Melanoma Vasculogenic Mimicry Research Articles

CD36 promotes vasculogenic mimicry in melanoma by mediating adhesion to the extracellular matrix

BackgroundThe formation of blood vessels within solid tumors directly contributes to cancer growth and metastasis. Until recently, tumor vasculature was thought to occur exclusively via endothelial cell (EC) lined structures (i.e. angiogenesis), but a second source of tumor vasculature arises from the cancer cells themselves, a process known as vasculogenic mimicry (VM). While it is generally understood that the function of VM vessels is the same as that of EC-lined vessels (i.e. to supply oxygen and nutrients to the proliferating cancer cells), the molecular mechanisms underpinning VM are yet to be fully elucidated.MethodsHuman VM-competent melanoma cell lines were examined for their VM potential using the in vitro angiogenesis assays (Matrigel), together with inhibition studies using small interfering RNA and blocking monoclonal antibodies. Invasion assays and adhesion assays were used to examine cancer cell function.ResultsHerein we demonstrate that CD36, a cell surface glycoprotein known to promote angiogenesis by ECs, also supports VM formation by human melanoma cancer cells. In silico analysis of CD36 expression within the melanoma cohort of The Cancer Genome Atlas suggests that melanoma patients with high expression of CD36 have a poorer clinical outcome. Using in vitro ‘angiogenesis’ assays and CD36-knockdown approaches, we reveal that CD36 supports VM formation by human melanoma cells as well as adhesion to, and invasion through, a cancer derived extracellular matrix substrate. Interestingly, thrombospondin-1 (TSP-1), a ligand for CD36 on ECs that inhibits angiogenesis, has no effect on VM formation. Further investigation revealed a role for laminin, but not collagen or fibronectin, as ligands for CD36 expressing melanoma cells.ConclusionsTaken together, this study suggests that CD36 is a novel regulator of VM by melanoma cancer cells that is facilitated, at least in part, via integrin-α3 and laminin. Unlike angiogenesis, VM is not perturbed by the presence of TSP-1, thus providing new information on differences between these two processes of tumor vascularization which may be exploited to combat cancer progression.

Vasculogenic mimicry in melanoma: molecular mechanisms and clinical significance

The concept of vasculogenic mimicry (VM) was introduced to describe the unique ability of highly aggressive tumor cells to form capillary-like structures and matrix-rich patterned network in three-dimensional culture that mimic embryonic vasculogenic network. VM has been reported in several aggressive tumors including ovaries, breast, liver, lung cancer, sarcoma, glioblastoma. It is worth to note, that VM in melanocyte-originated tumors is the most studied. Although much attention has been focused on factors that stimulate or suppress vascular channel formation by tumor cells, the molecular mechanisms underlying this phenomenon remain enigmatic. This review will focus on molecular determinants and key signaling pathways involved in tumor VM. The exploration of drugs targeted at molecular signaling pathways in VM is a field of challenges and hopes. The research on VM will increase our knowledge of the molecular events causing aggressive tumor cells to gain plasticity resulting in their ability to mimic vasculature. To date, little functional data exist that show how tumor cell-lined channels contribute to the overall survival of the tumor. However, even among researches who have questioned the concept of VM as a crucial circulatory system, there is generally a consensus that the prognostic significance of PAS-positive patterns is valid.

IL-33/ST2 Axis Regulates Vasculogenic Mimicry via ERK1/2-MMP-2/9 Pathway in Melanoma

