Basic fibroblast growth factor and ultraviolet B transform melanocytes in human skin

HDAC2 Is Involved in the Regulation of BRN3A in Melanocytes and Melanoma

The neural crest transcription factor BRN3A is essential for the proliferation and survival of melanoma cells. It is frequently expressed in melanoma but not in normal melanocytes or benign nevi. The mechanisms underlying the aberrant expression of BRN3A are unknown. Here, we investigated the epigenetic regulation of BRN3A in melanocytes and melanoma cell lines treated with DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC) inhibitors. DNMT and HAT inhibition did not significantly alter BRN3A expression levels, whereas panHDAC inhibition by trichostatin A led to increased expression. Treatment with the isoform-specific HDAC inhibitor mocetinostat, but not with PCI-34051, also increased BRN3A expression levels, suggesting that class I HDACs HDAC1, HDAC2, and HDAC3, and class IV HDAC11, were involved in the regulation of BRN3A expression. Transient silencing of HDACs 1, 2, 3, and 11 by siRNAs revealed that, specifically, HDAC2 inhibition was able to increase BRN3A expression. ChIP-Seq analysis uncovered that HDAC2 inhibition specifically increased H3K27ac levels at a distal enhancer region of the BRN3A gene. Altogether, our data suggest that HDAC2 is a key epigenetic regulator of BRN3A in melanocytes and melanoma cells. These results highlight the importance of epigenetic mechanisms in regulating melanoma oncogenes.

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.

Risk factors for the development of a second melanoma in patients with cutaneous melanoma

BACKGROUND

Cutaneous melanoma patients have an increased risk of developing other neoplasms, especially cutaneous neoplasms and other melanomas. Identifying factors associated with an increased risk might be useful in the development of melanoma guidelines.

OBJECTIVES

To identify risk factors related to the development of a second primary melanoma in a series of patients diagnosed with sporadic melanoma and to establish the estimated incidence rate.

METHODS

A longitudinal study based on prospective follow-up information of patients diagnosed with sporadic cutaneous melanoma at our centre from 2000 to 2015 was performed. Cumulative incidence was estimated based on competing risk models, and the association of characteristics with the risk of a second melanoma was performed by Cox proportional hazard models.

RESULTS

Out of 1447 patients included in the study, after a median follow-up of 61 months, 55 patients (3.8%) developed a second melanoma. Fair hair colour, more than 100 common melanocytic nevi and the presence of more than 50 cherry angiomas were independently associated with the development of a second melanoma. The site and the histological subtype of the first and second melanomas were not consistent. The second melanomas were thinner than the first ones.

CONCLUSIONS

Fair-haired and multiple-nevi patients might benefit from more intensive prevention measures. The finding of cherry angiomas as a risk factor suggests that these lesions could be markers of skin sun damage in the setting of certain degree of genetic susceptibility.

Nongenetic Mechanisms of Drug Resistance in Melanoma

Resistance to targeted and immune-based therapies limits cures in patients with metastatic melanoma. A growing number of reports have identified nongenetic primary resistance mechanisms including intrinsic microenvironment- and lineage plasticity–mediated processes serving critical functions in the persistence of disease throughout therapy. There is a temporally shifting spectrum of cellular identities fluidly occupied by therapy-persisting melanoma cells responsible for driving therapeutic resistance and metastasis. The key epigenetic, metabolic, and phenotypic reprogramming events requisite for the manifestation and maintenance of so-called persister melanoma populations remain poorly understood and underscore the need to comprehensively investigate actionable vulnerabilities. Here we attempt to integrate the field's observations on nongenetic mechanisms of drug resistance in melanoma. We postulate that the future design of therapeutic strategies specifically addressing therapy-persisting subpopulations of melanoma will improve the curative potential of therapy for patients with metastatic disease.

Fibroblast Growth Factor Receptor Signaling in Skin Cancers

Fibroblast growth factor (FGF)/Fibroblast growth factor receptor (FGFR) signaling regulates various cellular processes during the embryonic development and in the adult organism. In the skin, fibroblasts and keratinocytes control proliferation and survival of melanocytes in a paracrine manner via several signaling molecules, including FGFs. FGF/FGFR signaling contributes to the skin surface expansion in childhood or during wound healing, and skin protection from UV light damage. Aberrant FGF/FGFR signaling has been implicated in many disorders, including cancer. In melanoma cells, the FGFR expression is low, probably because of the strong endogenous mutation-driven constitutive activation of the downstream mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK-ERK) signaling pathway. FGFR1 is exceptional as it is expressed in the majority of melanomas at a high level. Melanoma cells that acquired the capacity to synthesize FGFs can influence the neighboring cells in the tumor niche, such as endothelial cells, fibroblasts, or other melanoma cells. In this way, FGF/FGFR signaling contributes to intratumoral angiogenesis, melanoma cell survival, and development of resistance to therapeutics. Therefore, inhibitors of aberrant FGF/FGFR signaling are considered as drugs in combination treatment. The ongoing LOGIC-2 phase II clinical trial aims to find out whether targeting the FGF/FGFR signaling pathway with BGJ398 may be a good therapeutic strategy in melanoma patients who develop resistance to v-Raf murine sarcoma viral oncogene homolog B (BRAF)/MEK inhibitors.

Palladium based nanoparticles for the treatment of advanced melanoma

IGF1R and CD44 are overexpressed in most advanced melanomas so we designed chemotherapeutic nanoparticles to target those receptors. Tris(dibenzylideneacetone)dipalladium (Tris DBA-Pd) is a novel inhibitor of N-myristoyltransferase 1 (NMT-1) and has proven in vivo activity against melanoma. However, poor solubility impairs its effectiveness. To improve its therapeutic efficacy and overcome drug resistance in advanced melanomas, we synthesized Tris DBA-Pd hyaluronic acid nanoparticles (Tris DBA-Pd HANP) and evaluated them against in vivo xenografts of LM36R, an aggressive BRAF mutant human melanoma resistant to BRAF inhibitors. We treated xenografted mice in four arms: empty HANPs, free Tris DBA-Pd, Tris DBA-Pd HANPs, and Tris DBA-Pd HANPs with IGF1R antibody. The Tris DBA-Pd HANP group was the most responsive to treatment and showed the greatest depletion of CD44-positive cells on IHC. Surprisingly, the HANP containing IGF1R antibody was less effective than particles without antibody, possibly due to steric hindrance of IGF1R and CD44 binding. Tris DBA-Pd nanoparticles are an effective therapy for CD44-positive tumors like melanoma, and further development of these nanoparticles should be pursued.

