Downregulation of endothelin B receptor in human melanoma cell lines parallel to differentiation genes

Identification of significant genes as prognostic markers and potential tumor suppressors in lung adenocarcinoma via bioinformatical analysis

Background

Lung adenocarcinoma (LAC) is the predominant histologic subtype of lung cancer and has a complicated pathogenesis with high mortality. The purpose of this study was to identify differentially expressed genes (DEGs) with prognostic value and determine their underlying mechanisms.

Methods

Gene expression data of GSE27262 and GSE118370 were acquired from the Gene Expression Omnibus database, enrolling 31 LAC and 31 normal tissues. Common DEGs between LAC and normal tissues were identified using the GEO2R tool and Venn diagram software. Next, the Database for Annotation, Visualization, and Integrated Discovery (DAVID) was used to analyze the Gene Ontology and Kyoto Encyclopedia of Gene and Genome (KEGG) pathways. Then, protein-protein interaction (PPI) network of DEGs was visualized by Cytoscape with Search Tool for the Retrieval of Interacting Genes and central genes were identified via Molecular Complex Detection. Furthermore, the expression and prognostic information of central genes were validated via Gene Expression Profiling Interactive Analysis (GEPIA) and Kaplan-Meier analysis, respectively. Finally, DAVID, real-time PCR and immunohistochemistry were applied to re-analyze the identified genes, which were also further validated in two additional datasets from ArrayExpress database.

Results

First, 189 common DEGs were identified among the two datasets, including 162 downregulated and 27 upregulated genes. Next, Gene Ontology and KEGG pathway analysis of the DEGs were conducted through DAVID. Then, PPI network of DEGs was constructed and 17 downregulated central genes were identified. Furthermore, the 17 downregulated central genes were validated via GEPIA and datasets from ArrayExpress, and 12 of them showed a significantly better prognosis. Finally, six genes were identified significantly enriched in neuroactive ligand-receptor interactions (EDNRB, RXFP1, P2RY1, CALCRL) and Rap1 signaling pathway (TEK, P2RY1, ANGPT1) via DAVID, which were further validated to be weakly expressed in LAC tissues via RNA quantification and immunohistochemistry analysis.

Conclusions

The low expression pattern and relation to prognosis indicated that the six genes were potential tumor suppressor genes in LAC. In conclusion, we identified six significantly downregulated DEGs as prognostic markers and potential tumor suppressor genes in LAC based on integrated bioinformatics methods, which could act as potential molecular markers and therapeutic targets for LAC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08308-3.

Multifunctional system for combined chemodynamic–photodynamic therapy employing the endothelin axis based on conjugated polymer nanoparticles

Most nanomedicines that attack tumors by Reactive Oxygen Species (ROS) based on lipid peroxidation mechanisms require external activation to work.

Ca2+ transients in melanocyte dendrites and dendritic spine-like structures evoked by cell-to-cell signaling

Melanocytes are the neural crest-derived pigment-producing cells of the skin that possess dendrites. Yet little is known about how melanocyte dendrites receive and process information from neighboring cells. Here, using a co-culture system to interrogate the interaction between melanocyte dendrites and keratinocytes, we show that signals from neighboring keratinocytes trigger local compartmentalized Ca2+ transients within the melanocyte dendrites. The localized dendritic Ca2+ transients could be triggered by two keratinocyte-secreted factors, endothelin and acetylcholine, which acted via specific melanocyte receptors. Furthermore, compartmentalized Ca2+ transients were also generated on discrete dendritic spine-like structures on the melanocytes. These spines were also present in intact human skin. Our findings provide insights into how melanocyte dendrites communicate with neighboring cells and offer a new model system for studying compartmentalized signaling in dendritic structures.

Ultrastable and Biofunctionalizable Conjugated Polymer Nanoparticles with Encapsulated Iron for Ferroptosis Assisted Chemodynamic Therapy

We report the development of novel tumor-targeted conjugated polymer nanoparticles (CPNPs) carrying iron for chemodynamic therapy (CDT). Tumor cell killing proceeds through ferroptosis, a reactive oxygen species (ROS) mechanism that is not dependent on external activation by, for example, light, as is the case in photodynamic therapy (PDT). The ferroptosis mechanism is also not heavily reliant on oxygen availability and is, therefore, promising for the treatment of hypoxic tumors. In this work, we apply this development to the case study of melanoma, a difficult to treat cancer in advanced stages due to resistance to chemotherapy. The iron-carrying CPNPs reported here are targeted to endothelin-B receptors (EDNRB) through endothelin-3 surface moieties (EDN3-CPNPs). Our results show excellent targeting to tumor cells that overexpress EDNRB, specifically for melanoma and bladder tumor cells. In these cases, efficient cell killing, over 80% at higher doses, was found. Conversely, tumor cells not targeted by the EDN3-CPNPs show little effects of CDT, with tumor cell death under 20% in most cases. The outcomes of our work demonstrate that EDN3-CPNPs enable ferroptosis-assisted CDT and present a new therapeutic avenue for tumor treatment.

