Adhesion, migration and communication in melanocytes and melanoma

The clinicopathological and gene expression patterns associated with ulceration of primary melanoma

Ulceration of primary melanomas is associated with poor prognosis yet is reported to predict benefit from adjuvant interferon. To better understand the biological processes involved, clinicopathological factors associated with ulceration were determined in 1804 patients. From this cohort, 348 primary tumor blocks were sampled to generate gene expression data using a 502-gene cancer panel and 195 blocks were used for immunohistochemistry to detect macrophage infiltration and vessel density. Gene expression results were validated using a whole genome array in two independent sample sets. Ulceration of primary melanomas was associated with more proliferative tumors, tumor vessel invasion, and increased microvessel density. Infiltration of tumors with greater number of macrophages and gene expression pathways associated with wound healing and up-regulation of pro-inflammatory cytokines suggests that ulceration is associated with tumor-related inflammation. The relative benefit from interferon reported in patients with ulcerated tumors may reflect modification of signaling pathways involved in inflammation.

The role of microRNAs and long non-coding RNAs in the pathology, diagnosis, and management of melanoma

Melanoma is frequently lethal and its global incidence is steadily increasing. Despite the rapid development of different modes of targeted treatment, durable clinical responses remain elusive. A complete understanding of the molecular mechanisms that drive melanomagenesis is required, both genetic and epigenetic, in order to improve prevention, diagnosis, and treatment. There is increased appreciation of the role of microRNAs (miRNAs) in melanoma biology, including in proliferation, cell cycle, migration, invasion, and immune evasion. Data are also emerging on the role of long non-coding RNAs (lncRNAs), such as SPRY4-IT1, BANCR, and HOTAIR, in melanomagenesis. Here we review the data on the miRNAs and lncRNAs implicated in melanoma biology. An overview of these studies will be useful for providing insights into mechanisms of melanoma development and the miRNAs and lncRNAs that might be useful biomarkers or future therapeutic targets.

Thrombomodulin modulates cell migration in human melanoma cell lines

Malignant melanoma cells are known to have altered expressions of growth factors as compared with normal melanocytes. Thrombomodulin (TM) is a thrombin receptor on endothelial cells that converts thrombin from a procoagulant to an anticoagulant enzyme. TM expression is downregulated in tumor cells, and this phenomenon correlates with tumor cell invasiveness and a poor prognosis in patients with cancer. In this study, we evaluated TM expression in two human melanoma cell lines that are known to have either low (WM35) or high (A375) aggressive phenotypes. Analysis by quantitative real-time PCR (qPCR) showed that the mRNA expression of TM is modestly (WM35) or dramatically (A375) downregulated in melanoma cells, as compared with human primary melanocytes. TM expression levels inversely correlated with in-vitro migration properties of tumor cells. In addition, interleukin-8 expression also correlated with the degree of aggressiveness, as indicated by high expression levels of this cytokine in A375 cells. Overexpression of TM in A375 cells by transient transfection reversed their aggressive phenotype and dramatically decreased interleukin-8 expression by these cells. Taken together, these results suggest that downregulation of TM plays a crucial role in melanocyte transformation and melanoma progression.

RGDechi-hCit: αvβ3 selective pro-apoptotic peptide as potential carrier for drug delivery into melanoma metastatic cells

αvβ3 integrin is an important tumor marker widely expressed on the surface of cancer cells. Recently, we reported some biological features of RGDechi-hCit, an αvβ3 selective peptide antagonist. In the present work, we mainly investigated the pro-apoptotic activity of the molecule and its ability to penetrate the membrane of WM266 cells, human malignant melanoma cells expressing high levels of αvβ3 integrin. For the first time we demonstrated the pro-apoptotic effect and the ability of RGDechi-hCit to enter into cell overexpressing αvβ3 integrin mainly by clathrin- and caveolin-mediated endocytosis. Furthermore, we deepened and confirmed the selectivity, anti-adhesion, and anti-proliferative features of the peptide. Altogether these experiments give insight into the biological behavior of RGDechi-hCit and have important implications for the employment of the peptide as a new selective carrier to deliver drugs into the cell and as a therapeutic and diagnostic tool for metastatic melanoma. Moreover, since the peptide shows a pro-apoptotic effect, a great perspective could be the development of a new class of selective systems containing RGDechi-hCit and pro-apoptotic molecules or other therapeutic agents to attain a synergic action.

The combination of Cl-IB-MECA with paclitaxel: a new anti-metastatic therapeutic strategy for melanoma

PURPOSE

Metastatic melanoma is considered one of the most aggressive malignant tumours, representing the deadliest form of skin cancer. Melanoma progression is associated with the abrogation of normal controls that limit cell proliferation, migration, and invasion, eventually leading to metastasis. Based on the variety of cellular mechanisms involved in metastatic progression, we aimed to evaluate the effect of inosine (50 μM) and of the combination of Cl-IB-MECA (10 μM) with paclitaxel (10 ng/mL) on several stages of melanoma progression.

METHODS

Proliferation, migration, adhesion, invasion, and colony formation assays were performed on human C32 and A375 metastatic melanoma cells. Levels of ERK1/2 were also determined using an ELISA kit. Moreover, mouse aortic rings were treated with vascular endothelial growth factor in order to assess the microvessel sprouting (an indicator of angiogenesis) in the presence of the referred compounds.

RESULTS

We demonstrate that inosine induced, through A3 adenosine receptor activation, proliferation, migration, adhesion, and invasion on C32 and A375 melanoma cells, although with dissimilar importance on the two melanoma cell lines. Inosine also increased colony formation on A375 cells. Levels of ERK1/2 were increased after inosine exposure and that increase was dependent on A3 adenosine receptor activation in both cell lines. Moreover, microvessel sprouting stimulated by inosine was decreased by the combination of Cl-IB-MECA with paclitaxel.

