Melanocyte transformation associated with substrate adhesion impediment

Genome-wide promoter methylation profiling in a cellular model of melanoma progression reveals markers of malignancy and metastasis that predict melanoma survival

The epigenetic changes associated with melanoma progression to advanced and metastatic stages are still poorly understood. To shed light on the CpG methylation dynamics during melanoma development, we analyzed the methylome profiles of a four-stage cell line model of melanoma progression: non-tumorigenic melanocytes (melan-a), premalignant melanocytes (4C), non-metastatic melanoma cells (4C11−), and metastatic melanoma cells (4C11+). We identified 540 hypo- and 37 hypermethylated gene promoters that together characterized a malignancy signature, and 646 hypo- and 520 hypermethylated promoters that distinguished a metastasis signature. Differentially methylated genes from these signatures were correlated with overall survival using TCGA-SKCM methylation data. Moreover, multivariate Cox analyses with LASSO regularization identified panels of 33 and 31 CpGs, respectively, from the malignancy and metastasis signatures that predicted poor survival. We found a concordant relationship between DNA methylation and transcriptional levels for genes from the malignancy (Pyroxd2 and Ptgfrn) and metastasis (Arnt2, Igfbp4 and Ptprf) signatures, which were both also correlated with melanoma prognosis. Altogether, this study reveals novel CpGs methylation markers associated with malignancy and metastasis that collectively could improve the survival prediction of melanoma patients.

Genes regulated by DNA methylation are involved in distinct phenotypes during melanoma progression and are prognostic factors for patients

In addition to mutations, epigenetic alterations are important contributors to malignant transformation and tumor progression. The aim of this work was to identify epigenetic events in which promoter or gene body DNA methylation induces gene expression changes that drive melanocyte malignant transformation and metastasis. We previously developed a linear mouse model of melanoma progression consisting of spontaneously immortalized melanocytes, premalignant melanocytes, a nonmetastatic tumorigenic, and a metastatic cell line. Here, through the integrative analysis of methylome and transcriptome data, we identified the relationship between promoter and/or gene body DNA methylation alterations and gene expression in early, intermediate, and late stages of melanoma progression. We identified adenylate cyclase type 3 (Adcy3) and inositol polyphosphate 4-phosphatase type II (Inpp4b), which affect tumor growth and metastatic potential, respectively. Importantly, the gene expression and DNA methylation profiles found in this murine model of melanoma progression were correlated with available clinical data from large population-based primary melanoma cohorts, revealing potential prognostic markers.

Cellular Model of Malignant Transformation of Primary Human Astrocytes Induced by Deadhesion/Readhesion Cycles

Astrocytoma is the most common and aggressive tumor of the central nervous system. Genetic and environmental factors, bacterial infection, and several other factors are known to be involved in gliomagenesis, although the complete underlying molecular mechanism is not fully understood. Tumorigenesis is a multistep process involving initiation, promotion, and progression. We present a human model of malignant astrocyte transformation established by subjecting primary astrocytes from healthy adults to four sequential cycles of forced anchorage impediment (deadhesion). After limiting dilution of the surviving cells obtained after the fourth deadhesion/readhesion cycle, three clones were randomly selected, and exhibited malignant characteristics, including increased proliferation rate and capacity for colony formation, migration, and anchorage-independent growth in soft agar. Functional assay results for these clonal cells, including response to temozolomide, were comparable to U87MG—a human glioblastoma-derived cell lineage—reinforcing malignant cell transformation. RNA-Seq analysis by next-generation sequencing of the transformed clones relative to the primary astrocytes revealed upregulation of genes involved in the PI3K/AKT and Wnt/β-catenin signaling pathways, in addition to upregulation of genes related to epithelial–mesenchymal transition, and downregulation of genes related to aerobic respiration. These findings, at a molecular level, corroborate the change in cell behavior towards mesenchymal-like cell dedifferentiation. This linear progressive model of malignant human astrocyte transformation is unique in that neither genetic manipulation nor treatment with carcinogens are used, representing a promising tool for testing combined therapeutic strategies for glioblastoma patients, and furthering knowledge of astrocytoma transformation and progression.

Acetylation-dependent regulation of BRAF oncogenic function

Aberrant BRAF activation, including the BRAF^V600E mutation, is frequently observed in human cancers. However, it remains largely elusive whether other types of post-translational modification(s) in addition to phosphorylation and ubiquitination-dependent regulation also modulate BRAF kinase activity. Here, we report that the acetyltransferase p300 activates the BRAF kinase by promoting BRAF K601 acetylation, a process that is antagonized by the deacetylase SIRT1. Notably, K601 acetylation facilitates BRAF dimerization with RAF proteins and KSR1. Furthermore, K601 acetylation promotes melanoma cell proliferation and contributes to BRAF^V600E inhibitor resistance in BRAF^V600E harboring melanoma cells. As such, melanoma patient-derived K601E oncogenic mutation mimics K601 acetylation to augment BRAF kinase activity. Our findings, therefore, uncover a layer of BRAF regulation and suggest p300 hyperactivation or SIRT1 deficiency as potential biomarkers to determine ERK activation in melanomas.

In tumor cells, hyperactivation of the BRAF protein kinase propels uncontrolled cell proliferation. BRAF hyperactivation is also achieved through several post-translational mechanisms. Dai et al. present an acetylation-dependent regulation of BRAF kinase function in melanoma cells, which serves to enhance BRAF oncogenic function and contributes to BRAF inhibitor resistance.

Metastatic Melanoma Progression Is Associated with Endothelial Nitric Oxide Synthase Uncoupling Induced by Loss of eNOS:BH4 Stoichiometry

Melanoma is the most aggressive type of skin cancer due to its high capability of developing metastasis and acquiring chemoresistance. Altered redox homeostasis induced by increased reactive oxygen species is associated with melanomagenesis through modulation of redox signaling pathways. Dysfunctional endothelial nitric oxide synthase (eNOS) produces superoxide anion (O2-•) and contributes to the establishment of a pro-oxidant environment in melanoma. Although decreased tetrahydrobiopterin (BH4) bioavailability is associated with eNOS uncoupling in endothelial and human melanoma cells, in the present work we show that eNOS uncoupling in metastatic melanoma cells expressing the genes from de novo biopterin synthesis pathway Gch1, Pts, and Spr, and high BH4 concentration and BH4:BH2 ratio. Western blot analysis showed increased expression of Nos3, altering the stoichiometry balance between eNOS and BH4, contributing to NOS uncoupling. Both treatment with L-sepiapterin and eNOS downregulation induced increased nitric oxide (NO) and decreased O2• levels, triggering NOS coupling and reducing cell growth and resistance to anoikis and dacarbazine chemotherapy. Moreover, restoration of eNOS activity impaired tumor growth in vivo. Finally, NOS3 expression was found to be increased in human metastatic melanoma samples compared with the primary site. eNOS dysfunction may be an important mechanism supporting metastatic melanoma growth and hence a potential target for therapy.

miR-138-5p induces aggressive traits by targeting Trp53 expression in murine melanoma cells, and correlates with poor prognosis of melanoma patients

Deregulation of miRNAs contributes to the development of distinct cancer types, including melanoma, an aggressive form of skin cancer characterized by high metastatic potential and poor prognosis. The expression of a set of 580 miRNAs was investigated in a model of murine melanoma progression, comprising non-metastatic (4C11-) and metastatic melanoma (4C11+) cells. A significant increase in miR-138-5p expression was found in the metastatic 4C11+ melanoma cells compared to 4C11-, which prompted us to investigate its role in melanoma aggressiveness. Functional assays, including anoikis resistance, colony formation, collective migration, serum-deprived growth capacity, as well as in vivo tumor growth and experimental metastasis were performed in 4C11- cells stably overexpressing miR-138-5p. miR-138-5p induced an aggressive phenotype in mouse melanoma cell lines leading to increased proliferation, migration and cell viability under stress conditions. Moreover, by overexpressing miR-138-5p, low-growing and non-metastatic 4C11- cells became highly proliferative and metastatic in vivo, similar to the metastatic 4C11+ cells. Luciferase reporter analysis identified the tumor suppressor Trp53 as a direct target of miR-138-5p. Using data sets from independent melanoma cohorts, miR-138-5p and P53 expression were also found deregulated in human melanoma samples, with their levels negatively and positively correlated with prognosis, respectively. Our data shows that the overexpression of miR-138-5p contributes to melanoma metastasis through the direct suppression of Trp53.