Background: Melanoma, an extremely malignant form of cancer, poses a significant health risk. Vasculogenic mimicry (VM), blood vessels formed by tumor cells instead of endothelial cells, is an important factor for the rapid progression of melanoma. Interleukin (IL)-33 is an inflammatory factor commonly found in the tumor microenvironment and plays an important role in the progression of many tumors. IL-33 acts on immune cells and tumor cells through its receptor ST2. This study hypothesized that IL-33 directly affects the progression of melanoma. Objectives: This study was designed to investigate the effect of IL-33 on VM of melanoma and its potential mechanism of action. Methods: The expression of ST2 was evaluated in 66 cases of melanoma collected from human patients, and the differences were analyzed. In vitro experiments were conducted to study the effects of the IL-33/ST2 axis on cell migration and invasion and to elucidate possible mechanisms. Results: ST2 expression is associated with that of matrix metalloproteinase (MMP)-2 and VM in melanoma of patients. IL-33 increases the abilities of proliferation, migration and invasion of melanoma cells and VM tube formation through ST2. IL-33 induces the production of MMP-2/9 via ERK1/2 phosphorylation. Conclusion: IL-33 can directly act on melanoma cells and promote its development.

Rictor regulates the vasculogenic mimicry of melanoma via the AKT-MMP-2/9 pathway.

Vasculogenic mimicry (VM)‐positive melanomas are usually associated with poor prognosis. Rictor, the key component of the rapamycin‐insensitive complex of mTOR (mTORC2), is up‐regulated in several cancers, especially in melanomas with poor prognosis. The aim of this study was to investigate the role of Rictor in the regulation of VM and the mechanism underlying this possible regulation. VM channels were found in 35 of 81 tested melanoma samples and high Rictor expression correlated with VM structures. Moreover, Kaplan–Meier survival curves indicated that VM structures and high Rictor expression correlated with shorter survival in patients with melanoma. In vitro, Rictor knockdown by short hairpin RNA (shRNA) significantly inhibited the ability of A375 and MUM‐2B melanoma cells to form VM structures, as evidenced by most tubes remaining open. Cell cycle analysis revealed that Rictor knockdown blocked cell growth and resulted in the accumulation of cells in G2/M phase, and cell migration and invasion were greatly affected after Rictor down‐regulation. Western blotting assays indicated that down‐regulating Rictor significantly inhibited the phosphorylation of AKT at Ser473 and Thr308, which subsequently inhibited the expression and activity of downstream MMP‐2/9, as confirmed by real‐time PCR and gelatin Zymography. MK‐2206, a small‐molecule inhibitor of AKT, similarly inhibited the activity of AKT and secretion of MMP‐2/9, further supporting that Rictor down‐regulation inhibits the phosphorylation of AKT and activity of downstream MMP‐2/9 to affect VM formation. In conclusion, Rictor plays an important role in melanoma VM via the Rictor—AKT—MMP‐2/9 signalling pathway.

The involvement of autophagy in melanoma vasculogenic mimicry

Introduction. Autophagy, a catabolic process of protein and organelle recycling by transferring defective cytoplasm and organelles into double-membraned vesicles to degrade and regenerate materials, plays a critical role in maintaining energy homeostasis. Autophagy also protects against stress and infection, participates at the development of autoimmune disease. In recent years, the existence of alternative blood circulation system in tumors, vasculogenic mimicry (VM), which can partially compensate the lack of nutrients and oxygen under the hypoxic conditions, has been described. Objective. To elucidate the relationship between autophagy and VM. Materials and methods. In this study we used 2D- and 3D-culturing of melanoma cells derived from surgical species of patients with disseminated melanoma, electrophoresis and western blot, knockdown of the genes by using small interfering RNA (siRNA), flow cytometry, fluorescence microscopy. Results. We detected the basal level autophagy by examining the expression of autophagy-specific protein (LC-3B) by flow cytometry and cellular immunofluorescence staining by monodancylcadaverine. Both assays are the markers of autophagy late stage. Here we show that the level of autophagy in melanoma cells mel P, participated in capillary-like structures (CLS) formation in matrigel, was considerably higher than in mel Me cells which do not involve in VM. To explore the function of autophagy in the ability of melanoma cells to form CLS 3-methyladenine (3-MA) or chloroquine - inhibitors of initiation and terminal stage of autophagy - were used. Both inhibitors reduced the ability of melanoma cells to engage in VM. The data obtained were confirmed by siRNA-mediated gene silencing of BECN1 involved in the initiation of autophagy and ATG5 gene which is considered to be a marker of late stage of autophagy. Knockdown of BECN1 or ATG5 in mel P melanoma cells reduced the level of protein Beclin-1 and Atg5 about 70-75 %, and suppressed CLS formation in matrigel. Melanoma cells with the ATG5 gene knockdown changed the shape but maintained the ability to migrate and recognize each other, the formation of CLS was not observed. Low molecular weight VM inhibitor LCS-1269, significantly reduced the basic level of autophagy. Conclusion. Our data indicate that autophagy participates in CLS formation, and inhibition of autophagy suppresses CLS formation. We suggest that autophagy plays a dual role in the survival and development of tumors: autophagy helps cancer cells against environment stress and provides a temporary survival pathway by promoting energy regeneration, autophagy also promotes VM formation which supplies nutrients and oxygen to less vascularized area of tumor.

