GLI2-mediated melanoma invasion and metastasis

Gli2 Facilitates Tumor Immune Evasion and Immunotherapeutic Resistance by Coordinating Wnt Ligand and Prostaglandin Signaling

Therapeutic resistance to immune checkpoint blockade has been commonly linked to the process of mesenchymal transformation (MT) and remains a prevalent obstacle across many cancer types. An improved mechanistic understanding for MT-mediated immune evasion promises to lead to more effective combination therapeutic regimens. Herein, we identify the Hedgehog transcription factor, Gli2, as a key node of tumor-mediated immune evasion and immunotherapy resistance during MT. Mechanistic studies reveal that Gli2 generates an immunotolerant tumor microenvironment through the upregulation of Wnt ligand production and increased prostaglandin synthesis. This pathway drives the recruitment, viability, and function of granulocytic myeloid-derived suppressor cells (PMN-MDSCs) while also impairing type I conventional dendritic cell, CD8 + T cell, and NK cell functionality. Pharmacologic EP2/EP4 prostaglandin receptor inhibition and Wnt ligand inhibition each reverses a subset of these effects, while preventing primary and adaptive resistance to anti-PD-1 immunotherapy, respectively. A transcriptional Gli2 signature correlates with resistance to anti-PD-1 immunotherapy in stage IV melanoma patients, providing a translational roadmap to direct combination immunotherapeutics in the clinic.

SIGNIFICANCE

Gli2-induced EMT promotes immune evasion and immunotherapeutic resistance via coordinated prostaglandin and Wnt signaling.

Assessing the genetic risk of nodular melanoma using a candidate gene approach

BACKGROUND

Nodular melanoma (NM) is a challenge to diagnose early due to its rapid growth and more atypical clinical presentation, making it the largest contributor to melanoma mortality.

OBJECTIVES

Our study aim was to perform a rare-variant allele (RVA) analysis of whole-exome sequencing of patients with NM and non-NM (minor allele frequency ≤ 1% non-Finnish European) for a set of 500 candidate genes potentially implicated in melanoma.

METHODS

This study recruited 131 participants with NM and 194 with non-NM from South-east Queensland and patients with NM from Victoria to perform a comparative analysis of possible genetic differences or similarities between the two melanoma cohorts.

RESULTS

Phenotypic analysis revealed that a majority of patients diagnosed with NM were older males with a higher frequency of fair skin and red hair than is seen in the general population. The distribution of common melanoma polygenic risk scores was similar in patients with NM and non-NM, with over 28% in the highest quantile of scores. There was also a similar frequency of carriage of familial/high-penetrant melanoma gene and loss-of-function variants. We identified 39 genes by filtering 500 candidate genes based on the greatest frequency in NM compared with non-NM cases. The genes with RVAs of greatest frequency in NM included PTCH1, ARID2 and GHR. Rare variants in the SMO gene, which interacts with PTCH1 as ligand and receptor, were also identified, providing evidence that the Hedgehog pathway may contribute to NM risk. There was a cumulative effect in carrying multiple rare variants in the NM-associated genes. A 14.8-fold increased ratio for NM compared with non-NM was seen when two RVAs of the 39 genes were carried by a patient.

CONCLUSIONS

This study highlights the importance of considering frequency of RVA to identify those at risk of NM in addition to known high penetrance genes.

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

Disrupting Hedgehog signaling in melanocytes by SUFU knockout leads to ocular melanocytosis and anterior segment malformation

Hedgehog (Hh) signaling is well known for its crucial role during development, but its specific role in individual cell lineages is less well characterized. Here, we disrupted Hh signaling specifically in melanocytes by using Cre-mediated cell-type-specific knockout of the Hh regulator suppressor of fused (Sufu). Interestingly, corresponding mice were fully pigmented and showed no developmental alterations in melanocyte numbers or distribution in skin and hair follicles. However, there were ectopic melanoblasts visible in the anterior chamber of the eye that eventually displayed severe malformation. Choroidal melanocytes remained unaltered. Surprisingly, the abnormal accumulation of anterior uveal melanoblasts was not the result of increased cell proliferation but of increased migration to ectopic locations such as the cornea. In melanoblasts in vitro, Sufu knockdown replicated the increase in cell migration without affecting proliferation and was mediated by an increased level of phosphorylated-ERK brought about by a reduction in the levels of the repressor form of GLI3. These results highlight the developmental divergence of distinct melanocyte subpopulations and may shed light on the pathogenesis of human ocular melanocytosis.

The Hedgehog/GLI signaling pathway activates transcription of Slug (Snail2) in melanoma cells

In melanoma and other cancers, invasion, epithelial-to-mesenchymal transition, metastasis and cancer stem cell maintenance are regulated by transcription factors including the Snail family. Slug (Snail2) protein generally supports migration and apoptosis resistance. However, its role in melanoma is not completely understood. The present study investigated the transcriptional regulation of the SLUG gene in melanoma. It demonstrated that SLUG is under the control of the Hedgehog/GLI signaling pathway and is activated predominantly by the transcription factor GLI2. The SLUG gene promoter contains a high number of GLI-binding sites. Slug expression is activated by GLI factors in reporter assays and inhibited by GANT61 (GLI inhibitor) and cyclopamine (SMO inhibitor). SLUG mRNA levels are lowered by GANT61 as assessed by reverse transcription-quantitative PCR. Chromatin immunoprecipitation revealed abundant binding of factors GLI1-3 in the four subregions of the proximal SLUG promoter. Notably, melanoma-associated transcription factor (MITF) is an imperfect activator of the SLUG promoter in reporter assays, and downregulation of MITF had no effect on endogenous Slug protein levels. Immunohistochemical analysis confirmed the above findings and showed MITF-negative regions in metastatic melanoma that were positive for GLI2 and Slug. Taken together, the results demonstrated a previously unrecognized transcriptional activation mechanism of the SLUG gene, which may represent its main regulation of expression in melanoma cells.

From simplicity to complexity in current melanoma models

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

Hedgehog/GLI signaling in hematopoietic development and acute myeloid leukemia—From bench to bedside

While the underlying genetic alterations and biology of acute myeloid leukemia (AML), an aggressive hematologic malignancy characterized by clonal expansion of undifferentiated myeloid cells, have been gradually unraveled in the last decades, translation into clinical treatment approaches has only just begun. High relapse rates remain a major challenge in AML therapy and are to a large extent attributed to the persistence of treatment-resistant leukemic stem cells (LSCs). The Hedgehog (HH) signaling pathway is crucial for the development and progression of multiple cancer stem cell driven tumors, including AML, and has therefore gained interest as a therapeutic target. In this review, we give an overview of the major components of the HH signaling pathway, dissect HH functions in normal and malignant hematopoiesis, and specifically elaborate on the role of HH signaling in AML pathogenesis and resistance. Furthermore, we summarize preclinical and clinical HH inhibitor studies, leading to the approval of the HH pathway inhibitor glasdegib, in combination with low-dose cytarabine, for AML treatment.

