Melanoma

The status of microRNA-21 expression and its clinical significance in human cutaneous malignant melanoma

Dysregulation of microRNA-21 plays critical roles in tumor initiation and progression. The purpose of this study was to investigate the status of microRNA-21 expression in human cutaneous malignant melanoma and determine its clinical significance. TaqMan(®) real-time RT-PCR assay was performed to examine the expression of microRNA-21 in 10 cases of dysplastic nevi, 86 cases of primary cutaneous melanomas, 10 cases of melanoma metastases. The correlation of microRNA-21 expression with clinicopathological factors or prognosis of patients with cutaneous melanoma was statistically analyzed. Additionally, the effects of microRNA-21 expression on growth, apoptosis and chemo- or radiosensitivity of melanoma cells were also investigated by transfection of microRNA-21 inhibitor. We firstly showed that increased levels of microRNA-21 expression were shown from dysplastic nevi to primary cutaneous melanomas to melanoma metastases. Moreover, high miR-21 expression was found to be correlated with Breslow thickness and advanced clinical stage. Patients with high microRNA-21 expression showed shorter 5-year disease-free or overall survival than those with low microRNA-21 expression. Furthermore, multivariate regression analysis showed that the status of microRNA-21 expression was an independent prognostic factor for overall survival of patients. Antisense-mediated microRNA-21 inhibition could significantly suppress growth, increase apoptosis and enhance chemo- or radiosensitivity of human cutaneous melanoma cells by inducing the increased Bax/Bcl-2 ratio. Thus, the status of microRNA-21 might be an independent prognostic factor for patients with cutaneous melanoma, and microRNA-21 has the potential of being a novel molecular target for the treatment of human cutaneous melanoma.

Novel multiple markers to distinguish melanoma from dysplastic nevi

Background

Distinguishing melanoma from dysplastic nevi can be challenging.

Objective

To assess which putative molecular biomarkers can be optimally combined to aid in the clinical diagnosis of melanoma from dysplastic nevi.

Methods

Immunohistochemical expressions of 12 promising biomarkers (pAkt, Bim, BRG1, BRMS1, CTHRC1, Cul1, ING4, MCL1, NQO1, SKP2, SNF5 and SOX4) were studied in 122 melanomas and 33 dysplastic nevi on tissue microarrays. The expression difference between melanoma and dysplastic nevi was performed by univariate and multiple logistic regression analysis, diagnostic accuracy of single marker and optimal combinations were performed by receiver operating characteristic (ROC) curve and artificial neural network (ANN) analysis. Classification and regression tree (CART) was used to examine markers simultaneous optimizing the accuracy of melanoma. Ten-fold cross-validation was analyzed for estimating generalization error for classification.

Results

Four (Bim, BRG1, Cul1 and ING4) of 12 markers were significantly differentially expressed in melanoma compared with dysplastic nevi by both univariate and multiple logistic regression analysis (p < 0.01). These four combined markers achieved 94.3% sensitivity, 81.8% specificity and attained 84.3% area under the ROC curve (AUC) and the ANN classified accuracy with training of 83.2% and testing of 81.2% for distinguishing melanoma from dysplastic nevi. The classification trees identified ING4, Cul1 and BRG1 were the most important classification parameters in ranking top-performing biomarkers with cross-validation error of 0.03.

Conclusions

The multiple biomarkers ING4, Cul1, BRG1 and Bim described here can aid in the discrimination of melanoma from dysplastic nevi and provide a new insight to help clinicians recognize melanoma.

Hic-5 affects proliferation, migration and invasion of B16 murine melanoma cells

Hic-5 is a shuttling protein between the cell membrane and the nucleus which functions as a focal adhesion adaptor protein and a nuclear receptor coactivator. Although several studies have shown its involvement in other types of cancer, the role of Hic-5 in melanoma is unknown. Herein, we show for the first time that Hic-5 is expressed in B16-F1 murine melanoma cells. To determine its function in melanoma cells, we used shRNA-mediated RNA interference and established stable clones with down-regulated Hic-5 expression. These clones had impaired growth and metastatic potential compared with controls in vivo, which correlated with decreased proliferation, migration and invasion in vitro. Moreover, silencing of Hic-5 expression in B16-F1 activated RhoA with an amoeboid phenotypic change, indicating that Hic-5 is a key regulator of B16-F1 metastasis in the context of Rho-dependent motility. These results provide new evidence that Hic-5 is a possible molecular target for treatment of melanoma.

Comparative exome sequencing of metastatic lesions provides insights into the mutational progression of melanoma

Background

Metastasis is characterized by spreading of neoplastic cells to an organ other than where they originated and is the predominant cause of death among cancer patients. This holds true for melanoma, whose incidence is increasing more rapidly than any other cancer and once disseminated has few therapeutic options. Here we performed whole exome sequencing of two sets of matched normal and metastatic tumor DNAs.

Results

Using stringent criteria, we evaluated the similarities and differences between the lesions. We find that in both cases, 96% of the single nucleotide variants are shared between the two metastases indicating that clonal populations gave rise to the distant metastases. Analysis of copy number variation patterns of both metastatic sets revealed a trend similar to that seen with our single nucleotide variants. Analysis of pathway enrichment on tumor sets shows commonly mutated pathways enriched between individual sets of metastases and all metastases combined.

Conclusions

These data provide a proof-of-concept suggesting that individual metastases may have sufficient similarity for successful targeting of driver mutations.

Adenovirus-mediated expression of mutated forkhead human transcription like-1 suppresses tumor growth in a mouse melanoma xenograft model

Melanoma is generally resistant to chemotherapy, which may be related to defects in death receptor signaling and to defects in induction of apoptosis. Forkhead family transcription factors induce the expression of death receptor ligands such as Fas ligand (Fas-L) resulting in apoptosis. We therefore investigated whether a triple mutant form of forkhead transcription factor FKHRL1 (FKHRL1/TM) can enhance Fas-L mediated-apoptosis in melanoma cells. Two melanoma cells A2058 or DM6 were tested for their sensitivity to agonistic anti-Fas antibody (CH-11); adenovirus expressing FKHRL1/TM (Ad-FKHRL1/TM) was assessed for its capability to induce activation of the caspase pathway; the role of Fas-L in the Ad-FKHRL1/TM mediated-cell death was also assessed in vitro. Ad-FKHRL1/TM antitumor activity in vivo was also evaluated in a mouse melanoma xenograft model. We found that DM6 melanoma cells were more resistant to Fas/Fas-L-mediated apoptosis induced by agonistic anti-Fas antibody than A2058 melanoma cells. Ectopic expression of FKHRL1/TM in melanoma cells upregulated Fas-L expression, decreased procaspase-8 levels, and significantly increased Fas/FasL-mediated cell death in both cells lines; this induced cell death was partially blocked by a Fas/Fas-L antagonist. Importantly, Ad-FKHRL1/TM treatment of subcutaneous melanoma xenografts in mice resulted in approximately 70% decrease in tumor size compared with controls. These data indicate that overexpression of FKHRL1/TM can induce the Fas-L pathway in melanoma cells. Ad-FKHRL1/TM therefore might represent a promising vector for melanoma treatment.

