A switch in the expression of embryonic EMT-inducers drives the development of malignant melanoma

SMAD signaling promotes melanoma metastasis independently of phenotype switching

The development of metastatic melanoma is thought to require the dynamic shifting of neoplastic cells between proliferative and invasive phenotypes. Contrary to this conventional "phenotype switching" model, we now show that disease progression can involve malignant melanoma cells simultaneously displaying proliferative and invasive properties. Using a genetic mouse model of melanoma in combination with in vitro analyses of melanoma cell lines, we found that conditional deletion of the downstream signaling molecule Smad4, which abrogates all canonical TGF-β signaling, indeed inhibits both tumor growth and metastasis. Conditional deletion of the inhibitory signaling factor Smad7, however, generated cells that are both highly invasive and proliferative, indicating that invasiveness is compatible with a high proliferation rate. In fact, conditional Smad7 deletion led to sustained melanoma growth and at the same time promoted massive metastasis formation, a result consistent with data indicating that low SMAD7 levels in patient tumors are associated with a poor survival. Our findings reveal that modulation of SMAD7 levels can overcome the need for phenotype switching during tumor progression and may thus represent a novel therapeutic target in metastatic disease.

Epithelial Mesenchymal Transition in Tumor Metastasis

Metastasis is the major cause of cancer-related deaths; therefore, the prevention and treatment of metastasis are fundamental to improving clinical outcomes. Epithelial mesenchymal transition (EMT), an evolutionarily conserved developmental program, has been implicated in carcinogenesis and confers metastatic properties upon cancer cells by enhancing mobility, invasion, and resistance to apoptotic stimuli. Furthermore, EMT-derived tumor cells acquire stem cell properties and exhibit marked therapeutic resistance. Given these attributes, the complex biological process of EMT has been heralded as a key hallmark of carcinogenesis, and targeting EMT pathways constitutes an attractive strategy for cancer treatment. However, demonstrating the necessity of EMT for metastasis in vivo has been technically challenging, and recent efforts to demonstrate a functional contribution of EMT to metastasis have yielded unexpected results. Therefore, determining the functional role of EMT in metastasis remains an area of active investigation. Studies using improved lineage tracing systems, dynamic in vivo imaging, and clinically relevant in vivo models have the potential to uncover the direct link between EMT and metastasis. This review focuses primarily on recent advances in and emerging concepts of the biology of EMT in metastasis in vivo and discusses future directions in the context of novel diagnostic and therapeutic opportunities.

Preclinical pharmacodynamic evaluation of a new Src/FOSL1 inhibitor, LY-1816, in pancreatic ductal adenocarcinoma

Despite tremendous efforts, the clinical prognosis of pancreatic ductal adenocarcinoma (PDAC) remains disappointing. There is an urgent need to develop more effective treatment strategies to improve the prognosis of patients with PDAC. In this study, we evaluate the anti‐PDAC effects of LY‐1816, a new multikinase inhibitor developed by us. In in vitro assays, LY‐1816 showed significant inhibitory effects on the proliferation, migration, and invasion of human PDAC cells, and induced PDAC cell apoptosis. Western blot analysis revealed that LY‐1816 markedly suppressed the Src signaling, and downregulated the expression of FOSL1; FOSL1 is an oncogene vulnerability in KRAS‐driven pancreatic cancer. In in vivo models of PDAC xenografts (Aspc‐1 and Bxpc‐3), LY‐1816 showed more potent antitumor activity than dasatinib and gemcitabine. Moreover, mice treated with LY‐1816 showed a much more significant survival advantage in a metastatic model of PDAC compared with those treated with vehicle, dasatinib, or gemcitabine. These results provide effective support for the subsequent clinical evaluation of LY‐1816 in the treatment of PDAC.

Get with the Program! Stemness and Reprogramming in Melanoma Metastasis

Cancer cells are highly plastic and adopt multiple phenotypic states that contribute to tumor progression. Heppt et al. demonstrate that the homeodomain transcription factor Msh homeobox 1 reprograms melanoma cells to a precursor state associated with melanoma progression and increased liver metastasis. Identification of this new role for Msh homeobox 1 may facilitate the development of new therapies that limit melanoma dissemination.

The tumor suppressor BAP1 cooperates with BRAFV600E to promote tumor formation in cutaneous melanoma

The deubiquitinating enzyme BAP1 is mutated in a hereditary cancer syndrome with a high risk of mesothelioma and melanocytic tumors. Here, we show that Bap1 deletion in melanocytes cooperates with the constitutively active, oncogenic form of BRAF (BRAFV600E ) and UV to cause melanoma in mice, albeit at very low frequency. In addition, Bap1-null melanoma cells derived from mouse tumors are more aggressive and colonize and grow at distant sites more than their wild-type counterparts. Molecularly, Bap1-null melanoma cell lines have increased DNA damage measured by γH2aX and hyperubiquitination of histone H2a. Therapeutically, these Bap1-null tumors are completely responsive to BRAF- and MEK-targeted therapies. Therefore, BAP1 functions as a tumor suppressor and limits tumor progression in melanoma.

The effect of Helicobacter pylori on the expression of FRA-1 in gastric epithelial cells and its mechanism

Gastric cancer is a major global health threat and is often related with Helicobacter pylori (H. pylori) infection. FRA-1 is a subunit of the activator protein-1 transcription factor complex, which played a central role in cell proliferation and migration. It has also been implicated in stomach inflammation and malignancy. The present study aimed to clarify the relationship between H. pylori infection and production of FRA-1 in controlling cell proliferation and migration and its molecular mechanisms. Cell proliferation was measured by colony formation assay. Cell migration was monitored by transwell migration assay. Gastric mucosal epithelial cells were treated with FRA-1-specific siRNA with or without H. pylori infection in vitro, and RNA and proteins were extracted. The expression of FRA-1 and indicators in cells was determined by RT-PCR and western blot analysis. β-Catenin and TGF-β activities were then assessed by western blotting and immunofluorescence. The expression of FRA-1 increased after H. pylori infection. Additional analysis identified that knockdown of FRA-1 attenuated the H. pylori-induced proliferative activity and migration of gastric cancer cells. Furthermore, upregulation of FRA-1 by H. pylori led to increase in Wnt/β-Catenin levels and TGF-β dependent signaling events. These results demonstrate that the upregulation of FRA-1 in H. pylori-infected gastric epithelial cells plays a key role in the carcinogenic process.

Tripartite motif-containing 14 (TRIM14) promotes epithelial-mesenchymal transition via ZEB2 in glioblastoma cells

BACKGROUND

Several members of the tripartite motif-containing (TRIM) protein family have been reported to serve as vital regulators of tumorigenesis. Recent studies have demonstrated an oncogenic role of TRIM 14 in multiple human cancers; however, the importance of this protein in glioblastoma remains to be elucidated.

METHODS

The expression levels of TRIM14 were analyzed in a series of database and were examined in a variety of glioblastoma cell lines. Two independent TRIM14 shRNA were transfected into LN229 and U251 cells, and the effect of TRIM14 depletion was confirmed. Transwell assay and wound healing assay assay were carried out to assess the effect of TRIM14 depletion on glioblastoma cell invasion and migration. Western blotting was performed to screen the downstream gene of TRIM14. The stability analysis and Ubiquitylation assays and Orthotopic xenograft studies were also performed to investigate the role of TRIM14 and the relationship with downstream gene. Human glioblastoma tissues were obtained and immunohistochemical staining were carried out to confirm the clinical significance of TRIM14.

