GLI2-Mediated Melanoma Invasion and Metastasis

Background The transforming growth factor-β (TGF-β) pathway, which has both tumor suppressor and pro-oncogenic activities, is often constitutively active in melanoma and is a marker of poor prognosis. Recently, we identified GLI2, a mediator of the hedgehog pathway, as a transcriptional target of TGF-β signaling. Methods We used real-time reverse transcription-polymerase chain reaction (RT-PCR) and western blotting to determine GLI2 expression in human melanoma cell lines and subsequently classified them as GLI2high or as GLI2low according to their relative GLI2 mRNA and protein expression levels. GLI2 expression was reduced in a GLI2high cell line with lentiviral expression of short hairpin RNA targeting GLI2. We assessed the role of GLI2 in melanoma cell invasiveness in Matrigel assays. We measured secretion of matrix metalloproteinase (MMP)-2 and MMP-9 by gelatin zymography and expression of E-cadherin by western blotting and RT-PCR. The role of GLI2 in development of bone metastases was determined following intracardiac injection of melanoma cells in immunocompromised mice (n = 5-13). Human melanoma samples (n = 79) at various stages of disease progression were analyzed for GLI2 and E-cadherin expression by immunohistochemistry, in situ hybridization, or RT-PCR. All statistical tests were two-sided. Results Among melanoma cell lines, increased GLI2 expression was associated with loss of E-cadherin expression and with increased capacity to invade Matrigel and to form bone metastases in mice (mean osteolytic tumor area: GLI2high vs GLI2low, 2.81 vs 0.93 mm2, difference = 1.88 mm2, 95% confidence interval [CI] = 1.16 to 2.60, P < .001). Reduction of GLI2 expression in melanoma cells that had expressed high levels of GLI2 substantially inhibited both basal and TGF-β-induced cell migration, invasion (mean number of Matrigel invading cells: shGLI2 vs shCtrl (control), 52.6 vs 100, difference = 47.4, 95% CI = 37.0 to 57.8, P = .024; for shGLI2 + TGF-β vs shCtrl + TGF-β, 31.0 vs 161.9, difference = −130.9, 95% CI = −96.2 to −165.5, P = .002), and MMP secretion in vitro and the development of experimental bone metastases in mice. Within human melanoma lesions, GLI2 expression was heterogeneous, associated with tumor regions in which E-cadherin was lost and increased in the most aggressive tumors. Conclusion GLI2 was directly involved in driving melanoma invasion and metastasis in this preclinical stud

Rôle de la E-cadhérine et de béta-caténine dans le développement normal et pathologique du lignage mélanocytaire

Les mélanocytes synthétisent la mélanine, et la distribuent aux kératinocytes environnants avec qui ils forment l'unité épidermique de mélanisation. Les deux types cellulaires adhèrent par l'intermédiaire notamment des jonctions adhérentes. Celles-ci sont composées de la E-cadhérine et de b-caténine. Au cours de ma thèse, nous avons montré que l'absence de E-cadhérine dans les mélanocytes in vivo provoque un défaut de prolifération et de la morphologie des cellules affectant l'organisation de l'unité épidermique de mélanisation et donc de la pigmentation épidermique. La E-cadhérine est également connue comme gène suppresseur de tumeurs. Nous avons montré, au sein d'un modèle in vivo favorisant la transformation mélanocytaire, que l'absence de E-cadhérine peut augmenter le caractère agressif du mélanome. Dans le lignage mélanocytaire, b-caténine intervient également dans la voie de signalisation Wnt et régule la transcription de gènes cibles. L'élaboration de modèle gain- et perte-de-fonction de b-caténine dans les mélanocytes, a mis en évidence un défaut de prolifération des mélanocytes. La quantité de b-caténine apparaît essentielle pour la prolifération mélanocytaire, dont l'action s'effectue via Mitf-M. Mitf-M agit directement sur la prolifération ou indirectement en inhibant l'activité transcriptionnelle de b-caténine sur ses cibles, notamment c-myc et cycline-D1. Enfin, b-caténine contribue à l'immortalisation lors de la transformation des mélanocytes in vivo. La forme stabilisée de b-caténine inhibe l'expression de la protéine p16Ink4a. L'activation de b-caténine permet donc de court-circuiter le processus de sénescence lors de la progression tumorale des mélanomes.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Melanoblast proliferation dynamics during mouse embryonic development: Modeling and validation