Inhibition of Gli2 suppresses tumorigenicity in glioblastoma stem cells derived from a de novo murine brain cancer model

The prognosis of glioblastoma remains poor despite intensive research efforts. Glioblastoma stem cells (GSCs) contribute to tumorigenesis, invasive capacity, and therapy resistance. Leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5), a stem cell marker, is involved in the maintenance of GSCs, although the properties of Lgr5-positive GSCs remain unclear. Here, the Sleeping-Beauty transposon-induced glioblastoma model was used in Lgr5-GFP knock-in mice identify GFP-positive cells in neurosphere cultures from mouse glioblastoma tissues. Global gene expression analysis showed that Gli2 was highly expressed in GFP-positive GSCs. Gli2 knockdown using lentiviral-mediated shRNA downregulated Hedgehog-related and Wnt signaling pathway-related genes, including Lgr5; suppressed tumor cell proliferation and invasion capacity; and induced apoptosis. Pharmacological Gli inhibition with GANT61 suppressed tumor cell proliferation. Silencing Gli2 suppressed the tumorigenicity of GSCs in an orthotopic transplantation model in vivo. These findings suggest that Gli2 affects the Hedgehog and Wnt pathways and plays an important role in GSC maintenance, suggesting Gli2 as a therapeutic target for glioblastoma treatment.

Melanoma Plasticity: Promoter of Metastasis and Resistance to Therapy

Melanoma is the deadliest form of skin cancer. Although targeted therapies and immunotherapies have revolutionized the treatment of metastatic melanoma, most patients are not cured. Therapy resistance remains a significant clinical challenge. Melanoma comprises phenotypically distinct subpopulations of cells, exhibiting distinct gene signatures leading to tumor heterogeneity and favoring therapeutic resistance. Cellular plasticity in melanoma is referred to as phenotype switching. Regardless of their genomic classification, melanomas switch from a proliferative and differentiated phenotype to an invasive, dedifferentiated and often therapy-resistant state. In this review we discuss potential mechanisms underpinning melanoma phenotype switching, how this cellular plasticity contributes to resistance to both targeted therapies and immunotherapies. Finally, we highlight novel strategies to target plasticity and their potential clinical impact in melanoma.

Hedgehog/GLI Signaling Pathway: Transduction, Regulation, and Implications for Disease

Simple Summary

The Hedgehog/GLI (Hh/GLI) pathway plays a major role during development and it is commonly dysregulated in many diseases, including cancer. This highly concerted series of ligands, receptors, cytoplasmic signaling molecules, transcription factors, and co-regulators is involved in regulating the biological functions controlled by this pathway. Activation of Hh/GLI in cancer is most often through a non-canonical method of activation, independent of ligand binding. This review is intended to summarize our current understanding of the Hh/GLI signaling, non-canonical mechanisms of pathway activation, its implication in disease, and the current therapeutic strategies targeting this cascade.

Abstract

The Hh/GLI signaling pathway was originally discovered in Drosophila as a major regulator of segment patterning in development. This pathway consists of a series of ligands (Shh, Ihh, and Dhh), transmembrane receptors (Ptch1 and Ptch2), transcription factors (GLI1–3), and signaling regulators (SMO, HHIP, SUFU, PKA, CK1, GSK3β, etc.) that work in concert to repress (Ptch1, Ptch2, SUFU, PKA, CK1, GSK3β) or activate (Shh, Ihh, Dhh, SMO, GLI1–3) the signaling cascade. Not long after the initial discovery, dysregulation of the Hh/GLI signaling pathway was implicated in human disease. Activation of this signaling pathway is observed in many types of cancer, including basal cell carcinoma, medulloblastoma, colorectal, prostate, pancreatic, and many more. Most often, the activation of the Hh/GLI pathway in cancer occurs through a ligand-independent mechanism. However, in benign disease, this activation is mostly ligand-dependent. The upstream signaling component of the receptor complex, SMO, is bypassed, and the GLI family of transcription factors can be activated regardless of ligand binding. Additional mechanisms of pathway activation exist whereby the entirety of the downstream signaling pathway is bypassed, and PTCH1 promotes cell cycle progression and prevents caspase-mediated apoptosis. Throughout this review, we summarize each component of the signaling cascade, non-canonical modes of pathway activation, and the implications in human disease, including cancer.

MDM2 induces EMT via the B‑Raf signaling pathway through 14‑3‑3

MDM2 proto-oncogene, E3 ubiquitin protein ligase (MDM2) is a well-known oncogene and has been reported to be closely associated with epithelial-to-mesenchymal transition (EMT). The present study first demonstrated that the expression levels of MDM2 were markedly increased in TGF-β-induced EMT using quantitative PCR and western blotting. In addition, MDM2 was demonstrated to be associated with pathological grade in clinical glioma samples by immunohistochemical staining. Furthermore, overexpression of MDM2 promoted EMT in glioma, lung cancer and breast cancer cell lines using a scratch wound migration assay. Subsequently, the present study explored the mechanism by which MDM2 promoted EMT and revealed that MDM2 induced EMT by upregulating EMT-related transcription factors via activation of the B-Raf signaling pathway through tyrosine 3-monooxygenase activation protein ε using RNA sequencing and western blotting. This mechanism depended on the p53 gene. Furthermore, in vivo experiments and the colony formation experiment demonstrated that MDM2 could promote tumor progression and induce EMT via the B-Raf signaling pathway. Since EMT contributes to increased drug resistance in tumor cells, the present study also explored the relationship between MDM2 and drug sensitivity using an MTT assay, and identified that MDM2 promoted cell insensitivity to silibinin treatment in an EMT-dependent manner. This finding is crucial for the development of cancer therapies and can also provide novel research avenues for future biological and clinical studies.

Treatment of Cutaneous Melanoma Harboring SMO p.Gln216Arg Mutation with Imiquimod: An Old Drug with New Results

Melanoma is the most lethal form of skin cancer and its incidence is growing worldwide. In the last ten years, the therapeutic scenario of this disease has been revolutionized by the introduction of targeted therapies and immune-checkpoint inhibitors. However, in patients with many lesions and bulky tumors, in which surgery is no longer feasible, there is a need for new treatment options. Here we report, for the first time to our knowledge, a clinical case where a melanoma patient harboring the SMO p.Gln216Arg mutation has been treated with imiquimod, showing a complete and durable response. To better explain this outstanding response to the treatment, we transfected a melanoma cell line (MeWo) with the SMO p.Gln216Arg mutation in order to evaluate its role in response to the imiquimod treatment. Moreover, to better demonstrate that the antitumor activity of imiquimod was due to its role in suppressing the oncogenic SMO signaling pathway, independently of its immune modulating function, an in vivo experiment has been performed. This clinical case opens up a new scenario for the treatment of melanoma patients identifying a new potentially druggable target.

Positive feedback of SuFu negating protein 1 on Hedgehog signaling promotes colorectal tumor growth

Hedgehog (Hh) signaling plays a critical role in embryogenesis and tissue homeostasis, and its deregulation has been associated with tumor growth. The tumor suppressor SuFu inhibits Hh signaling by preventing the nuclear translocation of Gli and suppressing cell proliferation. Regulation of SuFu activity and stability is key to controlling Hh signaling. Here, we unveil SuFu Negating Protein 1 (SNEP1) as a novel Hh target, that enhances the ubiquitination and proteasomal degradation of SuFu and thus promotes Hh signaling. We further show that the E3 ubiquitin ligase LNX1 plays a critical role in the SNEP1-mediated degradation of SuFu. Accordingly, SNEP1 promotes colorectal cancer (CRC) cell proliferation and tumor growth. High levels of SNEP1 are detected in CRC tissues and are well correlated with poor prognosis in CRC patients. Moreover, SNEP1 overexpression reduces sensitivity to anti-Hh inhibitor in CRC cells. Altogether, our findings demonstrate that SNEP1 acts as a novel feedback regulator of Hh signaling by destabilizing SuFu and promoting tumor growth and anti-Hh resistance.