Transcriptional signatures underlying dynamic phenotypic switching and novel disease biomarkers in a linear cellular model of melanoma progression

Despite advances in therapeutics, the progression of melanoma to metastasis still confers a poor outcome to patients. Nevertheless, there is a scarcity of biological models to understand cellular and molecular changes taking place along disease progression. Here, we characterized the transcriptome profiles of a multi-stage murine model of melanoma progression comprising a nontumorigenic melanocyte lineage (melan-a), premalignant melanocytes (4C), nonmetastatic (4C11-) and metastasis-prone (4C11+) melanoma cells. Clustering analyses have grouped the 4 cell lines according to their differentiated (melan-a and 4C11+) or undifferentiated/"mesenchymal-like" (4C and 4C11-) morphologies, suggesting dynamic gene expression patterns associated with the transition between these phenotypes. The cell plasticity observed in the murine melanoma progression model was corroborated by molecular markers described during stepwise human melanoma differentiation, as the differentiated cell lines in our model exhibit upregulation of transitory and melanocytic markers, whereas "mesenchymal-like" cells show increased expression of undifferentiated and neural crest-like markers. Sets of differentially expressed genes (DEGs) were detected at each transition step of tumor progression, and transcriptional signatures related to malignancy, metastasis and epithelial-to-mesenchymal transition were identified. Finally, DEGs were mapped to their human orthologs and evaluated in uni- and multivariate survival analyses using gene expression and clinical data of 703 drug-naïve primary melanoma patients, revealing several independent candidate prognostic markers. Altogether, these results provide novel insights into the molecular mechanisms underlying the phenotypic switch taking place during melanoma progression, reveal potential drug targets and prognostic biomarkers, and corroborate the translational relevance of this unique sequential model of melanoma progression.

Community-based network analyses reveal emerging connectivity patterns of protein-protein interactions in murine melanoma secretome

Protein-protein interaction networks (PPINs) are static representations of protein connections in which topological features such as subgraphs (communities) may contain proteins functionally related, revealing an additional layer of interactome complexity. We created two PPINs from the secretomes of a paired set of murine melanocytes (a normal melanocyte and its transformed phenotype). Community structures, identified by a graph clustering algorithm, resulted in the identification of subgraphs in both networks. Interestingly, the underlying structure of such communities revealed shared and exclusive proteins (core and exclusive nodes, respectively), in addition to proteins that changed their location within each community (rewired nodes). Functional enrichment analysis of core nodes revealed conserved biological functions in both networks whereas exclusive and rewired nodes in the tumoral phenotype network were enriched in cancer-related processes, including TGFβ signaling. We found a remarkable shift in the tumoral interactome, resulting in an emerging pattern which was driven by the presence of exclusive nodes and may represent functional network motifs. Our findings suggest that the rearrangement in the tumoral interactome may be correlated with the malignant transformation of melanocytes associated with substrate adhesion impediment. The interactions found in core and new/rewired nodes might potentially be targeted for therapeutic intervention in melanoma treatment. SIGNIFICANCE: Malignant transformation is a result of synergistic action of multiple molecular factors in which genetic alterations as well as protein expression play paramount roles. During oncogenesis, cellular crosstalk through the secretion of soluble mediators modulates the phenotype of transformed cells which ultimately enables them to successfully disrupt important signaling pathways, including those related to cell growth and proliferation. Therefore, in this work we profiled the secretomes of a paired set of normal and transformed phenotypes of a murine melanocyte. After assembling the two interactomes, clusters of functionally related proteins (network communities) were observed as well as emerging patterns of network rewiring which may represent an interactome signature of transformed cells. In summary, the significance of this study relies on the understanding of the repertoire of 'normal' and 'tumoral' secretomes and, more importantly, the set of interacting proteins (the interactome) in both of these conditions, which may reveal key components that might be potentially targeted for therapeutic intervention.

Gene co-expression and histone modification signatures are associated with melanoma progression, epithelial-to-mesenchymal transition, and metastasis

BACKGROUND

We have previously developed a murine cellular system that models the transformation from melanocytes to metastatic melanoma cells. This model was established by cycles of anchorage impediment of melanocytes and consists of four cell lines: differentiated melanocytes (melan-a), pre-malignant melanocytes (4C), malignant (4C11-), and metastasis-prone (4C11+) melanoma cells. Here, we searched for transcriptional and epigenetic signatures associated with melanoma progression and metastasis by performing a gene co-expression analysis of transcriptome data and a mass-spectrometry-based profiling of histone modifications in this model.

RESULTS

Eighteen modules of co-expressed genes were identified, and some of them were associated with melanoma progression, epithelial-to-mesenchymal transition (EMT), and metastasis. The genes in these modules participate in biological processes like focal adhesion, cell migration, extracellular matrix organization, endocytosis, cell cycle, DNA repair, protein ubiquitination, and autophagy. Modules and hub signatures related to EMT and metastasis (turquoise, green yellow, and yellow) were significantly enriched in genes associated to patient survival in two independent melanoma cohorts (TCGA and Leeds), suggesting they could be sources of novel prognostic biomarkers. Clusters of histone modifications were also linked to melanoma progression, EMT, and metastasis. Reduced levels of H4K5ac and H4K8ac marks were seen in the pre-malignant and tumorigenic cell lines, whereas the methylation patterns of H3K4, H3K56, and H4K20 were related to EMT. Moreover, the metastatic 4C11+ cell line showed higher H3K9me2 and H3K36me3 methylation, lower H3K18me1, H3K23me1, H3K79me2, and H3K36me2 marks and, in agreement, downregulation of the H3K36me2 methyltransferase Nsd1.

CONCLUSIONS

We uncovered transcriptional and histone modification signatures that may be molecular events driving melanoma progression and metastasis, which can aid in the identification of novel prognostic genes and drug targets for treating the disease.

Isothermal Microcalorimetry of Tumor Cells: Enhanced Thermogenesis by Metastatic Cells

Tumor cells exhibit rewired metabolism. We carried out comparative analyses attempting to investigate whether metabolic reprograming could be measured by isothermal microcalorimetry. Intact metastatic cell lines of tongue cell carcinoma, human and murine melanoma, lung, and breast tumors consistently released more heat than non-metastatic cells or cells displaying lower metastatic potential. In tongue squamous carcinoma cells mitochondrial enriched extract reproduced the heat release pattern of intact cells. Cytochalasin D, an actin filament inhibitor, and suppression of metastasis marker Melanoma associated gene 10 (MAGEA10) decreased heat release. Uncoupling protein 2 was highly expressed in metastatic cells, but not in non-metastatic cells. Carnitine palmitoyl transferase-1 inhibitor, Etomoxir strongly inhibited heat release by metastatic cells, thus linking lipid metabolism to thermogenesis. We propose that heat release may be a quantifiable trait of the metastatic process.

Can the plasma PD-1 levels predict the presence and efficiency of tumor-infiltrating lymphocytes in patients with metastatic melanoma?

BACKGROUND

The immune response in melanoma patients is locally affected by presence of tumor-infiltrating lymphocytes (TILs), generally divided into brisk, nonbrisk, and absent. Several studies have shown that a greater presence of TILs, especially brisk, in primary melanoma is associated with a better prognosis and higher survival rate.

PATIENTS AND METHODS

We investigated by enzyme-linked immunosorbent assay (ELISA) the correlation between PD-1 levels in plasma and the presence/absence of TILs in 28 patients with metastatic melanoma.

RESULTS

Low plasma PD-1 levels were correlated with brisk TILs in primary melanoma, whereas intermediate values correlated with the nonbrisk TILs, and high PD-1 levels with absent TILs. Although the low number of samples did not allow us to obtain a statistically significant correlation between the plasma PD-1 levels and the patients' overall survival depending on the absence/presence of TILs, the median survival of patients having brisk type TILs was 5 months higher than that of patients with absent and nonbrisk TILs.

