An epigenetic switch induced by Shh signalling regulates gene activation during development and medulloblastoma growth

Cerebellar heterotopia in an 11-year-old child with KDM6B-related neurodevelopmental disorder: A case report and review of the literature

Heterozygous pathogenic variants in KDM6B have recently been associated to a rare neurodevelopmental disorder referred to as "Neurodevelopmental disorder with coarse facies and mild distal skeletal abnormalities" and characterized by non-pathognomonic facial and body dysmorphisms, a wide range of neurodevelopmental and behavioral disorders and nonspecific neuroradiological findings. KDM6B encodes a histone demethylase, expressed in different tissues during development, which regulates gene expression through the modulation of chromatin accessibility by RNA polymerase. We herein describe a 11-year-old male patient carrying a novel de novo pathogenic variant in KDM6B exhibiting facial dysmorphisms, dysgraphia, behavioral traits relatable to oppositional defiant, autism spectrum, and attention deficit hyperactivity disorders, a single seizure episode, and a neuroimaging finding of a single cerebellar heterotopic nodule, never described to date in this genetic condition. These findings expand the phenotypic spectrum of this syndrome, highlighting the potential role for KDM6B in cerebellar development and providing valuable insights for genetic counseling.

Cancer-specific epigenome identifies oncogenic hijacking by nuclear factor I family proteins for medulloblastoma progression

Normal cells coordinate proliferation and differentiation by precise tuning of gene expression based on the dynamic shifts of the epigenome throughout the developmental timeline. Although non-mutational epigenetic reprogramming is an emerging hallmark of cancer, the epigenomic shifts that occur during the transition from normal to malignant cells remain elusive. Here, we capture the epigenomic changes that occur during tumorigenesis in a prototypic embryonal brain tumor, medulloblastoma. By comparing the epigenomes of the different stages of transforming cells in mice, we identify nuclear factor I family of transcription factors, known to be cell fate determinants in development, as oncogenic regulators in the epigenomes of precancerous and cancerous cells. Furthermore, genetic and pharmacological inhibition of NFIB validated a crucial role of this transcription factor by disrupting the cancer epigenome in medulloblastoma. Thus, this study exemplifies how epigenomic changes contribute to tumorigenesis via non-mutational mechanisms involving developmental transcription factors.

Specification of human regional brain lineages using orthogonal gradients of WNT and SHH in organoids

The repertory of neurons generated by progenitor cells depends on their location along antero-posterior and dorso-ventral axes of the neural tube. To understand if recreating those axes was sufficient to specify human brain neuronal diversity, we designed a mesofluidic device termed Duo-MAPS to expose induced pluripotent stem cells (iPSC) to concomitant orthogonal gradients of a posteriorizing and a ventralizing morphogen, activating WNT and SHH signaling, respectively. Comparison of single cell transcriptomes with fetal human brain revealed that Duo-MAPS-patterned organoids generated the major neuronal lineages of the forebrain, midbrain, and hindbrain. Morphogens crosstalk translated into early patterns of gene expression programs predicting the generation of specific brain lineages. Human iPSC lines from six different genetic backgrounds showed substantial differences in response to morphogens, suggesting that interindividual genomic and epigenomic variations could impact brain lineages formation. Morphogen gradients promise to be a key approach to model the brain in its entirety.

Neuroblastoma and its Target Therapies: A Medicinal Chemistry Review

Neuroblastoma (NB) is a childhood malignant tumour belonging to a group of embryonic tumours originating from progenitor cells of the sympathoadrenal lineage. The heterogeneity of NB is reflected in the survival rates of those with low and intermediate risk diseases who have survival rates ranging from 85 to 90 %. However, for those identified with high-risk Stage 4 NB, the treatment options are much more limited. For this group, current treatment consists of immunotherapy (monoclonal antibodies) in combination with anti-cancer drugs and has a 40 to 50 % survival rate. The purpose of this review is to summarise NB research from a medicinal chemistry perspective and to highlight advances in targeted drug therapy in the field. The review examines the medicinal chemistry of a number of drugs tested in research, some of which are currently under clinical trial. It concludes by proposing that future medicinal chemistry research into NB should consider other possible target therapies and adopt a multi-target drug approach rather than a one-drug-one-target approach for improved efficacy and less drug-drug interaction for the treatment of NB Stage 4 (NBS4) patients.

Therapeutic potential of hedgehog signaling in advanced cancer types

In this chapter, we have made an attempt to elucidate the relevance of hedgehog signaling pathway in tumorigenesis. Here, we have described different types of hedgehog signaling (canonical and non-canonical) with emphasis on the different mechanisms (mutation-driven, autocrine, paracrine and reverse paracrine) it adopts during tumorigenesis. We have discussed the role of hedgehog signaling in regulating cell proliferation, invasion and epithelial-to-mesenchymal transition in both local and advanced cancer types, as reported in different studies based on preclinical and clinical models. We have specifically addressed the role of hedgehog signaling in aggressive neuroendocrine tumors as well. We have also elaborated on the studies showing therapeutic relevance of the inhibitors of hedgehog signaling in cancer. Evidence of the crosstalk of hedgehog signaling components with other signaling pathways and treatment resistance due to tumor heterogeneity have also been briefly discussed. Together, we have tried to put forward a compilation of the studies on therapeutic potential of hedgehog signaling in various cancers, specifically aggressive tumor types with a perspective into what is lacking and demands further investigation.

Compartments in medulloblastoma with extensive nodularity are connected through differentiation along the granular precursor lineage

Medulloblastomas with extensive nodularity are cerebellar tumors characterized by two distinct compartments and variable disease progression. The mechanisms governing the balance between proliferation and differentiation in MBEN remain poorly understood. Here, we employ a multi-modal single cell transcriptome analysis to dissect this process. In the internodular compartment, we identify proliferating cerebellar granular neuronal precursor-like malignant cells, along with stromal, vascular, and immune cells. In contrast, the nodular compartment comprises postmitotic, neuronally differentiated malignant cells. Both compartments are connected through an intermediate cell stage resembling actively migrating CGNPs. Notably, we also discover astrocytic-like malignant cells, found in proximity to migrating and differentiated cells at the transition zone between the two compartments. Our study sheds light on the spatial tissue organization and its link to the developmental trajectory, resulting in a more benign tumor phenotype. This integrative approach holds promise to explore intercompartmental interactions in other cancers with varying histology.

The BAF chromatin complex component SMARCC1 does not mediate GLI transcriptional repression of Hedgehog target genes in limb buds

Transcriptional responses to the Hedgehog (HH) signaling pathway are primarily modulated by GLI repression in the mouse limb. Previous studies suggested a role for the BAF chromatin remodeling complex in mediating GLI repression. Consistent with this possibility, the core BAF complex protein SMARCC1 is present at most active limb enhancers including the majority of GLI enhancers. However, in contrast to GLI repression which reduces chromatin accessibility, SMARCC1 maintains chromatin accessibility at most enhancers, including those bound by GLI. Moreover, SMARCC1 binding at GLI-regulated enhancers occurs independently of GLI3. Consistent with previous studies, some individual GLI target genes are mis-regulated in Smarcc1 conditional knockouts, though most GLI target genes are unaffected. Moreover, SMARCC1 is not necessary for mediating constitutive GLI repression in HH mutant limb buds. We conclude that SMARCC1 does not mediate GLI3 repression, which we propose utilizes alternative chromatin remodeling complexes.