Inhibitory effect of norcantharidin on melanoma tumor growth and vasculogenic mimicry by suppressing MMP-2 expression

A form of microcirculation called vasculogenic mimicry (VM), which constitutes a novel approach for tumor blood supply in certain highly aggressive malignant tumors, was recently reported to contribute to tumor metastasis and poor prognosis in melanoma patients. Development of strategies to target tumor VM may be significant to reduce the recurrence and metastasis of melanoma. Norcantharidin (NCTD) has been shown to inhibit tumor growth and VM of human gallbladder carcinomas. Besides, NCTD could induce melanoma cell apoptosis. However, whether NCTD can inhibit the growth and VM formation of melanoma has not been evaluated. The present study aims to investigate the anti-VM activity of NCTD as a VM inhibitor for melanoma and its potential mechanisms. The anti-VM activity of NCTD was determined in human melanoma A375 cells and xenografts in vitro and in vivo. The findings indicate that NCTD inhibits tumor growth and VM formation of melanoma both in vitro and in vivo by suppressing matrix metalloproteinase-2 expression. The results suggest that NCTD is a potential therapeutic agent targeting VM in melanoma.

Desmoglein 2 promotes vasculogenic mimicry in melanoma and is associated with poor clinical outcome.

Tumors can develop a blood supply not only by promoting angiogenesis but also by forming vessel-like structures directly from tumor cells, known as vasculogenic mimicry (VM). Understanding mechanisms that regulate VM is important, as these might be exploitable to inhibit tumor progression. Here, we reveal the adhesion molecule desmoglein 2 (DSG2) as a novel mediator of VM in melanoma. Analysis of patient-derived melanoma cell lines and tumor tissues, and interrogation of The Cancer Genome Atlas (TCGA) data, revealed that DSG2 is frequently overexpressed in primary and metastatic melanomas compared to normal melanocytes. Notably, this overexpression was associated with poor clinical outcome. DSG2+ melanoma cells self-organized into tube-like structures on Matrigel, indicative of VM activity, which was inhibited by DSG2 knockdown or treatment with a DSG2-blocking peptide. Mechanistic studies revealed that DSG2 regulates adhesion and cell-cell interactions during tube formation, but does not control melanoma cell viability, proliferation or motility. Finally, analysis of patient tumors revealed a correlation between DSG2 expression, VM network density and expression of VM-associated genes. These studies identify DSG2 as a key regulator of VM activity in human melanoma and suggest this molecule might be therapeutically targeted to reduce tumor blood supply and metastatic spread.

The mechanisms of microenvironments influence on vasculogenic mimicry between intraocular and subcutaneous melanoma