CONCLUSIONS

This work highlights the ability of measuring the plasma PD-1 levels in order to predict the prognosis of patients with untreated metastatic melanoma without a BRAF mutation at the time of diagnosis.

Nutritional shortage augments cisplatin-effects on murine melanoma cells

Melanoma incidence increases every year worldwide and is responsible for 80% of skin cancer deaths. Due to its metastatic potential and resistance to almost any treatments such as chemo, radio, immune and targeted-therapy, the patients still have a poor prognosis, especially at metastatic stage. Considering that, it is crucial to find new therapeutic approaches to overcome melanoma resistance. Here we investigated the effect of cisplatin (CDDP), one of the chemotherapeutic agents used for melanoma treatment, in association with nutritional deprivation in murine melanoma cell lines. Cell death and autophagy were evaluated after the treatment with cisplatin, nutritional deprivation and its association using an in vitro model of murine melanocytes malignant transformation to metastatic melanoma. Our results showed that nutritional deprivation augmented cell death induced by cisplatin in melanoma cells, especially at the metastatic subtype, with slight effects on melanocytes. Mechanistic studies revealed that although autophagy was present at high levels in basal conditions in melanoma cells, was not essential for cell death process that involved mitochondrial damage, reactive oxygen species production and possible glycolysis inhibition. In conclusion, nutritional shortage in combination with chemotherapeutic drugs as cisplatin can be a valuable new therapeutic strategy to overcome melanoma resistance.

Malignant transformation in melanocytes is associated with increased production of procoagulant microvesicles

Shedding of microvesicles (MVs) by cancer cells is implicated in a variety of biological effects, including the establishment of cancer-associated hypercoagulable states. However, the mechanisms underlying malignant transformation and the acquisition of procoagulant properties by tumour-derived MVs are poorly understood. Here we investigated the procoagulant and prothrombotic properties of MVs produced by a melanocyte-derived cell line (melan-a) as compared to its tumourigenic melanoma counterpart Tm1. Tumour cells exhibit a two-fold higher rate of MVs production as compared to melan-a. Melanoma MVs display greater procoagulant activity and elevated levels of the clotting initiator protein tissue factor (TF). On the other hand, tumour- and melanocyte- derived MVs expose similar levels of the procoagulant lipid phosphatidylserine, displaying identical abilities to support thrombin generation by the prothrombinase complex. By using an arterial thrombosis model, we observed that melanoma- but not melanocyte-derived MVs strongly accelerate thrombus formation in a TF-dependent manner, and accumulate at the site of vascular injury. Analysis of plasma obtained from melanoma-bearing mice showed the presence of MVs with a similar procoagulant pattern as compared to Tm1 MVs produced in vitro. Remarkably, flow-cytometric analysis demonstrated that 60% of ex vivo MVs are TF-positive and carry the melanoma-associated antigen, demonstrating its tumour origin. Altogether our data suggest that malignant transformation in melanocytes increases the production of procoagulant MVs, which may contribute for a variety of coagulation- related protumoural responses.

SIRT1 regulates Mxd1 during malignant melanoma progression

In a murine melanoma model, malignant transformation promoted by a sustained stress condition was causally related to increased levels of reactive oxygen species resulting in DNA damage and massive epigenetic alterations. Since the chromatin modifier Sirtuin-1 (SIRT1) is a protein attracted to double-stranded DNA break (DSB) sites and can recruit other components of the epigenetic machinery, we aimed to define the role of SIRT1 in melanomagenesis through our melanoma model. The DNA damage marker, γH2AX was found increased in melanocytes after 24 hours of deadhesion, accompanied by increased SIRT1 expression and decreased levels of its target, H4K16ac. Moreover, SIRT1 started to be associated to DNMT3B during the stress condition, and this complex was maintained along malignant progression. Mxd1 was identified by ChIP-seq among the DNA sequences differentially associated with SIRT1 during deadhesion and was shown to be a common target of both, SIRT1 and DNMT3B. In addition, Mxd1 was found downregulated from pre-malignant melanocytes to metastatic melanoma cells. Treatment with DNMT inhibitor 5AzaCdR reversed the Mxd1 expression. Sirt1 stable silencing increased Mxd1 mRNA expression and led to down-regulation of MYC targets, such as Cdkn1a, Bcl2 and Psen2, whose upregulation is associated with human melanoma aggressiveness and poor prognosis. We demonstrated a novel role of the stress responsive protein SIRT1 in malignant transformation of melanocytes associated with deadhesion. Mxd1 was identified as a new SIRT1 target gene. SIRT1 promoted Mxd1 silencing, which led to increased activity of MYC oncogene contributing to melanoma progression.

The role of nitric oxide in melanoma

Nitric oxide (NO) is a small gaseous signaling molecule that mediates its effects in melanoma through free radical formation and enzymatic processes. Investigations have demonstrated multiple roles for NO in melanoma pathology via immune surveillance, apoptosis, angiogenesis, melanogenesis, and on the melanoma cell itself. In general, elevated levels of NO prognosticate a poor outcome for melanoma patients. However, there are processes where the relative concentration of NO in different environments may also serve to limit melanoma proliferation. This review serves to outline the roles of NO in melanoma development and proliferation. As demonstrated by multiple in vivo murine models and observations from human tissue, NO may promote melanoma formation and proliferation through its interaction via inhibitory immune cells, inhibition of apoptosis, stimulation of pro-tumorigenic cytokines, activation of tumor associated macrophages, alteration of angiogenic processes, and stimulation of melanoma formation itself.

Timp1 Promotes Cell Survival by Activating the PDK1 Signaling Pathway in Melanoma

High TIMP1 expression is associated with poor prognosis in melanoma, where it can bind to CD63 and β1 integrin, inducing PI3-kinase pathway and cell survival. Phosphatidylinositol (3,4,5)-trisphosphate (PIP3), generated under phosphatidylinositol-3-kinase (PI3K) activation, enables the recruitment and activation of protein kinase B (PKB/AKT) and phosphoinositide-dependent kinase 1 (PDK1) at the membrane, resulting in the phosphorylation of a host of other proteins. Using a melanoma progression model, we evaluated the impact of Timp1 and AKT silencing, as well as PI3K, PDK1, and protein kinase C (PKC) inhibitors on aggressiveness characteristics. Timp1 downregulation resulted in decreased anoikis resistance, clonogenicity, dacarbazine resistance, and in vivo tumor growth and lung colonization. In metastatic cells, pAKT^Thr308 is highly expressed, contributing to anoikis resistance. We showed that PDK1^Ser241 and PKCβII^Ser660 are activated by Timp1 in different stages of melanoma progression, contributing to colony formation and anoikis resistance. Moreover, simultaneous inhibition of Timp1 and AKT in metastatic cells resulted in more effective anoikis inhibition. Our findings demonstrate that Timp1 promotes cell survival with the participation of PDK1 and PKC in melanoma. In addition, Timp1 and AKT act synergistically to confer anoikis resistance in advanced tumor stages. This study brings new insights about the mechanisms by which Timp1 promotes cell survival in melanoma, and points to novel perspectives for therapeutic approaches.

NMR metabolic fingerprints of murine melanocyte and melanoma cell lines: application to biomarker discovery

Melanoma is the most aggressive type of skin cancer and efforts to improve the diagnosis of this neoplasia are largely based on the use of cell lines. Metabolomics is currently undergoing great advancements towards its use to screening for disease biomarkers. Although NMR metabolomics includes both 1D and 2D methodologies, there is a lack of data in the literature regarding heteronuclear 2D NMR assignments of the metabolome from eukaryotic cell lines. The present study applied NMR-based metabolomics strategies to characterize aqueous and lipid extracts from murine melanocytes and melanoma cell lines with distinct tumorigenic potential, successfully obtaining fingerprints of the metabolites from the extracts of the cell lines by means of 2D NMR HSQC correlation maps. Relative amounts of the identified metabolites were compared between the 4 cell lines. Multivariate analysis of ¹H NMR data was able not only to differentiate the melanocyte cell line from the tumorigenic ones but also distinguish among the 3 tumorigenic cell lines. We also investigated the effects of mitogenic agents, and found that they can markedly influence the metabolome of the melanocyte cell line, resembling the pattern of most proliferative cell lines.