Alleviation of Ultraviolet-B Radiation-Induced Photoaging by a TNFR Antagonistic Peptide, TNFR2-SKE

Ultraviolet (UV) radiation of the sunlight, especially UVA and UVB, is the primary environmental cause of skin damage, including topical inflammation, premature skin aging, and skin cancer. Previous reports show that activation of nuclear factor-κB (NF-κB) in human skin fibroblasts and keratinocytes after UV exposure induces the expression and release of proinflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α), and subsequently leads to the production of matrix metalloproteases (MMPs) and growth factor basic fibroblast growth factor (bFGF). Here, we demonstrated that TNFR2-SKEE and TNFR2-SKE, oligopeptides from TNF receptor-associated factor 2 (TRAF2)-binding site of TNF receptor 2 (TNFR2), strongly inhibited the interaction of TNFR1 as well as TNFR2 with TRAF2. In particular, TNFR2-SKE suppressed UVB- or TNF-α-induced nuclear translocalization of activated NF-κB in mouse fibroblasts. It decreased the expression of bFGF, MMPs, and COX2, which were upregulated by TNF-α, and increased procollagen production, which was reduced by TNF-α. Furthermore, TNFR2-SKE inhibited the UVB-induced proliferation of keratinocytes and melanocytes in the mouse skin and the infiltration of immune cells into inflamed tissues. These results suggest that TNFR2-SKE may possess the clinical potency to alleviate UV-induced photoaging in human skin.

The myelin protein PMP2 is regulated by SOX10 and drives melanoma cell invasion

The transcription factor sex determining region Y-box 10 (SOX10) plays a key role in the development of melanocytes and glial cells from neural crest precursors. SOX10 is involved in melanoma initiation, proliferation, invasion, and survival. However, specific mediators which impart its oncogenic properties remain widely unknown. To identify target genes of SOX10, we performed RNA sequencing after ectopic expression of SOX10 in human melanoma cells. Among nine differentially regulated genes, peripheral myelin protein 2 (PMP2) was consistently upregulated in several cell lines. Direct regulation of PMP2 by SOX10 was shown by chromatin immunoprecipitation, electrophoretic mobility shift, and luciferase reporter assays. Moreover, a coregulation of PMP2 by SOX10 and early growth response 2 in melanoma cells was found. Phenotypical investigation demonstrated that PMP2 expression can increase melanoma cell invasion. As PMP2 protein was detected only in a subset of melanoma cell lines, it might contribute to melanoma heterogeneity.

SOX10 promotes melanoma cell invasion by regulating melanoma inhibitory activity

The transcription factor SOX10 (SRY (sex determining region Y)-box 10) has a key role in the embryonic development of melanocytes. Recently, it has been suggested that SOX10 is highly relevant for melanoma development and survival. However, the distinct functions and downstream targets of SOX10 in melanoma remain widely unknown. In this study, we inhibited SOX10 via RNA interference in different human melanoma cell lines and found a significantly reduced invasion capacity in vitro and in the chick embryo model. At later time points, SOX10 inhibition reduced proliferation and induced cell death. We identified melanoma inhibitory activity (MIA) as a direct target gene of SOX10, which is an essential protein for melanoma cell migration and invasion. Expression levels of SOX10 and MIA strictly correlated in melanoma cell lines, and SOX10 inhibition reduced MIA expression and promoter activity. Direct binding of SOX10 to the MIA promoter was demonstrated by electrophoretic mobility shift assay and chromatin immunoprecipitation. Ectopic expression of MIA in SOX10-inhibited melanoma cells restored the invasion capacity, supporting the hypothesis that MIA is responsible for SOX10-mediated melanoma cell invasion. Our data provide evidence for a critical role of SOX10 in melanoma cell invasion through the regulation of MIA and highlight its role as a therapeutic target in melanoma.

Targeting nitric oxide signaling with nNOS inhibitors as a novel strategy for the therapy and prevention of human melanoma

AIMS

Our previous studies have shown that nitric oxide (NO) plays an important role in increasing the invasion and proliferation of human melanoma cells, suggesting that targeting NO signaling may facilitate therapy and prevention. Neuronal nitric oxide synthase (nNOS) is present in melanocytes, a cell type that originates from the neural crest. The aims of this study were to determine the role of nNOS in melanoma progression and the potential antitumor effects of novel synthesized nNOS inhibitors.

RESULTS

In vitro studies demonstrated abundant expression of nNOS in melanoma compared to melanocytes, which was inducible by ultraviolet radiation and was associated with increased NO generation. nNOS was also detected in melanoma biopsies that increased with disease stage. Knockdown of nNOS in melanoma cells diminished L-arginine-induced NO production; the metastatic capacity was also reduced as well as the levels of MMP-1, Bcl-2, JunD, and APE/Ref-1. Similar inhibition of NO and invasion potential was observed utilizing novel, highly selective nNOS inhibitors. In three-dimensional human skin reconstructs, the nNOS inhibitor cpd8 effectively reversed the melanoma overgrowth stimulated by NO stress.

INNOVATION

Our work lays the foundation for development of clinical "drug-like" nNOS inhibitors as a new and promising strategy for the chemoprevention of early melanoma progression and the inhibition of secondary melanoma in high-risk individuals.

CONCLUSION

Based on our observations, we propose that nNOS in melanoma results in constitutive overproduction of NO, which stimulates proliferation and increases invasion potential, leading to subsequent development of metastases.

Stat3-targeted therapies overcome the acquired resistance to vemurafenib in melanomas

Vemurafenib (PLX4032), a selective inhibitor of Braf, has been approved by the US Food and Drug Administration for the treatment of unresectable or metastatic melanoma in patients with Braf(V600E) mutations. Many patients treated with vemurafenib initially display dramatic improvement, with decreases in both risk of death and tumor progression. Acquired resistance, however, rapidly arises in previously sensitive cells. We attempted to overcome this resistance by targeting the signal transducer and activator of transcription 3 (STAT3)-paired box homeotic gene 3 (PAX3)-signaling pathway, which is upregulated, owing to fibroblast growth factor 2 (FGF2) secretion or increased kinase activity, with the Braf(V600E) mutation. We found that activation of Stat3 or overexpression of PAX3 induced resistance to vemurafenib in melanoma cells. In addition, PAX3 or Stat3 silencing inhibited the growth of melanoma cells with acquired resistance to vemurafenib. Furthermore, treatment with the Stat3 inhibitor, WP1066, resulted in growth inhibition in both vemurafenib-sensitive and -resistant melanoma cells. Significantly, vemurafenib stimulation induced FGF2 secretion from keratinocytes and fibroblasts, which might uncover, at least in part, the mechanisms underlying targeting Stat3-PAX3 signaling to overcome the acquired resistance to vemurafenib. Our results suggest that Stat3-targeted therapy is a new therapeutic strategy to overcome the acquired resistance to vemurafenib in the treatment of melanoma.