RESULTS

In this study, we showed that TRIM14 was upregulated in human glioblastoma specimens and cell lines, and correlated with glioblastoma progression and shorter patient survival times. Functional experiments showed that decreased TRIM14 expression reduced glioblastoma cell invasion and migration. Furthermore, we identified that zinc finger E-box binding homeobox 2 (ZEB2), a transcription factor involved in epithelial-mesenchymal transition, is a downstream target of TRIM14. Further investigation revealed that TRIM14 inactivation significantly facilitated ZEB2 ubiquitination and proteasomal degradation, which led to aggressive invasion and migration. Our findings provide insight into the specific biological role of TRIM14 in tumor invasion.

CONCLUSIONS

Our findings provide insight into the specific biological role of TRIM14 in tumor invasion, and suggest that targeting the TRIM14/ZEB2 axis might be a novel therapeutic approach for blocking glioblastoma.

ERK2 regulates epithelial-to-mesenchymal plasticity through DOCK10-dependent Rac1/FoxO1 activation

ERK is a key coordinator of the epithelial-to-mesenchymal transition (EMT) in that a variety of EMT-inducing factors activate signaling pathways that converge on ERK to regulate EMT transcription programs. However, the mechanisms by which ERK controls the EMT program are not well understood. Through an analysis of the global changes of gene expression mediated by ERK2, we identified the transcription factor FoxO1 as a potential mediator of ERK2-induced EMT, and thus we investigated the mechanism by which ERK2 regulates FoxO1. Additionally, our analysis revealed that ERK2 induced the expression of Dock10, a Rac1/Cdc42 GEF, during EMT. We demonstrate that the activation of the Rac1/JNK signaling axis downstream of Dock10 leads to an increase in FoxO1 expression and EMT. Taken together, our study uncovers mechanisms by which epithelial cells acquire less proliferative but more migratory mesenchymal properties and reveals potential therapeutic targets for cancers evolving into a metastatic disease state.

WNT1-inducible signaling pathway protein 1 (WISP1/CCN4) stimulates melanoma invasion and metastasis by promoting the epithelial-mesenchymal transition

Besides intrinsic changes, malignant cells also release soluble signals that reshape their microenvironment. Among these signals is WNT1-inducible signaling pathway protein 1 (WISP1), a secreted matricellular protein whose expression is elevated in several cancers, including melanoma, and is associated with reduced survival of patients diagnosed with primary melanoma. Here, we found that WISP1 knockout increases cell proliferation and represses wound healing, migration, and invasion of mouse and human melanoma cells in multiple in vitro assays. Metastasis assays revealed that WISP1 knockout represses tumor metastasis of B16F10 and YUMM1.7 melanoma cells in both C57BL/6Ncrl and NOD-scid IL2Rγ^null (NSG) mice. WT B16F10 cells having an invasion phenotype in a transwell assay possessed a gene expression signature similar to that observed in the epithelial-mesenchymal transition (EMT), including E-cadherin repression and fibronectin and N-cadherin induction. Upon WISP1 knockout, expression of these EMT signature genes went in the opposite direction in both mouse and human cell lines, and EMT-associated gene expression was restored upon exposure to media containing WISP1 or to recombinant WISP1 protein. In vivo, Wisp1 knockout-associated metastasis repression was reversed by the reintroduction of either WISP1 or snail family transcriptional repressor 1 (SNAI1). Experiments testing EMT gene activation and inhibition with recombinant WISP1 or kinase inhibitors in B16F10 and YUMM1.7 cells suggested that WISP1 activates AKT Ser/Thr kinase and that MEK/ERK signaling pathways shift melanoma cells from proliferation to invasion. Our results indicate that WISP1 present within the tumor microenvironment stimulates melanoma invasion and metastasis by promoting an EMT-like process.

Autophagy, cancer stem cells and drug resistance

Autophagy is a cellular survival mechanism that is induced by cancer therapy, among other stresses, and frequently contributes to cancer cell survival during long periods of dormancy and the eventual outgrowth of metastatic disease. Autophagy degrades large cellular structures that, once broken down, contribute to cellular survival through the recycling of their constituent metabolites. However, the extent to which this fuel function of autophagy is key to its role in promoting stemness, dormancy and drug resistance remains to be determined. Other roles for autophagy in determining cell fate more directly through targeted degradation of key transcription factors, such as p53 and FoxO3A, or by enforcing a reversible quiescent growth arrest, are discussed in this review. This review also highlights the need to parse out the roles of different forms of selective autophagy in stemness, CD44 expression and dormancy that, for example, are increasingly being attributed explicitly to mitophagy. The clinical relevance of this work and how an increased understanding of functions of autophagy in stemness, dormancy and drug resistance could be manipulated for increased therapeutic benefit, including eliminating minimal residual disease and preventing metastasis, are discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

An actionable axis linking NFATc2 to EZH2 controls the EMT-like program of melanoma cells

Discovery of new actionable targets and functional networks in melanoma is an urgent need as only a fraction of metastatic patients achieves durable clinical benefit by targeted therapy or immunotherapy approaches. Here we show that NFATc2 expression is associated with an EMT-like transcriptional program and with an invasive melanoma phenotype, as shown by analysis of melanoma cell lines at the mRNA and protein levels, interrogation of the TCGA melanoma dataset and characterization of melanoma lesions by immunohistochemistry. Gene silencing or pharmacological inhibition of NFATc2 downregulated EMT-related genes and AXL, and suppressed c-Myc, FOXM1, and EZH2. Targeting of c-Myc suppressed FOXM1 and EZH2, while targeting of FOXM1 suppressed EZH2. Inhibition of c-Myc, or FOXM1, or EZH2 downregulated EMT-related gene expression, upregulated MITF and suppressed migratory and invasive activity of neoplastic cells. Stable silencing of NFATc2 impaired melanoma cell proliferation in vitro and tumor growth in vivo in SCID mice. In NFATc2⁺ EZH2⁺ melanoma cell lines pharmacological co-targeting of NFATc2 and EZH2 exerted strong anti-proliferative and pro-apoptotic activity, irrespective of BRAF or NRAS mutations and of BRAF inhibitor resistance. These results provide preclinical evidence for a role of NFATc2 in shaping the EMT-like melanoma phenotype and reveal a targetable vulnerability associated with NFATc2 and EZH2 expression in melanoma cells belonging to different mutational subsets.

Cirsiliol Suppressed Epithelial to Mesenchymal Transition in B16F10 Malignant Melanoma Cells through Alteration of the PI3K/Akt/NF-κB Signaling Pathway

Malignant melanoma is a highly aggressive form of skin cancer which has a propensity for metastasis. Epithelial mesenchymal transition (EMT) plays a primordial role in the progression of metastatic disease. Metastatic melanoma is resistant to conventional therapies. Hence, researchers have been exploring alternative approaches, including the utility of bioactive phytochemicals to manage metastatic disease. In the present study, we investigated the potential of cirsiliol, a flavonoid isolated from Centaurea jacea L., in modulating the aggressive behavior of B16F10 metastatic melanoma cells, including EMT, and associated molecular mechanisms of action. Cirsiliol was found to be effective in restraining the colony formation and migration of fibronectin-induced B16F10 metastatic melanoma cells. Cirsiliol inhibited the activity and expression of matrix metalloproteinase-9 (MMP-9). Cirsiliol also suppressed the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (also known as Akt)/nuclear factor-κB (NF-κB) signaling pathway which, in turn, caused upregulation of E-cadherin and downregulation of N-cadherin, Snail and Twist. Based on these results, cirsiliol may be considered a promising compound against EMT in the therapeutic management of malignant melanoma.

