Publications by authors named "Robert Ballotti"

89 Publications

The ERK signaling pathway returns to the limelight in uveal melanomas.

Pigment Cell Melanoma Res 2021 Feb 6. Epub 2021 Feb 6.

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http://dx.doi.org/10.1111/pcmr.12965DOI Listing
February 2021

Single-cell RNA sequencing reveals intratumoral heterogeneity in primary uveal melanomas and identifies HES6 as a driver of the metastatic disease.

Cell Death Differ 2021 Jan 18. Epub 2021 Jan 18.

Université Côte d'Azur, Nice, France.

Intratumor heterogeneity has been recognized in numerous cancers as a major source of metastatic dissemination. In uveal melanomas, the existence and identity of specific subpopulations, their biological function and their contribution to metastasis remain unknown. Here, in multiscale analyses using single-cell RNA sequencing of six different primary uveal melanomas, we uncover an intratumoral heterogeneity at the genomic and transcriptomic level. We identify distinct transcriptional cell states and diverse tumor-associated populations in a subset of the samples. We also decipher a gene regulatory network underlying an invasive and poor prognosis state driven in part by the transcription factor HES6. HES6 heterogenous expression has been validated by RNAscope assays within primary human uveal melanomas, which further unveils the existence of these cells conveying a dismal prognosis in tumors diagnosed with a favorable outcome using bulk analyses. Depletion of HES6 impairs proliferation, migration and metastatic dissemination in vitro and in vivo using the chick chorioallantoic membrane assay, demonstrating the essential role of HES6 in uveal melanomas. Thus, single-cell analysis offers an unprecedented view of primary uveal melanoma heterogeneity, identifies bona fide biomarkers for metastatic cells in the primary tumor, and reveals targetable modules driving growth and metastasis formation. Significantly, our findings demonstrate that HES6 is a valid target to stop uveal melanoma progression.
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http://dx.doi.org/10.1038/s41418-020-00730-7DOI Listing
January 2021

FBXO32 links ubiquitination to epigenetic reprograming of melanoma cells.

Cell Death Differ 2021 Jan 18. Epub 2021 Jan 18.

Université Nice Côte d'Azur, Nice, France.

Ubiquitination by serving as a major degradation signal of proteins, but also by controlling protein functioning and localization, plays critical roles in most key cellular processes. Here, we show that MITF, the master transcription factor in melanocytes, controls ubiquitination in melanoma cells. We identified FBXO32, a component of the SCF E3 ligase complex as a new MITF target gene. FBXO32 favors melanoma cell migration, proliferation, and tumor development in vivo. Transcriptomic analysis shows that FBXO32 knockdown induces a global change in melanoma gene expression profile. These include the inhibition of CDK6 in agreement with an inhibition of cell proliferation and invasion upon FBXO32 silencing. Furthermore, proteomic analysis identifies SMARC4, a component of the chromatin remodeling complexes BAF/PBAF, as a FBXO32 partner. FBXO32 and SMARCA4 co-localize at loci regulated by FBXO32, such as CDK6 suggesting that FBXO32 controls transcription through the regulation of chromatin remodeling complex activity. FBXO32 and SMARCA4 are the components of a molecular cascade, linking MITF to epigenetics, in melanoma cells.
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http://dx.doi.org/10.1038/s41418-020-00710-xDOI Listing
January 2021

Germline variants in exonic regions have limited impact on immune checkpoint blockade clinical outcomes in advanced melanoma.

Pigment Cell Melanoma Res 2021 Jan 15. Epub 2021 Jan 15.

Centre Méditerranéen de Médecine Moléculaire (C3M), Université Nice Côte d'Azur, INSERM, Nice, France.

Immune checkpoint inhibition (ICI) treatments improve outcomes for metastatic melanoma; however, up to 60% of treated patients do not respond to ICI and/or develop immune-related adverse events (irAEs). Currently, robust and reliable biomarker to predict response and/or occurrence of irAEs to ICI are missing. Herein, we wanted to explore whether germline variants (SNPs) could predict the clinical outcomes of melanoma patients treated with ICIs. We performed a whole exome sequencing using gDNA isolated from blood, from a discovery cohort of 57 patients with metastatic melanoma. The top associations were then tested in a validation cohort of 57 patients. Our work suggests that individual germline genetic variants have no or weak impact on the response to ICIs. Only, variants in IL1RL1 have a significant impact in treatment response. The role of IL1RL1 in the immune response against melanoma and as a theranostic marker warrants further investigations.
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http://dx.doi.org/10.1111/pcmr.12958DOI Listing
January 2021

Discovery of a new molecule inducing melanoma cell death: dual AMPK/MELK targeting for novel melanoma therapies.