FGF2 regulates melanocytes viability through the STAT3-transactivated PAX3 transcription

PAX3 (paired box 3) is known to have an important role in melanocyte development through modulation of microphthalmia-associated transcription factor transcription. Here we found that PAX3 transcriptional activity could be regulated through FGF2 (basic fibroblast growth factor)-STAT3 (signal transducer and activator of transcription 3) signaling in the pigment cells. To study its function in vivo, we have generated a transgenic mouse model expressing PAX3 driven by tyrosinase promoter in a tissue-specific fashion. These animals exhibit hyperpigmentation in the epidermis, evident in the skin color of their ears and tails. We showed that the darker skin color results from both increased melanocyte numbers and melanin synthesis. Together, our study delineated a novel pathway in the melanocyte lineage, linking FGF2-STAT3 signaling to increased PAX3 transcription. Moreover, our results suggest that this pathway might contribute to the regulation of melanocyte numbers and melanin levels, and thereby provide an alternative strategy to induce pigmentation.

Prognostic parameters for the primary care of melanoma patients: what is really risky in melanoma?

Due to intensified research in recent years, the understanding of the molecular mechanisms involved in the development of melanoma has dramatically improved. The discovery of specific, causal mutations such as BRAF or KIT oncogenes not only renders a targeted and thus more effective therapeutic approach possible, but also gives rise to a new genetic-based classification. Targeting just a few out of several potential mutations, BRAF-Inhibitors such as PLX 4032 achieved already tremendous results in the therapy of metastatic melanoma. Up to now, the correlation of clinical, histomorphologic, and genetic features is, however, not understood. Even more, is it not well known precisely what kind of molecular changes predispose the primary melanoma for metastasis. The identification of morphological surrogates and prognostic parameters in tumors with such genetic alteration seems therefore crucial when differentiating and classifying this heterogeneous tumor entity in more detail and thus facilitates the stratification of prognosis as well as therapy. This review summarizes the current understanding of carcinogenesis and gives a detailed overview of known morphologic and potentially future genetic prognostic parameters in malignant melanoma.

The role of ultraviolet radiation in melanomagenesis

The role of ultraviolet radiation (UV) in the pathogenesis has been discussed controversially for many decades. Studies in mice (SCID, HGF/SF, SV40T) which develop malignant melanoma, show a role of UVB in melanomagenesis. In contrast to this, the role of UVA is less clear. We will review the recent in vitro and in vivo data in support of the hypothesis that UVA is also involved in the development of malignant melanoma. The role of UVA in p53 activation, apoptosis, cell cycle arrest and photoproduct formation is discussed.

Cellular dichotomy between anchorage-independent growth responses to bFGF and TPA reflects molecular switch in commitment to carcinogenesis

We have investigated gene expression patterns underlying reversible and irreversible anchorage-independent growth (AIG) phenotypes to identify more sensitive markers of cell transformation for studies directed at interrogating carcinogenesis responses. In JB6 mouse epidermal cells, basic fibroblast growth factor (bFGF) induces an unusually efficient and reversible AIG response, relative to 12-O-tetradecanoyl phorbol-13-acetate (TPA)-induced AIG which is irreversible. The reversible and irreversible AIG phenotypes are characterized by largely nonoverlapping global gene expression profiles. However, a subset of differentially expressed genes were identified as common to reversible and irreversible AIG phenotypes, including genes regulated in a reciprocal fashion. Hepatic leukemia factor (HLF) and D-site albumin promoter-binding protein (DBP) were increased in both bFGF and TPA soft agar colonies and selected for functional validation. Ectopic expression of human HLF and DBP in JB6 cells resulted in a marked increase in TPA- and bFGF-regulated AIG responses. HLF and DBP expression were increased in soft agar colonies arising from JB6 cells exposed to gamma radiation and in a human basal cell carcinoma tumor tissue, relative to paired nontumor tissue. Subsequent biological network analysis suggests that many of the differentially expressed genes that are common to bFGF- and TPA-dependent AIG are regulated by c-Myc, SP-1, and HNF-4 transcription factors. Collectively, we have identified a potential molecular switch that mediates the transition from reversible to irreversible AIG.

Expression of fibroblast growth factor binding protein in head and neck cancer

OBJECTIVES

To characterize the expression of fibroblast growth factor binding protein (FGF-BP) messenger RNA (mRNA) in head and neck squamous cell carcinoma (HNSCC) and to study the association of FGF-BP with vascularity.

DESIGN

The expression of FGF-BP mRNA in HNSCC was studied in 35 primary and 8 metastatic HNSCC specimens and 7 control tissues using in situ hybridization and reverse transcriptase-polymerase chain reaction (RT-PCR). Microvessels in tumor specimens were identified with endothelial cell markers (von Willebrand factor [vWF] and CD34-specific antibodies). Correlates between FGF-BP and microvessel counts were evaluated statistically.

SETTING

University of Minnesota Hospitals and Clinics.

PATIENTS

Forty-two surgically treated patients with HNSCC.

INTERVENTIONS

The patients were routinely treated in the study hospitals and clinics.

MAIN OUTCOME MEASURES

The expression of FGF-BP and angiogenesis in tumors were evaluated.

RESULTS

In situ hybridization and RT-PCR demonstrated that FGF-BP mRNA transcripts were expressed in 34 of 35 primary HNSCC specimens and 5 of 8 metastatic tumor specimens but not in adjacent control tissues. The microvessel counts in HNSCC specimens were closely related to the expression level of FGF-BP (P < .001).

CONCLUSION

The expression of FGF-BP is statistically linked to the angiogenesis of HNSCC, suggesting that FGF-BP participates in the angiogenesis of HNSCC.

Genetic variants in FGFR2 and FGFR4 genes and skin cancer risk in the Nurses' Health Study

Background

The human fibroblast growth factor (FGF) and its receptor (FGFR) play an important role in tumorigenesis. Deregulation of the FGFR2 gene has been identified in a number of cancer sites. Overexpression of the FGFR4 protein has been linked to cutaneous melanoma progression. Previous studies reported associations between genetic variants in the FGFR2 and FGFR4 genes and development of various cancers.

Methods

We evaluated the associations of four genetic variants in the FGFR2 gene highly related to breast cancer risk and the three common tag-SNPs in the FGFR4 gene with skin cancer risk in a nested case-control study of Caucasians within the Nurses' Health Study (NHS) among 218 melanoma cases, 285 squamous cell carcinoma (SCC) cases, 300 basal cell carcinoma (BCC) cases, and 870 controls.

Results

We found no evidence for associations between these seven genetic variants and the risks of melanoma and nonmelanocytic skin cancer.

Conclusion

Given the power of this study, we did not detect any contribution of genetic variants in the FGFR2 or FGFR4 genes to inherited predisposition to skin cancer among Caucasian women.