CONCLUSIONS

Cl-IB-MECA combined with paclitaxel was able to impair almost all of the referred metastatic related mechanisms induced by inosine, making this approach a valuable tool for combinatory therapy against metastatic melanoma.

Glycosylation modulates melanoma cell α2β1 and α3β1 integrin interactions with type IV collagen

Although type IV collagen is heavily glycosylated, the influence of this post-translational modification on integrin binding has not been investigated. In the present study, galactosylated and nongalactosylated triple-helical peptides have been constructed containing the α1(IV)382-393 and α1(IV)531-543 sequences, which are binding sites for the α2β1 and α3β1 integrins, respectively. All peptides had triple-helical stabilities of 37 °C or greater. The galactosylation of Hyl(393) in α1(IV)382-393 and Hyl(540) and Hyl(543) in α1(IV)531-543 had a dose-dependent influence on melanoma cell adhesion that was much more pronounced in the case of α3β1 integrin binding. Molecular modeling indicated that galactosylation occurred on the periphery of α2β1 integrin interaction with α1(IV)382-393 but right in the middle of α3β1 integrin interaction with α1(IV)531-543. The possibility of extracellular deglycosylation of type IV collagen was investigated, but no β-galactosidase-like activity capable of collagen modification was found. Thus, glycosylation of collagen can modulate integrin binding, and levels of glycosylation could be altered by reduction in expression of glycosylation enzymes but most likely not by extracellular deglycosylation activity.

Sequential molecular analysis of circulating MCAM/MUC18 expression: a promising disease biomarker related to clinical outcome in melanoma

MCAM/MUC18 is a cell adhesion molecule associated with higher incidence of relapse in melanoma. The purpose of our study was to evaluate its role as a promising disease biomarker of progression through sequential molecular MCAM/MUC18 RT-PCR assay on serial blood samples collected during the clinical follow-up of 175 melanoma patients in different American Joint Committee on Cancer (AJCC) stages. MCAM/MUC18 molecular detection, found at least once in 22 out of the 175 patients, was significantly associated with poor prognosis and death (p < 0.001), regardless of the AJCC stages. Positive expression, either if primarily present or later acquired, was associated with melanoma progression, whereas patients primarily negative or with subsequent loss gained clinical remission or stable disease, even if in advanced stages (p < 0.005). Six AJCC advanced stages always MCAM/MUC18 negative are in complete remission or with a stable disease (p < 0.007). Semiquantitative immunohistochemical MCAM/MUC18 staining on corresponding primary melanomas was related to peripheral molecular expression. Correlations between circulating molecular and tissutal immunohistochemical detection, primary tumour thickness, AJCC stages and clinical outcome were statistically evaluated using Student's t test, ANOVA, Spearman's rank correlation test, Pearson χ (2)-test and McNemar's test. In our investigation, MCAM/MUC18 expression behaves as a "molecular warning of progression" even in early AJCC patients otherwise in disease-free conditions. Achievement of this molecule predicted the emergence of a clinically apparent status, whereas absence or persistent loss was related to a stable disease or to a disease-free status. If confirmed in larger case series, MCAM/MUC18 molecular expression could predict good or poor clinical outcome, possibly becoming a promising prognostic factor.

Increased frequency of minimal homozygous deletions is associated with poor prognosis in primary malignant melanoma patients

Identification of prognostic melanoma-associated copy number alterations (CNAs) is still an area of active research. Here, we investigated by high-resolution array comparative genomic hybridization (aCGH) a cohort of 31 paraffin-preserved primary malignant melanomas (MMs), whose prognosis was not predictable on the basis of conventional histopathological parameters. Although we identified a variety of highly recurrent sites of genomic lesions, the total number of CNAs per patient was not a discriminator of MM outcome. Furthermore, validation of aCGH by quantitative PCR on an extended population of 65 MM samples confirmed the absence of predictive value for the most recurrent CNA loci. Instead, our analysis revealed specific prognostic potential of the frequency of homozygous deletions (representing less than 3% of the total CNAs on average per sample), which was strongly associated with sentinel lymph node (SLN) invasion (P = 0.003), and distant metastasis (P = 0.003). Increased number of homozygous deletions was also indicative of poor patient survival (P = 0.01), both in our samples and in an independent validation of public dataset of primary and metastatic MMs. Moreover, we identified 77 hotspots of minimal common homozygous deletions, enriched in genes involved in cell adhesion processes and cell-communication functions, which preferentially accumulated in primary MMs showing the most severe outcome. Therefore, specific loss of gene loci in regions of minimal homozygous deletion may represent a pivotal type of genomic alteration accumulating during MM progression with potential prognostic implication.

Melanoma's connections to the tumour microenvironment

SUMMARY

Melanoma cells interact with and depend on seemingly normal cells in their tumour microenvironment to allow the acquisition of the hallmarks of solid cancer. In general, there are three types of interaction of melanoma cells with their microenvironment. First, there is bilateral communication between melanoma cells and the stroma, which includes fibroblasts, endothelial cells, immune cells, soluble molecules, and the extracellular matrix. Second, while under normal conditions keratinocytes control localisation and proliferative behaviour of melanocytes in the epidermis, once this balance is disturbed and a melanoma has developed, melanoma cells may take over the control of their epidermal tumour microenvironment. Finally, there are subcompartments within tumours with different microenvironmental milieu defined by their access to oxygen and nutrients. Therefore, different melanoma cells within a tumour face different microenvironments. Interactions between melanoma cells among each other and with the cell types in their microenvironment happen through endocrine and paracrine communication and/or through direct contact via cell-cell and cell-matrix adhesion, and gap junctional intercellular communication (GJIC). Connexins have been identified as key molecules for direct cell-cell communication and are also thought to be important for the release of signalling molecules from cells to the microenvironment. In this review we provide an update of the alterations in cell-cell communication in melanoma and the tumour microenvironment associated with melanoma development and progression.