Inhibition of Ezh2 redistributes bivalent domains within transcriptional regulators associated with WNT and Hedgehog pathways in osteoblasts

Bivalent epigenomic regulatory domains containing both activating histone 3 lysine 4 (H3K4me3) and repressive lysine 27 (H3K27me3) trimethylation are associated with key developmental genes. These bivalent domains repress transcription in the absence of differentiation signals but maintain regulatory genes in a poised state to allow for timely activation. Previous studies demonstrated that enhancer of zeste homolog 2 (Ezh2), a histone 3 lysine 27 (H3K27) methyltransferase, suppresses osteogenic differentiation and that inhibition of Ezh2 enhances commitment of osteoblast progenitors in vitro and bone formation in vivo. Here, we examined the mechanistic effects of Tazemetostat (EPZ6438), an Food and Drug Administration approved Ezh2 inhibitor for epithelioid sarcoma treatment, because this drug could potentially be repurposed to stimulate osteogenesis for clinical indications. We find that Tazemetostat reduces H3K27me3 marks in bivalent domains in enhancers required for bone formation and stimulates maturation of MC3T3 preosteoblasts. Furthermore, Tazemetostat activates bivalent genes associated with the Wingless/integrated (WNT), adenylyl cyclase (cAMP), and Hedgehog (Hh) signaling pathways based on transcriptomic (RNA-seq) and epigenomic (chromatin immunoprecipitation [ChIP]-seq) data. Functional analyses using selective pathway inhibitors and silencing RNAs demonstrate that the WNT and Hh pathways modulate osteogenic differentiation after Ezh2 inhibition. Strikingly, we show that loss of the Hh-responsive transcriptional regulator Gli1, but not Gli2, synergizes with Tazemetostat to accelerate osteoblast differentiation. These studies establish epigenetic cooperativity of Ezh2, Hh-Gli1 signaling, and bivalent regulatory genes in suppressing osteogenesis. Our findings may have important translational ramifications for anabolic applications requiring bone mass accrual and/or reversal of bone loss.

Epigenetic control of cell signalling in cancer stem cells

The self-renewing cancer stem cells (CSCs) represent one of the distinct cell populations occurring in a tumour that can differentiate into multiple lineages. This group of sparsely abundant cells play a vital role in tumour survival and resistance to different treatments during cancer. The lack of exclusive markers associated with CSCs makes diagnosis and prognosis in cancer patients extremely difficult. This calls for the identification of unique regulators and markers for CSCs. Various signalling pathways like the Wnt/β-catenin pathway, Hedgehog pathway, Notch pathway, and TGFβ/BMP play a major role in the regulation and maintenance of CSCs. Epigenetic regulatory mechanisms add another layer of complexity to control these signalling pathways. In this chapter, we discuss about the role of epigenetic mechanisms in regulating the cellular signalling pathways in CSCs. The epigenetic regulatory mechanisms such as DNA methylation, histone modification and microRNAs can modulate the diverse effectors of signalling pathways and consequently the growth, differentiation and tumorigenicity of CSCs. In the end, we briefly discuss the therapeutic potential of targeting these epigenetic regulators and their target genes in CSCs.

Devo-Aging: Intersections Between Development and Aging

There are two fundamental questions in developmental biology. How does a single fertilized cell give rise to a whole body? and how does this body later produce progeny? Synchronization of these embryonic and postembryonic developments ensures continuity of life from one generation to the next. An enormous amount of work has been done to unravel the molecular mechanisms behind these processes, but more recently, modern developmental biology has been expanded to study development in wider contexts, including regeneration, environment, disease, and even aging. However, we have just started to understand how the mechanisms that govern development also regulate aging. This review discusses examples of signaling pathways involved in development to elucidate how their regulation influences healthspan and lifespan. Therefore, a better knowledge of developmental signaling pathways stresses the possibility of using them as innovative biomarkers and targets for aging and age-related diseases.

The BAF chromatin complex component SMARCC1 does not mediate GLI transcriptional repression of Hedgehog target genes in limb buds

Transcriptional responses to the Hedgehog (HH) signaling pathway are primarily modulated by GLI repression in the mouse limb. Previous studies suggested a role for the BAF chromatin remodeling complex in mediating GLI repression. Consistent with this possibility, the core BAF complex protein SMARCC1 is present at most active limb enhancers including the majority of GLI enhancers. However, in contrast to GLI repression which reduces chromatin accessibility, SMARCC1 maintains chromatin accessibility at most enhancers, including those bound by GLI. Moreover, SMARCC1 binding at GLI-regulated enhancers occurs independently of GLI3. Consistent with previous studies, some individual GLI target genes are mis-regulated in Smarcc1 conditional knockouts, though most GLI target genes are unaffected. Moreover, SMARCC1 is not necessary for mediating constitutive GLI repression in HH mutant limb buds. We conclude that SMARCC1 does not mediate GLI3 repression, which we propose utilizes alternative chromatin remodeling complexes.

Hedgehog pathway orchestrates the interplay of histone modifications and tailors combination epigenetic therapies in breast cancer

Epigenetic therapies that cause genome-wide epigenetic alterations, could trigger local interplay between different histone marks, leading to a switch of transcriptional outcome and therapeutic responses of epigenetic treatment. However, in human cancers with diverse oncogenic activation, how oncogenic pathways cooperate with epigenetic modifiers to regulate the histone mark interplay is poorly understood. We herein discover that the hedgehog (Hh) pathway reprograms the histone methylation landscape in breast cancer, especially in triple-negative breast cancer (TNBC). This facilitates the histone acetylation caused by histone deacetylase (HDAC) inhibitors and gives rise to new therapeutic vulnerability of combination therapies. Specifically, overexpression of zinc finger protein of the cerebellum 1 (ZIC1) in breast cancer promotes Hh activation, facilitating the switch of H3K27 methylation (H3K27me) to acetylation (H3K27ac). The mutually exclusive relationship of H3K27me and H3K27ac allows their functional interplay at oncogenic gene locus and switches therapeutic outcomes. Using multiple in vivo breast cancer models including patient-derived TNBC xenograft, we show that Hh signaling-orchestrated H3K27me and H3K27ac interplay tailors combination epigenetic drugs in treating breast cancer. Together, this study reveals the new role of Hh signaling-regulated histone modifications interplay in responding to HDAC inhibitors and suggests new epigenetically-targeted therapeutic solutions for treating TNBC.

PRC2 disruption in cerebellar progenitors produces cerebellar hypoplasia and aberrant myoid differentiation without blocking medulloblastoma growth

We show that Polycomb Repressive Complex-2 (PRC2) components EED and EZH2 maintain neural identity in cerebellar granule neuron progenitors (CGNPs) and SHH-driven medulloblastoma, a cancer of CGNPs. Proliferating CGNPs and medulloblastoma cells inherit neural fate commitment through epigenetic mechanisms. The PRC2 is an epigenetic regulator that has been proposed as a therapeutic target in medulloblastoma. To define PRC2 function in cerebellar development and medulloblastoma, we conditionally deleted PRC2 components Eed or Ezh2 in CGNPs and analyzed medulloblastomas induced in Eed-deleted and Ezh2-deleted CGNPs by expressing SmoM2, an oncogenic allele of Smo. Eed deletion destabilized the PRC2, depleting EED and EZH2 proteins, while Ezh2 deletion did not deplete EED. Eed-deleted cerebella were hypoplastic, with reduced proliferation, increased apoptosis, and inappropriate muscle-like differentiation. Ezh2-deleted cerebella showed similar, milder phenotypes, with fewer muscle-like cells and without reduced growth. Eed-deleted and Ezh2-deleted medulloblastomas both demonstrated myoid differentiation and progressed more rapidly than PRC2-intact controls. The PRC2 thus maintains neural commitment in CGNPs and medulloblastoma, but is not required for SHH medulloblastoma progression. Our data define a role for the PRC2 in preventing inappropriate, non-neural fates during postnatal neurogenesis, and caution that targeting the PRC2 in SHH medulloblastoma may not produce durable therapeutic effects.