The role of BRAF mutation and p53 inactivation during transformation of a subpopulation of primary human melanocytes

Melanocytic nevi frequently harbor oncogenic BRAF mutations, but only a minority progress to melanoma. In human melanocytes, persistent BRAF(V600E) expression triggers oncogene-induced senescence, which implies that bypass of oncogene-induced senescence is necessary for malignant transformation of melanocytes. We show that a subpopulation of primary human melanocytes with persistent expression of BRAF(V600E) do not enter oncogene-induced senescence, but instead survive despite heightened MAPK activity. Disruption of the p53 pathway using short-hairpin RNA initiated rapid growth of these V600E(+) melanocytes in vitro. The resultant V600E(+)/p53(sh) melanocytes grew anchorage-independently in soft agar, formed pigmented lesions reminiscent of in situ melanoma in artificial skin reconstructs, and were weakly tumorigenic in vivo. Array comparative genomic hybridization analysis demonstrated that the transformed melanocytes acquired a substantial deletion in chromosome 13, which encodes the Rb1 tumor suppressor gene. Gene expression profiling study of nevi and melanomas showed that p53 target genes were differentially expressed in melanomas compared with nevi, suggesting a dysfunctional p53 pathway in melanoma in vivo. In summary, these data demonstrate that a subpopulation of melanocytes possesses the ability to survive BRAF(V600E)-induced senescence, and suggest that p53 inactivation may promote malignant transformation of these cells.

SOX9 and SOX10 but not BRN2 are required for nestin expression in human melanoma cells

Nestin is an intermediate filament protein and a marker of neuroectodermal stem cells indicating multipotentiality and regenerative capability. In melanoma tissues, nestin re-expression was correlated with tumor progression. Activation of the nestin neural enhancer was shown to be dependent on the binding of class III POU transcription factors, with brain-2 (BRN2) suggested to play a key role. We found both nestin and BRN2 mRNA in almost all of 13 analyzed melanoma cell lines of different progression stages, but expression levels did not correlate. Nestin protein was detected in 11 of 13 and BRN2 protein in 7 of 13 melanoma cell lines independent of progression stage. Downregulation of BRN2 by small-interfering RNA did not alter nestin expression in melanoma cells. However, POU proteins, such as BRN2, commonly cooperate with transcription factors of the Sry-box (SOX) family by binding to a nearby DNA site necessary for their action. SOX9 and SOX10 have been shown to be expressed in melanocyte precursors, with SOX10 downregulated upon differentiation. We now demonstrate SOX9 and SOX10 protein expression in melanoma tissues and cell lines. Downregulation of SOX9 and of SOX10 markedly decreased nestin levels in melanoma cells in a cooperative manner. Thus, SOX9 and SOX10 but not BRN2 seem to be required for nestin expression in human melanoma.

The RTK/RAS/BRAF/PI3K pathways in melanoma: biology, small molecule inhibitors, and potential applications

The discovery of mutations in the BRAF signaling molecule in a large proportion of cutaneous melanomas immediately suggested the prospect of effective therapies for this disease. The most appealing initial target has been BRAF itself, as most mutations involve a single residue in the kinase domain of the protein. But the identification of the high mutation rate in this signaling intermediate also suggests that other molecules up- and downstream of BRAF might be productively targeted. Indeed, several receptor tyrosine kinases, as well as RAS, are mutated in a small number of melanoma cases. Moreover, genetic alterations in the phosphotidylinositol-3-kinase (PI3K) pathway, especially in PTEN, suggest that this route also poses opportunities for therapeutic exploitation. We will review here the genetic evidence suggesting the utility of targets on these pathways. We will also summarize the recent clinical data that have accumulated from initial trials designed to test BRAF inhibition and targeting of other molecules. Finally, we provide an overview of molecules entering the clinic and soon to be tested in clinical studies, as well as strategies for their employment as monotherapy and in combinations.

Models and mechanisms in malignant melanoma

Human melanoma represents the fastest growing malignancy in the US. The etiology of melanoma is highly debated as is the role of ultraviolet (UV) radiation in the initiation and progression of melanoma. This article discusses data from UV exposure and its relationship to the development of melanoma from various models of melanoma as well as various genetic alterations seen in oncogenic transformation of melanocytes. Genetic alterations such as the p16(INK4a) deletion, melanocortin 1 receptor (MC1R), RAS, and v-raf murine sarcoma viral oncogene homolog B1 (BRAF) may be indicative of a predisposition to melanoma development. Historical research as well as current data on the significance of the hot spot mutation in BRAF is discussed in its relative potential to the activating mutation in RAS.

The role of p53 in pigmentation, tanning and melanoma

p53 has a central role in skin pigmentation and may impact on melanoma at all stages, however, as it's mutation frequency in melanoma is low, it's role has been somewhat under-appreciated. During normal skin function, p53 in the keratinocyte is a transducer of the skin tanning signal and an essential component of what is effectively a keratinocyte-melanocyte signaling cycle that regulates skin pigmentation. It is clear that this cycle functions optimally in skin of dark pigmentation. When melanin biosynthesis is genetically disrupted in skin of white complexion, we propose that this cycle operates as a promoter of melanocyte proliferation. The cell autonomous function of p53 in melanocytes is not well described, however, the balance of the evidence suggests that p53 is an effective tumor suppressor and the myriad of mechanisms by which the p53 pathway may be dysregulated in tumors attests to it importance as a tumor suppressor. In this review, we outline the known mechanisms that impair p53 itself and its immediate regulators or target genes during melanomagenesis. Due to the importance of this pathway, it is clear that p53 disruptions may relate directly to a patient's prognosis. This pathway will continue to be a focus of investigation, particularly with respect to targeted experimental chemotherapeutics.

The effects of dickkopf 1 on gene expression and Wnt signaling by melanocytes: mechanisms underlying its suppression of melanocyte function and proliferation

Dickkopf 1 (DKK1), which is expressed at high mRNA levels by fibroblasts in the dermis of human skin on the palms and soles, inhibits the function and proliferation of melanocytes in the epidermis of those areas via the suppression of beta-catenin and microphthalmia-associated transcription factor (MITF). In this study, we investigated the protein expression levels of DKK1 between palmoplantar and non-palmoplantar areas and the effects of DKK1 on melanocyte gene expression profiles and on Wnt signaling pathways using DNA microarray technology, reverse transcriptase-PCR, Western blot, 3-dimensional reconstructed skin, immunocytochemistry, and immunohistochemistry. DKK1-responsive genes included those encoding proteins involved in the regulation of melanocyte development, growth, differentiation, and apoptosis (including Kremen 1, G-coupled receptor 51, lipoprotein receptor-related protein 6, low-density lipoprotein receptor, tumor necrosis factor receptor super-family 10, growth arrest and DNA-damage-inducible gene 45beta, and MITF). Of special interest was the rapid decrease in expression of MITF in melanocytes treated with DKK1, which is concurrent with the decreased activities of beta-catenin and of glucose-synthase kinase 3beta via phosphorylation at Ser9 and with the upregulated expression of protein kinase C alpha. These results further clarify the mechanism by which DKK1 suppresses melanocyte density and differentiation, and help explain why DKK1-rich palmoplantar epidermis is paler than non-palmoplantar epidermis via mesenchymal-epithelial interactions.