To investigate the influence of different microenvironments on melanoma vasculogenic mimicry, invasiveness and metastasis behavior. It was an experimental study. Sixty C57BL/6J mice were randomly divided into two groups with 30 mice per group. Melanoma B16 cells were injected into the subretinal space and groin area of mice synchronously. The number of each type of microcirculation pattern was counted. The invasion and metastasis were observed. EphA2, MMP-2 and MMP-9 expression and their mRNA levels were detected by immunohistochemical staining and real time RT-PCR and compared between two groups. Five invasions and six lung metastases were found in the subretinal group while no invasion and metastasis were found in the groin group. The number of VM channels was significantly higher in subretinal group (t = 4. 188, P = 0.000). However, no significant difference of mosaic vessel and endothelium-dependent vessel was observed between two groups (t = 1.473, 1.805; P = 0.146, 0.076, respectively). EphA2, MMP-2 and MMP-9 expression was significantly higher in the subretinal group (data not shown). The mRNA levels of EphA2, MMP-2 and MMP-9 were rather higher in the subretinal tumor (t = 3.642, 8.109, 9.357; P = 0.002, 0.001 and 0.001, respectively). There was a positive association in melanoma cells of the VM between expression of EphA2 (r = 0.412, P = 0.021) but no statistically significant correlation between VM and MMP-2 (P > 0.05), nor between VM and MMP-9. Different microenvironments affect invasiveness and blood supply patterns of melanoma. Melanoma cells in intraocular microenvironment increased EphA2 expression which induced the formation of VM channels. Moreover, the expression of MMP-2 and MMP-9 in tumor tissue increased to enhance the invasiveness and metastasis behavior.

Merkel cell carcinoma expresses vasculogenic mimicry: demonstration in patients and experimental manipulation in xenografts

Merkel cell carcinoma (MCC) is a highly virulent cutaneous neoplasm that, like melanoma, is a frequent cause of patient morbidity and mortality. The cellular mechanisms responsible for the aggressive behavior of MCC remain unknown. Vasculogenic mimicry (VM) is a phenomenon associated with cancer virulence, including in melanoma, whereby anastomosing laminin networks form in association with tumor cells that express certain endothelial genes. To determine whether VM is a factor in MCC, we employed a relevant xenograft model using two independent human MCC lines. Experimentally induced tumors were remarkably similar histologically to patient MCC, and both contained laminin networks associated with vascular endothelial-cadherin (CD144) and vascular endothelial growth factor receptor 1, as well as Nodal expression typical of VM in melanoma. Moreover, two established chemotherapeutic agents utilized for human MCC, etoposide and carboplatin, induced necrosis in xenografts on systemic administration while enriching for laminin networks in apparently resistant viable tumor regions that persisted. These findings for the first time establish VM-like laminin networks as a biomarker in MCC, demonstrate the experimental utility of the MCC xenograft model, and suggest that VM-rich regions of MCC may be refractory to conventional chemotherapeutic agents.

The involvement of Notch signaling in melanoma vasculogenic mimicry

Notch signaling plays an important role in tumor angiogenesis. Recent studies suggest that Notch signaling also regulates the progression of primary melanomas toward an aggressive phenotype. The aim of this study was to investigate the involvement of Notch signaling pathway in organization of tumor cells into capillary-like structures (CLS), the phenomenon also known as vasculogenic mimicry (VM). Here, we show that Notch signaling cascade was constitutively active in melanoma cell lines we used. Blocking Notch signaling with the γ-secretase inhibitors, DAPT, dibenzazepine or Jagged1 neutralizing antibody resulted in stabilization of CLS indicating that Notch signaling pathway attenuates melanoma VM. We further studied this phenomenon on melanomas grafted in nude mice. Compared to control, VM channels in DAPT-treated grafted melanoma became larger and more branched. DAPT-treated melanomas also exhibited an up-regulation of MMP-2 and VEGFR1, both known as VM mediators. Moreover, we did not observe necrosis in VM channels areas of DAPT-treated melanomas. These findings indicate that VM regulated by Notch signaling may present a novel target in melanoma therapy.

