Characterization of the human suppressor of fused, a negative regulator of the zinc-finger transcription factor Gli

Multiple ossified intracranial and spinal meningiomas: a rare case report and literature review

Ossified intracranial meningiomas (OIM) and ossified spinal meningiomas (OSM) are rare neoplasms of mesenchymal origin that predominantly manifest in the spinal cord and infrequently in the cranial region, accounting for ~0. 7-5.5% of all meningiomas. It is extremely rare to have multiple intracranial and spinal lesions accompanied by ossification. Herein, we report this rare case for the first time. A 34-year-old woman presented with paresthesia and limb weakness in the right lower limb and gradually worsened. Approximately half a year later, she could only walk with crutches. Magnetic resonance imaging of the brain and spinal cord showed multiple meningiomas, and histopathological examination confirmed multiple OIM and OSM (WHO grade 1). Multiple OIM and OSM are extremely rare with diverse imaging features, and it is easily confused with other tumors. Histopathological examination is the final diagnostic method.

Hedgehog-Related Mutation Causes Bone Malformations with or without Hereditary Gene Mutations

The hedgehog (Hh) family consists of numerous signaling mediators that play important roles at various stages of development. Thus, the Hh pathway is essential for bone tissue development and tumorigenesis. Gorlin syndrome is a skeletal and tumorigenic disorder caused by gain-of-function mutations in Hh signaling. In this review, we first present the phenotype of Gorlin syndrome and the relationship between genotype and phenotype in bone and craniofacial tissues, including the causative gene as well as other Hh-related genes. Next, the importance of new diagnostic methods using next-generation sequencing and multiple gene panels will be discussed. We summarize Hh-related genetic disorders, including cilia disease, and the genetics of Hh-related bone diseases.

SUFU promotes GLI activity in a Hedgehog-independent manner in pancreatic cancer

Aberrant activation of the Hedgehog (Hh) signaling pathway, through which the GLI family of transcription factors (TF) is stimulated, is commonly observed in cancer cells. One well-established mechanism of this increased activity is through the inactivation of Suppressor of Fused (SUFU), a negative regulator of the Hh pathway. Relief from negative regulation by SUFU facilitates GLI activity and induction of target gene expression. Here, we demonstrate a novel role for SUFU as a promoter of GLI activity in pancreatic ductal adenocarcinoma (PDAC). In non-ciliated PDAC cells unresponsive to Smoothened agonism, SUFU overexpression increases GLI transcriptional activity. Conversely, knockdown (KD) of SUFU reduces the activity of GLI in PDAC cells. Through array PCR analysis of GLI target genes, we identified B-cell lymphoma 2 (BCL2) among the top candidates down-regulated by SUFU KD. We demonstrate that SUFU KD results in reduced PDAC cell viability, and overexpression of BCL2 partially rescues the effect of reduced cell viability by SUFU KD. Further analysis using as a model GLI1, a major TF activator of the GLI family in PDAC cells, shows the interaction of SUFU and GLI1 in the nucleus through previously characterized domains. Chromatin immunoprecipitation (ChIP) assay shows the binding of both SUFU and GLI1 at the promoter of BCL2 in PDAC cells. Finally, we demonstrate that SUFU promotes GLI1 activity without affecting its protein stability. Through our findings, we propose a novel role of SUFU as a positive regulator of GLI1 in PDAC, adding a new mechanism of Hh/GLI signaling pathway regulation in cancer cells.

Sonic Hedgehog Signaling Pathway: A Role in Pain Processing

Pain, as one of the most prevalent clinical symptoms, is a complex physiological and psychological activity. Long-term severe pain can become unbearable to the body. However, existing treatments do not provide satisfactory results. Therefore, new mechanisms and therapeutic targets need to be urgently explored for pain management. The Sonic hedgehog (Shh) signaling pathway is crucial in embryonic development, cell differentiation and proliferation, and nervous system regulation. Here, we review the recent studies on the Shh signaling pathway and its action in multiple pain-related diseases. The Shh signaling pathway is dysregulated under various pain conditions, such as pancreatic cancer pain, bone cancer pain, chronic post-thoracotomy pain, pain caused by degenerative lumbar disc disease, and toothache. Further studies on the Shh signaling pathway may provide new therapeutic options for pain patients.

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.

The Role of Sonic Hedgehog Pathway in the Development of the Central Nervous System and Aging-Related Neurodegenerative Diseases

The Sonic hedgehog (SHH) pathway affects neurogenesis and neural patterning during the development of the central nervous system. Dysregulation of the SHH pathway in the brain contributes to aging-related neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. At present, the SHH signaling pathway can be divided into the canonical signaling pathway and non-canonical signaling pathway, which directly or indirectly mediates other related pathways involved in the development of neurodegenerative diseases. Hence, an in-depth knowledge of the SHH signaling pathway may open an avenue of possibilities for the treatment of neurodegenerative diseases. Here, we summarize the role and mechanism of the SHH signaling pathway in the development of the central nervous system and aging-related neurodegenerative diseases. In this review, we will also highlight the potential of the SHH pathway as a therapeutic target for treating neurodegenerative diseases.

Repurposing Niclosamide for Targeting Pancreatic Cancer by Inhibiting Hh/Gli Non-Canonical Axis of Gsk3β

Simple Summary

The current obstacles for discovering new drugs for cancer therapy have necessitated the development of the alternative strategy of drug repurposing, the identification of new uses for approved or investigational drugs for new therapeutic purposes. Niclosamide (Nic) is a Food and Drug Administration (FDA)-approved anti-helminthic drug, reported to have anti-cancer effects, and is being assessed in various clinical trials. In the current study, we assessed the therapeutic efficacy of Nic on pancreatic cancer (PC) in vitro. Our results revealed mitochondrial stress and mTORC1-dependent autophagy as the predominant players of Nic-induced PC cell death. This study provided a novel mechanistic insight for anti-cancer efficacy of Nic by increasing p-Gsk3β that modulates molecular signaling(s), including inhibition of hedgehog (Hh) signaling-mediated cellular proliferation and increased apoptosis through mTORC1-dependent autophagy may prove helpful for the development of novel PC therapies.

Abstract

Niclosamide (Nic), an FDA-approved anthelmintic drug, is reported to have anti-cancer efficacy and is being assessed in clinical trials for various solid tumors. Based on its ability to target multiple signaling pathways, in the present study, we evaluated the therapeutic efficacy of Nic on pancreatic cancer (PC) in vitro. We observed an anti-cancerous effect of this drug as shown by the G0/G1 phase cell cycle arrest, inhibition of PC cell viability, colony formation, and migration. Our results revealed the involvement of mitochondrial stress and mTORC1-dependent autophagy as the predominant players of Nic-induced PC cell death. Significant reduction of Nic-induced reactive oxygen species (ROS) and cell death in the presence of a selective autophagy inhibitor spautin-1 demonstrated autophagy as a major contributor to Nic-mediated cell death. Mechanistically, Nic inhibited the interaction between BCL2 and Beclin-1 that supported the crosstalk of autophagy and apoptosis. Further, Nic treatment resulted in Gsk3β inactivation by phosphorylating its Ser-9 residue leading to upregulation of Sufu and Gli3, thereby negatively impacting hedgehog signaling and cell survival. Nic induced autophagic cell death, and p-Gsk3b mediated Sufu/Gli3 cascade was further confirmed by Gsk3β activator, LY-294002, by rescuing inactivation of Hh signaling upon Nic treatment. These results suggested the involvement of a non-canonical mechanism of Hh signaling, where p-Gsk3β acts as a negative regulator of Hh/Gli1 cascade and a positive regulator of autophagy-mediated cell death. Overall, this study established the therapeutic efficacy of Nic for PC by targeting p-Gsk3β mediated non-canonical Hh signaling and promoting mTORC1-dependent autophagy and cell death.