Cell Death Dis 2021 Jan 11;12(1):64. Epub 2021 Jan 11.

INSERM, U1065, Equipe 12, Centre Méditerranéen de Médecine Moléculaire (C3M), Bâtiment ARCHIMED, 151 route de saint Antoine de Ginestière, 06204, Nice cedex 3, France.

In the search of biguanide-derived molecules against melanoma, we have discovered and developed a series of bioactive products and identified the promising new compound CRO15. This molecule exerted anti-melanoma effects on cells lines and cells isolated from patients including the ones derived from tumors resistant to BRAF inhibitors. Moreover, CRO15 was able to decrease viability of cells lines from a broad range of cancer types. This compound acts by two distinct mechanisms. First by activating the AMPK pathway induced by a mitochondrial disorder. Second by inhibition of MELK kinase activity, which induces cell cycle arrest and activation of DNA damage repair pathways by p53 and REDD1 activation. All of these mechanisms activate autophagic and apoptotic processes resulting in melanoma cell death. The strong efficacy of CRO15 to reduce the growth of melanoma xenograft sensitive or resistant to BRAF inhibitors opens interesting perspective.
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http://dx.doi.org/10.1038/s41419-020-03344-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7801734PMC
January 2021

ITGBL1 is a new immunomodulator that favors development of melanoma tumors by inhibiting natural killer cells cytotoxicity.

Mol Cancer 2021 01 7;20(1):12. Epub 2021 Jan 7.

Université Nice Côte d'Azur, INSERM U1065, Team1 Biology and pathologies of melanocytes. Equipe labellisée ARC 2019, 06000, Nice, France.

Resistances to immunotherapies remains a major hurdle towards a cure for melanoma in numerous patients. An increase in the mesenchymal phenotype and a loss of differentiation have been clearly associated with resistance to targeted therapies. Similar phenotypes have been more recently also linked to resistance to immune checkpoint therapies. We demonstrated here that the loss of MIcrophthalmia associated Transcription Factor (MITF), a pivotal player in melanocyte differentiation, favors the escape of melanoma cells from the immune system. We identified Integrin beta-like protein 1 (ITGBL1), a secreted protein, upregulated in anti-PD1 resistant patients and in MITF melanoma cells, as the key immunomodulator. ITGBL1 inhibited immune cell cytotoxicity against melanoma cells by inhibiting NK cells cytotoxicity and counteracting beneficial effects of anti-PD1 treatment, both in vitro and in vivo. Mechanistically, MITF inhibited RUNX2, an activator of ITGBL1 transcription. Interestingly, VitaminD3, an inhibitor of RUNX2, improved melanoma cells to death by immune cells. In conclusion, our data suggest that inhibition of ITGBL1 might improve melanoma response to immunotherapies.
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http://dx.doi.org/10.1186/s12943-020-01306-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7789764PMC
January 2021

The complex relationship between MITF and the immune system: a Melanoma ImmunoTherapy (response) Factor?

Mol Cancer 2020 12 5;19(1):170. Epub 2020 Dec 5.

Université Côte d'Azur, Nice, France.

The clinical benefit of immune checkpoint inhibitory therapy (ICT) in advanced melanomas is limited by primary and acquired resistance. The molecular determinants of the resistance have been extensively studied, but these discoveries have not yet been translated into therapeutic benefits. As such, a paradigm shift in melanoma treatment, to surmount the therapeutic impasses linked to the resistance, is an important ongoing challenge.This review outlines the multifaceted interplay between microphthalmia-associated transcription factor (MITF), a major determinant of the biology of melanoma cells, and the immune system. In melanomas, MITF functions downstream oncogenic pathways and microenvironment stimuli that restrain the immune responses. We highlight how MITF, by controlling differentiation and genome integrity, may regulate melanoma-specific antigen expression by interfering with the endolysosomal pathway, KARS1, and antigen processing and presentation. MITF also modulates the expression of coinhibitory receptors, i.e., PD-L1 and HVEM, and the production of an inflammatory secretome, which directly affects the infiltration and/or activation of the immune cells.Furthermore, MITF is also a key determinant of melanoma cell plasticity and tumor heterogeneity, which are undoubtedly one of the major hurdles for an effective immunotherapy. Finally, we briefly discuss the role of MITF in kidney cancer, where it also plays a key role, and in immune cells, establishing MITF as a central mediator in the regulation of immune responses in melanoma and other cancers.We propose that a better understanding of MITF and immune system intersections could help in the tailoring of current ICT in melanomas and pave the way for clinical benefits and long-lasting responses.
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http://dx.doi.org/10.1186/s12943-020-01290-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7718690PMC
December 2020

Endoplasmic reticulum stress mediates resistance to BCL-2 inhibitor in uveal melanoma cells.