Advances on Epigenetic Drugs for Pediatric Brain Tumors

Pediatric malignant brain tumors represent the most frequent cause of cancer-related deaths in childhood. The therapeutic scheme of surgery, radiotherapy and chemotherapy has improved patient management, but with minimal progress in patients' prognosis. Emerging molecular targets and mechanisms have revealed novel approaches for pediatric brain tumor therapy, enabling personalized medical treatment. Advances in the field of epigenetic research and their interplay with genetic changes have enriched our knowledge of the molecular heterogeneity of these neoplasms and have revealed important genes that affect crucial signaling pathways involved in tumor progression. The great potential of epigenetic therapy lies mainly in the widespread location and the reversibility of epigenetic alterations, proposing a wide range of targeting options, including the possible combination of chemoand immunotherapy, significantly increasing their efficacy. Epigenetic drugs, including inhibitors of DNA methyltransferases, histone deacetylases and demethylases, are currently being tested in clinical trials on pediatric brain tumors. Additional novel epigenetic drugs include protein and enzyme inhibitors that modulate epigenetic modification pathways, such as Bromodomain and Extraterminal (BET) proteins, Cyclin-Dependent Kinase 9 (CDK9), AXL, Facilitates Chromatin Transcription (FACT), BMI1, and CREB Binding Protein (CBP) inhibitors, which can be used either as standalone or in combination with current treatment approaches. In this review, we discuss recent progress on epigenetic drugs that could possibly be used against the most common malignant tumors of childhood, such as medulloblastomas, high-grade gliomas and ependymomas.

Targeting H3K27me3 demethylase to inhibit Shh signaling and cholesterol metabolism in medulloblastoma growth

Previously we uncovered the epigenetic regulation of medulloblastoma that low levels of H3K27me3 are required for Shh target gene expression and medulloblastoma growth. Since Jmjd3, an H3K27me3 demethylase, is responsible for maintaining low H3K27me3 at Shh target genes, targeting Jmjd3 could be an efficient way to inhibit Shh signaling and medulloblastoma growth. Here we show that the small molecule GSK-J4, an inhibitor of Jmjd3, significantly inhibited the expression of Shh target genes in Shh responsive cell models and primary cerebellar granule neuron precursors. GSK-J4 also significantly reduced the growth of primary Shh medulloblastoma cultures. Treating human medulloblastoma cell line DaoY by GSK-J4 led to cell cycle arrest at G0/G1 phase with decreased cells in S-phase. Tumor cell proliferation was significantly inhibited by GSK-J4 treatment. Gene expression analyses showed that GSK-J4 additionally constrained the expression of key genes in cholesterol biosynthesis. Our results highlight the possibility that targeting H3K27me3 demethylase Jmjd3 with GSK-J4 to inhibit Shh signaling and cholesterol metabolism is a potential application to treat Shh medulloblastoma.

Multiprotein GLI Transcriptional Complexes as Therapeutic Targets in Cancer

The Hedgehog signaling pathway functions in both embryonic development and adult tissue homeostasis. Importantly, its aberrant activation is also implicated in the progression of multiple types of cancer, including basal cell carcinoma and medulloblastoma. GLI transcription factors function as the ultimate effectors of the Hedgehog signaling pathway. Their activity is regulated by this signaling cascade via their mRNA expression, protein stability, subcellular localization, and ultimately their transcriptional activity. Further, GLI proteins are also regulated by a variety of non-canonical mechanisms in addition to the canonical Hedgehog pathway. Recently, with an increased understanding of epigenetic gene regulation, novel transcriptional regulators have been identified that interact with GLI proteins in multi-protein complexes to regulate GLI transcriptional activity. Such complexes have added another layer of complexity to the regulation of GLI proteins. Here, we summarize recent work on the regulation of GLI transcriptional activity by these novel protein complexes and describe their relevance to cancer, as such GLI regulators represent alternative and innovative druggable targets in GLI-dependent cancers.

Hedgehog signaling mechanism and role in cancer

Cell-cell communication through evolutionarily conserved signaling pathways governs embryonic development and adult tissue homeostasis. Deregulation of these signaling pathways has been implicated in a wide range of human diseases including cancer. One such pathway is the Hedgehog (Hh) pathway, which was originally discovered in Drosophila and later found to play a fundamental role in human development and diseases. Abnormal Hh pathway activation is a major driver of basal cell carcinomas (BCC) and medulloblastoma. Hh exerts it biological influence through a largely conserved signal transduction pathway from the activation of the GPCR family transmembrane protein Smoothened (Smo) to the conversion of latent Zn-finger transcription factors Gli/Ci proteins from their repressor (GliR/CiR) to activator (GliA/CiA) forms. Studies from model organisms and human patients have provided deep insight into the Hh signal transduction mechanisms, revealed roles of Hh signaling in a wide range of human cancers, and suggested multiple strategies for targeting this pathway in cancer treatment.

Hedgehog signaling activates a mammalian heterochronic gene regulatory network controlling differentiation timing across lineages

Many developmental signaling pathways have been implicated in lineage-specific differentiation; however, mechanisms that explicitly control differentiation timing remain poorly defined in mammals. We report that murine Hedgehog signaling is a heterochronic pathway that determines the timing of progenitor differentiation. Hedgehog activity was necessary to prevent premature differentiation of second heart field (SHF) cardiac progenitors in mouse embryos, and the Hedgehog transcription factor GLI1 was sufficient to delay differentiation of cardiac progenitors in vitro. GLI1 directly activated a de novo progenitor-specific network in vitro, akin to that of SHF progenitors in vivo, which prevented the onset of the cardiac differentiation program. A Hedgehog signaling-dependent active-to-repressive GLI transition functioned as a differentiation timer, restricting the progenitor network to the SHF. GLI1 expression was associated with progenitor status across germ layers, and it delayed the differentiation of neural progenitors in vitro, suggesting a broad role for Hedgehog signaling as a heterochronic pathway.

PRC2 Heterogeneity Drives Tumor Growth in Medulloblastoma

Intratumor epigenetic heterogeneity is emerging as a key mechanism underlying tumor evolution and drug resistance. Epigenetic abnormalities frequently occur in medulloblastoma, the most common childhood malignant brain tumor. Medulloblastoma is classified into four subtypes including SHH medulloblastoma, which is characterized by elevated sonic hedgehog (SHH) signaling and a cerebellum granule neuron precursor (CGNP) cell-of-origin. Here, we report that the histone H3K27 methyltransferase polycomb repressor complex 2 (PRC2) is often heterogeneous within individual SHH medulloblastoma tumors. In mouse models, complete deletion of the PRC2 core subunit EED inhibited medulloblastoma growth, while a mosaic deletion of EED significantly enhanced tumor growth. EED is intrinsically required for CGNP maintenance by inhibiting both neural differentiation and cell death. Complete deletion of EED led to CGNP depletion and reduced occurrence of medulloblastoma. Surprisingly, medulloblastomas with mosaic EED levels grew faster than control wild-type tumors and expressed increased levels of oncogenes such as Igf2, which is directly repressed by PRC2 and has been demonstrated to be both necessary and sufficient for SHH medulloblastoma progression. Insulin-like growth factor 2 (IGF2) mediated the oncogenic effects of PRC2 heterogeneity in tumor growth. Assessing clones of a human medulloblastoma cell line with different EED levels confirmed that EEDlow cells can stimulate the growth of EEDhigh cells through paracrine IGF2 signaling. Thus, PRC2 heterogeneity plays an oncogenic role in medulloblastoma through both intrinsic growth competence and non-cell autonomous mechanisms in distinct tumor subclones.

SIGNIFICANCE

The identification of an oncogenic function of PRC2 heterogeneity in medulloblastoma provides insights into subclone competition and cooperation during heterogeneous tumor evolution.