Endothelin receptor B, a candidate gene from human studies at high altitude, improves cardiac tolerance to hypoxia in genetically engineered heterozygote mice

To better understand human adaptation to stress, and in particular to hypoxia, we took advantage of one of nature's experiments at high altitude (HA) and studied Ethiopians, a population that is well-adapted to HA hypoxic stress. Using whole-genome sequencing, we discovered that EDNRB (Endothelin receptor type B) is a candidate gene involved in HA adaptation. To test whether EDNRB plays a critical role in hypoxia tolerance and adaptation, we generated EdnrB knockout mice and found that when EdnrB (-/+) heterozygote mice are treated with lower levels of oxygen (O2), they tolerate various levels of hypoxia (even extreme hypoxia, e.g., 5% O2) very well. For example, they maintain ejection fraction, cardiac contractility, and cardiac output in severe hypoxia. Furthermore, O2 delivery to vital organs was significantly higher and blood lactate was lower in EdnrB (-/+) compared with wild type in hypoxia. Tissue hypoxia in brain, heart, and kidney was lower in EdnrB (-/+) mice as well. These data demonstrate that a lower level of EDNRB significantly improves cardiac performance and tissue perfusion under various levels of hypoxia. Transcriptomic profiling of left ventricles revealed three specific genes [natriuretic peptide type A (Nppa), sarcolipin (Sln), and myosin light polypeptide 4 (Myl4)] that were oppositely expressed (q < 0.05) between EdnrB (-/+) and wild type. Functions related to these gene networks were consistent with a better cardiac contractility and performance. We conclude that EDNRB plays a key role in hypoxia tolerance and that a lower level of EDNRB contributes, at least in part, to HA adaptation in humans.

Low expression of endothelin receptor B (EDNRB) is related to H3K9me3 binding with the EDNRB promoter region and is associated with the clinical T tumor stage in salivary adenoid cystic carcinoma

OBJECTIVE

To investigate the endothelin receptor B (EDNRB) expression in salivary adenoid cystic carcinoma (ACC) and the mechanism of the regulation of EDNRB expression.

STUDY DESIGN

After screening, EDNRB was selected, and the expression was detected using immunohistochemistry in 33 ACC samples (including 6 clinical tumor stage 1 [T1] patients, 13 T2 patients, 9 T3 patients, and 5 T4 patients) and 20 adjacent glands. Interaction between the EDNRB promoter region and histone H3 lysine 9 trimethylation (H3K9me3) was examined using chromatin immunoprecipitation (ChIP) in combination with ChIP-polymerase chain reaction (ChIP-PCR). EDNRB expression in ACC cells treated with chaetocin was detected using quantitative real-time PCR (qRT-PCR) and Western blot tests.

RESULTS

EDNRB expression was lower in ACC than that in adjacent glands (P = .006). The expression of EDNRB in patients with advanced T stage was lower than that in patients with early T stage (P = .024). The low EDNRB gene expression group had more H3K9me3 binding regions in the gene promoter (P = .003). EDNRB gene expression significantly increased in the ACC cell lines after treatment with chaetocin. Chaetocin could reduce the interaction between the EDNRB promoter and H3K9me3.

CONCLUSIONS

H3K9me3 binding to the EDNRB promoter region could reduce the EDNRB expression. Low EDNRB expression played a role in the progression of ACC tumors.

Hypermethylation of EDNRB promoter contributes to the risk of colorectal cancer

OBJECTIVE

Colorectal cancer (CRC) is one of the most common digestive malignancies in the world. EDNRB is a new candidate tumor suppressor gene which is often down-regulated or even silenced by promoter hypermethylation in various human cancers. However, the function of EDNRB gene in CRC remains unknown. In this study, we examined the expression and DNA methylation of EDNRB in CRC tissues.

METHODS

A total of 42 paired CRC and adjacent normal tissue samples were used to determine mRNA levels and DNA methylation status of EDNRB gene by qRT-PCR and methylation-specific PCR (MSP), respectively.

RESULTS

Our study showed that EDNRB promoter hypermethylation was more frequently in CRC tissues than in the normal tissues (92.86 versus 59.52, p = 0.001). Consequently, significantly lower level of EDNRB mRNA was found in CRC tumor samples than in normal samples (0.31 ± 0.91 versus 0.70 ± 1.18, p = 0.032).

CONCLUSIONS

Our results suggested that EDNRB promoter hypermethylation might downregulate its gene expression in CRC, and thus played an important role in the development of CRC.

THE VIRTUAL SLIDE

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/7420980471113303.

Methylation analysis of EDNRB in human colon tissues of Hirschsprung's disease

PURPOSE

Hirschsprung's disease (HSCR) is characterized by absence of the enteric nervous system in a variable portion of the distal gut. The endothelin receptor type B (EDNRB) gene has been localized to the chromosome 13q22 region and encodes a G-protein coupled receptor, is generally accepted as a crucial gene for HSCR. This study is to identify the epigenetic changes of EDNRB in the pathogenesis of HSCR.

METHODS

We investigated the expression levels of EDNRB in 58 HSCR patients and 25 unrelated controls, using reverse transcriptase polymerase chain reaction (RT-PCR) and western blot assay. Moreover, using the methylation-specific polymerase chain reaction, we examined the methylation status of the promoter region of EDNRB.

RESULTS

Aberrant high expression level of EDNRB was detected in HSCR patients compared with the control group (P = 0.023). Besides, western blot assay confirmed the up-regulation of EDNRB in the post transcription level in the aganglionosis segment of HSCR patients. Furthermore, there was a significantly lower ratio of methylation level of EDNRB in HSCR.

CONCLUSIONS

Our study demonstrates that epigenetic inactivation of the EDNRB gene may play a role in the development of HSCR.