Cell Death Discov 2020 17;6:22. Epub 2020 Apr 17.

1Université Nice Côte d'Azur, Inserm, C3M Nice, France.

To address unmet clinical need for uveal melanomas, we assessed the effects of BH3-mimetic molecules, the ABT family, known to exert pro-apoptotic activities in cancer cells. Our results uncovered that ABT-263 (Navitoclax), a potent and orally bioavailable BCL-2 family inhibitor, induced antiproliferative effects in metastatic human uveal melanoma cells through cell cycle arrest at the G0/G1 phase, loss of mitochondrial membrane potential, and subsequently apoptotic cell death monitored by caspase activation and poly-ADP ribose polymerase cleavage. ABT-263-mediated reduction in tumor growth was also observed in vivo. We observed in some cells that ABT-263 treatment mounted a pro-survival response through activation of the ER stress signaling pathway. Blocking the PERK signaling pathway increased the pro-apoptotic ABT-263 effect. We thus uncovered a resistance mechanism in uveal melanoma cells mediated by activation of endoplasmic reticulum stress pathway. Therefore, our study identifies ABT-263 as a valid therapeutic option for patients suffering from uveal melanoma.
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http://dx.doi.org/10.1038/s41420-020-0259-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7165182PMC
April 2020

Regulation of Melanogenesis by the Amino Acid Transporter SLC7A5.

J Invest Dermatol 2020 Nov 30;140(11):2253-2259.e4. Epub 2020 Mar 30.

Université Nice Côte d'Azur, C3M, INSERM, U1065, Biology and pathologies of melanocytes, Nice, France. Electronic address:

Integration of chromatin immunoprecipitation-sequencing and microarray data enabled us to identify previously unreported MITF-target genes, among which the amino acid transporter SLC7A5 is also included. We reported that small interfering RNA-mediated SLC7A5 knockdown decreased pigmentation in B16F10 cells but neither affected morphology nor dendricity. Treatment with the SLC7A5 inhibitors 2-amino-2-norbornanecarboxylic acid (BCH) or JPH203 also decreased melanin synthesis in B16F10 cells. Our findings indicated that BCH was as potent as reference depigmenting agent, kojic acid, but acted through a different pathway not affecting tyrosinase activity. BCH also decreased pigmentation in human MNT1 melanoma cells or normal human melanocytes. Finally, we tested BCH on a more physiological model, using reconstructed human epidermis and confirmed a strong inhibition of pigmentation, revealing the clinical potential of SLC7A5 inhibition and positioning BCH as a depigmenting agent suitable for cosmetic or dermatological intervention in hyperpigmentation diseases.
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http://dx.doi.org/10.1016/j.jid.2020.03.941DOI Listing
November 2020

The "ART" of Epigenetics in Melanoma: From histone "Alterations, to Resistance and Therapies".

Theranostics 2020 1;10(4):1777-1797. Epub 2020 Jan 1.

Université Nice Côte d'Azur, Inserm, C3M, France.

Malignant melanoma is the most deadly form of skin cancer. It originates from melanocytic cells and can also arise at other body sites. Early diagnosis and appropriate medical care offer excellent prognosis with up to 5-year survival rate in more than 95% of all patients. However, long-term survival rate for metastatic melanoma patients remains at only 5%. Indeed, malignant melanoma is known for its notorious resistance to most current therapies and is characterized by both genetic and epigenetic alterations. In cutaneous melanoma (CM), genetic alterations have been implicated in drug resistance, yet the main cause of this resistance seems to be non-genetic in nature with a change in transcription programs within cell subpopulations. This change can adapt and escape targeted therapy and immunotherapy cytotoxic effects favoring relapse. Because they are reversible in nature, epigenetic changes are a growing focus in cancer research aiming to prevent or revert the drug resistance with current therapies. As such, the field of epigenetic therapeutics is among the most active area of preclinical and clinical research with effects of many classes of epigenetic drugs being investigated. Here, we review the multiplicity of epigenetic alterations, mainly histone alterations and chromatin remodeling in both cutaneous and uveal melanomas, opening opportunities for further research in the field and providing clues to specifically control these modifications. We also discuss how epigenetic dysregulations may be exploited to achieve clinical benefits for the patients, the limitations of these therapies, and recent data exploring this potential through combinatorial epigenetic and traditional therapeutic approaches.
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http://dx.doi.org/10.7150/thno.36218DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6993228PMC
January 2020

HVEM has a broader expression than PD-L1 and constitutes a negative prognostic marker and potential treatment target for melanoma.

