proliferation and survival. Wnt/ß-catenin signaling is frequently activated in melanoma through oncogenic mutations of ß-catenin and elevated ß-catenin levels are positively correlated with melanoma aggressiveness. Molecular mechanisms that regulate ß-catenin expression in melanoma are not fully understood. MicroRNA-214 is known to function as a tumor suppressor by targeting ß-catenin in several types of cancer cells. Here, we investigated the regulation of ß-catenin by miR-214 and its role in melanoma. We show that ß-catenin mRNA levels are negatively correlated with miR-214 in melanoma. However, overexpression of miR-214 paradoxically increased ß-catenin protein levels and promoted malignant properties of melanoma cells including resistance to mitogen-activated protein kinase inhibitors (MAPKi). RNA-seq analysis revealed that melanoma cells predominantly express a ß-catenin mRNA isoform lacking miR-214 target site. Using matched miRNA and mRNA-seq and bioinformatics analysis, we identified novel miR-214 targets, ankyrin repeat domain 6 (ANKRD6) and C-terminal binding protein 1 (CTBP1), that are involved in negative regulation of Wnt signaling. Overexpression of miR-214 or knockdown of the novel miR-214 targets, ANKRD6 or CTBP1, increased melanoma cell proliferation, migration, and decreased sensitivity to MAPKi. Our data suggest that in melanoma cells ß-catenin is not regulated by miR-214 and the functions of miR-214 in melanoma are mediated partly by regulating proteins involved in attenuation of Wnt/ß-catenin signaling.