Vaccination using melanoma cells treated with p19arf and interferon beta gene transfer in a mouse model: a novel combination for cancer immunotherapy

Previously, we combined p19(Arf) (Cdkn2a, tumor suppressor protein) and interferon beta (IFN-β, immunomodulatory cytokine) gene transfer in order to enhance cell death in a murine model of melanoma. Here, we present evidence of the immune response induced when B16 cells succumbing to death due to treatment with p19(Arf) and IFN-β are applied in vaccine models. Use of dying cells for prophylactic vaccination was investigated, identifying conditions for tumor-free survival. After combined p19(Arf) and IFN-β treatment, we observed immune rejection at the vaccine site in immune competent and nude mice with normal NK activity, but not in NOD-SCID and dexamethasone immunosuppressed mice (NK deficient). Combined treatment induced IL-15, ULBP1, FAS/APO1 and KILLER/DR5 expression, providing a mechanism for NK activation. Prophylactic vaccination protected against tumor challenge, where markedly delayed progression and leukocyte infiltration were observed. Analysis of primed lymphocytes revealed secretion of TH1-related cytokines and depletion protocols showed that both CD4(+) and CD8(+) T lymphocytes are necessary for immune protection. However, application of this prophylactic vaccine where cells were treated either with IFN-β alone or combined with p19(Arf) conferred similar immune protection and cytokine activation, yet only the combination was associated with increased overall survival. In a therapeutic vaccine protocol, only the combination was associated with reduced tumor progression. Our results indicate that by harnessing cell death in an immunogenic context, our p19(Arf) and IFN-β combination offers a clear advantage when both genes are included in the vaccine and warrants further development as a novel immunotherapy for melanoma.

Enhanced OXPHOS, glutaminolysis and β-oxidation constitute the metastatic phenotype of melanoma cells

Tumours display different cell populations with distinct metabolic phenotypes. Thus, subpopulations can adjust to different environments, particularly with regard to oxygen and nutrient availability. Our results indicate that progression to metastasis requires mitochondrial function. Our research, centered on cell lines that display increasing degrees of malignancy, focused on metabolic events, especially those involving mitochondria, which could reveal which stages are mechanistically associated with metastasis. Melanocytes were subjected to several cycles of adhesion impairment, producing stable cell lines exhibiting phenotypes representing a progression from non-tumorigenic to metastatic cells. Metastatic cells (4C11+) released the highest amounts of lactate, part of which was derived from glutamine catabolism. The 4C11+ cells also displayed an increased oxidative metabolism, accompanied by enhanced rates of oxygen consumption coupled to ATP synthesis. Enhanced mitochondrial function could not be explained by an increase in mitochondrial content or mitochondrial biogenesis. Furthermore, 4C11+ cells had a higher ATP content, and increased succinate oxidation (complex II activity) and fatty acid oxidation. In addition, 4C11+ cells exhibited a 2-fold increase in mitochondrial membrane potential (ΔΨmit). Consistently, functional assays showed that the migration of cells depended on glutaminase activity. Metabolomic analysis revealed that 4C11+ cells could be grouped as a subpopulation with a profile that was quite distinct from the other cells investigated in the present study. The results presented here have centred on how the multiple metabolic inputs of tumour cells may converge to compose the so-called metastatic phenotype.

The Roles of miR-26, miR-29, and miR-203 in the Silencing of the Epigenetic Machinery during Melanocyte Transformation

The epigenetic marks located throughout the genome exhibit great variation between normal and transformed cancer cells. While normal cells contain hypomethylated CpG islands near gene promoters and hypermethylated repetitive DNA, the opposite pattern is observed in cancer cells. Recently, it has been reported that alteration in the microenvironment of melanocyte cells, such as substrate adhesion blockade, results in the selection of anoikis-resistant cells, which have tumorigenic characteristics. Melanoma cells obtained through this model show an altered epigenetic pattern, which represents one of the first events during the melanocytes malignant transformation. Because microRNAs are involved in controlling components of the epigenetic machinery, the aim of this work was to evaluate the potential association between the expression of miR-203, miR-26, and miR-29 family members and the genes Dnmt3a, Dnmt3b, Mecp2, and Ezh2 during cells transformation. Our results show that microRNAs and their validated or predicted targets are inversely expressed, indicating that these molecules are involved in epigenetic reprogramming. We also show that miR-203 downregulates Dnmt3b in mouse melanocyte cells. In addition, treatment with 5-aza-CdR promotes the expression of miR-26 and miR-29 in a nonmetastatic melanoma cell line. Considering the occurrence of CpG islands near the miR-26 and miR-29 promoters, these data suggest that they might be epigenetically regulated in cancer.

HaCaT anchorage blockade leads to oxidative stress, DNA damage and DNA methylation changes

Cell adhesion plays an important role in neoplastic transformation. Thus, anchorage-independent growth and epithelial-mesenchymal transition, which are features associated to anoikis-resistance, are vital steps in cancer progression and metastatic colonization. Cell attachment loss may induce intracellular oxidative stress, which triggers DNA damage as methylation changes. HaCaT lineage cells were submitted to periods of 1, 3, 5 and 24 h of anchorage blockage with the purpose of study of oxidative stress effect on changes in the DNA methylation pattern, derived from attachment blockade. Through this study, HaCaT anchorage blockage-induced oxidative stress was reported to mediate alterations in global DNA methylation changes and into TP53 gene promoter pattern during anoikis-resistance acquisition. Furthermore, at the first experimental time-periods (1, 3 and 5 h), genome hypermethylation was found; however, genome hypomethylation was observed in later time-periods (24 h) of attachment impediment. The TP 53 methylation analyses were performed after 24 h of replated anoikis-resistance cells and same methylation pattern was observed, occurring an early (1 and 3 h) hypermethylation that was followed by late (5 and 24 h) hypomethylation. However, LINE-1, a marker of genomic instability, was perceived in time-dependent hypomethylation. The mRNA levels of the DNMTs enzymes were influenced by cell attachment blockage, but non-conclusive results were obtained in order to match DNMTs transcription to pattern methylation results. In conclusion, DNA damage was found, leaded by oxidative stress that has come up from HaCaT anchorage blockade, which rises a global genome hypomethylation tendency as consequence, which might denote genomic instability.

Acquisition of anoikis resistance up-regulates syndecan-4 expression in endothelial cells

Anoikis is a programmed cell death induced upon cell detachment from extracellular matrix, behaving as a critical mechanism in preventing adherent-independent cell growth and attachment to an inappropriate matrix, thus avoiding colonization of distant organs. Cell adhesion plays an important role in neoplastic transformation. Tumors produce several molecules that facilitate their proliferation, invasion and maintenance, especially proteoglycans. The syndecan-4, a heparan sulfate proteoglycan, can act as a co-receptor of growth factors and proteins of the extracellular matrix by increasing the affinity of adhesion molecules to their specific receptors. It participates together with integrins in cell adhesion at focal contacts connecting the extracellular matrix to the cytoskeleton. Changes in the expression of syndecan-4 have been observed in tumor cells, indicating its involvement in cancer. This study investigates the role of syndecan-4 in the process of anoikis and cell transformation. Endothelial cells were submitted to sequential cycles of forced anchorage impediment and distinct lineages were obtained. Anoikis-resistant endothelial cells display morphological alterations, high rate of proliferation, poor adhesion to fibronectin, laminin and collagen IV and deregulation of the cell cycle, becoming less serum-dependent. Furthermore, anoikis-resistant cell lines display a high invasive potential and a low rate of apoptosis. This is accompanied by an increase in the levels of heparan sulfate and chondroitin sulfate as well as by changes in the expression of syndecan-4 and heparanase. These results indicate that syndecan-4 plays a important role in acquisition of anoikis resistance and that the conferral of anoikis resistance may suffice to transform endothelial cells.

