Hedgehog: functions and mechanisms

Keeping the balance between proliferation and differentiation: the primary cilium

Primary cilia are post-mitotic cellular organelles that are present in the vast majority of cell types in the human body. An extensive body of data gathered in recent years is demonstrating a crucial role for this organelle in a number of cellular processes that include mechano and chemo-sensation as well as the transduction of signaling cascades critical for the development and maintenance of different tissues and organs. Consequently, cilia are currently viewed as cellular antennae playing a critical role at the interphase between cells and their environment, integrating a range of stimuli to modulate cell fate decisions including cell proliferation, migration and differentiation. Importantly, this regulatory role is not just a consequence of their participation in signal transduction but is also the outcome of both the tight synchronization/regulation of ciliogenesis with the cell cycle and the role of individual ciliary proteins in cilia-dependent and independent processes. Here we review the role of primary cilia in the regulation of cell proliferation and differentiation and illustrate how this knowledge has provided insight to understand the phenotypic consequences of ciliary dysfunction.

Major signaling pathways in intestinal stem cells

BACKGROUND

The discovery of markers to identify the intestinal stem cell population and the generation of powerful transgenic mouse models to study stem cell physiology have led to seminal discoveries in stem cell biology.

SCOPE OF REVIEW

In this review we give an overview of the current knowledge in the field of intestinal stem cells (ISCs) highlighting the most recent progress on markers defining the ISC population and pathways governing intestinal stem cell maintenance and differentiation. Furthermore we review their interaction with other stem cell related pathways. Finally we give an overview of alteration of these pathways in human inflammatory gastrointestinal diseases.

MAJOR CONCLUSIONS

We highlight the complex network of interactions occurring among different pathways and put in perspective the many layers of regulation that occur in maintaining the intestinal homeostasis.

GENERAL SIGNIFICANCE

Understanding the involvement of ISCs in inflammatory diseases can potentially lead to new therapeutic approaches to treat inflammatory GI pathologies such as IBD and celiac disease and could reveal the molecular mechanisms leading to the pathogenesis of dysplasia and cancer in inflammatory chronic conditions. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Hedgehog signaling is a novel therapeutic target in tamoxifen-resistant breast cancer aberrantly activated by PI3K/AKT pathway

Endocrine resistance is a major challenge in the management of estrogen receptor (ER)-positive breast cancers. Although multiple mechanisms leading to endocrine resistance have been proposed, the poor outcome of patients developing resistance to endocrine therapy warrants additional studies. Here we show that noncanonical Hedgehog (Hh) signaling is an alternative growth promoting mechanism that is activated in tamoxifen-resistant tumors. Importantly, phosphoinositide 3-kinase inhibitor/protein kinase B (PI3K/AKT) pathway plays a key role in regulating Hh signaling by protecting key components of this pathway from proteasomal degradation. The levels of Hh-signaling molecules SMO and GLI1 and the targets were significantly elevated in tamoxifen-resistant MCF-7 cells and T47D cells. Serial passage of the resistant cells in mice resulted in aggressive tumors that metastasized to distant organs with concurrent increases in Hh marker expression and epithelial mesenchymal transition. RNAi-mediated depletion of SMO or GLI1 in the resistant cells resulted in reduced proliferation, clonogenic survival and delayed G(1)-S transition. Notably, treatment of resistant cells with PI3K inhibitors decreased SMO and GLI1 protein levels and activity that was rescued upon blocking GSK3β and proteasomal degradation. Furthermore, treatment of tamoxifen-resistant xenografts with anti-Hh compound GDC-0449 blocked tumor growth in mice. Importantly, high GLI1 expression correlated inversely with disease-free and overall survival in a cohort of 315 patients with breast cancer. In summary, our results describe a signaling event linking PI3K/AKT pathway with Hh signaling that promotes tamoxifen resistance. Targeting Hh pathway alone or in combination with PI3K/AKT pathway could therefore be a novel therapeutic option in treating endocrine-resistant breast cancer.

Signaling in colon cancer stem cells

: Colorectal cancer is the fourth most common form of cancer worldwide and ranks third among the cancer-related deaths in the US and other Western countries. It occurs with equal frequency in men and women, constituting 10% of new cancer cases in men and 11% in women. Despite recent advancement in therapeutics, the survival rates from metastatic are less than 5%. Growing evidence supports the contention that epithelial cancers including colorectal cancer, the incidence of which increases with aging, are diseases driven by the pluripotent, self-renewing cancer stem cells (CSCs). Dysregulation of Wnt, Notch, Hedgehog and/or TGF-β signaling pathways that are involved in proliferation and maintenance of CSCs leads to the development of CRC. This review focuses on the signaling pathways relevant for CRC to understand the mechanisms leading to tumor progression and therapy resistance, which may help in the development of therapeutic strategies for CRC.

Triparanol suppresses human tumor growth in vitro and in vivo

Despite the improved contemporary multidisciplinary regimens treating cancer, majority of cancer patients still suffer from adverse effects and relapse, therefore posing a significant challenge to uncover more efficacious molecular therapeutics targeting signaling pathways central to tumorigenesis. Here, our study have demonstrated that Triparanol, a cholesterol synthesis inhibitor, can block proliferation and induce apoptosis in multiple human cancer cells including lung, breast, liver, pancreatic, prostate cancer and melanoma cells, and growth inhibition can be rescued by exogenous addition of cholesterol. Remarkably, we have proved Triparanol can significantly repress Hedgehog pathway signaling in these human cancer cells. Furthermore, study in a mouse xenograft model of human lung cancer has validated that Triparanol can impede tumor growth in vivo. We have therefore uncovered Triparanol as potential new cancer therapeutic in treating multiple types of human cancers with deregulated Hedgehog signaling.

The utility of hedgehog signaling pathway inhibition for cancer

The Hedgehog (Hh) signaling pathway has been implicated in tumor initiation and metastasis across different malignancies. Major mechanisms by which the Hh pathway is aberrantly activated can be attributed to mutations of members of Hh pathway or excessive/inappropriate expression of Hh pathway ligands. The Hh signaling pathway also affects the regulation of cancer stem cells, leading to their capabilities in tumor formation, disease progression, and metastasis. Preliminary results of early phase clinical trials of Hh inhibitors administered as monotherapy demonstrated promising results in patients with basal cell carcinoma and medulloblastoma, but clinically meaningful anticancer efficacy across other tumor types seems to be lacking. Additionally, cases of resistance have been already observed. Mutations of SMO, activation of Hh pathway components downstream to SMO, and upregulation of alternative signaling pathways are possible mechanisms of resistance development. Determination of effective Hh inhibitor-based combination regimens and development of correlative biomarkers relevant to this pathway should remain as clear priorities for future research.