Non-redundant functions of EMT transcription factors

Epithelial-mesenchymal transition (EMT) is a crucial embryonic programme that is executed by various EMT transcription factors (EMT-TFs) and is aberrantly activated in cancer and other diseases. However, the causal role of EMT and EMT-TFs in different disease processes, especially cancer and metastasis, continues to be debated. In this Review, we identify and describe specific, non-redundant functions of the different EMT-TFs and discuss the reasons that may underlie disputes about EMT in cancer.

The Curious Case of ZEB1

The Zinc Finger E-box binding homeobox (ZEB1/TCF8 or DeltaEF1) is at the forefront of transcription factors involved in controlling epithelial-to-mesenchymal transitions (EMT). Essentially, EMT allows for the reorganization of epithelial cells to become migratory cells with a mesenchymal phenotype.  In addition to ZEB1 being involved in embryonic development, ZEB1 has also been linked to processes involving micro-RNAs, long non-coding RNAs and stem cells. In recent years there has been an accumulation of evidence with regard to ZEB1 in various cancers. Although increased ZEB1 expression has largely been associated with EMT, cancer invasion, and tumorigenicity, there have been some episodic reports that have gone against the traditional reporting of the role of ZEB1. Indicating that the function of ZEB1 and the mechanisms by which ZEB1 facilitates its activities is more complex than was once appreciated. This complexity is further exacerbated by the notion that ZEB1 can act not only as a transcriptional repressor but a transcriptional activator as well. This review seeks to shed light on the complexity of ZEB1 with respect to cancer.

Transforming of the Tumor Microenvironment: Implications for TGF-β Inhibition in the Context of Immune-Checkpoint Therapy

Significant breakthroughs have been achieved in the fields of oncogenic signaling inhibition and particularly immune-checkpoint blockade has triggered substantial enthusiasm during the last decade. Antibody-mediated blockade of negative immune-checkpoint molecules (e.g., PD-1/PD-L1, CTLA-4) has been shown to achieve profound responses in several of solid cancers. Unfortunately, these responses only occur in a subset of patients or, after initial therapy response, these tumors eventually relapse. Thus, elucidating the determinants of intrinsic or therapy-induced resistance is the key to improve outcomes and developing new treatment strategies. Several cytokines and growth factors are involved in the tight regulation of either antitumor immunity or immunosuppressive tumor-promoting inflammation within the tumor microenvironment (TME), of which transforming growth factor beta (TGF-β) is of particular importance. This review will therefore summarize the recent progress that has been made in the understanding of how TGF-β blockade may have the capacity to enhance efficacy of immune-checkpoint therapy which presents a rational strategy to sustain the antitumor inflammatory response to improve response rates in tumor patients. Finally, I will conclude with a comprehensive summary of clinical trials in which TGF-β blockade revealed therapeutic benefit for patients by counteracting tumor relapses.

The convergent roles of CD271/p75 in neural crest-derived melanoma plasticity

The embryonic microenvironment is an important source of signals that promote multipotent cells to adopt a specific fate and direct cells along distinct migratory pathways. Yet, the ability of the embryonic microenvironment to retain multipotent progenitors or reprogram de-differentiated cells is less clear. Mistakes in cell differentiation or migration often result in developmental defects and tumorigenesis, including aggressive cancers that share many characteristics with embryonic progenitor cells. This is a striking feature of the vertebrate neural crest, a multipotent and highly migratory cell population first identified by His (1868) with the potential to metamorphose into aggressive melanoma cancer. In this perspective, we address the roles of CD271/p75 in tumor initiation, phenotype switching and reprogramming of metastatic melanoma and discuss the convergence of these roles in melanoma plasticity.

Invasiveness-triggered state transition in malignant melanoma cells

Cancer cells are considered to have high morphological heterogeneity in human melanoma tissue. Here, we report that epithelial cancer cells are dominant in different development stages of human melanoma tissues. The cellular and molecular mechanisms that maintain melanoma cells in the epithelial state are further investigated in the A2058 cell line. We find that micropore (8 µm) transwell invasion, but not superficial migration in the scratch assay, can induce remarkable morphological changes between epithelial and mesenchymal melanoma cells within 4 days. The morphological switch is associated with dynamic changes of epithelial-mesenchymal transition (EMT) hallmarks E-cadherin and vimentin. Further immunoflurencent staining and co-immunoprecipitation assay showed the uncoupling of the M3 muscarinic acetylcholine receptor (mAChR) and the p75 neurotrophin receptor (p75NTR) in epithelial melanoma cells. Specific knockdown of M3 mAChR by small interfering RNA (siRNA) significantly abrogates the transition of spindle-shaped mesenchymal cells to epithelial cells. Collectively, we report a cellular model of invasiveness-triggered state transition (ITST) in which melanoma cell invasion can induce morphological changes between epithelial and mesenchymal cells. ITST is one of the biological basis for maintaining metastatic melanoma cells in the epithelial state. Furthermore, M3 mAChR receptor-mediated ITST provides a novel therapeutic strategy to inhibit the development of malignant melanoma.

DNp73-induced degradation of tyrosinase links depigmentation with EMT-driven melanoma progression

Melanoma is an aggressive cancer with poor prognosis, requiring personalized management of advanced stages and establishment of molecular markers. Melanomas derive from melanocytes, which specifically express tyrosinase, the rate-limiting enzyme of melanin-synthesis. We demonstrate that melanomas with high levels of DNp73, a cancer-specific variant of the p53 family member p73 and driver of melanoma progression show, in contrast to their less-aggressive low-DNp73 counterparts, hypopigmentation in vivo. Mechanistically, reduced melanin-synthesis is mediated by a DNp73-activated IGF1R/PI3K/AKT axis leading to tyrosinase ER-arrest and proteasomal degradation. Tyrosinase loss triggers reactivation of the EMT signaling cascade, a mesenchymal-like cell phenotype and increased invasiveness. DNp73-induced depigmentation, Slug increase and changes in cell motility are recapitulated in neural crest-derived melanophores of Xenopus embryos, underscoring a previously unnoticed physiological role of tyrosinase as EMT inhibitor. This data provides a mechanism of hypopigmentation accompanying cancer progression, which can be exploited in precision diagnosis of patients with melanoma-associated hypopigmentation (MAH), currently seen as a favorable prognostic factor. The DNp73/IGF1R/Slug signature in colorless lesions might aid to clinically discriminate between patients with MAH-associated metastatic disease and those, where MAH is indeed a sign of regression.

EMT: A mechanism for escape from EGFR-targeted therapy in lung cancer

Epithelial mesenchymal transition (EMT) is a reversible developmental genetic programme of transdifferentiation of polarised epithelial cells to mesenchymal cells. In cancer, EMT is an important factor of tumour cell plasticity and has received increasing attention for its role in the resistance to conventional and targeted therapies. In this paper we provide an overview of EMT in human malignancies, and discuss contribution of EMT to the development of the resistance to Epidermal Growth Factor Receptor (EGFR)-targeted therapies in non-small cell lung cancer (NSCLC). Patients with the tumours bearing specific mutations in EGFR have a good clinical response to selective EGFR inhibitors, but the resistance inevitably develops. Several mechanisms responsible for the resistance include secondary mutations in the EGFR gene, genetic or non-mutational activation of alternative survival pathways, transdifferentiation of NSCLC to the small cell lung cancer histotype, or formation of resistant tumours with mesenchymal characteristics. Mechanistically, application of an EGFR inhibitor does not kill all cancer cells; some cells survive the exposure to a drug, and undergo genetic evolution towards resistance. Here, we present a theory that these quiescent or slow-proliferating drug-tolerant cell populations, or so-called "persisters", are generated via EMT pathways. We review the EMT-activated mechanisms of cell survival in NSCLC, which include activation of ABC transporters and EMT-associated receptor tyrosine kinase AXL, immune evasion, and epigenetic reprogramming. We propose that therapeutic inhibition of these pathways would eliminate pools of persister cells and prevent or delay cancer recurrence when applied in combination with the agents targeting EGFR.