Bone metastasis: mechanisms, therapies, and biomarkers

Skeletal metastases are frequent complications of many cancers, causing bone complications (fractures, bone pain, disability) that negatively affect the patient's quality of life. Here, we first discuss the burden of skeletal complications in cancer bone metastasis. We then describe the pathophysiology of bone metastasis. Bone metastasis is a multistage process: long before the development of clinically detectable metastases, circulating tumor cells settle and enter a dormant state in normal vascular and endosteal niches present in the bone marrow, which provide immediate attachment and shelter, and only become active years later as they proliferate and alter the functions of bone-resorbing (osteoclasts) and bone-forming (osteoblasts) cells, promoting skeletal destruction. The molecular mechanisms involved in mediating each of these steps are described, and we also explain how tumor cells interact with a myriad of interconnected cell populations in the bone marrow, including a rich vascular network, immune cells, adipocytes, and nerves. We discuss metabolic programs that tumor cells could engage with to specifically grow in bone. We also describe the progress and future directions of existing bone-targeted agents and report emerging therapies that have arisen from recent advances in our understanding of the pathophysiology of bone metastases. Finally, we discuss the value of bone turnover biomarkers in detection and monitoring of progression and therapeutic effects in patients with bone metastasis.

Sonic Hedgehog Signature in Pediatric Primary Bone Tumors: Effects of the GLI Antagonist GANT61 on Ewing's Sarcoma Tumor Growth

Simple Summary

The poor clinical outcomes for Osteosarcoma (OS) and Ewing’s sarcoma (ES) patients underscore the urgency of developing novel therapeutic strategies for these pathologies. In this context, the emerging role of Sonic hedgehog (SHH) signaling in cancer has been critically evaluated, focusing on the potential for targeting SHH signaling as an anticancer strategy. The aims of this work were (1) to highlight and to compare a possible SHH/Gli signature between OS and ES, (2) to strengthen our knowledge concerning the role of EWS-FLI1 in the SHH signature in ES and (3) to evaluate the effect of the specific Gli inhibitor GANT61 in vivo on the growth of ES tumors using an orthotopic mice model. Our work identifies Gli1 as a promising therapeutic target in ES and demonstrates that GANT61, through inhibition of Gli1 transcriptional activity, may be a promising therapeutic strategy hindering ES tumor progression, and specifically primary tumor growth.

Abstract

Osteosarcoma (OS) and Ewing’s sarcoma (ES) are the most common malignant bone tumors in children and adolescents. In many cases, the prognosis remains very poor. The Sonic hedgehog (SHH) signaling pathway, strongly involved in the development of many cancers, regulate transcription via the transcriptional factors Gli1-3. In this context, RNAseq analysis of OS and ES cell lines reveals an increase of some major compounds of the SHH signaling cascade in ES cells, such as the transcriptional factor Gli1. This increase leads to an augmentation of the transcriptional response of Gli1 in ES cell lines, demonstrating a dysregulation of Gli1 signaling in ES cells and thus the rationale for targeting Gli1 in ES. The use of a preclinical model of ES demonstrates that GANT61, an inhibitor of the transcriptional factor Gli1, reduces ES primary tumor growth. In vitro experiments show that GANT61 decreases the viability of ES cell, mainly through its ability to induce caspase-3/7-dependent cell apoptosis. Taken together, these results demonstrates that GANT61 may be a promising therapeutic strategy for inhibiting the progression of primary ES tumors.

ST3GAL1 is a target of the SOX2-GLI1 transcriptional complex and promotes melanoma metastasis through AXL

Understanding the molecular events controlling melanoma progression is of paramount importance for the development of alternative treatment options for this devastating disease. Here we report a mechanism regulated by the oncogenic SOX2-GLI1 transcriptional complex driving melanoma invasion through the induction of the sialyltransferase ST3GAL1. Using in vitro and in vivo studies, we demonstrate that ST3GAL1 drives melanoma metastasis. Silencing of this enzyme suppresses melanoma invasion and significantly reduces the ability of aggressive melanoma cells to enter the blood stream, colonize distal organs, seed and survive in the metastatic environment. Analysis of glycosylated proteins reveals that the receptor tyrosine kinase AXL is a major effector of ST3GAL1 pro-invasive function. ST3GAL1 induces AXL dimerization and activation that, in turn, promotes melanoma invasion. Our data support a key role of the ST3GAL1-AXL axis as driver of melanoma metastasis, and highlight the therapeutic potential of targeting this axis to treat metastatic melanoma.

Targeting the GLI family of transcription factors for the development of anti-cancer drugs

INTRODUCTION

GLI1 is a transcription factor that has been identified as a downstream effector for multiple tumorigenic signaling pathways. These include the Hedgehog, RAS-RAF-MEK-ERK, and PI3K-AKT-mTOR pathways, which have all been separately validated as individual anti-cancer drug targets. The identification of GLI1 as a key transcriptional regulator for each of these pathways highlights its promise as a therapeutic target. Small molecule GLI1 inhibitors are potentially efficacious against human malignancies arising from multiple oncogenic mechanisms.

AREAS COVERED

This review provides an overview of the key oncogenic cellular pathways that regulate GLI1 transcriptional activity. It also provides a detailed account of small molecule GLI1 inhibitors that are currently under development as potential anti-cancer chemotherapeutics.

EXPERT OPINION

Interest in developing inhibitors of GLI1-mediated transcription has significantly increased as its role in multiple oncogenic signaling pathways has been elucidated. To date, it has proven difficult to directly target GLI1 with small molecules, and the majority of compounds that inhibit GLI1 activity function through indirect mechanisms. To date, no direct-acting GLI1 inhibitor has entered clinical trials. The identification and development of new scaffolds that can bind and directly inhibit GLI1 are essential to further advance this class of chemotherapeutics.

Range of SHH signaling in adrenal gland is limited by membrane contact to cells with primary cilia

The signaling protein Sonic Hedgehog (SHH) is crucial for the development and function of many vertebrate tissues. It remains largely unclear, however, what defines the range and specificity of pathway activation. The adrenal gland represents a useful model to address this question, where the SHH pathway is activated in a very specific subset of cells lying near the SHH-producing cells, even though there is an abundance of lipoproteins that would allow SHH to travel and signal long-range. We determine that, whereas adrenal cells can secrete SHH on lipoproteins, this form of SHH is inactive due to the presence of cosecreted inhibitors, potentially explaining the absence of long-range signaling. Instead, we find that SHH-producing cells signal at short range via membrane-bound SHH, only to receiving cells with primary cilia. Finally, our data from NCI-H295R adrenocortical carcinoma cells suggest that adrenocortical tumors may evade these regulatory control mechanisms by acquiring the ability to activate SHH target genes in response to TGF-β.

