The role of altered cell-cell communication in melanoma progression

Generation of 3D melanoma models using an assembloid-based approach

While 3D tumor models have greatly evolved over the past years, there is still a strong requirement for more biosimilar models which are capable of recapitulating cellular crosstalk within the tumor microenvironment while equally displaying representative levels of tumor aggressiveness and invasion. Herein, we disclose an assembloid melanoma model based on the fusion of individual stromal multicellular spheroids (MCSs). In contrast to more traditional tumor models, we show that it is possible to develop self-organizing, heterotypic melanoma models where tumor cells present stem-cell like features like up-regulated pluripotency master regulators SOX2, POU5F1 and NANOG. Additionally, these assembloids display high levels of invasiveness while embedded in 3D matrices as evidenced by stromal cell promotion of melanoma cell invasion via metalloproteinase production. Furthermore, sensitivity to anticancer drug doxorubicin was demonstrated for the melanoma assembloid model. These findings suggest that melanoma assembloids may play a significant role in the field of 3D cancer models as they more closely mimic the tumor microenvironment when compared to more traditional MCSs, opening the doors to a better understanding of the role of tumor microenvironment in supporting tumor progression. STATEMENT OF SIGNIFICANCE: The development of complex 3D tumor models that better recapitulate the tumor microenvironment is crucial for both an improved comprehension of intercellular crosstalk and for more efficient drug screening. We have herein developed a self-organizing heterotypic assembloid-based melanoma model capable of closely mimicking the tumor microenvironment. Key features recapitulated were the preservation of cancer cell stemness, sensitivity to anti-cancer agents and tumor cell invasion promoted by stromal cells. The approach of pre-establishing distinct stromal domains for subsequent combination into more complex tumor constructs provides a route for developing superior tumor models with a higher degree of similarity to native cancer tissues.

Na+ /H+ exchanger NHE1 is active at cell-cell contacts and facilitates cell dissemination during collective migration of melanoma cells

Tumour cell detachment from the primary tumour is an early and crucial step of the metastatic cascade. At the single cell level, it was already shown that migrating melanoma cells establish both intra- and extracellular pH gradients and that the Na+ /H+ exchanger NHE1 accumulates at the leading edges to strengthen cell-matrix interactions. However, less is known about the role of NHE1 in collective cell migration and the specific pH microenvironment at tumour cell-cell contacts. We used MV3 melanoma cells transfected with a NHE1-expressing vector or a control vector. NHE1 localization at cell-cell contacts was assessed via immunofluorescence imaging. Collective migration was analysed by live-cell imaging. The NHE1 activity and the perimembranous pH were measured both intra- and extracellularly by ratiometric fluorescence microscopy. NHE1 clearly localizes at cell-cell contacts. Its overexpression further increases migratory speed and translocation in multidirectional pathway analyses. NHE1 overexpressing MV3 cells also move further away from their neighbouring cells during wound closure assays. pH measurements revealed that the NHE1 is highly active at cell-cell contacts of melanoma cells. NHE1-mediated pH dynamics at such contact sites are more prominent in NHE1-overexpressing melanoma cells. Our findings highlight the contribution of the NHE1 towards modulation and plasticity of melanoma cell-cell contacts. We propose that its localization and functional activity at cell-cell contacts promotes evasion of single melanoma cells from the primary tumour.

A mechanism of melanogenesis mediated by E-cadherin downregulation and its involvement in solar lentigines

OBJECTIVE

Intensive studies have revealed that pleiotropic melanocytic factors are associated with age-spot formation. Dysfunctional keratinocyte differentiation is thought to be an upstream cause of age-spot formation. Although it has been shown that keratinocyte differentiation is mediated by the cell-cell contact factor E-cadherin, its involvement in age-spot formation remains unknown. Thus, to determine the origin of age-spots and an integrated solution for the same, we focused on E-cadherin expression in the present study.

METHODS

First, we assessed the solar lentigines in cutaneous and cultured cells by means of immunofluorescence staining. Following that, keratinocytes treated with siRNAs against E-cadherin were co-cultured with melanocytes, and the secreted factors were identified by means of proteomic analysis of the culture supernatants. We also performed quantitative PCR to assess melanogenesis activity and screen ingredients. For behavioural analysis of melanocytes, we performed time-lapse imaging using confocal laser scanning microscopy.

RESULTS

E-cadherin expression was downregulated in the epidermis of the solar lentigines, suggesting its involvement in age-spot formation. E-cadherin knocked down keratinocytes not only promoted the secretion of melanocytic/inflammatory factors but also increased melanogenesis by upregulating the expression of melanogenesis factors. Furthermore, live-imaging showed that the downregulation of E-cadherin inhibited melanocyte dynamics and accelerated melanin uptake. Finally, we identified Rosa multiflora fruit extract as a solution that can upregulate E-cadherin expression in keratinocytes.

CONCLUSION

Our findings showed that E-cadherin downregulation triggers various downstream melanocytic processes, such as the secretion of melanocytic factors and melanogenesis. Additionally, we showed that the Rosa multiflora fruit extract upregulated E-cadherin expression in keratinocytes.

Heterotypic communication as the promoter of phenotypic plasticity of cancer cells: The role of cancer secretomes

Cellular communication relies on signaling circuits whose statuses are mainly modulated by soluble biomolecules such as carbohydrates, lipids, proteins, and metabolites as well as extracellular vesicles (EVs). Therefore, the active secretion of such biomolecules is critical for both cell homeostasis and proper pathophysiological responses in a timely fashion. In this context, proteins are among the main modulators of such biological responses. Hence, profiling cell line secretomes may be an opportunity for the identification of "signatures" of specific cell types (i.e., stromal or metastatic cells) with important prognostic/therapeutic value. This review will focus on the biological implications of cell secretomes in the context of cancer, as well as their functional roles in shaping the tumoral microenvironment (TME) and communication status of participating cells.

From simplicity to complexity in current melanoma models

Despite the recent impressive clinical success of immunotherapy against melanoma, development of primary and adaptive resistance against immune checkpoint inhibitors remains a major issue in a large number of treated patients. This highlights the need for melanoma models that replicate the tumor's intricate dynamics in the tumor microenvironment (TME) and associated immune suppression to study possible resistance mechanisms in order to improve current and test novel therapeutics. While two-dimensional melanoma cell cultures have been widely used to perform functional genomics screens in a high-throughput fashion, they are not suitable to answer more complex scientific questions. Melanoma models have also been established in a variety of experimental (humanized) animals. However, due to differences in physiology, such models do not fully represent human melanoma development. Therefore, fully human three-dimensional in vitro models mimicking melanoma cell interactions with the TME are being developed to address this need for more physiologically relevant models. Such models include melanoma organoids, spheroids, and reconstructed human melanoma-in-skin cultures. Still, while major advances have been made to complement and replace animals, these in vitro systems have yet to fully recapitulate human tumor complexity. Lastly, technical advancements have been made in the organ-on-chip field to replicate functions and microstructures of in vivo human tissues and organs. This review summarizes advancements made in understanding and treating melanoma and specifically aims to discuss the progress made towards developing melanoma models, their applications, limitations, and the advances still needed to further facilitate the development of therapeutics.