Scutellaria barbata D. Don inhibits tumor angiogenesis via suppression of Hedgehog pathway in a mouse model of colorectal cancer

Angiogenesis, which plays a critical role during tumor development, is tightly regulated by the Sonic Hedgehog (SHH) pathway, which has been known to malfunction in many types of cancer. Therefore, inhibition of angiogenesis via modulation of the SHH signaling pathway has become very attractive for cancer chemotherapy. Scutellaria barbata D. Don (SB) has long been used in China to treat various cancers including colorectal cancer (CRC). Our published data suggested that the ethanol extract of SB (EESB) is able to induce apoptosis of colon cancer cells and inhibit angiogenesis in a chick embryo chorioallantoic membrane model. To further elucidate the precise mechanisms of its anti-tumor activity, in the present study we used a CRC mouse xenograft model to evaluate the effect of EESB on tumor growth and angiogenesis in vivo. Our current data indicated that EESB reduces tumor size without affecting on the body weight gain in CRC mice. In addition, EESB treatment suppresses the expression of key mediators of the SHH pathway in tumor tissues, which in turn resulted in the inhibition of tumor angiogenesis. Furthermore, EESB treatment inhibits the expression of vascular endothelial growth factor A (VEGF-A), an important target gene of SHH signaling and functioning as one of the strongest stimulators of angiogenesis. Our findings suggest that inhibition of tumor angiogenesis via suppression of the SHH pathway might be one of the mechanisms by which Scutellaria barbata D. Don can be effective in the treatment of cancers.

Kinesins and cancer

Kinesins are a family of molecular motors that travel unidirectionally along microtubule tracks to fulfil their many roles in intracellular transport or cell division. Over the past few years kinesins that are involved in mitosis have emerged as potential targets for cancer drug development. Several compounds that inhibit two mitotic kinesins (EG5 (also known as KIF11) and centromere-associated protein E (CENPE)) have entered Phase I and II clinical trials either as monotherapies or in combination with other drugs. Additional mitotic kinesins are currently being validated as drug targets, raising the possibility that the range of kinesin-based drug targets may expand in the future.

Neogenin regulates Sonic Hedgehog pathway activity during digit patterning

BACKGROUND

Digit patterning integrates signaling by the Sonic Hedgehog (SHH), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP) pathways. GLI3, a component of the SHH pathway, is a major regulator of digit number and identity. Neogenin (encoded by Neo1) is a cell surface protein that serves to transduce signals from several ligands, including BMPs, in various developmental contexts. Although neogenin is implicated in BMP signaling, it has not been linked to SHH signaling and its role in digit patterning is unknown.

RESULTS

We report that Neo1 mutant mice have preaxial polydactyly with low penetrance. Expression of SHH target genes, but not BMP target genes, is altered in Neo1 mutant limb buds. Analysis of mice carrying mutations in both Neo1 and Gli3 reveals that, although neogenin plays a role in constraint of digit numbers, suppressing polydactyly, it is also required for the severe polydactyly caused by loss of GLI3. Furthermore, embryo fibroblasts from Neo1 mutant mice are sensitized to SHH pathway activation in vitro.

CONCLUSIONS

Our findings indicate that neogenin regulates SHH signaling in the limb bud to achieve proper digit patterning.

The Hedgehog receptor patched functions in multidrug transport and chemotherapy resistance

Most anticancer drugs fail to eradicate tumors, leading to the development of drug resistance and disease recurrence. The Hedgehog signaling plays a crucial role during embryonic development, but is also involved in cancer development, progression, and metastasis. The Hedgehog receptor Patched (Ptc) is a Hedgehog signaling target gene that is overexpressed in many cancer cells. Here, we show a link between Ptc and resistance to chemotherapy, and provide new insight into Ptc function. Ptc is cleared from the plasma membrane upon interaction with its ligand Hedgehog, or upon treatment of cells with the Hedgehog signaling antagonist cyclopamine. In both cases, after incubation of cells with doxorubicin, a chemotherapeutic agent that is used for the clinical management of recurrent cancers, we observed an inhibition of the efflux of doxorubicin from Hedgehog-responding fibroblasts, and an increase of doxorubicin accumulation in two different cancer cell lines that are known to express aberrant levels of Hedgehog signaling components. Using heterologous expression system, we stringently showed that the expression of human Ptc conferred resistance to growth inhibition by several drugs from which chemotherapeutic agents such as doxorubicin, methotrexate, temozolomide, and 5-fluorouracil. Resistance to doxorubicin correlated with Ptc function, as shown using mutations from Gorlin's syndrome patients in which the Ptc-mediated effect on Hedgehog signaling is lost. Our results show that Ptc is involved in drug efflux and multidrug resistance, and suggest that Ptc contributes to chemotherapy resistance of cancer cells.

Role of hedgehog signaling in malignant pleural mesothelioma

PURPOSE

The aim of this study was to assess the activity of hedgehog signaling pathway in malignant pleural mesothelioma (MPM).

EXPERIMENTAL DESIGN

The expression of hedgehog signaling components was assessed by quantitative PCR and in situ hybridization in 45 clinical samples. Primary MPM cultures were developed in serum-free condition in 3% oxygen and were used to investigate the effects of smoothened (SMO) inhibitors or GLI1 silencing on cell growth and hedgehog signaling. In vivo effects of SMO antagonists were determined in an MPM xenograft growing in nude mice.

RESULTS

A significant increase in GLI1, sonic hedgehog, and human hedgehog interacting protein gene expression was observed in MPM tumors compared with nontumoral pleural tissue. SMO antagonists inhibited GLI1 expression and cell growth in sensitive primary cultures. This effect was mimicked by GLI1 silencing. Reduced survivin and YAP protein levels were also observed. Survivin protein levels were rescued by overexpression of GLI1 or constitutively active YAP1. Treatment of tumor-bearing mice with the SMO inhibitor HhAntag led to a significant inhibition of tumor growth in vivo accompanied by decreased Ki-67 and nuclear YAP immunostaining and a significant difference in selected gene expression profile in tumors.