Exploring Sonic Hedgehog Cell Signaling in Neurogenesis: Its Potential Role in Depressive Behavior

Depression is the most prevalent form of neuropsychiatric disorder affecting all age groups globally. As per the estimation of the World Health Organization (WHO), depression will develop into the foremost reason for disability globally by the year 2030. The primary neurobiological mechanism implicated in depression remains ambiguous; however, dysregulation of molecular and signaling transductions results in depressive disorders. Several theories have been developed to explain the pathogenesis of depression, however, none of them completely explained all aspects of depressive-pathogenesis. In the current review, we aimed to explore the role of the sonic hedgehog (Shh) signaling pathway in the development of the depressive disorder and its potential as the therapeutic target. Shh signaling has a crucial function in neurogenesis and neural tube patterning during the development of the central nervous system (CNS). Shh signaling performs a basic function in embryogenesis and hippocampal neurogenesis. Moreover, antidepressants are also known to enhance neurogenesis in the hippocampus, which further suggests the potential of Shh signaling. Furthermore, there is decreased expression of a glioma-associated oncogene (Gli1) and Smoothened (Smo) in depression. Moreover, antidepressants also regulate brain-derived neurotrophic factor (BDNF) and wingless protein (Wnt) signaling, therefore, Shh may be implicated in the pathogenesis of the depressive disorder. Deregulation of Shh signaling in CNS results in neurological disorders such as depression.

Zfx-induced upregulation of UBE2J1 facilitates endometrial cancer progression via PI3K/AKT pathway

Emerging documents revealed that E2 enzyme family has been implicated in regulating the progression of numerous human cancers. Ubiquitin-conjugating enzyme E2 J1 (UBE2J1), a member of E2 enzyme family, has been reported to participate in the biological process of medulloblastoma, while little is known about its functionality in endometrial cancer (EC). Gene expression at the mRNA and protein levels were identified using RT-qPCR and western blot analysis, separately. The alteration on cell proliferation, adhesion, migration, invasion, and epithelial-mesenchymal transition (EMT) process was determined through 5-Ethynyl-2'-deoxyuridine, cell adhesion, wound healing and transwell assays as well as western blot analysis. The role of UBE2J1 in xenograft tumor in mice was determined. Luciferase reporter and chromatin immunoprecipitation assays were conducted to reveal the undering mechanism of UBE2J1. Our results indicated that UBE2J1 displayed high level in EC tissues and cells and predicted poor prognosis of EC patients. In addition, UBE2J1 depletion inhibited cell proliferation, adhesion, motion, EMT process invitro, and repressed tumor growth invivo. Rescue assays manifested that ethyl 2-amino-6-chloro-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate treatment reversed the effects of UBE2J1 on PI3K/AKT pathway activation and malignant phenotypes of EC cells. Finally, zinc finger X-chromosomal protein (zfx), with high expression in EC tissues, was verified to activate UBE2J1 transcription by binding to UBE2J1 promoter. In conclusion, all facts signified that zfx-induced upregulation of UBE2J1 accelerated the progression of EC via regulating the PI3K/AKT signaling pathway, which suggested that UBE2J1 might be of great significance in probing into the underlying therapeutic strategies of EC.

Suppressor of Fused Inhibits Skin Wound Healing

Objectives: To investigate the effect of suppressor of fused (Sufu) on epidermal and dermal cellular properties and in wound healing. Approach: Transgenic (TG) mice overexpressing human Sufu (hSufu) in the epidermis were applied to investigate the effects of Sufu on epidermal and dermal cellular properties and in wound healing. Results: Histological staining revealed a reduction of epidermal and dermal thickness and an increase of hypodermal adipose tissue in homozygous K14-hSufu TG mice when compared with wild-type (WT) controls. TG mice exhibited significantly delayed skin wound healing. Moreover, the migratory and proliferative capabilities of cultured keratinocytes were decreased in K14-hSufuTG mice. Transforming growth factor-β treatment increased the expression of α-smooth muscle actin more in WT than in TG fibroblasts. Sufu overexpression significantly decreased the expression of β-catenin, glioma transcription factor 1 (Gli1), and matrix metalloproteinase-3 in wounds of K14-hSufu TG mice when compared with controls, probably indicating a delaying effect of Sufu on wound healing via blocking the hedgehog (Hh)/Gli and Wnt/β-catenin pathway. Innovation: Our results indicate a new property of Sufu in the process of skin wound healing. It provides an important basis for Sufu as a potential target for skin wound healing. Conclusion: Our findings suggest that Sufu overexpression in the epidermis impairs wound healing via dampening the Hh/Gli and Wnt/β-catenin signaling pathway. These data provide an important basis for further analyses of Sufu in skin wound healing.

Wnt, Notch, and TGF-β Pathways Impinge on Hedgehog Signaling Complexity: An Open Window on Cancer

Constitutive activation of the Hedgehog (Hh) signaling pathway is associated with increased risk of developing several malignancies. The biological and pathogenic importance of Hh signaling emphasizes the need to control its action tightly, both physiologically and therapeutically. Evidence of crosstalk between Hh and other signaling pathways is reported in many tumor types. Here, we provide an overview of the current knowledge about the communication between Hh and major signaling pathways, such as Notch, Wnt, and transforming growth factor β (TGF-β), which play critical roles in both embryonic and adult life. When these pathways are unbalanced, impaired crosstalk contributes to disease development. It is reported that more than one of these pathways are active in different type of tumors, at the same time. Therefore, starting from a plethora of stimuli that activate multiple signaling pathways, we describe the signals that preferentially converge on the Hh signaling cascade that influence its activity. Moreover, we highlight several connection points between Hh and Notch, Wnt, or TGF-β pathways, showing a reciprocal synergism that contributes to tumorigenesis, supporting a more malignant behavior by tumor cells, such as in leukemia and brain tumors. Understanding the importance of these molecular interlinking networks will provide a rational basis for combined anticancer drug development.

