[Show abstract][Hide abstract] ABSTRACT: To identify 'melanoma-specific' microRNAs (miRNAs) we used an unbiased microRNA profiling approach to comprehensively study cutaneous melanoma in relation to other solid malignancies, which revealed 233 differentially expressed (≥ 2 fold, p < 0.05) miRNAs. Among the top 20 most significantly different miRNAs was hsa-miR-514a-3p. miR-514a is a member of a cluster of miRNAs (miR-506-514) involved in initiating melanocyte transformation and promotion of melanoma growth. We found miR-514a was expressed in 38/55 (69%) melanoma cell lines but in only 1/34 (3%) other solid cancers. To identify miR-514a regulated targets we conducted a miR-514a-mRNA 'pull-down' experiment, which revealed hundreds of genes, including: CTNNB1, CDK2, MC1R, and NF1, previously associated with melanoma. NF1 was selected for functional validation because of its recent implication inacquired resistance to BRAFV600E-targeted therapy. Luciferase-reporter assays confirmed NF1 as a direct target of miR-514a and over-expression of miR-514a in melanoma cell lines inhibited NF1 expression, which correlated with increased survival of BRAFV600E cells treated with PLX4032. These data provide another mechanism for the dysregulation of the MAPK pathway which may contribute to the profound resistance associated with current RAF-targeted therapies.
[Show abstract][Hide abstract] ABSTRACT: Neurofibromatosis type 1 (NF1) is a frequent genetic disease leading to the development of Schwann cell-derived neurofibromas or melanocytic lesions called café-au-lait macules (CALMs). The molecular mechanisms involved in CALMs formation remain largely unknown. In this report, we show for the first time pathophysiological mechanisms of abnormal melanocyte differentiation in a human NF1(+/-) induced pluripotent stem cell (iPSC)-based model. We demonstrate that NF1 patient-derived fibroblasts can be successfully reprogrammed in NF1(+/-) iPSCs with active RAS signaling and that NF1 loss induces senescence during melanocyte differentiation as well as in patient's-derived CALMs, revealing a new role for NF1 in the melanocyte lineage. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Understanding the molecular and cellular processes underlying melanoma plasticity and heterogeneity is of paramount importance to improve the efficiency of current treatment and to overcome resistance to chemotherapy drugs. The notion of plasticity and heterogeneity implies the existence of melanoma cell populations with different phenotypic and tumorigenic properties.
Using melanoma cell lines and melanoma cells freshly isolated from patient biopsies, we investigated the relationship between ABCB5+, CD271+ and low-MITF, expressing populations that were reported to display melanoma initiating cell properties. Here, we showed that ABCB5+ and CD271+ populations poorly overlap. However, we found that the CD271+ population is enriched in low-MITF cells and expresses a higher level of stemness genes, such as OCT4, NANOG and NES. These features could explain the increased tumorigenicity of the CD271+ cells. The rapid conversion of CD271+ to CD271− cells in vitro demonstrates the plasticity ability of melanoma cells. Finally, we observed that the transient slow-growing population contains only CD271+ cells that are highly tumorigenic. However, the fast growing/CD271+ population exhibits a poor tumorigenic ability. Taking together, our data show that CD271 is an imperfect marker for melanoma initiating cells, but may be useful to identify melanoma cells with an increased stemness and tumorigenic potential.
[Show abstract][Hide abstract] ABSTRACT: Metformin is the most widely used antidiabetic drug that belongs to the biguanide class. It is very well-tolerated and has the major clinical advantage of not inducing hypoglycemia. Metformin decreases hepatic glucose production via a mechanism requiring liver kinase B1, which controls the metabolic checkpoint, AMP-activated protein kinase-mammalian target of rapamycin and neoglucogenic genes. The effects of metformin on this pathway results in reduced protein synthesis and cell proliferation. These observations have given the impetus for many investigations on the role of metformin in the regulation of tumor cell proliferation, cell cycle regulation, apoptosis and autophagy. Encouraging results from these studies have shown that metformin could potentially be used as an efficient anticancer drug in various neoplasms such as prostate, breast, lung, pancreas cancers and melanoma. These findings are strengthened by retrospective epidemiological studies that have found a decrease in cancer risk in diabetic patients treated with metformin. In this review, we have focused our discussion on recent the molecular mechanisms of metformin that have been described in various solid tumors in general, and in melanoma in particular. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Several reports have demonstrated inhibitory effect of metformin, a widely used drug in treatment of type 2 diabetes, on the proliferation of many cancers including melanoma. Recently it has been shown that metformin is able to modulate cAMP level in liver. Since, cAMP plays a crucial role in melanin synthesis and skin pigmentation, we investigated the effect of metformin on melanogenesis both in vitro and in vivo. We showed that metformin led to reduced melanin content in melanoma cells and in normal human melanocytes by decreasing cAMP accumulation and CREB phosphorylation. This inhibitory effect is correlated with decreased expression of master genes of melanogenesis, MITF, Tyrosinase, DCT and TRP1. Furthermore, we demonstrated that the anti-melanogenic effect of metformin is independent of AMPK pathway. Interestingly, topically application of metformin induced tail whitening in mice. Finally, we confirmed the anti-melanogenesis effect of metformin on reconstituted human epidermis and on human skin biopsies. These data emphasize the depigmenting effect of metformin and suggest a clinical strategy for using metformin in topical treatment of hyperpigmentation disorders.Journal of Investigative Dermatology accepted article peview online, 22 April 2014. doi:10.1038/jid.2014.202.