Quantitative analysis of promoter methylation of the EDNRB gene in gastric cancer

Hypermethylation has been shown in the promoter region of the endothelin receptor B (EDNRB) gene in several human tumors. However, its role in gastric cancer formation is still unclear. In this study, the methylation status of the EDNRB gene in paired gastric cancer tissues and adjacent normal tissues from 96 patients was detected quantitatively using pyrosequencing. The results showed the methylation of promoter of EDNRB gene in gastric cancer (50.42 ± 9.03%) was significantly higher than in adjacent normal tissues (6.47 ± 2.98%) (P < 0.01). Among 96 tumor tissues, promoter hypermethylation of the EDNRB gene was correlated with tumor infiltration (T1: 47.4 ± 7.31% T2:48.2 ± 9.17% T3:52.9 ± 6.48% T4:53.2 ± 10.45%), lymph node metastasis (N0:45.4 ± 6.99% N1:49.0 ± 9.10% N2:52.0 ± 8.40% N3:53.7 ± 9.92%), and distant metastasis (M0:48.9 ± 6.99% M1:53.9 ± 11.98%) (P < 0.05), but it was not associated with other clinicopathological characteristics. In addition, the treatment of the human gastric cancer cell line, SGC-7901, with demethylation agent can restore the expression of EDNRB. Our results suggest that promoter hypermethylation of EDNRB gene is highly prevalent in gastric cancer, which may play a role in the pathogenesis of gastric cancer. Futhermore, hypermethylation of EDNRB gene was remarkably related to infiltration and metastasis of gastric cancer and may attribute to the tumor progression.

Roles of endothelin signaling in melanocyte development and melanoma

Endothelin (Edn) signaling via the G-coupled, Edn receptor type B (Ednrb) is essential for the development of melanocytes from the neural crest (NC) and has been associated with melanoma progression. Edn3 plays varying roles during melanocyte development, promoting the proliferation and self-renewal of NC-derived multi- and bi-potential precursors as well as the survival, proliferation, differentiation and migration of committed melanocyte precursors. Melanocyte differentiation is achieved via the interaction of Ednrb and Kit signaling, with Ednrb being specifically required in the final differentiation step, rather than in the initial specification of melanocytic fate. Ednrb has also been implicated in the de-differentiation of mature melanocytes, a process that takes place during the malignant transformation of these cells. Ednrb was found to be upregulated in melanoma metastases and was shown to alter tumor-host interactions leading to melanoma progression. Antagonists to this receptor were shown to inhibit melanoma cell growth and increase the apoptotic rate of these cells, and to lead to disease stabilization in melanoma patients. Thus, Edn signaling inhibition may prove useful in the treatment of certain types of melanoma.

Melanoma biology and the promise of zebrafish

Advantageous organismal and technical attributes of the zebrafish are being increasingly applied to study cancer biology. Along with other tumor models, zebrafish that develop melanomas have been generated. In both genetics and phenotype, zebrafish melanomas are strikingly similar to their human counterparts. For this reason, studies in the zebrafish are poised to make significant contributions to melanoma biology. In this review, we summarize important features of human melanoma and discuss how the zebrafish can be used to address many questions that remain unanswered about this devastating disease.

PDGF receptor activation induces p120-catenin phosphorylation at serine 879 via a PKCalpha-dependent pathway

p120-catenin (p120) is required for cadherin stability and is thought to have a central role in modulating cell-cell adhesion. Several lines of evidence suggest that S/T phosphorylation may regulate p120 activity, but the upstream kinases involved have not been established, nor has a discreet measurable function been assigned to an individual site. To approach these issues, we have generated p120 phospho-specific monoclonal antibodies to several individual phosphorylation sites and are using them to pinpoint upstream kinases and signaling pathways that control p120 activity. Protein Kinase C (PKC) has been implicated as a signaling intermediate in several cadherin-associated cellular activities. Signaling events that activate PKC induce rapid phosphorylation at p120 Serine 879 (S879), suggesting that p120 activity is regulated, in part, by one or more PKC isoforms. Here, we find that physiologic activation of a G-protein coupled receptor (i.e., endothelin receptor), as well as several Receptor Tyrosine Kinases, induce rapid and robust p120 phosphorylation at S879, suggesting that these pathways crosstalk to cadherin complexes via p120. Using Va2 cells and PDGF stimulation, we show for the first time that PDGFR-mediated phosphorylation at this site is dependent on PKCalpha, a conventional PKC isoform implicated previously in disruption of adherens junctions.

Endothelin-3 is produced by metastatic melanoma cells and promotes melanoma cell survival

BACKGROUND

Endothelin-3 (ET-3) is an essential paracrine factor for the proliferation, migration, and survival of embryonic melanocytes during fetal development. Its expression is tightly regulated, being completely turned off in adult skin.

OBJECTIVE

In this study, results are presented that demonstrate abnormal expression of ET-3 by metastatic melanoma cells in both tissue biopsies and cell culture. Further, in vitro experiments showed that metastatic melanoma cells have the capacity to respond to ET-3 stimulation by increasing survival.

CONCLUSION

Therefore, an abnormal autocrine stimulation pathway involving ET-3 is present in metastatic melanoma cells. Blocking this signal transduction pathway may prove useful for the treatment of metastatic melanoma.