Melanoma Vasculogenic Mimicry Capillary-Like Structure Formation Depends on Integrin and Calcium Signaling

We recently demonstrated that the formation of CLSs in vitro, which are thought to be a reconstitution of VM, is controlled by VEGFA. CLS formation also requires the extracellular matrix signals, presumably transduced by integrins. Both pathways are affected by Ca(2+). Therefore, we directly tested the roles of Ca(2+) and integrin in melanoma VM. The investigation was performed by immunocytochemical, histochemical, and 3D co-culture assays. We have also used an in vivo animal model. The extracellular and intracellular Ca(2+) chelators, EGTA and BAPTA-AM, prevented CLS formation on Matrigel, caused actin rearrangement, and completely destroyed the preformed CLS. Addition of colcemid or cytochalasin D prevented the CLS formation and destroyed the preformed CLS network. Herein, we also show that blocking antibodies to ανβ3 and ανβ5 integrins disrupted the CLS network. Control blocking antibody to β1 integrin had no effect. In vivo experiments indicated that Ca(2+) chelation dramatically reduced the signs of VM in melanoma tumors grafted in mice. Our results indicate that the formation of CLS is tightly regulated by extracellular and intracellular Ca(2+) levels; ανβ3 and ανβ5 integrins are primarily responsible for CLS formation, whereas β1 integrin does not participate in CLS formation.

VEGFR1 and PKCα signaling control melanoma vasculogenic mimicry in a VEGFR2 kinase-independent manner

We have recently shown that vascular endothelial growth factor-A (VEGFA), a major regulator of tumor vascularization, is essential for the organization of tumor cells into capillary-like structure (CLS), which is a hallmark of tumor vasculogenic mimicry (VM). Herein we further dissect the involvement of VEGFA and its downstream transducers, VEGF receptor 1 (VEGFR1), VEGFR2, and protein kinase C (PKC) in melanoma VM. The knockdown of VEGFR1 in three melanoma cell lines completely disrupts Matrigel-induced CLS formation, whereas inhibition of VEGFR2 kinase with a specific inhibitor, protein tyrosine kinase inhibitor II (PTKi-II), does not affect the process, indicating that VEGFR2 signaling is not involved in VEGFA-mediated melanoma VM. Furthermore, among tested PKC isoforms, only PKCα and δ are expressed in the melanoma cells during CLS formation. Pretreatment with selective PKCα and δ inhibitors blocked CLS formation. However, inhibition of PKCα, but not PKCδ, completely destroyed the previously formed CLS. Moreover, knockdown of PKCα, but not PKCδ, using small interfering RNAs abrogated CLS formation, suggesting that PKCα is the major contributory factor in melanoma VM. In-vivo experiments indicate that disruption of PKCα signaling significantly reduces the signs of VM in allografted B16/F10 melanoma. These findings may contribute to the development of new therapeutic agents that target melanoma VM.

Inhibition of tumor growth and vasculogenic mimicry by curcumin through down-regulation of the EphA2/PI3K/MMP pathway in a murine choroidal melanoma model

This study aims to investigate the underlying mechanism by which curcumin inhibits tumor growth and reduces vasculogenic mimicry (VM) in a murine choroidal melanoma model. Sixty mice were given subretinal injection with B16F10 cells and divided into a treatment and a control group. Curcumin was administered to the treatment group once a day at a dose of 100 mg/kg for 18 days starting at d3 (the day of inoculation is designated as d0); an equivalent volume of poloxamer-F68 was administered to the control group. Immunohistochemical and histochemical double staining were ued to detect the different blood supply patterns. The amounts of epithelial cell kinase (EphA2), phosphatidylinositol-3-kinase (PI3K), and matrixmetalloproteinase-2 and -9 (MMP-2, MMP-9) proteins expressed in the tumor tissue were analyzed using immunohistochemical staining; mRNA levels were measured using real-time PCR analysis. Results indicate that the tumor volume is reduced (P=0.000) and that the numbers of VM (P=0.000), mosaic vessels (P=0.031), and endothelium-dependent vessels (P=0.000) are significantly decreased by curcumin (P=0.001). The expression levels of EphA2, PI3K, MMP-2, and -9 are also lower in the treatment group than in the control group (P=0.001); similarly, mRNA levels in the treatment group are lower than those in the control group (P=0.000). In conclusion, curcumin has the ability to inhibit the growth of engrafted melanoma VM channels through the regulation of vasculogenic factors that could be related to the down-regulation of the EphA2/PI3K/MMPs signaling pathway. Thus, curcumin has the potential of being a clinical inhibitor of VM of choroidal melanoma.See commentary: Curcumin: A component of the golden spice, targets multiple angiogenic pathways