International audienceIn this paper, we are looking for mathematical modeling of mouse embryonic melanoblast proliferation dynamics, taking into account, the expression level of β-catenin. This protein plays an important role into the whole signal pathway process. Different assumptions on some unobservable features lead to different candidate models. From real data measured, from biological experiments and from a priori biological knowledge, it was able to validate or invalidate some of the candidate models. Data assimilation and parameter identification allowed us to derive a mathematical model that is in very good agreement with biological data. As a result, the produced model can give tracks for biologists into their biological investigations and experimental evidence. Another interest is the use of this model for robust hidden parameter identification like double times or number of founder melanoblasts

αMSH and Cyclic AMP Elevating Agents Control Melanosome pH through a Protein Kinase A-independent Mechanism

Melanins are synthesized in melanocytes within specialized organelles called melanosomes. Numerous studies have shown that the pH of melanosome plays a key role in the regulation of melanin synthesis. However, until now, acute regulation of melanosome pH by a physiological stimulus has never been demonstrated. In the present study, we show that the activation of the cAMP pathway by αMSH or forskolin leads to an alkalinization of melanosomes and a concomitant regulation of vacuolar ATPases and ion transporters of the solute carrier family. The solute carrier family members include SLC45A2, which is mutated in oculocutaneous albinism type IV, SLC24A4 and SLC24A5, proteins implicated in the control of eye, hair, and skin pigmentation, and the P protein, encoded by the oculocutaneous albinism type II locus. Interestingly, H89, a pharmacological inhibitor of protein kinase A (PKA), prevents the cAMP-induced pigmentation and induces acidification of melanosomes. The drastic depigmenting effect of H89 is not due to an inhibition of tyrosinase expression. Indeed, H89 blocks the induction of melanogenesis induced by LY294002, a potent inhibitor of the PI 3-kinase pathway, without any effect on tyrosinase expression. Furthermore, PKA is not involved in the inhibition of pigmentation promoted by H89 because LY294002 induces pigmentation independently of PKA. Also, other PKA inhibitors do not affect pigmentation. Taken together, our results strengthen the support for a key role of melanosome pH in the regulation of melanin synthesis and, for the first time, demonstrate that melanosome pH is regulated by cAMP and αMSH. Notably, these are both mediators of the response to solar UV radiation, the main physiological stimulus of skin pigmentation

Regulation of Melanoma Progression through the TCF4/miR-125b/NEDD9 Cascade

Melanoma progression from a primary lesion to a distant metastasis is a complex process associated with genetic alterations, epigenetic modifications, and phenotypic switches. Elucidation of these phenomena may indicate how to interfere with this fatal disease. The role of microRNAs as key negative regulators of gene expression, controlling all cellular processes including cell migration and invasion, is now being recognized. Here, we used in silico analysis of microRNA expression profiles of primary and metastatic melanomas and functional experiments to show that microRNA-125b (miR-125b) is a determinant candidate of melanoma progression: (i) miR-125b is more strongly expressed in aggressive metastatic than primary melanomas, (ii) there is an inverse correlation between the amount of miR-125b and overall patient survival, (iii) invasion/migration potentials in vitro are inversely correlated with the amount of miR-125b in a series of human melanoma cell lines, and (iv) inhibition of miR-125b reduces migratory and invasive potentials without affecting cell proliferation in vitro. Furthermore, we show that neural precursor cell expressed developmentally down-regulated protein 9 (i.e., NEDD9) is a direct target of miR-125b and is involved in modulating melanoma cell migration and invasion. Also, transcription factor 4, associated with epithelial-mesenchymal transition and invasion, induces the transcription of miR-125b-1. In conclusion, the transcription factor 4/miR-125b/NEDD9 cascade promotes melanoma cell migration/invasion.publisher: Elsevier articletitle: Regulation of Melanoma Progression through the TCF4/miR-125b/NEDD9 Cascade journaltitle: Journal of Investigative Dermatology articlelink: http://dx.doi.org/10.1016/j.jid.2016.02.803 content_type: article copyright: © 2016 The Authors. Published by Elsevier, Inc. on behalf of the Society for Investigative Dermatology.status: publishe

Stable overexpression of Smad7 in human melanoma cells impairs bone metastasis.