Hedgehog Signaling and Embryonic Craniofacial Disorders

Since its initial discovery in a Drosophila mutagenesis screen, the Hedgehog pathway has been revealed to be instrumental in the proper development of the vertebrate face. Vertebrates possess three hedgehog paralogs: Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). Of the three, Shh has the broadest range of functions both in the face and elsewhere in the embryo, while Ihh and Dhh play more limited roles. The Hedgehog pathway is instrumental from the period of prechordal plate formation early in the embryo, until the fusion of the lip and secondary palate, which complete the major patterning events of the face. Disruption of Hedgehog signaling results in an array of developmental disorders in the face, ranging from minor alterations in the distance between the eyes to more serious conditions such as severe clefting of the lip and palate. Despite its critical role, Hedgehog signaling seems to be disrupted through a number of mechanisms that may either be direct, as in mutation of a downstream target of the Hedgehog ligand, or indirect, such as mutation in a ciliary protein that is otherwise seemingly unrelated to the Hedgehog pathway. A number of teratogens such as alcohol, statins and steroidal alkaloids also disrupt key aspects of Hedgehog signal transduction, leading to developmental defects that are similar, if not identical, to those of Hedgehog pathway mutations. The aim of this review is to highlight the variety of roles that Hedgehog signaling plays in developmental disorders of the vertebrate face.

Effects of miRNA-342-3p in modulating Hedgehog signaling pathway of human umbilical cord mesenchymal stem cells by down-regulating Sufu

OBJECTIVE

Previously, we have shown that miRNA-342-3p was increased during osteogenic differentiation of human umbilical mesenchymal stem cells (hUCMSCs) via regulating the sonic hedgehog (Shh) pathway. In this study, our objective is to further investigate the role of miRNA-342-3p in activation of Shh pathway by targeting suppressor of fused protein (Sufu), a suppressor of transcriptional factor Gli, as well as the potential interaction with transforming growth factor beta (TGF-β) signaling pathway during osteogenic induction of hUCMSCs.

MATERIALS AND METHODS

HUCMSCs that stable overexpression or knockdown of miRNA-342-3p were established by infection with lentiviral vectors. mRNA and protein levels of Hedgehog signaling pathway and osteogenic genes were measured by RT-qPCR and western blot assays. Luciferase reporter assay was performed to test the direct binding site of Sufu 5'UTR targeted by miRNA-342-3p.

RESULTS

Overexpression of miRNA-342-3p in hUCMSCs enhanced the expression of osteogenic genes by targeting Sufu. And the potential of osteogenic differentiation of hUCMSCs was inhibited while knocking down miRNA-342-3p. Meanwhile, induced the TGF-β expression level was also observed upon overexpressing miRNA-342-3p, suggesting activation of TGF-β signaling pathway was a potential mechanism of miRNA-342-3p-mediated osteogenesis in hUCMSCs.

CONCLUSIONS

Our findings provide new mechanistic evidence that miRNA-342-3p might be a valuable therapeutic target in bone regeneration.

Misactivation of Hedgehog signaling causes inherited and sporadic cancers

The Hedgehog pathway is critical for the development of diverse organs. Misactivation of the Hedgehog pathway can cause developmental abnormalities and cancers, including medulloblastoma, the most common pediatric brain tumor, and basal cell carcinoma, the most common cancer in the United States. Here, we review how basic, translational, and clinical studies of the Hedgehog pathway have helped reveal how cells communicate, how intercellular communication controls development, how signaling goes awry to cause cancer, and how to use targeted molecular agents to treat both inherited and sporadic cancers.

Dual Regulatory Functions of SUFU and Targetome of GLI2 in SHH Subgroup Medulloblastoma

SUFU alterations are common in human Sonic Hedgehog (SHH) subgroup medulloblastoma (MB). However, its tumorigenic mechanisms have remained elusive. Here, we report that loss of Sufu alone is unable to induce MB formation in mice, due to insufficient Gli2 activation. Simultaneous loss of Spop, an E3 ubiquitin ligase targeting Gli2, restores robust Gli2 activation and induces rapid MB formation in Sufu knockout background. We also demonstrated a tumor-promoting role of Sufu in Smo-activated MB (∼60% of human SHH MB) by maintaining robust Gli activity. Having established Gli2 activation as a key driver of SHH MB, we report a comprehensive analysis of its targetome. Furthermore, we identified Atoh1 as a target and molecular accomplice of Gli2 that activates core SHH MB signature genes in a synergistic manner. Overall, our work establishes the dual role of SUFU in SHH MB and provides mechanistic insights into transcriptional regulation underlying Gli2-mediated SHH MB tumorigenesis.

Proteostasis in the Hedgehog signaling pathway

The Hedgehog (Hh) signaling pathway is crucial for the development of vertebrate and invertebrate animals alike. Hh ligand binds its receptor Patched (Ptc), allowing the activation of the obligate signal transducer Smoothened (Smo). The levels and localizations of both Ptc and Smo are regulated by ubiquitination, and Smo is under additional regulation by phosphorylation and SUMOylation. Downstream of Smo, the Ci/Gli family of transcription factors regulates the transcriptional responses to Hh. Phosphorylation, ubiquitination and SUMOylation are important for the stability and localization of Ci/Gli proteins and Hh signaling output. Finally, Suppressor of Fused directly regulates Ci/Gli proteins and itself is under proteolytic regulation that is critical for normal Hh signaling.

Itch/β-arrestin2-dependent non-proteolytic ubiquitylation of SuFu controls Hedgehog signalling and medulloblastoma tumorigenesis

Suppressor of Fused (SuFu), a tumour suppressor mutated in medulloblastoma, is a central player of Hh signalling, a pathway crucial for development and deregulated in cancer. Although the control of Gli transcription factors by SuFu is critical in Hh signalling, our understanding of the mechanism regulating this key event remains limited. Here, we show that the Itch/β-arrestin2 complex binds SuFu and induces its Lys63-linked polyubiquitylation without affecting its stability. This process increases the association of SuFu with Gli3, promoting the conversion of Gli3 into a repressor, which keeps Hh signalling off. Activation of Hh signalling antagonises the Itch-dependent polyubiquitylation of SuFu. Notably, different SuFu mutations occurring in medulloblastoma patients are insensitive to Itch activity, thus leading to deregulated Hh signalling and enhancing medulloblastoma cell growth. Our findings uncover mechanisms controlling the tumour suppressive functions of SuFu and reveal that their alterations are implicated in medulloblastoma tumorigenesis.

SuFu is a tumour suppressor in medulloblastoma and regulates Gli proteins in the Sonic Hedgehog pathway; however, the molecular mechanisms behind this regulation are unclear. Here, the authors show that the Itch/β-arrestin2 complex binds and ubiquitylates SuFu, facilitating the interaction with Gli3 and its conversion into the repressive form, thus counteracting medulloblastoma formation.

Molecular mechanisms of suppressor of fused in regulating the hedgehog signalling pathway

Highly conserved throughout evolution, the hedgehog (Hh) signalling pathway has been demonstrated to be involved in embryonic development, stem cell maintenance and tissue homeostasis in animals ranging from invertebrates to vertebrates. In the human body, a variety of cancer types are associated with the aberrantly activated Hh signalling pathway. Multiple studies have revealed suppressor of fused (Sufu) as a key negative regulator of this signalling pathway. In vertebrates, Sufu primarily functions as a tumor suppressor factor by interacting with and inhibiting glioma-associated oncogene homologues (GLIs), which are the terminal transcription factors of the Hh signalling pathway and belong to the Kruppel family of zinc finger proteins; by contrast, the regulation of Sufu itself remains relatively unclear. In the present review article, we focus on the effects of Sufu on the Hh signalling pathway in tumourigenesis and the molecular mechanisms underlying the regulation of GLI by Sufu. In addition, the factors modulating the activity of Sufu at post-transcriptional levels are also discussed.