Metabolism under hypoxia in Tm1 murine melanoma cells is affected by the presence of galectin-3, a metabolomics approach

Metabolomics has proven an useful tool for systems biology. Here we have used a metabolomics approach to identify conditions in which de novo expression of an established tumor marker, galectin-3, would confer a potential selective advantage for melanoma growth and survival. A murine melanoma cell line (Tm1) that lacks galectin-3 was modified to express it or not (Tm1.G2 and Tm1.N3, respectively). These variant cell line were then exposed to conditions of controlled oxygen tensions and glucose levels. Metabolic profiling of intracellular metabolites of cells exposed to these conditions was obtained in steady state using high resolution ¹H Magnetic Resonance Spectroscopy (¹H-MRS) and multivariate statistical analysis. The Nuclear Magnetic Resonance (NMR) spectra contained a large number of absorption lines from which we were able to distinguish 20 metabolites, 3 fatty acids and some absorption lines and clusters were not identified. Principal Components Analysis (PCA) allowed for the discrimination of 2 experimental conditions in which expression of the tumor marker galectin-3 may play a significant role, namely exposure of cells to hypoxia under high glucose. Interestingly, under all other experimental conditions tested, the cellular system was quite robust. Our results suggest that the Metabolomics approach can be used to access information about changes in many metabolic pathways induced in tumorigenic cells and to allow the evaluation of their behavior in controlled environmental conditions or selective pressures.

A natural bacterial-derived product, the metalloprotease arazyme, inhibits metastatic murine melanoma by inducing MMP-8 cross-reactive antibodies

The increased incidence, high rates of mortality and few effective means of treatment of malignant melanoma, stimulate the search for new anti-tumor agents and therapeutic targets to control this deadly metastatic disease. In the present work the antitumor effect of arazyme, a natural bacterial-derived metalloprotease secreted by Serratia proteomaculans, was investigated. Arazyme significantly reduced the number of pulmonary metastatic nodules after intravenous inoculation of B16F10 melanoma cells in syngeneic mice. In vitro, the enzyme showed a dose-dependent cytostatic effect in human and murine tumor cells, and this effect was associated to the proteolytic activity of arazyme, reducing the CD44 expression at the cell surface, and also reducing in vitro adhesion and in vitro/in vivo invasion of these cells. Arazyme treatment or immunization induced the production of protease-specific IgG that cross-reacted with melanoma MMP-8. In vitro, this antibody was cytotoxic to tumor cells, an effect increased by complement. In vivo, arazyme-specific IgG inhibited melanoma lung metastasis. We suggest that the antitumor activity of arazyme in a preclinical model may be due to a direct cytostatic activity of the protease in combination with the elicited anti-protease antibody, which cross-reacts with MMP-8 produced by tumor cells. Our results show that the bacterial metalloprotease arazyme is a promising novel antitumor chemotherapeutic agent.

Heparan sulfate proteoglycans and heparin regulate melanoma cell functions

BACKGROUND

The solid melanoma tumor consists of transformed melanoma cells, and the associated stromal cells including fibroblasts, endothelial cells, immune cells, as well as, soluble macro- and micro-molecules of the extracellular matrix (ECM) forming the complex network of the tumor microenvironment. Heparan sulfate proteoglycans (HSPGs) are an important component of the melanoma tumor ECM. Importantly, there appears to be both a quantitative and a qualitative shift in the content of HSPGs, in parallel to the nevi-radial growth phase-vertical growth phase melanoma progression. Moreover, these changes in HSPG expression are correlated to modulations of key melanoma cell functions.

SCOPE OF REVIEW

This review will critically discuss the roles of HSPGs/heparin in melanoma development and progression.

MAJOR CONCLUSIONS

We have correlated HSPGs' expression and distribution with melanoma cell signaling and functions as well as angiogenesis.

GENERAL SIGNIFICANCE

The current knowledge of HSPGs/heparin biology in melanoma provides a foundation we can utilize in the ongoing search for new approaches in designing anti-tumor therapy. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Galectin-3 disruption impaired tumoral angiogenesis by reducing VEGF secretion from TGFβ1-induced macrophages

In order to study the role of galectin-3 in tumor angiogenesis associated with tumor-associated macrophages (TAM) and tumor parenchyma, the galectin-3 expression was reconstituted in Tm1 melanoma cell line that lacks this protein. Galectin-3-expressing cells (Tm1G3) and mock-vector transfected cells (Tm1N3) were injected into wild-type (WT) and galectin-3 knockout (KO) C57Bl/6 mice. Tumors originated from Tm1G3 were larger in tumor volume with enlarged functional vessels, decreased necrotic areas, and increased vascular endothelial growth factor (VEGF) protein levels. Galectin-3-nonexpressing-cells injected into WT and KO showed increased levels of transforming growth factor beta 1 (TGFβ1) and, in WT animals this feature was also accompanied by increased VEGFR2 expression and its phosphorylation. In KO animals, tumors derived from galectin-3-expressing cells were infiltrated by CD68(+)-cells, whereas in tumors derived from galectin-3-nonexpressing-cells, CD68(+) cells failed to infiltrate tumors and accumulated in the periphery of the tumor mass. In vitro studies showed that Tm1G3 secreted more VEGF than Tm1N3 cells. In the latter case, TGFβ1 induced VEGF production. Basal secretion of VEGF was higher in WT-bone marrow-derived macrophages (BMDM) than in KO-BMDM. TGFβ1 induced secretion of VEGF only in WT-BMDM. Tm1G3-induced tumors had the Arginase I mRNA increased, which upregulated alternative macrophage (M2)/TAM induction. M2 stimuli, such as interleukin-4 (IL4) and TGFβ1, increased Arginase I protein levels and galectin-3 expression in WT- BMDM, but not in cells from KO mice. Hence, we report that galectin-3 disruption in tumor stroma and parenchyma decreases angiogenesis through interfering with the responses of macrophages to the interdependent VEGF and TGFβ1 signaling pathways.

Ras and Rac1, frequently mutated in melanomas, are activated by superoxide anion, modulate Dnmt1 level and are causally related to melanocyte malignant transformation

A melanocyte malignant transformation model was developed in our laboratory, in which different melanoma cell lines were obtained after submitting the non-tumorigenic melanocyte lineage melan-a to sequential cycles of anchorage impediment. Our group has already showed that increased superoxide level leads to global DNA hypermemethylation as well increased Dnmt1 expression few hours after melanocyte anchorage blockade. Here, we showed that Ras/Rac1/ERK signaling pathway is activated in melanocytes submitted to anchorage impediment, regulating superoxide levels, global DNA methylation, and Dnmt1 expression. Interestingly, Ras and Rac1 activation is not related to codon mutations, but instead regulated by superoxide. Moreover, the malignant transformation was drastically compromised when melan-a melanocytes were submitted to sequential cycles of anchorage blockage in the presence of a superoxide scavenger. This aberrant signaling pathway associated with a sustained stressful condition, which might be similar to conditions such as UV radiation and inflammation, seems to be an early step in malignant transformation and to contribute to an epigenetic reprogramming and the melanoma development.