A Pan-Cancer Analysis Revealing the Dual Roles of Lysine (K)-Specific Demethylase 6B in Tumorigenesis and Immunity

Introduction: Epigenetic-targeted therapy has been increasingly applied in the treatment of cancers. Lysine (K)-specific demethylase 6B (KDM6B) is an epigenetic enzyme involved in the coordinated control between cellular intrinsic regulators and the tissue microenvironment whereas the pan-cancer analysis of KDM6B remains unavailable.

Methods: The dual role of KDM6B in 33 cancers was investigated based on the GEO (Gene Expression Omnibus) and TCGA (The Cancer Genome Atlas) databases. TIMER2 and GEPIA2 were applied to investigate the KDM6B levels in different subtypes or stages of tumors. Besides, the Human Protein Atlas database allowed us to conduct a pan-cancer study of the KDM6B protein levels. GEPIA2 and Kaplan–Meier plotter were used for the prognosis analysis in different cancers. Characterization of genetic modifications of the KDM6B gene was analyzed by the cBioPortal. DNA methylation levels of different KDM6B probes in different TCGA tumors were analyzed by MEXPRESS. TIMER2 was applied to determine the association of the KDM6B expression and immune infiltration and DNA methyltransferases. Spearman correlation analysis was used to assess the association of the KDM6B expression with TMB (tumor mutation burden) and MSI (microsatellite instability). The KEGG (Kyoto encyclopedia of genes and genomes) pathway analysis and GO (Gene ontology) enrichment analysis were used to further investigate the potential mechanism of KDM6B in tumor pathophysiology.

Results: KDM6B was downregulated in 11 cancer types and upregulated across five types. In KIRC (kidney renal clear cell carcinoma) and OV (ovarian serous cystadenocarcinoma), the KDM6B level was significantly associated with the pathological stage. A high level of KDM6B was related to poor OS (overall survival) outcomes for THCA (thyroid carcinoma), while a low level was correlated with poor OS and DFS (disease-free survival) prognosis of KIRC. The KDM6B expression level was associated with TMB, MSI, and immune cell infiltration, particularly cancer-associated fibroblasts, across various cancer types with different correlations. Furthermore, the enrichment analysis revealed the relationship between H3K4 and H3K27 methylation and KDM6B function.

Conclusion: Dysregulation of the DNA methyltransferase activity and methylation levels of H3K4 and H3K27 may involve in the dual role of KDM6B in tumorigenesis and development. Our study offered a relatively comprehensive understanding of KDM6B’s dual role in cancer development and response to immunotherapy.

Sonic Hedgehog Signaling in Cerebellar Development and Cancer

The sonic hedgehog (SHH) pathway regulates the development of the central nervous system in vertebrates. Aberrant regulation of SHH signaling pathways often causes neurodevelopmental diseases and brain tumors. In the cerebellum, SHH secreted by Purkinje cells is a potent mitogen for granule cell progenitors, which are the most abundant cell type in the mature brain. While a reduction in SHH signaling induces cerebellar structural abnormalities, such as hypoplasia in various genetic disorders, the constitutive activation of SHH signaling often induces medulloblastoma (MB), one of the most common pediatric malignant brain tumors. Based on the existing literature on canonical and non-canonical SHH signaling pathways, emerging basic and clinical studies are exploring novel therapeutic approaches for MB by targeting SHH signaling at distinct molecular levels. In this review, we discuss the present consensus on SHH signaling mechanisms, their roles in cerebellar development and tumorigenesis, and the recent advances in clinical trials for MB.

GLI transcriptional repression is inert prior to Hedgehog pathway activation

The Hedgehog (HH) pathway regulates a spectrum of developmental processes through the transcriptional mediation of GLI proteins. GLI repressors control tissue patterning by preventing sub-threshold activation of HH target genes, presumably even before HH induction, while lack of GLI repression activates most targets. Despite GLI repression being central to HH regulation, it is unknown when it first becomes established in HH-responsive tissues. Here, we investigate whether GLI3 prevents precocious gene expression during limb development. Contrary to current dogma, we find that GLI3 is inert prior to HH signaling. While GLI3 binds to most targets, loss of Gli3 does not increase target gene expression, enhancer acetylation or accessibility, as it does post-HH signaling. Furthermore, GLI repression is established independently of HH signaling, but after its onset. Collectively, these surprising results challenge current GLI pre-patterning models and demonstrate that GLI repression is not a default state for the HH pathway.

GLI repression has been presumed to be the default transcriptional state and important for pre-patterning tissues. Challenging current models, the authors show that GLI3 repression is inert in the limb bud before the onset of Hedgehog signaling.

Pro-angiogenic approach for skeletal muscle regeneration

The angiogenesis process is a phenomenon in which numerous molecules participate in the stimulation of the new vessels' formation from pre-existing vessels. Angiogenesis is a crucial step in tissue regeneration and recovery of organ and tissue function. Muscle diseases affect millions of people worldwide overcome the ability of skeletal muscle to self-repair. Pro-angiogenic therapies are key in skeletal muscle regeneration where both myogenesis and angiogenesis occur. These therapies have been based on mesenchymal stem cells (MSCs), exosomes, microRNAs (miRs) and delivery of biological factors. The use of different calls of biomaterials is another approach, including ceramics, composites, and polymers. Natural polymers are use due its bioactivity and biocompatibility in addition to its use as scaffolds and in drug delivery systems. One of these polymers is the natural rubber latex (NRL) which is biocompatible, bioactive, versatile, low-costing, and capable of promoting tissue regeneration and angiogenesis. In this review, the advances in the field of pro-angiogenic therapies are discussed.

A systematic analysis of genetic interactions and their underlying biology in childhood cancer

Childhood cancer is a major cause of child death in developed countries. Genetic interactions between mutated genes play an important role in cancer development. They can be detected by searching for pairs of mutated genes that co-occur more (or less) often than expected. Co-occurrence suggests a cooperative role in cancer development, while mutual exclusivity points to synthetic lethality, a phenomenon of interest in cancer treatment research. Little is known about genetic interactions in childhood cancer. We apply a statistical pipeline to detect genetic interactions in a combined dataset comprising over 2,500 tumors from 23 cancer types. The resulting genetic interaction map of childhood cancers comprises 15 co-occurring and 27 mutually exclusive candidates. The biological explanation of most candidates points to either tumor subtype, pathway epistasis or cooperation while synthetic lethality plays a much smaller role. Thus, other explanations beyond synthetic lethality should be considered when interpreting genetic interaction test results.

Small Extracellular Vesicles in the Development, Diagnosis, and Possible Therapeutic Application of Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) persists among the most lethal and broad-spreading malignancies in China. The exosome is a kind of extracellular vesicle (EV) from about 30 to 200 nm in diameter, contributing to the transfer of specific functional molecules, such as metabolites, proteins, lipids, and nucleic acids. The paramount role of exosomes in the formation and development of ESCC, which relies on promoting intercellular communication in the tumor microenvironment (TME), is manifested with immense amounts. Tumor-derived exosomes (TDEs) participate in most hallmarks of ESCC, including tumorigenesis, invasion, angiogenesis, immunologic escape, metastasis, radioresistance, and chemoresistance. Published reports have delineated that exosome-encapsulated cargos like miRNAs may have utility in the diagnosis, as prognostic biomarkers, and in the treatment of ESCC. This review summarizes the function of exosomes in the neoplasia, progression, and metastasis of ESCC, which improves our understanding of the etiology and pathogenesis of ESCC, and presents a promising target for early diagnostics in ESCC. However, recent studies of exosomes in the treatment of ESCC are sparse. Thus, we introduce the advances in exosome-based methods and indicate the possible applications for ESCC therapy in the future.