The use of skin models in drug development

Three dimensional (3D) tissue models of the human skin are probably the most developed and understood in vitro engineered constructs. The motivation to accomplish organotypic structures was driven by the clinics to enable transplantation of in vitro grown tissue substitutes and by the cosmetics industry as alternative test substrates in order to replace animal models. Today a huge variety of 3D human skin models exist, covering a multitude of scientific and/or technical demands. This review summarizes and discusses different approaches of skin model development and sets them into the context of drug development. Although human skin models have become indispensable for the cosmetics industry, they have not yet started their triumphal procession in pharmaceutical research and development. For drug development these tissue models may be of particular interest for a) systemically acting drugs applied on the skin, and b) drugs acting at the site of application in the case of skin diseases or disorders. Although quite a broad spectrum of models covering different aspects of the skin as a biologically acting surface exists, these are most often single stand-alone approaches. In order to enable the comprehensive application into drug development processes, the approaches have to be synchronized to allow a cross-over comparison. Besides the development of biological relevant models, other issues are not less important in the context of drug development: standardized production procedures, process automation, establishment of significant analytical methods, and data correlation. For the successful routine use of engineered human skin models in drug development, major requirements were defined. If these requirements can be accomplished in the next few years, human organotypic skin models will become indispensable for drug development, too.

Capturing the biological impact of CDKN2A and MC1R genes as an early predisposing event in melanoma and non melanoma skin cancer

Germline mutations in CDKN2A and/or red hair color variants in MC1R genes are associated with an increased susceptibility to develop cutaneous melanoma or non melanoma skin cancer. We studied the impact of the CDKN2A germinal mutation p.G101W and MC1R variants on gene expression and transcription profiles associated with skin cancer. To this end we set-up primary skin cell co-cultures from siblings of melanoma prone-families that were later analyzed using the expression array approach. As a result, we found that 1535 transcripts were deregulated in CDKN2A mutated cells, with over-expression of immunity-related genes (HLA-DPB1, CLEC2B, IFI44, IFI44L, IFI27, IFIT1, IFIT2, SP110 and IFNK) and down-regulation of genes playing a role in the Notch signaling pathway. 3570 transcripts were deregulated in MC1R variant carriers. In particular, genes related to oxidative stress and DNA damage pathways were up-regulated as well as genes associated with neurodegenerative diseases such as Parkinson's, Alzheimer and Huntington. Finally, we observed that the expression signatures indentified in phenotypically normal cells carrying CDKN2A mutations or MC1R variants are maintained in skin cancer tumors (melanoma and squamous cell carcinoma). These results indicate that transcriptome deregulation represents an early event critical for skin cancer development.

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.

Morphology of melanocytic lesions in situ

Melanoma is a solid tumour with its own specificity from the biological and morphological viewpoint. On one hand, numerous mutations are already known affecting different pathways. They usually concern proliferation rate, apoptosis, cell senescence and cell behaviour. On the other hand, several visual criteria at the tissue level are used by physicians in order to diagnose skin lesions. Nevertheless, the mechanisms between the changes from the mutations at the cell level to the morphology exhibited at the tissue level are still not fully understood. Using physical tools, we develop a simple model. We demonstrate analytically that it contains the necessary ingredients to understand several specificities of melanoma such as the presence of microstructures inside a skin lesion or the absence of a necrotic core. We also explain the importance of senescence for growth arrest in benign skin lesions. Thanks to numerical simulations, we successfully compare this model to biological data.

Why is melanoma so metastatic?

Malignant melanoma is one of the most aggressive cancers and can disseminate from a relatively small primary tumor and metastasize to multiple sites, including the lung, liver, brain, bone, and lymph nodes. Elucidating the molecular and genetic changes that take place during the metastatic process has led to a better understanding of why melanoma is so metastatic. Herein, we describe the unique features that distinguish melanoma from other solid tumors and contribute to the malignant phenotype of melanoma cells. For example, although melanoma cells are highly antigenic, they are extremely efficient at evading host immune response. Melanoma cells share numerous cell surface molecules with vascular cells, are highly angiogenic, are mesenchymal in nature, and possess a higher degree of 'stemness' than do other solid tumors. Finally, analysis of melanoma mutations has revealed that the gene expression profile of malignant melanoma is different from that of other cancers. Elucidating these molecular and genetic processes in highly metastatic melanoma can lead to the development of improved treatment and individualized therapy options.

Modeling Melanoma In Vitro and In Vivo

The behavior of melanoma cells has traditionally been studied in vitro in two-dimensional cell culture with cells adhering to plastic dishes. However, in order to mimic the three-dimensional architecture of a melanoma, as well as its interactions with the tumor microenvironment, there has been the need for more physiologically relevant models. This has been achieved by designing 3D in vitro models of melanoma, such as melanoma spheroids embedded in extracellular matrix or organotypic skin reconstructs. In vivo melanoma models have typically relied on the growth of tumor xenografts in immunocompromised mice. Several genetically engineered mouse models have now been developed which allow the generation of spontaneous melanoma. Melanoma models have also been established in other species such as zebrafish, which are more conducive to imaging and high throughput studies. We will discuss these models as well as novel techniques that are relevant to the study of the molecular mechanisms underlying melanoma progression.

Molecular and cellular pathogenesis of melanoma initiation and progression

Melanoma is a malignant tumor of melanocytes that can spread to other organs of the body, resulting in severe and/or lethal malignancies. Melanocytes are pigment-producing cells found in the deep layer of the epidermis and are originated from melanocytes stem cells through a cellular process called melanogenesis. Several genes and epigenetic and micro-environmental factors are involved in this process via the regulation and maintenance of the balance between melanocytes stem cells proliferation and their differentiation into melanocytes. Dysregulation of this balance through gain or loss of function of key genes implicated in the control and regulation of cell cycle progression and/or differentiation results in melanoma initiation and progression. This review aims to provide a comprehensive overview about the origin of melanocytes, the oncogenic events involved in melanocytes stem cells transformation, and the mechanisms implicated in the perpetuation of melanoma malignant phenotype.