De novo galectin-3 expression influences the response of melanoma cells to isatin-Schiff base copper (II) complex-induced oxidative stimulus

Galectin-3, a ubiquitous member of the galectin family, has been shown to control cellular proliferation, adhesion, migration and apoptosis; thus, it has a role in tumor development and progression. Galectin-3 expression is both up- and down-regulated during melanoma progression. However, conflicting data regarding its roles in tumor biology prompted us to investigate if the presence of galectin-3 influences the response of melanoma cells to a novel metallodrug because metastatic melanoma acquires chemo resistance and is reported to be redox-sensitive. Previously, it was demonstrated that the complex [bis-(2-oxindol-3-yl-imino)-2-(2-aminoethyl) pyridine-N,N'] copper (II) perchlorate, herein referred to as [Cu(isaepy)], induces ROS formation and apoptosis in neuroblastoma cells through mitochondrial uncoupling and the activation of AMPK/p38/p53 signaling. Here, we used a model of vertical growth melanoma (TM1), in which GAL3 expression is lost during tumor progression. When de novo expressed, galectin-3 was found to be ubiquitously present in all subcellular compartments. Our results demonstrate that de novo galectin-3 expression impairs the cellular antioxidant system and renders TM1G3 cells more susceptible than GAL3-null TM1MNG3 cells to [Cu(isaepy)] treatment. This compound, in contrast with the redox inactive [dichloro (2-oxindol-3-yl-imino)-2-(2-aminoethyl) pyridine-N,N'] zinc (II), herein referred to as [Zn(isaepy)], leads to increased intracellular ROS accumulation, increased carbonyl stress, increased mitochondrial depolarization, decreased cell adhesion, increased p38 activation and apoptosis in TM1G3, compared with TM1MNG3. Cell death was shown to be dependent on a hydrogen peroxide-derived species and on the activation of p38. Because mitochondria are a target of both [Cu(isaepy)] and galectin-3, we propose that the presence of galectin-3 in this organelle favors increased ROS production, thereby inducing oxidative cellular damage and apoptotic death. Therefore, [Cu(isaepy)] may be envisaged as a possible anti-melanoma strategy, particularly for melanomas that express galectin-3.

Activation of the kinin B1 receptor attenuates melanoma tumor growth and metastasis

Melanoma is a very aggressive tumor that does not respond well to standard therapeutic approaches, such as radio- and chemotherapies. Furthermore, acquiring the ability to metastasize in melanoma and many other tumor types is directly related to incurable disease. The B1 kinin receptor participates in a variety of cancer-related pathophysiological events, such as inflammation and angiogenesis. Therefore, we investigated whether this G protein-coupled receptor plays a role in tumor progression. We used a murine melanoma cell line that expresses the kinin B1 receptor and does not express the kinin B2 receptor to investigate the precise contribution of activation of the B1 receptor in tumor progression and correlated events using various in vitro and in vivo approaches. Activation of the kinin B1 receptor in the absence of B2 receptor inhibits cell migration in vitro and decreases tumor formation in vivo. Moreover, tumors formed from cells stimulated with B1-specific agonist showed several features of decreased aggressiveness, such as smaller size and infiltration of inflammatory cells within the tumor area, higher levels of pro-inflammatory cytokines implicated in the host anti-tumor immune response, lower number of cells undergoing mitosis, a poorer vascular network, no signs of invasion of surrounding tissues or metastasis and increased animal survival. Our findings reveal that activation of the kinin B1 receptor has a host protective role during murine melanoma tumor progression, suggesting that the B1 receptor could be a new anti-tumor GPCR and provide new opportunities for therapeutic targeting.

Timp1 interacts with beta-1 integrin and CD63 along melanoma genesis and confers anoikis resistance by activating PI3-K signaling pathway independently of Akt phosphorylation

BACKGROUND

Anoikis resistance is one of the abilities acquired along tumor progression. This characteristic is associated with metastasis development, since tumorigenic cells must survive independently of cell-matrix interactions in this process. In our laboratory, it was developed a murine melanocyte malignant transformation model associated with a sustained stressful condition. After subjecting melan-a melanocytes to 1, 2, 3 and 4 cycles of anchorage impediment, anoikis resistant cells were established and named 1C, 2C, 3C and 4C, respectively. These cells showed altered morphology and PMA independent cell growth, but were not tumorigenic, corresponding to pre-malignant cells. After limiting dilution of 4C pre-malignant cells, melanoma cell lines with different characteristics were obtained. Previous data from our group showed that increased Timp1 expression correlated with anoikis-resistant phenotype. Timp1 was shown to confer anchorage-independent growth capability to melan-a melanocytes and render melanoma cells more aggressive when injected into mice. However, the mechanisms involved in anoikis regulation by Timp1 in tumorigenic cells are not clear yet.

METHODS

The β1-integrin and Timp1 expression were evaluated by Western blotting and CD63 protein expression by flow cytometry using specific antibodies. To analyze the interaction among Timp1, CD63 and β1-integrin, immunoprecipitation assays were performed, anoikis resistance capability was evaluated in the presence or not of the PI3-K inhibitors, Wortmannin and LY294002. Relative expression of TIMP1 and CD63 in human metastatic melanoma cells was analyzed by real time PCR.

RESULTS

Differential association among Timp1, CD63 and β1-integrins was observed in melan-a melanocytes, 4C pre-malignant melanocytes and 4C11- and 4C11+ melanoma cells. Timp1 present in conditioned medium of melanoma cells rendered melan-a melanocytes anoikis-resistant through PI3-K signaling pathway independently of Akt activation. In human melanoma cell lines, in which TIMP1 and beta-1 integrin were also found to be interacting, TIMP1 and CD63 levels together was shown to correlate significantly with colony formation capacity.

CONCLUSIONS

Our results show that Timp1 is assembled in a supramolecular complex containing CD63 and β1-integrins along melanoma genesis and confers anoikis resistance by activating PI3-K signaling pathway, independently of Akt phosphorylation. In addition, our data point TIMP1, mainly together with CD63, as a potential biomarker of melanoma.

Mining gene expression signature for the detection of pre-malignant melanocytes and early melanomas with risk for metastasis

BACKGROUND

Metastatic melanoma is a highly aggressive skin cancer and currently resistant to systemic therapy. Melanomas may involve genetic, epigenetic and metabolic abnormalities. Evidence is emerging that epigenetic changes might play a significant role in tumor cell plasticity and metastatic phenotype of melanoma cells.

PRINCIPAL FINDINGS

In this study, we developed a systematic approach to identify genes implicated in melanoma progression. To do this, we used the Affymetrix GeneChip Arrays to screen 34,000 mouse transcripts in melan-a melanocytes, 4C pre-malignant melanocytes, 4C11- non-metastatic and 4C11+ metastatic melanoma cell lines. The genome-wide association studies revealed pathways commonly over-represented in the transition from immortalized to pre-malignant stage, and under-represented in the transition from non-metastatic to metastatic stage. Additionally, the treatment of cells with 10 µM 5-aza-2'-deoxycytidine (5AzaCdR) for 48 hours allowed us to identify genes differentially re-expressed at specific stages of melan-a malignant transformation. Treatment of human primary melanocytes with the demethylating agent 5AzaCdR in combination to the histone deacetylase inhibitor Trichostatin A (TSA) revealed changes on melanocyte morphology and gene expression which could be an indicator of epigenetic flexibility in normal melanocytes. Moreover, changes on gene expression recognized by affecting the melanocyte biology (NDRG2 and VDR), phenotype of metastatic melanoma cells (HSPB1 and SERPINE1) and response to cancer therapy (CTCF, NSD1 and SRC) were found when Mel-2 and/or Mel-3-derived patient metastases were exposed to 5AzaCdR plus TSA treatment. Hierarchical clustering and network analyses in a panel of five patient-derived metastatic melanoma cells showed gene interactions that have never been described in melanomas.

SIGNIFICANCE

Despite the heterogeneity observed in melanomas, this study demonstrates the utility of our murine melanoma progression model to identify molecular markers commonly perturbed in metastasis. Additionally, the novel gene expression signature identified here may be useful in the future into a model more closely related to translational research.

L1CAM from human melanoma carries a novel type of N-glycan with Galβ1-4Galβ1- motif. Involvement of N-linked glycans in migratory and invasive behaviour of melanoma cells

Dramatic changes in glycan biosynthesis during oncogenic transformation result in the emergence of marker glycans on the cell surface. We analysed the N-linked glycans of L1CAM from different stages of melanoma progression, using high-performance liquid chromatography combined with exoglycosidase sequencing, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, and lectin probes. L1CAM oligosaccharides are heavily sialylated, mainly digalactosylated, biantennary complex-type structures with galactose β1-4/3-linked to GlcNAc and with or without fucose α1-3/6-linked to GlcNAc. Hybrid, bisected hybrid, bisected triantennary and tetraantennary complex oligosaccharides, and β1-6-branched complex-type glycans with or without lactosamine extensions are expresses at lower abundance. We found that metastatic L1CAM possesses only α2-6-linked sialic acid and the loss of α2-3-linked sialic acid in L1CAM is a phenomenon observed during the transition of melanoma cells from VGP to a metastatic stage. Unexpectedly, we found a novel monoantennary complex-type oligosaccharide with a Galβ1-4Galβ1- epitope capped with sialic acid residues A1[3]G(4)2S2-3. To our knowledge this is the first report documenting the presence of this oligosaccharide in human cancer. The novel and unique N-glycan should be recognised as a new class of human melanoma marker. In functional tests we demonstrated that the presence of cell surface α2-3-linked sialic acid facilitates the migratory behaviour and increases the invasiveness of primary melanoma cells, and it enhances the motility of metastatic cells. The presence of cell surface α2-6-linked sialic acid enhances the invasive potential of both primary and metastatic melanoma cells. Complex-type oligosaccharides in L1CAM enhance the invasiveness of metastatic melanoma cells.