Lithium Suppresses Hedgehog Signaling via Promoting ITCH E3 Ligase Activity and Gli1-SUFU Interaction in PDA Cells

Dysregulation of Hedgehog (Hh) signaling pathway is one of the hallmarks of pancreatic ductal adenocarcinoma (PDA). Lithium, a clinical mood stabilizer for the treatment of mental disorders, is known to suppress tumorigenic potential of PDA cells by targeting the Hh/Gli signaling pathway. In this study, we investigated the molecular mechanism of lithium induced down-regulation of Hh/Gli1. Our data show that lithium promotes the poly-ubiquitination and proteasome-mediated degradation of Gli1 through activating E3 ligase ITCH. Additionally, lithium enhances interaction between Gli1 and SUFU via suppressing GSK3β, which phosphorylates SUFU and destabilizes the SUFU-Gli1 inhibitory complex. Our studies illustrate a novel mechanism by which lithium suppresses Hh signaling via simultaneously promoting ITCH-dependent Gli1 ubiquitination/degradation and SUFU-mediated Gli1 inhibition.

Discovery of Novel Macrocyclic Hedgehog Pathway Inhibitors Acting by Suppressing the Gli-Mediated Transcription

A systemic medicinal chemistry campaign was conducted based on a literature hit compound 5 bearing the 4,5-dihydro-2H-benzo[b][1,5]oxazocin-6(3H)-one core through cyclization of two side substituents of the bicyclic skeleton combined with N-atom walking or ring walking and the central ring expansion or extraction approaches, leading to several series of structurally unique tricyclic compounds. Among these, compound 29a was identified as the most potent against the Hedgehog (Hh) signaling pathway showing an IC₅₀ value of 23 nM. Mechanism studies indicated that compound 29a inhibited the Hh signaling pathway by suppressing the expression of the transcriptional factors Gli rather than by interrupting the binding of Gli with DNA. We further observed that 29a was equally potent against both Smo wild type and the two major resistant mutants (Smo D473H and Smo W535L). It potently inhibited the proliferation of medulloblastoma cells and showed significant tumor growth inhibition in the ptch± ;p53-/- medulloblastoma allograft mice model. Though more studies are needed to clarify the precise interaction pattern of 29a with Gli, its promising in vitro and in vivo properties encourage further profiling as a new-generation Hh signaling inhibitor to treat tumors primarily or secondarily resistant to current Smo inhibitors.

The regulation of Hh/Gli1 signaling cascade involves Gsk3β- mediated mechanism in estrogen-derived endometrial hyperplasia

The present study was undertaken to explore the functional involvement of Hh signaling and its regulatory mechanism in endometrial hyperplasia. Differential expression of Hh signaling molecules i.e., Ihh, Shh, Gli1 or Gsk3β was observed in endometrial hyperplasial (EH) cells as compared to normal endometrial cells. Estradiol induced the expression of Hh signaling molecules and attenuated the expression of Gsk3β whereas anti-estrogen (K1) or progestin (MPA) suppressed these effects in EH cells. Cyclopamine treatment or Gli1 siRNA knockdown suppressed the growth of EH cells and reduced the expression of proliferative markers. Estradiol also induced the nuclear translocation of Gli1 which was suppressed by both MPA and K1 in EH cells. While exploring non-canonical mechanism, LY-294002 (Gsk3β activator) caused a decrease in Gli1 expression indicating the involvement of Gsk3β in Gli1 regulation. Further, Gsk3β silencing promoted the expression and nuclear translocation of Gli1 demonstrating that Gsk3β serves as a negative kinase regulator of Gli1 in EH cells. Similar attenuation of Hh signaling molecules was observed in rats with uterine hyperplasia undergoing anti-estrogen treatment. The study suggested that Hh/Gli1 cascade (canonical pathway) as well as Gsk3β-Gli1 crosstalk (non-canonical pathway) play crucial role in estrogen-dependent cell proliferation in endometrial hyperplasia.

Differential requirement of SUFU in tissue development discovered in a hypomorphic mouse model

Suppressor of Fused (SUFU) is an essential negative regulator of the Hedgehog (HH) pathway and involved in GLI transcription factor regulation. Due to early embryonic lethality of Sufu^-/- mice, investigations of SUFU's role later in development are limited to conditional, tissue-specific knockout models. In this study we developed a mouse model (Sufu^{Ex456(fl)/Ex456(fl)}) with hypomorphic features where embryos were viable up to E18.5, although with a spectrum of developmental defects of varying severity, including polydactyly, exencephaly and omphalocele. Development of certain tissues, like the skeleton, was more affected than that of others such as skin, which remained largely normal. Interestingly, no apparent changes in the dorso-ventral patterning of the neural tube at E9.0 could be seen. Thus, this model provides an opportunity to globally study SUFU's molecular function in organogenesis beyond E9.5. Molecularly, Sufu^{Ex456(fl)/Ex456(fl)} embryos displayed aberrant mRNA splicing and drastically reduced levels of Sufu wild-type mRNA and SUFU protein in all tissues. As a consequence, at E9.5 the levels of all three different GLI proteins were reduced. Interestingly, despite the reduction of GLI3 protein levels, the critical ratio of the GLI3 full-length transcriptional activator versus GLI3 truncated repressor remained unchanged compared to wild-type embryos. This suggests that the limited amount of SUFU protein present is sufficient for GLI processing but not for stabilization. Our data demonstrate that tissue development is differentially affected in response to the reduced SUFU levels, providing novel insight regarding the requirements of different levels of SUFU for proper organogenesis.

Hedgehog Signal Transduction: Key Players, Oncogenic Drivers, and Cancer Therapy

The Hedgehog (Hh) signaling pathway governs complex developmental processes, including proliferation and patterning within diverse tissues. These activities rely on a tightly regulated transduction system that converts graded Hh input signals into specific levels of pathway activity. Uncontrolled activation of Hh signaling drives tumor initiation and maintenance. However, recent entry of pathway-specific inhibitors into the clinic reveals mixed patient responses and thus prompts further exploration of pathway activation and inhibition. In this review, we share emerging insights into regulated and oncogenic Hh signaling, supplemented with updates on the development and use of Hh pathway-targeted therapies.