Oncoimmunology 2019;8(12):e1665976. Epub 2019 Sep 25.

Tumor Immunology Team, IBISA Immunomonitoring platform, Cancer Research Center of Marseille, INSERM U1068, CNRS U7258, Aix-Marseille University, Institut Paoli-Calmettes, Marseille, France.

HVEM (Herpes Virus Entry Mediator) engagement of BTLA (B and T Lymphocyte Attenuator) triggers inhibitory signals in T cells and could play a role in evading antitumor immunity. Here, HVEM expression levels in melanoma metastases were analyzed by immunohistochemistry, correlated with overall survival (OS) in 116 patients, and validated by TCGA transcriptomic data. Coincident expression of HVEM and its ligand BTLA was studied in tumor cells and tumor-infiltrating lymphocytes (TILs) by flow cytometry (n = 21) and immunofluorescence (n = 5). Candidate genes controlling expression in melanoma were defined by bioinformatics studies and validated by siRNA gene silencing. We found that in patients with AJCC stage III and IV melanoma, OS was poorer in those with high HVEM expression on melanoma cells, than in those with a low expression, by immunohistochemistry ( = .0160) or TCGA transcriptomics ( = .0282). We showed a coincident expression of HVEM at the surface of melanoma cells and of BTLA on TILs. HVEM was more widely expressed than PD-L1 in melanoma cells. From a mechanistic perspective, in contrast to PDL1, expression did not correlate with an IFNγ signature but with an aggressive gene signature. Interestingly, this signature contained , a key player in melanoma biology, whose expression correlated strongly with . Finally, siRNA gene silencing validated control of expression. In conclusion, HVEM expression seems to be a prognosis marker and targeting this axis by checkpoint-inhibitors may be of interest in metastatic melanoma.
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http://dx.doi.org/10.1080/2162402X.2019.1665976DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6844309PMC
September 2019

Genetic Heterogeneity of BRAF Fusion Kinases in Melanoma Affects Drug Responses.

Cell Rep 2019 10;29(3):573-588.e7

Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Dermatology, University of California, San Francisco, San Francisco, CA 94115, USA; Department of Pathology, University of California, San Francisco, San Francisco, CA 94115, USA. Electronic address:

BRAF fusions are detected in numerous neoplasms, but their clinical management remains unresolved. We identified six melanoma lines harboring BRAF fusions representative of the clinical cases reported in the literature. Their unexpected heterogeneous responses to RAF and MEK inhibitors could be categorized upon specific features of the fusion kinases. Higher expression level correlated with resistance, and fusion partners containing a dimerization domain promoted paradoxical activation of the mitogen-activated protein kinase (MAPK) pathway and hyperproliferation in response to first- and second-generation RAF inhibitors. By contrast, next-generation αC-IN/DFG-OUT RAF inhibitors blunted paradoxical activation across all lines and had their therapeutic efficacy further increased in vitro and in vivo by combination with MEK inhibitors, opening perspectives in the clinical management of tumors harboring BRAF fusions.
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http://dx.doi.org/10.1016/j.celrep.2019.09.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6939448PMC
October 2019

Innate lymphocyte-induced CXCR3B-mediated melanocyte apoptosis is a potential initiator of T-cell autoreactivity in vitiligo.

Nat Commun 2019 05 16;10(1):2178. Epub 2019 May 16.

Team 12, Université Côte d'Azur, INSERM U1065, Centre Méditerranéen de Médecine Moléculaire (C3M), Nice, 06200, France.

T-cells play a crucial role in progression of autoimmunity, including vitiligo, yet the initial steps triggering their activation and tissue damage remain unknown. Here we demonstrate increased presence of type-1 innate lymphoid cells (NK and ILC1)-producing interferon gamma (IFNγ) in the blood and in non-lesional skin of vitiligo patients. Melanocytes of vitiligo patients have strong basal expression of chemokine-receptor-3 (CXCR3) isoform B which is directly regulated by IFNγ. CXCR3B activation by CXCL10 at the surface of cultured human melanocytes induces their apoptosis. The remaining melanocytes, activated by the IFNγ production, express co-stimulatory markers which trigger T-cell proliferation and subsequent anti-melanocytic immunity. Inhibiting the CXCR3B activation prevents this apoptosis and the further activation of T cells. Our results emphasize the key role of CXCR3B in apoptosis of melanocytes and identify CXCR3B as a potential target to prevent and to treat vitiligo by acting at the early stages of melanocyte destruction.
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http://dx.doi.org/10.1038/s41467-019-09963-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6522502PMC
May 2019

Nicotinamide as a chemopreventive therapy of skin cancers. Too much of good thing?