CONCLUSIONS

An aberrant hedgehog signaling is present in MPM, and inhibition of hedgehog signaling decreases tumor growth indicating potential new therapeutic approach.

The progesterone receptor regulates implantation, decidualization, and glandular development via a complex paracrine signaling network

Many women are affected by infertility and reproductive-associated disease such as endometriosis or endometrial cancer. Successful pregnancy is dependent on a healthy uterus that is fit to receive and support a fertilized embryo. The uterus is an endocrine organ, responsive to the presence of the ovarian steroid hormones, estrogen and progesterone, which activate transcription of target genes through the binding of their cognate receptors, the estrogen receptor and the progesterone receptor. Progesterone signaling has been demonstrated to be critical for the initiation and continuance of pregnancy. Through the induction of Ihh, Wnt, and Bmp pathways within the epithelial and stromal compartments of the uterus, embryo attachment and implantation occur followed by decidualization of the surrounding stroma. Furthermore, these pathways have been shown to be involved in uterine glandular development. This review highlights the integral role of uterine progesterone-mediated paracrine signaling in gland development and pregnancy.

Scube/You activity mediates release of dually lipid-modified Hedgehog signal in soluble form

Owing to their covalent modification by cholesterol and palmitate, Hedgehog (Hh) signaling proteins are localized predominantly to the plasma membrane of expressing cells. Yet Hh proteins are also capable of mobilizing to and eliciting direct responses from distant cells. The zebrafish you gene, identified genetically >15 years ago, was more recently shown to encode a secreted glycoprotein that acts cell-nonautonomously in the Hh signaling pathway by an unknown mechanism. We investigated the function of the protein encoded by murine Scube2, an ortholog of you, and found that it mediates release in soluble form of the mature, cholesterol- and palmitate-modified Sonic hedgehog protein signal (ShhNp) when added to cultured cells or purified detergent-resistant membrane microdomains containing ShhNp. The efficiency of Scube2-mediated release of ShhNp is enhanced by the palmitate adduct of ShhNp and by coexpression in ShhNp-producing cells of mDispatchedA (mDispA), a transporter-like protein with a previously defined role in the release of lipid-modified Hh signals. The structural determinants of Scube2 required for its activity in cultured cell assays match those required for rescue of you mutant zebrafish embryos, and we thus conclude that the role of Scube/You proteins in Hh signaling in vivo is to facilitate the release and mobilization of Hh proteins for distant action.

Sex and hedgehog: roles of genes in the hedgehog signaling pathway in mammalian sexual differentiation

The chromosome status of the mammalian embryo initiates a multistage process of sexual development in which the bipotential reproductive system establishes itself as either male or female. These events are governed by intricate cell-cell and interorgan communication that is regulated by multiple signaling pathways. The hedgehog signaling pathway was originally identified for its key role in the development of Drosophila, but is now recognized as a critical developmental regulator in many species, including humans. In addition to its developmental roles, the hedgehog signaling pathway also modulates adult organ function, and misregulation of this pathway often leads to diseases, such as cancer. The hedgehog signaling pathway acts through its morphogenetic ligands that signal from ligand-producing cells to target cells over a specified distance. The target cells then respond in a graded manner based on the concentration of the ligands that they are exposed to. Through this unique mechanism of action, the hedgehog signaling pathway elicits cell fate determination, epithelial-mesenchymal interactions, and cellular homeostasis. Here, we review current findings on the roles of hedgehog signaling in the sexually dimorphic development of the reproductive organs with an emphasis on mammals and comparative evidence in other species.

Comparative genomics of the Hedgehog loci in chordates and the origins of Shh regulatory novelties

The origin and evolution of the complex regulatory landscapes of some vertebrate developmental genes, often spanning hundreds of Kbp and including neighboring genes, remain poorly understood. The Sonic Hedgehog (Shh) genomic regulatory block (GRB) is one of the best functionally characterized examples, with several discrete enhancers reported within its introns, vast upstream gene-free region and neighboring genes (Lmbr1 and Rnf32). To investigate the origin and evolution of this GRB, we sequenced and characterized the Hedgehog (Hh) loci from three invertebrate chordate amphioxus species, which share several early expression domains with Shh. Using phylogenetic footprinting within and between chordate lineages, and reporter assays in zebrafish probing >30 Kbp of amphioxus Hh, we report large sequence and functional divergence between both groups. In addition, we show that the linkage of Shh to Lmbr1 and Rnf32, necessary for the unique gnatostomate-specific Shh limb expression, is a vertebrate novelty occurred between the two whole-genome duplications.

The Development of a High-Content Screening Binding Assay for the Smoothened Receptor

In this study, the development of an image-based high-content screening (HCS) binding assay for the seven-transmembrane (7TM) receptor Smoothened (Smo) is described. Using BacMam-based gene delivery of Smo, BODIPY-cyclopamine as a fluorescent probe, and a confocal imaging system, a robust 384-well assay that could be used for high-throughput compound profiling activities was developed. The statistically robust HCS binding assay was developed through optimization of multiple parameters, including cell transduction conditions, Smo expression levels, the image analysis algorithm, and staining procedures. Evaluation of structurally diverse compounds, including functional Smo activators, inhibitors, and related analogs, demonstrated good compound potency correlations between high-content imaging binding, membrane fluorescence polarization binding, and gene reporter assays. Statistical analysis of data from a screening test set of compounds at a single 10-µM concentration suggested that the high-content imaging Smo binding assay is amenable for use in hit identification. The 384-well HCS assay was rapidly developed and met statistical assay performance targets, thus demonstrating its utility as a fluorescent whole-cell binding assay suitable for compound screening and profiling.

Sonic hedgehog regulates presynaptic terminal size, ultrastructure and function in hippocampal neurons

Sonic hedgehog (Shh) signaling is essential to the patterning of the embryonic neural tube, but its presence and function in the postmitotic differentiated neurons in the brain remain largely uncharacterized. We recently showed that Shh and its signaling components, Patched and Smoothened, are expressed in postnatal and adult hippocampal neurons. We have now examined whether Shh signaling has a function in these neurons. Using cultured hippocampal neurons as a model system, we found that presynaptic terminals become significantly larger in response to the application of Shh. Ultrastructural examination confirmed the enlarged presynaptic profiles and also revealed variable increases in the size of synaptic vesicles, with a resulting loss of uniformity. Furthermore, electrophysiological analyses showed significant increases in the frequency, but not the amplitude, of spontaneous miniature excitatory postsynaptic currents (mEPSCs) in response to Shh, providing functional evidence of the selective role of Shh in presynaptic terminals. Thus, we conclude that Shh signaling regulates the structure and functional properties of presynaptic terminals of hippocampal neurons.