Nomegestrol Acetate Suppresses Human Endometrial Cancer RL95-2 Cells Proliferation In Vitro and In Vivo Possibly Related to Upregulating Expression of SUFU and Wnt7a

Nomegestrol acetate (NOMAC) has been successfully used for the treatment of some gynecological disorders, and as a combined oral contraceptive with approval in many countries. In this study, we investigated the effects of NOMAC on human endometrial cancer cells in vitro and in vivo. The proliferation of human endometrial cancer cells (RL95-2 and KLE) were assessed using CCK-8 and EdU incorporation assays. Whole-genome cDNA microarray analysis was used to identify the effects of NOMAC on gene expression profiles in RL95-2 cells. RL95-2 xenograft nude mice were treated with NOMAC (50, 100, and 200 mg/kg) or medroxyprogesterone acetate (MPA; 100 and 200 mg/kg) for 28 consecutive days. The results showed that NOMAC significantly inhibited the growth of RL95-2 cells in a concentration-dependent manner, but not in KLE cells. Further investigation demonstrated that NOMAC produced a stronger inhibition of tumor growth (inhibition rates for 50, 100, and 200 mg/kg NOMAC were 24.74%, 47.04%, and 58.06%, respectively) than did MPA (inhibition rates for 100 and 200 mg/kg MPA were 41.06% and 27.01%, respectively) in the nude mice bearing the cell line of RL95-2. NOMAC altered the expression of several genes related to cancer cell proliferation, including SUFU and Wnt7a. The upregulation of SUFU and Wnt7a was confirmed using real-time quantitative polymerase chain reaction and Western blotting in RL95-2 cells and RL95-2 xenograft tumor tissues, but not in KLE cells. These data indicate that NOMAC can inhibit the proliferation of RL95-2 cell in vitro and suppress the growth of xenografts in the nude mice bearing the cell line of RL95-2 in vivo. This effect could be related to the upregulating expression of SUFU and Wnt7a.

Design, Synthesis and Biological Evaluation of novel Hedgehog Inhibitors for treating Pancreatic Cancer

Hedgehog (Hh) pathway is involved in epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) maintenance resulting in tumor progression. GDC-0449, an inhibitor of Hh pathway component smoothened (Smo) has shown promise in the treatment of various cancers including pancreatic cancer. However, the emergence of resistance during GDC-0449 treatment with numerous side effects limits its use. Therefore, here we report the design, synthesis and evaluation of novel GDC-0449 analogs using N-[3-(2-pyridinyl) phenyl] benzamide scaffold. Cell-based screening followed by molecular simulation revealed 2-chloro-N¹-[4-chloro-3-(2-pyridinyl)phenyl]-N⁴,N⁴-bis(2-pyridinylmethyl)-1,4-benzenedicarboxamide (MDB5) as most potent analog, binding with an extra interactions in seven-transmembrane (7-TM) domain of Smo due to an additional 2-pyridylmethyl group than GDC-0449. Moreover, MDB5 was more efficient in inhibiting Hh pathway components as measured by Gli-1 and Shh at transcriptional and translational levels. Additionally, a significant reduction of ALDH1, CD44 and Oct-3/4, key markers of pancreatic CSC was observed when MIA PaCa-2 cells were treated with MDB5 compared to GDC-0449. In a pancreatic tumor mouse model, MDB5 containing nanoparticles treated group showed significant inhibition of tumor growth without loss in body weight. These evidence highlight the enhanced Hh pathway inhibition and anticancer properties of MDB5 leaving a platform for mono and/or combination therapy.

Spop regulates Gli3 activity and Shh signaling in dorsoventral patterning of the mouse spinal cord

Sonic Hedgehog (Shh) signaling regulates the patterning of ventral spinal cord through the effector Gli family of transcription factors. Previous in vitro studies showed that an E3 ubiquitin ligase containing Speckle-type POZ protein (Spop) targets Gli2 and Gli3 for ubiquitination and degradation, but the role of Spop in Shh signaling and mammalian spinal cord patterning remains unknown. Here, we show that loss of Spop does not alter spinal cord patterning, but it suppresses the loss of floor plate and V3 interneuron phenotype of Gli2 mutants, suggesting a negative role of Spop in Gli3 activator activity, Shh signaling and the specification of ventral cell fates in the spinal cord. This correlates with a moderate but significant increase in the level of Gli3 protein in the Spop mutant spinal cords. Furthermore, loss of Spop restores the maximal Shh pathway activation and ventral cell fate specification in the Gli1;Sufu double mutant spinal cord. Finally, we show that loss of Spop-like does not change the spinal cord patterning in either wild type or Spop mutants, suggesting that it does not compensate for the loss of Spop in Shh signaling and spinal cord patterning. Therefore, our results demonstrate a negative role of Spop in the level and activity of Gli3, Shh signaling and ventral spinal cord patterning.

Development of anticancer agents targeting the Hedgehog signaling

Hedgehog signaling is an evolutionarily conserved pathway which is essential in embryonic and postnatal development as well as adult organ homeostasis. Abnormal regulation of Hedgehog signaling is implicated in many diseases including cancer. Consequently, substantial efforts have made in the past to develop potential therapeutic agents that specifically target the Hedgehog signaling for cancer treatment. Here, we review the therapeutic agents for inhibition of the Hedgehog signaling and their clinical advances in cancer treatment.

Hedgehog Signaling: From Basic Biology to Cancer Therapy

The Hedgehog (HH) signaling pathway was discovered originally as a key pathway in embryonic patterning and development. Since its discovery, it has become increasingly clear that the HH pathway also plays important roles in a multitude of cancers. Therefore, HH signaling has emerged as a therapeutic target of interest for cancer therapy. In this review, we provide a brief overview of HH signaling and the key molecular players involved and offer an up-to-date summary of our current knowledge of endogenous and exogenous small molecules that modulate HH signaling. We discuss experiences and lessons learned from the decades-long efforts toward the development of cancer therapies targeting the HH pathway. Challenges to develop next-generation cancer therapies are highlighted.

Nek2A/SuFu feedback loop regulates Gli-mediated Hedgehog signaling pathway

Suppressor of Fused (SuFu), one of the most conserved components of the Hedgehog (Hh) signaling, binds Gli transcription factors and impedes activation of target gene expression in mammalian cells. Despite the central importance of SuFu in the Hh pathway, little is known about SuFu regulation. In a previous study, we identified NIMA-related expressed kinase 2A (Nek2A) as a SuFu-interacting protein. Here, we show that Nek2A stabilizes SuFu through impairing ubiquitin/proteasome degradation of SuFu. In addition, Nek2A negatively regulates target genes of Hh signaling as well as Gli2 transcriptional activity. In turn, inhibition of Hh signaling by GANT61 diminishes mRNA and protein levels of Nek2A, and Hh agonist promotes transcription of NEK2A gene. Chromatin immunoprecipitation assays revealed that Gli1 and Gli2 directly bind to the promoter regions of NEK2A gene and induced its transcription. Thus, we uncovered one of the mechanisms by which Nek2A acts as a modulator of the Hh signaling pathway in the context of a novel negative-feedback loop, which may offer new insights into Gli-mediated Hh signaling regulation in development and human diseases.