Ganglioside signatures of primary and nodal metastatic melanoma cell lines from the same patient

The primary cutaneous melanoma initially migrates to the regional lymph nodes (LNs). Human melanoma overexpresses gangliosides, the sialylglycosphingolipids. The ganglioside signatures may differ between primary and LN melanomas owing to the differences in the tumor microenvironments. The melanoma cells obtained from the primary and LN of the same patient might be useful to evaluate the above hypothesis. For this purpose, the cryopreserved cell lines from a primary cutaneous melanoma (IGR-39) and its nodal metastasis (IGR-37) from the same patient were used. We have also compared the ganglioside signatures of freshly obtained melanoma cells from primary, LN and organ metastases from different patients. Gangliosides were extracted, purified and identified by resorcinol and specific murine monoclonal antibodies. Comparison of the primary cell line with the nodal metastatic line obtained from the same patient distinctly showed the following features: (i) an increased production of gangliosides, (ii) O-acetylation of GM2 and GD3, (iii) an increased and altered O-acetylation of GD2 and (iv) possibly de-N-acetylation of GD3. These findings suggest that the nodal microenvironment might favor activation of O-acetyl-transferases capable of O-acetylating both alpha2, 3 and alpha2, 8 sialic acids of gangliosides. Supporting this, the primary melanoma cells obtained from different patients, showed no O-acetylation of GD3 or GD2. The cell line from groin LN showed the presence of O-acetyl (O-Ac)GD3. The cell lines from thyroid, spleen and jejunum expressed O-AcGD2. In all metastatic melanoma cell lines GD1a is more prevalent than GD3, suggesting that GD1a may be a major melanoma-ganglioside.

Melanocyte receptors: clinical implications and therapeutic relevance

The activation or the inhibition of melanocyte-specific receptors offers novel means of augmenting normal melanocyte function, skin color, and photoprotection, or treating melanocytic disorders, namely at this time, metastatic melanoma. Melanocyte-specific receptors include melanocortin-1 (MCR1) and melatonin receptors. Other receptors that play an important role in melanoma progression are G-protein couple receptors such as Frizzled 5 and receptor tyrosine kinases such as c-Kit and hepatocyte growth factor (HGF) receptor. These receptors activate two crucial cell-signaling pathways, RAS/RAF/MEK/ERK and PI3K/AKT, integral to melanoma cell survival, and can serve as targets for therapy of disseminated melanoma. Activation of death receptors is another pathway that can be exploited with targeted therapeutics to control advanced melanoma. This article reviews the current understanding of melanocyte receptors, their agonists and inhibitors, and their potential to treat the melanocytic pathology.

Expression of endothelin receptors in frog, chicken, mouse and human pigment cells

Several reports have shown the participation of vasoactive endothelins (ETs) in the regulation of vertebrate pigment cells. In the present study, we identified ET receptors in pigment cells of vertebrate species by RT-PCR assays, and compared the differential expression of the various subtypes in each species by quantitative PCR. RT-PCR was performed with specific primers for ETC, ETA(X) or ETA in Xenopus laevis melanophores, ETA or ETB(2) in chicken melanocytes, ETA or ETB in murine (B-16, S-91 or Melan-A) or human (SK-Mel 23 or SK-Mel 28) melanoma cells, and the products obtained were confirmed by cloning and sequencing. The results showed the presence of ETA(X), but not ETA mRNA, and confirmed the expression of ETC in X. laevis melanophores. ETA and ETB(2) mRNAs were also demonstrated in chicken melanocytes. ETA and ETB receptor were identified in S-91, B16 and Melan-A murine cells. In human melanoma cells, SK-Mel 23 and SK-Mel 28, we confirmed the presence of ETB mRNA, and also found ETA mRNA. The comparison between the two subtypes present in the pigment cell of each species and among species demonstrated that the expression of ETAs in chicken, mouse, and human melanocytes is negligible, as is the expression of ETA(X) in Xenopus melanophores. The relative expression, as determined by quantitative PCR, was as follows: chicken ETB>SK-Mel 23 ETB>S91 ETB>>>Xenopus ETC, suggesting that the endothelin system plays a major role in avian and mammalian pigment cell regulation, as compared to lower vertebrates. The phylogenetic analysis revealed that subtype A receptors were probably the most primitive ET receptors, directly deriving from the ancestral type; all the other receptors, B subtypes and C, originated from diverse derivative molecules.

Resistance of melanoma cells to TRAIL does not result from upregulation of antiapoptotic proteins by NF-κB but is related to downregulation of initiator caspases and DR4

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted considerable attention as a novel anticancer agent. However, its efficiency may be diminished by occurring resistance in cancer cells. The mechanisms of TRAIL resistance in melanoma are still unsolved. Here we show for the first time that TRAIL-induced activation of NF-kappaB occurs in apoptosis-sensitive melanoma cell lines through TRAIL receptor 1/death receptor 4 (TRAIL-R1/DR4), whereas TRAIL failed to activate nuclear factor kappa B (NF-kappaB) in melanoma cells positive only for TRAIL receptor 2/death receptor 5 (TRAIL-R2/DR5). However, activation of NF-kappaB by TRAIL was not associated with enhanced expression of antiapoptotic factors: cellular FLICE-inhibitory protein (c-FLIP), Bcl-x(L), X-linked inhibitor of apoptosis protein (XIAP), Survivin, Livin. Rather in one of the cell lines, TRAIL induced the downregulation of DR4. In an established cell culture model for TRAIL resistance and regained TRAIL sensitivity, resistance was neither associated with increased NF-kappaB activity by TRAIL nor by an increased expression of antiapoptotic proteins. However, significant downregulation of caspase-8, caspase-10 and of DR4 was characteristic for TRAIL-resistant, DR4-positive melanoma cells, and regained TRAIL sensitivity coincided with re-expression of these factors. Sensitivity was also largely retained after their exogenous overexpression. Thus, initiator caspases and DR4 rather than NF-kappaB may control melanoma cell sensitivity to TRAIL, and strategies, which result in their upregulation, may be useful for enhancement of TRAIL sensitivity.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Chromatic effects of endothelin family peptides in non-innervated fish,Synbranchus marmoratus, melanophores