CCN3 controls 3D spatial localization of melanocytes in the human skin through DDR1

Melanocytes reside within the basal layer of the human epidermis, where they attach to the basement membrane and replicate at a rate proportionate to that of keratinocytes, maintaining a lifelong stable ratio. In this study, we report that coculturing melanocytes with keratinocytes up-regulated CCN3, a matricellular protein that we subsequently found to be critical for the spatial localization of melanocytes to the basement membrane. CCN3 knockdown cells were dissociated either upward to the suprabasal layers of the epidermis or downward into the dermis. The overexpression of CCN3 increased adhesion to collagen type IV, the major component of the basement membrane. As the receptor responsible for CCN3-mediated melanocyte localization, we identified discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase that acts as a collagen IV adhesion receptor. DDR1 knockdown decreased melanocyte adhesion to collagen IV and shifted melanocyte localization in a manner similar to CCN3 knockdown. These results demonstrate an intricate and necessary communication between keratinocytes and melanocytes in maintaining normal epidermal homeostasis.

FGFR4 Arg388 allele correlates with tumour thickness and FGFR4 protein expression with survival of melanoma patients

A single nucleotide polymorphism in the gene for FGFR4 (−Arg388) has been associated with progression in various types of human cancer. Although fibroblast growth factors (FGFs) belong to the most important growth factors in melanoma, expression of FGF receptor subtype 4 has not been investigated yet. In this study, the protein expression of this receptor was analysed in 137 melanoma tissues of different progression stages by immunohistochemistry. FGFR4 protein was expressed in 45% of the specimens and correlated with pTNM tumour stages (UICC, P=0.023 and AJCC, P=0.046), presence of microulceration (P=0.009), tumour vascularity (P=0.001), metastases (P=0.025), number of primary tumours (P=0.022), overall survival (P=0.047) and disease-free survival (P=0.024). Furthermore, FGFR4 Arg388 polymorphism was analysed in 185 melanoma patients by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The Arg388 allele was detected in 45% of the melanoma patients and was significantly associated with tumour thickness (by Clark's level of invasion (P=0.004) and by Breslow in mm (P=0.02)) and the tumour subtype nodular melanoma (P=0.002). However, there was no correlation of the FGFR4 Arg388 allele with overall and disease-free survival. In conclusion, the Arg388 genotype and the protein expression of FGFR4 may be potential markers for progression of melanoma.

Ultraviolet B sensitivity of peripheral lymphocytes as an independent risk factor for cutaneous melanoma

Susceptibility to solar ultraviolet is an important melanoma risk factor. We investigated the relationship between individual susceptibility to ultraviolet and risk of melanoma by measuring the apoptosis triggered in peripheral lymphocytes by a low-dose ultraviolet B irradiation (50 J/m(2)) in young and older melanoma patients and controls. Melanoma patients below the age of 40 are more sensitive to UVB-induced apoptosis than older melanoma patients and healthy controls. Analysis of data (adjusted for age and phototype) shows that UVB-induced apoptosis is an important risk factor for melanoma (OR 9.1, 95% CI [3-28], P=0.0001). UVB-induced apoptosis is independent of phototype (P=0.11, Wald test) and tumour thickness (P=0.88, Spearman correlation, for all cases and 0.26 for patients younger than 40 years), and may be used as a functional laboratory test for studying the genetic-environment interactions involved in melanoma occurrence.

Normal human melanocyte homeostasis as a paradigm for understanding melanoma

Melanocytes, after cell division, separate and migrate along the basement membrane; they extend their dendrites and establish multiple contacts with keratinocytes. Once adhesion is established, keratinocytes control melanocyte growth and expression of cell surface receptors. Most melanomas arise within the epidermis (melanoma in situ) and then invade across the basement membrane. These melanoma cells escape from control by keratinocytes through five major mechanisms: (1) downregulation of receptors important for communication with keratinocytes such as E-cadherin, P-cadherin, and desmoglein, which is achieved through growth factors such as hepatocyte growth factor, platelet-derived growth factor, and endothelin-1 produced by fibroblasts or keratinocytes; (2) upregulation of receptors and signaling molecules important for melanoma cell-melanoma cell and melanoma cell-fibroblast interactions such as N-cadherin, Mel-CAM, and zonula occludens protein-1; (3) deregulation of morphogens such as Notch receptors and their ligands; (4) loss of anchorage to the basement membrane because of an altered expression of cell-matrix adhesion molecules; (5) increased elaboration of metal-loproteinases. Thus, investigating normal melanocyte homeostasis helps us to better define how melanoma cells escape the microenvironment created by epidermal keratinocytes and how they develop new cellular partners in fibroblasts and endothelial cells, which support their growth and invasion.

Growth factors rescue cutaneous melanoma cells from apoptosis induced by knockdown of mutated (V 600 E) B-RAF

Constitutive activation of the RAS-RAF-MEK-ERK signaling cascade is a hallmark of cutaneous malignant melanoma. A single activating mutation (c.1799 T>A; p.V 600 E) in the gene encoding the serine/threonine kinase B-RAF occurs in >60% of the tumors. Previous work has shown that knockdown of (V 600 E)B-RAF by RNA interference induces a variety of phenotypic changes in cultured melanoma cells, including lower proliferation rates, reduced anchorage-independent growth and apoptosis. Here, we show that the majority of melanomas harboring the (V 600 E)B-RAF mutation have retained the wild-type (WT) B-RAF allele, and that these cells can be rescued from the effects of (V 600 E)B-RAF knockdown by stimulation with growth factors. Ectopic expression of short hairpin RNAs specifically suppressing (V 600 E)B-RAF in melanoma cell lines reduced colony formation by approximately 80%. This response could be rescued by basic fibroblast growth factor, hepatocyte growth factor or, to a lesser extent, endothelin-1. Rescue with growth factors was not possible in cell lines lacking (WT)B-RAF. Single-cell clones with efficient knockdown of (V 600 E)B-RAF could be propagated in the presence of basic fibroblast growth factor but underwent apoptosis or senescence-like growth arrest upon withdrawal of this growth factor. The ability of growth factors to modulate the response of (V 600 E)B-RAF knockdown in melanoma cells may have both experimental and therapeutic implications.

Activation of Notch1 signaling is required for beta-catenin-mediated human primary melanoma progression

Notch is a highly conserved transmembrane receptor that determines cell fate. Notch signaling denotes cleavage of the Notch intracellular domain, its translocation to the nucleus, and subsequent activation of target gene transcription. Involvement of Notch signaling in several cancers is well known, but its role in melanoma remains poorly characterized. Here we show that the Notch1 pathway is activated in human melanoma. Blocking Notch signaling suppressed whereas constitutive activation of the Notch1 pathway enhanced primary melanoma cell growth both in vitro and in vivo yet had little effect on metastatic melanoma cells. Activation of Notch1 signaling enabled primary melanoma cells to gain metastatic capability. Furthermore, the oncogenic effect of Notch1 on primary melanoma cells was mediated by beta-catenin, which was upregulated following Notch1 activation. Inhibiting beta-catenin expression reversed Notch1-enhanced tumor growth and metastasis. Our data therefore suggest a beta-catenin-dependent, stage-specific role for Notch1 signaling in promoting the progression of primary melanoma.

