ILEI (FAM3C) is a secreted factor that contributes to the epithelial-to-mesenchymal transition (EMT), a cell biological process that confers metastatic properties to a tumor cell.,Initially, we found that ILEI mRNA is highly expressed in melanoma metastases but not in primary tumors, suggesting that ILEI contributes to the malignant properties of melanoma.,While melanoma is not an epithelial cell-derived tumor and does not undergo a traditional EMT, melanoma undergoes a similar process known as phenotype switching in which high (micropthalmia-related transcription factor) MITF expressing (MITF-high) proliferative cells switch to a low expressing (MITF-low) invasive state.,We observed that MITF-high proliferative cells express low levels of ILEI (ILEI-low) and MITF-low invasive cells express high levels of ILEI (ILEI-high).,We found that inducing phenotype switching towards the MITF-low invasive state increases ILEI mRNA expression, whereas phenotype switching towards the MITF-high proliferative state decreases ILEI mRNA expression.,Next, we used in vitro assays to show that knockdown of ILEI attenuates invasive potential but not MITF expression or chemoresistance.,Finally, we used gene expression analysis to show that ILEI regulates several genes involved in the MITF-low invasive phenotype including JARID1B, HIF-2α, and BDNF.,Gene set enrichment analysis suggested that ILEI-regulated genes are enriched for JUN signaling, a known regulator of the MITF-low invasive phenotype.,In conclusion, we demonstrate that phenotype switching regulates ILEI expression, and that ILEI regulates partial phenotype switching in MITF-low melanoma cell lines.
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