Bone Tropism in Cancer Metastases

Bone is a frequent site of metastases in many cancers. Both bone properties and the tumor-intrinsic traits are associated with the metastatic propensity to bone (i.e., the bone tropism). Whereas an increasing body of mechanistic studies expanded our understanding on bone tropism, they also revealed complexity across the bone lesions originated from different cancer types. In this review, we will discuss the physical, chemical, and biological properties of bone microenvironment, identify potential players in every stage of bone metastases, and introduce some of the known mechanisms regulating the bone colonization. Our objectives are to integrate the knowledge established in different biological contexts and highlight the determinants of bone tropism.

TFII-I-mediated polymerase pausing antagonizes GLI2 induction by TGFβ

The modulation of GLI2, an oncogenic transcription factor commonly upregulated in cancer, is in many cases not due to genetic defects, suggesting dysregulation through alternative mechanisms. The identity of these molecular events remains for the most part unknown. Here, we identified TFII-I as a novel repressor of GLI2 expression. Mapping experiments suggest that the INR region of the GLI2 promoter is necessary for GLI2 repression. ChIP studies showed that TFII-I binds to this INR. TFII-I knockdown decreased the binding of NELF-A, a component of the promoter–proximal pausing complex at this site, and enriched phosphorylated RNAPII serine 2 in the GLI2 gene body. Immunoprecipitation studies demonstrate TFII-I interaction with SPT5, another pausing complex component. TFII-I overexpression antagonized GLI2 induction by TGFβ, a known activator of GLI2 in cancer cells. TGFβ reduced endogenous TFII-I binding to the INR and increased RNAPII SerP2 in the gene body. We demonstrate that this regulatory mechanism is not exclusive of GLI2. TGFβ-induced genes CCR7, TGFβ1 and EGR3 showed similar decreased TFII-I and NELF-A INR binding and increased RNAPII SerP2 in the gene body post-TGFβ treatment. Together these results identify TFII-I as a novel repressor of a subset of TGFβ-responsive genes through the regulation of RNAPII pausing.

Large-scale pan-cancer analysis reveals broad prognostic association between TGF-β ligands, not Hedgehog, and GLI1/2 expression in tumors

GLI1 expression is broadly accepted as a marker of Hedgehog pathway activation in tumors. Efficacy of Hedgehog inhibitors is essentially limited to tumors bearing activating mutations of the pathway. GLI2, a critical Hedgehog effector, is necessary for GLI1 expression and is a direct transcriptional target of TGF-β/SMAD signaling. We examined the expression correlations of GLI1/2 with TGFB and HH genes in 152 distinct transcriptome datasets totaling over 23,500 patients and representing 37 types of neoplasms. Their prognostic value was measured in over 15,000 clinically annotated tumor samples from 26 tumor types. In most tumor types, GLI1 and GLI2 follow a similar pattern of expression and are equally correlated with HH and TGFB genes. However, GLI1/2 broadly share prognostic value with TGFB genes and a mesenchymal/EMT signature, not with HH genes. Our results provide a likely explanation for the frequent failure of anti-Hedgehog therapies in tumors, as they suggest a key role for TGF-β, not Hedgehog, ligands, in tumors with elevated GLI1/2-expression.

Fine-Tuning of GLI Activity through Arginine Methylation: Its Mechanisms and Function

The glioma-associated oncogene (GLI) family consists of GLI1, GLI2, and GLI3 in mammals. This family has important roles in development and homeostasis. To achieve these roles, the GLI family has widespread outputs. GLI activity is therefore strictly regulated at multiple levels, including via post-translational modifications for context-dependent GLI target gene expression. The protein arginine methyl transferase (PRMT) family is also associated with embryogenesis, homeostasis, and cancer mainly via epigenetic modifications. In the PRMT family, PRMT1, PRMT5, and PRMT7 reportedly regulate GLI1 and GLI2 activity. PRMT1 methylates GLI1 to upregulate its activity and target gene expression. Cytoplasmic PRMT5 methylates GLI1 and promotes GLI1 protein stabilization. Conversely, nucleic PRMT5 interacts with MENIN to suppress growth arrest-specific protein 1 expression, which assists Hedgehog ligand binding to Patched, indirectly resulting in downregulated GLI1 activity. PRMT7-mediated GLI2 methylation upregulates its activity through the dissociation of GLI2 and Suppressor of Fused. Together, PRMT1, PRMT5, and PRMT7 regulate GLI activity at multiple revels. Furthermore, the GLI and PRMT families have strong links with various cancers through cancer stem cell maintenance. Therefore, PRMT-mediated regulation of GLI activity would have important roles in cancer stem cell maintenance.

SHH Signaling Pathway Drives Pediatric Bone Sarcoma Progression

Primary bone tumors can be divided into two classes, benign and malignant. Among the latter group, osteosarcoma and Ewing sarcoma are the most prevalent malignant primary bone tumors in children and adolescents. Despite intensive efforts to improve treatments, almost 40% of patients succumb to the disease. Specifically, the clinical outcome for metastatic osteosarcoma or Ewing sarcoma remains poor; less than 30% of patients who present metastases will survive 5 years after initial diagnosis. One common and specific point of these bone tumors is their ability to deregulate bone homeostasis and remodeling and divert them to their benefit. Over the past years, considerable interest in the Sonic Hedgehog (SHH) pathway has taken place within the cancer research community. The activation of this SHH cascade can be done through different ways and, schematically, two pathways can be described, the canonical and the non-canonical. This review discusses the current knowledge about the involvement of the SHH signaling pathway in skeletal development, pediatric bone sarcoma progression and the related therapeutic options that may be possible for these tumors.

The FDA-Approved Anti-Asthma Medicine Ciclesonide Inhibits Lung Cancer Stem Cells through Hedgehog Signaling-Mediated SOX2 Regulation

Ciclesonide is an FDA-approved glucocorticoid (GC) used to treat asthma and allergic rhinitis. However, its effects on cancer and cancer stem cells (CSCs) are unknown. Our study focuses on investigating the inhibitory effect of ciclesonide on lung cancer and CSCs and its underlying mechanism. In this study, we showed that ciclesonide inhibits the proliferation of lung cancer cells and the growth of CSCs. Similar glucocorticoids, such as dexamethasone and prednisone, do not inhibit CSC formation. We show that ciclesonide is important for CSC formation through the Hedgehog signaling pathway. Ciclesonide reduces the protein levels of GL1, GL2, and Smoothened (SMO), and a small interfering RNA (siRNA) targeting SMO inhibits tumorsphere formation. Additionally, ciclesonide reduces the transcript and protein levels of SOX2, and an siRNA targeting SOX2 inhibits tumorsphere formation. To regulate breast CSC formation, ciclesonide regulates GL1, GL2, SMO, and SOX2. Our results unveil a novel mechanism involving Hedgehog signaling and SOX2 regulated by ciclesonide in lung CSCs, and also open up the possibility of targeting Hedgehog signaling and SOX2 to prevent lung CSC formation.

GLI2-Mediated Inflammation in the Tumor Microenvironment

The tumor microenvironment (TME) plays an important role in the development and progression of cancer and has been shown to contribute to resistance to therapy. Inflammation is one of the hallmarks of cancer implicated in disease phenotype. Therefore, understanding the mechanisms that regulate inflammation in cancer and consequently how inflammatory mediators promote cancer progression is important for our understanding of cancer cell biology. The transcription factor GLI2 was initially identified as a member of the Hedgehog (HH) signaling pathway. During the last decade, studies have shown a novel mechanism of GLI2 regulation independent of HH signaling, where GLI2 consequently modulated several cytokine genes in the TME. These studies highlight a novel role for GLI2 as an inflammatory mediatory independent of HH stimulation. This chapter will discuss canonical and noncanonical pathways of GLI2 regulation and some of the downstream cytokine target genes regulated by GLI2.