Tumor-stroma interactions: their role in the control of tumor cell invasion

The development and progression of tumors result from the concerted activity not only of tumor cells with neighboring cells e.g., fibroblasts and inflammatory cells. Host-tumor interactions are considered critical in tumor invasion and metastasis. In vitro studies as well as established in vivo models have analysed the reciprocal effects of tumor-host interactions for the tumor invasion process. These studies have shown that modifications in the extracellular matrix composition surrounding the tumors as well as alterations in the expression of tumor cell receptors or in the expression of growth factors/cytokines and proteases, are critical regulators of a developing tumor. We shortly review the most important and well characterized mechanisms involved in the progression of tumor cells through tissues, especially those participating in cellular communication, cell adhesion, and proteolysis.

The fibroblast growth factor-2 is not essential for melanoma formation in a transgenic mouse model

Fibroblast growth factor 2 (FGF2) has been assigned a role in melanocyte proliferation and in development of human cutaneous melanoma. We have used a transgenic mouse melanoma model in combination with mice lacking mouse FGF2 to analyse the possible implication of FGF2 in melanomagenesis. Tyr::N-rasQ61K transgenic mice which are deficient for FGF2 and the tumor suppressors p16INK4a and p19ARF are hyperpigmented and develop cutaneous metastasizing melanoma, with no difference to mice wildtype for FGF2. We conclude from our data, that FGF2 is not essential for melanoma progression and metastasis.

Seasonal variation in the occurrence of cutaneous melanoma in Europe: influence of latitude. An analysis using the EUROCARE group of registries

The aim of our study was to analyse seasonal variations in melanoma incidence in Europe. Data from 28117 cutaneous melanoma cases reported during 1978-1993 to the EUROCARE group of registries were analysed. There is a clear summer peak in incidence in Western countries (summer-winter ratio: 1.31 P < 0.0001; Nam's test), which was not observed in Central Europe (ratio: 1.06; P = 0.0699). The amplitude of seasonality is higher for females (ratio = 1.38, 95% Confidence Interval (CI) [1.31-1.44]) than for males (ratio = 1.21 95%CI [1.14-1.29]). It is also higher for upper and lower limbs (1.44 and 1.46, respectively), than for head and neck or trunk regions (1.09 and 1.20, respectively). The amplitude of seasonality also varies with latitude and increases with time: in a linear regression adjusting for age, gender and anatomical localisation, the date of diagnosis was significantly closer to summer solstice with decreasing latitude (P = 0.0005) and for more recent year of diagnosis (P = 0.0123). The effect of latitude on the amplitude of the seasonal variation in melanoma incidence in Europe may be an indicator of ultraviolet B (UVB) exposure. Furthermore, an increase in intentional sun exposure could lead to an increase in melanoma promotion and thus to an increase in the amplitude of seasonal variation.

UV light from 290 to 325 nm, but not broad-band UVA or visible light, augments the formation of melanocytic nevi in a guinea-pig model for human nevi

We have previously described a guinea-pig model where pigmented nevi similar to human nevi can be produced by application of low-dose topical 7,12-dimethylbenzanthracene (DMBA) followed by solar-simulated light. Five groups of guinea-pigs were used to test the effect of various spectral bands of solar-simulated light on low-dose DMBA-induced melanocytic nevi. Animals were irradiated with either UVB to near UVA2 (290-325 nm), UVA, visible light, full solar spectrum or no irradiation three times per wk for 12 mo to determine the broad-band effect of nevi-inducing irradiation. There was a significant increase in nevi/animal in the UVB-treated group (mean 1.53) compared with all groups (versus UVA 0.3, p<0.001; versus visible light 0.24, p<0.001; versus full spectrum (UVB+UVA+visible) 0.68, p=0.02; versus control (nil irradiation) 0.37, p=0.01). No differences in skin thickness were found between any group (p=0.11). In conclusion, we present a report of the active waveband of melanocytic nevi induction; where UVB to near UVA2 is the likely responsible waveband. Furthermore, because there was a significant decrease in nevi/animal receiving the full solar spectrum compared with the UVB group, it is possible that broad-band UVA and or visible light may be inhibitory wavebands for nevi induction.

Recent advances in melanoma biology

The incidence and mortality rates of melanoma have increased at annual rates of 2%-3% for the last 30 years. Disseminated disease is largely refractory to cytotoxic chemotherapy and is almost universally fatal. Several recent advances in melanoma biology offer new strategies for potentially treating this aggressive malignancy. This review focuses on three significant advances involving tumor initiation, etiology, and progression. New experimental models reveal a direct role for UV-B light in initiating melanomas in human skin. Studies on E- and N-cadherin elucidate the importance of local homeostatic mechanisms in regulating tumor progression. Finally, several discoveries concerning apoptotic mechanisms in melanoma suggest strategies for future treatments.

Epidermotropic metastases from breast carcinoma showing different clinical and histopathological features on the trunk and on the scalp in a single patient

A 54-year-old female presented with the cutaneous metastases of the breast carcinoma that produced combination of pigmented zosteriform eruption on the trunk and eroded plaque on the scalp, 13 years after radical mastectomy. Histologically, zosteriform lesions displayed prominent infiltration of the epidermis in nesting or linear pattern by neoplastic cells with focal formation of intraepidermal and subepidermal vesicles due to discohesion of tumor cells and dermal edema. Examination of scalp plaque revealed ulcerations and infiltration of the epidermis with scattered basal and suprabasal malignant cells in pagetoid fashion. Immunohistochemically, tumor cells were cytokeratin 7- and estrogen receptor-positive and cytokeratin 20 negative. HMB-45 and Melan-A-stained numerous dendritic melanocytes intermingled with intraepidermal and superficial dermal tumor cells in the trunk lesion, whereas on the scalp, only occasional melanocytes surrounding intraepidermal carcinomatous cells were identified. Our case described, to our knowledge, so far unreported combination of individually rare, clinical and histological patterns of cutaneous metastases from breast carcinoma in a single patient.

Induction of Melanoma Phenotypes in Human Skin by Growth Factors and Ultraviolet B

Exposure to UV radiation likely plays a key role in melanoma development, whereas other etiologic agents remain unknown. Here we show that in normal human skin an increased expression of a combination of three growth factors, basic fibroblast growth factor, stem cell factor, and endothelin-3, along with exposure to UVB can transform normal melanocytes into a melanoma phenotype within 4 weeks. Invasion of melanoma lesions was found in skin from newborn donors, whereas melanomas in adult skin were of a noninvasive in situ type only. This suggests that susceptibility of skin to exogenous tumor promoters is dependent on age. This is the first report on human cancer initiation in vivo in which an imbalance of physiological factors combined with an environmental carcinogen can lead to transformation of normal tissue.