Regulating the response to targeted MEK inhibition in melanoma: enhancing apoptosis in NRAS- and BRAF-mutant melanoma cells with Wnt/β-catenin activation

The limitations of revolutionary new mutation-specific inhibitors of BRAF(V600E) include the universal recurrence seen in melanoma patients treated with this novel class of drugs. Recently, our lab showed that simultaneous activation of the Wnt/β-catenin signaling pathway and targeted inhibition of BRAF(V600E) by PLX4720 synergistically induces apoptosis across a spectrum of BRAF(V600E) melanoma cell lines. As a follow-up to that study, treatment of BRAF-mutant and NRAS-mutant melanoma lines with WNT3A and the MEK inhibitor AZD6244 also induces apoptosis. The susceptibility of BRAF-mutant lines and NRAS-mutant lines to apoptosis correlates with negative regulation of Wnt/β-catenin signaling by ERK/MAPK signaling and dynamic decreases in abundance of the downstream scaffolding protein, AXIN1. Apoptosis-resistant NRAS-mutant lines can sensitize to AZD6244 by pretreatment with AXIN1 siRNA, similar to what we previously reported in BRAF-mutant cell lines. Taken together, these findings indicate that NRAS-mutant melanoma share with BRAF-mutant melanoma the potential to regulate apoptosis upon MEK inhibition through WNT3A and dynamic regulation of cellular AXIN1. Understanding the cellular context that makes melanoma cells susceptible to this combination treatment will contribute to the study and development of novel therapeutic combinations that may lead to more durable responses.

Diagnosis and management of melanoma with regional lymph node metastases: a population-based study in France

BACKGROUND

Stage III melanoma represents a borderline situation regarding the potential curability of this potentially aggressive cancer and consequently, regional lymph node metastases (RLNM) are a major challenge for melanoma management.

OBJECTIVE

To describe the management of melanoma with RLNM as practised in France in 2008 and compare results with previous data from 2004, considering that new French recommendations were published in 2005.

METHODS

Retrospective population-based study in five regions of France totalling 8.3 million inhabitants, targeting all incident cases of RLNM diagnosed in 2008. Questionnaires were mailed to physicians to identify cases and collect data, with verification by cancer registries for cases diagnosed concomitantly with the primary tumour using sentinel lymph node biopsies (SLNB).

RESULTS

Data were collected for 101 patients in 2008, and compared to 89 cases treated in 2004. Palpation by a dermatologist was the most common circumstance of diagnosis of RLNM in 2008 (36%), followed by SLNB (29%), self-palpation by the patient (16%) and lymph node ultrasonography (6%), without significant modification from 2004. After lymphadenectomy an adjuvant therapy was proposed in 62% of cases, mainly consisting in high-dose interferon (HD-IFN) (80%). Overall, HD-IFN was proposed in 49% of cases, but effectively started in only 40% of cases after being proposed, and prematurely withdrawn in 28%, showing major changes as compared with 2004 (33%, 77% and 67%, respectively, P < 0.05). Adjuvant chemotherapy was not proposed to any patients in 2008, compared to 29% in 2004. Surveillance procedures included medical imaging less often in 2008 (76%) than in 2004 (92%) (P = 0.004), but more often included FDG-PET (23% vs. 12%, P = 0.09).

CONCLUSION

Overall, actual practice was in accordance with French recommendations. The main developments from 2004 to 2008 were the disappearance of adjuvant chemotherapies and a more accurate selection of patients for adjuvant interferon.

Regulation of cell cycle checkpoint kinase WEE1 by miR-195 in malignant melanoma

WEE1 kinase has been described as a major gate keeper at the G2 cell cycle checkpoint and to be involved in tumour progression in different malignant tumours. Here we analysed the expression levels of WEE1 in a series of melanoma patient samples and melanoma cell lines using immunoblotting, quantitative real-time PCR and immunohistochemistry. WEE1 expression was significantly downregulated in patient samples of metastatic origin as compared with primary melanomas and in melanoma cell lines of high aggressiveness as compared with cell lines of low aggressiveness. Moreover, there was an inverse correlation between the expression of WEE1 and WEE1-targeting microRNA miR-195. Further analyses showed that transfection of melanoma cell lines with miR-195 indeed reduced WEE1 mRNA and protein expression in these cells. Reporter gene analysis confirmed direct targeting of the WEE1 3' untranslated region (3'UTR) by miR-195. Overexpression of miR-195 in SK-Mel-28 melanoma cells was accompanied by WEE1 reduction and significantly reduced stress-induced G2-M cell cycle arrest, which could be restored by stable overexpression of WEE1. Moreover, miR-195 overexpression and WEE1 knockdown, respectively, increased melanoma cell proliferation. miR-195 overexpression also enhanced migration and invasiveness of melanoma cells. Taken together, the present study shows that WEE1 expression in malignant melanoma is directly regulated by miR-195. miR-195-mediated downregulation of WEE1 in metastatic lesions may help to overcome cell cycle arrest under stress conditions in the local tissue microenvironment to allow unrestricted growth of tumour cells.

Molecular testing in melanoma

Melanoma is the deadliest form of skin cancer and is increasing in incidence. Recent treatment advances have been made, but there remains a need for continued development of effective therapy options, as treatment rarely leads to cure. Many melanomas contain somatic mutations involved in tumor pathogenesis. Accurate identification of these mutations is necessary to stratify patients for the purpose of treatment and potential for clinical trials, given the absence or presence of a specific mutation. There are a number of techniques available that will identify genetic mutations and genomic aberrations present within melanoma tumor samples which are reviewed here. The type of mutation and sample number will drive selection of a given mutation detection strategy. The strengths and weaknesses, along with limitations, of the various methods will also be discussed. The discovery of somatic mutations integral in melanoma will increase our understanding of tumor pathogenesis and should facilitate identification of mutations relevant to clinical treatment decisions, advancing progress toward personalized medicine.