Expression profiles of p53/p73, NME and GLI families in metastatic melanoma tissue and cell lines

Unlike other tumours, TP53 is rarely mutated in melanoma; however, it fails to function as a tumour suppressor. We assume that its functions might be altered through interactions with several families of proteins, including p53/p73, NME and GLI. To elucidate the potential interplay among these families we analysed the expression profiles of aforementioned genes and proteins in a panel of melanoma cell lines, metastatic melanoma specimens and healthy corresponding tissue. Using qPCR a higher level of NME1 gene expression and lower levels of Δ40p53β, ΔNp73, GLI1, GLI2 and PTCH1 were observed in tumour samples compared to healthy tissue. Protein expression of Δ133p53α, Δ160p53α and ΔNp73α isoforms, NME1 and NME2, and N'ΔGLI1, GLI1FL, GLI2ΔN isoforms was elevated in tumour tissue, whereas ∆Np73β was downregulated. The results in melanoma cell lines, in general, support these findings. In addition, we correlated expression profiles with clinical features and outcome. Higher Δ133p53β and p53α mRNA and both GLI1 mRNA and GLI3R protein expression had a negative impact on the overall survival. Shorter overall survival was also connected with lower p53β and NME1 gene expression levels. In conclusion, all examined genes may have implications in melanoma development and functional inactivity of TP53.

Inhibition of the hedgehog pathway for the treatment of cancer using Itraconazole

Itraconazole (ITZ) is an anti-fungal drug that has been used in clinical practice for nearly 35 years. Recently, numerous experiments have shown that ITZ possesses anti-cancer properties. The Hedgehog (Hh) pathway plays a pivotal role in fundamental processes, including embryogenesis, structure, morphology and proliferation in various species. This pathway is typically silent in adult cells, and inappropriate activity is linked to various tumor types. The most important mechanism of ITZ in the treatment of cancer is inhibition of the Hh pathway through the inhibition of smoothened receptors (SMO), glioma-associated oncogene homologs (GLI), and their downstream targets. In this review, we discuss the mechanisms of ITZ in the treatment of cancer through inhibition of the Hh pathway, which includes anti-inflammation, prevention of tumor growth, induction of cell cycle arrest, induction of apoptosis and autophagy, prevention of angiogenesis, and drug resistance. We also discuss the clinical use of ITZ in many types of cancers. We hope this review will provide more information to support future studies on ITZ in the treatment of various cancers.

Phenotype plasticity as enabler of melanoma progression and therapy resistance

Malignant melanoma is notorious for its inter- and intratumour heterogeneity, based on transcriptionally distinct melanoma cell phenotypes. It is thought that these distinct phenotypes are plastic in nature and that their transcriptional reprogramming enables heterogeneous tumours both to undergo different stages of melanoma progression and to adjust to drug exposure during treatment. Recent advances in genomic technologies and the rapidly expanding availability of large gene expression datasets have allowed for a refined definition of the gene signatures that characterize these phenotypes and have revealed that phenotype plasticity plays a major role in the resistance to both targeted therapy and immunotherapy. In this Review we discuss the definition of melanoma phenotypes through particular transcriptional states and reveal the prognostic relevance of the related gene expression signatures. We review how the establishment of phenotypes is controlled and which roles phenotype plasticity plays in melanoma development and therapy. Because phenotype plasticity in melanoma bears a great resemblance to epithelial-mesenchymal transition, the lessons learned from melanoma will also benefit our understanding of other cancer types.

Non-canonical Hedgehog Signaling Pathway in Cancer: Activation of GLI Transcription Factors Beyond Smoothened

The Hedgehog-GLI (HH-GLI) pathway is a highly conserved signaling that plays a critical role in controlling cell specification, cell–cell interaction and tissue patterning during embryonic development. Canonical activation of HH-GLI signaling occurs through binding of HH ligands to the twelve-pass transmembrane receptor Patched 1 (PTCH1), which derepresses the seven-pass transmembrane G protein-coupled receptor Smoothened (SMO). Thus, active SMO initiates a complex intracellular cascade that leads to the activation of the three GLI transcription factors, the final effectors of the HH-GLI pathway. Aberrant activation of this signaling has been implicated in a wide variety of tumors, such as those of the brain, skin, breast, gastrointestinal, lung, pancreas, prostate and ovary. In several of these cases, activation of HH-GLI signaling is mediated by overproduction of HH ligands (e.g., prostate cancer), loss-of-function mutations in PTCH1 or gain-of-function mutations in SMO, which occur in the majority of basal cell carcinoma (BCC), SHH-subtype medulloblastoma and rhabdomyosarcoma. Besides the classical canonical ligand-PTCH1-SMO route, mounting evidence points toward additional, non-canonical ways of GLI activation in cancer. By non-canonical we refer to all those mechanisms of activation of the GLI transcription factors occurring independently of SMO. Often, in a given cancer type canonical and non-canonical activation of HH-GLI signaling co-exist, and in some cancer types, more than one mechanism of non-canonical activation may occur. Tumors harboring non-canonical HH-GLI signaling are less sensitive to SMO inhibition, posing a threat for therapeutic efficacy of these antagonists. Here we will review the most recent findings on the involvement of alternative signaling pathways in inducing GLI activity in cancer and stem cells. We will also discuss the rationale of targeting these oncogenic pathways in combination with HH-GLI inhibitors as a promising anti-cancer therapies.

Transcriptional control of subtype switching ensures adaptation and growth of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a heterogeneous disease comprised of a basal-like subtype with mesenchymal gene signatures, undifferentiated histopathology and worse prognosis compared to the classical subtype. Despite their prognostic and therapeutic value, the key drivers that establish and control subtype identity remain unknown. Here, we demonstrate that PDA subtypes are not permanently encoded, and identify the GLI2 transcription factor as a master regulator of subtype inter-conversion. GLI2 is elevated in basal-like PDA lines and patient specimens, and forced GLI2 activation is sufficient to convert classical PDA cells to basal-like. Mechanistically, GLI2 upregulates expression of the pro-tumorigenic secreted protein, Osteopontin (OPN), which is especially critical for metastatic growth in vivo and adaptation to oncogenic KRAS ablation. Accordingly, elevated GLI2 and OPN levels predict shortened overall survival of PDA patients. Thus, the GLI2-OPN circuit is a driver of PDA cell plasticity that establishes and maintains an aggressive variant of this disease.

MITF-the first 25 years

In this review, Goding and Arnheiter present the current understanding of MITF's role and regulation in development and disease and highlight key areas where our knowledge of MITF regulation and function is limited.

All transcription factors are equal, but some are more equal than others. In the 25 yr since the gene encoding the microphthalmia-associated transcription factor (MITF) was first isolated, MITF has emerged as a key coordinator of many aspects of melanocyte and melanoma biology. Like all transcription factors, MITF binds to specific DNA sequences and up-regulates or down-regulates its target genes. What marks MITF as being remarkable among its peers is the sheer range of biological processes that it appears to coordinate. These include cell survival, differentiation, proliferation, invasion, senescence, metabolism, and DNA damage repair. In this article we present our current understanding of MITF's role and regulation in development and disease, as well as those of the MITF-related factors TFEB and TFE3, and highlight key areas where our knowledge of MITF regulation and function is limited.