Management of small cell lung cancer: recent developments for optimal care

Small cell lung cancer (SCLC) represents approximately 13% of all lung cancer diagnoses and the incidence has reduced over the last 20 years. Treatment of SCLC remains challenging because of its rapid growth, early dissemination and development of drug resistance during the course of the disease. Chemotherapy remains the cornerstone of treatment for limited (LD) and extensive disease (ED), with concurrent chemotherapy and radical thoracic radiotherapy representing the best treatment option for fit patients with LD. Platinum-based chemotherapy is the treatment of choice in fit patients with good organ function, and the radiosensitizing effect of cisplatin is critically important for concurrent chemoradiotherapy in LD. Anthracycline-containing regimens represent a viable alternative for patients where platinum-based chemotherapy is contraindicated. Patients who relapse or progress after first-line chemotherapy have a very poor prognosis. Second-line therapy may produce a modest clinical benefit. Maintenance chemotherapy has not been shown to convincingly improve outcomes for SCLC. A number of targeted agents have been investigated in LD and ED, mostly in unselected populations, with disappointing results. Prophylactic cranial irradiation has been shown to reduce the incidence of brain metastases and prolong survival for both LD and ED without negative impact on quality of life (QOL) and cognitive function. Ongoing trials will shed some light on the impact of thoracic radiotherapy on QOL, symptom control and survival in ED SCLC patients who benefitted from first-line chemotherapy.

Targeting the Hedgehog signaling pathway for cancer therapy

INTRODUCTION

Hedgehog (Hh) signaling pathway plays key roles in embryonic development, formation and maintenance of cancer stem cells (CSCs) and acquisition of epithelial-to-mesenchymal transition (EMT). Since CSCs and EMT are important biological factors responsible for cancer cell invasion, metastasis, drug resistance and tumor recurrence, the Hh signaling pathway is believed to be an important target for cancer therapy.

AREAS COVERED

In recent years, small-molecule inhibitors of Hh signaling have been synthesized for cancer treatment. Clinical trials using these inhibitors are being conducted to determine their toxicity profiles and efficacies. In addition, nutraceuticals (such as isoflavones, curcumin, vitamin D, etc) have been shown to inhibit cancer growth through downregulation of Hh signaling.

EXPERT OPINION

Inhibition of Hh signaling is important for suppression of cancer growth, invasion, metastasis and recurrence in cancer therapy. However, targeting only one molecule in Hh signaling may not be sufficient to kill cancer cells because cancers show deregulation of multiple signals. Therefore, utilizing new technologies to determine alterations in Hh and other signals for individuals and designing combination strategies with small-molecule Hh inhibitors, nutraceuticals and other chemotherapeutics in targeted personalized therapy could have a significant effect on improving the overall survival of patients with cancers.

Crosstalk between TGF-β and hedgehog signaling in cancer

Hedgehog (HH) and TGF-β signals control various aspects of embryonic development and cancer progression. While their canonical signal transduction cascades have been well characterized, there is increasing evidence that these pathways are able to exert overlapping activities that challenge efficient therapeutic targeting. We herein review the current knowledge on HH signaling and summarize the recent findings on the crosstalks between the HH and TGF-β pathways in cancer.

Hedgehog regulates angiogenesis of intersegmental vessels through the VEGF signaling pathway

BACKGROUND

The cellular mechanisms regulating branching and growth of the intersegmental vessels (ISVs) are not well understood. We have carried out studies demonstrating that Hedgehog (Hh) signaling is a major regulator of intersomitic vessel growth.

RESULTS

Inhibition of Hh activity by cyclopamine completely blocks formation of intersomitic vessels in the avian embryo. Examination of gene expression patterns in Hh-deficient embryos shows that components of the VEGF and Notch signaling pathways are down-regulated. However, we find no evidence that Notch signaling plays a significant role in regulation of intersomitic vessel growth. Indeed, it appears that Hh modulation of Vascular Endothelial Growth Factor, VEGF, is the primary regulator of growth of intersomitic vessels in the avian embryo.

CONCLUSIONS

Inhibition of the VEGF pathway results in absence of ISVs, whereas stimulation of VEGF expression leads to precocious branching of ISVs. These results demonstrate that Hh is an essential modulator of VEGF expression during developmental angiogenesis.

Prevention of premature fusion of calvarial suture in GLI-Kruppel family member 3 (Gli3)-deficient mice by removing one allele of Runt-related transcription factor 2 (Runx2)

Mutations in the gene encoding the zinc finger transcription factor GLI3 (GLI-Kruppel family member 3) have been identified in patients with Grieg cephalopolysyndactyly syndrome in which premature fusion of calvarial suture (craniosynostosis) is an infrequent but important feature. Here, we show that Gli3 acts as a repressor in the developing murine calvaria and that Dlx5, Runx2 type II isoform (Runx2-II), and Bmp2 are expressed ectopically in the calvarial mesenchyme, which results in aberrant osteoblastic differentiation in Gli3-deficient mouse (Gli3(Xt-J/Xt-J)) and resulted in craniosynostosis. At the same time, enhanced activation of phospho-Smad1/5/8 (pSmad1/5/8), which is a downstream mediator of canonical Bmp signaling, was observed in Gli3(Xt-J/Xt-J) embryonic calvaria. Therefore, we generated Gli3;Runx2 compound mutant mice to study the effects of decreasing Runx2 dosage in a Gli3(Xt-J/Xt-J) background. Gli3(Xt-J/Xt-J) Runx2(+/-) mice have neither craniosynostosis nor additional ossification centers in interfrontal suture and displayed a normalization of Dlx5, Runx2-II, and pSmad1/5/8 expression as well as sutural mesenchymal cell proliferation. These findings suggest a novel role for Gli3 in regulating calvarial suture development by controlling canonical Bmp-Smad signaling, which integrates a Dlx5/Runx2-II cascade. We propose that targeting Runx2 might provide an attractive way of preventing craniosynostosis in patients.