The epithelial-mesenchymal transition (EMT) regulatory factor SLUG (SNAI2) is a downstream target of SPARC and AKT in promoting melanoma cell invasion

During progression of melanoma, malignant melanocytes can be reprogrammed into mesenchymal-like cells through a process similar to epithelial-mesenchymal transition (EMT), which is associated with downregulation of the junctional protein E-cadherin and acquisition of a migratory phenotype. Recent evidence supports a role for SLUG, a transcriptional repressor of E-cadherin, as a melanocyte lineage transcription factor that predisposes to melanoma metastasis. However, the signals responsible for SLUG expression in melanoma are unclear and its role in the invasive phenotype is not fully elucidated. Here, we report that SLUG expression and activation is driven by SPARC (also known as osteonectin), a secreted extracellular matrix-associated factor that promotes EMT-like changes. Ectopic expression or knockdown of SPARC resulted in increased or reduced expression of SLUG, respectively. SLUG increase occurred concomitantly with SPARC-mediated downregulation of E-cadherin and P-cadherin, and induction of mesenchymal traits in human melanocytes and melanoma cells. Pharmacological blockade of PI3 kinase/AKT signaling impeded SPARC-induced SLUG levels and cell migration, whereas adenoviral introduction of constitutively active AKT allowed rescue of SLUG and migratory capabilities of SPARC knockdown cells. We also observed that pharmacological inhibition of oncogenic BRAF^V600E using PLX4720 did not influence SLUG expression in melanoma cells harboring BRAF^V600E. Furthermore, SLUG is a bona fide transcriptional repressor of E-cadherin as well as a regulator of P-cadherin in melanoma cells and its knockdown attenuated invasive behavior and blocked SPARC-enhanced cell migration. Notably, inhibition of cell migration in SPARC-depleted cells was rescued by expression of a SLUG transgene. In freshly isolated metastatic melanoma cells, a positive association between SPARC and SLUG mRNA levels was also found. These findings reveal that autocrine SPARC maintains heightened SLUG expression in melanoma cells and indicate that SPARC may promote EMT-associated tumor invasion by supporting AKT-dependent upregulation of SLUG.

Epigenetic genes regulated by the BRAFV600E signaling are associated with alterations in the methylation and expression of tumor suppressor genes and patient survival in melanoma

We have previously reported that the BRAFV600E signaling causes genome-wide aberrations in gene methylation in melanoma cells. To explore the potential molecular mechanisms for this epigenetic effect of BRAFV600E, in this in silico study we analyzed 11 microarray datasets retrieved from NCBI GEO database and examined the relationship of the expression of the epigenetic genes (genes involved in epigenetic regulation) with BRAFV600E signaling, methylation and expression of tumor-suppressor genes (TSGs) in melanoma, and patient survival with this cancer. Among 273 epigenetic genes examined, 12 genes were down-regulated (named DD genes) and 16 were up-regulated (UU genes) by suppression of the BRAFV600E signaling using inhibitors. While the expression of 245 non-DD/UU genes overall had no correlation with the expression and methylation of a set of potential TSGs, the expression of DD genes was significantly correlated negatively with the TSG expression and positively with TSG methylation. Expression of UU genes was positively, albeit weakly, associated with the TSG expression. Overall, no correlation was found between UU gene expression and TSG methylation. Importantly, the expression of DD genes, but not UU genes, was significantly associated with decreased survival of patients with melanoma. Interestingly, the promoters of DD genes contain more binding motifs of c-fos and myc, two BRAFV600E signaling-related transcription factors, than those of UU and non-DD/UU genes. Thus, these results link epigenetic genes to methylation and suppression of tumor suppressor genes as a mechanism involved in BRAFV600E-promoted melanoma tumorigenesis and uncover a novel molecular signature that predicts a poor prognosis of melanoma.

RSK regulates activated BRAF signalling to mTORC1 and promotes melanoma growth

The Ras/mitogen-activated protein kinase (MAPK) signalling cascade regulates various biological functions, including cell growth, proliferation and survival. As such, this pathway is often deregulated in cancer, including melanomas, which frequently harbour activating mutations in the NRAS and BRAF oncogenes. Hyperactive MAPK signalling is known to promote protein synthesis, but the mechanisms by which this occurs remain poorly understood. Here, we show that expression of oncogenic forms of Ras and Raf promotes the constitutive activation of the mammalian target of rapamycin (mTOR). Using pharmacological inhibitors and RNA interference, we find that the MAPK-activated protein kinase RSK (p90 ribosomal S6 kinase) is partly required for these effects. Using melanoma cell lines carrying activating BRAF mutations, we show that ERK/RSK signalling regulates assembly of the translation initiation complex and polysome formation, as well as the translation of growth-related messenger RNAs containing a 5'-terminal oligopyrimidine (TOP) motif. Accordingly, we find that RSK inhibition abrogates tumour growth in mice. Our findings indicate that RSK may be a valuable therapeutic target for the treatment of tumours characterized by deregulated MAPK signalling, such as melanoma.

The environmental stressor ultraviolet B radiation inhibits murine antitumor immunity through its ability to generate platelet-activating factor agonists

Ubiquitous pro-oxidative stressor ultraviolet B radiation (UVB) to human or mouse skin generates platelet-activating factor (PAF) and novel oxidatively modified glycerophosphocholines (Ox-GPCs) with PAF-receptor (PAF-R) agonistic activity. These lipids mediate systemic immunosuppression in a process involving IL-10. The current studies sought to determine the functional significance of UVB-mediated systemic immunosuppression in an established model of murine melanoma. We show that UVB irradiation augments B16F10 tumor growth and is dependent on host, but not melanoma cell; PAF-R-expression as UVB or the PAF-R agonist, carbamoyl PAF (CPAF), both promote B16F10 tumor growth in wild-type (WT) mice, independent of whether B16F10 cells express PAF-Rs, but do not augment tumor growth in Pafr -/- mice. UVB-mediated augmentation of experimental murine tumor growth was inhibited with antioxidants, demonstrating the importance of Ox-GPC PAF-R agonists produced non-enzymatically. Host immune cells are required as CPAF-induced augmentation of tumor growth which is not seen in immunodeficient NOD SCID mice. Finally, depleting antibodies against IL-10 in WT mice or depletion of CD25-positive cells in FoxP3(EGFP) transgenic mice block UVB and/or CPAF-induced tumor growth supporting a requirement for IL-10 and Tregs in this process. These findings indicate that UVB-generated Ox-GPCs with PAF-R agonistic activity enhance experimental murine melanoma tumor growth through targeting host immune cells, most notably Tregs, to mediate systemic immunosuppression.