A preclinical model of cutaneous melanoma based on reconstructed human epidermis

Malignant melanoma is among the tumor entities with the highest increase of incidence worldwide. To elucidate melanoma progression and develop new effective therapies, rodent models are commonly used. While these do not adequately reflect human physiology, two-dimensional cell cultures lack crucial elements of the tumor microenvironment. To address this shortcoming, we have developed a melanoma skin equivalent based on an open-source epidermal model. Melanoma cell lines with different driver mutations were incorporated into these models forming distinguishable tumor aggregates within a stratified epidermis. Although barrier properties of the skin equivalents were not affected by incorporation of melanoma cells, their presence resulted in a higher metabolic activity indicated by an increased glucose consumption. Furthermore, we re-isolated single cells from the models to characterize the proliferation state within the respective model. The applicability of our model for tumor therapeutics was demonstrated by treatment with a commonly used v-raf murine sarcoma viral oncogene homolog B (BRAF) inhibitor vemurafenib. This selective BRAF inhibitor successfully reduced tumor growth in the models harboring BRAF-mutated melanoma cells. Hence, our model is a promising tool to investigate melanoma development and as a preclinical model for drug discovery.

Herpes simplex virus 1 as an oncolytic viral therapy for refractory cancers

The need for efficacious and non-toxic cancer therapies is paramount. Oncolytic viruses (OVs) are showing great promise and are introducing new possibilities in cancer treatment with their ability to selectively infect tumor cells and trigger antitumor immune responses. Herpes Simplex Virus 1 (HSV-1) is a commonly selected OV candidate due to its large genome, relative safety profile, and ability to infect a variety of cell types. Talimogene laherparevec (T-VEC) is an HSV-1-derived OV variant and the first and only OV therapy currently approved for clinical use by the United States Food and Drug Administration (FDA). This review provides a concise description of HSV-1 as an OV candidate and the genomic organization of T-VEC. Furthermore, this review focuses on the advantages and limitations in the use of T-VEC compared to other HSV-1 OV variants currently in clinical trials. In addition, approaches for future directions of HSV-1 OVs as cancer therapy is discussed.

Pituitary Adenylate Cyclase Activating Polypeptide Has Inhibitory Effects on Melanoma Cell Proliferation and Migration In Vitro

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide which is distributed throughout the body. PACAP influences development of various tissues and exerts protective function during cellular stress and in some tumour formation. No evidence is available on its role in neural crest derived melanocytes and its malignant transformation into melanoma. Expression of PACAP receptors was examined in human skin samples, melanoma lesions and in a primary melanocyte cell culture. A2058 and WM35 melanoma cell lines, representing two different stages of melanoma progression, were used to investigate the effects of PACAP. PAC1 receptor was identified in melanocytes in vivo and in vitro and in melanoma cell lines as well as in melanoma lesions. PACAP administration did not alter viability but decreased proliferation of melanoma cells. With live imaging random motility, average speed, vectorial distance and maximum distance of migration of cells were reduced upon PACAP treatment. PACAP administration did not alter viability but decreased proliferation capacity of melanoma cells. On the other hand, PACAP administration decreased the migration of melanoma cell lines towards fibronectin chemoattractant in the Boyden chamber. Furthermore, the presence of the neuropeptide inhibited the invasion capability of melanoma cell lines in Matrigel chambers. In summary, we provide evidence that PACAP receptors are expressed in melanocytes and in melanoma cells. Our results also prove that various aspects of the cellular motility were inhibited by this neuropeptide. On the basis of these results, we propose PACAP signalling as a possible target in melanoma progression.

Unraveling the Wide Spectrum of Melanoma Biomarkers

The use of biomarkers in medicine has become essential in clinical practice in order to help with diagnosis, prognostication and prediction of treatment response. Since Alexander Breslow’s original report on “melanoma and prognostic values of thickness”, providing the first biomarker for melanoma, many promising new biomarkers have followed. These include serum markers, such as lactate dehydrogenase and S100 calcium-binding protein B. However, as our understanding of the DNA mutational profile progresses, new gene targets and proteins have been identified. These include point mutations, such as mutations of the BRAF gene and tumour suppressor gene tP53. At present, only a small number of the available biomarkers are being utilised, but this may soon change as more studies are published. The aim of this article is to provide a comprehensive review of melanoma biomarkers and their utility for current and, potentially, future clinical practice.

Cell Adhesion Molecules in Plasticity and Metastasis

Prior to metastasis, modern therapeutics and surgical intervention can provide a favorable long-term survival for patients diagnosed with many types of cancers. However, prognosis is poor for patients with metastasized disease. Melanoma is the deadliest form of skin cancer, yet in situ and localized, thin melanomas can be biopsied with little to no postsurgical follow-up. However, patients with metastatic melanoma require significant clinical involvement and have a 5-year survival of only 34% to 52%, largely dependent on the site of colonization. Melanoma metastasis is a multi-step process requiring dynamic changes in cell surface proteins regulating adhesiveness to the extracellular matrix (ECM), stroma, and other cancer cells in varied tumor microenvironments. Here we will highlight recent literature to underscore how cell adhesion molecules (CAM) contribute to melanoma disease progression and metastasis.

Therapeutic strategies and potential implications of silver nanoparticles in the management of skin cancer

Skin cancer (SC) is the most common carcinoma affecting 3 million people annually in the United States and millions of people worldwide. It is classified as melanoma SC (MSC) and non-melanoma SC (NMSC). NMSC represents approximately 80% of SC and includes squamous cell carcinoma and basal cell carcinoma. MSC, however, has a higher mortality rate than SC because of its ability to metastasize. SC is a major health problem in the United States with significant morbidity and mortality in the Caucasian population. Treatment options for SC include cryotherapy, excisional surgery, Mohs surgery, curettage and electrodessication, radiation therapy, photodynamic therapy, immunotherapy, and chemotherapy. Treatment is chosen based on the type of SC and the potential for side effects. Novel targeted therapies are being used with increased frequency for large tumors and for metastatic disease. A scoping literature search on PubMed, Google Scholar, and Cancer Registry websites revealed that traditional chemotherapeutic drugs have little effect against SC after the cancer has metastasized. Following an overview of SC biology, epidemiology, and treatment options, this review focuses on the mechanisms of advanced technologies that use silver nanoparticles in SC treatment regimens.