Apoptotic cells contribute to melanoma progression and this effect is partially mediated by the platelet-activating factor receptor

There is evidence that the platelet-activating factor receptor (PAFR) is involved in the clearance of apoptotic cells by macrophages, and that this is associated with anti-inflammatory phenotype. Our group has previously shown that coinjection of a large number of apoptotic cells can promote tumor growth from a subtumorigenic dose of melanoma cells. Here, we studied the involvement of the PAFR in the tumor growth promoting effect of apoptotic cells. A sub-tumorigenic dose of melanoma cells (Tm1) was coinjected with apoptotic Tm1 cells, subcutaneously in the flank of C57Bl/6 mice, and the volume was monitored for 30 days. Animals received the PAFR antagonists, WEB2170 or PCA4248 (5 mg/kg body weight) or vehicle, by peritumoral daily injection for 5 days. Results showed that PAFR antagonists significantly inhibited the tumor growth induced by the coinjection of a sub-tumorigenic dose of melanoma cells together with apoptotic cells. This was accompanied by inhibition of early neutrophil and macrophage infiltration. Addition of (platelet-activating factor) to this system has no significant effect. PAFR antagonists did not affect the promoting effect of carrageenan. We suggest that the recognition of apoptotic cells by phagocytes leads to activation of PAFR pathways, resulting in a microenvironment response favorable to melanoma growth.

Biomarkers as key contributors in treating malignant melanoma metastases

Melanoma is a human neurocristopathy associated with developmental defects in the neural crest-derived epidermal melanocytes. At the present time, at least three hypotheses were identified that may explain melanoma aetiology, as follows: (1) a model of linear progression from differentiated melanocytes to metastatic cancer cells (2) a model involving the appearance of melanoma stem-like cells, and (3) an epigenetic progenitor model of cancer. Treating metastatic melanoma is one of the most serious challenges in the 21st century. This is justified because of a subpopulation of cells presenting a remarkable molecular heterogeneity, which is able to explain the drug resistance and the growing mortality rates worldwide. Fortunately, there are now evidences sustaining the importance of genetic, epigenetic, and metabolomic alterations as biomarkers for classification, staging, and better management of melanoma patients. To illustrate some fascinating insights in this field, the genes BRAF^V600E and CTLA4 have been recognized as bona fide targets to benefit melanoma patients. Our research attempts to carefully evaluate data from the literature in order to highlight the link between a molecular disease model and the key contribution of biomarkers in treating malignant melanoma metastases.

Tissue inhibitor of metalloproteinase 1 expression associated with gene demethylation confers anoikis resistance in early phases of melanocyte malignant transformation

Although anoikis resistance has been considered a hallmark of malignant phenotype, the causal relation between neoplastic transformation and anchorage-independent growth remains undefined. We developed an experimental model of murine melanocyte malignant transformation, where a melanocyte lineage (melan-a) was submitted to sequential cycles of anchorage blockade, resulting in progressive morphologic alterations, and malignant transformation. Throughout this process, cells corresponding to premalignant melanocytes and melanoma cell lines were established and show progressive anoikis resistance and increased expression of Timp1. In melan-a melanocytes, Timp1 expression is suppressed by DNA methylation as indicated by its reexpression after 5-aza-2'-deoxycytidine treatment. Methylation-sensitive single-nucleotide primer extension analysis showed increased demethylation in Timp1 in parallel with its expression along malignant transformation. Interestingly, TIMP1 expression has already been related with negative prognosis in some human cancers. Although described as a MMP inhibitor, this protein has been associated with apoptosis resistance in different cell types. Melan-a cells overexpressing Timp1 showed increased survival in suspension but were unable to form tumors in vivo, whereas Timp1-overexpressing melanoma cells showed reduced latency time for tumor appearance and increased metastatic potential. Here, we demonstrated for the first time an increment in Timp1 expression since the early phases of melanocyte malignant transformation, associated to a progressive gene demethylation, which confers anoikis resistance. In this way, Timp1 might be considered as a valued marker for melanocyte malignant transformation.

Endothelial nitric oxide synthase uncoupling as a key mediator of melanocyte malignant transformation associated with sustained stress conditions

Melanoma cell lines and cells corresponding to premalignant melanocytes were established by our group after subjecting a nontumorigenic murine melanocyte lineage, melan-a, to sequential cycles of anchorage blockade. Previous results showed that in melan-a cells the superoxide level increases after such procedure. Superoxide production during melanocyte de-adhesion was inhibited by L-sepiapterin, the precursor of eNOS cofactor BH4, and increased by the inhibitor of BH4 synthesis, DAHP, hence indicating a partial uncoupling state of eNOS. The eNOS uncoupling seems to be maintained in cells derived from melan-a, because they present decreased nitric oxide and increased superoxide levels. The inhibition of superoxide production in Tm5 melanoma cells with L-sepiapterin reinforces their eNOS-uncoupled state. The maintenance of oxidative stress seems to be important in melanoma apoptosis resistance because Mn(III)TBAP, a superoxide scavenger, or L-sepiapterin renders Tm5 cells more sensitive to anoikis and chemotherapy. More importantly, eNOS uncoupling seems to play a pivotal role in melanocyte malignant transformation induced by sustained anchorage impediment, because no malignant transformation was observed when L-NAME-treated melanocytes were subjected to sequential cycles of de-adhesion. Our results show that uncoupled eNOS contributes to superoxide production during melanocyte anchorage impediment, contributing to anoikis resistance and malignant transformation.

Epigenetic reprogramming as a key contributor to melanocyte malignant transformation

Melanoma progression requires deregulation of gene expression by currently uncharacterized epigenetic mechanisms. A mouse model based on changes in cell microenvironment was developed by our group to study melanocyte malignant transformation. Melanoma cell lines (4C11- and 4C11+) were obtained as result of 5 sequential anchorage blockades of non-tumorigenic melan-a melanocytes. Melan-a cells submitted to 4 de-adhesion cycles were also established (4C), are non-tumorigenic and represent an intermediary phase of tumor progression. The aim of this work was to identify factors contributing to epigenetic modifications in early and later phases of malignant transformation induced by anchorage impediment. Epigenetic alterations occur early in tumorigenesis; 4C cell line shows changes in global and gene-specific DNA methylation and histone marks. Many histone modifications differ between melan-a, 4C, 4C11- (non-metastatic melanoma cell line) and 4C11+ (metastatic melanoma cell line) which could be associated with changes in gene and microRNA expression. These epigenetic alterations seem to play a key role in malignant transformation since melanocytes treated with 5-Aza-2'-deoxycytidine before each anchorage blockade do not transform. Some epigenetic changes seem to be also responsible for the maintenance of malignant phenotype, since melanoma cell lines (4C11- and 4C11+) treated in vitro with 5-Aza-2'-deoxycytidine or Trichostatin A showed reduction of tumor growth in vivo. Changes in gene expression reflecting cell adaptation to new environment were also observed. We propose a model in which sustained microenvironmental stress in melanocytes results in epigenetic reprogramming. Thus, after adaptation, cells may acquire epigenetic marks that could contribute to the establishment of a malignant phenotype.