Good clinical and radiological response to BRAF inhibitor in patient with metastatic thin melanoma

The authors herein report the case of a 32-year-old man with advancing metastatic malignant melanoma, who has progressed through all previous lines of therapy, presenting with ongoing respiratory tract symptoms of exertional shortness of breath and cough. CT restaging confirmed clinical findings of deteriorating pulmonary disease; histological review revealed V600E BRAF mutation. He was started on targeted biological therapy with BRAF inhibitor GSK2118436, and is having a good clinical and radiological response without significant lasting toxicity.

Frequency of BRAF Mutation and Clinical Relevance for Primary Melanomas

BACKGROUND

This study was conducted to clarify the frequency of the BRAF mutation in primary melanomas and its correlation with clinicopathologic parameters.

METHODS

We analyzed the frequency of BRAF mutation in patients with primary cutaneous melanoma (n=58) or non-cutaneous one (n=27) by performing dual priming oligonucleotide-based multiplex real-time polymerase chain reaction to isolate and to purify the DNA from the formalin-fixed and paraffin-embedded tumors.

RESULTS

The BRAF mutation was found in 17.2% (10/58) of patients with primary cutaneous melanoma and 11.1% (3/27) of those with non-cutaneous melanoma. The frequency of BRAF mutation was not correlated with any clinicopathologic parameters with the exception of the patient age. The frequency of the BRAF mutation was significantly higher in patients younger than 60 years as compared with those older than 60 years (p=0.005).

CONCLUSIONS

Compared with previous reports, our results showed that the frequency of the BRAF mutation was relatively lower in patients with primary cutaneous melanoma. Besides, our results also showed that the frequency of the BRAF mutation had an inverse correlation with the age. Further studies are warranted to exclude methodological bias, to elucidate the difference in the frequency of the BRAF mutation from the previous reports from a Caucasian population and to provide an improved understanding of the molecular pathogenesis of malignant melanoma.

Role of Tip60 in human melanoma cell migration, metastasis, and patient survival

The tumor suppressor Tip60 regulates gene transcription, DNA damage response, apoptosis, and cancer development, but its role in melanoma is unknown. In this study, we investigated the expression pattern of Tip60 in melanoma and assessed its prognostic value. Using tissue microarrays consisting of 448 cases of melanomas (201 for the training set and 247 for the validation set) and 105 cases of nevi, we found that Tip60 expression was significantly reduced in metastatic melanoma compared to common nevi (P=0.045), dysplastic nevi (P=0.047), and primary melanoma (P=0.001). Kaplan-Meier survival curve and univariate Cox regression analyses showed that reduced Tip60 expression was associated with a poorer 5-year disease-specific survival in primary melanoma (P=0.016) and metastatic melanoma patients (P=0.027). Multivariate Cox regression analyses indicated that Tip60 expression was an independent prognostic marker for primary (P=0.024) and metastatic melanomas (P=0.035). In vitro wound healing assay showed that enforced Tip60 expression inhibited but Tip60 knockdown enhanced melanoma cell migration, suggesting that Tip60 might regulate melanoma metastasis. Finally, we showed that overexpression of Tip60 in melanoma cells resulted in significantly increased chemosensitivity. Our data indicate that Tip60 may serve as a potential biomarker for melanoma patient outcome as well as a potential therapeutic target.

MMP2 expression is a prognostic marker for primary melanoma patients

BACKGROUND

Matrix metalloproteinase 2 (MMP2) is a collagenase, which aids tumor growth and invasion by digesting the extracellular matrix surrounding the tumor tissue. Our study examined MMP2 expression in various stages of melanoma progression and tested the prognostic significance of MMP2 expression. We also analyzed the correlation between p-Akt status and MMP2 expression in melanoma patients.

METHODS

Tissue microarray (TMA) and immunohistochemistry were employed to study the expression of MMP2. A total of 482 melanoma (330 primary and 152 metastatic) tumor biopsies and 149 nevi biopsies (49 normal and 100 dysplastic nevi) were used for the analysis. MMP2 expression was correlated with melanoma progression. Kaplan-Meier survival curve and multivariate Cox regression analysis were applied to verify the prognostic significance of MMP2 expression. The correlation between MMP2 and p-Akt expression was analyzed in 92 cases which were common in the present and the previous study on p-Akt expression.

RESULTS

Strong MMP2 expression is significantly increased in primary (25 %) and metastatic melanoma (43 %) compared to normal (5 %) and dysplastic nevi (10 %). Patients with strong MMP2 had significantly poorer survival compared to those with negative-to-moderate MMP2 expression. MMP2 expression could predict the patient survival independent of tumor thickness and ulceration. Furthermore, in our cohort study MMP2 expression was associated with p-Akt status and patient survival.

CONCLUSIONS

Strong MMP2 staining is associated with worse survival of melanoma patients and is an independent molecular prognostic factor for primary melanoma.

Stathmin 1 is a potential novel oncogene in melanoma

In previous studies, we demonstrated that miR-193b expression is reduced in melanoma relative to benign nevi, and also that miR-193b represses cyclin D1 and Mcl-1 expression. We suggested that stathmin 1 (STMN1) might be a target of miR-193b. STMN1 normally regulates microtubule dynamics either by sequestering free tubulin heterodimers or by promoting microtubule catastrophe. Increased expression of STMN1 has been observed in a variety of human malignancies, but its association with melanoma is unknown. We now report that STMN1 is upregulated during the progression of melanoma relative to benign nevi, and that STMN1 is directly regulated by miR-193b. Using an experimental cell culture approach, overexpression of miR-193b using synthetic microRNAs repressed STMN1 expression, whereas inhibition of miR-193b with anti-miR oligos increased STMN1 expression in melanoma cells. The use of a luciferase reporter assay confirmed that miR-193b directly regulates STMN1 by targeting the 3'-untranslated region of STMN1 mRNA. We further demonstrated that STMN1 is overexpressed in malignant melanoma compared with nevi in two independent melanoma cohorts, and that its level is inversely correlated with miR-193b expression. However, STMN1 expression was not significantly associated with patient survival, Breslow depth, mitotic count or patient age. STMN1 knockdown by small-interfering RNA in melanoma cells drastically repressed cell proliferation and migration potential, whereas ectopic expression of STMN1 using lentivirus increased cell proliferation and migration rates. Subsequent gene expression analysis indicated that interconnected cytoskeletal networks are directly affected following STMN1 knockdown. In addition, we identified deregulated genes associated with proliferation and migration, and revealed that p21(Cip1/Waf1) and p27(Kip) could be downstream effectors of STMN1 signaling. Taken together, our study suggests that downregulation of miR-193b may contribute to increased STMN1 expression in melanoma, which consequently promotes migration and proliferation of tumor cells.