Pigment Cell Melanoma Res 2019 07 27;32(4):601-602. Epub 2019 Feb 27.

INSERM, C3M, Université Nice Côte d'Azur, Nice, France.

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http://dx.doi.org/10.1111/pcmr.12772DOI Listing
July 2019

[Key role of nicotinamide phosphoribosyltransferase (NAMPT) and NAD metabolism in the transition of melanoma cells to an invasive and drug-resistant phenotype].

Med Sci (Paris) 2018 12 9;34(12):1025-1028. Epub 2019 Jan 9.

Université Nice Côte d'Azur, Inserm, C3M, 151, route Saint Antoine de Ginestière, 06204 Nice, France - Inserm, U1065, Biology and pathologies of melanocytes. Équipe labellisée ARC 2015, Nice, France.

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http://dx.doi.org/10.1051/medsci/2018283DOI Listing
December 2018

Microphthalmia-Associated Transcription Factor (MITF) Regulates Immune Cell Migration into Melanoma.

Transl Oncol 2019 Feb 28;12(2):350-360. Epub 2018 Nov 28.

Center of Integrated Protein Science Munich (CIPS-M) and Division of Clinical Pharmacology, Klinikum der Universität München, Lindwurmstrasse 2a, 80337 Munich, Germany. Electronic address:

Microphthalmia-associated transcription factor (MITF) is a key transcription factor in melanoma development and progression. MITF amplification and downregulation have been observed in a significant proportion of melanoma patients and correlate with clinical outcomes. Here, we have investigated the effect of MITF on melanoma chemokine expression and immune cell attraction. In B16F10 melanoma cells, MITF knockdown reduced expression of CXCL10, with concomitantly decreased attraction of immune cells and accelerated tumor outgrowth. Conversely, overexpression of MITF in YUMM1.1 melanoma cells also led to an increased immune cell attraction in vitro. Subcutaneous YUMM1.1 melanomas overexpressing MITF however showed a reduced immune infiltration of lymphocytes and an increased tumor growth. In human melanoma cell lines, silencing of MITF enhanced chemokine production and immune cell attraction, while overexpression of MITF led to lower immune cell attraction. In summary, our results show that MITF regulates chemokine expression in murine and in human melanoma cells, and affects in vivo immune cell attraction and tumor growth. These results reveal a functional relationship between MITF and immune cell infiltration, which may be exploited for cancer therapy.
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http://dx.doi.org/10.1016/j.tranon.2018.10.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6290759PMC
February 2019

Lysosomal acid ceramidase ASAH1 controls the transition between invasive and proliferative phenotype in melanoma cells.

Oncogene 2019 02 25;38(8):1282-1295. Epub 2018 Sep 25.

Team 1, Biology and Pathologies of Melanocytes, Equipe labellisée ARC 2015, Université Côte d'Azur, Inserm U1065, C3M, Nice, France.

Phenotypic plasticity and subsequent generation of intratumoral heterogeneity underly key traits in malignant melanoma such as drug resistance and metastasis. Melanoma plasticity promotes a switch between proliferative and invasive phenotypes characterized by different transcriptional programs of which MITF is a critical regulator. Here, we show that the acid ceramidase ASAH1, which controls sphingolipid metabolism, acted as a rheostat of the phenotypic switch in melanoma cells. Low ASAH1 expression was associated with an invasive behavior mediated by activation of the integrin alphavbeta5-FAK signaling cascade. In line with that, human melanoma biopsies revealed heterogeneous staining of ASAH1 and low ASAH1 expression at the melanoma invasive front. We also identified ASAH1 as a new target of MITF, thereby involving MITF in the regulation of sphingolipid metabolism. Together, our findings provide new cues to the mechanisms underlying the phenotypic plasticity of melanoma cells and identify new anti-metastatic targets.
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http://dx.doi.org/10.1038/s41388-018-0500-0DOI Listing
February 2019

The pro-tumoral function of HACE1.

Oncoscience 2018 May 23;5(5-6):128-129. Epub 2018 Jun 23.

Team 1, Biology and pathologies of melanocytes, Equipe labellisée ARC 2015, Université Côte d'Azur, Inserm U1065, C3M, Nice, France.

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http://dx.doi.org/10.18632/oncoscience.418DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6049301PMC
May 2018

E2F1 inhibition mediates cell death of metastatic melanoma.

