Melanoma development and progression: a conspiracy between tumor and host

The Skin Molecular Ecosystem Holds the Key to Nevogenesis and Melanomagenesis

Early detection of melanoma is critical to good patient outcomes, but we still know little about the mechanisms of early melanoma development. Normal epidermis has many of the sequence variants and genetic architecture disruptions found in both benign nevi, melanomas, and other skin cancers, yet continues to behave more or less normally. One hypothesis is that many melanocytes in this context are "tumor competent" but are regulated by the microenvironment provided by the surrounding keratinocytes to inhibit progress to nevi or melanoma. There is evidence of accumulating disorder in several measures of the genomic and epigenomic landscape from normal skin through nevi to melanoma that may be key to promoting nevogenesis and melanomagenesis.

Biological role and diagnostic utility of ribosomal protein L23a pseudogene 53 in cutaneous melanoma

Background

Skin melanoma is one of the deadliest types of skin cancer and develops from melanocytes. The genetic aberrations in protein-coding genes are well characterized, but little is known about changes in non-coding RNAs (ncRNAs) such as pseudogenes. Ribosomal protein pseudogenes (RPPs) have been described as the largest group of pseudogenes which are dispersed in the human genome.

Materials and methids

We looked deeply at the role of one of them, ribosomal protein L23a pseudogene 53 (RPL23AP53), and its potential diagnostic use. The expression level of RPL23AP53 was profiled in melanoma cell lines using real time quantitative reverse transcription polymerase chain reaction (qRT-PCR) and analyzed based on the Cancer Genome Atlas (TCGA) data depending on BRAF status and clinicopathological parameters. Cellular phenotype, which was associated with RPL23AP53 levels, was described based on the REACTOME pathway browser, Gene Set Enrichment Analysis (GSEA) analysis as well as Immune and ESTIMATE Scores.

Results

We indicted in vitro changes in RPL23AP53 level depending on a cell line, and based on in silico analysis of TCGA samples demonstrated significant differences in RPL23AP53 expression between primary and metastatic melanoma, as well as correlation between RPL23AP53 and overall survival. No differences depending on BRAF status were observed. RPL23AP53 is associated with several signaling pathways and cellular processes.

Conclusions

This study showed that patients with higher expression of RPL23AP53 displayed changed infiltration of lymphocytes, macrophages, and neutrophils compared to groups with lower expression of RPL23AP53. RPL23AP53 pseudogene is differently expressed in melanoma compared with normal tissue and its expression is associated with cellular proliferation. Thus, it may be considered as an indicator of patients' survival and a marker for the immune profile assessment.

The Plasma Membrane Ca2+ Pump PMCA4b Regulates Melanoma Cell Migration through Remodeling of the Actin Cytoskeleton

Simple Summary

Earlier we demonstrated that the plasma membrane Ca²⁺ pump PMCA4b inhibits migration and metastatic activity of BRAF mutant melanoma cells, however, the exact mechanism has not been fully understood. Here we demonstrate that PMCA4b acted through actin cytoskeleton remodeling in generating a low migratory melanoma cell phenotype resulting in increased cell–cell connections, lamellipodia and stress fiber formation. Both proper trafficking and calcium transporting activity of the pump were essential to complete these tasks indicating that controlling Ca²⁺ concentration levels at specific plasma membrane locations such as the cell front played a role. Our findings suggest that PMCA4b downregulation is likely one of the mechanisms that leads to the perturbed cancer cell cytoskeleton organization resulting in enhanced melanoma cell migration and metastasis.

Abstract

We demonstrated that the plasma membrane Ca²⁺ ATPase PMCA4b inhibits migration and metastatic activity of BRAF mutant melanoma cells. Actin dynamics are essential for cells to move, invade and metastasize, therefore, we hypothesized that PMCA4b affected cell migration through remodeling of the actin cytoskeleton. We found that expression of PMCA4b in A375 BRAF mutant melanoma cells induced a profound change in cell shape, cell culture morphology, and displayed a polarized migratory character. Along with these changes the cells became more rounded with increased cell–cell connections, lamellipodia and stress fiber formation. Silencing PMCA4b in MCF-7 breast cancer cells had a similar effect, resulting in a dramatic loss of stress fibers. In addition, the PMCA4b expressing A375 cells maintained front-to-rear Ca²⁺ concentration gradient with the actin severing protein cofilin localizing to the lamellipodia, and preserved the integrity of the actin cytoskeleton from a destructive Ca²⁺ overload. We showed that both PMCA4b activity and trafficking were essential for the observed morphology and motility changes. In conclusion, our data suggest that PMCA4b plays a critical role in adopting front-to-rear polarity in a normally spindle-shaped cell type through F-actin rearrangement resulting in a less aggressive melanoma cell phenotype.

Stromal Cells Present in the Melanoma Niche Affect Tumor Invasiveness and Its Resistance to Therapy

Malignant melanoma is a highly metastatic type of cancer, which arises frequently from transformed pigment cells and melanocytes as a result of long-term UV radiation exposure. In recent years, the incidence of newly diagnosed melanoma patients reached 5% of all cancer cases. Despite the development of novel targeted therapies directed against melanoma-specific markers, patients' response to treatment is often weak or short-term due to a rapid acquisition of drug resistance. Among the factors affecting therapy effectiveness, elements of the tumor microenvironment play a major role. Melanoma niche encompasses adjacent cells, such as keratinocytes, cancer-associated fibroblasts (CAFs), adipocytes, and immune cells, as well as components of the extracellular matrix and tumor-specific physicochemical properties. In this review, we summarize the current knowledge concerning the influence of cancer-associated cells (keratinocytes, CAFs, adipocytes) on the process of melanomagenesis, tumor progression, invasiveness, and the emergence of drug resistance in melanoma. We also address how melanoma can alter the differentiation and activation status of cells present in the tumor microenvironment. Understanding these complex interactions between malignant and cancer-associated cells could improve the development of effective antitumor therapeutic strategies.