Human melanoblasts in culture: expression of BRN2 and synergistic regulation by fibroblast growth factor-2, stem cell factor, and endothelin-3

The BRN2 transcription factor (POU3F2, N-Oct-3) has been implicated in development of the melanocytic lineage and in melanoma. Using a low calcium medium supplemented with stem cell factor, fibroblast growth factor-2, endothelin-3 and cholera toxin, we have established and partially characterised human melanocyte precursor cells, which are unpigmented, contain immature melanosomes and lack L-dihydroxyphenylalanine reactivity. Melanoblast cultures expressed high levels of BRN2 compared to melanocytes, which decreased to a level similar to that of melanocytes when cultured in medium that contained phorbol ester but lacked endothelin-3, stem cell factor and fibroblast growth factor-2. This decrease in BRN2 accompanied a positive L-dihydroxyphenylalanine reaction and induction of melanosome maturation consistent with melanoblast differentiation seen during development. Culture of primary melanocytes in low calcium medium supplemented with stem cell factor, fibroblast growth factor-2 and endothelin-3 caused an increase in BRN2 protein levels with a concomitant change to a melanoblast-like morphology. Synergism between any two of these growth factors was required for BRN2 protein induction, whereas all three factors were required to alter melanocyte morphology and for maximal BRN2 protein expression. These finding implicate BRN2 as an early marker of melanoblasts that may contribute to the hierarchy of melanocytic gene control.

Sunscreens Inadequately Protect Against Ultraviolet-A-Induced Free Radicals in Skin: Implications for Skin Aging and Melanoma?

Sunscreens are employed to mitigate the adverse effects of sunlight on skin but are primarily designed to prevent ultraviolet-B-associated burning and damage. The increasingly recognized role of ultraviolet A in aging, and possibly melanoma, highlights the need to include ultraviolet A screens; however, validation remains difficult. We have used a novel method to establish the efficacy of sunscreens, by measuring ultraviolet-A-induced free-radical production (thought to contribute towards ultraviolet-A-related aging and malignant change). Electron spin resonance spectroscopy was used to detect free radicals directly in human Caucasian skin during irradiation with levels of ultraviolet comparable to solar intensities. Using this system the protection afforded by three high factor sunscreens (sun protection factor 20+) that claim ultraviolet A protection was examined. Each sunscreen behaved similarly: at recommended application levels (> or = 2 mg per cm2) the ultraviolet-induced free radicals were reduced by only about 55%, and by about 45% at 0.5-1.5 mg per cm (0.5 mg per cm2 reported for common usage). A "free-radical protection factor" calculated on the basis of these results was only 2 at the recommended application level, which contrasts strongly with the erythema-based sun protection factors (mainly indicative of ultraviolet B protection) quoted by the manufacturers (20+). The disparity between these protection factors suggests that prolonged sunbathing (encouraged by use of these creams) would disproportionately increase exposure to ultraviolet A and consequently the risk of ultraviolet-A-related skin damage.

Fibroblast growth factor-2 but not Mel-CAM and/or beta3 integrin promotes progression of melanocytes to melanoma

A variety of melanoma-associated antigens have been identified that mediate adhesion, growth, proteolysis, and modulation of immune response. However, the mechanisms by which human normal melanocytes become malignant are not clearly understood. Among the most consistent observations is the up-regulation of fibroblast growth factor-2 (FGF-2) and of the adhesion molecules beta3 integrin and Mel-CAM during melanoma progression. To evaluate the potential role of FGF-2, beta3 integrin and Mel-CAM in melanoma development we overexpressed FGF-2, beta3 integrin and Mel-CAM in normal human melanocytes using replication-deficient adenoviruses as a gene delivery vehicle. Fibroblast growth factor-2 overexpressing melanocytes in monolayer culture displayed cytological atypia. Furthermore, in human skin reconstructs where the physiological milieu is recreated in vitro, FGF-2-overexpressing melanocytes exhibited marked proliferation, upwards migration, cluster formation and type IV collagen expression within the epidermal compartment, simulating early radial growth phase melanoma. In contrast, overexpression of beta3 integrin and/or Mel-CAM in melanocytes did not affect their biological behaviour in human skin reconstructs. The described results of the current and previous studies emphasise the key role of FGF-2 in melanoma development and progression, underscoring the promise of FGF-2 as a target for therapy.

Stroma formation and angiogenesis by overexpression of growth factors, cytokines, and proteolytic enzymes in human skin grafted to SCID mice

Reorganization of skin during wound healing, inflammatory disorders, or cancer growth is the result of expression changes of multiple genes associated with tissue morphogenesis. We wanted to identify proteins involved in skin remodeling and select those that may be targeted for agonistic or antagonist therapeutic approaches in various disease processes. Full-thickness human skin was grafted to severe combined immunodeficient mice and injected intradermally with 38 different adenoviral vectors inserted with 37 different genes coding for growth factors, cytokines, proteolytic enzymes and their inhibitors, adhesion receptors, oncogenes, and tumor suppressor genes. Responses were characterized for infiltration of inflammatory cells, vascular density, matrix formation, fibroblast-like cell proliferation, and epidermal hyperplasia. Of the 17 growth factor vectors, 16 induced histological changes in human skin. Members of the VEGF and angiopoietin families induced neovascularization. PDGFs and TGF-betas stimulated connective tissue formation, and the chemokines IL-8 and MCP-1 attracted inflammatory neutrophils and monocytes, respectively. The serine protease uPA induced a vascular response similar to that of VEGF. Vectors with adhesion receptors, oncogenes and tumor suppressor genes had, with few exceptions, little effects on skin architecture. The overall results suggest that adenoviral vectors can effectively remodel the architecture of human skin for studies in morphogenesis, inflammatory skin disorders, wound healing, and cancer development.

Modeling gene-environment interactions in malignant melanoma

Many cancers are the pathological consequence of environmentally initiated disruptions to cellular genetic control mechanisms. For most cancers the relevant environmental carcinogens have not been identified, but one major exception is cutaneous malignant melanoma, for which the primary environmental agent is solar ultraviolet (UV) radiation. Hence, melanomagenesis represents a potential model of detrimental gene-environment interaction. Although the underlying genetic basis of melanoma is currently being elucidated, fundamental questions concerning UV and the mechanisms by which it operates remain unanswered. Significant progress has recently been made in creating UV-responsive, genetically tractable mouse models of melanoma that accurately recapitulate human disease. These models are providing novel insights into how the genome and environment interact in vivo.