Molecular networks in melanoma invasion and metastasis

Metastatic melanoma accounts for approximately 80% of skin cancer-related deaths. Up to now there has been no effective treatment for stage IV melanoma patients due to the complexity and dissemination potential of this disease. Melanomas are heterogeneous tumors in which conventional therapies fail to improve overall survival. Targeted therapies are being developed, but the final outcome can be hampered by the incomplete knowledge of the process of melanoma progression. Even if the intracellular pathways are similar, the interaction of the cells with the surrounding environment should be taken into consideration. This article seeks to highlight some of the advances in the understanding of the molecular mechanisms underlying melanoma dissemination.

Delivery of interleukin-15 to B16 melanoma by electroporation leads to tumor regression and long-term survival

Electroporation (EP) is a method used to physically deliver therapeutic molecules such as plasmid DNA directly to tissues. It has been used safely and successfully in clinical studies and preclinical cancer models to deliver genes to a variety of tissues. In cancer research cytokine therapy is emerging as a promising tool that can be used to boost the host response to tumor antigens. The delivery of cytokines as recombinant proteins can result in toxicity and other adverse effects; however the delivery of cytokine genes using EP has been shown to be safe and effective. Interleukin 15 (IL-15) is a cytokine that promotes the innate as well as the adaptive immune response to cancer cells and bacterial pathogens. In this study we used EP to deliver a human IL-15 plasmid (phIL-15) directly to tumors to examine its anti-cancer effects. B16.F10 melanoma tumors were induced in C57BL/6J mice and phIL-15 was delivered three times over the course of a week. Expression of the transgene, tumor volume, long-term survival and resistance to challenge were monitored in these animals. Delivery of IL-15 plasmid by EP resulted in increased IL-15 expression within the tumor compared to the injection only control. This expression peaked at 12 to 18 hours after the first delivery and was sustained at lower levels after the second and third deliveries. The delivery of the phIL-15 resulted in tumor regression, long-term survival and greater protection against tumor recurrence when cancer cells were reintroduced compared to control plasmid. From these results we can conclude that the delivery of IL-15 plasmid to tumors using EP is a promising avenue to investigate for its anti-tumor effects, however more work needs to be done to increase the stability of the gene once it is delivered and to elucidate the anti-tumor mechanism.

Narrow-band UVB radiation promotes dendrite formation by activating Rac1 in B16 melanoma cells

Melanocytes are found scattered throughout the basal layer of the epidermis. Following hormone or ultraviolet (UV) light stimulation, the melanin pigments contained in melanocytes are transferred through the dendrites to the surrounding keratinocytes to protect against UV light damage or carcinogenesis. This has been considered as a morphological indicator of melanocytes and melanoma cells. Small GTPases of the Rho family have been implicated in the regulation of actin reorganization underlying dendrite formation in melanocytes and melanoma cells. It has been proven that ultraviolet light plays a pivotal role in melanocyte dendrite formation; however, the molecular mechanism underlying this process has not been fully elucidated. The effect of small GTPases, such as Rac1 and RhoA, on the morphology of B16 melanoma cells treated with narrow-band UVB radiation was investigated. The morphological changes were observed under a phase contrast microscope and the F-actin microfilament of the cytoskeleton was observed under a laser scanning confocal microscope. The pull-down assay was performed to detect the activity of the small GTPases Rac1 and RhoA. The morphological changes were evident, with globular cell bodies and increased numbers of tree branch-like dendrites. The cytoskeletal F-actin appeared disassembled following narrow-band UVB irradiation of B16 melanoma cells. Treatment of B16 melanoma cells with narrow-band UVB radiation resulted in the activation of Rac1 in a time-dependent manner. In conclusion, the present study may provide a novel method through which narrow-band UVB radiation may be used to promote dendrite formation by activating the Rac1 signaling pathway, resulting in F-actin rearrangement in B16 melanoma cells.

The role of the hippo pathway in melanocytes and melanoma

The Hippo signaling pathway comprises a series of cytoplasmic tumor suppressor proteins including Merlin and the Lats1/2 and MST1/2 kinases, and is thought to play a critical role in determining the sizes of organs and tissues. The Hippo pathway is regulated upstream by extracellular mechanosensory signaling arising from cell shape and polarity, as well as by a variety of extracellular signaling molecules. When active, the pathway maintains the transcriptional activators Yes-associated protein (YAP) and TAZ in phosphorylated forms in the cytoplasm, preventing cell proliferation. When the Hippo pathway is inactivated, YAP and TAZ are translocated to the nucleus and induce the expression of a variety of proteins concerned with entry into the cell division cycle, such as cyclin D1 and Fox M1, as well as the inhibition of apoptosis. The failure of the Hippo pathway has been implicated in the development of many different types of cancer but there is limited information available as to its involvement in melanoma. We hypothesize here firstly that the Hippo pathway is involved in maintaining density of cutaneous melanocytes on the basement membrane at the junction of the epidermis and the dermis, and secondly, that its function is disturbed in melanoma. We have analyzed a series of 23 low passage human melanoma lines as well as cultured normal melanoma, and find that melanocytes, as well as all melanoma cell lines examined express TAZ. Melanocytes and most melanoma lines also express YAP. E-cadherin, an upstream regulator of the Hippo pathway, and Axl, a receptor tyrosine kinase regulated by the Hippo pathway, are expressed in melanocytes and in several melanoma cell lines. These observations, together with published evidence for the presence of Merlin, Lats1/2, and MST1/2 in melanocytes and melanoma cells, support the hypothesis that the Hippo pathway is an important component of melanocyte and melanoma behavior.