Melanoma has a propensity to metastasize to bone, where it is exposed to high concentrations of transforming growth factor-beta (TGF-beta). Because TGF-beta promotes bone metastases from other solid tumors, such as breast cancer, we tested the role of TGF-beta in melanoma metastases to bone. 1205Lu melanoma cells, stably transfected to overexpress the natural TGF-beta/Smad signaling inhibitor Smad7, were studied in an experimental model of bone metastasis whereby tumor cells are inoculated into the left cardiac ventricle of nude mice. All mice bearing parental and mock-transfected 1205Lu cells developed osteolytic bone metastases 5 weeks post-tumor inoculation. Mice bearing 1205Lu-Smad7 tumors had significantly less osteolysis on radiographs and longer survival compared with parental and mock-transfected 1205Lu mice. To determine if the reduced bone metastases observed in mice bearing 1205Lu-Smad7 clones was due to reduced expression of TGF-beta target genes known to enhance metastases to bone from breast cancer cells, we analyzed gene expression of osteolytic factors, parathyroid hormone-related protein (PTHrP) and interleukin-11 (IL-11), the chemotactic receptor CXCR4, and osteopontin in 1205Lu cells. Quantitative reverse transcription-PCR analysis indicated that PTHrP, IL-11, CXCR4, and osteopontin mRNA steady-state levels were robustly increased in response to TGF-beta and that Smad7 and the TbetaRI small-molecule inhibitor, SB431542, prevented such induction. In addition, 1205Lu-Smad7 bone metastases expressed significantly lower levels of IL-11, connective tissue growth factor, and PTHrP. These data suggest that TGF-beta promotes osteolytic bone metastases due to melanoma by stimulating the expression of prometastatic factors via the Smad pathway. Blockade of TGF-beta signaling may be an effective treatment for melanoma metastasis to bone

TET2-dependent hydroxymethylome plasticity reduces melanoma initiation and progression

Although numerous epigenetic aberrancies accumulate in melanoma, their contribution to initiation and progression remain unclear. The epigenetic mark 5-hydroxymethylcyto-sine (5hmC), generated through TET-mediated DNA modification, is now referred to as the sixth base of DNA and has recently been reported as a potential biomarker for multiple types of cancer. Loss of 5hmC is an epigenetic hallmark of melanoma, but whether a decrease in 5hmc levels contributes directly to pathogenesis or whether it merely results from disease progression-associated epigenetic remodeling remains to be established. Here, we show that NRAS-driven melanomagenesis in mice is accompanied by an overall decrease in 5hmC and specific 5hmC gains in selected gene bodies. Strikingly, genetic ablation of Tet2 in mice cooperated with oncogenic NRASQ61K to promote melanoma initiation while suppressing specific gains in 5hmC. We conclude that TET2 acts as a barrier to melanoma initiation and progression, partly by promoting 5hmC gains in specific gene bodies. Significance: This work emphasizes the importance of epigenome plasticity in cancer development and highlights the involvement of druggable epigenetic factors in cancer.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

β-Catenin induces immortalization of melanocytes by suppressing p16INK4a expression and cooperates with N-Ras in melanoma development

Tumor progression is a multistep process in which proproliferation mutations must be accompanied by suppression of senescence. In melanoma, proproliferative signals are provided by activating mutations in NRAS and BRAF, whereas senescence is bypassed by inactivation of the p16Ink4a gene. Melanomas also frequently exhibit constitutive activation of the Wnt/β-catenin pathway that is presumed to induce proliferation, as it does in carcinomas. We show here that, contrary to expectations, stabilized β-catenin reduces the number of melanoblasts in vivo and immortalizes primary skin melanocytes by silencing the p16Ink4a promoter. Significantly, in a novel mouse model for melanoma, stabilized β-catenin bypasses the requirement for p16Ink4a mutations and, together with an activated N-Ras oncogene, leads to melanoma with high penetrance and short latency. The results reveal that synergy between the Wnt and mitogen-activated protein (MAP) kinase pathways may represent an important mechanism underpinning the genesis of melanoma, a highly aggressive and increasingly common disease

Decoding the regulatory landscape of melanoma reveals TEADS as regulators of the invasive cell state

Transcriptional reprogramming of proliferative melanoma cells into a phenotypically distinct invasive cell subpopulation is a critical event at the origin of metastatic spreading. Here we generate transcriptome, open chromatin and histone modification maps of melanoma cultures; and integrate this data with existing transcriptome and DNA methylation profiles from tumour biopsies to gain insight into the mechanisms underlying this key reprogramming event. This shows thousands of genomic regulatory regions underlying the proliferative and invasive states, identifying SOX10/MITF and AP-1/TEAD as regulators, respectively. Knockdown of TEADs shows a previously unrecognized role in the invasive gene network and establishes a causative link between these transcription factors, cell invasion and sensitivity to MAPK inhibitors. Using regulatory landscapes and in silico analysis, we show that transcriptional reprogramming underlies the distinct cellular states present in melanoma. Furthermore, it reveals an essential role for the TEADs, linking it to clinically relevant mechanisms such as invasion and resistance.SCOPUS: ar.jinfo:eu-repo/semantics/publishe