The molecular basis of human congenital limb malformations

This review focuses predominantly on the human congenital malformations caused by alterations affecting the morphoregulatory gene networks that control early limb bud patterning and outgrowth. Limb defects are among the most frequent congenital malformations in humans that are caused by genetic mutations or teratogenic effects resulting either in abnormal, loss of, or additional skeletal elements. Spontaneous and engineered mouse models have been used to identify and study the molecular alterations and disrupted gene networks that underlie human congenital limb malformations. More recently, mouse genetics has begun to reveal the alterations that affect the often-large cis-regulatory landscapes that control gene expression in limb buds and cause devastating effects on limb bud development. These findings have paved the way to identifying mutations in cis-regulatory regions as causal to an increasing number of congenital limb malformations in humans. In these cases, no mutations in the coding region of a presumed candidate were previously detected. This review highlights how the current understanding of the molecular gene networks and interactions that control mouse limb bud development provides insight into the etiology of human congenital limb malformations.

Cytoneme-mediated delivery of hedgehog regulates the expression of bone morphogenetic proteins to maintain germline stem cells in Drosophila

Stem cells reside in specialised microenvironments, or niches, which often contain support cells that control stem cell maintenance and proliferation. Hedgehog (Hh) proteins mediate homeostasis in several adult niches, but a detailed understanding of Hh signalling in stem cell regulation is lacking. Studying the Drosophila female germline stem cell (GSC) niche, we show that Hh acts as a critical juxtacrine signal to maintain the normal GSC population of the ovary. Hh production in cap cells, a type of niche support cells, is regulated by the Engrailed transcription factor. Hh is then secreted to a second, adjacent population of niche cells, the escort cells, where it activates transcription of the GSC essential factors Decapentaplegic (Dpp) and Glass bottom boat (Gbb). In wild-type niches, Hh protein decorates short filopodia that originate in the support cap cells and that are functionally relevant, as they are required to transduce the Hh pathway in the escort cells and to maintain a normal population of GSCs. These filopodia, reminiscent of wing disc cytonemes, grow several fold in length if Hh signalling is impaired within the niche. Because these long cytonemes project directionally towards the signalling-deficient region, cap cells sense and react to the strength of Hh pathway transduction in the niche. Thus, the GSC niche responds to insufficient Hh signalling by increasing the range of Hh spreading. Although the signal(s) perceived by the cap cells and the receptor(s) involved are still unknown, our results emphasise the integration of signals necessary to maintain a functional niche and the plasticity of cellular niches to respond to challenging physiological conditions.

Adipogenesis: from stem cell to adipocyte

Excessive caloric intake without a rise in energy expenditure promotes adipocyte hyperplasia and adiposity. The rise in adipocyte number is triggered by signaling factors that induce conversion of mesenchymal stem cells (MSCs) to preadipocytes that differentiate into adipocytes. MSCs, which are recruited from the vascular stroma of adipose tissue, provide an unlimited supply of adipocyte precursors. Members of the BMP and Wnt families are key mediators of stem cell commitment to produce preadipocytes. Following commitment, exposure of growth-arrested preadipocytes to differentiation inducers [insulin-like growth factor 1 (IGF1), glucocorticoid, and cyclic AMP (cAMP)] triggers DNA replication and reentry into the cell cycle (mitotic clonal expansion). Mitotic clonal expansion involves a transcription factor cascade, followed by the expression of adipocyte genes. Critical to these events are phosphorylations of the transcription factor CCATT enhancer-binding protein β (C/EBPβ) by MAP kinase and GSK3β to produce a conformational change that gives rise to DNA-binding activity. "Activated" C/EBPβ then triggers transcription of peroxisome proliferator-activated receptor-γ (PPARγ) and C/EBPα, which in turn coordinately activate genes whose expression produces the adipocyte phenotype.

Tissue plasminogen activator and plasminogen activator inhibitor 1 contribute to sonic hedgehog-induced in vitro cerebral angiogenesis

The molecular mechanisms underlying cerebral angiogenesis have not been fully investigated. Using primary mouse brain endothelial cells (MBECs) and a capillary-like tube formation assay, we investigated whether the sonic hedgehog (Shh) signaling pathway is coupled with the plasminogen/plasmin system in mediating cerebral angiogenesis. We found that incubation of MBECs with recombinant human Shh (rhShh) substantially increased the tube formation in naïve MBECs. This was associated with increases in tissue plasminogen activator (tPA) activation and reduction of plasminogen activator inhibitor 1 (PAI-1). Blockage of the Shh pathway with cyclopamine abolished the induction of tube formation and the effect of rhShh on tPA and PAI-1. Addition of PAI-1 reduced rhShh-augmented tube formation. Genetic ablation of tPA in MBECs impaired tube formation and downregulated of vascular endothelial growth factor (VEGF) and angiopoietin 1 (Ang1). Addition of rhShh to tPA−/− MBECs only partially restored the tube formation and upregulated Ang1, but not VEGF, although rhShh increased VEGF and Ang1 expression on wild-type MBECs. Complete restoration of tube formation in tPA−/− MBECs was observed only when both exogenous Shh and tPA were added. The present study provides evidence that tPA and PAI-1 contribute to Shh-induced in vitro cerebral angiogenesis.

Subcellular localization of Patched and Smoothened, the receptors for Sonic hedgehog signaling, in the hippocampal neuron

Cumulative evidence suggests that, aside from patterning the embryonic neural tube, Sonic hedgehog (Shh) signaling plays important roles in the mature nervous system. In this study, we investigate the expression and localization of the Shh signaling receptors, Patched (Ptch) and Smoothened (Smo), in the hippocampal neurons of young and mature rats. Reverse transcriptase-polymerase chain reaction and immunoblotting analyses show that the expression of Ptch and Smo remains at a moderate level in young postnatal and adult brains. By using immunofluorescence light microscopy and immunoelectron microscopy, we examine the spatial distribution of Ptch and Smo within the hippocampal neurons. In young developing neurons, Ptch and Smo are present in the processes and are clustered at their growth cones. In mature neurons, Ptch and Smo are concentrated in dendrites, spines, and postsynaptic sites. Synaptic Ptch and Smo often co-exist with unusual structures-synaptic spinules and autophagosomes. Our results reveal the anatomical organization of the Shh receptors within both the young and the mature hippocampal neurons.