Nodal as a biomarker for melanoma progression and a new therapeutic target for clinical intervention

Nodal, an embryonic morphogen belonging to the TGF-β superfamily, is an important regulator of embryonic stem cell fate. We have recently demonstrated that Nodal is expressed significantly in aggressive melanoma. Surprisingly, expression of the Nodal coreceptor, Cripto-1, was detected in only a small fraction of the melanoma tumor cell population, indicating a primary role for Cripto-1-independent signaling of Nodal in melanoma. In this review, we discuss how regulatory factors present in an embryonic environment, such as Lefty, can downregulate Nodal expression and inhibit tumorigenicity and plasticity of melanoma cells. Our translational studies show that antibodies against Nodal are capable of repressing melanoma vasculogenic mimicry and of inducing apoptosis in melanoma tumors in an in vivo lung-colonization assay. Our previous work and ongoing studies suggest that Nodal may represent a novel diagnostic marker and therapeutic target in melanoma.

Molecular regulation of vasculogenic mimicry in human uveal melanoma cells: role of helix–loop–helix Id2 (inhibitor of DNA binding 2)

Vasculogenic mimicry (VM) is a tumor angiogenesis process in which highly aggressive melanoma cells form patterned, tubular networks in an in vitro, three-dimensional culture that mimics vasculogenic networks formed by endothelial cells. These cells also express endothelial cell-associated genes such as vascular endothelial-cadherin (VE-cadherin) and are correlated with poor clinical prognosis in patients. However, the molecular underpinnings of this phenomenon remain elusive. Three-dimensional cultures of highly and poorly aggressive uveal melanoma cells were observed by inverted light microscope and scanning electronic microscope for VM. RNAi (RNA interference) technology was used to examine whether inhibitor of DNA binding 2 (Id2) was involved in the uveal melanoma vasculogenic mimicry. Western blot analysis showed changes of Id2 and VE-cadherin expression in highly and poorly aggressive melanoma cells in vitro. Migration analysis of highly and poorly aggressive uveal melanoma cells in vitro illuminated the role of Id2 in tumor cells migration. We show here that a transient knockdown of Id2 by RNA interference abrogates VM and VE-cadherin expression in highly aggressive uveal melanoma cells. Furthermore, inhibition of Id2 changes cellular stability and creates a more dynamic condition. Transfected cells also migrate better than untransfected cells. This study shows that Id2 is an important regulator of VM. Specifically, Id2 affects VE-cadherin expression, and is critical for the formation of vasculogenic-like networks.

Melanoma vasculogenic mimicry is strongly related to reactive oxygen species level

The concept of 'vasculogenic mimicry' (VM) was introduced to describe the unique ability of highly invasive tumor cells to form capillary-like structures (CLS) and matrix-rich patterned network in three-dimensional culture that mimic embryonic vasculogenic network. Recently, we have shown that CLS formation requires apoptotic cell death through activation of caspase-3-dependent mechanism. In this study, to identify some molecular determinants driving aggressive melanoma cells to express a latent 'angiogenic program' that recapitulates the early events of CLS formation, we focused on the involvement of antioxidants (AOs) in the process of melanoma VM. We have studied the effects of resveratrol, (-)-epigallocathechin gallate, N-acetyl-cysteine (NAC) and Trolox on the ability of melanoma cells to form/destroy CLS. We observed that the formation of CLS was strongly related to reactive oxygen species level. In vivo animal experiments confirmed the involvement of reactive oxygen species level in melanoma VM. To understand the molecular mechanisms of this phenomenon, we specifically looked for induction of apoptosis and vascular endothelial growth factor (VEGF) release. Western blot analysis revealed that the level of VEGF, VEGF receptors (VEGF-Rs) and active caspase-3 dramatically decreased in cells treated with AOs. Here, we also report further experiments designed to determine whether the crosstalk between AOs and apoptosis exists in melanoma VM.