Cell Death Dis 2018 05 1;9(5):527. Epub 2018 May 1.

INSERM, U1065, team 12, Study of molecular mechanisms involved in pigmentation and melanoma using translational approaches, Centre Méditerranéen de Médecine Moléculaire (C3M), Nice, France.

Melanoma is one of the most lethal cancers when it reaches a metastatic stage. Despite advancements in targeted therapies (BRAF inhibitors) or immunotherapies (anti-CTLA-4 or anti-PD1), most patients with melanoma will need additional treatment. Thus, there is an urgent need to develop new therapeutical approaches to bypass resistance and achieve more prolonged responses. In this context, we were interested in E2F1, a transcription factor that plays a major role in the control of cell cycle under physiological and pathological conditions. Here we confirmed that E2F1 is highly expressed in melanoma cells. Inhibition of E2F1 activity further increased melanoma cell death and senescence, both in vitro and in vivo. Moreover, blocking E2F1 also induced death of melanoma cells resistant to BRAF inhibitors. In conclusion, our studies suggest that targeting the E2F1 signaling pathway may be therapeutically relevant for melanoma.
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http://dx.doi.org/10.1038/s41419-018-0566-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5943238PMC
May 2018

Pivotal role of NAMPT in the switch of melanoma cells toward an invasive and drug-resistant phenotype.

Genes Dev 2018 03 22;32(5-6):448-461. Epub 2018 Mar 22.

U1065, Institut National de la Santé et de la Recherche Médicale (INSERM), Biology and Pathologies of Melanocytes, Equipe Labellisée L'Association pour la Recherche sur le Cancer (ARC) 2015, Université Nice Côte d'Azur, INSERM, Centre Méditerranéen de Médecine Moléculaire (C3M), 06204 Nice, France.

In BRAF melanoma cells, a global metabolomic analysis discloses a decrease in nicotinamide adenine dinucleotide (NAD) levels upon PLX4032 treatment that is conveyed by a STAT5 inhibition and a transcriptional regulation of the nicotinamide phosphoribosyltransferase (NAMPT) gene. NAMPT inhibition decreases melanoma cell proliferation both in vitro and in vivo, while forced NAMPT expression renders melanoma cells resistant to PLX4032. NAMPT expression induces transcriptomic and epigenetic reshufflings that steer melanoma cells toward an invasive phenotype associated with resistance to targeted therapies and immunotherapies. Therefore, NAMPT, the key enzyme in the NAD salvage pathway, appears as a rational target in targeted therapy-resistant melanoma cells and a key player in phenotypic plasticity of melanoma cells.
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http://dx.doi.org/10.1101/gad.305854.117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5900716PMC
March 2018

Uncovering and deciphering the pro-invasive role of HACE1 in melanoma cells.

Cell Death Differ 2018 11 7;25(11):2010-2022. Epub 2018 Mar 7.

Biology and pathologies of melanocytes, Team 1, Inserm U1065, Equipe labellisée ARC 2015, C3M, Université Nice Côte d'Azur, Nice, France.

HACE1 is an E3 ubiquitin ligase described as a tumour suppressor because HACE1-knockout mice develop multi-organ, late-onset cancers and because HACE1 expression is lost in several neoplasms, such as Wilms' tumours and colorectal cancer. However, a search of public databases indicated that HACE1 expression is maintained in melanomas. We demonstrated that HACE1 promoted melanoma cell migration and adhesion in vitro and was required for mouse lung colonisation by melanoma cells in vivo. Transcriptomic analysis of HACE1-depleted melanoma cells revealed an inhibition of ITGAV and ITGB1 as well changes in other genes involved in cell migration. We revealed that HACE1 promoted the K27 ubiquitination of fibronectin and regulated its secretion. Secreted fibronectin regulated ITGAV and ITGB1 expression, as well as melanoma cell adhesion and migration. Our findings disclose a novel molecular cascade involved in the regulation of fibronectin secretion, integrin expression and melanoma cell adhesion. By controlling this cascade, HACE1 displays pro-tumoural properties and is an important regulator of melanoma cell invasive properties.
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http://dx.doi.org/10.1038/s41418-018-0090-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219503PMC
November 2018

Deregulated MITF sumoylation: A route to melanoma.

Mol Cell Oncol 2017 26;4(4):e1331154. Epub 2017 May 26.

INSERM, U1065 (Équipe 1), Equipe Labélisée ARC 2016, C3M, Nice, France; Université Côte d'Azur, Inserm, C3M, Nice, France.