Assessment of Nuclear ZEB2 as a Biomarker for Colorectal Cancer Outcome and TNM Risk Stratification

IMPORTANCE

At present, patients with colorectal cancer (CRC) are risk stratified using TNM histologic features. More recently, an association between a mesenchymal phenotype and a high risk of disease recurrence and micrometastases has been recognized.

OBJECTIVE

To investigate the association of the epithelial to mesenchymal transition (EMT)-inducing transcription factor ZEB2 (zinc finger E box-binding homeobox 2), survival outcomes, and the efficacy of ZEB2 as a biomarker when added as refinement to TNM staging after curative intent surgery for CRC.

DESIGN, SETTING, AND PARTICIPANTS

ZEB2 expression was assessed using a previously validated scoring system as part of a prospective, observational, masked diagnostic study from January 1, 2008, to December 31, 2013. Data were prospectively collected and analyzed for association with oncologic outcomes from January 1, 2017, to December 31, 2018. An initial test cohort from an academic university medical center of 126 consecutive patients with CRC and, subsequently, an independent validation cohort of 210 patients were examined. ZEB2 positivity was scored by 2 independent, masked pathologists. External validity was tested using an open access gene expression portal. Nomograms were developed with or without ZEB2.

MAIN OUTCOMES AND MEASURES

Systemic and local recurrence of CRC.

RESULTS

The test cohort consisted of 126 consecutive patients (mean [SD] age, 72.7 [11.7] years; 61 [48.4%] male) and the validation cohort of 210 patients (mean [SD] age, 72.0 [10.6] years; 111 [52.9%] male). A total of 52 tumors (41.3%) in the test cohort and 104 (49.5%) in the validation cohort were scored nuclear ZEB2 positive. Survival analysis by the log-rank test found that ZEB2 expression was associated with a significant reduction in overall survival and disease-free survival in both cohorts. Cox proportional hazards regression analysis highlighted ZEB2 as an independent biomarker of shorter overall survival and disease-free survival. Analysis of node-negative disease (n = 222) identified ZEB2 as an independent biomarker of early recurrence and reduced survival. External validation confirmed these findings. Addition of ZEB2 expression to nomograms composed of conventional TNM risk factors improved the ability to identify patients at high risk of recurrence demonstrated by the improvement in concordance index in both test (0.73 to 0.77) and validation (0.82 to 0.87) cohorts.

CONCLUSIONS AND RELEVANCE

The findings suggest that expression of ZEB2 is associated with poor oncologic outcome and distant recurrence. The study also found that the addition of ZEB2 to existing TNM classification improved the ability to stratify patients for risk of recurrence. The results of this study suggest that addition of ZEB2 expression status to the TNM staging system improves the ability to stratify patients at high risk of recurrence.

EnABLing Tumor Growth and Progression: Recent progress in unraveling the functions of ABL kinases in solid tumor cells

PURPOSE OF REVIEW

The goal of this review is to summarize our current knowledge regarding how ABL family kinases are activated in solid tumors and impact on solid tumor development/progression, with a focus on recent advances in the field.

RECENT FINDINGS

Although ABL kinases are known drivers of human leukemia, emerging data also implicates the kinases in a large number of solid tumor types where they promote diverse processes such as proliferation, survival, cytoskeletal reorganization, cellular polarity, EMT (epithelial-mesenchymal-transition), metabolic reprogramming, migration, invasion and metastasis via unique signaling pathways. ABL1 and ABL2 appear to have overlapping but also unique roles in driving these processes. In some tumor types, the kinases may act to integrate pro- and anti-proliferative and -invasive signals, and also may serve as a switch during EMT/MET (mesenchymal-epithelial) transitions.

CONCLUSIONS

Most data indicate that targeting ABL kinases may be effective for reducing tumor growth and preventing metastasis; however, ABL kinases also may have a tumor suppressive role in some tumor types and in some cellular contexts. Understanding the functions of ABL kinases in solid tumors is critical for developing successful clinical trials aimed at targeting ABL kinases for the treatment of solid tumors.

Compromised vitamin D receptor signalling in malignant melanoma is associated with tumour progression and mitogen-activated protein kinase activity

The aims of this study were to investigate, in cutaneous malignant melanoma (MM), the integrity of nuclear vitamin D receptor (VDR) signalling, as implied by VDR subcellular location; to investigate the relationship between VDR and tumour progression and the inhibitory effect on VDR by mitogen-activated protein kinase (MAPK) overactivity. Archived tissue from 34 benign melanocytic naevi, 149 MMs and 44 matched metastases were stained by immunohistochemistry for VDR and a subset of primary MMs were stained for phosphorylated-extracellular signal-regulated kinase as a marker of MAPK activity. MM cell lines were investigated to show the subcellular location of VDR and cell viability in response to ligand±MAPK inhibitor. Benign melanocytic naevi showed mainly a strong nuclear VDR staining in contrast to MM where decreased nuclear and emergent cytoplasmic VDRs were associated with malignant progression in terms of dermal invasion and metastasis. MMs that retained exclusive nuclear VDR at the tumour base did not metastasize, a potentially important prognostic indicator. Decreased nuclear VDR correlated with increased cytoplasmic staining, suggesting the failure of nuclear entry as a primary cause of defective VDR signalling in MM. The histological subset analysis and MM cell line studies confirmed the inhibitory effect of MAPK activity on VDR signalling, but the pattern of VDR subcellular localization suggested failure of VDR nuclear entry as a primary effect of MAPK activity rather than direct inhibition of VDR-regulated transcription. Furthermore, high MAPK activity in tumours expressing cytoplasmic VDR was associated with worsened prognosis.

Loss of neural crest-associated gene FOXD1 impairs melanoma invasion and migration via RAC1B downregulation

Recent studies suggest that malignant melanoma heterogeneity includes subpopulations of cells with features of multipotent neural crest (NC) cells. Zebrafish and mouse models have shown that reactivation of neural crest-specific pathways during transformation determines the invasiveness of melanoma cells. In our study, we show that the neural crest-associated transcription factor FOXD1 plays a key role in the invasion and the migration capacities of metastatic melanomas both in vivo and in vitro. Gene expression profiling analysis identified both an upregulation of FOXD1 in NC and melanoma cells, as well as a downregulation of several genes related to cell invasion in FOXD1 knockdown cells, including MMP9 and RAC1B. Furthermore, we demonstrate that knockdown of RAC1B a tumor-specific isoform of RAC1, significantly impaired melanoma cell migration and invasion and could abrogate enhanced invasiveness induced by FOXD1 overexpression. We conclude that FOXD1 may influence invasion and migration via indirect regulation of MMP9 and RAC1B alternative splicing in melanoma cells.