The biological activity of endothelins (ETs) in non-innervated Synbranchus marmoratus melanophores was demonstrated. These peptides induced a dose-dependent pigment aggregation (lightening skin) in these cells. However, they presented EC50's (effective concentration required to produce 50% of response) 26, 106 and 35 times higher than, respectively, the melanin concentrating hormone (MCH) EC50, and exhibited a characteristic temporal and dose-dependent autodessensibilization of the aggregative effect on the melanophores of this fish. The receptor characterization suggested the presence of the ET(B) subtype, since BQ-788 (selective antagonist of ET(B)) but not BQ-485 (selective antagonist of ET(A)) blocked the aggregative effect of the hormones. Confirming these data, sarafotoxin (SRTX) S6c, a toxin selective for ET(B), induced maximal aggregation of pigment granules. S6c presented an EC50 6.8 times higher than the MCH EC50, and 3.9, 15.6 and 5.1 times lower than the EC50's ETs, respectively. The melanotropic effect of SRTX S6b and vasoactive intestinal contractor (VIC) were demonstrated for the first time in this work. SRTX S6b induced a dose-dependent pigment aggregation and presented an EC50 2.54 and 17.2 times higher than the S6c and MCH EC50's, respectively. Compared to the ETs it was 1.53, 6.19 and 2.03 times lower, respectively.

Endothelin receptor antagonists: rationale, clinical development, and role in prostate cancer therapeutics

The endothelins (ETs), which include ET-1, ET-2, ET-3, and their receptors ET-A and ET-B, play a major role in tumor growth, proliferation, apoptosis, angiogenesis, and bone metastasis. Atrasentan is a novel and selective inhibitor of ET-1 and ET-A. In vitro and in vivo data show that this oral agent is capable of inhibiting tumor cells in vitro. More recently, this agent was studied in several phase I trials with refractory carcinoma patients. Subsequently, phase II and III clinical trials evaluating atrasentan in patients with hormone-refractory prostate carcinoma have suggested that targeting this pathway may be a new therapeutic strategy in the treatment of solid malignancies, specifically, prostate cancer.

Caspase-independent induction of apoptosis in human melanoma cells by the proapoptotic Bcl-2-related protein Nbk / Bik

The proapoptotic BH3-only protein natural born killer / Bcl-2 interacting killer (Nbk/Bik) has been described to inhibit Bcl-2 and Bcl-xL, thereby supporting the death promoting ability of Bax. In order to evaluate its function in melanoma, we investigated the response after Nbk/Bik overexpression in cultured human melanoma cells and in a melanoma mouse model. Untransfected melanoma cell lines expressed Nbk/Bik only weakly at the mRNA and protein level. Conditional expression of Nbk/Bik by applying the inducible tetracycline-responsive expression system triggered apoptosis and enhanced sensitivity to proapoptotic stimuli as to agonistic CD95 activation and to chemotherapeutics etoposide, doxorubicin and pamidronate. For investigating the effects of Nbk/Bik in vivo, stably transfected melanoma cells were subcutaneously injected into nude mice. Significantly delayed tumor growth was the result when mice received doxycycline for induction of Nbk/Bik expression. By investigating the mechanism of Nbk/Bik-induced cell death, typical hallmarks of apoptosis such as DNA fragmentation and chromatin condensation were seen after induction. Interestingly, no indications for cytochrome c release and caspase processing were found, and selective caspase inhibition remained without effect. These data indicate the high potential of Nbk/Bik in regulating apoptosis in melanoma by a caspase-independent pathway and may corroborate the potency of novel antimelanoma strategies based on activation of BH3-only proteins such as Nbk/Bik.

A novel Bcl-x splice product, Bcl-xAK, triggers apoptosis in human melanoma cells without BH3 domain

Pro- and antiapoptotic proteins of the large Bcl-2 family are critical regulators of apoptosis via the mitochondrial pathway. Whereas antiapoptotic proteins of the family share all four Bcl-2 homology domains (BH1-BH4), proapoptotic members may lack some of these domains, but all so far described proapoptotic Bcl-2 proteins enclose BH3. The bcl-x gene gives rise to several alternative splice products resulting in proteins with distinct functions as the antiapoptotic Bcl-xL and proapoptotic Bcl-xS. Here, we describe a novel Bcl-x splice product of 138 amino acids termed Bcl-xAK (Atypical Killer), which encloses the Bcl-2 homology domains BH2 and BH4 as well as the transmembrane domain, but lacks BH1 and BH3. Weak endogenous expression of Bcl-xAK was seen in melanoma and other tumor cells. Interestingly, its overexpression by applying a tetracycline-inducible expression system resulted in significant induction of apoptosis in melanoma cells, which occurred in synergism with drug-induced apoptosis. After exogenous overexpression, Bcl-xAK was localized both in mitochondrial and in cytosolic cell fractions. By these findings, a completely new class of Bcl-2-related proteins is introduced, which promotes apoptosis independently from the BH3 domain and implies additional, new mechanisms for apoptosis regulation in melanoma cells.

Efficient TRAIL-R1/DR4-Mediated Apoptosis in Melanoma Cells by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Therapy resistance is crucial for the high mortality of melanoma. The death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) bears high potential as a new anticancer agent, as binding to the death receptors TRAIL receptor 1/death receptor 4 (TRAIL-R1/DR4) or TRAIL receptor 2/death receptor 5 (TRAIL-R2/DR5) triggers apoptosis in most cancer cells. For melanoma, however, only a weak responsiveness of primary cultures was reported, and in particular the role of DR4 was neglected. For evaluating melanoma susceptibility, we studied the functionality of DR4 and DR5 in melanoma cells as well as their expression in vivo. DR5 was consistently expressed in melanoma cell lines, whereas DR4 was found in only 2/7 cell lines. High sensitivity to TRAIL-induced apoptosis was characteristic for DR4-positive melanoma cells, whereas DR4-negative cells showed less and delayed response or were resistant. The use of selective DR4/DR5 blocking antibodies unequivocally proved the prevalent role of DR4 in those melanoma cells, where it was expressed. The significance of these data for the in vivo situation was finally evaluated by immunohistochemistry, which proved pronounced expression of DR4 as well as of DR5 in melanoma primary tumors. Thus, DR4 expression in vivo and the high efficiency of DR4-mediated apoptosis may suggest reassessment of the suitability of TRAIL and especially of DR4-based strategies for melanoma treatment.