A Framework of Major Tumor-Promoting Signal Transduction Pathways Implicated in Melanoma-Fibroblast Dialogue

Simple Summary

Melanoma cells reside in a complex stromal microenvironment, which is a critical component of disease onset and progression. Mesenchymal or fibroblastic cell type are the most abundant cellular element of tumor stroma. Factors secreted by melanoma cells can activate non-malignant associated fibroblasts to become melanoma associate fibroblasts (MAFs). MAFs promote tumorigenic features by remodeling the extracellular matrix, supporting tumor cells proliferation, neo-angiogenesis and drug resistance. Additionally, environmental factors may contribute to the acquisition of pro-tumorigenic phenotype of fibroblasts. Overall, in melanoma, perturbed tissue homeostasis contributes to modulation of major oncogenic intracellular signaling pathways not only in tumor cells but also in neighboring cells. Thus, targeted molecular therapies need to be considered from the reciprocal point of view of melanoma and stromal cells.

Abstract

The development of a modified stromal microenvironment in response to neoplastic onset is a common feature of many tumors including cutaneous melanoma. At all stages, melanoma cells are embedded in a complex tissue composed by extracellular matrix components and several different cell populations. Thus, melanomagenesis is not only driven by malignant melanocytes, but also by the altered communication between melanocytes and non-malignant cell populations, including fibroblasts, endothelial and immune cells. In particular, cancer-associated fibroblasts (CAFs), also referred as melanoma-associated fibroblasts (MAFs) in the case of melanoma, are the most abundant stromal cells and play a significant contextual role in melanoma initiation, progression and metastasis. As a result of dynamic intercellular molecular dialogue between tumor and the stroma, non-neoplastic cells gain specific phenotypes and functions that are pro-tumorigenic. Targeting MAFs is thus considered a promising avenue to improve melanoma therapy. Growing evidence demonstrates that aberrant regulation of oncogenic signaling is not restricted to transformed cells but also occurs in MAFs. However, in some cases, signaling pathways present opposite regulation in melanoma and surrounding area, suggesting that therapeutic strategies need to carefully consider the tumor–stroma equilibrium. In this novel review, we analyze four major signaling pathways implicated in melanomagenesis, TGF-β, MAPK, Wnt/β-catenin and Hyppo signaling, from the complementary point of view of tumor cells and the microenvironment.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Interleukin-33 pretreatment promotes metastatic growth of murine melanoma by reducing the cytotoxic capacity of CD8+ T cells and enhancing regulatory T cells

Interleukin-33 (IL-33) regulates innate and acquired immune response to pathogens, self-antigens and tumors. IL-33 effects on tumors depend on the dose and mode of administration along with the type of malignancy. We studied the effects of IL-33 on the development of primary and metastatic melanoma induced by B16-F1 cell line in C57BL/6 mice. Intraperitoneally applied IL-33 restricts primary tumor growth. When administered intranasally 3 days prior to the intravenous injection of the tumor cells, IL-33 promoted growth of B16-F1 melanoma metastases, while B16-F10 gave massive metastases independently of IL-33. To mimic natural dissemination, we next used a limited number (5 × 10⁴) of B16-F1 cells intravenously followed by application of IL-33 intraperitoneally. IL-33 increased the size of metastases (10.96 ± 3.96 mm²) when compared to the control group (0.86 ± 0.39 mm²), without changing incidence and number of metastases. IL-33 increased expression of ST2 on both tumor and immune cells in metastases. Also, IL-33 enhanced eosinophils and anti-tumor NK cells in the lung. The striking finding was reduced cytotoxicity of CD8⁺ T cells derived from metastatic lung of IL-33 injected mice. IL-33 reduced the percentage of TNF-α⁺ and IFN-γ⁺ CD8⁺ T cells while increasing the frequency of CD8⁺ T cells that express inhibitory molecules (PD-1, KLRG-1 and CTLA-4). There was a significant accumulation of CD11b⁺Gr-1⁺ myeloid suppressor cells and FoxP3⁺, IL-10⁺ and CTLA-4⁺ regulatory T cells in the metastatic lung of IL-33 injected mice. The relevance of IL-33 for melanoma metastases was also documented in a significantly increased level of serum IL-33 in stage III melanoma patients.

Tumour Microenvironment in Skin Carcinogenesis

Tumour microenvironment is a complex system comprising cells and molecules that will provide the necessary conditions for tumour development and progression. Cells residing in the tumour microenvironment gain specific phenotypes and specific functions that are pro-tumorigenic. Tumour progression is in fact a combination between tumour cell characteristics and its interplay with tumour microenvironment. This dynamic network will allow tumour cells to grow, migrate and invade tissues. In the present chapter, we are highlighting some traits that characterise tumour microenvironment in basal cell carcinoma, squamous cell carcinoma and cutaneous melanoma. In skin cancers, there are some common tumour microenvironment characteristics such as the presence of tumour-associated macrophages and regulatory T lymphocytes that are non-tumour cells promoting tumorigenesis. There are also skin cancer type differences in terms of tumour microenvironment characteristics. Thus, markers such as macrophage migration inhibitory factor in melanoma or the extraordinary diverse genetic make-up in the cancer-associated fibroblasts associated to squamous cell carcinoma are just a few of specific traits in skin cancer types. New technological advances for evaluation of tumour environment are presented. Thus, non-invasive skin imaging techniques such as reflectance confocal microscopy can evaluate skin tumour inflammatory infiltrates for density and cellular populations. Analysing tumour micromedium in depth may offer new insights into cancer therapy and identify new therapy targets.