Heterogeneity of neural crest-derived melanocytes

The majority of melanocytes originate from the neural crest cells (NCC) that migrate, spread on the whole embryo’s body to form elements of the nervous system and skeleton, endocrinal glands, muscles and melanocytes. Human melanocytes differentiate mainly from the cranial and trunk NCC. Although melanocyte development has traditionally been associated with the dorsally migrating trunk NCC, there is evidence that a part of melanocytes arise from cells migrating ventrally. The ventral NCC differentiate into neurons and glia of the ganglia or Schwann cells. It has been suggested that the precursors for Schwann cells differentiate into melanocytes. As melanoblasts travel through the dermis, they multiply, follow the process of differentiation and invade the forming human fetal epidermis up to third month. After birth, melanocytes lose the ability to proliferate, except the hair melanocytes that renew during the hair cycle. The localization of neural crest-derived melanocytes in non-cutaneous places e.g. eye (the choroid and stroma of the iris and the ciliary body), ear (cells of the vestibular organ, cochlear stria vascularis), meninges of the brain, heart seems to indicate that repertoire of melanocyte functions is much wider than we expected e.g. the protection of tissues from potentially harmful factors (e.g. free radicals, binding toxins), storage ions, and anti-inflammatory action.

In vitro three-dimensional tumor microenvironment models for anticancer drug discovery

Anticancer drug discovery has long been hampered by the poor predictivity of the preclinical models. There is a growing realization that the tumor microenvironment is a critical determinant of the response of cancer cells to therapeutic agents. The past 5 years have seen a great deal of progress in our understanding of how the three-dimensional microenvironment modulates the signaling behavior of tumor cells. The present review discusses how three-dimensional in vitro cell culture models can benefit cancer drug discovery through an accurate modeling of the tumor microenvironment, leading to more physiologically relevant experimental outcomes.

Skin melanocytes: biology and development

In the human skin, melanocytes are present in the epidermis and hair follicles. The basic features of these cells are the ability to melanin production and the origin from neural crest cells. This last element is important because there are other cells able to produce melanin but of different embryonic origin (pigmented epithelium of retina, some neurons, adipocytes). The life cycle of melanocyte consists of several steps including differentiation of melanocyte lineage/s from neural crest, migration and proliferation of melanoblasts, differentiation of melanoblasts into melanocytes, proliferation and maturation of melanocytes at the target places (activity of melanogenic enzymes, melanosome formation and transport to keratinocytes) and eventual cell death (hair melanocytes). Melanocytes of the epidermis and hair are cells sharing some common features but in general they form biologically different populations living in unique niches of the skin.

Topobiology of human pigmentation: P-cadherin selectively stimulates hair follicle melanogenesis

P-cadherin serves as a major topobiological cue in mammalian epithelium. In human hair follicles (HFs), it is prominently expressed in the inner hair matrix that harbors the HF pigmentary unit. However, the role of P-cadherin in normal human pigmentation remains unknown. As patients with mutations in the gene that encodes P-cadherin show hypotrichosis and fair hair, we explored the hypothesis that P-cadherin may control HF pigmentation. When P-cadherin was silenced in melanogenically active organ-cultured human scalp HFs, this significantly reduced HF melanogenesis and tyrosinase activity as well as gene and/or protein expression of gp100, stem cell factor, c-Kit, and microphthalmia-associated transcription factor (MITF), both in situ and in isolated human HF melanocytes. Instead, epidermal pigmentation was unaffected by P-cadherin knockdown in organ-cultured human skin. In hair matrix keratinocytes, P-cadherin silencing reduced plasma membrane β-catenin, whereas glycogen synthase kinase 3 beta (GSK3β) and phospho-β-catenin expression were significantly upregulated. This suggests that P-cadherin-GSK3β/Wnt signaling is required for maintaining the expression of MITF to sustain intrafollicular melanogenesis. Thus, P-cadherin-mediated signaling is a melanocyte subtype-specific topobiological regulator of normal human pigmentation, possibly via GSK3β-mediated canonical Wnt signaling.

Oncogenic B-RAF(V600E) signaling induces the T-Box3 transcriptional repressor to repress E-cadherin and enhance melanoma cell invasion

Approximately 50% of melanomas require oncogenic B-RAF^V600E signaling for proliferation, survival and metastasis, and the use of highly selective B-RAF inhibitors has yielded remarkable, albeit short term, clinical responses. Re-activation of signaling downstream of B-RAF is frequently associated with acquired resistance to B-RAF inhibitors, and the identification of B-RAF targets may therefore provide new strategies for managing melanoma. In this report, we applied whole genome expression analyses to reveal that oncogenic B-RAF^V600E regulates genes associated with epithelial-mesenchymal transition in normal cutaneous human melanocytes. Most prominent was the B-RAF-mediated transcriptional repression of E-cadherin, a keratinocyte-melanoma adhesion molecule whose loss is intimately associated with melanoma invasion and metastasis. Here we identify a link between oncogenic B-RAF, the transcriptional repressor Tbx3 and E-cadherin. We show that B-RAF^V600E induces the expression of Tbx3, which potently represses E-cadherin expression in melanocytes and melanoma cells. Tbx3 expression is normally restricted to developmental embryonic tissues, promoting cell motility but is also aberrantly increased in various cancers and has been linked to tumor cell invasion and metastasis. We propose that this B-RAF/Tbx3/E-cadherin pathway plays a critical role in promoting the metastasis of B-RAF mutant melanomas.