Disruption of rack1 suppresses SHH-type medulloblastoma formation in mice

Introduction

Medulloblastoma (MB) is a malignant pediatric brain tumor that arises in the cerebellar granular neurons. Sonic Hedgehog subtype of MB (SHH‐MB) is one of the major subtypes of MB in the clinic. However, the molecular mechanisms underlying MB tumorigenesis are still not fully understood.

Aims

Our previous work demonstrated that the receptor for activated C kinase 1 (Rack1) is essential for SHH signaling activation in granule neuron progenitors (GNPs) during cerebellar development. To investigate the potential role of Rack1 in MB development, human MB tissue array and SHH‐MB genetic mouse model were used to study the expression of function of Rack1 in MB pathogenesis.

Results

We found that the expression of Rack1 was significantly upregulated in the majority of human cerebellar MB tumors. Genetic ablation of Rack1 expression in SHH‐MB tumor mice could significantly inhibit MB proliferation, reduce the tumor size, and prolong the survival of tumor rescue mice. Interestingly, neither apoptosis nor autophagy levels were affected in Rack1‐deletion rescue mice compared to WT mice, but the expression of Gli1 and HDAC2 was significantly decreased suggesting the inactivation of SHH signaling pathway in rescue mice.

Conclusion

Our results demonstrated that Rack1 may serve as a potential candidate for the diagnostic marker and therapeutic target of MB, including SHH‐MB.

Epigenetic Control of Autophagy Related Genes Transcription in Pulpitis via JMJD3

Autophagy is an intracellular self-cannibalization process delivering cytoplasmic components to lysosomes for digestion. Autophagy has been reported to be involved in pulpitis, but the regulation of autophagy during pulpitis progression is largely unknown. To figure out the epigenetic regulation of autophagy during pulpitis, we screened several groups of histone methyltransferases and demethylases in response to TNFα treatment. It was found JMJD3, a histone demethylase reducing di- and tri-methylation of H3K27, regulated the expression of several key autophagy genes via demethylation of H3K27me3 at the gene promoters. Our study highlighted the epigenetic regulation of autophagy genes during pulpitis, which will potentially provide a novel therapeutic strategy.

KDM6B promotes ESCC cell proliferation and metastasis by facilitating C/EBPβ transcription

Background

As an H3K27me3 demethylase and counteracts polycomb-mediated transcription repression, KDM6B has been implicated in the development and malignant progression in various types of cancers. However, its potential roles in esophageal squamous cell carcinoma (ESCC) have not been explored.

Methods

The expression of KDM6B in human ESCC tissues and cell lines was examined using RT-qPCR, immunohistochemical staining and immunoblotting. The effects of KDM6B on the proliferation and metastasis of ESCC were examined using in vitro and in vivo functional tests. RNA-seq and ChIP-seq assay were used to demonstrate the molecular biological mechanism of KDM6B in ESCC.

Results

We show that the expression level of KDM6B increased significantly in patients with lymph node metastasis. Furthermore, we confirmed that KDM6B knockdown reduces proliferation and metastasis of ESCC cells, while KDM6B overexpression has the opposite effects. Mechanistically, KDM6B regulates TNFA_SIGNALING_VIA_NFκB signalling pathways, and H3K27me3 binds to the promoter region of C/EBPβ, leading to the promotion of C/EBPβ transcription. Besides, we show that GSK-J4, a chemical inhibitor of KDM6B, markedly inhibits proliferation and metastasis of ESCC cells.

Conclusions

The present study demonstrated that KDM6B promotes ESCC progression by increasing the transcriptional activity of C/EBPβ depending on its H3K27 demethylase activity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08282-w.

The Functions of the Demethylase JMJD3 in Cancer

Cancer is a major cause of death worldwide. Epigenetic changes in response to external (diet, sports activities, etc.) and internal events are increasingly implicated in tumor initiation and progression. In this review, we focused on post-translational changes in histones and, more particularly, the tri methylation of lysine from histone 3 (H3K27me3) mark, a repressive epigenetic mark often under- or overexpressed in a wide range of cancers. Two actors regulate H3K27 methylation: Jumonji Domain-Containing Protein 3 demethylase (JMJD3) and Enhancer of zeste homolog 2 (EZH2) methyltransferase. A number of studies have highlighted the deregulation of these actors, which is why this scientific review will focus on the role of JMJD3 and, consequently, H3K27me3 in cancer development. Data on JMJD3’s involvement in cancer are classified by cancer type: nervous system, prostate, blood, colorectal, breast, lung, liver, ovarian, and gastric cancers.

Histone demethylase UTX/KDM6A enhances tumor immune cell recruitment, promotes differentiation and suppresses medulloblastoma

The deregulation of epigenetic pathways has been implicated as a critical step in tumorigenesis including in childhood brain tumor medulloblastoma. The H3K27me3 demethylase UTX/KDM6A plays important roles in development and is frequently mutated in various types of cancer. However, how UTX regulates tumor development remains largely unclear. Here, we report the generation of a UTX-deleted mouse model of SHH medulloblastoma that demonstrates the tumor suppressor functions of UTX, which could be antagonized by the deletion of another H3K27me3 demethylase JMJD3/KDM6B. Intriguingly, UTX deletion in cancerous cerebellar granule neuron precursors (CGNPs) resulted in the impaired recruitment of host CD8⁺ T cells to the tumor microenvironment through a non-cell autonomous mechanism. In both mouse medulloblastoma models and in human medulloblastoma cells, we showed that UTX activates Th1-type chemokines, which are responsible for T cell migration. Surprisingly, our results showed that the depletion of cytotoxic CD8⁺ T cells did not affect mouse medulloblastoma growth. Nevertheless, the UTX/chemokine/T cell recruitment pathway we identified may be applied to many other cancers and may be important for improving cancer immunotherapy. In addition, UTX is required for the expression of NeuroD2 in precancerous progenitors, which encodes a potent proneural transcription factor. Overexpression of NEUROD2 in CGNPs decreased cell proliferation and increased neuron differentiation. We showed that UTX deletion led to impaired neural differentiation, which could coordinate with active SHH signaling to accelerate medulloblastoma development. Thus, UTX regulates both cell-intrinsic oncogenic processes and the tumor microenvironment in medulloblastoma. Our study provides insights into both medulloblastoma development and context dependent functions of UTX in tumorigenesis.

A large-scale drug screen identifies selective inhibitors of class I HDACs as a potential therapeutic option for SHH medulloblastoma

BACKGROUND

Medulloblastoma (MB) is one of the most frequent malignant brain tumors of children, and a large set of these tumors is characterized by aberrant activation of the sonic hedgehog (SHH) pathway. While some tumors initially respond to inhibition of the SHH pathway component Smoothened (SMO), tumors ultimately recur due to downstream resistance mechanisms, indicating a need for novel therapeutic options.

METHODS

Here we performed a targeted small-molecule screen on a stable, SHH-dependent murine MB cell line (SMB21). Comprehensive isotype profiling of histone deacetylase (HDAC) inhibitors was performed, and effects of HDAC inhibition were evaluated in cell lines both sensitive and resistant to SMO inhibition. Lastly, distinct mouse models of SHH MB were used to demonstrate pharmacologic efficacy in vivo.

RESULTS

A subset of the HDAC inhibitors tested significantly inhibit tumor growth of SMB21 cells by preventing SHH pathway activation. Isotype profiling of HDAC inhibitors, together with genetic approaches suggested that concerted inhibition of multiple class I HDACs is necessary to achieve pathway inhibition. Of note, class I HDAC inhibitors were also efficacious in suppressing growth of diverse SMO inhibitor‒resistant clones of SMB21 cells. Finally, we show that the novel HDAC inhibitor quisinostat targets multiple class I HDACs, is well tolerated in mouse models, and robustly inhibits growth of SHH MB cells in vivo as well as in vitro.