Exploring Additional Valuable Information From Single-Cell RNA-Seq Data

Single-cell RNA-seq (scRNA-seq) technologies are broadly applied to dissect the cellular heterogeneity and expression dynamics, providing unprecedented insights into single-cell biology. Most of the scRNA-seq studies mainly focused on the dissection of cell types/states, developmental trajectory, gene regulatory network, and alternative splicing. However, besides these routine analyses, many other valuable scRNA-seq investigations can be conducted. Here, we first review cell-to-cell communication exploration, RNA velocity inference, identification of large-scale copy number variations and single nucleotide changes, and chromatin accessibility prediction based on single-cell transcriptomics data. Next, we discuss the identification of novel genes/transcripts through transcriptome reconstruction approaches, as well as the profiling of long non-coding RNAs and circular RNAs. Additionally, we survey the integration of single-cell and bulk RNA-seq datasets for deconvoluting the cell composition of large-scale bulk samples and linking single-cell signatures to patient outcomes. These additional analyses could largely facilitate corresponding basic science and clinical applications.

Discoidin Domain Receptors in Melanoma: Potential Therapeutic Targets to Overcome MAPK Inhibitor Resistance

Melanoma is a highly malignant skin cancer with high propensity to metastasize and develop drug resistance, making it a difficult cancer to treat. Current therapies targeting BRAF (V600) mutations are initially effective, but eventually tumors overcome drug sensitivity and reoccur. This process is accomplished in part by reactivating alternate signaling networks that reinstate melanoma proliferative and survival capacity, mostly through reprogramming of receptor tyrosine kinase (RTK) signaling. Evidence indicates that the discoidin domain receptors (DDRs), a set of RTKs that signal in response to collagen, are part of the kinome network that confer drug resistance. We previously reported that DDR1 is expressed in melanomas, where it can promote tumor malignancy in mouse models of melanoma, and thus, DDR1 could be a promising target to overcome drug resistance. In this review, we summarize the current knowledge on DDRs in melanoma and their implication for therapy, with emphasis in resistance to MAPK inhibitors.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

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

Selectively-Packaged Proteins in Breast Cancer Extracellular Vesicles Involved in Metastasis

Cancer-derived extracellular vesicles are known to play a role in the progression of the disease. In this rapidly-growing field, there are many reports of phenotypic changes in cells following exposure to cancer-derived extracellular vesicles. This study examines the protein contents of vesicles derived from three well-known breast cancer cell lines, MCF-7, MDA-MB-231 and T47D, using peptide-centric LC-MS/MS and cytokine multiplex immunoassay analysis to understand the molecular basis of these changes. Through these techniques a large number of proteins within these vesicles were identified. A large proportion of these proteins are known to be important in cancer formation and progression and associated with cancer signaling, angiogenesis, metastasis and invasion and immune regulation. This highlights the importance of extracellular vesicles (EVs) in cancer communications and shows some of the mechanisms the vesicles use to assist in cancer progression.

A Triple Co-Delivery Liposomal Carrier That Enhances Apoptosis via an Intrinsic Pathway in Melanoma Cells

The effectiveness of existing anti-cancer therapies is based mainly on the stimulation of apoptosis of cancer cells. Most of the existing therapies are somewhat toxic to normal cells. Therefore, the quest for nontoxic, cancer-specific therapies remains. We have demonstrated the ability of liposomes containing anacardic acid, mitoxantrone and ammonium ascorbate to induce the mitochondrial pathway of apoptosis via reactive oxygen species (ROS) production by the killing of cancer cells in monolayer culture and shown its specificity towards melanoma cells. Liposomes were prepared by a lipid hydration, freeze-and-thaw (FAT) procedure and extrusion through polycarbonate filters, a remote loading method was used for dug encapsulation. Following characterization, hemolytic activity, cytotoxicity and apoptosis inducing effects of loaded nanoparticles were investigated. To identify the anticancer activity mechanism of these liposomes, ROS level and caspase 9 activity were measured by fluorescence and by chemiluminescence respectively. We have demonstrated that the developed liposomal formulations produced a high ROS level, enhanced apoptosis and cell death in melanoma cells, but not in normal cells. The proposed mechanism of the cytotoxic action of these liposomes involved specific generation of free radicals by the iron ions mechanism.

Mycobacterium bovis BCG in metastatic melanoma therapy

Melanoma is the most aggressive form of skin cancer, with a high mortality rate and with 96,480 new cases expected in 2019 in the USS. BRAF^V600E, the most common driver mutation, is found in around 50% of melanomas, contributing to tumor growth, angiogenesis, and metastatic progression. Dacarbazine (DTIC), an alkylate agent, was the first chemotherapeutic agent approved by the US Food and Drug Administration (FDA) used as a standard treatment. Since then, immunotherapies have been approved for metastatic melanoma (MM) including ipilimumab and pembrolizumab checkpoint inhibitors that help decrease the risk of progression. Moreover, Mycobacterium bovis Bacillus Calmette-Guerin (BCG) serves as an adjuvant therapy that induces the recruitment of natural killer NK, CD4⁺, and CD8⁺ T cells and contributes to antitumor immunity. BCG can be administered in combination with chemotherapeutic and immunotherapeutic agents and can be genetically manipulated to produce recombinant BCG (rBCG) strains that express heterologous proteins or overexpress immunogenic proteins, increasing the immune response and improving patient survival. In this review, we highlight several studies utilizing rBCG immunotherapy for MM in combination with other therapeutic agents.

Cutaneous pH landscape as a facilitator of melanoma initiation and progression

Melanoma incidence is on the rise and currently causes the majority of skin cancer-related deaths. Yet, therapies for metastatic melanoma are still insufficient so that new concepts are essential. Malignant transformation of melanocytes and melanoma progression are intimately linked to the cutaneous pH landscape and its dysregulation in tumour lesions. The pH landscape of normal skin is characterized by a large pH gradient of up to 3 pH units between surface and dermis. The Na⁺ /H⁺ exchanger NHE1 is one of the major contributors of acidity in superficial skin layers. It is also activated by the most frequent mutation in melanoma, BRAF^{V 600E} , thereby causing pH dysregulation during melanoma initiation. Melanoma progression is supported by an extracellular acidification and/or NHE1 activity which promote the escape of single melanoma cells from the primary tumour, migration and metastatic spreading. We propose that viewing melanoma against the background of the acid-base physiology of the skin provides a better understanding of the pathophysiology of this disease and allows the development of novel therapeutic concepts.