CXCR7 mediates SDF1-induced melanocyte migration

Melanoblasts are derived from the neural crest and migrate to the dermal/epidermal border of skin and hair bulges. Although melanoblast migration during embryogenesis has been well investigated, there are only a few reports regarding the migration of mature melanocytes. Here, we demonstrate that a chemokine, stromal-derived factor-1 (SDF1, also known as CXCL12), and one of its receptor CXCR7 regulate normal human epidermal melanocyte (NHEM) migration. We found that SDF1 induces the directional migration of NHEMs. Interestingly, although both CXCR4 and CXCR7 are expressed in NHEMs, blockade of CXCR4 using a CXCR4-specific neutralizing antibody did not exert any influence on the SDF1-induced migration of NHEMs, whereas blockade of CXCR7 using a CXCR7-specific neutralizing antibody did influence migration. Furthermore, SDF1-induced NHEMs migration exhibited the early hallmark events of CXCR7 signaling associated with MAP kinase activation. It is known that the phosphorylation of ERK through CXCR7 signaling is mediated by β-arrestins. The treatment of NHEMs with SDF1 resulted in the phosphorylation of ERK in a β-arrestin 2-dependent manner. These results suggest that melanocytes may have a unique mechanism of migration via SDF1/CXCR7 signaling that is different from that of other cell types.

Human eccrine sweat gland cells turn into melanin-uptaking keratinocytes in dermo-epidermal skin substitutes

Recently, Biedermann et al. (2010) have demonstrated that human eccrine sweat gland cells can develop a multilayered epidermis. The question still remains whether these cells can fulfill exclusive and very specific functional properties of epidermal keratinocytes, such as the incorporation of melanin, a feature absent in sweat gland cells. We added human melanocytes to eccrine sweat gland cells to let them develop into an epidermal analog in vivo. The interaction between melanocytes and sweat gland-derived keratinocytes was investigated. The following results were gained: (1) macroscopically, a pigmentation of the substitutes was seen 2-3 weeks after transplantation; (2) we confirmed the development of a multilayered, stratified epidermis with melanocytes distributed evenly throughout the basal layer; (3) melanocytic dendrites projected to suprabasal layers; and (4) melanin was observed to be integrated into former eccrine sweat gland cells. These skin substitutes were similar or equal to skin substitutes cultured from human epidermal keratinocytes. The only differences observed were a delay in pigmentation and less melanin uptake. These data suggest that eccrine sweat gland cells can form a functional epidermal melanin unit, thereby providing striking evidence that they can assume one of the most characteristic keratinocyte properties.

Constitutive gray hair in mice induced by melanocyte-specific deletion of c-Myc

c-Myc is involved in the control of diverse cellular processes and implicated in the maintenance of different tissues including the neural crest. Here, we report that c-Myc is particularly important for pigment cell development and homeostasis. Targeting c-Myc specifically in the melanocyte lineage using the floxed allele of c-Myc and Tyr::Cre transgenic mice results in a congenital gray hair phenotype. The gray coat color is associated with a reduced number of functional melanocytes in the hair bulb and melanocyte stem cells in the hair bulge. Importantly, the gray phenotype does not progress with time, suggesting that maintenance of the melanocyte through the hair cycle does not involve c-Myc function. In embryos, at E13.5, c-Myc-deficient melanocyte precursors are affected in proliferation in concordance with a reduction in numbers, showing that c-Myc is required for the proper melanocyte development. Interestingly, melanocytes from c-Myc-deficient mice display elevated levels of the c-Myc paralog N-Myc. Double deletion of c-Myc and N-Myc results in nearly complete loss of the residual pigmentation, indicating that N-Myc is capable of compensating for c-Myc loss of function in melanocytes.

Melanophore migration and survival during zebrafish adult pigment stripe development require the immunoglobulin superfamily adhesion molecule Igsf11

The zebrafish adult pigment pattern has emerged as a useful model for understanding the development and evolution of adult form as well as pattern-forming mechanisms more generally. In this species, a series of horizontal melanophore stripes arises during the larval-to-adult transformation, but the genetic and cellular bases for stripe formation remain largely unknown. Here, we show that the seurat mutant phenotype, consisting of an irregular spotted pattern, arises from lesions in the gene encoding Immunoglobulin superfamily member 11 (Igsf11). We find that Igsf11 is expressed by melanophores and their precursors, and we demonstrate by cell transplantation and genetic rescue that igsf11 functions autonomously to this lineage in promoting adult stripe development. Further analyses of cell behaviors in vitro, in vivo, and in explant cultures ex vivo demonstrate that Igsf11 mediates adhesive interactions and that mutants for igsf11 exhibit defects in both the migration and survival of melanophores and their precursors. These findings identify the first in vivo requirements for igsf11 as well as the first instance of an immunoglobulin superfamily member functioning in pigment cell development and patterning. Our results provide new insights into adult pigment pattern morphogenesis and how cellular interactions mediate pattern formation.

Vertebrate pigment patterns are stunningly diverse and have been an important model of pattern formation for more than a century. Nevertheless, we still know remarkably little about the genes and cell behaviors that underlie the generation of specific patterns. To elucidate such mechanisms, a large number of pigment pattern mutants have been isolated in the genetically tractable zebrafish. Instead of the normal horizontal stripe pattern, many of these mutants exhibit spots of varying sizes and degrees of organization. Here, we show that one such mutant, seurat, named for the 19th century pointillist, George Seurat, exhibits lesions in the gene encoding a classical cell adhesion molecule (CAM) of the immunoglobulin superfamily, Igsf11. We find that Igsf11 mediates cell adhesion and promotes the migration and survival of melanophores and their precursors during adult stripe formation. These results are exciting because they are the first time that a CAM has been implicated in pigment pattern formation, despite the long-standing expectation that such molecules might be required to regulate adhesive interactions during these events. These cellular phenotypes further represent the first known in vivo functions for Igsf11 and point to the potential for similar activities amongst the rich diversity of immunoglobulin superfamily members.