Adipocytes sensitize melanoma cells to environmental TGF-β cues by repressing the expression of miR-211

Transforming growth factor-β (TGF-β) superfamily members are critical signals in tissue homeostasis and pathogenesis. Melanoma grows in the epidermis and invades the dermis before metastasizing. This disease progression is accompanied by increased sensitivity to microenvironmental TGF-β. Here, we found that skin fat cells (adipocytes) promoted metastatic initiation by sensitizing melanoma cells to TGF-β. Analysis of melanoma clinical samples revealed that adipocytes, usually located in the deeper hypodermis layer, were present in the upper dermis layer within proximity to in situ melanoma cells, an observation that correlated with disease aggressiveness. In a coculture system, adipocytes secreted the cytokines IL-6 and TNF-α, which induced a proliferative-to-invasive phenotypic switch in melanoma cells by repressing the expression of the microRNA miR-211. In a xenograft model, miR-211 exhibited a dual role in melanoma progression, promoting cell proliferation while inhibiting metastatic spread. Bioinformatics and molecular analyses indicated that miR-211 directly targeted and repressed the translation of TGFBR1 mRNA, which encodes the type I TGF-β receptor. Hence, through this axis of cytokine-mediated repression of miR-211, adipocytes increased the abundance of the TGF-β receptor in melanoma cells, thereby enhancing cellular responsiveness to TGF-β ligands. The induction of TGF-β signaling, in turn, resulted in a proliferative-to-invasive phenotypic switch in cultured melanoma cells. Pharmacological inhibition of TGF-β prevented these effects. Our findings further reveal a molecular link between fat cells and metastatic progression in melanoma that might be therapeutically targeted in patients.

Molecular targets for tivantinib (ARQ 197) and vasculogenic mimicry in human melanoma cells

Tivantinib (TivB) was reported previously to target MET and microtubule assembly in different cells resulting in cytotoxicity. However, its other cellular targets remain unknown, especially the proteins involved in focal adhesion and cytoskeletal organization. We studied the effect of TivB on vinculin a focal adhesion protein, and RhoC, a GTPase which promote the reorganization of cytoskeleton. Biomolecules involved in vasculogenic mimicry (VM) previously not reported in melanoma, and their susceptibility to TivB was also evaluated. TivB affects the viability and apoptosis of human melanoma cells depending on the cell type. Vinculin and RhoC were increased in the presence of TivB and affected the integrity of actin filaments and altered the cellular morphology. TivB disrupts the VM exhibited by melanoma cells in 3D matrix. Roundabout Guidance Receptor 4 (Robo4), a receptor protein implicated in axonal guidance and angiogenesis and its ligand Slit2 are expressed in human C8161 and WM793 melanoma cells, but absent in other melanoma cells including normal melanocytes. VM is more prominent in C8161 cells and could be blocked by siRNA mediated silencing of Robo4 mRNA, but TivB does not affect Robo4 in C8161 cells. Immunoblot analysis indicated no changes in Robo4 and Slit2 protein expression, however, both vinculin and RhoC protein increased in TivB treated melanoma cells. These results suggest that TivB affects cell cytoskeleton and morphology by altering proteins such as vinculin and RhoC. Our studies indicate TivB could target molecules other than MET in melanoma cells, which may provide insight into its alternate mechanism of action.

BRN2, a POUerful driver of melanoma phenotype switching and metastasis

The POU domain family of transcription factors play a central role in embryogenesis and are highly expressed in neural crest cells and the developing brain. BRN2 is a class III POU domain protein that is a key mediator of neuroendocrine and melanocytic development and differentiation. While BRN2 is a central regulator in numerous developmental programs, it has also emerged as a major player in the biology of tumourigenesis. In melanoma, BRN2 has been implicated as one of the master regulators of the acquisition of invasive behaviour within the phenotype switching model of progression. As a mediator of melanoma cell phenotype switching, it coordinates the transition to a dedifferentiated, slow cycling and highly motile cell type. Its inverse expression relationship with MITF is believed to mediate tumour progression and metastasis within this model. Recent evidence has now outlined a potential epigenetic switching mechanism in melanoma cells driven by BRN2 expression that induces melanoma cell invasion. We summarize the role of BRN2 in tumour cell dissemination and metastasis in melanoma, while also examining it as a potential metastatic regulator in other tumour models.

A 3D Organotypic Melanoma Spheroid Skin Model

Malignant transformation of melanocytes, the pigment cells of human skin, causes formation of melanoma, a highly aggressive cancer with increased metastatic potential. Recently, mono-chemotherapies continue to improve by melanoma specific combination therapies with targeted kinase inhibitors. Still, metastatic melanoma remains a life-threatening disease because tumors exhibit primary resistance or develop resistance to novel therapies, thereby regaining tumorigenic capacity. In order to improve the therapeutic success of malignant melanoma, the determination of molecular mechanisms conferring resistance against conventional treatment approaches is necessary; however, it requires innovative cellular in vitro models. Here, we introduce an in vitro three-dimensional (3D) organotypic melanoma spheroid model that can portray the in vivo architecture of malignant melanoma and may warrant new insights into intra-tumoral as well as tumor-host interactions. The model incorporates defined numbers of mature and differentiated melanoma spheroids in a 3D human full skin reconstruction model consisting of primary skin cells. The cellular composition and differentiation status of the embedded melanoma spheroids is similar to the one of cutaneous melanoma metastasis in vivo. Using this organotypic melanoma spheroid model as a drug screening platform may support the identification of responders to selected combination therapies, while sparing the unnecessary treatment burden for non-responders, thereby increasing the benefit of therapeutic interventions.

Spatiotemporal Labeling of Melanocytes in Mice

Melanocytes are pigment producing cells in the skin that give rise to cutaneous malignant melanoma, which is a highly aggressive and the deadliest form of skin cancer. Studying melanocytes in vivo is often difficult due to their small proportion in the skin and the lack of specific cell surface markers. Several genetically-engineered mouse models (GEMMs) have been created to specifically label the melanocyte compartment. These models give both spatial and temporal control over the expression of a cellular ‘beacon’ that has an added benefit of inducible expression that can be activated on demand. Two powerful models that are discussed in this review include the melanocyte-specific, tetracycline-inducible green fluorescent protein expression system (iDct-GFP), and the fluorescent ubiquitination-based cell cycle indicator (FUCCI) model that allows for the monitoring of the cell-cycle. These two systems are powerful tools in studying melanocyte and melanoma biology. We discuss their current uses and how they could be employed to help answer unresolved questions in the fields of melanocyte and melanoma biology.