Metastatic melanoma is a deadly form of skin cancer. Extraordinary breakthroughs have been recently achieved in the treatment of the disease, leading to objective increase in patient survival. However, early detection of potential dangerous melanocytic lesions remains the best strategy to avoid metastatic dissemination, which is still the main cause of death in melanoma patients. In 2011, our team identified a germline mutation in microphthalmia-associated transcription factor ( ) that predisposes carriers to melanoma. Recently, we demonstrated that this mutation interfered with oncogene-induced senescence, one of the first events that should be overcome to allow melanoma development. Therefore, our works provide important clues on the early steps of melanomagenesis and as such might be useful for prevention or early therapeutic interventions in at risk-patients.
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http://dx.doi.org/10.1080/23723556.2017.1331154DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5540212PMC
May 2017

Focus on cutaneous and uveal melanoma specificities.

Genes Dev 2017 04;31(8):724-743

U1065, Institut National de la Santé et de la Recherche Médicale Centre Méditerranéen de Médecine Moléculaire, Université Côte d'Azur, 06200 Nice, France.

Cutaneous melanoma (CM) and uveal melanoma (UM) derive from cutaneous and uveal melanocytes that share the same embryonic origin and display the same cellular function. However, the etiopathogenesis and biological behaviors of these melanomas are very different. CM and UM display distinct landscapes of genetic alterations and show different metastatic routes and tropisms. Hence, therapeutic improvements achieved in the last few years for the treatment of CM have failed to ameliorate the clinical outcomes of patients with UM. The scope of this review is to discuss the differences in tumorigenic processes (etiologic factors and genetic alterations) and tumor biology (gene expression and signaling pathways) between CM and UM. We develop hypotheses to explain these differences, which might provide important clues for research avenues and the identification of actionable vulnerabilities suitable for the development of new therapeutic strategies for metastatic UM.
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http://dx.doi.org/10.1101/gad.296962.117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5435887PMC
April 2017

Deciphering the Role of Oncogenic MITFE318K in Senescence Delay and Melanoma Progression.

J Natl Cancer Inst 2017 08;109(8)

INSERM, U1065 (équipe 1), Equipe labélisée ARC 2016, C3M, Nice, France.

Background: MITF encodes an oncogenic lineage-specific transcription factor in which a germline mutation ( MITFE318K ) was identified in human patients predisposed to both nevus formation and, among other tumor types, melanoma. The molecular mechanisms underlying the oncogenic activity of MITF E318K remained uncharacterized.

Methods: Here, we compared the SUMOylation status of endogenous MITF by proximity ligation assay in melanocytes isolated from wild-type (n = 3) or E318K (n = 4) MITF donors. We also used a newly generated Mitf E318K knock-in (KI) mouse model to assess the role of Mitf E318K (n = 7 to 13 mice per group) in tumor development in vivo and performed transcriptomic analysis of the tumors to identify the molecular mechanisms. Finally, using immortalized or normal melanocytes (wild-type or E318K MITF, n = 2 per group), we assessed the role of MITF E318K on the induction of senescence mediated by BRAF V600E . All statistical tests were two-sided.

Results: We demonstrated a decrease in endogenous MITF SUMOylation in melanocytes from MITF E318K patients (mean of cells with hypoSUMOylated MITF, MITF E318K vs MITF WT , 94% vs 44%, difference = 50%, 95% CI = 21.8% to 67.2%, P  = .004). The Mitf E318K mice were slightly hypopigmented (mean melanin content Mitf WT vs Mitf E318K/+ , 0.54 arbitrary units [AU] vs 0.36 AU, difference = -0.18, 95% CI = -0.36 to -0.007, P  = .04). We provided genetic evidence that Mitf E318K enhances BRaf V600E -induced nevus formation in vivo (mean nevus number for Mitf E318K , BRaf V600E vs Mitf WT , BRaf V600E , 68 vs 44, difference = 24, 95% CI = 9.1 to 38.9, P  = .006). Importantly, although Mitf E318K was not sufficient to cooperate with BRaf V600E alone in promoting metastatic melanoma, it accelerated tumor formation on a BRaf V600E , Pten-deficient background (median survival, Mitf E318K/+  = 42 days, 95% CI = 31 to 46 vs Mitf WT  = 51 days, 95% CI = 50 to 55, P  < .001). Transcriptome analysis suggested a decrease in senescence in tumors from Mitf E318K mice. We confirmed this hypothesis by in vitro experiments, demonstrating that Mitf E318K impaired the ability of human melanocytes to undergo BRAF V600E -induced senescence.