Identification of a novel alternative splicing transcript variant of the suppressor of fused: Relationship with lymph node metastasis in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most fatal diseases, and the median survival time is very short. Upregulation of hedgehog signaling pathway activity is a vital factor in pathogenesis of PDAC. However, as a negative regulator of hedgehog signaling, it is not very clear what role the suppressor of fused (SUFU) plays in PDAC tissue. In our study for the identification of alternative splicing transcripts of SUFU gene in human PDAC cells, a novel transcript variant of SUFU (SUFUvN) was discovered by 3' rapid amplification of cDNA ends (3'RACE) and cDNA clone. SUFUvN contained an additional new protein-coding exon compared with the transcript variant 1 of SUFU (SUFUv1, NM_016169) published in NCBI website. The sequence of the new protein-coding exon was the same as a fragment of intron between exon 10 and 11 of SUFUv1. Thus, an exon skipping occurred in transcription of SUFUv1. Compared with the expression vector of SUFUvN transfected PDAC cells, the corresponding protein expression encoded by SUFUvN (SUFU isoform N) was detected in PDAC tissue. Furthermore, it was observed that elevated SUFUvN transcription level was related with lymph node metastasis in PDAC tissues, while neither SUFUv1 nor transcript variant 2 of SUFU (SUFUv2, NM_001178133) did. Our data indicate that there exists a novel transcript variant of SUFU which can be transcribed and translated into corresponding protein and its transcription is related with metastasis of lymph nodes in PDAC.

Members of the Rusc protein family interact with Sufu and inhibit vertebrate Hedgehog signaling

Hedgehog (Hh) signaling is fundamentally important for development and adult tissue homeostasis. It is well established that in vertebrates Sufu directly binds and inhibits Gli proteins, the downstream mediators of Hh signaling. However, it is unclear how the inhibitory function of Sufu towards Gli is regulated. Here we report that the Rusc family of proteins, the biological functions of which are poorly understood, form a heterotrimeric complex with Sufu and Gli. Upon Hh signaling, Rusc is displaced from this complex, followed by dissociation of Gli from Sufu. In mammalian fibroblast cells, knockdown of Rusc2 potentiates Hh signaling by accelerating signaling-induced dissociation of the Sufu-Gli protein complexes. In Xenopus embryos, knockdown of Rusc1 or overexpression of a dominant-negative Rusc enhances Hh signaling during eye development, leading to severe eye defects. Our study thus uncovers a novel regulatory mechanism controlling the response of cells to Hh signaling in vertebrates.

Nek2A phosphorylates and stabilizes SuFu: A new strategy of Gli2/Hedgehog signaling regulatory mechanism

Suppressor of Fused (SuFu) plays a conservative role in the regulation of the Gli transcription factors within the Hedgehog (Hh) signaling pathway. Despite the central importance of SuFu in the Hh pathway, little is known about its regulation. Here, we performed a GAL4-based yeast two-hybrid screen using human SuFu as bait, and identified NIMA-related expressed kinase 2A (Nek2A) as a new SuFu-interacting protein, which was also confirmed by glutathione-S-transferase pull-down and co-immunoprecipitation assays. Intriguingly, Nek2A is found to stabilize SuFu at least partly depending on its kinase activity, thereby triggering phosphorylation of the SuFu protein. Moreover, the phosphorylated SuFu inhibits the nuclear localization and transcriptional activity of Gli2/Hh signaling. These findings reveal a new mechanism of mammalian SuFu regulation, and offers novel insights into Hh signaling regulation in development and human disease.

Hedgehog receptor function during craniofacial development

The Hedgehog signalling pathway plays a fundamental role in orchestrating normal craniofacial development in vertebrates. In particular, Sonic hedgehog (Shh) is produced in three key domains during the early formation of the head; neuroectoderm of the ventral forebrain, facial ectoderm and the pharyngeal endoderm; with signal transduction evident in both ectodermal and mesenchymal tissue compartments. Shh signalling from the prechordal plate and ventral midline of the diencephalon is required for appropriate division of the eyefield and forebrain, with mutation in a number of pathway components associated with Holoprosencephaly, a clinically heterogeneous developmental defect characterized by a failure of the early forebrain vesicle to divide into distinct halves. In addition, signalling from the pharyngeal endoderm and facial ectoderm plays an essential role during development of the face, influencing cranial neural crest cells that migrate into the early facial processes. In recent years, the complexity of Shh signalling has been highlighted by the identification of multiple novel proteins that are involved in regulating both the release and reception of this protein. Here, we review the contributions of Shh signalling during early craniofacial development, focusing on Hedgehog receptor function and describing the consequences of disruption for inherited anomalies of this region in both mouse models and human populations.

Hedgehog signaling pathway: a novel model and molecular mechanisms of signal transduction

The Hedgehog (Hh) signaling pathway has numerous roles in the control of cell proliferation, tissue patterning and stem cell maintenance. In spite of intensive study, the mechanisms of Hh signal transduction are not completely understood. Here I review published data and present a novel model of vertebrate Hh signaling suggesting that Smoothened (Smo) functions as a G-protein-coupled receptor in cilia. This is the first model to propose molecular mechanisms for the major steps of Hh signaling, including inhibition of Smo by Patched, Smo activation, and signal transduction from active Smo to Gli transcription factors. It also suggests a novel role for the negative pathway regulators Sufu and PKA in these processes.

GLI2 cell-specific activity is controlled at the level of transcription and RNA processing: Consequences to cancer metastasis

High activity of GLI family zinc finger protein 2 (GLI2) promotes tumor progression. Removal of the repressor domain at the N terminus (GLI2∆N) by recombinant methods converts GLI2 into a powerful transcriptional activator. However, molecular mechanisms leading to the formation of GLI2∆N activator proteins have not been established. Herein we report for the first time that the functional activities of GLI2 are parted into different protein isoforms by alternative promoter usage, selection of alternative splicing, transcription initiation and termination sites. Functional studies using melanoma cells revealed that transcriptional regulation of GLI2 is TGFbeta-dependent and supports the predominant production of GLI2∆N and C-terminally truncated GLI2 (GLI2∆C) isoforms in cells with high migratory and invasive phenotype. Taken together, these results highlight the role of transcription and RNA processing as major processes in the regulation of GLI2 activity with severe impacts in cancer development.

A Comparison of Ci/Gli Activity as Regulated by Sufu in Drosophila and Mammalian Hedgehog Response

Suppressor of fused (Su(fu)/Sufu), one of the most conserved components of the Hedgehog (Hh) signaling pathway, binds Ci/Gli transcription factors and impedes activation of target gene expression. In Drosophila, the Su(fu) mutation has a minimal phenotype, and we show here that Ci transcriptional activity in large part is regulated independently of Su(fu) by other pathway components. Mutant mice lacking Sufu in contrast show excessive pathway activity and die as embryos with patterning defects. Here we show that in cultured cells Hh stimulation can augment transcriptional activity of a Gli2 variant lacking Sufu interaction and, surprisingly, that regulation of Hh pathway targets is nearly normal in the neural tube of Sufu^-/- mutant embryos that also lack Gli1 function. Some degree of Hh-induced transcriptional activation of Ci/Gli thus can occur independently of Sufu in both flies and mammals. We further note that Sufu loss can also reduce Hh induction of high-threshold neural tube fates, such as floor plate, suggesting a possible positive pathway role for Sufu.