[Show abstract][Hide abstract] ABSTRACT: El color de la piel es el resultado de una sutil mezcla de pigmentos melánicos producidos por células especializadas, los melanocitos, cuyo origen embriológico es el tubo neural. En la piel, los melanocitos se localizan en la capa basal de la epidermis y en el bulbo piloso. La melanogénesis representa el mecanismo que da lugar a la síntesis de melanina, la cual se efectúa en el seno de una organela intracitoplasmática, de la familia de los lisosomas secretores, llamada «melanosoma». Se producen dos familias de melaninas: la eumelanina, de color marrón o negro, y la feomelanina, de color amarillo o rojo anaranjado, que es menos fotoprotectora. Se han identificado tres enzimas principales de la melanogénesis: la tirosinasa y las proteínas relacionadas con la tirosinasa 1 y 2. Un número importante de genes controla la embriogénesis de los melanocitos, la biogénesis de los melanosomas, su transporte en los melanocitos y su paso a los queratinocitos. Se han identificado numerosos factores de regulación de la melanogénesis (ultravioletas, hormonas melanotrópicas, citocinas, etc.). Se han analizado progresivamente los mecanismos de señalización celular implicados en la melanogénesis. Estos conocimientos recientes permitirán conocer mejor las bases genéticas de la fotoprotección melánica de la piel. Han permitido identificar numerosas dianas potenciales para futuras estrategias terapéuticas de la hipermelanosis y la hipomelanosis cutáneas.
[Show abstract][Hide abstract] ABSTRACT: SIRT1 operates as both a tumor suppressor and oncogenic factor depending on the cell context. Whether SIRT1 plays a role in melanoma biology remained poorly elucidated. Here, we demonstrate that SIRT1 is a critical regulator of melanoma cell proliferation. SIRT1 suppression by genetic or pharmacological approaches induces cell cycle arrest and a senescence-like phenotype. Gain and loss of function experiments show that M-MITF regulates SIRT1 expression, thereby revealing a melanocyte-specific control of SIRT1. SIRT1 over-expression relieves the senescence-like phenotype and the proliferation arrest caused by MITF suppression, demonstrating that SIRT1 is an effector of MITF-induced proliferation in melanoma cells. Interestingly, SIRT1 level and activity are enhanced in the PLX4032-resistant BRAFV600E-mutated melanoma cells compared with their sensitive counterpart. SIRT1 inhibition decreases melanoma cell growth and rescues the sensibility to PLX4032 of PLX4032-resistant BRAFV600E-mutated melanoma cells. In conclusion, we provide the first evidence that inhibition of SIRT1 warrants consideration as an anti-melanoma therapeutic option.
[Show abstract][Hide abstract] ABSTRACT: Here, we showed that the secretome of senescent melanoma cells drives basal melanoma cells towards a mesenchymal phenotype, with characteristic of stems illustrated by increased level of the prototype genes FN1, SNAIL, OCT4 and NANOG. This molecular reprogramming leads to an increase in the low-MITF and slow-growing cell population endowed with melanoma-initiating cell features. The secretome of senescent melanoma cells induces a panel of 52 genes, involved in cell movement and cell/cell interaction, among which AXL and ALDH1A3 have been implicated in melanoma development. We found that the secretome of senescent melanoma cells activates the STAT3 pathway and STAT3 inhibition prevents secretome effects, including the acquisition of tumorigenic properties. Collectively, the findings provide insights into how the secretome of melanoma cells entering senescence upon chemotherapy treatments increases the tumorigenicity of naïve melanoma cells by inducing, through STAT3 activation, a melanoma-initiating cell phenotype that could favor chemotherapy resistance and relapse.
[Show abstract][Hide abstract] ABSTRACT: BRAF is the most prevalent oncogene and an important therapeutic target in melanoma. In some cancers BRAF is activated by rearrangements that fuse its kinase domain to 5' partner genes. We examined 848 comparative genomic hybridization profiles of melanocytic tumors and found copy number transitions within BRAF in 10 tumors, of which six could be further characterized by sequencing. In all, the BRAF kinase domain was fused in-frame to six different N-terminal partners. No other mutations were identified in melanoma oncogenes. One of seven melanoma cell lines without known oncogenic mutations harbored a similar BRAF fusion, which constitutively activated the MAP-kinase pathway. Sorafenib, but not vemurafenib, could block MAP-kinase pathway activation and proliferation of the cell line at clinically relevant concentrations, whereas BRAF(V) (600E) mutant melanoma cell lines were significantly more sensitive to vemurafenib. The patient from whom the cell line was derived showed a durable clinical response to sorafenib. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: As a young researcher, I was working on insulin receptor signaling and seeking my way in the maze of basic research. In fact, I was fascinated by melanocytes and skin pigmentation but my knowledge in the field was minimal. Living in Nice and being a fan of seaside leisure, I knew that exposure to sunlight leads to a beautiful golden pigmentation of the skin, commonly known as tanning. I also knew that tanning was due to pigments being synthesized by specialized cells called melanocytes. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Metformin was reported to inhibit the proliferation of many cancer cells including melanoma cells. In this report, we investigated the effect of metformin on melanoma invasion and metastasis development. Using different in vitro approaches, we found that metformin inhibits cell invasion without affecting cell migration and independently of anti-proliferation action. This inhibition is correlated with modulation of expression of proteins involved in epithelial mesenchymal transition such as Slug, Snail, SPARC, fibronectin and N-Cadherin and with inhibition of MMP-2 and MMP-9 activation. Further our data indicate that this process is dependent of activation of AMPK and tumor suppressor protein, p53. Finally, we demonstrated that metformin inhibits melanoma metastasis development in mice using extravasation and metastasis models. The presented data reinforce the fact that metformin might be a good candidate for clinical trial in melanoma treatment.
Molecular Cancer Therapeutics 06/2013; 12(8). DOI:10.1158/1535-7163.MCT-12-1226-T · 6.11 Impact Factor