Transcriptional regulation of autophagy-lysosomal function in BRAF-driven melanoma progression and chemoresistance

Autophagy maintains homeostasis and is induced upon stress. Yet, its mechanistic interaction with oncogenic signaling remains elusive. Here, we show that in BRAFV600E-melanoma, autophagy is induced by BRAF inhibitor (BRAFi), as part of a transcriptional program coordinating lysosome biogenesis/function, mediated by the TFEB transcription factor. TFEB is phosphorylated and thus inactivated by BRAFV600E via its downstream ERK independently of mTORC1. BRAFi disrupts TFEB phosphorylation, allowing its nuclear translocation, which is synergized by increased phosphorylation/inactivation of the ZKSCAN3 transcriptional repressor by JNK2/p38-MAPK. Blockade of BRAFi-induced transcriptional activation of autophagy-lysosomal function in melanoma xenografts causes enhanced tumor progression, EMT-transdifferentiation, metastatic dissemination, and chemoresistance, which is associated with elevated TGF-β levels and enhanced TGF-β signaling. Inhibition of TGF-β signaling restores tumor differentiation and drug responsiveness in melanoma cells. Thus, the "BRAF-TFEB-autophagy-lysosome" axis represents an intrinsic regulatory pathway in BRAF-mutant melanoma, coupling BRAF signaling with TGF-β signaling to drive tumor progression and chemoresistance.

Transcriptional repression of the tyrosinase-related protein 2 gene by transforming growth factor-β and the Kruppel-like transcription factor GLI2

BACKGROUND

Tyrosinase-Related Protein 2 (TRP2) is an enzyme involved in melanogenesis, that also exerts proliferative, anti-apoptotic and immunogenic functions in melanoma cells. TRP2 transcription is regulated by the melanocytic master transcription factor MITF. GLI2, a transcription factor that acts downstream of Hedgehog signaling, is also a direct transcriptional target of the TGF-β/SMAD pathway that contributes to melanoma progression and exerts transcriptional antagonistic activities against MITF.

OBJECTIVES

To characterize the molecular events responsible for TGF-β and GLI2 repression of TRP2 expression.

METHODS

In silico promoter analysis, transient cell transfection experiments with 5'-end TRP2 promoter deletion constructs, chromatin immuno-precipitation, and site-directed promoter mutagenesis were used to dissect the molecular mechanisms of TRP2 gene regulation by TGF-β and GLI2.

RESULTS

We demonstrate that TGF-β and GLI2-specific TRP2 repression involves direct mechanisms that occur in addition to MITF downregulation by TGF-β and GLI2. We identify two functional GLI2 binding sites within the TRP2 promoter that are critical for TGF-β and GLI2 responsiveness, one of them overlapping a CREB binding site. GLI2 and CREB competing for the same cis-element is associated with opposite transcriptional outcome.

CONCLUSION

Our results further refine the understanding of how TGF-β and GLI2 control the phenotypic plasticity of melanoma cells. In particular, we identify critical GLI2-binding cis-elements within the TRP2 promoter region that allow for its transcriptional repression independently from MITF concomitant downregulation.

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.

How Bad Is the Hedgehog? GLI-Dependent, Hedgehog-Independent Cancers on the Importance of Biomarkers for Proper Patients Selection

Hedgehog (HH) signaling plays an important role both during embryonic development and adult life. It is involved in the regulation of cell differentiation, cell proliferation and tissue polarity, as well as in the maintenance of stem cells, tissue repair, and regeneration (Briscoe and Therond, 2013; Jiang and Hui, 2008). Three ligands, Indian, Sonic, and Desert HH, can activate this pathway. Binding of HH ligands to their receptor, PTCH1 (Figure 1) lift its inhibition on SMO, resulting in activation and nuclear translocation of GLI transcription factors (Javelaud et al., 2012). The vertebrate GLI gene family is composed of three distinct genes GLI1, GLI2, and GLI3, encoding Krüppel-like transcription factors. GLI proteins exhibit distinct regulations, biochemical properties, and target genes. GLI3 acts as the main repressor of the pathway in the absence of HH ligands, whereas, in their presence, GLI2 is the main HH effector that drives the expression of GLI1 (Briscoe and Therond, 2013).

Widespread Expression of Hedgehog Pathway Components in a Large Panel of Human Tumor Cells and Inhibition of Tumor Growth by GANT61: Implications for Cancer Therapy

The sonic Hedgehog/GLI signaling pathway (HH) is critical for maintaining tissue polarity in development and contributes to tumor stemness. Transcription factors GLI1–3 are the downstream effectors of HH and activate oncogenic targets. To explore the completeness of the expression of HH components in tumor cells, we performed a screen for all HH proteins in a wide spectrum of 56 tumor cell lines of various origin using Western blot analysis. Generally, all HH proteins were expressed. Important factors GLI1 and GLI2 were always expressed, only exceptionally one of them was lowered, suggesting the functionality of HH in all tumors tested. We determined the effect of a GLI inhibitor GANT61 on proliferation in 16 chosen cell lines. More than half of tumor cells were sensitive to GANT61 to various extents. GANT61 killed the sensitive cells through apoptosis. The inhibition of reporter activity containing 12xGLI consensus sites by GANT61 and cyclopamine roughly correlated with cell proliferation influenced by GANT61. Our results recognize the sensitivity of tumor cell types to GANT61 in cell culture and support a critical role for GLI factors in tumor progression through restraining apoptosis. The use of GANT61 in combined targeted therapy of sensitive tumors, such as melanomas, seems to be immensely helpful.

Gli2 is required for the induction and migration of Xenopus laevis neural crest

The neural crest (NC) is a multipotent migratory embryonic population that is formed during late gastrulation and gives rise to a wide array of derivatives, including cells from the peripheral nervous system (PNS), the craniofacial bones and cartilages, peripheral glial cells, and melanocyte cells, among others. In this work we analyzed the role of the Hedgehog signaling pathway effector gli2 in Xenopus NC. We provide evidence that the gli2 gene is expressed in the prospective, premigratory and migratory NC. The use of a specific morpholino against gli2 and the pharmacological specific inhibitor GANT61 in different experimental approaches allowed us to determine that gli2 is required for the induction and specification of NC cells as a transcriptional activator. Moreover, gli2 also acts by reducing apoptosis in the NC without affecting its cell proliferation status. We also demonstrated that gli2 is required cell-autonomously for NC migration, and for the formation of NC derivatives such as the craniofacial cartilages, melanocytes and the cranial ganglia. Altogether, our results showed that gli2 is a key transcriptional activator to accomplish the proper specification and development of Xenopus NC cells.