Endothelin-1 induces CXCL1 and CXCL8 secretion in human melanoma cells

The endothelin pathway plays a critical role in melanoma tumor progression by a variety of mechanisms that enhance tumor cell growth, invasion, and metastasis. Here, we investigate the effect of this pathway on CXC chemokine expression in human melanoma cells and melanocytes. As determined by ELISA, endothelin-1 (ET-1) induces CXCL1 and CXCL8 secretion in three human melanoma cell lines in a concentration-dependent fashion. These responses are mediated by the endothelin-B receptor and are sustained over a 40 h time course. ET-1 does not induce CXCL1 secretion in primary human melanocytes but ET-3, an endothelin isoform, induces a low level of CXCL1 secretion in certain cultures. Neither ET-1 nor ET-3 induces secretion of CXCL8 in primary human melanocytes; thus, this response may be specific for melanocytic cells that have undergone malignant transformation. We have previously demonstrated that ET-1 induces changes in the expression of adhesion molecules in melanoma cells such that invasion and metastasis are favored. This study demonstrates that ET-1 additionally induces secretion of CXC chemokines critical for melanoma metastasis and tumor progression.

Association Between Endothelin Receptor B Nonsynonymous Variants and Melanoma Risk

The endothelin signaling pathway plays a crucial role in melanocyte differentiation and migration. In this study, we investigated whether germline mutations of endothelin receptor B (EDNRB), a gene involved in Hirschsprung disease (HSCR), could also predispose for malignant melanoma (MM). The coding region of EDNRB was sequenced in 137 MM patients and in 130 ethnically matched Caucasian control subjects. Six nonsynonymous EDNRB variants were found in 15 patients (11%), but only two were found in four control subjects (3%, odds ratio [OR] = 3.87, 95% confidence interval [CI] = 1.25 to 12; P = .012). Overall, 14 out of 15 MM patients carried EDNRB mutations reported in HSCR, some of which had previously been shown to lead to loss of function. In multivariable logistic regression analysis including skin type, eye and hair color, number of nevi, and dorsal lentigines (freckles), the association between EDNRB mutations and MM risk remained statistically significant (OR = 19.9, 95% CI = 1.34 to 296.2; P = .03). Our data strongly suggest that EDNRB is involved in predisposition for two different multigenic disorders, HSCR and melanoma.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

The Endothelin/Sarafotoxin-Induced Increase of the Proliferation of Undifferentiated and DMSO-Differentiated GEM-81 Goldfish Erythrophoroma Cells is Mediated by ETB Receptors

Endothelins (ETs) and sarafotoxins (SRTXs) have been reported to exert ET(B)-mediated effects on vertebrate pigment cells. GEM-81 cell line, a red pigment cell-derived cutaneous tumor of the teleost Carassius auratus, expresses ET(B) receptors and can be differentiated with 1.5% DMSO treatment, thus constituting an useful model to investigate ET and SRTX effects on cultured fish pigment cells. Our aim was to characterize the pharmacology and biological effects mediated by ET receptors in DMSO-differentiated and undifferentiated cells. ET subtype receptors and their respective Ki values in both cell types were determined by competitive binding assays using (125)I ET-1 and BQ-485 (an ET(A) antagonist) or BQ-788 (an ET(B) antagonist). BQ-788, but not BQ-485, significantly reduced (125)I-ET-1 binding in both cell types, with similar low (Ki > nM) affinities. To determine the proliferation effects of ETs/SRTXs, cells were treated for 72 h with the hormones, and counted in a hemocytometer. The proliferation assays were repeated for SRTX S6c in the presence or absence of BQ-788. The results demonstrated that, with the exception of ET-1 (biphasic effect) and ET-3 (no significant effect) in undifferentiated GEM-81 cells, all the tested hormones induced increases in the proliferation of both types of cells. The hormones were equipotent in DMSO-differentiated cells, which exhibited increased sensitivity to ETs, but not to SRTXs, as compared with undifferentiated cells. The BQ-788 antagonistic effect was also exerted on the proliferation responses to SRTX S6c. These results corroborate the long and important evolutionary history of the ET/SRTX receptor system in vertebrate pigment cells.

Prognostic signs in melanoma: state of the art

Prognoses for melanoma patients are currently based on statistically confirmed parameters, above all the Breslow thickness and number of lymph node and/or distant metastases. However, metastases can develop even with "thin" melanomas (< 0.7 mm), while survival has been recorded in patients with tumours classified as "thick" (> 4 mm). This review of the literature examines the most recent advances in prognostic markers for melanoma (serological, immunohistochemical, histological, genetic and surgical). These markers offer interesting possibilities in terms of diagnostic certainty, identification of early growth phases and estimation of the tumour's potential for progression and metastasis. It is reasonable to assume that their combined use can provide useful information for formulating prognoses that are not only statistically valid but also individualized.