CONCLUSIONS

Our data provide strong evidence that quisinostat or other class I HDAC inhibitors might be therapeutically useful for patients with SHH MB, including those resistant to SMO inhibition.

Cancer Stem Cells Equipped with Powerful Hedgehog Signaling and Better Epigenetic Memory: Avenues to Look for Cancer Therapeutics

Complex nature of the tumor is depicted at the cellular landscape by showing heterogeneity in the presence of cancer cells, cancer-associated stromal cells, mesenchymal stem cells and cancer stem cells (CSCs). One of the plausible views in cancer formation is suggested as the theory of cancer CSCs that is known as a source of initiation of tumorigenesis. In essence, these powerful CSCs are equipped with high Sonic Hedgehog (SHH) signaling and epigenetic memory power that support various tumor hallmarks. Truly, nature justifies its intent by limiting these stem cells with a potential to turn into CSCs and in turn suppressing the high risk of humans and other organisms. In short, this mini-review addresses the contribution of SHH signaling to allow reprogramming of epigenetic memory within CSCs that support tumor hallmarks. Besides, this paper explores therapeutic approaches to mitigate SHH signaling that may lead to a blockade of the pro-tumor potential of CSCs.

Medulloblastoma epigenetics and the path to clinical innovation

INTRODUCTION

In the last decade, a number of genomic and pharmacological studies have demonstrated the importance of epigenetic dysregulation in medulloblastoma initiation and progression. High throughput approaches including gene expression array, next-generation sequencing (NGS), and methylation profiling have now clearly identified at least four molecular subgroups within medulloblastoma, each with distinct clinical and prognostic characteristics. These studies have clearly shown that despite the overall paucity of mutations, clinically relevant events do occur within the cellular epigenetic machinery. Thus, this review aims to provide an overview of our current understanding of the spectrum of epi-oncogenetic perturbations in medulloblastoma.

METHODS

Comprehensive review of epigenetic profiles of different subgroups of medulloblastoma in the context of molecular features. Epigenetic regulation is mediated mainly by DNA methylation, histone modifications and microRNAs (miRNA). Importantly, epigenetic mis-events are reversible and have immense therapeutic potential.

CONCLUSION

The widespread epigenetic alterations present in these tumors has generated intense interest in their use as therapeutic targets. We provide an assessment of the progress that has been made towards the development of molecular subtypes-targeted therapies and the current status of clinical trials that have leveraged these recent advances.

RNF220 is required for cerebellum development and regulates medulloblastoma progression through epigenetic modulation of Shh signaling

Sonic hedgehog (Shh) signaling is essential for proliferation of cerebellar granule neuron progenitors (CGNPs) and its mis-regulation is linked to various disorders, including the cerebellar cancer medulloblastoma (MB). We recently identified RNF220, a ubiquitin E3 ligase promoting K63-linked polyubiquitylation and nuclear exportation of Gli transcription factors, as an Shh/Gli regulator involved in ventral neural patterning. Here, we report that RNF220 is required for the proliferation of CGNPs and Daoy cells (an Shh-grouped MB cell line), working as a positive regulator of Shh signaling. Mechanistic investigation demonstrated that RNF220 promotes Shh target gene expression by targeting the PRC2 component EED, and alters levels of epigenetic modification marks on Shh target promoters. We provided evidence that RNF220^+/-; Ptch1^+/- mice showed lower spontaneous MB occurrence compared with Ptch1^+/- mice. Furthermore, in human clinical MB samples, RNF220 expression correlated well with that of GAB1, an Shh-group MB marker. Our findings provide new insights into the epigenetic regulation of Shh signaling and identify RNF220 as a potential new diagnostic marker and therapeutic target for Shh-group MB.

Transient Primary Cilia Mediate Robust Hedgehog Pathway-Dependent Cell Cycle Control

The regulation of proliferation is a primary function of Hedgehog (Hh) signaling in development. Hh signal transduction requires the primary cilium for several steps in the pathway [1-5]. Many cells only build a primary cilium upon cell cycle exit, in G0. In those proliferating cells that do make a cilium, it is a transient organelle, being assembled in G1 and disassembled sometime prior to mitosis [6-9]. Thus, the requirement for primary cilia presents a conundrum: how are proliferative signals conveyed through an organelle that is present for only part of the cell cycle? Here, we investigate this question in a mouse medulloblastoma cell line, SMB55, that requires cilium-mediated Hh pathway activity for proliferation [10]. We show that SMB55 cells, and the primary cerebellar granule neuron precursors (GNPs) from which they derive, are often ciliated beyond G1 into S phase, and the presence of the cilium in SMB55 cells determines the periods of Hh pathway activity. Using live imaging over multiple cell cycles, we demonstrate that Hh pathway activity in either G1-S of the previous cell cycle or G1 of the cell cycle in which the decision is made is sufficient for cell cycle entry. We also show that cyclin D1 contributes to the persistent effects of pathway activity over multiple cell cycles. Together, our results reveal that, even though the signaling organelle itself is transient, Hh pathway control of proliferation is remarkably robust. Further, primary cilium transience may have implications for other Hh-mediated events in development.

GLI transcriptional repression regulates tissue-specific enhancer activity in response to Hedgehog signaling

Transcriptional repression needs to be rapidly reversible during embryonic development. This extends to the Hedgehog pathway, which primarily serves to counter GLI repression by processing GLI proteins into transcriptional activators. In investigating the mechanisms underlying GLI repression, we find that a subset of GLI binding regions, termed HH-responsive enhancers, specifically loses acetylation in the absence of HH signaling. These regions are highly enriched around HH target genes and primarily drive HH-specific transcriptional activity in the mouse limb bud. They also retain H3K27ac enrichment in limb buds devoid of GLI activator and repressor, indicating that their activity is primarily regulated by GLI repression. Furthermore, the Polycomb repression complex is not active at most of these regions, suggesting it is not a major mechanism of GLI repression. We propose a model for tissue-specific enhancer activity in which an HDAC-associated GLI repression complex regulates target genes by altering the acetylation status at enhancers.

Epigenetics and cell cycle regulation in cystogenesis

The role of genetic mutations in the development of polycystic kidney disease (PKD), such as alterations in PKD1 and PKD2 genes in autosomal dominant PKD (ADPKD), is well understood. However, the significance of epigenetic mechanisms in the progression of PKD remains unclear and is increasingly being investigated. The term of epigenetics describes a range of mechanisms in genome function that do not solely result from the DNA sequence itself. Epigenetic information can be inherited during mammalian cell division to sustain phenotype specifically and physiologically responsive gene expression in the progeny cells. A multitude of functional studies of epigenetic modifiers and systematic genome-wide mapping of epigenetic marks reveal the importance of epigenomic mechanisms, including DNA methylation, histone/chromatin modifications and non-coding RNAs, in PKD pathologies. Deregulated proliferation is a characteristic feature of cystic renal epithelial cells. Moreover, defects in many of the molecules that regulate the cell cycle have been implicated in cyst formation and progression. Recent evidence suggests that alterations of DNA methylation and histone modifications on specific genes and the whole genome involved in cell cycle regulation and contribute to the pathogenesis of PKD. This review summarizes the recent advances of epigenetic mechanisms in PKD, which helps us to define the term of "PKD epigenetics" and group PKD epigenetic changes in three categories. In particularly, this review focuses on the interplay of epigenetic mechanisms with cell cycle regulation during normal cell cycle progression and cystic cell proliferation, and discusses the potential to detect and quantify DNA methylation from body fluids as diagnostic/prognostic biomarkers. Collectively, this review provides concepts and examples of epigenetics in cell cycle regulation to reveal a broad view of different aspects of epigenetics in biology and PKD, which may facilitate to identify possible novel therapeutic intervention points and to explore epigenetic biomarkers in PKD.