Lysosomal acid ceramidase ASAH1 controls the transition between invasive and proliferative phenotype in melanoma cells

Phenotypic plasticity and subsequent generation of intratumoral heterogeneity underly key traits in malignant melanoma such as drug resistance and metastasis. Melanoma plasticity promotes a switch between proliferative and invasive phenotypes characterized by different transcriptional programs of which MITF is a critical regulator. Here, we show that the acid ceramidase ASAH1, which controls sphingolipid metabolism, acted as a rheostat of the phenotypic switch in melanoma cells. Low ASAH1 expression was associated with an invasive behavior mediated by activation of the integrin alphavbeta5-FAK signaling cascade. In line with that, human melanoma biopsies revealed heterogeneous staining of ASAH1 and low ASAH1 expression at the melanoma invasive front. We also identified ASAH1 as a new target of MITF, thereby involving MITF in the regulation of sphingolipid metabolism. Together, our findings provide new cues to the mechanisms underlying the phenotypic plasticity of melanoma cells and identify new anti-metastatic targets.

CEACAM1 promotes melanoma metastasis and is involved in the regulation of the EMT associated gene network in melanoma cells

We investigated the functional role of CEACAM1 in a spontaneous metastasis xenograft model of human melanoma in scid mice using BRAF wildtype MeWo cells with and without RNAi mediated knockdown of CEACAM1. Tumors from the xenograft model were subjected to whole genome expression analysis and metastasis was quantified histologically. Results and identified markers were verified using tissue samples of over 100 melanoma patients. Knockdown of CEACAM1 prolonged the animals' survival by significantly reducing subcutaneous growth of MeWo tumors and spontaneous lung metastasis. Microarray analysis revealed a strong influence of CEACAM1 knockdown on the network of EMT associated genes in the xenograft tumors (e.g. downregulation of BRAF, FOSL1, NRAS and TWIST). IGFBP7 and Latexin (highest up- and downregulated expression in microarray analysis) were found to be associated with longer and shorter survival, respectively, of melanoma patients. High FOSL1 and altered TWIST1 expression were found to be correlated with shortened survival in the cohort of melanoma patients. After a stepwise selection procedure combining above markers, multivariate analysis revealed IGFBP7, Latexin and altered TWIST to be prognostic markers for death. CEACAM1 could be a target for melanoma therapy as an alternative to (or in combination with) immune checkpoint and BRAF inhibitors.

Seed targeting with tiny anti-miR-1297 inhibits EMT in melanoma cells

MicroRNAs (miRNAs) are small, noncoding RNAs that have tissue- and cell-specific expression. They have the ability to regulate the malignant proliferation and transformation of tumour cells. The research focussed on the expression and role of miR-1297 in melanoma. We firstly found that miR-1297 is up-regulated in melanoma tissues and cell lines. Functionally, phosphatase and tension homology deleted on chromsome ten gene (PTEN) was used as a potential target for miR-1297 and detected using Western blotting and immunohistochemistry (IHC). We then used chemical synthesis of anti-miR1297 to explore the influence on melanoma cells and examined the effects on A375 cell proliferation using MTT and western blotting methods. The results showed that anti-miR-1297 transfected A375 cells could inhibit the growth. Furthermore, transfection with anti-miR-1297 reduced PTEN protein expression and partially restrained A375 cells proliferation, migration and reversed Epithelial-Mesenchymal Transition (EMT) progression. In conclusion, we tentatively put forward that miR-1297 might be the key oncomiR in melanoma, and seed-targeted anti-miR-1297 might serve as a new tactic for miR-1297-based therapies.

RAC1-GTP promotes epithelial-mesenchymal transition and invasion of colorectal cancer by activation of STAT3

Epithelial-mesenchymal transition (EMT) plays a critical role in initiating tumor invasion and metastasis of colorectal cancer (CRC), although the underlying mechanisms remain to be clarified. Herein, we demonstrate that the active form of Rac family small GTPase 1 (RAC1-GTP) is overexpressed in CRCs and promotes the EMT-mediated invasion of CRC cells through activation of the signal transducers and activators of transcription 3 (STAT3) pathway. Increased expression of RAC1-GTP in CRC tissues was positively correlated with the TNM stages of CRCs and indicated poor prognosis of CRC patients. Targeting RAC1-GTP activity by its specific inhibitor NSC23766 markedly suppressed the migration and invasion of CRC cells. Mechanistically, RAC1-GTP directly interacted with STAT3 to promote STAT3 phosphorylation, thus promoted EMT of CRC cells. Enforced expression of constitutively activated STAT3 (STAT3-C) abrogated the suppressive effect of RAC1-GTP disruption on the migration and invasion of CRC cells. Importantly, NSC23766 disrupted EMT in CRC cells and significantly diminished growth of CRC xenografts. Taken together, our data indicate that RAC1-GTP is an important player in EMT-mediated tumor invasion and a potential therapeutic target for CRCs.

Genome-wide analysis of endogenously expressed ZEB2 binding sites reveals inverse correlations between ZEB2 and GalNAc-transferase GALNT3 in human tumors

BACKGROUND

ZEB2 is a transcriptional repressor that regulates epithelial-to-mesenchymal transition (EMT) through binding to bipartite E-box motifs in gene regulatory regions. Despite the abundant presence of E-boxes within the human genome and the multiplicity of pathophysiological processes regulated during ZEB2-induced EMT, only a small fraction of ZEB2 targets has been identified so far. Hence, we explored genome-wide ZEB2 binding by chromatin immunoprecipitation-sequencing (ChIP-seq) under endogenous ZEB2 expression conditions.

METHODS

For ChIP-Seq we used an anti-ZEB2 monoclonal antibody, clone 6E5, in SNU398 hepatocellular carcinoma cells exhibiting a high endogenous ZEB2 expression. The ChIP-Seq targets were validated using ChIP-qPCR, whereas ZEB2-dependent expression of target genes was assessed by RT-qPCR and Western blotting in shRNA-mediated ZEB2 silenced SNU398 cells and doxycycline-induced ZEB2 overexpressing colorectal carcinoma DLD1 cells. Changes in target gene expression were also assessed using primary human tumor cDNA arrays in conjunction with RT-qPCR. Additional differential expression and correlation analyses were performed using expO and Human Protein Atlas datasets.

RESULTS

Over 500 ChIP-Seq positive genes were annotated, and intervals related to these genes were found to include the ZEB2 binding motif CACCTG according to TOMTOM motif analysis in the MEME Suite database. Assessment of ZEB2-dependent expression of target genes in ZEB2-silenced SNU398 cells and ZEB2-induced DLD1 cells revealed that the GALNT3 gene serves as a ZEB2 target with the highest, but inversely correlated, expression level. Remarkably, GALNT3 also exhibited the highest enrichment in the ChIP-qPCR validation assays. Through the analyses of primary tumor cDNA arrays and expO datasets a significant differential expression and a significant inverse correlation between ZEB2 and GALNT3 expression were detected in most of the tumors. We also explored ZEB2 and GALNT3 protein expression using the Human Protein Atlas dataset and, again, observed an inverse correlation in all analyzed tumor types, except malignant melanoma. In contrast to a generally negative or weak ZEB2 expression, we found that most tumor tissues exhibited a strong or moderate GALNT3 expression.

CONCLUSIONS

Our observation that ZEB2 negatively regulates a GalNAc-transferase (GALNT3) that is involved in O-glycosylation adds another layer of complexity to the role of ZEB2 in cancer progression and metastasis. Proteins glycosylated by GALNT3 may be exploited as novel diagnostics and/or therapeutic targets.