Characterization of a new human melanoma cell line with CD133 expression

A novel human malignant melanoma cell line, designated MEL-RC08, was established from a pericranial metastasis of a malignant melanoma of the skin. The cell line has been subcultured for more than 150 passages and is tumorigenic in nude mice. Growth kinetics, cytogenetics, flow cytometry, and molecular techniques for analysis of the genes implicated in cell cycle control; mutations in BRAF, NRAS, C-KiT, RB, and TP53 genes; and amplification of MDM2, CDK4, and cyclin D1 have been studied. Cytogenetically, the tumor and the cell line showed a hypertriploid karyotype with many clonal numeric and structural abnormalities. DNA flow cytometry showed an aneuploid peak with a DNA index value of 1.5. Mutations in TP53 and BRAF genes were demonstrated in both tumor and cell line. Furthermore, stem cell marker CD133 expression was detected in most cells, together with other stem cell markers, suggesting the presence of cells with tumor-initiating potential in this cell line.

The immune response to melanoma is limited by thymic selection of self-antigens

The expression of melanoma-associated antigens (MAA) being limited to normal melanocytes and melanomas, MAAs are ideal targets for immunotherapy and melanoma vaccines. As MAAs are derived from self, immune responses to these may be limited by thymic tolerance. The extent to which self-tolerance prevents efficient immune responses to MAAs remains unknown. The autoimmune regulator (AIRE) controls the expression of tissue-specific self-antigens in thymic epithelial cells (TECs). The level of antigens expressed in the TECs determines the fate of auto-reactive thymocytes. Deficiency in AIRE leads in both humans (APECED patients) and mice to enlarged autoreactive immune repertoires. Here we show increased IgG levels to melanoma cells in APECED patients correlating with autoimmune skin features. Similarly, the enlarged T cell repertoire in AIRE^−/− mice enables them to mount anti-MAA and anti-melanoma responses as shown by increased anti-melanoma antibodies, and enhanced CD4⁺ and MAA-specific CD8⁺ T cell responses after melanoma challenge. We show that thymic expression of gp100 is under the control of AIRE, leading to increased gp100-specific CD8⁺ T cell frequencies in AIRE^−/− mice. TRP-2 (tyrosinase-related protein), on the other hand, is absent from TECs and consequently TRP-2 specific CD8⁺ T cells were found in both AIRE^−/− and AIRE^+/+ mice. This study emphasizes the importance of investigating thymic expression of self-antigens prior to their inclusion in vaccination and immunotherapy strategies.

Triggering apoptotic death of human malignant melanoma a375.s2 cells by bufalin: involvement of caspase cascade-dependent and independent mitochondrial signaling pathways

Bufalin was obtained from the skin and parotid venom glands of toad and has been shown to induce cytotoxic effects in various types of cancer cell lines, but there is no report to show that whether bufalin affects human skin cancer cells. The aim of this investigation was to study the effects of bufalin on human malignant melanoma A375.S2 cells and to elucidate possible mechanisms involved in induction of apoptosis. A375.S2 cells were treated with different concentrations of bufalin for a specific time period and investigated for effects on apoptotic analyses. Our results indicated that cells after exposure to bufalin significantly decreased cell viability, and induced cell morphological changes and chromatin condensation in a concentration-dependent manner. Flow cytometric assays indicated that bufalin promoted ROS productions, loss of mitochondrial membrane potential (ΔΨ_m), intracellular Ca²⁺ release, and nitric oxide (NO) formations in A375.S2 cells. Additionally, the apoptotic induction of bufalin on A375.S2 cells resulted from mitochondrial dysfunction-related responses (disruption of the ΔΨ_m and releases of cytochrome c, AIF, and Endo G), and activations of caspase-3, caspase-8 and caspase-9 expressions. Based on those observations, we suggest that bufalin-triggered apoptosis in A375.S2 cells is correlated with extrinsic- and mitochondria-mediated multiple signal pathways.

Genetics and epigenetics of cutaneous malignant melanoma: a concert out of tune

Cutaneous malignant melanoma (CMM) is the most life-threatening neoplasm of the skin and is considered a major health problem as both incidence and mortality rates continue to rise. Once CMM has metastasized it becomes therapy-resistant and is an inevitably deadly disease. Understanding the molecular mechanisms that are involved in the initiation and progression of CMM is crucial for overcoming the commonly observed drug resistance as well as developing novel targeted treatment strategies. This molecular knowledge may further lead to the identification of clinically relevant biomarkers for early CMM detection, risk stratification, or prediction of response to therapy, altogether improving the clinical management of this disease. In this review we summarize the currently identified genetic and epigenetic alterations in CMM development. Although the genetic components underlying CMM are clearly emerging, a complete picture of the epigenetic alterations on DNA (DNA methylation), RNA (non-coding RNAs), and protein level (histone modifications, Polycomb group proteins, and chromatin remodeling) and the combinatorial interactions between these events is lacking. More detailed knowledge, however, is accumulating for genetic and epigenetic interactions in the aberrant regulation of the INK4b-ARF-INK4a and microphthalmia-associated transcription factor (MITF) loci. Importantly, we point out that it is this interplay of genetics and epigenetics that effectively leads to distorted gene expression patterns in CMM.

Predictive markers in early research and companion diagnostic developments in oncology

Predictive biomarkers are discovered and used in oncology research to formulate hypotheses aimed at the identification of patients benefiting from specific therapeutic intervention(s). They pave the way to the development of companion diagnostic tests which are tools readily implemented in the clinic and serve to qualify a patient for treatment with a particular targeted drug or the continued use of a particular drug, thus maximizing the benefit to risk ratio of the medical intervention to the patient. Predictive biomarkers are defined by biological characteristics of the patient's or tumor status that can be measured objectively and correlated with clinical outcome: these can be molecular, cellular or biochemical features. Predictive markers need extensive analytical validation - specific for the tool utilized for their assessment - as well as rigorous clinical qualification in the context of the drug treatment for which they define clinical utility. The process of companion diagnostic development is a highly interdisciplinary and complex one, driven by key crucial milestones and accompanying the same and typical process of a whole drug discovery and development continuum, from marker discovery and validation, assay development, clinical qualification until test approval and commercialization.