Differential gene expression and clonal selection during cellular transformation induced by adhesion deprivation

Background

Anchorage independent growth is an important hallmark of oncogenic transformation. Previous studies have shown that when adhesion dependent fibroblasts were prevented from adhering to a substrate they underwent anoikis. In the present study we have demonstrated how anoikis resistant cells gain the transformation related properties with sequential selection of genes. We have proposed this process as a model system for selection of transformed cells from normal cells.

Results

This report demonstrates that some fibroblasts can survive during late stages of anoikis, at which time they exhibit transformation-associated properties such as in vitro colony formation in soft agar and in vivo subcutaneous tumour formation in nude mice. Cytogenetic characterisation of these cells revealed that they contained a t (2; 2) derivative chromosome and they have a selective survival advantage in non adherent conditions. Gene expression profile indicated that these cells over expressed genes related to hypoxia, glycolysis and tumor suppression/metastasis which could be helpful in their retaining a transformed phenotype.

Conclusion

Our results reveal some new links between anoikis and cell transformation and they provide a reproducible model system which can potentially be useful to study multistage cancer and to identify new targets for drug development.

Telomere-centromere-driven genomic instability contributes to karyotype evolution in a mouse model of melanoma

Aneuploidy and chromosomal instability (CIN) are hallmarks of most solid tumors. These alterations may result from inaccurate chromosomal segregation during mitosis, which can occur through several mechanisms including defective telomere metabolism, centrosome amplification, dysfunctional centromeres, and/or defective spindle checkpoint control. In this work, we used an in vitro murine melanoma model that uses a cellular adhesion blockade as a transforming factor to characterize telomeric and centromeric alterations that accompany melanocyte transformation. To study the timing of the occurrence of telomere shortening in this transformation model, we analyzed the profile of telomere length by quantitative fluorescent in situ hybridization and found that telomere length significantly decreased as additional rounds of cell adhesion blockages were performed. Together with it, an increase in telomere-free ends and complex karyotypic aberrations were also found, which include Robertsonian fusions in 100% of metaphases of the metastatic melanoma cells. These findings are in agreement with the idea that telomere length abnormalities seem to be one of the earliest genetic alterations acquired in the multistep process of malignant transformation and that telomere abnormalities result in telomere aggregation, breakage-bridge-fusion cycles, and CIN. Another remarkable feature of this model is the abundance of centromeric instability manifested as centromere fragments and centromeric fusions. Taken together, our results illustrate for this melanoma model CIN with a structural signature of centromere breakage and telomeric loss.

Heparan sulfate proteoglycans: structure, protein interactions and cell signaling

Heparan sulfate proteoglycans are ubiquitously found at the cell surface and extracellular matrix in all the animal species. This review will focus on the structural characteristics of the heparan sulfate proteoglycans related to protein interactions leading to cell signaling. The heparan sulfate chains due to their vast structural diversity are able to bind and interact with a wide variety of proteins, such as growth factors, chemokines, morphogens, extracellular matrix components, enzymes, among others. There is a specificity directing the interactions of heparan sulfates and target proteins, regarding both the fine structure of the polysaccharide chain as well precise protein motifs. Heparan sulfates play a role in cellular signaling either as receptor or co-receptor for different ligands, and the activation of downstream pathways is related to phosphorylation of different cytosolic proteins either directly or involving cytoskeleton interactions leading to gene regulation. The role of the heparan sulfate proteoglycans in cellular signaling and endocytic uptake pathways is also discussed.

B-1 cell: the precursor of a novel mononuclear phagocyte with immuno-regulatory properties

Characterization of the origin, properties, functions and fate of cells is a fundamental task for the understanding of physiological and pathological phenomena. Despite the bulk of knowledge concerning the diverse characteristics of mammalian cells, some of them, such as B-1 cells, are still poorly understood. Here we report the results obtained in our laboratory on these cells in the last 10 years. After showing that B-1 cells could be cultured and amplified in vitro, a series of experiments were performed with these cells. They showed that B1 cells reside mostly in the peritoneal and pleural cavities, migrate to distant inflammatory foci, coalesce to form giant cells and participate in granuloma formation, both in vitro and in vivo. They are also able to present antigens to immunologically responsive cells and are endowed with regulatory properties. Further, we have also shown that these cells facilitate different types of infection as well as tumor growth and spreading. These data are presently reviewed pointing to a pivotal role that these cells may play in innate and acquired immunity.

Redox-based escape mechanism from death: the cancer lesson

We review here current evidence on the role of reactive oxygen species (ROS) and of the intracellular redox state in governing crucial steps of the metastatic process, from cell detachment from the primary tumor to final colonization of the distant site. In particular, we discuss the redox-dependent aspects of cell glycolytic metabolism (Warburg effect), of cell juggling between different motility styles (epithelial-to-mesenchymal and mesenchymal-to-amoeboid transition), of cell resistance to anoikis and of cell interaction with the stromal components of the metastatic niche. Central to this overview is the concept that metastasis can be viewed as an integrated "escape program" triggered by redox changes and instrumental at avoiding oxidative stress within the primary tumor. In this novel perspective, metabolic, motility, and prosurvival choices of the cell along the entire metastatic process can be interpreted as exploiting redox-signaling cascades to monitor oxidative/reductive environmental cues and escape oxidative damage. We also propose that this theoretic framework be applied to "normal" evasion/invasion programs such as in inflammation and development. Furthermore, we suggest that the intimate connection between metastasis, inflammation, and stem cells results, at least in part, by the sharing of a common redox-dependent strategy for infiltration, survival, dissemination, and patterning.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.

A recombinant protein based on Trypanosoma cruzi surface molecule gp82 induces apoptotic cell death in melanoma cells

Trypanosoma cruzi infection is known to confer resistance to tumor development in mice, and in-vitro studies have shown the toxic effects of parasite extracts on cancer cell cultures. Investigations in which T. cruzi molecules exhibit antitumor activity have just begun. Here, we used a tumorigenic cell line Tm5, derived from mouse melanocytes melan-a, to test the effect of J18, a recombinant protein based on T. cruzi surface molecule gp82 fused to glutathione-S-transferase (GST). J18 induced actin cytoskeleton disruption in Tm5 but not in melan-a cells. Several changes indicative of apoptosis were detected in Tm5 melanoma cells but not in melan-a cells treated with J18, such as the flipping of phosphatidylserine from the inner to the external side of the plasma membrane, altered nuclear morphology, DNA fragmentation, increase in mitochondria depolarization, and in caspase-3 activity. Retention of NF-kappaB in the cytoplasm was another alteration observed specifically in J18-treated Tm5 cells. No such alterations were found in Tm5 cells treated with GST. In-vivo experiments showed that C57BL/6 mice inoculated with Tm5 cells, treated at the site of tumor cell inoculation with J18, developed tumors of smaller size than mice treated with phosphate-buffered saline or GST and survived longer.

Oxidative stress modulates DNA methylation during melanocyte anchorage blockade associated with malignant transformation

Both oxidative/nitrosative stress and alterations in DNA methylation are observed during carcinogenesis of different tumor types, but no clear correlation between these events has been demonstrated until now. Melanoma cell lines were previously established after submitting the nontumorigenicmelanocyte lineage, melan-a, to cycles of anchorage blockade. In this work, increased intracellular oxidative species and nitric oxide levels, as well as alterations in the DNA methylation, were observed after melan-a detachment, which were also associated with a decrease in intracellular homocysteine (Hcy), an element in the methionine (universal methyl donor) cycle. This alteration was accompanied by increase in glutathione (GSH) levels and methylated DNA content. Furthermore, a significant increase in dnmt1 and 3b expression was identified along melan-a anchorage blockade. L(G)-Nitro-L-arginine methyl esther (L-NAME), known as a nitric oxide synthase (NOS) inhibitor, and N-acetyl-L-cysteine (NAC) prevented the increase in global DNA methylation, as well as the increase in dnmt1 and 3b expression, observed during melan-a detachment. Interestingly, both L-NAME and NAC did not inhibit nitric oxide (NO) production in these cells, but abrogated superoxide anion production during anchorage blockade. In conclusion, oxidative stress observed during melanocyte anchorage blockade seems to modulate DNA methylation levels and may directly contribute to the acquisition of an anoikis-resistant phenotype through an epigenetic mechanism.