Angiotropism and extravascular migratory metastasis in cutaneous and uveal melanoma progression in a zebrafish model

Cutaneous melanoma is a highly aggressive cancer with a propensity for distant metastasis to various organs. In contrast, melanoma arising in pigmented uveal layers of the eye metastasizes mostly in the liver. The mechanisms of these metastases, which are ultimately resistant to therapy, are still unclear. Metastasis via intravascular dissemination of tumour cells is widely accepted as a central paradigm. However, we have previously described an alternative mode of tumour dissemination, extravascular migratory metastasis, based on clinical and experimental data. This mechanism is characterised by the interaction of cancer cells with the abluminal vascular surface, which defines angiotropism. Here, we employed our 3D co-culture approach to monitor cutaneous and uveal human melanoma cells dynamics in presence of vascular tubules. Using time-lapse microscopy, we evaluated angiotropism, the migration of tumour cells along vascular tubules and the morphological changes occurring during these processes. Cutaneous and uveal melanoma cells were injected in zebrafish embryos in order to develop xenografts. Employing in vivo imaging coupled with 3D reconstruction, we monitored the interactions between cancer cells and the external surface of zebrafish vessels. Overall, our results indicate that cutaneous and uveal melanoma cells spread similarly along the abluminal vascular surfaces, in vitro and in vivo.

Mitotic polarization of transcription factors during asymmetric division establishes fate of forming cancer cells

A model of K-Ras-initiated lung cancer was used to follow the transition of precancerous adenoma to adenocarcinoma. In hypoxic, Tgf-β1-rich interiors of adenomas, we show that adenoma cells divide asymmetrically to produce cancer-generating cells highlighted by epithelial mesenchymal transition and a CD44/Zeb1 loop. In these cells, Zeb1 represses the Smad inhibitor Zeb2/Sip1, causing Pten loss and launching Tgf-β1 signaling that drives nuclear translocation of Yap1. Surprisingly, the nuclear polarization of transcription factors during mitosis establishes parent and daughter fates prior to cytokinesis in sequential asymmetric divisions that generate cancer cells from precancerous lesions. Mutation or knockdown of Zeb1 in the lung blocked the production of CD44^hi, Zeb1^hi cancer-generating cells from adenoma cells. A CD44/Zeb1 loop then initiates two-step transition of precancerous cells to cancer cells via a stable intermediate population of cancer-generating cells. We show these initial cancer-generating cells are independent of cancer stem cells generated in tumors by p53-regulated reprogramming of existing cancer cells.

Transition from premalignant lesion to cancer cell highlights tumor initiation. Here, the authors use a model of K-Ras-initiated lung cancer to document two successive asymmetric divisions, each driven by mitotic polarization of key transcription factors, which lead to generation of initial cancer cells.

FOXP3 and miR-155 cooperate to control the invasive potential of human breast cancer cells by down regulating ZEB2 independently of ZEB1

Control of oncogenes, including ZEB1 and ZEB2, is a major checkpoint for preventing cancer, and loss of this control contributes to many cancers, including breast cancer. Thus tumour suppressors, such as FOXP3, which is mutated or lost in many cancer tissues, play an important role in maintaining normal tissue homeostasis. Here we show for the first time that ZEB2 is selectively down regulated by FOXP3 and also by the FOXP3 induced microRNA, miR-155. Interestingly, neither FOXP3 nor miR-155 directly altered the expression of ZEB1. In breast cancer cells repression of ZEB2, independently of ZEB1, resulted in reduced expression of a mesenchymal marker, Vimentin and reduced invasion. However, there was no de-repression of E-cadherin and migration was enhanced. Small interfering RNAs targeting ZEB2 suggest that this was a direct effect of ZEB2 and not FOXP3/miR-155. In normal human mammary epithelial cells, depletion of endogenous FOXP3 resulted in de-repression of ZEB2, accompanied by upregulated expression of vimentin, increased E-cadherin expression and cell morphological changes. We suggest that FOXP3 may help maintain normal breast epithelial characteristics through regulation of ZEB2, and loss of FOXP3 in breast cancer cells results in deregulation of ZEB2.

Role of miR-23a/Zeb1 negative feedback loop in regulating epithelial-mesenchymal transition and tumorigenicity of intraocular tumors

Role of the two-way negative feedback regulation channel formed by miR-23a and Zeb1 in epithelial-mesenchymal transition (EMT), tumorigenic ability, and migration and metastasis capacity of the intraocular malignant tumor cells was investigated. Molecular biological methods such as real time-quantitative PCR (RT-qPCR), immunoblotting method, and immunofluorescence were used to detect the expression levels of mRNA and protein in the Zeb1 factor in OCM-1, WERI-RB1, and Y79 cells before and after miR-23a transfection. Transwell cells were used to detect the in vitro membrane permeation and migration ability in OCM-1, WERI-RB1, and Y79 cells (non-transfection group, blank control transfection group, mimic transfection group, inhibitor transfection group). The results revealed that the relative expression of miR-23a in the cells in the miR-23a mimic transfection group increased significantly compared with that in the control group (p<0.05). There were significant differences in the relative expression of mRNA between the mimic transfection and control group (p<0.05). RT-qPCR detection showed that the relative expression of mRNA of the epithelial-labeled factor E-cadherin increased significantly in the miR-23a mimics group (p<0.05). Expression of the protein E-cadherin increased while the expression of the mesenchyme-labeled proteins of vimentin and N-cadherin decreased in the mimics group. Zeb1 has a negative feedback effect on miR-23a. They can form a negative feedback loop. The results showed that miR-23a and Zeb1 form a bidirectional inhibitory negative feedback loop, which plays an important role in regulating EMT. In conclusion, the significant changes in the mesenchymal phenotype of the stable strains with Zeb1 overexpressed in the OCM-1 cells cannot be completely explained with the changes in cytoskeleton caused by EMT.

Embryonic bone morphogenetic protein and nodal induce invasion in melanocytes and melanoma cells

Despite recent progress in melanoma therapy via inhibition of activated oncogenes or immune stimulation, most stage IV melanoma patients still have limited survival times. Existing therapeutic approaches eventually fail to prevent further invasion and metastasis, which is driven by a morphological process termed epithelial-mesenchymal transition (EMT). We previously demonstrated that inhibition of EMT in melanoma cells via antagonizing the bone morphogenetic protein (BMP)-pathway abrogated EMT and neural crest migration of melanoma cells in chick embryos. Here, we show that BMP-2 is highly expressed in invasive melanoma cells and is elevated in the serum of stage IV melanoma patients compared to stage IB-IIC patients and healthy controls. Highly BMP-2-expressing melanoma cells display enhanced invasion in the rhombencephalon of the chick embryo. In addition to driving neural crest migration in the zebrafish embryo, the agonists BMP-2, BMP-7 and nodal induce EMT/invasion in radial growth phase melanoma cells and in human melanocytes in skin reconstructs. Blocking either BMP or nodal signaling by antagonists (noggin, lefty), or the Alk4/5/7-receptor inhibitor SB431542, decreases EMT and invasion of melanoma cells in human epidermal skin reconstructs. Together, our data suggest that inhibition of EMT-inducing pathways in melanoma might be a therapeutic approach to attenuate melanoma cell invasiveness.

Summary: We show that bone morphogenetic protein and nodal drive epithelial-mesenchymal transition (EMT) and invasiveness in melanoma cells, induce EMT and a melanoma-like invasive phenotype in melanocytes.