Novel immunotherapy for malignant melanoma with a monoclonal antibody that blocks CEACAM1 homophilic interactions

CEACAM1 (biliary glycoprotein-1, CD66a) was reported as a strong clinical predictor of poor prognosis in melanoma. We have previously identified CEACAM1 as a tumor escape mechanism from cytotoxic lymphocytes. Here, we present substantial evidence in vitro and in vivo that blocking of CEACAM1 function with a novel monoclonal antibody (MRG1) is a promising strategy for cancer immunotherapy. MRG1, a murine IgG1 monoclonal antibody, was raised against human CEACAM1. It recognizes the CEACAM1-specific N-domain with high affinity (K(D) ~ 2 nmol/L). Furthermore, MRG1 is a potent inhibitor of CEACAM1 homophilic binding and does not induce any agonistic effect. We show using cytotoxicity assays that MRG1 renders multiple melanoma cell lines more vulnerable to T cells in a dose-dependent manner, only following antigen-restricted recognition. Accordingly, MRG1 significantly enhances the antitumor effect of adoptively transferred, melanoma-reactive human lymphocytes using human melanoma xenograft models in severe combined immunodeficient/nonobese diabetic (SCID/NOD) mice. A significant antibody-dependent cell cytotoxicity response was excluded. It is shown that MRG1 reaches the tumor and is cleared within a week. Importantly, approximately 90% of melanoma specimens are CEACAM1(+), implying that the majority of patients with melanoma could be amenable to MRG1-based therapy. Normal human tissue microarray displays limited binding to luminal epithelial cells on some secretory ducts, which was weaker than the broad normal cell binding of other anticancer antibodies in clinical use. Importantly, MRG1 does not directly affect CEACAM1(+) cells. CEACAM1 blockade is different from other immunomodulatory approaches, as MRG1 targets inhibitory interactions between tumor cells and late effector lymphocytes, which is thus a more specific and compartmentalized immune stimulation with potentially superior safety profile.

Identification of biomarkers to distinguish clear cell sarcoma from malignant melanoma

Clear cell sarcoma is a rare and malignant soft tissue tumor that shows phenotypic and immunohistochemical overlap with cutaneous malignant melanoma; identification of biomarkers that differentiate clear cell sarcoma from malignant melanoma is therefore needed. In this study, we performed mutation analysis of BRAF and NRAS, investigated the EWSR1 gene rearrangement and evaluated the protein expression of insulin-like growth factor 2 and insulin-like growth factor 1R in 31 cases of malignant melanoma and 16 cases of clear cell sarcoma. By direct sequencing and high-resolution melting analysis, we identified BRAF and NRAS mutations in 51.6% and 12.9% of malignant melanoma cases, respectively, while none of clear cell sarcoma harbored BRAF or NRAS mutations. Fluorescence in situ hybridization showed that 78.6% of clear cell sarcoma exhibited the t(12;22)(q13;q12) translocation. The presence of type 1, 2, and 3 EWSR1/ATF1 fusion gene transcripts was confirmed by reverse transcriptase polymerase chain reaction analysis, but type 4 and EWSR1/CREB1 fusion gene transcripts were not found. No fusion transcript could be detected in any of the malignant melanoma cases. Additionally, immunohistochemistry showed that the majority of clear cell sarcoma and malignant melanoma had insulin-like growth factor 2 and insulin-like growth factor receptor 1 expression; however the expression of insulin-like growth factor 1R was significantly higher in clear cell sarcoma compared to melanoma (p = .006). Our results suggest that the combination of BRAF and NRAS mutation analysis with fusion gene detection contributes to diagnosis of malignant melanoma and clear cell sarcoma, and that insulin-like growth factor 1R might be a novel target for the treatment of these two malignancies.

Insulin resistance in relation to melanoma risk

Obesity, deregulation of adipocytokines, and insulin resistance are interrelated and have been implicated in carcinogenesis. In search of novel risk factors for melanoma, we explored the association of this disease with insulin resistance in a small size, case-control study. Homeostasis Model Assessment for Insulin Resistance (HOMA-IR), serum leptin, and adiponectin levels were determined in 55 patients with incident melanoma and 165 age-matched and sex-matched controls. Odds ratios were derived after adjusting for skin type, medical history, sociodemographic, lifestyle, and anthropometric parameters. Among the controls, HOMA-IR correlated positively with BMI (r=0.34; P=0.0001), waist-to-hip ratio (r=0.20; P=0.01) and negatively with serum adiponectin (r=-0.21; P=0.006), whereas the correlation with leptin was essentially null (r=0.09; P=0.27). The mean HOMA-IR was approximately 1.5 times higher in cases than in controls (P=0.05). The established positive association of melanoma with skin type was evident in multiple logistic regression models and so was the association with increasing HOMA-IR quintile (odds ratio for the fifth quintile=3.68; 95% confidence intervals 1.15-11.79, P=0.02). The latter persisted after adjustment for anthropometric variables and adiponectin but was attenuated when leptin was introduced in the model. These findings point to insulin resistance as a potentially independent risk factor for melanoma and need to be confirmed by future larger studies, ideally allowing the control of the directionality of the association.

Cytoplasmic BRMS1 expression in malignant melanoma is associated with increased disease-free survival

Background/aims

Breast cancer metastasis suppressor 1 (BRMS1) blocks metastasis in melanoma xenografts; however, its usefulness as a biomarker in human melanomas has not been widely studied. The goal was to measure BRMS1 expression in benign nevi, primary and metastatic melanomas and evaluate its impact on disease progression and prognosis.

Methods

Paraffin-embedded tissue from 155 primary melanomas, 69 metastases and 15 nevi was examined for BRMS1 expression using immunohistochemistry. siRNA mediated BRMS1 down-regulation was used to study impact on invasion and migration in melanoma cell lines.

Results

A significantly higher percentage of nevi (87%), compared to primary melanomas (20%) and metastases (48%), expressed BRMS1 in the nucelus (p < 0.0001). Strong nuclear staining intensity was observed in 67% of nevi, and in 9% and 24% of the primary and metastatic melanomas, respectively (p < 0.0001). Comparable cytoplasmic expression was observed (nevi; 87%, primaries; 86%, metastases; 72%). However, a decline in cytoplasmic staining intensity was observed in metastases compared to nevi and primary tumors (26%, 47%, and 58%, respectively, p < 0.0001). Score index (percentage immunopositive celles multiplied with staining intensity) revealed that high cytoplasmic score index (≥ 4) was associated with thinner tumors (p = 0.04), lack of ulceration (p = 0.02) and increased disease-free survival (p = 0.036). When intensity and percentage BRMS1 positive cells were analyzed separately, intensity remained associated with tumor thickness (p = 0.024) and ulceration (p = 0.004) but was inversely associated with expression of proliferation markers (cyclin D3 (p = 0.008), cyclin A (p = 0.007), and p21^Waf1/Cip1 (p = 0.009)). Cytoplasmic score index was inversely associated with nuclear p-Akt (p = 0.013) and positively associated with cytoplasmic p-ERK1/2 expression (p = 0.033). Nuclear BRMS1 expression in ≥ 10% of primary melanoma cells was associated with thicker tumors (p = 0.016) and decreased relapse-free period (p = 0.043). Nuclear BRMS1 was associated with expression of fatty acid binding protein 7 (FABP7; p = 0.011), a marker of invasion in melanomas. In line with this, repression of BRMS1 expression reduced the ability of melanoma cells to migrate and invade in vitro.