Animal models of melanoma: an HGF/SF transgenic mouse model may facilitate experimental access to UV initiating events

Cutaneous malignant melanoma, the most lethal of the skin cancers, known for its intractability to current therapies, continues to increase in incidence, providing a significant public health challenge. There is a consensus that skin cancer is initiated by sunlight exposure. For non-melanoma skin cancer there is substantial evidence that chronic exposure to the ultraviolet B radiation (UVB) (280-320 nm) portion of the sunlight spectrum is responsible. Experimentally, UVB is mutagenic and chronic UVB exposure can cause non-melanoma skin cancer in laboratory animals. Non-melanoma tumors in animals and in humans show characteristic UVB signature lesions in the tumor suppressor p53 and/or in the patched (PTCH) gene. An action spectrum or wavelength dependence for squamous cell carcinoma in the mouse shows a major peak of efficacy in the UVB. For malignant melanoma, however, the situation is unclear and the critical direct target(s) of sunlight in initiating melanoma and even the wavelengths responsible are as yet unidentified. This lack of information is in major part a result of a paucity of animal models for melanoma which recapitulate the role of sunlight in initiating this disease. The epidemiology of melanoma differs significantly from non-melanoma skin cancer. Intense sporadic sunlight exposure in childhood, probably exacerbated by additional adult exposure, is associated with elevated melanoma risk. Melanoma is also a disease of gene-environment interactions with underlying genetic factors playing a significant role. These major differences indicate that extrapolation from information for non-melanoma skin cancer to melanoma is unlikely to be useful. We summarize in this review the experimental information available on the role of UV radiation in melanoma and give an overview of animal melanoma models. A new model derived by neonatal UV irradiation of hepatocyte growth factor/scatter factor (HGF/SF) transgenic mice is described which recapitulates the etiology, the histopathology and molecular pathogenesis of human disease. It is anticipated that the HGF/SF transgenic model will provide a means to access the mechanism(s) by which sunlight initiates this lethal disease and provide an appropriate vehicle for derivation of appropriate therapeutic and preventive strategies.

Dermatological perspectives of malignant melanoma

Early recognition and treatment of thin cutaneous melanoma have contributed to a decreased case-fatality rate over the past 60 years. The only known preventive measure for melanoma is sun protection in childhood, which directly affects the number of melanocytic nevi developing as an adult. Additional melanoma risk factors, clinical features, and malignant potential of precursor lesions are discussed. The four major clinicopathologic subtypes of melanoma are described, with recommendations for appropriate biopsy techniques for suspected melanoma. Nationwide skin cancer screenings by dermatologists and greater public awareness of the warning signs of melanoma have enhanced detection of early melanoma, and promoted chances for cure.

Melanoma development and progression: a conspiracy between tumor and host

While a genome-centric paradigm in human cancer development was useful for the understanding of some malignancies such as leukemias, causative molecular defects intrinsic to melanocytes have not been defined in the majority of human melanomas. Recent work, however, has shown that regulatory signals governing melanocytic cell growth and differentiation may originate from the surrounding host cells either directly through physical contact or indirectly through soluble factors and extracellular matrix molecules. In this review, we present experimental systems useful for dissecting melanoma-host interactions and highlight evidence that the tumor microenvironment contributes to the oncogenic process. Thus, melanomagenesis is not merely an act of a single outlaw but a conspiracy orchestrated by multiple partners in the neighborhood who come into play in a precise spatiotemporal order. Defining intercellular molecular dialogues in human skin promises to provide key information for the development of novel treatment strategies that target the functional unit of stroma and tumor.

Progress in cutaneous cancer research

Cutaneous cancers represent a major public health concern due to the very high incidence, associated medical costs, substantial mortality, and cosmetic deformities associated with treatment. Considerable progress in basic research has provided new insights into the underlying genetic basis of the major human cutaneous cancers, malignant melanoma, basal cell carcinoma, and squamous cell carcinoma. In turn, these genetic insights have illuminated biochemical pathways that promise to provide new approaches to the prevention and treatment of cutaneous neoplasms. This review will detail the evolving genetic information and indicate how this information is being used to refine experimental models that serve to both define the biochemistry of cancer pathogenesis and test novel approaches to cancer therapy. Combined with preventive measures to reduce exposure to sunlight, these advances are likely to reduce this major public health burden in the coming decade.

p53 alone or in combination with antisense cyclin D1 induces apoptosis and reduces tumor size in human melanoma

Melanoma incidence is growing at a faster rate than any other human malignancy. Wild-type (wt) p53 is important in both G(1) and G(2) cell cycle arrest, and cyclin D1 (CD1) is necessary for G(1)-->S progression in melanoma cells. We reported that an adenoviral vector containing wt p53 significantly reduced [(3)H]thymidine uptake in melanoma cells containing mutant but not wt p53. Subsequently we showed that CD1 decreased melanoma proliferation and increased apoptosis. We now extend these findings by evaluating the effect on preformed melanomas of (1) intratumoral therapy with wt p53 alone, (2) wt p53 in combination with antisense (AS) CD1, both short (< or =14 days) and longer term, and (3) doubling the dose or repeat doses of wt p53 or AS CD1. Two melanoma cells lines that metastasize in SCID mice (451 and 1205) were used, one containing a p53 mutation (451) and the other a normal p53 gene sequence (1205). Compared to injection with a control adenoviral vector containing beta-galactosidase (LacZ), intratumoral injection of wt p53 slowed the growth of tumors formed from 451 cells. Using 5 x 10(8) plaque forming units as our standard intratumoral dose, neither doubling the dose of LacZ, p53 or AS CD1, nor repeat doses of the vectors, was as effective as combined therapy with wt p53+AS CD1, which resulted in the shrinkage of all tumors treated and 4/7 (57%) tumors vanished. No tumors treated with wt p53 or AS CD1 alone vanished. Wt p53+AS CD1 treatment resulted in significantly more cells undergoing apoptosis compared to either therapy alone. In summary, combining the separately effective treatment vectors p53 and AS CD1 led to an enhanced growth-suppressive and apoptotic effect, supporting a role for combination gene therapy to treat human malignant melanoma.

A melanocyte-keratinocyte coculture model to assess regulators of pigmentation in vitro

Many melanocyte or skin equivalent models have been used to evaluate the potential efficacy of melanogenic compounds to regulate pigmentation, but there has been great variation in results, partially stemming from the use of different cell lines and diverse conditions for the melanogenic assays. In an earlier report, we optimized a microtiter format assay system to screen potential bioactive compounds using immortalized melan-a melanocytes. That assay system, termed the STOPR protocol, allowed effects on melanocyte proliferation and differentiation to be assessed in a highly sensitive, reproducible, and cost-effective manner. However, in the skin and hair, melanocytes interact with keratinocytes, fibroblasts, and other cell types, and testing of putative bioactive compounds on melanocytes alone in culture does not allow one to observe the interactions with those other cell types, such as would occur in vivo. Therefore, we developed a melanocyte-keratinocyte coculture protocol that allows testing of compounds for potential effects on pigmentation in a more physiologically relevant context. It is a sensitive, reproducible, and reliable model for testing melanogenic regulators, and we have standardized it with known melanogenic inhibitors (hydroquinone, arbutin, kojic acid, and niacinamide) and stimulators (alpha-melanocyte-stimulating hormone, 8-methoxypsoralen, and 3,4-dihydroxyphenylalanine). This coculture system allows for large-scale screening of candidate compounds in conjunction with the STOPR protocol and provides a more physiologically relevant system to study melanocyte-keratinocyte interactions and to elucidate the regulatory mechanisms of melanogenic compounds.