[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.
Pigment Cell & Melanoma Research 05/2014; · 5.84 Impact Factor
[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.
Journal of Investigative Dermatology 04/2014; · 6.19 Impact Factor
[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.
Pigment Cell & Melanoma Research 07/2013; · 5.84 Impact Factor
[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.
Pigment Cell & Melanoma Research 07/2013; · 5.84 Impact Factor
[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; · 5.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Metastatic melanoma is a deadly skin cancer and is resistant to almost all existing treatment. Vemurafenib, which targets the BRAFV600E mutation, is one of the drugs that improves patient outcome, but the patients next develop secondary resistance and a return to cancer. Thus, new therapeutic strategies are needed to treat melanomas and to increase the duration of v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor response. The ERK pathway controls cell proliferation, and Aurora B plays a pivotal role in cell division. Here, we confirm that Aurora B is highly expressed in metastatic melanoma cells and that Aurora B inhibition triggers both senescence-like phenotypes and cell death in melanoma cells. Furthermore, we show that the BRAF/ERK axis controls Aurora B expression at the transcriptional level, likely through the transcription factor FOXM1. Our results provide insight into the mechanism of Aurora B regulation and the first molecular basis of Aurora B regulation in melanoma cells. The inhibition of Aurora B expression that we observed in vemurafenib-sensitive melanoma cells was rescued in cells resistant to this drug. Consistently, these latter cells remain sensitive to the effect of the Aurora B inhibitor. Noteworthy, wild-type BRAF melanoma cells are also sensitive to Aurora B inhibition. Collectively, our findings, showing that Aurora B is a potential target in melanoma cells, particularly in those vemurafenib-resistant, may open new avenues to improve the treatment of metastatic melanoma.
Journal of Biological Chemistry 07/2012; 287(35):29887-98. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cystinosis is a rare autosomal recessive disease characterized by cystine crystal accumulation leading to multiorgan dysfunctions and caused by mutation in CTNS. CTNS encodes cystinosin, a cystine/H(+) symporter that exports cystine out of the lysosomes. Patients with cystinosis frequently exhibit blond hair and fair complexion, suggesting an alteration in melanogenesis. However, the pigmentation singularities of these patients have not been studied, and the role of cystinosin in melanogenesis has remained unknown. In our study, a clinical evaluation of 27 patients with cystinosis showed that 44% had a cutaneous pigmentation dilution compared to their relatives. Analysis of the hair melanin content in these patients by HPLC demonstrated a 50% decrease in eumelanin (4360 vs. 9360 ng/mg), and a 2-fold increase in pheomelanin (53 vs. 20 ng/mg), the yellow/red pigments. Cystinosin-deficient mice also showed a 4-fold increase in hair pheomelanin content. In vitro studies showed that cystinosin was located at melanosomes. CTNS silencing led to a 75% reduction of melanin synthesis that was caused by a degradation of tyrosinase by lysosomal proteases. Our results objectify the pigmentation defect in patients with cystinosis. We also identify the role of CTNS in melanogenesis and add a new gene to the list of the genes involved in the control of skin and hair pigmentation.