Chronic hypoxia-induced slug promotes invasive behavior of prostate cancer cells by activating expression of ephrin-B1

Advanced solid tumors are exposed to hypoxic conditions over longer periods of time as they grow. Tumor hypoxia is a major factor that induces malignant progression, but most previous studies on tumor hypoxia were performed under short-term hypoxia for up to 72 hours and few studies have focused on tumor response to chronic hypoxic conditions. Here we show a molecular mechanism by which chronic hypoxia promotes invasive behavior in prostate cancer cells. We found that an epithelial-mesenchymal transition (EMT)-driving transcription factor, slug, is specifically upregulated under chronic hypoxia and promotes tumor cell migration and invasion. Unexpectedly, processes associated with EMT, such as loss of E-cadherin, are not observed under chronic hypoxia. Instead, expression of ephrin-B1, a ligand of Eph-related receptor tyrosine kinases, is markedly induced by slug through E-box motifs and promotes cell migration and invasion. Furthermore, slug and ephrin-B1 are highly coexpressed in chronic hypoxic cells of human prostate adenocarcinoma tissues after androgen deprivation, which is known to cause tumor hypoxia. Taken together, these results indicate that chronic hypoxia-induced slug promotes invasive behavior of prostate cancer cells by activating the expression of ephrin-B1. In addition, ephrin-B1 may be a novel therapeutic target in combination with androgen deprivation therapy for aggressive prostate cancer.

Dioscin augments HSV-tk-mediated suicide gene therapy for melanoma by promoting connexin-based intercellular communication

Suicide gene therapy is a promising strategy against melanoma. However, the low efficiency of the gene transfer technique can limit its application. Our preliminary data showed that dioscin, a glucoside saponin, could upregulate the expression of connexins Cx26 and Cx43, major components of gap junctions, in melanoma cells. We hypothesized that dioscin may increase the bystander effect of herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) through increasing the formation of gap junctions. Further analysis showed that dioscin indeed could increase the gap junctional intercellular communication in B16 melanoma cells, resulting in more efficient GCV-induced bystander killing in B16^tk cells. By contrast, overexpression of dominant negative Cx43 impaired the cell-cell communication of B16 cells and subsequently weakened the bystander effect of HSV-tk/GCV gene therapy. In vivo, combination treatment with dioscin and GCV of tumor-bearing mice with 30% positive B16^tk cells and 70% wild-type B16 cells caused a significant reduction in tumor volume and weight compared to treatment with GCV or dioscin alone. Taken together, these results demonstrated that dioscin could augment the bystander effect of the HSV-tk/GCV system through increasing connexin-mediated gap junction coupling.

DNA demethylation of claudin-4 suppresses migration and invasion in laryngeal squamous carcinoma cells

Claudin-4 (CLDN4) is a member of the claudin transmembrane protein family, which consists of integral membrane proteins that are components of the epithelial cell tight junctions; these tight junctions regulate movement of solutes and ions through the paracellular space. CLDN4 is also a differentiation marker and is believed to indicate an epithelial phenotype. However, the role of CLDN4 in laryngeal squamous carcinoma is still unclear. Here, we showed that CLDN4 expression was down-regulated in laryngeal squamous carcinoma tissues and negatively correlated with methyl-CpG-binding protein 2. In addition, CLDN4 was hypermethylated in HEp-2 cells. DNA demethylation of CLDN4 by 5-aza-2'-deoxycytidine suppressed migration and invasion of HEp-2 cells, whereas CLDN4 silencing restored the migration and invasion of HEp-2 cells. Therefore, CLDN4 plays a key role in laryngeal squamous carcinoma progression.

Inhibitors of connexin and pannexin channels as potential therapeutics

While gap junctions support the exchange of a number of molecules between neighboring cells, connexin hemichannels provide communication between the cytosol and the extracellular environment of an individual cell. The latter equally holds true for channels composed of pannexin proteins, which display an architecture reminiscent of connexin hemichannels. In physiological conditions, gap junctions are usually open, while connexin hemichannels and, to a lesser extent, pannexin channels are typically closed, yet they can be activated by a number of pathological triggers. Several agents are available to inhibit channels built up by connexin and pannexin proteins, including alcoholic substances, glycyrrhetinic acid, anesthetics and fatty acids. These compounds not always strictly distinguish between gap junctions, connexin hemichannels and pannexin channels, and may have effects on other targets as well. An exception lies with mimetic peptides, which reproduce specific amino acid sequences in connexin or pannexin primary protein structure. In this paper, a state-of-the-art overview is provided on inhibitors of cellular channels consisting of connexins and pannexins with specific focus on their mode-of-action and therapeutic potential.

Mouse Cutaneous Melanoma Induced by Mutant BRaf Arises from Expansion and Dedifferentiation of Mature Pigmented Melanocytes

To identify the cells at the origin of melanoma, we combined single-cell lineage-tracing and transcriptomics approaches with time-lapse imaging. A mouse model that recapitulates key histopathological features of human melanomagenesis was created by inducing a BRafV600E-driven melanomagenic program in tail interfollicular melanocytes. Most targeted mature, melanin-producing melanocytes expanded clonally within the epidermis before losing their differentiated features through transcriptional reprogramming and eventually invading the dermis. Tumors did not form within interscales, which contain both mature and dormant amelanotic melanocytes. The hair follicle bulge, which contains melanocyte stem cells, was also refractory to melanomagenesis. These studies identify varying tumor susceptibilities within the melanocytic lineage, highlighting pigment-producing cells as the melanoma cell of origin, and indicate that regional variation in tumor predisposition is dictated by microenvironmental cues rather than intrinsic differences in cellular origin. Critically, this work provides in vivo evidence that differentiated somatic cells can be reprogrammed into cancer initiating cells.