Matrix metalloproteinase-2 promotes αvβ3 integrin-mediated adhesion and migration of human melanoma cells by cleaving fibronectin

BACKGROUND

Matrix metalloproteinase-2 (MMP-2) is a key regulator in the migration of tumor cells. αvβ3 integrin has been reported to play a critical role in cell adhesion and regulate the migration of tumor cells by promoting MMP-2 activation. However, little is known about the effects of MMP-2 on αvβ3 integrin activity and αvβ3 integrin-mediated adhesion and migration of tumor cells.

METHODOLOGY/PRINCIPAL FINDINGS

Human melanoma cells were seeded using an agarose drop model and/or subjected to in vitro analysis using immunofluorescence, adhesion, migration and invasion assays to investigate the relationship between active MMP-2 and αvβ3 integrin during the adhesion and migration of the tumor cells. We found that MMP-2 was localized at the leading edge of spreading cells before αvβ3 integrin. αvβ3 integrin-mediated adhesion and migration of the tumor cells were inhibited by a MMP-2 inhibitor. MMP-2 cleaved fibronectin into small fragments, which promoted the adhesion and migration of the tumor cells.

CONCLUSION/SIGNIFICANCE

MMP-2 cleaves fibronectin into small fragments to enhance the adhesion and migration of human melanoma cells mediated by αvβ3 integrin. These results indicate that MMP-2 may guide the direction of the tumor cell migration.

GSK3β inhibition blocks melanoma cell/host interactions by downregulating N-cadherin expression and decreasing FAK phosphorylation

This study addresses the role of glycogen synthase kinase (GSK)-3β signaling in the tumorigenic behavior of melanoma. Immunohistochemical staining revealed GSK3β to be focally expressed in the invasive portions of 12 and 33% of primary and metastatic melanomas, respectively. GSK3 inhibitors and small interfering RNA (siRNA) knockdown of GSK3β were found to inhibit the motile behavior of melanoma cells in scratch wound, three-dimensional collagen-implanted spheroid, and modified Boyden chamber assays. Functionally, inhibition of GSK3β signaling was found to suppress N-cadherin expression at the messenger RNA and protein levels, and was associated with decreased expression of the transcription factor Slug. Pharmacological and genetic ablation of GSK3β signaling inhibited the adhesion of melanoma cells to both endothelial cells and fibroblasts and prevented transendothelial migration, an effect rescued by the forced overexpression of N-cadherin. A further role for GSK3β signaling in invasion was suggested by the ability of GSK3β inhibitors and siRNA knockdown to block phosphorylation of focal adhesion kinase (FAK) and increase the size of focal adhesions. In summary, we have, to our knowledge, demonstrated a previously unreported role for GSK3β in modulating the motile and invasive behavior of melanoma cells through N-cadherin and FAK. These studies suggest the potential therapeutic utility of inhibiting GSK3β in defined subsets of melanoma.

E-cadherin polymorphisms and susceptibility to arsenic-related skin lesions in West Bengal, India

OBJECTIVES

Although suppression of E-cadherin gene (CDH1) expression and exposure to arsenic have separately been associated with skin lesions, the combined effects of this "gene-environment" interaction have not been explored previously.

STUDY DESIGN

A population-based cross-sectional survey.

METHOD

This study involved 100 cases with skin lesions and 100 controls who were family members with no lesions. The subjects were recruited from villages and hamlets in northern Nadia Province, West Bengal. Each participant was required to undergo a detailed face-to-face interview; provide spot urine sample; provide saliva sample; and sign a consent form. The type and severity of skin lesions were assessed during a general medical examination of each participant in the field. The following 16 single nucleotide polymorphisms (SNPs) of the CDH1 were measured using DNA extracted from saliva samples: rs16260, rs5030625, rs155364, rs155808, rs155807, rs2303646, rs2059254, rs9925923, rs12919719, rs7188750, rs9989407, rs7196495, rs7196661, rs13689, rs12599393, and rs1862748.

RESULTS

The main effects of SNPs on the risk for skin lesions were borderline for rs7196661 (p-value=0.092), rs7196495 (p-value=0.090), and rs12919719 (p-value=0.065); the strongest association was found for rs9989407 (p-value=0.058). Several SNPs, however, showed that the T>T genotype carriers are at higher relative risk for skin lesions compared to carriers of the C>C or C>T genotypes; these results need to be confirmed in a larger study. The main effects of some of the SNPs and genotype frequencies on the severity of skin lesions were found to be relatively weak.

CONCLUSIONS

This is the first study that indicates that CDH1 polymorphisms can contribute to the etiology of premalignant skin lesions in people chronically exposed to arsenic in drinking water, and that this gene may be a factor in individual susceptibility to cutaneous diseases.

The use of an in vitro 3D melanoma model to predict in vivo plasmid transfection using electroporation

A large-scale in vitro 3D tumor model was generated to evaluate gene delivery procedures in vivo. This 3D tumor model consists of a "tissue-like" spheroid that provides a micro-environment supportive of melanoma proliferation, allowing cells to behave similarly to cells in vivo. This functional spheroid measures approximately 1 cm in diameter and can be used to effectively evaluate plasmid transfection when testing various electroporation (EP) electrode applicators. In this study, we identified EP conditions that efficiently transfect green fluorescent protein (GFP) and interleukin 15 (IL-15) plasmids into tumor cells residing in the 3D construct. We found that plasmids delivered using a 6-plate electrode applying 6 pulses with nominal electric field strength of 500 V/cm and pulse-length of 20 ms produced significant increase of GFP (7.3-fold) and IL-15 (3.0-fold) expression compared to controls. This in vitro 3D model demonstrates the predictability of cellular response toward delivery techniques, limits the numbers of animals employed for transfection studies, and may facilitate future developments of clinical trials for cancer therapies in vivo.

