Oncogenic mutations in BRAF and NRAS occur in 70% of melanomas.,In this study, we identify a microRNA, miR-146a, that is highly upregulated by oncogenic BRAF and NRAS.,Expression of miR-146a increases the ability of human melanoma cells to proliferate in culture and form tumors in mice, whereas knockdown of miR-146a has the opposite effects.,We show these oncogenic activities are due to miR-146a targeting the NUMB mRNA, a repressor of Notch signaling.,Previous studies have shown that pre-miR-146a contains a single nucleotide polymorphism (C>G rs2910164).,We find that the ability of pre-miR-146a/G to activate Notch signaling and promote oncogenesis is substantially higher than that of pre-miR-146a/C.,Analysis of melanoma cell lines and matched patient samples indicates that during melanoma progression pre-miR-146a/G is enriched relative to pre-miR-146a/C, resulting from a C-to-G somatic mutation in pre-miR-146a/C.,Collectively, our results reveal a central role for miR-146a in the initiation and progression of melanoma.,DOI:http://dx.doi.org/10.7554/eLife.01460.001,Cancer is a leading cause of death worldwide, and although cancer can have many causes, mutations to a small number of genes are often responsible for a large number of cancer cases.,For example, about 70% of cases of the deadliest form of skin cancer have mutations in two specific genes.,Many cancer-causing genes are regulated by small RNA molecules that impede the function of other genes by blocking the machinery that turns a gene into a functional protein.,However, until recently there was a limited understanding of the role of these microRNAs in the skin cancers caused by the most common mutations.,Now, Forloni et al. have looked at all the microRNAs present in cells carrying a mutated form of the one of these genes, and compared these with the microRNAs found in healthy cells.,A microRNA, called miR-146a, was discovered to be much more common in the cancer cells.,Moreover, production of this microRNA was increased by the two cancer-causing mutations.,Forloni et al. found that increasing production of this microRNA caused human skin cancer cells to grow faster, and also caused tumors to develop in mice.,Reducing the level of miR-146a had the opposite effect.,Forloni et al. also looked at cancer cells taken from individuals at different stages of skin cancer and found that, as the disease progresses, an unprocessed form of miR-146a tends to acquire a mutation, which leads to much higher levels of the active, processed form of miR-146a in the cancer cells.,High levels of miR-146a also switched off a gene that encodes for a protein that, in turn, switches off a protein called NOTCH that is linked to skin cancer.,As such, excess miR-146a actually increases the activation of the NOTCH protein.,These results led Forloni et al. to test if delivering drugs that block the production of miR-146a by inhibiting skin cancer-causing genes, along with other drugs that inhibit the Notch signaling pathway, could be more effective than treatment with either drug on its own.,The combined treatment was very effective against human skin cancer cells and could represent a promising development in the treatment of this disease.,DOI:http://dx.doi.org/10.7554/eLife.01460.002
Targeted therapies directed at commonly overexpressed pathways in melanoma have clinical activity in numerous trials.,Little is known about how these therapies influence microRNA (miRNA) expression, particularly with combination regimens.,Knowledge of miRNAs altered with treatment may contribute to understanding mechanisms of therapeutic effects, as well as mechanisms of tumor escape from therapy.,We analyzed miRNA expression in metastatic melanoma tissue samples treated with a novel combination regimen of Temsirolimus and Bevacizumab.,Given the preliminary clinical activity observed with this combination regimen, we hypothesized that we would see significant changes in miRNA expression with combination treatment.,Using microarray analysis we analyzed miRNA expression levels in melanoma samples from a Cancer Therapy Evaluation Program-sponsored phase II trial of combination Temsirolimus and Bevacizumab in advanced melanoma, which elicited clinical benefit in a subset of patients.,Pre-treatment and post-treatment miRNA levels were compared using paired t-tests between sample groups (patients), using a p-value < 0.01 for significance.,microRNA expression remained unchanged with Temsirolimus alone; however, expression of 15 microRNAs was significantly upregulated (1.4 to 2.5-fold) with combination treatment, compared to pre-treatment levels.,Interestingly, twelve of these fifteen miRNAs possess tumor suppressor capabilities.,We identified 15 putative oncogenes as potential targets of the 12 tumor suppressor miRNAs, based on published experimental evidence.,For 15 of 25 miRNA-target mRNA pairings, changes in gene expression from pre-treatment to post-combination treatment samples were inversely correlated with changes in miRNA expression, supporting a functional effect of those miRNA changes.,Clustering analyses based on selected miRNAs suggest preliminary signatures characteristic of clinical response to combination treatment and of tumor BRAF mutational status.,To our knowledge, this is the first study analyzing miRNA expression in pre-treatment and post-treatment human metastatic melanoma tissue samples.,This preliminary investigation suggests miRNAs that may be involved in the mechanism of action of combination Temsirolimus and Bevacizumab in metastatic melanoma, possibly through inhibition of oncogenic pathways, and provides the preliminary basis for further functional studies of these miRNAs.