E-cadherin mediates ultraviolet radiation- and calcium-induced melanin transfer in human skin cells

Skin pigmentation is directed by epidermal melanin units, characterized by long-lived and dendritic epidermal melanocytes (MC) that interact with viable keratinocytes (KC) to contribute melanin to the epidermis. Previously, we reported that MC:KC contact is required for melanosome transfer that can be enhanced by filopodi, and by UVR/UVA irradiation, which can upregulate melanosome transfer via Myosin X-mediated control of MC filopodia. Both MC and KC express Ca²⁺ -dependent E-cadherins. These homophilic adhesion contacts induce transient increases in intra-KC Ca²⁺ , while ultraviolet radiation (UVR) raises intra-MC Ca²⁺ via calcium-selective ORAI1 ion channels; both are associated with regulating melanogenesis. However, how Ca²⁺ triggers melanin transfer remains unclear. Here we evaluated the role of E-cadherin in UVR-mediated melanin transfer in human skin cells. MC and KC in human epidermis variably express filopodia-associated E-cadherin, Cdc42, VASP and β-catenin, all of which were upregulated by UVR in human MC in vitro. Knockdown of E-cadherin revealed that this cadherin is essential for UVR-induced MC filopodia formation and melanin transfer. Moreover, Ca²⁺ induced a dose-dependent increase in filopodia formation and melanin transfer, as well as increased β-catenin, Cdc42, Myosin X and E-cadherin expression in these skin cells. Together, these data suggest that filopodial proteins and E-cadherin, which are upregulated by intracellular (UVR-stimulated) and extracellular Ca²⁺ availability, are required for filopodia formation and melanin transfer. This may open new avenues to explore how Ca²⁺ signalling influences human pigmentation.

Preventive effect of celecoxib use against cancer progression and occurrence of oral squamous cell carcinoma

Overexpression of cyclooxygenase-2 in oral cancer increases lymph node metastasis and is associated with a poor prognosis. The potential of celecoxib (CXB) use is reported in cancer treatment by inhibiting proliferation through apoptosis, but the effects on the epithelial-mesenchymal transition (EMT) and cancer cell mobility remain unclear. We performed a preclinical study and population-based study to evaluate CXB use in the prevention of oral cancer progression and occurrence. The in-vitro findings showed that CXB is involved in the inhibition of EMT and cell mobility through blocking transcription factors (Slug, Snail and ZEB1), cytoplasmic mediators (focal adhesion kinase (FAK), vimentin and β-catenin), cell adhesion molecules (cadherins and integrins), and surface receptors (AMFR and EGFR). The murine xenograft model showed a 65% inhibition in tumour growth after a 5-week treatment of CXB compared to placebo. Xenograft tumours in placebo-treated mice displayed a well-to-moderate/moderate differentiated SCC grade, while those from CXB-treated mice were well differentiated. The expression levels of membrane EGFR, and nuclear FAK, Slug and ZEB1 were decreased in the xenograft tumours of CXB-treated mice. A retrospective cohort study showed that increasing the daily dose and medication time of CXB was associated with oral cancer prevention. The findings provide an alternative prevention strategy for oral cancer development with CXB use.

Intercellular crosstalk in human malignant melanoma

Incidence of malignant melanoma is increasing globally. While the initial stages of tumors can be easily treated by a simple surgery, the therapy of advanced stages is rather limited. Melanoma cells spread rapidly through the body of a patient to form multiple metastases. Consequently, the survival rate is poor. Therefore, emphasis in melanoma research is given on early diagnosis and development of novel and more potent therapeutic options. The malignant melanoma is arising from melanocytes, cells protecting mitotically active keratinocytes against damage caused by UV light irradiation. The melanocytes originate in the neural crest and consequently migrate to the epidermis. The relationship between the melanoma cells, the melanocytes, and neural crest stem cells manifests when the melanoma cells are implanted to an early embryo: they use similar migratory routes as the normal neural crest cells. Moreover, malignant potential of these melanoma cells is overdriven in this experimental model, probably due to microenvironmental reprogramming. This observation demonstrates the crucial role of the microenvironment in melanoma biology. Indeed, malignant tumors in general represent complex ecosystems, where multiple cell types influence the growth of genetically mutated cancer cells. This concept is directly applicable to the malignant melanoma. Our review article focuses on possible strategies to modify the intercellular crosstalk in melanoma that can be employed for therapeutic purposes.

Design, synthesis and evaluation of antiproliferative activity of melanoma-targeted histone deacetylase inhibitors

The clinical validation of histone deacetylase inhibition as a cancer therapeutic modality has stimulated interest in the development of new generation of potent and tumor selective histone deacetylase inhibitors (HDACi). With the goal of selective delivery of the HDACi to melanoma cells, we incorporated the benzamide, a high affinity melanin-binding template, into the design of HDACi to generate a new series of compounds 10a-b and 11a-b which display high potency towards HDAC1 and HDAC6. However, these compounds have attenuated antiproliferative activities relative to the untargeted HDACi. An alternative strategy furnished compound 14, a prodrug bearing the benzamide template linked via a labile bond to a hydroxamate-based HDACi. This pro-drug compound showed promising antiproliferative activity and warrant further study.

Protein kinase C inhibitor Gö6976 but not Gö6983 induces the reversion of E- to N-cadherin switch and metastatic phenotype in melanoma: identification of the role of protein kinase D1

Background

Melanoma is a highly metastatic type of cancer that is resistant to all standard anticancer therapies and thus has a poor prognosis. Therefore, metastatic melanoma represents a significant clinical problem and requires novel and effective targeted therapies. The protein kinase C (PKC) family comprises multiple isoforms of serine/threonine kinases that possess distinct roles in cancer development and progression. In this study, we determined whether inhibition of PKC could revert a major process required for melanoma progression and metastasis; i.e. the E- to N-cadherin switch.

Methods

The cadherin switch was analyzed in different patient-derived primary tumors and their respective metastatic melanoma cells to determine the appropriate cellular model (aggressive E-cadherin-negative/N-cadherin-positive metastasis-derived melanoma cells). Next, PKC inhibition in two selected metastatic melanoma cell lines, was performed by using either pharmacological inhibitors (Gö6976 and Gö6983) or stable lentiviral shRNA transduction. The expression of E-cadherin and N-cadherin was determined by western blot. The consequences of cadherin switch reversion were analyzed: cell morphology, intercellular interactions, and β-catenin subcellular localization were analyzed by immunofluorescence labeling and confocal microscopy; cyclin D1 expression was analyzed by western blot; cell metastatic potential was determined by anchorage-independent growth assay using methylcellulose as semi-solid medium and cell migration potential by wound healing and transwell assays.