T396I mutation of mouse Sufu reduces the stability and activity of Gli3 repressor

Hedgehog signaling is primarily transduced by two transcription factors: Gli2, which mainly acts as a full-length activator, and Gli3, which tends to be proteolytically processed from a full-length form (Gli3^FL) to an N-terminal repressor (Gli3^REP). Recent studies using a Sufu knockout mouse have indicated that Sufu is involved in regulating Gli2 and Gli3 activator and repressor activity at multiple steps of the signaling cascade; however, the mechanism of specific Gli2 and Gli3 regulation remains to be elucidated. In this study, we established an allelic series of ENU-induced mouse strains. Analysis of one of the missense alleles, Sufu^T396I, showed that Thr³⁹⁶ residue of Sufu played a key role in regulation of Gli3 activity. Sufu^T396I/T396I embryos exhibited severe polydactyly, which is indicative of compromised Gli3 activity. Concomitantly, significant quantitative reductions of unprocessed Gli3 (Gli3^FL) and processed Gli3 (Gli3^REP) were observed in vivo as well as in vitro. Genetic experiments showed that patterning defects in the limb buds of Sufu^T396I/T396I were rescued by a constitutive Gli3^REP allele (Gli3^∆699), strongly suggesting that Sufu^T396I reduced the truncated Gli3 repressor. In contrast, Sufu^T396I qualitatively exhibited no mutational effects on Gli2 regulation. Taken together, the results of this study show that the Thr³⁹⁶ residue of Sufu is specifically required for regulation of Gli3 but not Gli2. This implies a novel Sufu-mediated mechanism in which Gli2 activator and Gli3 repressor are differentially regulated.

Genomic analysis of smoothened inhibitor resistance in basal cell carcinoma

Smoothened (SMO) inhibitors are under clinical investigation for the treatment of several cancers. Vismodegib is approved for the treatment of locally advanced and metastatic basal cell carcinoma (BCC). Most BCC patients experience significant clinical benefit on vismodegib, but some develop resistance. Genomic analysis of tumor biopsies revealed that vismodegib resistance is associated with Hedgehog (Hh) pathway reactivation, predominantly through mutation of the drug target SMO and to a lesser extent through concurrent copy number changes in SUFU and GLI2. SMO mutations either directly impaired drug binding or activated SMO to varying levels. Furthermore, we found evidence for intra-tumor heterogeneity, suggesting that a combination of therapies targeting components at multiple levels of the Hh pathway is required to overcome resistance.

Regulation of Sufu activity by p66β and Mycbp provides new insight into vertebrate Hedgehog signaling

Control of Gli function by Sufu, a major negative regulator, is a key step in mammalian Hedgehog (Hh) signaling. Lin et al. identified several Sufu-interacting proteins, including p66β and Mycbp. Sufu recruits p66β to block Gli-mediated Hh target gene expression. Meanwhile, Mycbp forms a complex with Gli and Sufu without Hh stimulation but remains inactive. Hh pathway activation leads to dissociation of Sufu/p66β from Gli, enabling Mycbp to promote Gli protein activity and Hh target gene expression.

Control of Gli function by Suppressor of Fused (Sufu), a major negative regulator, is a key step in mammalian Hedgehog (Hh) signaling, but how this is achieved in the nucleus is unknown. We found that Hh signaling results in reduced Sufu protein levels and Sufu dissociation from Gli proteins in the nucleus, highlighting critical functions of Sufu in the nucleus. Through a proteomic approach, we identified several Sufu-interacting proteins, including p66β (a member of the NuRD [nucleosome remodeling and histone deacetylase] repressor complex) and Mycbp (a Myc-binding protein). p66β negatively and Mycbp positively regulate Hh signaling in cell-based assays and zebrafish. They function downstream from the membrane receptors, Patched and Smoothened, and the primary cilium. Sufu, p66β, Mycbp, and Gli are also detected on the promoters of Hh targets in a dynamic manner. Our results support a new model of Hh signaling in the nucleus. Sufu recruits p66β to block Gli-mediated Hh target gene expression. Meanwhile, Mycbp forms a complex with Gli and Sufu without Hh stimulation but remains inactive. Hh pathway activation leads to dissociation of Sufu/p66β from Gli, enabling Mycbp to promote Gli protein activity and Hh target gene expression. These studies provide novel insight into how Sufu controls Hh signaling in the nucleus.

Structural insight into the mutual recognition and regulation between Suppressor of Fused and Gli/Ci

Hedgehog (Hh) signalling regulates embryonic development and adult tissue homoeostasis. Mutations of its pathway components including Suppressor of Fused (Sufu) and Gli/Ci predispose to cancers and congenital anomalies. The Sufu-Gli protein complex occupies a central position in the vertebrate Hh signalling pathway, especially in mammals. Here structures of full-length human and Drosophila Sufu, the human Sufu-Gli complex, along with normal mode analysis and FRET measurement results, reveal that Sufu alternates between 'open' and 'closed' conformations. The 'closed' form of Sufu is stabilized by Gli binding and inhibited by Hh treatment, whereas the 'open' state of Sufu is promoted by Gli-dissociation and Hh signalling. Mutations of critical interface residues disrupt the Sufu-Gli complex and prevent Sufu from repressing Gli-mediated transcription, tethering Gli in the cytoplasm and protecting Gli from the 26S proteasome-mediated degradation. Our study thus provides mechanistic insight into the mutual recognition and regulation between Sufu and Gli/Ci.

G-protein-coupled receptors, Hedgehog signaling and primary cilia

The Hedgehog (Hh) pathway has become an important model to study the cell biology of primary cilia, and reciprocally, the study of ciliary processes provides an opportunity to solve longstanding mysteries in the mechanism of vertebrate Hh signal transduction. The cilium is emerging as an unique compartment for G-protein-coupled receptor (GPCR) signaling in many systems. Two members of the GPCR family, Smoothened and Gpr161, play important roles in the Hh pathway. We review the current understanding of how these proteins may function to regulate Hh signaling and also highlight some of the critical unanswered questions being tackled by the field. Uncovering GPCR-regulated mechanisms important in Hh signaling may provide therapeutic strategies against the Hh pathway that plays important roles in development, regeneration and cancer.

Effects of inhibition of hedgehog signaling on cell growth and migration of uveal melanoma cells

The Hedgehog (Hh) signaling pathway has been demonstrated to play a critical role in controlling embryonic development, tissue patterning, wound healing and a variety of cell functions. Aberrant activation of Hh signaling is implicated in the pathogenesis of many human cancers, and in angiogenesis. However, the role of this pathway in uveal melanoma (UM) carcinogenesis remains unknown. In this study, we investigated the effects of Hh inhibition using the specific Smoothened (Smo) antagonist cyclopamine to block Hh signaling in cultured human UM cell lines expressing Hh signaling components. Cyclopamine treatment effectively increased apoptosis and inhibited cell proliferation, migration, and epithelial-to-mesenchymal transition (EMT) by downregulating the Hh final arbiter glioblastoma 1 (Gli1), which regulates the transcription of target genes in the nucleus. Changes in gene and protein expression levels were detected by real-time PCR and by western blotting and immunocytochemistry, respectively. Cell cycle and apoptosis regulation induced by cyclopamine were demonstrated by flow cytometry. In addition, the migration capability of UM cells was reduced, as demonstrated by transwell migration and scratch assays. The effects of Hh inhibition on the levels of angiogenesis factors secreted by UM cells were examined by tube-formation assay.