CD146 mediates an E-cadherin-to-N-cadherin switch during TGF-β signaling-induced epithelial-mesenchymal transition

Cadherin switch is an initiating factor of epithelial-mesenchymal transition (EMT) and is intimately correlated with cancer metastatic potential; however, its underlying mechanisms remain unclear. Here, using a transforming growth factor-β (TGF-β)-induced EMT model, we provide explicit evidence that CD146, with elevated expression and activity in a variety of cancers, is a key factor involved in the cadherin switch. We show that CD146 can be induced by TGF-β signaling. Moreover, CD146 expression is positively correlated with the activation levels of STAT3/Twist and ERK pathways. Transcriptional response of the CD146/STAT3/Twist cascade inhibits E-cadherin expression, whereas the CD146/ERK cascade enhances N-cadherin expression. CD146 overexpression also significantly promotes EMT in both mouse embryonic fibroblasts (MEFs) and ovarian cancer cells. Clinically, ovarian cancer patients with detectable CD146 expression had a significantly lower survival rate than that of patients without CD146 expression. Furthermore, CD146-deficient MEFs exhibited decreased motility as a result of reversion in this cadherin switch, strongly suggesting that targeting CD146 is a potential strategy for cancer treatment. Therefore, CD146-mediated regulation of the E-cadherin-to-N-cadherin switch provides an insight into the general mechanisms of EMT as well as cancer metastasis.

Itraconazole exerts its anti-melanoma effect by suppressing Hedgehog, Wnt, and PI3K/mTOR signaling pathways

Malignant melanoma is the deadliest form of all skin cancers. Itraconazole, a commonly used systemic antifungal drug, has been tested for its anti-tumor effects on basal cell carcinoma, prostate cancer, and non-small cell lung cancer. Whether itraconazole has any specific anti-tumor effect on melanoma remains unknown. However, the goal of this study is to investigate the effect of itraconazole on melanoma and to reveal some details of its underlying mechanism. In the in vivo xenograft mouse model, we find that itraconazole can inhibit melanoma growth and extend the survival of melanoma xenograft mice, compared to non-itraconazole-treated mice. Also, itraconazole can significantly inhibit cell proliferation, as demonstrated by Ki-67 staining in itraconazole-treated tumor tissues. In in vitro, we show that itraconazole inhibits the proliferation and colony formation of both SK-MEL-28 and A375 human melanoma cells. Moreover, we demonstrate that itraconazole significantly down-regulates Gli-1, Gli-2, Wnt3A, β-catenin and cyclin D1, while it up-regulates Gli-3 and Axin-1, indicating potent inhibitory effects of itraconazole on Hedgehog (Hh) and Wnt signaling pathways. Furthermore, itraconazole significantly suppresses the PI3K/mTOR signaling pathway – indicated by the down-regulated phosphorylation of p70S6K, 4E-BP1 and AKT – but has no effect on the phosphorylation of MEK or ERK. Our data suggest that itraconazole inhibits melanoma growth through an interacting regulatory network that includes Hh, Wnt, and PI3K/mTOR signaling pathways. These results suggest that this agent has several potent anti-melanoma features and may be useful in the synergesis of other anti-cancer drugs via blockage of the Hh, Wnt and PI3K/mTOR signaling pathways.

Identification of a gene expression signature associated with the metastasis suppressor function of NME1: prognostic value in human melanoma

Although NME1 is well known for its ability to suppress metastasis of melanoma, the molecular mechanisms underlying this activity are not completely understood. Herein, we utilized a bioinformatics approach to systematically identify genes whose expression is correlated with the metastasis suppressor function of NME1. This was accomplished through a search for genes that were regulated by NME1, but not by NME1 variants lacking metastasis suppressor activity. This approach identified a number of novel genes, such as ALDOC, CXCL11, LRP1b, and XAGE1 as well as known targets such as NETO2, which were collectively designated as an NME1-Regulated Metastasis Suppressor Signature (MSS). The MSS was associated with prolonged overall survival in a large cohort of melanoma patients in The Cancer Genome Atlas (TCGA). The median overall survival of melanoma patients with elevated expression of the MSS genes was >5.6 years longer compared with that of patients with lower expression of the MSS genes. These data demonstrate that NMEl represents a powerful tool for identifying genes whose expression is associated with metastasis and survival of melanoma patients, suggesting their potential applications as prognostic markers and therapeutic targets in advanced forms of this lethal cancer.

Gli promotes epithelial-mesenchymal transition in human lung adenocarcinomas

Adenocarcinoma is the most common type of lung cancer. Epithelial-mesenchymal transition (EMT) is required for tumor invasion/metastasis and the components that control this process are potential therapeutic targets. This study we examined the role of Gli in lung adenocarcinoma and whether its activation regulates metastasis through EMT in lung adenocarcinoma. We found that tumors with high Gli expression had significantly lower E-Cadherin expression in two independent cohorts of patients with lung adenocarcinoma that we studied. In vitro up-regulation of SHh resulted in increased cell migration while small molecule inhibitors of Smo or Gli significantly reduced cell mobility both in a wound healing assay and in a 3D cell invasion assay. Inhibition of Gli in vivo decreased tumor growth and induced an increase in E-Cadherin expression. Our results indicate that Gli may be critical for lung adenocarcinoma metastasis and that a novel Gli inhibitor shows promise as a therapeutic agent by preventing cell migration and invasion in vitro and significantly reducing tumor growth and increasing E-Cadherin expression in vivo.

Analysis of hedgehog signaling in periocular sebaceous carcinoma

PURPOSE

Sebaceous carcinoma (SC) is a clinical masquerader of benign conditions resulting in significant eye morbidity, sometimes leading to extensive surgical treatment including exenteration, and even mortality. Little is known about the genetic or molecular basis of SC. This study identifies the involvement of Hedgehog (Hh) signaling in periocular SC.

METHODS

Fifteen patients with periocular SC patients were compared to 15 patients with eyelid nodular basal cell carcinoma (nBCC; a known Hh tumor), alongside four normal individuals as a control for physiological Hh expression. Expression of Patched 1 (PTCH1), Smoothened (SMO), and glioma-associated zinc transcription factors (Gli1 and Gli2) were assessed in histological sections using immunohistochemistry and immunofluorescence (IF) techniques. Antibody specificity was verified using Western-blot analysis of a Gli1 over-expressed cancer cell line, LNCaP-Gli1. Semi-quantification compared tumors and control tissue using IF analysis by ImageJ software.

RESULTS

Expression of the Hh pathway was observed in SC for all four major components of the pathway. PTCH1, SMO, and Gli2 were more significantly upregulated in SC (P < 0.01) compared to nBCC. Stromal expression of PTCH1 and Gli2 was observed in SC (P < 0.01). In contrast, stromal expression of these proteins in nBCC was similar or down-regulated compared to physiological Hh controls.

CONCLUSIONS

The Hh signaling pathway is significantly more upregulated in periocular SC compared to nBCC, a known aberrant Hh pathway tumor. Furthermore, the stroma of the SC demonstrated Hh upregulation, in particular Gli2, compared to nBCC. Targeting of this pathway may be a potential treatment strategy for SC.

MICAL2 promotes breast cancer cell migration by maintaining epidermal growth factor receptor (EGFR) stability and EGFR/P38 signalling activation

AIM

MICAL2, a cytoskeleton dynamics regulator, is identified associated with survival and metastasis of several types of cancers recently. This study was designed to investigate the role of MICAL2 in breast cancer cell migration as well as its underlying mechanisms.

METHODS

The relationship between MICAL2 and EGF/EGFR signalling was analysed by gene overexpression and knock-down techniques. Cell migration was measured by wound-healing assays. Activation of EGF/EGFR signalling pathways were evaluated by immunofluorescence, qPCR, Western blotting and zymography techniques. Rac1 activity was assessed by pull-down assay. Correlation of MICAL2 and EGFR in breast cancer specimens was examined by immunohistochemical analysis.