Conclusion

Our data suggest that BRMS1 is localized in cytoplasm and nucleus of melanocytic cells and that cellular localization determines its in vivo effect. We hypothesize that cytoplasmic BRMS1 restricts melanoma progression while nuclear BRMS1 possibly promotes melanoma cell invasion.

Please see related article: http://www.biomedcentral.com/1741-7015/10/19

Anti-oncogenic microRNA-203 induces senescence by targeting E2F3 protein in human melanoma cells

MicroRNAs regulate gene expression by repressing translation or directing sequence-specific degradation of their complementary mRNA. We recently reported that miR-203 is down-regulated, and its exogenous expression inhibits cell growth in canine oral malignant melanoma tissue specimens as well as in canine and human malignant melanoma cells. A microRNA target database predicted E2F3 and ZBP-89 as putative targets of microRNA-203 (miR-203). The expression levels of E2F3a, E2F3b, and ZBP-89 were markedly up-regulated in human malignant melanoma Mewo cells compared with those in human epidermal melanocytes. miR-203 significantly suppressed the luciferase activity of reporter plasmids containing the 3'-UTR sequence of either E2F3 or ZBP-89 complementary to miR-203. The ectopic expression of miR-203 in melanoma cells reduced the levels of E2F3a, E2F3b, and ZBP-89 protein expression. At the same time, miR-203 induced cell cycle arrest and senescence phenotypes, such as elevated expression of hypophosphorylated retinoblastoma and other markers for senescence. Silencing of E2F3, but not of ZBP-89, inhibited cell growth and induced cell cycle arrest and senescence. These results demonstrate a novel role for miR-203 as a tumor suppressor acting by inducing senescence in melanoma cells.

Cutaneous malignancies of the upper extremity

Cutaneous malignancies are the most common primary malignancies of the hand. The hand surgeon may be the first physician to see these patients or may have the patients referred to them because of expertise in this anatomical region. This article reviews diagnosis and treatment, including margin of resection and need for sentinel lymph node biopsy, for the 3 most common cutaneous malignancies: basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.

Relationship between Latitude and Melanoma in Italy

Objective. Evaluate the ecological relationship between skin melanoma epidemiology and latitude in Italy. Methods. We used data from the Italian network of cancer registries (Airtum). In a Poisson model, we evaluated the effect on incidence, mortality, and survival of latitude, adjusting for some demographic, social, phenotypic, and behavioural variables. Results. Incidence increased in Italy by 17% for each degree of increase in latitude. The effect of latitude was statistically significantly present also adjusting for other variables (incidence rate ratio = 1.08). The effect of latitude on increasing mortality (mortality rate ratio = 1.27) and improving survival (relative excess risk of death = 0.93) was no longer present in the multivariate model. Conclusion. Melanoma incidence, mortality, and survival vary in Italy according to latitude. After adjustment for several confounders, incidence still grows with growing latitude. Presumably, latitude expresses other variables that might be related to individual susceptibility and/or local care.

The BRAF(V600E) causes widespread alterations in gene methylation in the genome of melanoma cells

Although BRAF(V600E) is well known to play an important role in the tumorigenesis of melanoma, its molecular mechanism, particularly the epigenetic aspect, has been incompletely understood. Here, we investigated the role of BRAF(V600E) signaling in altering gene methylation in the genome of melanoma cells using a methylated CpG island amplification/CpG island microarray system and searched for genes coupled to the BRAF(V600E) signaling through methylation aberrations. The results indicated that a wide range of genes with broad functions were linked to BRAF(V600E) signaling through their hyper- or hypomethylation. Expression of 59 genes hypermethylated upon BRAF knockdown was selectively tested and found to be largely correspondingly underexpressed, suggesting that these genes were naturally hypomethylated, and overexpressed with BRAF(V600E) in melanoma. This BRAF(V600E)-promoted hypomethylation was confirmed on genes selectively examined in primary melanoma tumors. Some of these genes were functionally tested and demonstrated to play a role in melanoma cell proliferation and invasion. As a mechanism of aberrant gene methylation driven by BRAF(V600E), expression of the DNA methyltransferase 1 and histone methyltransferase EZH2 was profoundly affected by BRAF(V600E). We have thus uncovered a previously unrecognized prominent epigenetic mechanism in the tumorigenesis of melanoma driven by BRAF(V600E). Many of the functionally important genes controlled by the BRAF(V600E) signaling through aberrant methylation may prove to be novel therapeutic targets for melanoma.

Polymorphisms in nevus-associated genes MTAP, PLA2G6, and IRF4 and the risk of invasive cutaneous melanoma

An evolving hypothesis postulates that melanomas may arise through 'nevus-associated' and 'chronic sun exposure' pathways. We explored this hypothesis by examining associations between nevus-associated loci and melanoma risk across strata of body site and histological subtype. We genotyped 1028 invasive case patients and 1469 controls for variants in methylthioadenosine phosphorylase (MTAP), phospholipase A2, group VI (PLA2G6), and Interferon regulatory factor 4 (IRF4), and compared allelic frequencies globally and by anatomical site and histological subtype of melanoma. Odds-ratios (ORs) and 95% confidence intervals (CIs) were calculated using classical and multinomial logistic regression models. Among controls, MTAP rs10757257, PLA2G6 rs132985 and IRF4 rs12203592 were the variants most significantly associated with number of nevi. In adjusted models, a significant association was found between MTAP rs10757257 and overall melanoma risk (OR = 1.32, 95% CI = 1.14-1.53), with no evidence of heterogeneity across sites (Phomogeneity =.52). In contrast, MTAP rs10757257 was associated with superficial spreading/nodular melanoma (OR = 1.34, 95% CI = 1.15- 1.57), but not with lentigo maligna melanoma (OR = 0.79, 95% CI = 0.46-1.35) (Phomogeneity =.06), the subtype associated with chronic sun exposure. Melanoma was significantly inversely associated with rs12203592 in children (OR = 0.35, 95% CI = 0.16-0.77) and adolescents (OR = 0.61, 95% CI = 0.42-0.91), but not in adults (Phomogeneity =.0008). Our results suggest that the relationship between MTAP and melanoma is subtype-specific, and that the association between IRF4 and melanoma is more evident for cases with a younger age at onset. These findings lend some support to the 'divergent pathways' hypothesis and may provide at least one candidate gene underlying this model. Further studies are warranted to confirm these findings and improve our understanding of these relationships.