Macrovipecetin, a C-type lectin from Macrovipera lebetina venom, inhibits proliferation migration and invasion of SK-MEL-28 human melanoma cells and enhances their sensitivity to cisplatin

BACKGROUND

The resistance of melanoma cells to cisplatin restricts its clinical use. Therefore, the search for novel tumor inhibitors and effective combination treatments that sensitize tumor cells to this drug are still needed. We purified macrovipecetin, a novel heterodimeric C-type lectin, from Macrovipera lebetina snake venom and investigated its anti-tumoral effect on its own or combined with cisplatin, in human melanoma cells.

METHODS

Biochemical characterization, in vitro cells assays such as viability, apoptosis, adhesion, migration, invasion, Western blotting and in silico analysis were used in this study.

RESULTS

Macrovipecetin decreased melanoma cell viability 100 times more than cisplatin. Interestingly, when combined with the drug, macrovipecetin enhanced the sensitivity of SK-MEL-28 cells by augmenting their apoptosis through increased expression of the apoptosis inducing factor (AIF) and activation of ERK_1/2, p38, AKT and NF-κB. Moreover, macrovipecetin alone or combined with cisplatin induced the expression of TRADD, p53, Bax, Bim and Bad and down-regulated the Bcl-2 expression and ROS levels in SK-MEL-28 cells. Interestingly, these treatments impaired SK-MEL-28 cell adhesion, migration and invasion through modulating the function and expression of αvβ3 integrin along with regulating E-cadherin, vimentin, β-catenin, c-Src and RhoA expression. In silico study suggested that only the α chain of macrovipecetin interacts with a region overlapping the RGD motif binding site on this integrin.

CONCLUSIONS

We validated the antitumor effect of macrovipecetin when combined, or not, with cisplatin on SK-MEL-28 cells.

GENERAL SIGNIFICANCE

The presented work proposes the potential use of macrovipecetin and cisplatin in combination as an effective anti-melanoma treatment.

Biomarkers in Bladder Cancer: Present Status and Perspectives

Bladder cancers are a mixture of heterogeneous cell populations, and numerous factors are likely to be involved in dictating their recurrence, progression and the patient's survival. For any candidate prognostic marker to have considerable clinical relevance, it must add some predictive capacity beyond that offered by conventional clinical and pathologic parameters. Here, the current situation in bladder cancer research with respect to identification of suitable prognostic markers is reviewed. A number of individual molecular markers that might predict bladder cancer recurrence and progression have been identified but many are not sufficiently sensitive or specific for the whole spectrum of bladder cancer diseases seen in routine clinical practice. These limitations have led to interest in other molecular parameters that could enable more accurate prognosis for bladder cancer patients. Of particular interest is the epigenetic silencing of tumor suppressor genes. Since the methylation of these genes can correlate with a poor prognosis, the methylation profile may represent a new biomarker that indicates the risk of transitional cell carcinoma development. In addition, bladder cancer research is likely to be revolutionized by high-throughput molecular technologies, which allow rapid and global gene expression analysis of thousands of tumor samples. Initial studies employing these technologies have considerably expanded our ability to classify bladder cancers with respect to their survivability. Future microarray analyses are likely to reveal particular gene expression signatures that predict the likelihood of bladder cancer progression and recurrence, as well as patient's survival and responsiveness to different anti-cancer therapies, with great specificity and sensitivity.

Emerging Non-Canonical Functions and Regulation by p53: p53 and Stemness

Since its discovery nearly 40 years ago, p53 has ascended to the forefront of investigated genes and proteins across diverse research disciplines and is recognized most exclusively for its role in cancer as a tumor suppressor. Levine and Oren (2009) reviewed the evolution of p53 detailing the significant discoveries of each decade since its first report in 1979. In this review, we will highlight the emerging non-canonical functions and regulation of p53 in stem cells. We will focus on general themes shared among p53's functions in non-malignant stem cells and cancer stem-like cells (CSCs) and the influence of p53 on the microenvironment and CSC niche. We will also examine p53 gain of function (GOF) roles in stemness. Mutant p53 (mutp53) GOFs that lead to survival, drug resistance and colonization are reviewed in the context of the acquisition of advantageous transformation processes, such as differentiation and dedifferentiation, epithelial-to-mesenchymal transition (EMT) and stem cell senescence and quiescence. Finally, we will conclude with therapeutic strategies that restore wild-type p53 (wtp53) function in cancer and CSCs, including RING finger E3 ligases and CSC maintenance. The mechanisms by which wtp53 and mutp53 influence stemness in non-malignant stem cells and CSCs or tumor-initiating cells (TICs) are poorly understood thus far. Further elucidation of p53's effects on stemness could lead to novel therapeutic strategies in cancer research.

Optical clearing of melanoma in vivo: characterization by diffuse reflectance spectroscopy and optical coherence tomography

Melanoma is the most aggressive type of skin cancer, with significant risk of fatality. Due to its pigmentation, light-based imaging and treatment techniques are limited to near the tumor surface, which is inadequate, for example, to evaluate the microvascular density that is associated with prognosis. White-light diffuse reflectance spectroscopy (DRS) and near-infrared optical coherence tomography (OCT) were used to evaluate the effect of a topically applied optical clearing agent (OCA) in melanoma in vivo and to image the microvascular network. DRS was performed using a contact fiber optic probe in the range from 450 to 650 nm. OCT imaging was performed using a swept-source system at 1310 nm. The OCT image data were processed using speckle variance and depth-encoded algorithms. Diffuse reflectance signals decreased with clearing, dropping by ∼ 90% after 45 min. OCT was able to image the microvasculature in the pigmented melanoma tissue with good spatial resolution up to a depth of ∼ 300 μm without the use of OCA; improved contrast resolution was achieved with optical clearing to a depth of ∼ 750 μm in tumor. These findings are relevant to potential clinical applications in melanoma, such as assessing prognosis and treatment responses. Optical clearing may also facilitate the use of light-based treatments such as photodynamic therapy.