Fibroblasts contribute to melanoma tumor growth and drug resistance

The role of tumor-stromal interactions in progression is generally well accepted, but their role in initiation or treatment is less well understood. It is now generally agreed that, rather than consisting solely of malignant cells, tumors consist of a complex dynamic mixture of cancer cells, host fibroblasts, endothelial cells and immune cells that interact with each other and microenvironmental factors to drive tumor progression. We are particularly interested in stromal cells (for example fibroblasts) and stromal factors (for example fibronectin) as important players in tumor progression since they have also been implicated in drug resistance. Here we develop an integrated approach to understand the role of such stromal cells and factors in the growth and maintenance of tumors as well as their potential impact on treatment resistance, specifically in application to melanoma. Using a suite of experimental assays we show that melanoma cells can stimulate the recruitment of fibroblasts and activate them, resulting in melanoma cell growth by providing both structural (extracellular matrix proteins) and chemical support (growth factors). Motivated by these experimental results we construct a compartment model and use it to investigate the roles of both stromal activation and tumor aggressiveness in melanoma growth and progression. We utilize this model to investigate the role fibroblasts might play in melanoma treatment resistance and the clinically observed flare phenomenon that is seen when a patient, who appears resistant to a targeted drug, is removed from that treatment. Our model makes the unexpected prediction that targeted therapies may actually hasten tumor progression once resistance has occurred. If confirmed experimentally, this provocative prediction may bring important new insights into how drug resistance could be managed clinically.

Gene network analyses point to the importance of human tissue kallikreins in melanoma progression

Background

A wide variety of high-throughput microarray platforms have been used to identify molecular targets associated with biological and clinical tumor phenotypes by comparing samples representing distinct pathological states.

Methods

The gene expression profiles of human cutaneous melanomas were determined by cDNA microarray analysis. Next, a robust analysis to determine functional classifications and make predictions based on data-oriented hypotheses was performed. Relevant networks that may be implicated in melanoma progression were also considered.

Results

In this study we aimed to analyze coordinated gene expression changes to find molecular pathways involved in melanoma progression. To achieve this goal, ontologically-linked modules with coordinated expression changes in melanoma samples were identified. With this approach, we detected several gene networks related to different modules that were induced or repressed during melanoma progression. Among them we observed high coordinated expression levels of genes involved in a) cell communication (KRT4, VWF and COMP); b) epidermal development (KLK7, LAMA3 and EVPL); and c) functionally related to kallikreins (EVPL, KLK6, KLK7, KLK8, SERPINB13, SERPING1 and SLPI). Our data also indicated that hKLK7 protein expression was significantly associated with good prognosis and survival.

Conclusions

Our findings, derived from a different type of analysis of microarray data, highlight the importance of analyzing coordinated gene expression to find molecular pathways involved in melanoma progression.

Characteristic distribution of melanin columns in the cornified layer of acquired acral nevus: an important clue for histopathologic differentiation from early acral melanoma

Clinical and histopathologic differentiation between early acral melanoma and acral nevus is often difficult. Dermoscopy is helpful in this differentiation. On dermoscopy, early acral melanoma shows the parallel ridge pattern showing band-like pigmentation on the ridges of the surface skin markings, whereas a representative dermoscopic pattern in acquired acral nevus is the parallel furrow pattern showing parallel linear pigmentation along the surface furrows. The parallel furrow pattern suggests that melanocytes of acral nevus preferentially proliferate in the crista profunda limitans, an epidermal rete ridge underlying the surface furrow. In the present study, however, we found that in 13 of 18 acquired acral nevi, proliferation of melanocytes were detected not only in the crista profunda limitans but also in the crista profunda intermedia (CPI), an epidermal rete ridge underlying the surface ridge. Very interestingly, Fontana-Masson staining of these acral nevi revealed that even when proliferation of melanocytes was prominent in the CPI, melanin granules in the cornified layer were observed as regular melanin columns situated under the surface furrows and were hardly detected under the surface ridges. These findings indicate that in acral nevus, melanin granules produced by melanocytes in the CPI are not transferred to the upper epidermis. Hence, we must be careful not to overdiagnose an acral melanocytic lesion in which an increased number of melanocytes are detected in the CPI. Even in such a case, if melanin granules in the cornified layer are detected as melanin columns regularly distributed under the surface furrows, the lesion is strongly suggested to be a benign acral nevus.

The "intraepidermal epithelioma" revisited: immunohistochemical study of the borst-jadassohn phenomenon

The true nature of the so-called intraepidermal epithelioma of Borst-Jadassohn is poorly understood; whether this represents a distinct tumor or a morphological phenomenon [Borst-Jadassohn phenomenon (BJP)] shared by different entities has been debated. So far, no detailed immunohistochemical studies have been performed to address this issue. The aim of our study was to get further insight into the pathogenesis of the intraepidermal epithelioma of Borst-Jadassohn/BJP. Tumors showing the BJP [mainly clonal seborrheic keratoses (cSK) and clonal Bowen disease (cBD)] were studied and compared with typical (nonclonal) counterparts. Cell nests in cSK, cBD, hidroacanthoma simplex (HS), and porocarcinoma (PC) showed strong expression of epidermal growth factor-receptors (EGF-R), Ki-67, p63, and p53. Cell nests of clonal SK and HS (but not of clonal BD or PC) expressed keratin 5/6. The expression of E-cadherin and the number of CD1a+ Langerhans cells were reduced within the nests of all lesions, whereas melanocytes were increased in all of them. Keratins 7 and 19 were not expressed in any of the lesions. Tumors showing the BJP exhibit some immunohistochemical differences, suggesting that they represent separate entities. However, they all show strong expression of EGF-R within intraepidermal keratinocyte nests, suggesting that the epithelial growth factor pathway plays a role in the development of the BJP.