Apoptosis and melanoma: molecular mechanisms

Melanoma cells can undergo self-destruction via programmed cell death, i.e. apoptosis. In these tumours, the molecular components of apoptosis include positive (apoptotic) and negative (anti-apoptotic) regulators. The former include p53, Bid, Noxa, PUMA, Bax, TNF, TRAIL, Fas/FasL, PITSLRE, interferons, and c-KIT/SCF. The latter include Bcl-2, Bcl-X(L), Mcl-1, NF-(K)B, survivin, livin, and ML-IAP. Alternatively, some molecules such as TRAF-2, c-Myc, endothelins, and integrins may have either pro- or anti-apoptotic effects. Some of these molecules are of potential therapeutic use, such as: (1) p53, which influences resistance to chemotherapy; (2) Mcl-1 and Bcl-X(L), which can override apoptosis; (3) TRAIL, which has selective fatal effects on tumour cells; (4) NF-(K)B, which when downregulated sensitizes cells to TRAIL and TNF; (5) the PITSLRE kinases, whose alteration appears to result in Fas resistance; (6) interferons, which sensitize cells to other factors; and (7) survivin and other IAPs that inhibit apoptosis. This review summarizes the state of current knowledge about the key molecular components and mechanisms of apoptosis in melanoma, discusses potential therapeutic ramifications, and provides directions for future research.

The endothelin axis: emerging role in cancer

Collectively, the endothelins and their receptors--referred to as the endothelin (ET) axis--have key physiological functions in normal tissue, acting as modulators of vasomotor tone, tissue differentiation, development, cell proliferation and hormone production. Based on new data, the ET axis also functions in the growth and progression of various tumours. Preliminary results from clinical trials, such as those with atrasentan--an ET(A)-receptor antagonist--in prostate cancer, are encouraging. The place of ET-receptor antagonists in cancer therapy for a range of malignancies merits further investigation.

Endothelin-1 decreases basic apoptotic rates in human melanoma cell lines

Normal human melanocytes respond to endothelin-1 with induced proliferation and differentiation. Whereas in cultured melanoma cells the predominant endothelin receptor, ET(B)-R, is consistently downregulated, ET(B)-R upregulation was recently reported for melanoma tumors. Contrary to the pro-survival activity described for endothelin in vascular cells, a proapoptotic activity of endothelin-1 has been reported for melanoma cells, in previous studies. We therefore investigated the role of endothelin for melanoma cells with respect to apoptosis and proliferation. Treatment with 10 nM endothelin-1 was a strong mitogenic signal for normal human melanocytes, which responded with a 4-6-fold increase of thymidine incorporation, whereas the response was only 1.2-fold for SK-Mel-19, the melanoma cell line characterized by the highest ET(B)-R expression, and it was even less in other cell lines. Determination of the apoptotic rates revealed that endothelin-1 significantly reduced basic apoptotic rates to 75% both in SK-Mel-19 and in normal melanocytes. After cell synchronization, an antiapoptotic effect of endothelin-1 was seen in five of seven cell lines investigated. In the cell line Bro, which showed no response and which lacks ET(B)-R expression, responsibility could be restored by overexpression of ET(B)-R after stable transfection, indicating that the effectors of the endothelin-1 signal cascade were active in these cells, and that the antiapoptotic effect of endothelin-1 is mediated in a receptor-specific way. This antiapoptotic activity of endothelin for melanoma cells combined with upregulation of endothelin receptors in the tumor may be a crucial step for melanoma progression.

UV-induction of keratinocyte endothelin-1 downregulates E-cadherin in melanocytes and melanoma cells

Endothelin-1 (ET-1), a peptide that is secreted by keratinocytes in the skin in response to ultraviolet irradiation, is a ligand for the endothelin-B (ET(B)) receptor. Blockade of this receptor inhibits melanoma cell growth and induces cell death in vivo and in vitro. Additionally, ET(B) is a melanoma progression marker. These findings suggest that the ET-1/ET(B) receptor pathway contributes to melanoma development or progression. Here, we demonstrate that activation of the ET-1/ET(B) pathway downregulates E-cadherin and associated catenin proteins in human melanocytes and melanoma cells. E-cadherin is an established suppressor of melanoma cell invasion in vitro and in vivo. Downregulation of E-cadherin by ET-1/ET(B) involves the downstream activation of caspase-8 but not of distal, executioner caspases, and does not lead to apoptosis. ET-1 also induces a transient association between caspase-8 and E-cadherin:beta-catenin complexes. Hence, activation of the ET-1/ET(B) pathway promotes molecular events known to promote melanoma invasion.

Decreased proliferation of human melanoma cell lines caused by antisense RNA against translation factor eIF-4A1

Control of translation initiation was recognised as a critical checkpoint for cell proliferation and tumorigenesis. In human melanoma cells, we have previously reported consistent overexpression of translation initiation factor eIF-4A1. Here, we investigated by transfection of antisense constructs its significance for the control of melanoma cell growth. The tetracycline-inducible expression system was established in melanoma cells, and three fragments of the 5'-, central-, and 3'-portion of the eIF-4A1 cDNA were subcloned in antisense and in sense orientation after a tetracycline inducible promoter. Significant proliferation decrease was obtained after transient transfection and induction of antisense RNA directed against the 5'- and the central portion (up to 10%), whereas, no effects were seen after induction of the 3'-fragment and the sense controls. Cell clones stably transfected with the central antisense fragment revealed after doxycycline induction reduced expression of endogeneous eIF-4A1 mRNA correlated with decreased proliferation rates (up to 6%). These data demonstrate the applicability of antisense strategies against translation factors in melanoma cells. Translation initiation factor eIF-4A1 contributes to the control of melanoma cell proliferation and may be taken into consideration when scheduling new therapeutic approaches targeting the translational control.