sFRP2 in the aged microenvironment drives melanoma metastasis and therapy resistance

Cancer is a disease of ageing. Clinically, aged cancer patients tend to have a poorer prognosis than young. This may be due to accumulated cellular damage, decreases in adaptive immunity, and chronic inflammation. However, the effects of the aged microenvironment on tumour progression have been largely unexplored. Since dermal fibroblasts can have profound impacts on melanoma progression, we examined whether age-related changes in dermal fibroblasts could drive melanoma metastasis and response to targeted therapy. Here we find that aged fibroblasts secrete a Wnt antagonist, sFRP2, which activates a multi-step signalling cascade in melanoma cells that results in a decrease in β-catenin and microphthalmia-associated transcription factor (MITF), and ultimately the loss of a key redox effector, APE1. Loss of APE1 attenuates the response of melanoma cells to DNA damage induced by reactive oxygen species, rendering the cells more resistant to targeted therapy (vemurafenib). Age-related increases in sFRP2 also augment both angiogenesis and metastasis of melanoma cells. These data provide an integrated view of how fibroblasts in the aged microenvironment contribute to tumour progression, offering new possibilities for the design of therapy for the elderly.

β1,6-branched complex-type N-glycans affect FAK signaling in metastatic melanoma cells

Integrin-dependent binding of the cell to extracellular matrix (ECM) is a key activator of the focal adhesion kinase (FAK) signaling pathway. N-glycosylation of integrins affects their interactions with ECM proteins. Using WM266-4 cells with overexpression of β1,6-acetylglucosaminyltransferase V, we showed that β1,6-branched N-glycans increased tyrosine phosphorylation of FAK in metastatic melanoma cells, resulting in enhanced migration on vitronectin (VN). The co-localization of αvβ3 integrin and FAK in focal adhesions of melanoma cells growing on VN indicates their interaction in signal transduction. Melanoma cell migration on VN was mediated by αvβ3 caring overexpressed β1,6-branched structures, important for FAK upregulation.

Developing strategies to predict photodynamic therapy outcome: the role of melanoma microenvironment

Melanoma is among the most aggressive and treatment-resistant human skin cancer. Photodynamic therapy (PDT), a minimally invasive therapeutic modality, is a promising approach to treating melanoma. It combines a non-toxic photoactivatable drug called photosensitizer with harmless visible light to generate reactive oxygen species which mediate the antitumor effects. The aim of this review was to compile the available data about PDT on melanoma. Our comparative analysis revealed a disconnection between several hypotheses generated by in vitro therapeutic studies and in vivo and clinical assays. This fact led us to highlight new preclinical experimental platforms that mimic the complexity of tumor biology. The tumor and its stromal microenvironment have a dynamic and reciprocal interaction that plays a critical role in tumor resistance, and these interactions can be exploited for novel therapeutic targets. In this sense, we review two strategies used by photodynamic researchers: (a) developing 3D culture systems which mimic tumor architecture and (b) heterotypic cultures that resemble tumor microenvironment to favor therapeutic regimen design. After this comprehensive review of the literature, we suggest that new complementary preclinical models are required to better optimize the clinical outcome of PDT on skin melanoma.

Interactions of Melanoma Cells with Distal Keratinocytes Trigger Metastasis via Notch Signaling Inhibition of MITF

The most critical stage in initiation of melanoma metastasis is the radial to vertical growth transition, yet the triggers of this transition remain elusive. We suggest that the microenvironment drives melanoma metastasis independently of mutation acquisition. Here we examined the changes in microenvironment that occur during melanoma radial growth. We show that direct contact of melanoma cells with the remote epidermal layer triggers vertical invasion via Notch signaling activation, the latter serving to inhibit MITF function. Briefly, within the native Notch ligand-free microenvironment, MITF, the melanocyte lineage master regulator, binds and represses miR-222/221 promoter in an RBPJK-dependent manner. However, when radial growth brings melanoma cells into contact with distal differentiated keratinocytes that express Notch ligands, the activated Notch intracellular domain impairs MITF binding to miR-222/221 promoter. This de-repression of miR-222/221 expression triggers initiation of invasion. Our findings may direct melanoma prevention opportunities via targeting specific microenvironments.

Hair follicle disruption facilitates pathogenesis to UVB-induced cutaneous inflammation and basal cell carcinoma development in Ptch(+/-) mice

Hairless mice carrying homozygous mutations in hairless gene manifest rudimentary hair follicles (HFs), epidermal cysts, hairless phenotype, and enhanced susceptibility to squamous cell carcinomas. However, their susceptibility to basal cell carcinomas (BCCs), a neoplasm considered originated from HF-localized stem cells, is unknown. To demonstrate the role of HFs in BCC development, we bred Ptch(+/-)/C57BL6 with SKH-1 hairless mice, followed by brother-sister cross to get F2 homozygous mutant (hairless) or wild-type (haired) mice. UVB-induced inflammation was less pronounced in shaved haired than in hairless mice. In hairless mice, inflammatory infiltrate was found around the rudimentary HFs and epidermal cysts. Expression of epidermal IL1f6, S100a8, vitamin D receptor, repetin, and major histocompatibility complex II, biomarkers depicting susceptibility to cutaneous inflammation, was also higher. In these animals, HF disruption altered susceptibility to UVB-induced BCCs. Tumor onset in hairless mice was 10 weeks earlier than in haired littermates. The incidence of BCCs was significantly higher in hairless than in haired animals; however, the magnitude of sonic hedgehog signaling did not differ significantly. Overall, 100% of hairless mice developed >12 tumors per mouse after 32 weeks of UVB therapy, whereas haired mice developed fewer than three tumors per mouse after 44 weeks of long-term UVB irradiation. Tumors in hairless mice were more aggressive than in haired littermates and manifested decreased E-cadherin and enhanced mesenchymal proteins. These data provide novel evidence that disruption of HFs in Ptch(+/-) mice enhances cutaneous susceptibility to inflammation and BCCs.

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.

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.