Conclusions: We characterized the functions of melanoma-associated MITF E318K mutations. Our results demonstrate that MITF E318K reduces the program of senescence to potentially favor melanoma progression in vivo.
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http://dx.doi.org/10.1093/jnci/djw340DOI Listing
August 2017

FANCD2 functions as a critical factor downstream of MiTF to maintain the proliferation and survival of melanoma cells.

Sci Rep 2016 11 9;6:36539. Epub 2016 Nov 9.

Equipe Labellisée "ARC", C3M, Nice, F-06204, France.

Proteins involved in genetic stability maintenance and safeguarding DNA replication act not only against cancer initiation but could also play a major role in sustaining cancer progression. Here, we report that the FANC pathway is highly expressed in metastatic melanoma harboring the oncogenic microphthalmia-associated transcription factor (MiTF). We show that MiTF downregulation in melanoma cells lowers the expression of several FANC genes and proteins. Moreover, we observe that, similarly to the consequence of MiTF downregulation, FANC pathway silencing alters proliferation, migration and senescence of human melanoma cells. We demonstrate that the FANC pathway acts downstream MiTF and establish the existence of an epistatic relationship between MiTF and the FANC pathway. Our findings point to a central role of the FANC pathway in cellular and chromosomal resistance to both DNA damage and targeted therapies in melanoma cells. Thus, the FANC pathway is a promising new therapeutic target in melanoma treatment.
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http://dx.doi.org/10.1038/srep36539DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5101529PMC
November 2016

ZEB1-mediated melanoma cell plasticity enhances resistance to MAPK inhibitors.

EMBO Mol Med 2016 10 4;8(10):1143-1161. Epub 2016 Oct 4.

Cancer Research Center of Lyon, INSERM U1052, Lyon, France Cancer Research Center of Lyon, CNRS UMR 5286, Lyon, France Université de Lyon, Lyon, France ISPB Université Lyon 1, Lyon, France Centre Léon Bérard, Lyon, France

Targeted therapies with MAPK inhibitors (MAPKi) are faced with severe problems of resistance in BRAF-mutant melanoma. In parallel to the acquisition of genetic mutations, melanoma cells may also adapt to the drugs through phenotype switching. The ZEB1 transcription factor, a known inducer of EMT and invasiveness, is now considered as a genuine oncogenic factor required for tumor initiation, cancer cell plasticity, and drug resistance in carcinomas. Here, we show that high levels of ZEB1 expression are associated with inherent resistance to MAPKi in BRAF-mutated cell lines and tumors. ZEB1 levels are also elevated in melanoma cells with acquired resistance and in biopsies from patients relapsing while under treatment. ZEB1 overexpression is sufficient to drive the emergence of resistance to MAPKi by promoting a reversible transition toward a MITF/p75 stem-like and tumorigenic phenotype. ZEB1 inhibition promotes cell differentiation, prevents tumorigenic growth in vivo, sensitizes naive melanoma cells to MAPKi, and induces cell death in resistant cells. Overall, our results demonstrate that ZEB1 is a major driver of melanoma cell plasticity, driving drug adaptation and phenotypic resistance to MAPKi.
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http://dx.doi.org/10.15252/emmm.201505971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5048365PMC
October 2016

Compounds Triggering ER Stress Exert Anti-Melanoma Effects and Overcome BRAF Inhibitor Resistance.

Cancer Cell 2016 06 26;29(6):805-819. Epub 2016 May 26.

INSERM, U1065, Equipe Biologie et Pathologie des cellules mélanocytaire: de la pigmentation cutanée au mélanome, Centre Méditerranéen de Médecine Moléculaire (C3M), Bâtiment ARCHIMED, 151 route de Saint Antoine de Ginestière, 06204 Nice cedex 3, France; UFR de Médecine, Université de Nice Sophia Antipolis, 06000 Nice, France; Service de Dermatologie, Hôpital Archet II, CHU, 06204 Nice, France. Electronic address:

We have discovered and developed a series of molecules (thiazole benzenesulfonamides). HA15, the lead compound of this series, displayed anti-cancerous activity on all melanoma cells tested, including cells isolated from patients and cells that developed resistance to BRAF inhibitors. Our molecule displayed activity against other liquid and solid tumors. HA15 also exhibited strong efficacy in xenograft mouse models with melanoma cells either sensitive or resistant to BRAF inhibitors. Transcriptomic, proteomic, and biochemical studies identified the chaperone BiP/GRP78/HSPA5 as the specific target of HA15 and demonstrated that the interaction increases ER stress, leading to melanoma cell death by concomitant induction of autophagic and apoptotic mechanisms.
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http://dx.doi.org/10.1016/j.ccell.2016.04.013DOI Listing
June 2016