RESULTS

Ectopic expression of MICAL2 in MCF-7 cells augmented EGFR protein level, accompanied by the promotion of cell migration. Silencing MICAL2 in MDA-MB-231 cells destabilized EGFR and inhibited cell migration. In mechanism, the maintaining effect of MICAL2 on EGFR protein content was due to a delay in EGFR degradation. Expression of MICAL2 was also shown positively correlated with the activation of P38/HSP27 and P38/MMP9 signallings, which are the main downstream signalling cascades of EGF/EGFR involved in cell migration. Further analysis indicated that Rac1 activation contributed to the maintaining effect of MICAL2 on EGFR stability. In addition, analysis of breast cancer specimens revealed a positive correlation between MICAL2 and EGFR levels and an association between MICAL2 expression and worse prognosis.

CONCLUSION

MICAL2 is a major regulator of breast cancer cell migration, maintaining EGFR stability and subsequent EGFR/P38 signalling activation through inhibiting EGFR degradation in a Rac1-dependent manner.

Gli is activated and promotes epithelial-mesenchymal transition in human esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) accounts for the most esophageal cancer cases in the US, and is notoriously aggressive. This study examines the role of Sonic Hedgehog (SHh)/Gli signaling in the regulation of epithelial-mesenchymal transition (EMT), a process tied to invasion and metastasis, in EAC. Gli/EMT protein expression levels were examined by western blot in paired EAC patient tissues (n = 24) and cell lines (OE19, OE33). Functional analyses were performed (siRNA, treatment with Gli-inhibitor, AKT-inhibitor, and N-Shh recombinant proteins) to investigate SHh/Gli signaling and EMT, cell cycle, and prognostic markers in EAC cell lines. MTS, luciferase reporter, qRT-PCR, western blot, wound healing, and transwell assays were executed to analyze pathway activity, cell migration, and invasion. Aberrant Gli1/2 expression was found in EAC patient tissues, and was significantly associated with increased EMT and AKT pathway activity. Stimulation of SHh/Gli resulted in EMT signaling, including expression of E-cadherin, N-cadherin, Vimentin, β-catenin, Snail, and Slug, as well as cell cycle progression at mRNA and protein levels in EAC cell lines. Gli inhibition via small molecule administration and siRNA significantly reduced EMT, decreasing cell mobility and invasion. Both Gli and AKT inhibition rescued E-cadherin expression and suppressed AKT phosphorylation. This study provides evidence for a strong association between aberrant Gli1/2 expression and AKT/EMT markers in EAC; activated SHh/Gli signaling may be a critical component in promoting cell survival, metastases, and resistance to chemotherapy, and represents a promising avenue to target tumor proliferation and mobility.

Quantitative comparison of the spreading and invasion of radial growth phase and metastatic melanoma cells in a three-dimensional human skin equivalent model

BACKGROUND

Standard two-dimensional (2D) cell migration assays do not provide information about vertical invasion processes, which are critical for melanoma progression. We provide information about three-dimensional (3D) melanoma cell migration, proliferation and invasion in a 3D melanoma skin equivalent (MSE) model. In particular, we pay careful attention to compare the structure of the tissues in the MSE with similarly-prepared 3D human skin equivalent (HSE) models. The HSE model is identically prepared to the MSE model except that melanoma cells are omitted. Using the MSE model, we examine melanoma migration, proliferation and invasion from two different human melanoma cell lines. One cell line, WM35, is associated with the early phase of the disease where spreading is thought to be confined to the epidermis. The other cell line, SK-MEL-28, is associated with the later phase of the disease where spreading into the dermis is expected.

METHODS

3D MSE and HSE models are constructed using human de-epidermised dermis (DED) prepared from skin tissue. Primary fibroblasts and primary keratinocytes are used in the MSE and HSE models to ensure the formation of a stratified epidermis, with a well-defined basement membrane. Radial spreading of cells across the surface of the HSE and MSE models is observed. Vertical invasion of melanoma cells downward through the skin is observed and measured using immunohistochemistry. All measurements of invasion are made at day 0, 9, 15 and 20, providing detailed time course data.

RESULTS

Both HSE and MSE models are similar to native skin in vivo, with a well-defined stratification of the epidermis that is separated from the dermis by a basement membrane. In the HSE and MSE we find fibroblast cells confined to the dermis, and differentiated keratinocytes in the epidermis. In the MSE, melanoma cells form colonies in the epidermis during the early part of the experiment. In the later stage of the experiment, the melanoma cells in the MSE invade deeper into the tissues. Interestingly, both the WM35 and SK-MEL-28 melanoma cells lead to a breakdown of the basement membrane and eventually enter the dermis. However, these two cell lines invade at different rates, with the SK-MEL-28 melanoma cells invading faster than the WM35 cells.

DISCUSSION

The MSE and HSE models are a reliable platform for studying melanoma invasion in a 3D tissue that is similar to native human skin. Interestingly, we find that the WM35 cell line, that is thought to be associated with radial spreading only, is able to invade into the dermis. The vertical invasion of melanoma cells into the dermal region appears to be associated with a localised disruption of the basement membrane. Presenting our results in terms of time course data, along with images and quantitative measurements of the depth of invasion extends previous 3D work that has often been reported without these details.

Combined effects of EGFR and hedgehog signaling blockade on inhibition of head and neck squamous cell carcinoma

Head and neck cancer, the sixth most common cancer, has poor prognosis and short survival. Anti-epidermal growth factor receptor (EGFR) therapies have been recently developed for the treatment of multiple cancer types. JK184, an inhibitor of Hedgehog pathway, prevents the growth of many tumor cell lines in several studies. Whether it enhances chemosensitivity to block EGFR expression by shEGFR plasmid and blocks the Hedgehog pathway by JK184 remains unclear in sinonasal tumors. The changes in cell apoptosis and proteins have been detected by flow cytometry and Western blotting, respectively. In vivo, the maxillary sinus model was established to detect the inhibition of tumor growth and tumor weight. A synergistic effect has been observed with JK184 combined with shEGFR, which is positively correlated with increased autophagy. The maxillary sinus model results demonstrated that the inhibitory rate of the combined therapy was higher than that of JK184 or shEGFR alone. Our findings suggest that JK184 in combination with shEGFR might have potential as a new therapeutic regimen against sinonasal tumors.

Cancer metastasis through the prism of epithelial-to-mesenchymal transition in circulating tumor cells

Metastasis of epithelial cancer cells to distant sites is a particularly critical stage of cancer progression that typically marks the incurability of the disease. It is governed by a complex series of events including invasion and intravasation of tumor cells into the stroma and blood, respectively. Epithelial-to-mesenchymal transition (EMT), a phenotypic change marked by the loss of epithelial characteristics and the acquisition of invasive mesenchymal properties, is implicated in the dissemination of tumor cells. Circulating tumor cells (CTCs), the precursors of metastasis, can be used to interrogate the contribution of EMT in metastasis and therapeutic responses. The analysis of these CTCs and in particular the presence of inter- and intrapatient heterogeneity for markers of EMT has provided new insights into the metastatic process. This review will focus on epithelial-mesenchymal plasticity in CTCs and its potential clinical implications.