Stem cells and targeted approaches to melanoma cure

Melanoma stem cells, also known as malignant melanoma-initiating cells, are identifiable through expression of specific biomarkers such as ABCB5 (ATP-binding cassette, sub-family B (MDR/TAP), member 5), NGFR (nerve growth factor receptor, CD271) and ALDH (aldehyde dehydrogenase), and drive melanoma initiation and progression based on prolonged self-renewal capacity, vasculogenic differentiation and immune evasion. As we will review here, specific roles of these aggressive subpopulations have been documented in tumorigenic growth, metastatic dissemination, therapeutic resistance, and malignant recurrence. Moreover, recent findings have provided pre-clinical proof-of-concept for the potential therapeutic utility of the melanoma stem cell concept. Therefore, melanoma stem cell-directed therapeutic approaches represent promising novel strategies to improve therapy of this arguably most virulent human cancer.

Immune alterations in malignant melanoma and current immunotherapy concepts

INTRODUCTION

Malignant melanoma is a highly aggressive, immunogenic tumor that has the ability to modulate the immune system to its own advantage. Patients with melanoma present numerous cellular immune defects and cytokine abnormalities, all leading to suppression of the host anti-tumor immune response. Innovative treatment strategies can be achieved through employing our knowledge of the melanoma-induced immune alterations.

AREAS COVERED

The authors review comprehensively the immune abnormalities in individuals with melanoma, and provide a summary of currently available melanoma immunotherapy agents that are currently on the market or undergoing clinical trials.

EXPERT OPINION

Ipilimumab, a monoclonal antibody directed against the CTLA-4, is one of the current forefront treatment strategies in malignant melanoma. Novel immunomodulating agents have shown clear activity in patients with malignant melanoma. These include anti-PD-1 and anti-PD-1 ligand antibodies that may soon become important items in the anti-melanoma armamentarium. Combinations of different immunotherapy agents, between themselves or with other agents, are currently being studied in an attempt to further enhance the antineoplastic effect in patients with malignant melanoma.

Therapeutic improvement of a stroma-targeted CRAd by incorporating motives responsive to the melanoma microenvironment

We have previously designed a conditionally replicative oncolytic adenovirus (CRAd) named Ad-F512 that can target both the stromal and the malignant melanoma cell compartments. The replication capacity of this CRAd is driven by a 0.5-Kb SPARC promoter fragment (named F512). To improve CRAd's efficacy, we cloned into F512 motives responsive to hypoxia (hypoxia-responsive element (HRE)) and inflammation (nuclear factor kappa B) to obtain a chimeric promoter named κBF512HRE. Using luciferase as a reporter gene, we observed 10-15-fold increased activity under hypoxia and 10-80-fold induction upon tumor necrosis factor-α addition. We next constructed a CRAd (Ad-κBF512HRE) where E1A activity was under κBF512HRE regulation. Treatment of nude mice harboring established tumors made of a mix of SB2 melanoma cells and WI-38 fibroblasts with Ad-κBF512HRE led to the complete elimination of tumors in 100% of mice (8/8). Moreover, Ad-5/3-κBF512HRE, a viral variant pseudotyped with a chimeric 5/3 fiber, exerted a strong lytic effect on CAR-negative melanoma cells and was highly effective in vivo on established tumors made of melanoma cells and WI-38 fibroblasts, leading to the complete elimination of 4/5 tumors. These results indicate that this improved stroma-targeted oncolytic adenovirus can override the resistance of melanoma tumors and might become of significant importance for melanoma therapeutics.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Chemical biology for understanding matrix metalloproteinase function

The matrix metalloproteinase (MMP) family has long been associated with normal physiological processes such as embryonic implantation, tissue remodeling, organ development, and wound healing, as well as multiple aspects of cancer initiation and progression, osteoarthritis, inflammatory and vascular diseases, and neurodegenerative diseases. The development of chemically designed MMP probes has advanced our understanding of the roles of MMPs in disease in addition to shedding considerable light on the mechanisms of MMP action. The first generation of protease-activated agents has demonstrated proof of principle as well as providing impetus for in vivo applications. One common problem has been a lack of agent stability at nontargeted tissues and organs due to activation by multiple proteases. The present review considers how chemical biology has impacted the progress made in understanding the roles of MMPs in disease and the basic mechanisms of MMP action.

Epigenetic regulation by decitabine of melanoma differentiation in vitro and in vivo

Apoptosis genes, such as TP53 and p16/CDKN2A, that mediate responses to cytotoxic chemotherapy, are frequently nonfunctional in melanoma. Differentiation may be an alternative to apoptosis for inducing melanoma cell cycle exit. Epigenetic mechanisms regulate differentiation, and DNA methylation alterations are associated with the abnormal differentiation of melanoma cells. The effects of the deoxycytidine analogue decitabine (5-aza-2'-deoxycytidine), which depletes DNA methyl transferase 1 (DNMT1), on melanoma differentiation were examined. Treatment of human and murine melanoma cells in vitro with concentrations of decitabine that did not cause apoptosis inhibited proliferation accompanied by cellular differentiation. A decrease in promoter methylation, and increase in expression of the melanocyte late-differentiation driver SOX9, was followed by increases in cyclin-dependent kinase inhibitors (CDKN) p27/CDKN1B and p21/CDKN1A that mediate cell cycle exit with differentiation. Effects were independent of the TP53, p16/CDKN2A and also the BRAF status of the melanoma cells. Resistance, when observed, was pharmacologic, characterized by diminished ability of decitabine to deplete DNMT1. Treatment of murine melanoma models in vivo with intermittent, low-dose decitabine, administered sub-cutaneously to limit high peak drug levels that cause cytotoxicity and increase exposure time for DNMT1 depletion, and with tetrahydrouridine to decrease decitabine metabolism and further increase exposure time, inhibited tumor growth and increased molecular and tumor stromal factors implicated in melanocyte differentiation. Modification of decitabine dose, schedule and formulation for differentiation rather than cytotoxic objectives inhibits the growth of melanoma cells in vitro and in vivo.