Results

Gö6976 but not Gö6983 reversed the E- to N-cadherin switch and as a consequence induced intercellular interactions, profound morphological changes from elongated mesenchymal-like to cuboidal epithelial-like shape, β-catenin translocation from the nucleus to the plasma membrane inhibiting its oncogenic function, and reverting the metastatic potential of the aggressive melanoma cells. Comparison of the target spectrum of these inhibitors indicated that these observations were not the consequence of the inhibition of conventional PKCs (cPKCs), but allowed the identification of a novel serine/threonine kinase, i.e. protein kinase Cμ, also known as protein kinase D1 (PKD1), whose specific inhibition allows the reversion of the metastatic phenotype in aggressive melanoma.

Conclusion

In conclusion, our study suggests, for the first time, that while cPKCs don’t embody a pertinent therapeutic target, inhibition of PKD1 represents a novel attractive approach for the treatment of metastatic melanoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-3007-5) contains supplementary material, which is available to authorized users.

Signaling and Immune Regulation in Melanoma Development and Responses to Therapy

Melanoma is a complex and genomically diverse malignancy, and new genes and signaling pathways involved in pathogenesis continue to be discovered. Mechanistic insights into gene and immune regulation in melanoma have led to the development of numerous successful and innovative pharmacologic agents over recent years. Multiple targeted therapies and immunotherapies have already entered the clinic, becoming new standards of care and transforming the prognosis for many patients with malignant melanoma. In this review, we provide an overview of the current understanding of signaling and immune regulation in melanoma and implications for responses to treatment, organized in the framework of hallmark characteristics in cancer.

Connexins and their channels in inflammation

Inflammation may be caused by a variety of factors and is a hallmark of a plethora of acute and chronic diseases. The purpose of inflammation is to eliminate the initial cell injury trigger, to clear out dead cells from damaged tissue and to initiate tissue regeneration. Despite the wealth of knowledge regarding the involvement of cellular communication in inflammation, studies on the role of connexin-based channels in this process have only begun to emerge in the last few years. In this paper, a state-of-the-art overview of the effects of inflammation on connexin signaling is provided. Vice versa, the involvement of connexins and their channels in inflammation will be discussed by relying on studies that use a variety of experimental tools, such as genetically modified animals, small interfering RNA and connexin-based channel blockers. A better understanding of the importance of connexin signaling in inflammation may open up towards clinical perspectives.

Comparative Aspects of Canine Melanoma

Melanomas are malignant neoplasms originating from melanocytes. They occur in most animal species, but the dog is considered the best animal model for the disease. Melanomas in dogs are most frequently found in the buccal cavity, but the skin, eyes, and digits are other common locations for these neoplasms. The aim of this review is to report etiological, epidemiological, pathological, and molecular aspects of melanomas in dogs. Furthermore, the particular biological behaviors of these tumors in the different body locations are shown. Insights into the therapeutic approaches are described. Surgery, chemotherapy, radiotherapy, immunotherapy, and the outcomes after these treatments are presented. New therapeutic perspectives are also depicted. All efforts are geared toward better characterization and control of malignant melanomas in dogs, for the benefit of these companion animals, and also in an attempt to benefit the treatment of human melanomas.

Establishing Human Skin Grafts in Mice as Model for Melanoma Progression

Technological advances often dictate progress in cancer research. Melanoma research has been considerably influenced by implementation of novel techniques and has contributed to our understanding of the mechanism of tumor progression. The three-dimensional (3D) human skin reconstruct is an ideal model to dissect each step of melanoma development and progression. Reconstructed human skin consists of fibroblast-contracted collagen gels as a dermal compartment and a stratified epidermal compartment. The epidermis comprises keratinocytes and normal melanocytes or melanoma cells from different stages. Normal melanocytes in skin reconstructs remain singly distributed at the basement membrane within the basal layer of keratinocytes. The radial growth phase (RGP) melanoma cells grow as cell clusters in the epidermis. The vertical growth phase (VGP) melanoma cells invade the dermis of reconstructs. Metastatic melanoma cells aggressively invade deep into the dermis. Grafting melanoma skin reconstructs onto mice induces local tumor formation and metastatic foci in distant organs such as lungs. The growth patterns and the range of metastases reflect proliferation and metastatic capacity of the original tumors. Skin reconstruct as xenografts enable us to observe to which organs melanoma cells spread. In this chapter, we describe the usefulness of the model in studying not only melanocyte physiology but also pathophysiological conditions such as melanocyte transformation and melanoma progression. A better understanding of these processes will benefit the entire melanoma field.

The Selective Degradation of Synaptic Connexin 43 Protein by Hypoxia-induced Autophagy Impairs Natural Killer Cell-mediated Tumor Cell Killing

Although natural killer (NK) cells play an important role in the control of melanoma, hypoxic stress in the tumor microenvironment may impair NK-mediated tumor cell killing by mechanisms that are not fully understood. In this study, we investigated the effect of hypoxia on the expression and channel activity of connexin 43 (Cx43) in melanoma cells and its impact on their susceptibility to NK cell-mediated lysis. Our results demonstrated that hypoxic stress increases Cx43 expression in melanoma cells via hypoxia-inducible factor-1α (HIF-1α) transcriptional activity. Hypoxic cells displaying increased Cx43 expression were less susceptible to NK cell-mediated lysis compared with normoxic cells expressing a moderate level of Cx43. Conversely, when overexpressed in normoxic tumor cells, Cx43 improves their susceptibility to N cell-mediated killing. We show that the NK cell immune synapse formed with normoxic melanoma cells is more stable and contains a high level of gap-junctional Cx43 whereas that formed with hypoxic cells is less stable and contains a significant lower level of gap-junctional Cx43. We provide evidence that the activation of autophagy in hypoxic melanoma cells selectively degrades gap-junctional Cx43, leading to the destabilization of the immune synapse and the impairment of NK cell-mediated killing. Inhibition of autophagy by genetic or pharmacological approaches as well as expression of the non-degradable form of Cx43 significantly restore its accumulation at the immune synapse and improves N cell-mediated lysis of hypoxic melanoma cells. This study provides the first evidence that the hypoxic microenvironment negatively affects the immune surveillance of tumors by NK cells through the modulation of Cx43-mediated intercellular communications.

A draft network of ligand-receptor-mediated multicellular signalling in human

Cell-to-cell communication across multiple cell types and tissues strictly governs proper functioning of metazoans and extensively relies on interactions between secreted ligands and cell-surface receptors. Herein, we present the first large-scale map of cell-to-cell communication between 144 human primary cell types. We reveal that most cells express tens to hundreds of ligands and receptors to create a highly connected signalling network through multiple ligand-receptor paths. We also observe extensive autocrine signalling with approximately two-thirds of partners possibly interacting on the same cell type. We find that plasma membrane and secreted proteins have the highest cell-type specificity, they are evolutionarily younger than intracellular proteins, and that most receptors had evolved before their ligands. We provide an online tool to interactively query and visualize our networks and demonstrate how this tool can reveal novel cell-to-cell interactions with the prediction that mast cells signal to monoblastic lineages via the CSF1-CSF1R interacting pair.