Inducible nitric oxide synthase is expressed in normal human melanocytes but not in melanoma cells in response to tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Nitric oxide is a gaseous messenger involved in the regulation of several physiologic processes in various cell types, including skin cells. Three different nitric oxide synthases (neuronal nitric oxide synthase, endothelial nitric oxide synthase, inducible nitric oxide synthase) have been identified in human cells. For inducible nitric oxide synthase, an inducibility by cytokines and lipopolysaccharides have been found. For murine melanoma cells, a connection between elevated levels of nitric oxide after inducible nitric oxide synthase induction and consequent apoptosis had been described. By northern analysis, we detected inducible nitric oxide synthase mRNA in four of 15 human melanoma cell lines cultured without inducible nitric oxide synthase inducing cytokines. Induction of inducible nitric oxide synthase mRNA by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides was seen in normal human melanocytes but not in melanoma cell lines. In accordance, inducible nitric oxide synthase protein expression was clearly inducible in cultures of normal melanocytes, whereas in six melanoma cell lines investigated, inducible nitric oxide synthase was found weakly expressed already before treatment with tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides, and its expression was not inducible. The apoptotic rates both in normal melanocytes and in two melanoma cell lines (SK-Mel-19 and O-Mel-2) were increased by treatment with tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides; however, these effects could not be prevented by the specific nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine. These data reveal a clear-cut difference between human melanoma cell lines and cultured normal human melanocytes with respect to inducible nitric oxide synthase inducibility. Although the data do not support the hypothesis that inducible nitric oxide synthase is an important regulator for apoptosis in human melanoma cells, the regulation deficiency found for melanoma cells may be of importance for melanocytic transformation and tumor progression.

Promoter hypermethylation of the EDNRB gene in nasopharyngeal carcinoma

To identify the epigenetic changes in nasopharyngeal carcinoma (NPC), we performed methylation-sensitive restriction fingerprinting (MSRF) analysis on NPC cell lines and xenografts. A 190 bp sequence methylated in NPC tumors was isolated and showed high homology to the 5' CpG island of the endothelin receptor B (EDNRB) gene. Since the EDNRB gene is commonly inactivated in prostate and bladder cancers, it may be a candidate target gene involved in NPC tumorigenesis. By bisulfite sequencing, we have confirmed that hypermethylation of the 5' CpG island of EDNRB occurred in both xenografts and all 4 cell lines but not in 2 normal nasopharyngeal outgrowths. RT-PCR demonstrated that only original EDNRB transcripts, but not the splicing transcripts, were expressed in normal nasopharyngeal epithelial cells. Loss of the original EDNRB expression was consistently found in 2 xenografts and 3 cell lines with dense methylation patterns. Treatment of these 3 cell lines with 5'-aza-2'-deoxycytidine led to re-expression of the EDNRB transcript and demethylation of its promoter regions. Our results demonstrate that silencing of EDNRB gene expression in NPC is associated with promoter hypermethylation. Using methylation-specific PCR, we also detected methylation of the 5' CpG island of EDNRB in 19/21 (90.5%) primary tumors, while no methylation was found in all 6 normal nasopharyngeal epithelia. The high frequencies of promoter hypermethylation suggest that repression of the EDNRB gene may play a role in the development of NPC.

Differentiation therapy of human cancer: basic science and clinical applications

Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.

Stimulation of melanogenesis in murine melanoma cells by 2-mercapto-1-(beta-4-pyridethyl) benzimidazole (MPB)

The effects of 2-mercapto-1-(beta-4-pyridethyl) benzimidazole (MPB), one of the benzimidazole derivatives designed for a nucleic acid analogue, on melanogenesis of murine B16-F10 melanoma cell lines were investigated. MPB (40 microM) induced a striking dendricity in B16 melanoma cells within 12 h and maximal dendricity between 48 and 72 h. The stimulation of melanin synthesis was observed after only 2 days of treatment together with a dose-dependent growth inhibition. Moreover, MPB increased the activity of tyrosinase through the expression of tyrosinase mRNA without increasing the intracellular cyclic AMP content. MPB-induced melanogenesis was inhibited by novel protein kinase A inhibitors, KT-5720 and H-85. These findings indicate that MPB stimulated B16 cells to terminally differentiate and may be a useful drug in studying the regulation of melanogenesis.

Lessons from melanocyte development for understanding the biological events in naevus and melanoma formation

Recent advances in mouse genetics have identified molecular changes that are critical for melanocyte maturation and differentiation. This review briefly summarizes the current knowledge of distinct steps in melanocyte development, and identifies for each step the most important molecules such as the growth factors stem cell factor and endothelin-3, with their respective receptors. Classical cadherins, i.e. E-cadherin, N-cadherin and P-cadherin, determine melanocyte positioning in the skin. During naevus and melanoma development, the two growth factor signalling pathways are downregulated, whereas cadherin expression shifts concomitantly with re-positioning of the naevus and melanoma cells in the skin. Loss of E-cadherin and gain of N-cadherin by melanoma cells has profound consequences for the regulatory cross-talk between various types of cells in the skin. Naevus and melanoma cells that do not express E-cadherin are resistant to control by keratinocytes and establish close communications with fibroblasts and endothelial cells. However, forced expression of E-cadherin in melanoma cells can reverse the malignant phenotype by re-establishing the control of keratinocytes over the melanoma cells. Even highly aggressive metastatic melanoma cells can be signalled to turn off the expression of genes associated with tumour invasion and metastasis, suggesting that this strategy could be utilized in the therapy of melanoma.