CONCLUSION

Blocking the Hh pathway by cyclopamine decreased cell viability, migration, EMT, and angiogenesis, increased apoptosis, and induced G 1 phase cell cycle arrest in UM cells. Collectively, these results provide the first evidence of the significance of Gli1 activation downstream of Smo as a therapeutic target and the potential value of cyclopamine for the treatment of human UM.

Structural basis of SUFU-GLI interaction in human Hedgehog signalling regulation

Hedgehog signalling plays a fundamental role in the control of metazoan development, cell proliferation and differentiation, as highlighted by the fact that its deregulation is associated with the development of many human tumours. SUFU is an essential intracellular negative regulator of mammalian Hedgehog signalling and acts by binding and modulating the activity of GLI transcription factors. Despite its central importance, little is known about SUFU regulation and the nature of SUFU-GLI interaction. Here, the crystal and small-angle X-ray scattering structures of full-length human SUFU and its complex with the key SYGHL motif conserved in all GLIs are reported. It is demonstrated that GLI binding is associated with major conformational changes in SUFU, including an intrinsically disordered loop that is also crucial for pathway activation. These findings reveal the structure of the SUFU-GLI interface and suggest a mechanism for an essential regulatory step in Hedgehog signalling, offering possibilities for the development of novel pathway modulators and therapeutics.

Unraveling the therapeutic potential of the Hedgehog pathway in cancer. Nat Med. 2013;19:1410-1422. [PMID: 24202394 DOI: 10.1038/nm.3389]

Major progress has been made in recent years in the development of Hedgehog (Hh) pathway inhibitors for the treatment of patients with cancer. Promising clinical trial results have been obtained in cancers that harbor activating mutations of the Hh pathway, such as basal cell carcinoma and medulloblastoma. However, for many cancers, in which Hh ligand overexpression is thought to drive tumor growth, results have been disappointing. Here we review the preclinical data that continue to shape our understanding of the Hh pathway in tumorigenesis and the emerging clinical experience with smoothened inhibitors.

RIO kinase 3 acts as a SUFU-dependent positive regulator of Hedgehog signaling

Suppressor of fused (SUFU) is an essential negative regulator of the mammalian Hedgehog (HH) signaling pathway and its loss is associated with cancer development. On a cellular level, endogenous SUFU can mainly be detected in the cytoplasm and the nucleus. However, immunostaining of pancreatic cancer specimen revealed the existence of cell types showing selective enrichment of endogenous SUFU in the nucleus. Following up on this observation, we found that a SUFU construct which was experimentally tethered exclusively to the nucleus was unable to antagonize endogenous HH signaling, in contrast to control SUFU. These data suggest that alterations in the normal subcellular distribution of SUFU might interfere with its established negative role on the HH pathway. Performing a multi-well kinase screen in human cells identified RIO kinase 3 (RIOK3) as a novel modulator of SUFU subcellular distribution. Functionally, RIOK3 acts as a SUFU-dependent positive regulator of HH signaling. Taken together, we propose that factors modulating the nucleo-cytoplasmic distribution of SUFU impact on the normal function of this tumor suppressing protein.

Mutational analysis of hedgehog signaling pathway genes in human malignant mesothelioma

BACKGROUND

The Hedgehog (HH) signaling pathway is critical for embryonic development and adult homeostasis. Recent studies have identified regulatory roles for this pathway in certain cancers with mutations in the HH pathway genes. The extent to which mutations of the HH pathway genes are involved in the pathogenesis of malignant mesothelioma (MMe) is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Real-time PCR analysis of HH pathway genes PTCH1, GLI1 and GLI2 were performed on 7 human MMe cell lines. Exon sequencing of 13 HH pathway genes was also performed in cell lines and human MMe tumors. In silico programs were used to predict the likelihood that an amino-acid substitution would have a functional effect. GLI1, GLI2 and PTCH1 were highly expressed in MMe cells, indicative of active HH signaling. PTCH1, SMO and SUFU mutations were found in 2 of 11 MMe cell lines examined. A non-synonymous missense SUFU mutation (p.T411M) was identified in LO68 cells. In silico characterization of the SUFU mutant suggested that the p.T411M mutation might alter protein function. However, we were unable to demonstrate any functional effect of this mutation on Gli activity. Deletion of exons of the PTCH1 gene was found in JU77 cells, resulting in loss of one of two extracellular loops implicated in HH ligand binding and the intracellular C-terminal domain. A 3-bp insertion (69_70insCTG) in SMO, predicting an additional leucine residue in the signal peptide segment of SMO protein was also identified in LO68 cells and a MMe tumour.

CONCLUSIONS/SIGNIFICANCE

We identified the first novel mutations in PTCH1, SUFU and SMO associated with MMe. Although HH pathway mutations are relatively rare in MMe, these data suggest a possible role for dysfunctional HH pathway in the pathogenesis of a subgroup of MMe and help rationalize the exploration of HH pathway inhibitors for MMe therapy.

Extramacrochaetae imposes order on the Drosophila eye by refining the activity of the Hedgehog signaling gradient

The compound eye of Drosophila melanogaster is configured by a differentiating wave, the morphogenetic furrow, that sweeps across the eye imaginal disc and transforms thousands of undifferentiated cells into a precisely ordered repetitive array of 800 ommatidia. The initiation of the furrow at the posterior margin of the epithelium and its subsequent movement across the eye field is controlled by the activity of the Hedgehog (Hh) signaling pathway. Differentiating photoreceptors that lie behind the furrow produce and secrete the Hh morphogen, which is captured by cells within the furrow itself. This leads to the stabilization of the full-length form of the zinc-finger transcription factor Cubitus interruptus (Ci(155)), the main effector of Hh signaling. Ci(155) functions as a transcriptional activator of a number of downstream targets, including decapentaplegic (dpp), a TGFβ homolog. In this report, we describe a mechanism that is in place within the fly retina to limit Hh pathway activity within and ahead of the furrow. We demonstrate that the helix-loop-helix (HLH) protein Extramacrochaetae (Emc) regulates Ci(155) levels. Loss of emc leads to an increase in Ci(155) levels, nuclear migration, apical cell constriction and an acceleration of the furrow. We find that these roles are distinct from the bHLH protein Hairy (H), which we show restricts atonal (ato) expression ahead of the furrow. Secondary furrow initiation along the dorsal and ventral margins is blocked by the activity of the Wingless (Wg) pathway. We also show that Emc regulates and cooperates with Wg signaling to inhibit lateral furrow initiation.