The BAR Domain Superfamily Proteins from Subcellular Structures to Human Diseases

Eukaryotic cells have complicated membrane systems. The outermost plasma membrane contains various substructures, such as invaginations and protrusions, which are involved in endocytosis and cell migration. Moreover, the intracellular membrane compartments, such as autophagosomes and endosomes, are essential for cellular viability. The Bin-Amphiphysin-Rvs167 (BAR) domain superfamily proteins are important players in membrane remodeling through their structurally determined membrane binding surfaces. A variety of BAR domain superfamily proteins exist, and each family member appears to be involved in the formation of certain subcellular structures or intracellular membrane compartments. Most of the BAR domain superfamily proteins contain SH3 domains, which bind to the membrane scission molecule, dynamin, as well as the actin regulatory WASP/WAVE proteins and several signal transduction molecules, providing possible links between the membrane and the cytoskeleton or other machineries. In this review, we summarize the current information about each BAR superfamily protein with an SH3 domain(s). The involvement of BAR domain superfamily proteins in various diseases is also discussed.

Distinct phosphorylations on kinesin costal-2 mediate differential hedgehog signaling strength

The graded Hedgehog (Hh) signal is transduced by the transmembrane Smoothened (Smo) proteins in both vertebrates and invertebrates. In Drosophila, associations between Smo and the Fused (Fu)/Costal-2 (Cos2)/Cubitus Interruptus (Ci) cytoplasmic complex lead to pathway activation, but it remains unclear how the cytoplasmic complex responds to and transduces different levels of Hh signaling. We show here that, within the Hh gradient field, low- and high-magnitude Smo activations control differentially the phosphorylation of Cos2 on two distinct serines. We also provide evidence that these phosphorylations depend on the Fu kinase activity and lead to a shift of Cos2 distribution from the cytoplasm to the plasma membrane. Moreover, the distinct Cos2 phosphorylation states mediate differential Hh signaling magnitude, suggesting that phosphorylation and relocation of Cos2 to the plasma membrane facilitate high-level Hh signaling through the control of Ci nuclear translocation and transcriptional activity.

RACK1 promotes non-small-cell lung cancer tumorigenicity through activating sonic hedgehog signaling pathway

Non-small-cell lung cancer (NSCLC) is a deadly disease due to lack of effective diagnosis biomarker and therapeutic target. Much effort has been made in defining gene defects in NSCLC, but its full molecular pathogenesis remains unexplored. Here, we found RACK1 (receptor of activated kinase 1) was elevated in most NSCLC, and its expression level correlated with key pathological characteristics including tumor differentiation, stage, and metastasis. In addition, RACK1 activated sonic hedgehog signaling pathway by interacting with and activating Smoothened to mediate Gli1-dependent transcription in NSCLC cells. And silencing RACK1 dramatically inhibited in vivo tumor growth and metastasis by blocking the sonic hedgehog signaling pathway. These results suggest that RACK1 represents a new promising diagnosis biomarker and therapeutic target for NSCLC.

Hedgehog signaling in myofibroblasts directly promotes prostate tumor cell growth

Despite strong evidence for the involvement of the stroma in Hedgehog signaling, little is known about the identity of the stromal cells and the signaling mechanisms that mediate the growth promoting effect of Hh signaling. We developed an in vitro co-culture model using microchannel technology to examine the effect of paracrine Hh signaling on proliferation of prostate cancer cells. We show here that activation of Hh signaling in myofibroblasts is sufficient to accelerate tumor cell growth. This effect was independent of any direct effect of Hh ligand on tumor cells or other cellular components of the tumor stroma. Further, the trophic effect of Hh pathway activation in myofibroblasts does not require collaboration of other elements of the stroma or direct physical interaction with the cancer cells. By isolating the tropic effect of Hh pathway activation in prostate stroma, we have taken the first step toward identifying cell-specific mechanisms that mediate the effect of paracrine Hh signaling on tumor growth.

Oxysterols are allosteric activators of the oncoprotein Smoothened

Oxysterols are a class of endogenous signaling molecules that can activate the Hedgehog pathway, which has critical roles in development, regeneration and cancer. However, it has been unclear how oxysterols influence Hedgehog signaling, including whether their effects are mediated through a protein target or indirectly through effects on membrane properties. To answer this question, we synthesized the enantiomer and an epimer of the most potent oxysterol, 20(S)-hydroxycholesterol. Using these molecules, we show that the effects of oxysterols on Hedgehog signaling are exquisitely stereoselective, consistent with the hypothesis that they function through a specific protein target. We present several lines of evidence that this protein target is the seven-pass transmembrane protein Smoothened, a major drug target in oncology. Our work suggests that these enigmatic sterols, which have multiple effects on cell physiology, may act as ligands for signaling receptors and provides a generally applicable framework for probing sterol signaling mechanisms.

Sonic Hedgehog on microparticles and neovascularization

Neovascularization represents a pivotal process consisting in the development of vascular network during embryogenesis and adult life. Postnatally, it arises mainly through angiogenesis, which has physiological and pathological roles in health and disease. Blood vessel formation results as tightly regulated multistep process which needs coordination and precise regulation of the balance of proangiogenic and antiangiogenic factors. Sonic Hedgehog (SHH), a morphogen belonging to Hedgehog (HH) family proteins, is implicated in a remarkably wide variety of process, including vessel development. Recent evidence demonstrate that, in addition to the classic factors, microvesicles (MVs), both microparticles (MPs) and exosomes, small vesicles released distinct cellular compartments, are involved in modulation of neovascularization. MPs generated from T lymphocytes undergoing both activation and apoptosis harbor at their surface SHH and play a crucial role in modulation of neovascularization. They are able to modulate the different steps implicated in angiogenesis process in vitro and to enhance postischemic neovascularization in vivo. As the consequence, we suggest that the MPs carrying SHH contribute to generation of a vascular network and may represent a new therapeutic approach to treat pathologies associated with failed angiogenesis.

Hedgehog inhibition as an anti-cancer strategy

Dysregulated Hedgehog (Hh) signaling has been implicated in a growing number of human cancers. Although first identified as an important developmental signaling pathway crucial for cellular proliferation, differentiation, and migration during organogenesis in invertebrates, these fundamental processes have been co-opted in human cancers. Initial evidence for the Hh pathway in tumor biology comes from mutations of signaling pathway components in a hereditary cancer syndrome that typically results in basal-cell carcinoma and medulloblastoma. Subsequent analysis revealed that Hh pathway mutations are found in sporadic tumors as well as activated Hh signaling in several epithelial cancers independent of Hh pathway mutation status. Further, recent evidence has demonstrated paracrine Hh signaling within stromal cells of the tumor microenvironment with implications for drug delivery. Several Hh antagonists targeting the Hh receptor, Smoothened (SMO), have been developed and show efficacy in preclinical studies and early-stage clinical trials in humans. However, major issues with these small molecule compounds include rapid acquired resistance, potential developmental toxicities secondary to use in children, and limited efficacy in cancers driven by Hh signaling downstream of the SMO receptor.