Melanoma Suppressor Functions of the Carcinoma Oncogene FOXQ1

Lineage-specific regulation of tumor progression by the same transcription factor is understudied. We find that levels of the FOXQ1 transcription factor, an oncogene in carcinomas, are decreased during melanoma progression. Moreover, in contrast to carcinomas, FOXQ1 suppresses epithelial-to-mesenchymal transition, invasion, and metastasis in melanoma cells. We find that these lineage-specific functions of FOXQ1 largely depend on its ability to activate (in carcinomas) or repress (in melanoma) transcription of the N-cadherin gene (CDH2). We demonstrate that FOXQ1 interacts with nuclear β-catenin and TLE proteins, and the β-catenin/TLE ratio, which is higher in carcinoma than melanoma cells, determines the effect of FOXQ1 on CDH2 transcription. Accordingly, other FOXQ1-dependent phenotypes can be manipulated by altering nuclear β-catenin or TLE proteins levels. Our data identify FOXQ1 as a melanoma suppressor and establish a mechanism underlying its inverse lineage-specific transcriptional regulation of transformed phenotypes.

Interleukin-like EMT inducer (ILEI) promotes melanoma invasiveness and is transcriptionally up-regulated by upstream stimulatory factor-1 (USF-1)

Interleukin-like EMT inducer (ILEI, FAM3C) is a secreted factor that contributes to the epithelial-to-mesenchymal transition (EMT), a cell-biological process that confers metastatic properties to a tumor cell. However, very little is known about how ILEI is regulated. Here we demonstrate that ILEI is an in vivo regulator of melanoma invasiveness and is transcriptionally up-regulated by the upstream stimulatory factor-1 (USF-1), an E-box-binding, basic-helix-loop-helix family transcription factor. shRNA-mediated knockdown of ILEI in melanoma cell lines attenuated lung colonization but not primary tumor formation. We also identified the mechanism underlying ILEI transcriptional regulation, which was through a direct interaction of USF-1 with the ILEI promoter. Of note, stimulation of endogenous USF-1 by UV-mediated activation increased ILEI expression, whereas shRNA-mediated USF-1 knockdown decreased ILEI gene transcription. Finally, we report that knocking down USF-1 decreases tumor cell migration. In summary, our work reveals that ILEI contributes to melanoma cell invasiveness in vivo without affecting primary tumor growth and is transcriptionally up-regulated by USF-1.

Cutaneous Melanoma-A Long Road from Experimental Models to Clinical Outcome: A Review

Cutaneous melanoma is a complex disorder characterized by an elevated degree of heterogeneity, features that place it among the most aggressive types of cancer. Although significant progress was recorded in both the understanding of melanoma biology and genetics, and in therapeutic approaches, this malignancy still represents a major problem worldwide due to its high incidence and the lack of a curative treatment for advanced stages. This review offers a survey of the most recent information available regarding the melanoma epidemiology, etiology, and genetic profile. Also discussed was the topic of cutaneous melanoma murine models outlining the role of these models in understanding the molecular pathways involved in melanoma initiation, progression, and metastasis.

Multi-stage Differentiation Defines Melanoma Subtypes with Differential Vulnerability to Drug-Induced Iron-Dependent Oxidative Stress

Malignant transformation can result in melanoma cells that resemble different stages of their embryonic development. Our gene expression analysis of human melanoma cell lines and patient tumors revealed that melanoma follows a two-dimensional differentiation trajectory that can be subclassified into four progressive subtypes. This differentiation model is associated with subtype-specific sensitivity to iron-dependent oxidative stress and cell death known as ferroptosis. Receptor tyrosine kinase-mediated resistance to mitogen-activated protein kinase targeted therapies and activation of the inflammatory signaling associated with immune therapy involves transitions along this differentiation trajectory, which lead to increased sensitivity to ferroptosis. Therefore, ferroptosis-inducing drugs present an orthogonal therapeutic approach to target the differentiation plasticity of melanoma cells to increase the efficacy of targeted and immune therapies.

Atg7 inhibits Warburg effect by suppressing PKM2 phosphorylation resulting reduced epithelial-mesenchymal transition

Metabolic reprogramming is a distinct hallmark in tumorigenesis. Autophagy can rewire cell metabolism by regulating intracellular homeostasis. Warburg effect is a specific energy metabolic process that allows tumor cells to metabolize glucose via glycolysis into lactate even in the presence of oxygen. Although both autophagy and Warburg effect are involved in the stress response to energy crisis in tumor cells, their molecular relationship has remained largely elusive. We found that Atg7, a key molecule involved in autophagy, inhibits the Warburg effect. Mechanistically, Atg7 binds PKM2 and prevents its Tyr-105 phosphorylation by FGFR1. Furthermore, the hyperphosphorylation of PKM2 and its induced Warburg effect due to Atg7 deficiency promote epithelial-mesenchymal transition (EMT). Conversely, overexpression of Atg7 inhibits PKM2 phosphorylation and the Warburg effect, thereby inhibiting EMT of tumor cells. Our work reveals a molecular link between Atg7 and the Warburg effect, which may provide insight into novel strategies for cancer treatment.

Ovostatin 2 knockdown significantly inhibits the growth, migration, and tumorigenicity of cutaneous malignant melanoma cells

BACKGROUND

We previously identified ovostatin 2 (OVOS2) as a new candidate gene for cutaneous malignant melanoma (CMM) in a Chinese population. In this study, we aimed to investigate the exact role of OVOS2 in cell proliferation, invasion, and tumorigenesis of melanoma A375 cells.

METHODS

The downregulation of OVOS2 expression was performed using lentiviral vectors with specific shRNA. The effects of OVOS2 expression on cell proliferation, cell cycle, cell migration, cell invasion, and potential of tumorigenesis were further investigated.

RESULTS

The downregulation of OVOS2 significantly suppressed the proliferation of A375 cells and led to a G2/M phase block. The transwell cell migration assay showed that the reduced expression of OVOS2 also significantly inhibited the transmigration of A375 cells. The western blot results showed downregulated expression of p-FAK, p-AKT, and p-ERK. This was accompanied by the upregulated epithelial phenotypes E-cadherin and β-catenin, and downregulated expression of mesenchymal phenotype N-cadherin after OVOS2 knockdown. The transplantation tumor experiment in BALB/C nude mouse showed that after an observation period of 32 days, the growth speed and weight of the transplanted tumors were significantly suppressed in the BALB/c nude mice subcutaneously injected with OVOS2 knocked-down A375 cells.

CONCLUSION

The inhibition of OVOS2 had significant suppressive effects on the proliferation, motility, and migration capabilities of A375 cells, suggesting a crucial promotive role of OVOS2 in the pathogenesis and progression of CMM. The involved mechanisms are at least partly associated with the overactivation of FAK/MAPK/ERK and FAK/PI3K/AKT signals.

Living on the Edge: Diagnosing Sarcomatoid Melanoma Using Histopathologic Cues at the Edge of a Dedifferentiated Tumor: A Report of 2 Cases and Review of the Literature

Sarcomatoid melanoma is a rare type of melanoma lacking typical histologic features of melanoma and often lacks expression of S100 protein and melanocyte-specific markers. Given the rarity of this entity, its clinicopathologic findings are not well defined. We report 2 cases of sarcomatoid melanoma received in consultation: a 65-year-old woman with a right breast mass and a 62-year-old man with a left plantar heel mass. Both lesions were ulcerated, pedunculated, highly cellular proliferations of atypical spindle cells arranged as fascicles and/or sheets. The tumor cells of the breast mass expressed CD10 and vimentin diffusely but S100 protein only focally. The tumor cells of the heel mass lacked expression of melanocytic markers altogether, except for weak, very focal S100 protein expression. At the junctional edge of the breast mass and in the ulcer base of the heel mass, focal precursor melanoma was present and exhibited melanocytic differentiation. We report these cases to emphasize the importance of meticulous histologic inspection at the lesion's edge and/or ulcer base to correctly identify the conventional precursor melanoma in these rare lesions to ensure appropriate diagnosis and subsequent clinical management as treatment options may be significantly different from those offered for sarcomas.