Physiological roles of connexins in labour and lactation

The connexin family of proteins are best known as oligomerizing to form intercellular membrane channels (gap junctions) that metabolically and ionically couple cells to allow for coordinated cellular function. Nowhere in the body is this role better illustrated than in the uterine smooth muscle during parturition, where gap junctions conduct the contraction wave throughout the tissue to deliver the baby. Parturition is followed by the onset of lactation with connexins contributing to both the dramatic reorganization of mammary gland tissue leading up to lactation and the smooth muscle contraction of the myoepithelial cells which extrudes the milk. This review summarizes what is known about the expression and roles of individual connexin family members in the uterus during labour and in the mammary glands during development and lactation. Connexin loss or malfunction in mammary glands and the uterus can have serious implications for the health of both the mother and the newborn baby.

Overexpression of connexin 43 reduces melanoma proliferative and metastatic capacity

Background:

Alterations in connexin 43 (Cx43) expression and/or gap junction (GJ)-mediated intercellular communication are implicated in cancer pathogenesis. Herein, we have investigated the role of Cx43 in melanoma cell proliferation and apoptosis sensitivity in vitro, as well as metastatic capability and tumour growth in vivo.

Methods:

Connexin 43 expression levels, GJ coupling and proliferation rates were analysed in four different human melanoma cell lines. Furthermore, tumour growth and lung metastasis of high compared with low Cx43-expressing FMS cells were evaluated in vivo using a melanoma xenograft model.

Results:

Specific inhibition of Cx43 channel activity accelerated melanoma cell proliferation, whereas overexpression of Cx43 increased GJ coupling and reduced cell growth. Moreover, Cx43 overexpression in FMS cells increased basal and tumour necrosis factor-α-induced apoptosis and resulted in decreased melanoma tumour growth and lower number and size of metastatic foci in vivo.

Conclusions:

Our findings reveal an important role for Cx43 in intrinsically controlling melanoma growth, death and metastasis, and emphasise the potential use of compounds that selectively enhance Cx43 expression on melanoma in the future chemotherapy and/or immunotherapy protocols.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Molecular pathology of cutaneous melanoma

Cutaneous melanoma is associated with strong prognostic phenotypic features, such as gender, Breslow's thickness and ulceration, although the biological significance of these variables is largely unknown. It is likely that these features are surrogates of important biological events rather than directly promoting cutaneous melanoma progression. In this article, we address the molecular mechanisms that drive these phenotypic changes. Furthermore, we present a comprehensive overview of recurrent genetic abnormalities, both germline and somatic, in relation to cutaneous melanoma subtypes, ultraviolet exposure and anatomical localization, as well as pre-existing and targeted therapy-induced mutations that may contribute to resistance. The increasing knowledge of critically important oncogenes and tumor-suppressor genes is promoting a transition in melanoma diagnosis, in which single-gene testing will be replaced by multiplex and multidimensional analyses that combine classical histopathological characteristics with the molecular profile for the prognostication and selection of melanoma therapy.

Upregulation of Claudin-4, CAIX and GLUT-1 in distant breast cancer metastases

BACKGROUND

Several studies have shown that the immunophenotype of distant breast cancer metastases may differ significantly from that of the primary tumor, especially with regard to differences in the level of hormone receptor protein expression, a process known as receptor conversion. This study aimed to compare expression levels of several membrane proteins between primary breast tumors and their corresponding distant metastases in view of their potential applicability for molecular imaging and drug targeting.

METHODS

Expression of Claudin-4, EGFR, CAIX, GLUT-1 and IGF1R was assessed by immunohistochemistry on tissue microarrays composed of 97 paired primary breast tumors and their distant (non-bone) metastases.

RESULTS

In both the primary cancers and the metastases, Claudin-4 was most frequently expressed, followed by GLUT-1, CAIX and EGFR.From primary breast cancers to their distant metastases there was positive to negative conversion, e.g. protein expression in the primary tumor with no expression in its paired metastasis, in 6%, 19%, 12%, 38%, and 0% for Claudin-4 (n.s), GLUT-1 (n.s), CAIX (n.s), EGFR (n.s) and IGF1R (n.s) respectively. Negative to positive conversion was seen in 65%, 47%, 43%, 9% and 0% of cases for Claudin-4 (p = 0.049), GLUT-1 (p = 0.024), CAIX (p = 0.002), EGFR (n.s.) and IGF1R (n.s.) respectively. Negative to positive conversion of Claudin-4 in the metastasis was significantly associated with tumor size (p = 0.015), negative to positive conversion of EGFR with negative PR status (p = 0.046) and high MAI (p = 0.047) and GLUT-1 negative to positive conversion with (neo)adjuvant chemotherapy (p = 0.039) and time to metastasis formation (p = 0.034). CAIX and GLUT-1 expression in the primary tumor were significantly associated with high MAI (p = 0.008 and p = 0.038 respectively).

CONCLUSION

Claudin-4 is frequently expressed in primary breast cancers but especially in their metastases and is thereby an attractive membrane bound molecular imaging and drug target. Conversion in expression of the studied proteins from the primary tumor to metastases was fairly frequent, except for IGF1R, implying that the expression status of metastases cannot always be reliably predicted from the primary tumor, thereby necessitating biopsy for reliable assessment.

Melanoma's connections to the tumour microenvironment

SUMMARY

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

N-cadherin and P-cadherin are biomarkers for invasion, metastasis, and poor prognosis of gallbladder carcinomas

Gallbladder cancer (GBC) is a rare, but highly aggressive cancer. The most common type of gallbladder cancer is adenocarcinoma (AC), while squamous cell/adenosquamous carcinoma (SC/ASC) is a rare type of gallbladder cancer. The clinicopathologic and biological characteristics of SC/ASC have not been well documented. In this study, the protein expression of N-cadherin and P-cadherin in 46 SC/ASCs and 80 ACs was measured using immunohistochemistry. We demonstrated that positive N-cadherin and P-cadherin expression were significantly associated with large tumor size, invasion, and lymph node metastasis of both SC/ASC and AC. In contrast, positive N-cadherin and P-cadherin expression were significantly associated with differentiation and TNM stage in only AC. Univariate Kaplan-Meier analysis showed that positive N-cadherin and P-cadherin expression, differentiation, tumor size, TNM stage, invasion, lymph node metastasis, and surgical curability were significantly associated with overall survival in both SC/ASC and AC patients. Multivariate Cox regression analysis showed that positive N-cadherin and P-cadherin expression are independent poor-prognostic factors in both SC/ASC and AC patients. Our study suggested that positive N-cadherin and P-cadherin expression closely correlated with clinicopathological and biological behaviors, and poor-prognosis of gallbladder cancer.