Mechanisms of Hedgehog signalling in cancer

The Hedgehog (Hh) pathway is a conserved signalling system essential for embryonic development and for the maintenance of self-renewal pathways in progenitor cells. Mutations that deregulate Hh signalling are directly implicated in basal cell carcinoma and medulloblastoma. The mechanisms of Hh pathway activation in cancers in which no pathway mutations have been identified are less clear, but of great translational significance. Small molecule inhibitors of the pathway, many of which are in early phase clinical trials, may shed further light on this question. Canonical Hh signalling promotes the expression of target genes through the Glioma-associated oncogene (GLI) transcription factors. There is now increasing evidence suggesting that 'non-canonical' Hh signalling mechanisms, some of which are independent of GLI-mediated transcription, may be important in cancer and development. The focus of this review is to summarise some of the known mechanisms of Hh signalling as well as its emerging role in cancer.

Reduction of human embryonal rhabdomyosarcoma tumor growth by inhibition of the hedgehog signaling pathway

Rhabdomyosarcoma (RMS) is the most frequent soft-tissue sarcoma in children. Embryonal rhabdomyosarcoma (E-RMS) represents the most common RMS subtype, but the molecular events driving this tumor are still largely unknown. The hedgehog (HH) pathway, a major signal transduction cascade, is linked with many cancers, including RMS. As we previously have detected loss of heterozygosity of PTCH1 in E-RMS, we now examined 8 E-RMS tumor samples and 5 E-RMS cell lines for the presence of PTCH1 mutations, but none was detected. However, in the E-RMS cell lines, a variable pattern of up-regulated expression of certain HH signaling target genes, including HHIP, PTCH1, SFRP1, and GLI1, was observed. Moreover, treatment with the small molecule HH signaling inhibitors cyclopamine and GANT61 inhibited cell proliferation in all E-RMS cell lines analyzed. Interestingly, GANT61 was more effective, and this was accompanied by increased apoptosis, while cyclopamine promoted necrotic events. Specific knockdown of SMO had no effect on the proliferation of E-RMS cells, indicating the presence of an SMO-independent HH signaling pathway in the E-RMS cell lines. Furthermore, in an in vivo xenograft model, tumor growth was significantly reduced by GANT61 treatment of E-RMS cells. Additionally, siRNA experiments provided evidence that inhibition of GLI1 or GLI3 but not GLI2 was sufficient to reduce proliferation of these cell lines. As GANT61 is known to block GLI1/GLI2 transcriptional activity, the inhibition of E-RMS growth by GANT61 is likely to be mediated through GLI1. In conclusion, our findings implicate that GLI1 could constitute an effective therapeutic target in pediatric E-RMS.

Targeting the Hedgehog pathway in cancer

The Hedgehog (Hh) pathway is a major regulator of many fundamental processes in vertebrate embryonic development including stem cell maintenance, cell differentiation, tissue polarity and cell proliferation. Constitutive activation of the Hh pathway leading to tumorigenesis is seen in basal cell carcinomas and medulloblastoma. A variety of other human cancers, including brain, gastrointestinal, lung, breast and prostate cancers, also demonstrate inappropriate activation of this pathway. Paracrine Hh signaling from the tumor to the surrounding stroma was recently shown to promote tumorigenesis. This pathway has also been shown to regulate proliferation of cancer stem cells and to increase tumor invasiveness. Targeted inhibition of Hh signaling may be effective in the treatment and prevention of many types of human cancers. The discovery and synthesis of specific Hh pathway inhibitors have significant clinical implications in novel cancer therapeutics. Several synthetic Hh antagonists are now available, several of which are undergoing clinical evaluation. The orally available compound, GDC-0449, is the farthest along in clinical development. Initial clinical trials in basal cell carcinoma and treatment of select patients with medulloblastoma have shown good efficacy and safety. We review the molecular basis of Hh signaling, the current understanding of pathway activation in different types of human cancers and we discuss the clinical development of Hh pathway inhibitors in human cancer therapy.

Multipotent mesenchymal stromal cells increase tPA expression and concomitantly decrease PAI-1 expression in astrocytes through the sonic hedgehog signaling pathway after stroke (in vitro study)

Multipotent mesenchymal stromal cells (MSCs) increase tissue plasminogen activator (tPA) activity in astrocytes of the ischemic boundary zone, leading to increased neurite outgrowth in the brain. To probe the mechanisms that underlie MSC-mediated activation of tPA, we investigated the morphogenetic gene, sonic hedgehog (Shh) pathway. In vitro oxygen and glucose deprivation and coculture of astrocytes and MSCs were used to mimic an in vivo ischemic condition. Both real-time-PCR and western blot showed that MSC coculture significantly increased the Shh level and concomitantly increased tPA and decreased plasminogen activator inhibitor 1 (PAI-1) levels in astrocytes. Inhibiting the Shh signaling pathway with cyclopamine blocked the increase of tPA and the decrease of PAI-1 expression in astrocytes subjected to MSC coculture or recombinant mouse Shh (rm-Shh) treatment. Both MSCs and rm-Shh decreased the transforming growth factor-β1 level in astrocytes, and the Shh pathway inhibitor cyclopamine reversed these decreases. Both Shh-small-interfering RNA (siRNA) and Glil-siRNA downregulated Shh and Gli1 (a key mediator of the Shh transduction pathway) expression in cultured astrocytes and concomitantly decreased tPA expression and increased PAI-1 expression in these astrocytes after MSC or rm-Shh treatment. Our data indicate that MSCs increase astrocytic Shh, which subsequently increases tPA expression and decreases PAI-1 expression after ischemia.