Rack1 Controls Parallel Fiber-Purkinje Cell Synaptogenesis and Synaptic Transmission

Purkinje cells (PCs) in the cerebellum receive two excitatory afferents including granule cells-derived parallel fiber (PF) and the climbing fiber. Scaffolding protein Rack1 is highly expressed in the cerebellar PCs. Here, we found delayed formation of specific cerebellar vermis lobule and impaired motor coordination in PC-specific Rack1 conditional knockout mice. Our studies further revealed that Rack1 is essential for PF–PC synapse formation. In addition, Rack1 plays a critical role in regulating synaptic plasticity and long-term depression (LTD) induction of PF–PC synapses without changing the expression of postsynaptic proteins. Together, we have discovered Rack1 as the crucial molecule that controls PF–PC synaptogenesis and synaptic plasticity. Our studies provide a novel molecular insight into the mechanisms underlying the neural development and neuroplasticity in the cerebellum.

ASXL1 impairs osteoclast formation by epigenetic regulation of NFATc1

Additional sex comb-like 1 (ASXL1) mutations are commonly associated with myeloid malignancies and are markers of aggressive disease. The fact that ASXL1 is necessary for myeloid differentiation raises the possibility it also regulates osteoclasts. We find deletion of ASXL1 in myeloid cells results in bone loss with increased abundance of osteoclasts. Because ASXL1 is an enhancer of trithorax and polycomb (ETP) protein, we asked if it modulates osteoclast differentiation by maintaining balance between positive and negative epigenetic regulators. In fact, loss of ASXL1 induces concordant loss of inhibitory H3K27me3 with gain of H3K4me3 at key osteoclast differentiation genes, including nuclear factor for activated T cells 1 (NFATc1) and itgb3 In the setting of ASXL1 deficiency, increased NFATc1 binds to the Blimp1 (Prdm1) promoter thereby enhancing expression of this pro-osteoclastogenic gene. The global reduction of K27 trimethylation in ASXL1-deficient osteoclasts is also attended by a 40-fold increase in expression of the histone demethylase Jumonji domain-containing 3 (Jmjd3). Jmjd3 knockdown in ASXL1-deficient osteoclast precursors increases H3K27me3 on the NFATc1 promoter and impairs osteoclast formation. Thus, in addition to promoting myeloid malignancies, ASXL1 controls epigenetic reprogramming of osteoclasts to regulate bone resorption and mass.

Phosphorylation of Ci/Gli by Fused Family Kinases Promotes Hedgehog Signaling

Hedgehog (Hh) signaling culminates in the conversion of the latent transcription factor Cubitus interruptus (Ci)/Gli into its activator form (Ci^A/Gli^A), but the underlying mechanism remains poorly understood. Here, we demonstrate that Hh stimulates the phosphorylation of Ci by the Ser/Thr kinase Fused (Fu) and that Fu-mediated phosphorylation of Ci promotes its activation. We find that Fu directly phosphorylates Ci on Ser218 and Ser1230, which primes its further phosphorylation by CK1 on adjacent sties. These phosphorylation events alter Ci binding to the pathway inhibitor Suppressor of fused (Sufu) and facilitate the recruitment of Transportion and the transcriptional coactivator CBP. Furthermore, we provide evidence that Sonic hedgehog (Shh) activates Gli2 by stimulating its phosphorylation on conserved sites through the Fu-family kinases ULK3 and mFu/STK36 in a manner depending on Gli2 ciliary localization. Hence, Fu-family kinase-mediated phosphorylation of Ci/Gli serves as a conserved mechanism that activates the Hh pathway transcription factor.

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

Hedgehog pathway and smoothened inhibitors in cancer therapies

The hedgehog (Hh) pathway plays an important role in cancer development and maintenance, as ~25% of all cancers have aberrant Hh pathway activation. Targeted therapy for inhibition of the Hh pathway was thought to be promising for achieving clinical response in the Hh-dependent cancers. However, the results of new clinical trials with smoothened (SMO) antagonists do not show much success in cancers other than basal cell carcinoma. The studies suggest that the Hh pathway involves multiple mechanisms of activation or inhibition in primary cilia and interactions between several related pathways in different types of cells, which makes this pathway extremely complex. The SMO-specific antagonists may not stop all relevant pathways that may lead to escape or development of resistance. Therefore, in the Hh-dependent cancers, the inhibition of two or more oncogenic pathways (including the Hh pathway) with use of a single agent of a suitable multitarget profile or a combination of drugs seems promising for achieving clinical response in patients and decrease in resistance development with prolonged use of the specific SMO antagonists. Furthermore, for studying the effect of new treatments, the inclusion criteria should be more specific for selection of patients with aberrant Hh pathway activity confirmed by tests. These considerations will be very helpful for choosing the right patients and the right drugs for the best therapeutic outcome.

Hedgehog signaling inhibitors in solid and hematological cancers

BACKGROUND

The hedgehog signaling pathway is normally tightly regulated. Mutations in hedgehog pathway components may lead to abnormal activation. Aberrantly activated hedgehog signaling plays a major role in the development of solid and hematological cancer. In recent years, inhibitors have been developed that attenuate hedgehog signaling; 2 have been approved for use in basal cell carcinoma (BCC), while others are under development or in clinical trials. The aim of this review is to provide an overview of known hedgehog inhibitors (HHIs) and their potential for the treatment of hematological cancers and solid tumors beyond BCC.

DESIGN

Published literature was searched to identify articles relating to HHIs in noncutaneous cancer. Both preclinical and clinical research articles were included. In addition, relevant clinical trial results were identified from www.clinicaltrials.gov. Information on the pharmacology of HHIs is also included.

RESULTS

HHIs show activity in a variety of solid and hematological cancers. In preclinical studies, HHIs demonstrated efficacy in pancreatic cancer, rhabdomyosarcoma, breast cancer, and acute myeloid leukemia (AML). In clinical studies, HHIs showed activity in medulloblastoma, as well as prostate, pancreatic, and hematological cancers. Current clinical trials testing the efficacy of HHIs are underway for prostate, pancreatic, and breast cancers, as well as multiple myeloma and AML.

CONCLUSIONS

As clinical trial results become available, it will be possible to discern which additional tumor types are suited to HHI mono- or combination therapy with other anticancer agents. The latter strategy may be useful for delaying or overcoming drug resistance.

A proteomic approach identifies SAFB-like transcription modulator (SLTM) as a bidirectional regulator of GLI family zinc finger transcription factors

In Sonic hedgehog (SHH) signaling, GLI family zinc finger (GLI)-mediated diverse gene transcription outcomes are strictly regulated and are important for SHH function in both development and disease. However, how the GLI factors differentially regulate transcription in response to variable SHH activities is incompletely understood. Here, using a newly generated, tagged Gli3 knock-in mouse (Gli3^TAP ), we performed proteomic analyses and identified the chromatin-associated SAFB-like transcription modulator (SLTM) as a GLI-interacting protein that context-dependently regulates GLI activities. Using immunoprecipitation and immunoblotting, RT-quantitative PCR, and ChIP assays, we show that SLTM interacts with all three GLI proteins and that its cellular levels are regulated by SHH. We also found that SLTM enhances GLI3 binding to chromatin and increases GLI3 repressor (GLI3R) form protein levels. In a GLI3-dependent manner, SLTM promoted the formation of a repressive chromatin environment and functioned as a GLI3 co-repressor. In the absence of GLI3 or in the presence of low GLI3 levels, SLTM co-activated GLI activator (GLIA)-mediated target gene activation and cell differentiation. Moreover, in vivo Sltm deletion generated through CRISPR/Cas9-mediated gene editing caused perinatal lethality and SHH-related abnormal ventral neural tube phenotypes. We conclude that SLTM regulates GLI factor binding to chromatin and contributes to the transcriptional outcomes of SHH signaling via a novel molecular mechanism.