The FASEB Journal 05/2012; 26(9):3779-89. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During progression of melanoma, malignant melanocytes can be reprogrammed into mesenchymal-like cells through a process similar to epithelial-mesenchymal transition (EMT), which is associated with downregulation of the junctional protein E-cadherin and acquisition of a migratory phenotype. Recent evidence supports a role for SLUG, a transcriptional repressor of E-cadherin, as a melanocyte lineage transcription factor that predisposes to melanoma metastasis. However, the signals responsible for SLUG expression in melanoma are unclear and its role in the invasive phenotype is not fully elucidated. Here, we report that SLUG expression and activation is driven by SPARC (also known as osteonectin), a secreted extracellular matrix-associated factor that promotes EMT-like changes. Ectopic expression or knockdown of SPARC resulted in increased or reduced expression of SLUG, respectively. SLUG increase occurred concomitantly with SPARC-mediated downregulation of E-cadherin and P-cadherin, and induction of mesenchymal traits in human melanocytes and melanoma cells. Pharmacological blockade of PI3 kinase/AKT signaling impeded SPARC-induced SLUG levels and cell migration, whereas adenoviral introduction of constitutively active AKT allowed rescue of SLUG and migratory capabilities of SPARC knockdown cells. We also observed that pharmacological inhibition of oncogenic BRAF(V600E) using PLX4720 did not influence SLUG expression in melanoma cells harboring BRAF(V600E). Furthermore, SLUG is a bona fide transcriptional repressor of E-cadherin as well as a regulator of P-cadherin in melanoma cells and its knockdown attenuated invasive behavior and blocked SPARC-enhanced cell migration. Notably, inhibition of cell migration in SPARC-depleted cells was rescued by expression of a SLUG transgene. In freshly isolated metastatic melanoma cells, a positive association between SPARC and SLUG mRNA levels was also found. These findings reveal that autocrine SPARC maintains heightened SLUG expression in melanoma cells and indicate that SPARC may promote EMT-associated tumor invasion by supporting AKT-dependent upregulation of SLUG.
PLoS ONE 01/2012; 7(7):e40378. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Selection for targeted therapies in melanoma is currently based on the search for mutations in selected genes. We aimed at evaluating the interest of signalling and chemosensitivity studies in addition to genotyping for assessing the best suitable treatment in an individual patient. We extracted genomic DNA and melanoma cells from tumor tissue of a skin metastasis of a 17-year-old woman with stage IV melanoma progressing despite three successive lines of treatment. Despite the absence of mutation in BRAF, NRAS cKIT, the MAPK pathway was activated and a significant response to sorafenib, a mitogen-activated protein kinase (MAPK)/RAF inhibitor, was found in signalling and chemosensitivity assays. A treatment combining sorafenib and dacarbazine produced a partial response for 9 months, with marked necrosis in some lesions. Chemosensitivity assays and signalling pathway studies could be of great value in addition to genotyping for assessing the most appropriate treatment in melanoma.
[Show abstract][Hide abstract] ABSTRACT: So far, no common environmental and/or phenotypic factor has been associated with melanoma and renal cell carcinoma (RCC). The known risk factors for melanoma include sun exposure, pigmentation and nevus phenotypes; risk factors associated with RCC include smoking, obesity and hypertension. A recent study of coexisting melanoma and RCC in the same patients supports a genetic predisposition underlying the association between these two cancers. The microphthalmia-associated transcription factor (MITF) has been proposed to act as a melanoma oncogene; it also stimulates the transcription of hypoxia inducible factor (HIF1A), the pathway of which is targeted by kidney cancer susceptibility genes. We therefore proposed that MITF might have a role in conferring a genetic predisposition to co-occurring melanoma and RCC. Here we identify a germline missense substitution in MITF (Mi-E318K) that occurred at a significantly higher frequency in genetically enriched patients affected with melanoma, RCC or both cancers, when compared with controls. Overall, Mi-E318K carriers had a higher than fivefold increased risk of developing melanoma, RCC or both cancers. Codon 318 is located in a small-ubiquitin-like modifier (SUMO) consensus site (ΨKXE) and Mi-E318K severely impaired SUMOylation of MITF. Mi-E318K enhanced MITF protein binding to the HIF1A promoter and increased its transcriptional activity compared to wild-type MITF. Further, we observed a global increase in Mi-E318K-occupied loci. In an RCC cell line, gene expression profiling identified a Mi-E318K signature related to cell growth, proliferation and inflammation. Lastly, the mutant protein enhanced melanocytic and renal cell clonogenicity, migration and invasion, consistent with a gain-of-function role in tumorigenesis. Our data provide insights into the link between SUMOylation, transcription and cancer.