Cutting edge in medical management of cutaneous oncology

Traditional chemotherapy has resulted in only a modest response, if any, for the 3 most common cutaneous malignancies of basal cell carcinoma, squamous cell carcinoma, and melanoma. Recent advances in understanding of the defects in the pathways driving tumorigenesis have changed the way that we think of these cancers and paved the way to targeted therapy for specific tumors. In this review, we will introduce the novel systemic treatments currently available for these cancers in the context of what is understood about the tumor pathogenesis. We will also introduce ongoing studies that will hopefully broaden our options for highly effective and tolerable treatment.

Genome wide analysis of acute myeloid leukemia reveal leukemia specific methylome and subtype specific hypomethylation of repeats

Methylated DNA immunoprecipitation followed by high-throughput sequencing (MeDIP-seq) has the potential to identify changes in DNA methylation important in cancer development. In order to understand the role of epigenetic modulation in the development of acute myeloid leukemia (AML) we have applied MeDIP-seq to the DNA of 12 AML patients and 4 normal bone marrows. This analysis revealed leukemia-associated differentially methylated regions that included gene promoters, gene bodies, CpG islands and CpG island shores. Two genes (SPHKAP and DPP6) with significantly methylated promoters were of interest and further analysis of their expression showed them to be repressed in AML. We also demonstrated considerable cytogenetic subtype specificity in the methylomes affecting different genomic features. Significantly distinct patterns of hypomethylation of certain interspersed repeat elements were associated with cytogenetic subtypes. The methylation patterns of members of the SINE family tightly clustered all leukemic patients with an enrichment of Alu repeats with a high CpG density (P<0.0001). We were able to demonstrate significant inverse correlation between intragenic interspersed repeat sequence methylation and gene expression with SINEs showing the strongest inverse correlation (R² = 0.7). We conclude that the alterations in DNA methylation that accompany the development of AML affect not only the promoters, but also the non-promoter genomic features, with significant demethylation of certain interspersed repeat DNA elements being associated with AML cytogenetic subtypes. MeDIP-seq data were validated using bisulfite pyrosequencing and the Infinium array.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

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 Akt signaling pathway: an emerging therapeutic target in malignant melanoma

Studies using cultured melanoma cells and patient tumor biopsies have demonstrated deregulated PI3 kinase-Akt3 pathway activity in ~70% of melanomas. Furthermore, targeting Akt3 and downstream PRAS40 has been shown to inhibit melanoma tumor development in mice. Although these preclinical studies and several other reports using small interfering RNAs and pharmacological agents targeting key members of this pathway have been shown to retard melanoma development, analysis of early Phase I and Phase II clinical trials using pharmacological agents to target this pathway demonstrate the need for (1) selection of patients whose tumors have PI3 kinase-Akt pathway deregulation, (2) further optimization of therapeutic agents for increased potency and reduced toxicity, (3) the identification of additional targets in the same pathway or in other signaling cascades that synergistically inhibit the growth and progression of melanoma, and (4) better methods for targeted delivery of pharmaceutical agents inhibiting this pathway. In this review we discuss key potential targets in PI3K-Akt3 signaling, the status of pharmacological agents targeting these proteins, drugs under clinical development, and strategies to improve the efficacy of therapeutic agents targeting this pathway.

Sarcopenia as a prognostic factor among patients with stage III melanoma

BACKGROUND

Several hypotheses proposed to explain the worse prognosis for older melanoma patients include different tumor biology and diminished host response. If the latter were true, then biologic frailty, and not age, should be an independent prognostic factor in melanoma.

METHODS

Our prospective institutional review board (IRB)-approved database was queried for stage III patients with computed tomography (CT) scans at time of lymph node dissection (LND). Psoas area (PA) and density (PD) were determined in semi-automated fashion. Kaplan-Meier (K-M) survival estimates and Cox proportional-hazard models were used to determine PA and PD impact on survival and surgical complications.

RESULTS

Among 101 stage III patients, PD was significantly associated with both disease-free survival (DFS) (P = 0.04) and distant disease-free survival (DDFS) (P = 0.0002). Cox multivariate modeling incorporating thickness, age, ulceration, and N stage showed highly significant association with PD and both DFS and DDFS. DDFS was significantly associated with Breslow thickness (P = 0.04), number of positive nodes (P = 0.001), ulceration (P = 0.04), and decreasing muscle density (P = 0.01), with hazard ratio of 0.55 [95% confidence interval (CI) 0.35-0.87]. PD also correlated with surgical complications, with odds ratio (OR) of 1.081 [95% CI 1.016-1.150, P = 0.01].

CONCLUSIONS

Decreased psoas muscle density on CT, an objective measure of frailty, was as important a predictor of outcome as tumor factors in a cohort of stage III melanoma patients. On multivariate analysis, frailty, not age, was associated with decreased disease-free survival and distant disease-free survival, and higher rate of surgical complications.

Expression and function of the kallikrein-related peptidase 6 in the human melanoma microenvironment

Cutaneous malignant melanoma is an aggressive disease of poor prognosis. Clinical and experimental studies have provided major insight into the pathogenesis of the disease, including the functional interaction between melanoma cells and surrounding keratinocytes, fibroblasts and immune cells. Nevertheless, patients with metastasized melanoma have a very poor prognosis and are largely refractory to clinical therapies. Hence, novel diagnostic tools to monitor melanoma development as well as therapeutic targets are urgently needed. We investigated the expression pattern of the kallikrein-related peptidase 6 (KLK6) in human melanoma tissue sections throughout tumor development. Although, KLK6 was not detectable in tumor cells, we found strong KLK6 protein expression in keratinocytes and stromal cells located adjacent to benign nevi, primary melanomas and cutaneous metastatic lesions, suggesting a paracrine function of extracellular KLK6 during neoplastic transformation and malignant progression. Accordingly, recombinant Klk6 protein significantly induced melanoma cell migration and invasion accompanied by an accelerated intracellular Ca²⁺-flux. We could further demonstrate that KLK6-induced intracellular Ca²⁺-flux and tumor cell invasion critically depends on the protease-activated receptor PAR1. Our data provide experimental evidence that specific inhibition of the KLK6-PAR1 axis may interfere with the deleterious effect of tumor-microenvironment interaction and represent a potential option for translational melanoma research.