Context-dependent miR-204 and miR-211 affect the biological properties of amelanotic and melanotic melanoma cells

Despite increasing amounts of experimental evidence depicting the involvement of non-coding RNAs in cancer, the study of BRAFV600E-regulated genes has thus far focused mainly on protein-coding ones. Here, we identify and study the microRNAs that BRAFV600E regulates through the ERK pathway.

By performing small RNA sequencing on A375 melanoma cells and a vemurafenib-resistant clone that was taken as negative control, we discover miR-204 and miR-211 as the miRNAs most induced by vemurafenib. We also demonstrate that, although belonging to the same family, these two miRNAs have distinctive features. miR-204 is under the control of STAT3 and its expression is induced in amelanotic melanoma cells, where it acts as an effector of vemurafenib's anti-motility activity by targeting AP1S2. Conversely, miR-211, a known transcriptional target of MITF, is induced in melanotic melanoma cells, where it targets EDEM1 and consequently impairs the degradation of TYROSINASE (TYR) through the ER-associated degradation (ERAD) pathway. In doing so, miR-211 serves as an effector of vemurafenib's pro-pigmentation activity. We also show that such an increase in pigmentation in turn represents an adaptive response that needs to be overcome using appropriate inhibitors in order to increase the efficacy of vemurafenib.

In summary, we unveil the distinct and context-dependent activities exerted by miR-204 family members in melanoma cells. Our work challenges the widely accepted “same miRNA family = same function” rule and provides a rationale for a novel treatment strategy for melanotic melanomas that is based on the combination of ERK pathway inhibitors with pigmentation inhibitors.

Inducibly decreased MITF levels do not affect proliferation and phenotype switching but reduce differentiation of melanoma cells

Melanoma arises from neural crest-derived melanocytes which reside mostly in the skin in an adult organism. Epithelial-mesenchymal transition (EMT) is a tumorigenic programme through which cells acquire mesenchymal, more pro-oncogenic phenotype. The reversible phenotype switching is an event still not completely understood in melanoma. The EMT features and increased invasiveness are associated with lower levels of the pivotal lineage identity maintaining and melanoma-specific transcription factor MITF (microphthalmia-associated transcription factor), whereas increased proliferation is linked to higher MITF levels. However, the precise role of MITF in phenotype switching is still loosely characterized. To exclude the changes occurring upstream of MITF during MITF regulation in vivo, we employed a model whereby MITF expression was inducibly regulated by shRNA in melanoma cell lines. We found that the decrease in MITF caused only moderate attenuation of proliferation of the whole cell line population. Proliferation was decreased in five of 15 isolated clones, in three of them profoundly. Reduction in MITF levels alone did not generally produce EMT-like characteristics. The stem cell marker levels also did not change appreciably, only a sharp increase in SOX2 accompanied MITF down-regulation. Oppositely, the downstream differentiation markers and the MITF transcriptional targets melastatin and tyrosinase were profoundly decreased, as well as the downstream target livin. Surprisingly, after the MITF decline, invasiveness was not appreciably affected, independently of proliferation. The results suggest that low levels of MITF may still maintain relatively high proliferation and might reflect, rather than cause, the EMT-like changes occurring in melanoma.

Pivotal role of NAMPT in the switch of melanoma cells toward an invasive and drug-resistant phenotype

In BRAF^V600E melanoma cells, a global metabolomic analysis discloses a decrease in nicotinamide adenine dinucleotide (NAD⁺) levels upon PLX4032 treatment that is conveyed by a STAT5 inhibition and a transcriptional regulation of the nicotinamide phosphoribosyltransferase (NAMPT) gene. NAMPT inhibition decreases melanoma cell proliferation both in vitro and in vivo, while forced NAMPT expression renders melanoma cells resistant to PLX4032. NAMPT expression induces transcriptomic and epigenetic reshufflings that steer melanoma cells toward an invasive phenotype associated with resistance to targeted therapies and immunotherapies. Therefore, NAMPT, the key enzyme in the NAD⁺ salvage pathway, appears as a rational target in targeted therapy-resistant melanoma cells and a key player in phenotypic plasticity of melanoma cells.

Strengths and Weaknesses of Pre-Clinical Models for Human Melanoma Treatment: Dawn of Dogs' Revolution for Immunotherapy

Despite several therapeutic advances, malignant melanoma still remains a fatal disease for which novel and long-term curative treatments are needed. The successful development of innovative therapies strongly depends on the availability of appropriate pre-clinical models. For this purpose, several mouse models holding the promise to provide insight into molecular biology and clinical behavior of melanoma have been generated. The most relevant ones and their contribution for the advancement of therapeutic approaches for the treatment of human melanoma patients will be here summarized. However, as models, mice do not recapitulate all the features of human melanoma, thus their strengths and weaknesses need to be carefully identified and considered for the translation of the results into the human clinics. In this panorama, the concept of comparative oncology acquires a priceless value. The revolutionary importance of spontaneous canine melanoma as a translational model for the pre-clinical investigation of melanoma progression and treatment will be here discussed, with a special consideration to the development of innovative immunotherapeutic approaches.

Abl and Arg mediate cysteine cathepsin secretion to facilitate melanoma invasion and metastasis

The incidence of melanoma is increasing, particularly in young women, and the disease remains incurable for many because of its aggressive, metastatic nature and its high rate of resistance to conventional, targeted, and immunological agents. Cathepsins are proteases that are critical for melanoma progression and therapeutic resistance. Intracellular cathepsins cleave or degrade proteins that restrict cancer progression, whereas extracellular cathepsins directly cleave the extracellular matrix and activate proinvasive proteases in the tumor microenvironment. Cathepsin secretion is markedly increased in cancer cells. We investigated the signaling pathways leading to increased cathepsin secretion in melanoma cells. We found that the nonreceptor tyrosine kinases Abl and Arg (Abl/Arg) promoted the secretion of cathepsin B and cathepsin L by activating transcription factors (namely, Ets1, Sp1, and NF-κB/p65) that have key roles in the epithelial-mesenchymal transition (EMT), invasion, and therapeutic resistance. In some melanoma cell lines, Abl/Arg promoted the Ets1/p65-induced secretion of cathepsin B and cathepsin L in a kinase-independent manner, whereas in other melanoma lines, Abl/Arg promoted the kinase-dependent, Sp1/Ets1/p65-mediated induction of cathepsin L secretion and the Sp1/p65-mediated induction of cathepsin B secretion. As an indication of clinical relevance, the abundance of mRNAs encoding Abl/Arg, Sp1, Ets1, and cathepsins was positively correlated in primary melanomas, and Abl/Arg-driven invasion in culture and metastasis in vivo required cathepsin secretion. These data suggest that drugs targeting Abl kinases, many of which are FDA-approved, might inhibit cathepsin secretion in some melanomas and potentially other aggressive cancers harboring activated Abl kinases.