Intratumoral heterogeneity as a therapy resistance mechanism: role of melanoma subpopulations

Malignant melanoma is an aggressive form of skin cancer whose incidence continues to increase worldwide. Increased exposure to sun, ultraviolet radiation, and the use of tanning beds can increase the risk of melanoma. Early detection of melanomas is the key to successful treatment mainly through surgical excision of the primary tumor lesion. But in advanced stage melanomas, once the disease has spread beyond the primary site to distant organs, the tumors are difficult to treat and quickly develop resistance to most available forms of therapy. The advent of molecular and cellular techniques has led to a better characterization of tumor cells revealing the presence of heterogeneous melanoma subpopulations. The discovery of gene mutations and alterations of cell-signaling pathways in melanomas has led to the development of new targeted drugs that show dramatic response rates in patients. Single-agent therapies generally target one subpopulation of tumor cells while leaving others unharmed. The surviving subpopulations will have the ability to repopulate the original tumors that can continue to progress. Thus, a rational approach to target multiple subpopulations of tumor cells with a combination of drugs instead of single-agent therapy will be necessary for long-lasting inhibition of melanoma lesions. In this context, the recent development of immune checkpoint reagents provides an additional armor that can be used in combination with targeted drugs to expand the presence of melanoma reactive T cells in circulation to prevent tumor recurrence.

Exome sequencing identifies recurrent somatic MAP2K1 and MAP2K2 mutations in melanoma

We performed exome sequencing to detect somatic mutations in protein-coding regions in seven melanoma cell lines and donor-matched germline cells. All melanoma samples had high numbers of somatic mutations, which showed the hallmark of UV-induced DNA repair. Such a hallmark was absent in tumor sample-specific mutations in two metastases derived from the same individual. Two melanomas with non-canonical BRAF mutations harbored gain-of-function MAP2K1 and MAP2K2 (MEK1 and MEK2, respectively) mutations, resulting in constitutive ERK phosphorylation and higher resistance to MEK inhibitors. Screening a larger cohort of individuals with melanoma revealed the presence of recurring somatic MAP2K1 and MAP2K2 mutations, which occurred at an overall frequency of 8%. Furthermore, missense and nonsense somatic mutations were frequently found in three candidate melanoma genes, FAT4, LRP1B and DSC1.

RASSF10 promoter hypermethylation is frequent in malignant melanoma of the skin but uncommon in nevus cell nevi

The Ras association domain family (RASSF) consists of several tumor suppressor genes, which are frequently silenced in human cancers. We analyzed the epigenetic inactivation of RASSF2 and RASSF10 in malignant melanoma (MM) of the skin, including 5 MM cell lines, 28 primary MM, 33 metastases of MM, 47 nevus cell nevi (NCN), and 22 control tissues. The RASSF2 promoter was epigenetically downregulated in two MM cell lines only, but not in any of the investigated tumor samples. In contrast, hypermethylation of the RASSF10 promoter was found in all investigated cell lines, 19/28 (68%) of the primary MM and 30/33 (91%) of the MM metastases, 2/18 (11%) of the dysplastic NCN, and 0/29 (0%) of the non-dysplastic NCN (difference between MM and all nevi, P<0.001). RASSF10 promoter hypermethylation correlated with a reduced RASSF10 mRNA expression in 3/4 MM cell lines, and treatment with a DNA methylation inhibitor reactivated RASSF10 transcription. Furthermore, immunohistological RASSF10 expression corresponds negatively to its promoter methylation state. In summary, RASSF10 proved to be a characteristically epigenetically silenced tumor suppressor in melanomagenesis, and analysis of RASSF10 methylation status represents a new candidate tool to assist in discrimination between MM and NCN.

ABT-737 synergizes with Bortezomib to kill melanoma cells

The BH3 mimetic ABT-737 is a potent inhibitor of the anti-apoptotic proteins Bcl-2, Bcl-X_L, and Bcl-w. The Bcl-2 family modulates sensitivity to anticancer drugs in many cancers, including melanomas. In this study, we examined whether ABT-737 is effective in killing melanoma cells either alone or in combination with a proteasome inhibitor already in clinical use (Bortezomib) in vitro and in vivo, and further evaluated the mechanisms of action. Results showed that ABT-737 alone induced modest cytotoxicity in melanoma cells, but only at higher doses. Knock-down of the anti-apoptotic proteins Bcl-2, Bcl-X_L, or Mcl-1 with siRNAs demonstrated that Mcl-1 is the critical mediator of melanoma's resistance to ABT-737 treatment. However, ABT-737 displayed strong synergistic lethality when combined with Bortezomib. Immunoblot analyses demonstrated that Bortezomib increased expression of Noxa, a pro-apoptotic Bcl-2 member that antagonizes Mcl-1. Additionally, siRNA-mediated inhibition of Noxa expression protected melanoma cells from cytotoxicity induced by the combination treatment. These results demonstrate that Bortezomib synergizes with ABT-737 by neutralizing Mcl-1's function via increased levels of Noxa. In a xenograft mouse model, although drug doses were limited due to toxicity, ABT-737 or Bortezomib slowed melanoma tumor growth compared to the control, and the drug combination significantly decreased growth compared to either drug alone. These data imply that less toxic drugs fulfilling a function similar to Bortezomib to neutralize Mcl-1 are promising candidates for combination with ABT-737 for treating melanomas.

Citrus flavanone naringenin enhances melanogenesis through the activation of Wnt/β-catenin signalling in mouse melanoma cells

Citrus fruits are the major source of flavonoids for humans, and flavanones are the main flavonoids in the Citrus species. Among the Citrus flavanones, the glycoside derivatives of naringenin, naringin and narirutin, are the most abundant in grapefruit. The present study aimed to investigate the molecular events of melanogenesis induced by naringenin in murine B16-F10 melanoma cells. Melanin content, tyrosinase activity and Western blot analysis were performed to elucidate the possible underlying mechanisms. Exposure of melanoma cells to naringenin resulted in morphological changes accompanied by the induction of melanocyte differentiation-related markers, such as melanin synthesis, tyrosinase activity, and the expression of tyrosinase and microphthalmia-associated transcription factor (MITF). We also observed an increase in the intracellular accumulation of β-catenin as well as the phosphorylation of glycogen synthase kinase-3β (GSK3β) protein after treatment with naringenin. Moreover, the activity of phosphatidylinositol 3-kinase (PI3K) was up-regulated by naringenin since the phosphorylated level of downstream Akt protein was enhanced. Based on these results, we concluded that naringenin induced melanogenesis through the Wnt-β-catenin-signalling pathway.