Cutaneous melanoma: a model to study cancer metastasis

Nodal status in melanoma is a critically important prognostic factor for patient outcome. The survival rate drops to <10% when melanoma has spread beyond the regional lymph nodes and includes visceral involvement. In general, the process of melanoma metastasis is progressive in that dissemination of melanoma from the primary site to the regional lymph nodes occurs prior to systemic disease. The goal of this review article is to describe melanoma as a clinical model to study cancer metastasis. A future challenge is to develop a molecular taxonomy to subgroup melanoma patients at various stages of tumor progression for more accurate targeted treatment.

Melanoma stem cells: not rare, but well done

Since the identification of self-renewing cells in the hematopoietic system, stem cells have transformed the study of medicine. Cancer biologists have identified stem-like cells in multiple malignancies, including those of solid organs. This has led to the development of a stem cell theory of cancer, which purports that a subpopulation of self-renewing tumor cells is responsible for tumorigenesis. This contrasts with the stochastic model of tumor development, which advances that all tumor cells are capable of tumor formation. Within the field of melanoma, the identity and existence of cancer stem cells has been the subject of recent debate. Much of the controversy may be traced to differences in interpretations and definitions related to the cancer stem cell theory, and the use of dissimilar methodologies to study melanoma cells. Accumulating evidence suggests that cancer stem cells may exist in melanoma, although their frequency may vary and they may be capable of phenotypic plasticity. Importantly, these primitive melanoma cells are not only capable of self-renewal and differentiation plasticity, but also may confer virulence via immune evasion and multidrug resistance, and potentially via vasculogenic mimicry and transition to migratory and metastasizing derivatives. Therapeutic targeting of melanoma stem cells and the pathways that endow them with virulence hold promise for the design of more effective strategies for amelioration and eradication of this most lethal form of skin cancer.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

Therapeutic Implications of Targeting AKT Signaling in Melanoma

Identification of key enzymes regulating melanoma progression and drug resistance has the potential to lead to the development of novel, more effective targeted agents for inhibiting this deadly form of skin cancer. The Akt3, also known as protein kinase B gamma, pathway enzymes regulate diverse cellular processes including proliferation, survival, and invasion thereby promoting the development of melanoma. Accumulating preclinical evidence demonstrates that therapeutic agents targeting these kinases alone or in combination with other pathway members could be effective for the long-term treatment of advanced-stage disease. However, currently, no selective and effective therapeutic agent targeting these kinases has been identified for clinical use. This paper provides an overview of the key enzymes of the PI3K pathway with emphasis placed on Akt3 and the negative regulator of this kinase called PTEN (phosphatase and tensin homolog deleted on chromosome 10). Mechanisms regulating these enzymes, their substrates and therapeutic implications of targeting these proteins to treat melanoma are also discussed. Finally, key issues that remain to be answered and future directions for interested researchers pertaining to this signaling cascade are highlighted.

Metastasis suppressors in human benign prostate, intraepithelial neoplasia, and invasive cancer: their prospects as therapeutic agents

Despite advances in diagnosis and treatment of prostate cancer, development of metastases remains a major clinical challenge. Research efforts are dedicated to overcome this problem by understanding the molecular basis of the transition from benign cells to prostatic intraepithelial neoplasia (PIN), localized carcinoma, and metastatic cancer. Identification of proteins that inhibit dissemination of cancer cells will provide new perspectives to define novel therapeutics. Development of antimetastatic drugs that trigger or mimic the effect of metastasis suppressors represents new therapeutic approaches to improve patient survival. This review focuses on different biochemical and cellular functions of metastasis suppressors known to play a role in prostate carcinogenesis and progression. Ten putative metastasis suppressors implicated in prostate cancer are discussed. CD44s is decreased in both PIN and cancer; Drg-1, E-cadherin, KAI-1, RKIP, and SSeCKS show similar expression between benign epithelia and PIN, but are downregulated in invasive cancer; whereas, maspin, MKK4, Nm23 and PTEN are upregulated in PIN and downregulated in cancer. Moreover, the potential role of microRNA in prostate cancer progression, the understanding of the cellular distribution and localization of metastasis suppressors, their mechanism of action, their effect on prostate invasion and metastasis, and their potential use as therapeutics are addressed.

Melanocortin MC₁ receptor in human genetics and model systems

The melanocortin MC(1) receptor is a G-protein coupled receptor expressed in the melanocytes of the skin and hair and is known for its key role in the regulation of human pigmentation. Melanocortin MC(1) receptor activation after ultraviolet radiation exposure results in a switch from the red/yellow pheomelanin to the brown/black eumelanin pigment synthesis within cutaneous melanocytes; this pigment is then transferred to the surrounding keratinocytes of the skin. The increase in melanin maturation and uptake results in tanning of the skin, providing a physical protection of skin cells from ultraviolet radiation induced DNA damage. Melanocortin MC(1) receptor polymorphism is widespread within the Caucasian population and some variant alleles are associated with red hair colour, fair skin, poor tanning and increased risk of skin cancer. Here we will discuss the use of mouse coat colour models, human genetic association studies, and in vitro cell culture studies to determine the complex functions of the melanocortin MC(1) receptor and the molecular mechanisms underlying the association between melanocortin MC(1) receptor variant alleles and the red hair colour phenotype. Recent research indicates that melanocortin MC(1) receptor has many non-pigmentary functions, and that the increased risk of skin cancer conferred by melanocortin MC(1) receptor variant alleles is to some extent independent of pigmentation phenotypes. The use of new transgenic mouse models, the study of novel melanocortin MC(1) receptor response genes and the use of more advanced human skin models such as 3D skin reconstruction may provide key elements in understanding the pharmacogenetics of human melanocortin MC(1) receptor polymorphism.