Gli Proteins: Regulation in Development and Cancer

Gli proteins are transcriptional effectors of the Hedgehog signaling pathway. They play key roles in the development of many organs and tissues, and are deregulated in birth defects and cancer. We review the molecular mechanisms of Gli protein regulation in mammals, with special emphasis on posttranslational modifications and intracellular transport. We also discuss how Gli proteins interact with co-activators and co-repressors to fine-tune the expression of Hedgehog target genes. Finally, we provide an overview of the regulation of developmental processes and tissue regeneration by Gli proteins and discuss how these proteins are involved in cancer progression, both through canonical regulation via the Hedgehog pathway and through cross-talk with other signaling pathways.

Sonic Hedgehog Protein is Frequently Up-Regulated in Pancreatic Cancer Compared to Colorectal Cancer

Sonic hedgehog (SHH) is a secreted protein which functions in autocrine or paracrine fashion on target cells to activate hedgehog (HH) signalling cascade responsible for growth and proliferation. This study is an attempt to understand the expression dynamics of SHH protein in colon, rectal and pancreatic cancers. Protein expression of SHH was studied by Western Blotting in the histologically confirmed colon, rectum and pancreatic cancer tissue samples along with their adjacent normal tissues. Only 31.4% (11 of 35) and 26.9% (7 of 26) of colon and rectal cancer cases respectively showed an increase in SHH expression in tumours compared to 72.7% (24 of 33) of the pancreatic cancer cases when compared with their adjacent normal tissues. Our results suggest that SHH may have a strong role in the predisposition of Pancreatic cancer and could possibly be used as a diagnostic or prognostic biomarker.

GLI3 knockdown decreases stemness, cell proliferation and invasion in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is an extremely aggressive disease associated with a poor prognosis. Previous studies have established that cancer stem cells (CSCs) actively participate in OSCC development, progression and resistance to conventional treatments. Furthermore, CSCs frequently exhibit a deregulated expression of normal stem cell signalling pathways, thereby acquiring their distinctive abilities, of which self-renewal is an example. In this study, we examined the effects of GLI3 knockdown in OSCC, as well as the differentially expressed genes in CSC-like cells (CSCLCs) expressing high (CD44^high) or low (CD44^low) levels of CD44. The prognostic value of GLI3 in OSCC was also evaluated. The OSCC cell lines were sorted based on CD44 expression; gene expression was evaluated using a PCR array. Following this, we examined the effects of GLI3 knockdown on CD44 and ESA expression, colony and sphere formation capability, stem-related gene expression, proliferation and invasion. The overexpression of genes related to the Notch, transforming growth factor (TGF)β, FGF, Hedgehog, Wnt and pluripotency maintenance pathways was observed in the CD44^high cells. GLI3 knockdown was associated with a significant decrease in different CSCLC fractions, spheres and colonies in addition to the downregulation of the CD44, Octamer-binding transcription factor 4 (OCT4; also known as POU5F1) and BMI1 genes. This downregulation was accompanied by an increase in the expression of the Involucrin (IVL) and S100A9 genes. Cellular proliferation and invasion were inhibited following GLI3 knockdown. In OSCC samples, a high GLI3 expression was associated with tumour size but not with prognosis. On the whole, the findings of this study demonstrate for the first time, at least to the best of our knowledge, that GLI3 contributes to OSCC stemness and malignant behaviour. These findings suggest the potential for the development of novel therapies, either in isolation or in combination with other drugs, based on CSCs in OSCC.

Whole Exome Sequencing Identifies a Novel Hedgehog-Interacting Protein G516R Mutation in Locally Advanced Papillary Thyroid Cancer

Locally advanced thyroid cancer exhibits aggressive clinical features requiring extensive neck dissection. Therefore, it is important to identify changes in the tumor biology before local progression. Here, whole exome sequencing (WES) using tissues from locally advanced papillary thyroid cancer (PTC) presented a large number of single nucleotide variants (SNVs) in the metastatic lymph node (MLN), but not in normal tissues and primary tumors. Among those MLN-specific SNVs, a novel HHIP G516R (G1546A) mutation was also observed. Interestingly, in-depth analysis for exome sequencing data from the primary tumor presented altered nucleotide 'A' at a very low frequency indicating intra-tumor heterogeneity between the primary tumor and MLN. Computational prediction models such as PROVEAN and Polyphen suggested that HHIP G516R might affect protein function and stability. In vitro, HHIP G516R increased cell proliferation and promoted cell migration in thyroid cancer cells. HHIP G516R, a missense mutation, could be a representative example for the intra-tumor heterogeneity of locally advanced thyroid cancer, which can be a potential future therapeutic target for this disease.

JMJD3 facilitates C/EBPβ-centered transcriptional program to exert oncorepressor activity in AML

JMJD3, a stress-inducible H3K27 demethylase, plays a critical regulatory role in the initiation and progression of malignant hematopoiesis. However, how this histone modifier affects in a cell type-dependent manner remains unclear. Here, we show that in contrast to its oncogenic effect in preleukemia state and lymphoid malignancies, JMJD3 relieves the differentiation-arrest of certain subtypes (such as M2 and M3) of acute myeloid leukemia (AML) cells. RNA sequencing and ChIP−PCR analyses revealed that JMJD3 exerts anti-AML effect by directly modulating H3K4 and H3K27 methylation levels to activate the expression of a number of key myelopoietic regulatory genes. Mechanistic exploration identified a physical and functional association of JMJD3 with C/EBPβ that presides the regulatory network of JMJD3. Thus, the leukemia regulatory role of JMJD3 varies in a disease phase- and lineage-dependent manner, and acts as a potential oncorepressor in certain subsets of AML largely by coupling to C/EBPβ-centered myelopoietic program.

Histone demethylase JMJD3 is known to be oncogenic in preleukemic states and T-cell acute lymphocytic leukemia. Here, the authors show that in some acute myeloid leukemia subsets, JMJD3 can actually act as a potential oncorepressor via mediation of C/EBPβ-centered transcriptional programming.

Medulloblastoma, WNT-activated/SHH-activated: clinical impact of molecular analysis and histogenetic evaluation

PURPOSE

Medulloblastoma (MDB) is a small cell poorly differentiated embryonal tumor of the cerebellum, which more frequently compromises children. Overall prognosis is favorable, but dependent of stage, histopathological pattern and molecular group. Approximately 30% of the affected patients will die from the disease. WHO 2016 Classification of Tumors of the Central Nervous System (CNS) has been classified MDB into four principal groups: WNT-activated MDB, SHH-activated MDB, group 3 MDB, and group 4 MDB. WNT-activated MDB is associated to monosomy 6, CTNNB1, DDX3X and TP53 mutations, beta-catenin nuclear immunoexpression, and a better prognosis than SHH-activated MDB.

DISCUSSION

WNT-activated tumors account approximately for 10% of cases of MDBs, and are thought to arise from cells in the dorsal brain stem/lower rhombic lip progenitor cells. SHH-activated MDB more frequently arises in the lateral hemispheres of the cerebellum, and clinical outcome in this group is variable. TP53-mutant SHHactivated MDB usually shows the large cell/anaplastic pattern, and can be related to MYCN amplification, GLI2 amplification and 17p loss. TP53-wildtype SHH-activated MDB is more commonly of desmoplastic/nodular morphology, and can be related to PTCH1 deletion and 10q loss. Gene expression and methylation profiling is the gold standard for defining molecular groups of MDB. In immunohistochemistry assays, anti-GAB1 antibody expression is positive in tumors showing SHH pathway activation or PTCH mutation, while positive immunoexpression for YAP1 antibody can be only found in WNT-activated and SHH-activated MDB.