Hedgehog signaling and pancreatic tumor development

Numerous signaling pathways are misregulated in pancreatic ductal adenocarcinoma (PDAC), a highly malignant type of cancer. One of these is the Hedgehog (HH) pathway, which is normally involved in patterning processes in the developing embryo. Expression of the main ligand Sonic Hedgehog is an early event in carcinogenesis and correlates with the mutation of the KRAS oncogene, the cardinal molecular feature of pancreatic cancer. Recent data establish a functional role for HH signaling primarily in the tumor microenvironment, where it is involved in myofibroblast differentiation and the induction of stroma-derived growth promoting molecules. Given the protumorigenic functions of the abundant stromal desmoplasia typically associated with pancreatic cancer, targeting the HH pathway might prove beneficial in the treatment of the disease. First data using small molecule antagonists of HH signaling in mouse models of pancreatic cancer are promising and reveal a substantial, yet transient, effect on the myofibroblastic stroma. In this review, we try to give an outline on the current knowledge about HH signaling in pancreatic cancer including a perspective of using pharmacological inhibitors of this pathway in the clinic.

Nerve-derived sonic hedgehog defines a niche for hair follicle stem cells capable of becoming epidermal stem cells

In adult skin, stem cells in the hair follicle bulge cyclically regenerate the follicle, whereas a distinct stem cell population maintains the epidermis. The degree to which all bulge cells have equal regenerative potential is not known. We found that Sonic hedgehog (Shh) from neurons signals to a population of cells in the telogen bulge marked by the Hedgehog response gene Gli1. Gli1-expressing bulge cells function as multipotent stem cells in their native environment and repeatedly regenerate the anagen follicle. Shh-responding perineural bulge cells incorporate into healing skin wounds where, notably, they can change their lineage into epidermal stem cells. The perineural niche (including Shh) is dispensable for follicle contributions to acute wound healing and skin homeostasis, but is necessary to maintain bulge cells capable of becoming epidermal stem cells. Thus, nerves cultivate a microenvironment where Shh creates a molecularly and phenotypically distinct population of hair follicle stem cells.

In vivo RNAi screen reveals neddylation genes as novel regulators of Hedgehog signaling

Hedgehog (Hh) signaling is highly conserved in all metazoan animals and plays critical roles in many developmental processes. Dysregulation of the Hh signaling cascade has been implicated in many diseases, including cancer. Although key components of the Hh pathway have been identified, significant gaps remain in our understanding of the regulation of individual Hh signaling molecules. Here, we report the identification of novel regulators of the Hh pathway, obtained from an in vivo RNA interference (RNAi) screen in Drosophila. By selectively targeting critical genes functioning in post-translational modification systems utilizing ubiquitin (Ub) and Ub-like proteins, we identify two novel genes (dUba3 and dUbc12) that negatively regulate Hh signaling activity. We provide in vivo and in vitro evidence illustrating that dUba3 and dUbc12 are essential components of the neddylation pathway; they function in an enzyme cascade to conjugate the ubiquitin-like NEDD8 modifier to Cullin proteins. Neddylation activates the Cullin-containing ubiquitin ligase complex, which in turn promotes the degradation of Cubitus interruptus (Ci), the downstream transcription factor of the Hh pathway. Our study reveals a conserved molecular mechanism of the neddylation pathway in Drosophila and sheds light on the complex post-translational regulations in Hh signaling.

The hedgehog receptor patched is involved in cholesterol transport

Background

Sonic hedgehog (Shh) signaling plays a crucial role in growth and patterning during embryonic development, and also in stem cell maintenance and tissue regeneration in adults. Aberrant Shh pathway activation is involved in the development of many tumors, and one of the most affected Shh signaling steps found in these tumors is the regulation of the signaling receptor Smoothened by the Shh receptor Patched. In the present work, we investigated Patched activity and the mechanism by which Patched inhibits Smoothened.

Methodology/Principal Findings

Using the well-known Shh-responding cell line of mouse fibroblasts NIH 3T3, we first observed that enhancement of the intracellular cholesterol concentration induces Smoothened enrichment in the plasma membrane, which is a crucial step for the signaling activation. We found that binding of Shh protein to its receptor Patched, which involves Patched internalization, increases the intracellular concentration of cholesterol and decreases the efflux of a fluorescent cholesterol derivative (BODIPY-cholesterol) from these cells. Treatment of fibroblasts with cyclopamine, an antagonist of Shh signaling, inhibits Patched expression and reduces BODIPY-cholesterol efflux, while treatment with the Shh pathway agonist SAG enhances Patched protein expression and BODIPY-cholesterol efflux. We also show that over-expression of human Patched in the yeast S. cerevisiae results in a significant boost of BODIPY-cholesterol efflux. Furthermore, we demonstrate that purified Patched binds to cholesterol, and that the interaction of Shh with Patched inhibits the binding of Patched to cholesterol.

Conclusion/Significance

Our results suggest that Patched may contribute to cholesterol efflux from cells, and to modulation of the intracellular cholesterol concentration. This activity is likely responsible for the inhibition of the enrichment of Smoothened in the plasma membrane, which is an important step in Shh pathway activation.

HSulf-1 suppresses cell growth and down-regulates Hedgehog signaling in human gastric cancer cells

Gastric cancer is the second most lethal cancer worldwide. Despite the current surgical and adjuvant therapies, 5-year survival remains less than 20-25% in the US, Europe and China. Therefore, there is an urgent need to identify new therapeutic targets for treating this malignant disease. Accumulating evidence has supported that aberrant activation of the Hedgehog signaling pathway plays a crucial role in tumorigenesis and progression of gastric cancer. Human sulfatase-1 (HSulf-1) is a recently identified enzyme that desulfates cell surface heparan sulfate proteoglycans (HSPGs), which is critical for Hedgehog signal transduction under a highly sulfated state. HSulf-1 has recently emerged as a tumor suppressor gene in certain types of cancer, including ovarian, breast, myeloma and hepatocellular carcinoma; however, its role in gastric cancer remains to be elucidated. Therefore, we established HSulf-1-expressing monoclonal MKN28 gastric cancer cells to investigate its function in gastric cancer. Expression of HSulf-1 significantly suppressed cellular proliferation and growth in MKN28 gastric cancer cells. Notably, HSulf-1 inhibits Gli-mediated transcription and down-regulates the expression of Hedgehog target genes, including GLI1, PTCH1/2, HHIP, CCND1, C-MYC and BCL-2. Collectively, the study provides evidence that HSulf-1 may function as a tumor suppressor in gastric cancer. It suppresses gastric cancer cell proliferation, possibly through abrogating the Hedgehog signaling pathway. The study provides new mechanistic insight into HSulf-1- mediated tumor suppression, and supports the use of HSulf-1 as a potential new therapeutic target in treating gastric cancer.