Deciphering the signaling events that promote melanoma tumor cell vasculogenic mimicry and their link to embryonic vasculogenesis: Role of the Eph receptors

During embryogenesis, the primordial microcirculation is formed through a process known as vasculogenesis. The term "vasculogenic mimicry" has been used to describe the manner in which highly aggressive, but not poorly aggressive melanoma tumor cells express endothelial and epithelial markers and form vasculogenic-like networks similar to embryonic vasculogenesis. Vasculogenic mimicry is one example of the remarkable plasticity demonstrated by aggressive melanoma cells and suggests that these cells have acquired an embryonic-like phenotype. Since the initial discovery of tumor cell vasculogenic mimicry by our laboratory, we have been focusing on understanding the molecular mechanisms that regulate this process. This review will highlight recent findings identifying key signal transduction events that regulate melanoma vasculogenic mimicry and their similarity to the signal transduction events responsible for promoting embryonic vasculogenesis and angiogenesis. Specifically, this review will focus on the role of the Eph receptors and ligands in embryonic vasculogenesis, angiogenesis, and vasculogenic mimicry.

The involvement of apoptosis in melanoma vasculogenic mimicry

During development, the formation and remodeling of the primary vascular network occurs by vasculogenesis and angiogenesis. In 1999, the concept of vasculogenic mimicry was introduced to describe the unique ability of highly aggressive tumor cells to form a capillary-like structure and a matrix-rich patterned network in three-dimensional culture that mimic the embryonic vasculogenic network. In this study, we examined the ability of melanoma cells derived from patients with disseminated melanoma to engage in vasculogenic mimicry in order to identify key parameters in the complexity of the formation of capillary-like structure. We showed that disseminated melanoma as well as uveal and cutaneous melanoma adopts a vascular-related phenotype and engages in vasculogenic mimicry: the main geometrical features of capillary-like structure are determined during the first step of the vascular network assembly. We provided experimental evidence that capillary-like structure formation requires apoptotic cell death through activation of a caspase-dependent mechanism: a broad range caspase inhibitor zVAD-fmk and a caspase-3 inhibitor DEVD blocked capillary-like structure formation. Apoptosis occurs before capillary-like structure formation but not after capillary-like structures have assembled. These observations may provide a better understanding of the mechanisms involved in melanoma vasculogenic mimicry.

VE-cadherin regulates EphA2 in aggressive melanoma cells through a novel signaling pathway: Implications for vasculogenic mimicry

The formation of matrix-rich, vasculogenic-like networks, termed vasculogenic mimicry (VM), is a unique process characteristic of highly aggressive melanoma cells found to express genes previously thought to be exclusively associated with endothelial and epithelial cells. This study contributes new observations demonstrating that VE-cadherin can regulate the expression of EphA2 at the cell membrane by mediating its ability to become phosphorylated through interactions with its membrane bound ligand, ephrin-A1. VE-cadherin and EphA2 were also found to be co-localized in cell-cell adhesion junctions, both in vitro and in vivo. Immunoprecipitation studies revealed that EphA2 and VE-cadherin could interact, directly and/or indirectly, during VM. Furthermore, there was no change in the co-localization of EphA2 and VE-cadherin at cell-cell adhesion sites when EphA2 was phosphorylated on tyrosine residues. Although transient knockout of EphA2 expression did not alter VE-cadherin localization, transient knockout of VE-cadherin expression resulted in the reorganization of EphA2 on the cells’ surface, an accumulation of EphA2 in the cytoplasm, and subsequent dephosphorylation of EphA2. Collectively, these results suggest that VE-cadherin and EphA2 act in a coordinated manner as a key regulatory element in the process of melanoma VM and illuminate a novel signaling pathway that could be potentially exploited for therapeutic intervention.

149 Inhibition of vasculogenic mimicry in melanoma by the antivascular drug 5,6-dimethylxanthenone-4-acetic acid (DMXAA)

149 Inhibition of vasculogenic mimicry in melanoma by the antivascular drug 5,6-dimethylxanthenone-4-acetic acid (DMXAA)