Langerhans cell maturation is accompanied by induction of N-cadherin and the transcriptional regulators of epithelial-mesenchymal transition ZEB1/2

Langerhans cells (LCs) are a unique subset of dendritic cells (DCs) that express epithelial adhesion molecules, allowing them to form contacts with epithelial cells and reside in epidermal/epithelial tissues. The dynamic regulation of epithelial adhesion plays a decisive role in the life cycle of LCs. It controls whether LCs remain immature and sessile within the epidermis or mature and egress to initiate immune responses. So far, the molecular machinery regulating epithelial adhesion molecules during LC maturation remains elusive. Here, we generated pure populations of immature human LCs in vitro to systematically probe for gene-expression changes during LC maturation. LCs down-regulate a set of epithelial genes including E-cadherin, while they upregulate the mesenchymal marker N-cadherin known to facilitate cell migration. In addition, N-cadherin is constitutively expressed by monocyte-derived DCs known to exhibit characteristics of both inflammatory-type and interstitial/dermal DCs. Moreover, the transcription factors ZEB1 and ZEB2 (ZEB is zinc-finger E-box-binding homeobox) are upregulated in migratory LCs. ZEB1 and ZEB2 have been shown to induce epithelial-to-mesenchymal transition (EMT) and invasive behavior in cancer cells undergoing metastasis. Our results provide the first hint that the molecular EMT machinery might facilitate LC mobilization. Moreover, our study suggests that N-cadherin plays a role during DC migration.

Connexin43 reduces melanoma growth within a keratinocyte microenvironment and during tumorigenesis in vivo

Connexins (Cx) have been identified as tumor suppressors or enhancers, a distinction that appears to be dependent on the type and stage of disease. However, the role of connexins in melanoma tumorigenesis and their status during cancer onset and progression remain controversial and unclear. Here, we show that the aggressive B16-BL6 mouse melanoma cell line expresses low basal levels of Cx26 and Cx43, rendering them gap junctional intercellular communication-deficient as elucidated by immunofluorescence, Western blotting, and dye transfer studies. Following ectopic expression of green fluorescent protein-tagged Cx26 and Cx43 in these connexin-deficient melanomas, punctate gap junction-like plaques were evident at sites of cell-cell apposition, and the incidence of dye transfer was significantly increased similar to connexin-rich keratinocytes. We found that the expression of Cx43, but not Cx26, significantly reduced cellular proliferation and anchorage-independent growth from control melanomas, whereas migration was unaffected. Additionally, melanomas expressing Cx43 displayed significantly reduced growth within the in situ-like microenvironment of keratinocytes, despite a lack of heterocellular gap junctional intercellular communication between the two cell types. Furthermore, when grown in vivo in the chicken chorioallantoic membrane, primary tumors derived from Cx43-expressing melanomas were significantly smaller than controls, whereas Cx26-expressing melanomas produced tumors similar to controls. Collectively, these results suggest that Cx43, and not Cx26, can act as a tumor suppressor during melanoma tumorigenesis.

Molecular networks in melanoma invasion and metastasis

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

Cell proliferation and expression of connexins differ in melanotic and amelanotic canine oral melanomas

Melanoma is a malignant neoplasm occurring in several animal species, and is the most frequently found tumor in the oral cavity in dogs. Melanomas are classified into two types: melanotic and amelanotic. Prior research suggests that human amelanotic melanomas are more aggressive than their melanotic counterparts. This study evaluates the behavior of canine melanotic and amelanotic oral cavity melanomas and quantifies cell proliferation and the expression of connexins. Twenty-five melanomas (16 melanotic and 9 amelanotic) were collected from dogs during clinical procedures at the Veterinary Hospital of the School of Veterinary Medicine and Animal Science of the University of São Paulo, Brazil. After diagnosis, dogs were followed until death or euthanasia. Histopathology confirmed the gross melanotic or amelanotic characteristics and tumors were classified according to the WHO. HMB45 or Melan A immunostainings were performed to confirm the diagnosis of amelanotic melanomas. Cell proliferation was quantified both by counting mitotic figures and PCNA positive nuclei. Expressions of connexins 26 and 43 were evaluated by immunohistochemistry, qRT-PCR and Western blot. Dogs bearing amelanotic melanomas presented a shorter lifespan in comparison to those with melanotic melanomas. Cell proliferation was significantly higher in amelanotic melanomas. Expressions of Connexins 26 and 43 were significantly reduced in amelanotic melanomas. The results presented here suggest that oral cavity melanotic and amelanotic melanomas differ regarding their behavior, cell proliferation and connexin expression in dogs, indicating a higher aggressiveness of amelanotic variants.

The distinct expression patterns of claudin-2, -6, and -11 between human gastric neoplasms and adjacent non-neoplastic tissues

Background

Cancers have a multifactorial etiology a part of which is genetic. Recent data indicate that expression of the tight junction claudin proteins is involved in the etiology and progression of cancer.

Methods

To explore the correlations of the tight junction proteins claudin-2,-6, and −11 in the pathogenesis and clinical behavior of gastric cancer, 40 gastric cancer tissues and 28 samples of non-neoplastic tissues adjacent to the tumors were examined for expression of claudin-2,-6, and −11 by streptavidin-perosidase immunohistochemical staining method.

Results

The positive expression rates of claudin-2 in gastric cancer tissues and adjacent tissues were 25% and 68% respectively (P < 0.001). The positive expression rates of claudin-6 in gastric cancer tissues and adjacent tissues were 55% and 79% respectively (P = 0.045 < 0.05). In contrast, the positive expression rates of claudin-11 in gastric cancer tissues and gastric cancer adjacent tissues were 80% and 46% (P = 0.004 < 0.01). Thus in our study, the expression of claudin-2, and claudin-6 was down regulated in gastric cancer tissue while the expression of claudin-11 was up regulated. Correlations between claudin expression and clinical behavior were not observed.

Conclusion

Our study provides the first evidence that claudin-2,-6, and −11 protein expression varies between human gastric cancers and adjacent non-neoplastic tissues.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/5470513569630744