Developmental roles and clinical significance of hedgehog signaling

Hedgehog actively maintains adult lung quiescence and regulates repair and regeneration

Postnatal tissue quiescence is thought to be a default state in the absence of a proliferative stimulus such as injury. Previous studies have demonstrated that certain embryonic development programs are reactivated aberrantly in adult organs to drive repair and regeneration^1–3, it is not well understood how quiescence is maintained in organs such as the lung which displays a remarkably low level of cellular turnover^4,5. We now demonstrate that quiescence in the adult lung is an actively maintained state and is regulated by hedgehog signaling. Epithelial-specific deletion of sonic hedgehog during postnatal homeostasis in the lung results in a proliferative expansion of the adjacent lung mesenchyme. Hedgehog signaling is initially down-regulated during the acute phase of epithelial injury as the mesenchyme proliferates in response, but returns to baseline during injury resolution as quiescence is restored. Activation of hedgehog during acute epithelial injury attenuates the proliferative expansion of the lung mesenchyme, whereas inactivation of hedgehog signaling prevents the restoration of quiescence during injury resolution. Finally, we show that hedgehog also regulates epithelial quiescence and regeneration in response to injury via a mesenchymal feedback mechanism. These results demonstrate that epithelial-mesenchymal interactions coordinated by hedgehog actively maintains postnatal tissue homeostasis, and deregulation of hedgehog during injury leads to aberrant repair and regeneration in the lung.

An essential role for Gα(i2) in Smoothened-stimulated epithelial cell proliferation in the mammary gland

Hedgehog (Hh) signaling is critical for organogenesis, tissue homeostasis, and stem cell maintenance. The gene encoding Smoothened (SMO), the primary effector of Hh signaling, is expressed aberrantly in human breast cancer, as well as in other cancers. In mice that express a constitutively active form of SMO that does not require Hh stimulation in mammary glands, the cells near the transgenic cells proliferate and participate in hyperplasia formation. Although SMO is a seven-transmembrane receptor like G protein-coupled receptors (GPCRs), SMO-mediated activation of the Gli family of transcription factors is not known to involve G proteins. However, data from Drosophila and mammalian cell lines indicate that SMO functions as a GPCR that couples to heterotrimeric G proteins of the pertussis toxin (PTX)-sensitive Gαi class. Using genetically modified mice, we demonstrated that SMO signaling through G proteins occurred in the mammary gland in vivo. SMO-induced stimulation of proliferation was PTX-sensitive and required Gαi2, but not Gαi1, Gαi3, or activation of Gli1 or Gli2. Our findings show that activated SMO functions as a GPCR to stimulate proliferation in vivo, a finding that may have clinical importance because most SMO-targeted agents have been selected based largely on their ability to block Gli-mediated transcription.

Stem Cells in Teeth and Craniofacial Bones

Stem cells are remarkable, and stem cell-based tissue engineering is an emerging field of biomedical science aiming to restore damaged tissue or organs. In dentistry and reconstructive facial surgery, it is of great interest to restore lost teeth or craniofacial bone defects using stem cell-mediated therapy. In the craniofacial region, various stem cell populations have been identified with regeneration potential. In this review, we provide an overview of the current knowledge concerning the various types of tooth- and craniofacial bone-related stem cells and discuss their in vivo identities and regulating mechanisms.

Hedgehog Signaling in the Maintenance of Cancer Stem Cells

Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.

Fell-Muir Lecture: Heparan sulphate and the art of cell regulation: a polymer chain conducts the protein orchestra

Heparan sulphate (HS) sits at the interface of the cell and the extracellular matrix. It is a member of the glycosaminoglycan family of anionic polysaccharides with unique structural features designed for protein interaction and regulation. Its client proteins include soluble effectors (e.g. growth factors, morphogens, chemokines), membrane receptors and cell adhesion proteins such as fibronectin, fibrillin and various types of collagen. The protein-binding properties of HS, together with its strategic positioning in the pericellular domain, are indicative of key roles in mediating the flow of regulatory signals between cells and their microenvironment. The control of transmembrane signalling is a fundamental element in the complex biology of HS. It seems likely that, in some way, HS orchestrates diverse signalling pathways to facilitate information processing inside the cell. A dictionary definition of an orchestra is 'a large group of musicians who play together on various instruments …' to paraphrase, the HS orchestra is 'a large group of proteins that play together on various receptors'. HS conducts this orchestra to ensure that proteins hit the right notes on their receptors but, in the manner of a true conductor, does it also set 'the musical pulse' and create rhythm and harmony attractive to the cell? This is too big a question to answer but fun to think about as you read this review.

Molecular Characterization of Bovine SMO Gene and Effects of Its Genetic Variations on Body Size Traits in Qinchuan Cattle (Bos taurus)

Smoothened (Smo)-mediated Hedgehog (Hh) signaling pathway governs the patterning, morphogenesis and growth of many different regions within animal body plans. This study evaluated the effects of genetic variations of the bovine SMO gene on economically important body size traits in Chinese Qinchuan cattle. Altogether, eight single nucleotide polymorphisms (SNPs: 1-8) were identified and genotyped via direct sequencing covering most of the coding region and 3'UTR of the bovine SMO gene. Both the p.698Ser.>Ser. synonymous mutation resulted from SNP1 and the p.700Ser.>Pro. non-synonymous mutation caused by SNP2 mapped to the intracellular C-terminal tail of bovine Smo protein; the other six SNPs were non-coding variants located in the 3'UTR. The linkage disequilibrium was analyzed, and five haplotypes were discovered in 520 Qinchuan cattle. Association analyses showed that SNP2, SNP3/5, SNP4 and SNP6/7 were significantly associated with some body size traits (p < 0.05) except SNP1/8 (p > 0.05). Meanwhile, cattle with wild-type combined haplotype Hap1/Hap1 had significantly (p < 0.05) greater body length than those with Hap2/Hap2. Our results indicate that variations in the SMO gene could affect body size traits of Qinchuan cattle, and the wild-type haplotype Hap1 together with the wild-type alleles of these detected SNPs in the SMO gene could be used to breed cattle with superior body size traits. Therefore, our results could be helpful for marker-assisted selection in beef cattle breeding programs.

Effect of Rab23 on the proliferation and apoptosis in breast cancer

Rab23, as a negative regulatory molecule of the Hedgehog (Hh) signaling pathway, may be a new target for treating carcinoma. In the present study, we aimed to determine whether Rab23 is expressed in breast cancer cells and whether Rab23 affects the viability and proliferation of breast cancer cells. We evaluated Rab23 expression in several breast cancer cell lines including MDA-MB-231, Bcap37 and MCF-7 by reverse transcription-PCR (RT-PCR), western blotting and immunofluorescence in vitro. We assessed cell growth and proliferation by 3-(4,5-dimethylthiazol‑2-y1)‑3,5-diphenyltetrazolium bromide (MTT), colony formation and bromodeoxyuridine (BrdU) incorporation assays. The distribution of the cell cycle and the rate of apoptosis were assessed using flow cytometry (FCM). In addition, we determined the mechanisms by which Rab23 regulates the Hh pathway by detecting the level of Gli molecules by RT-PCR. We found that Rab23 mRNA and protein levels were expressed in breast cancer cells, and the expression of Rab23 in MDA-MB-231 cells was higher than that in the MCF-7 cells. Rab23 protein was primarily expressed and localized in the cytoplasm surrounding the nucleus. The MTT assay showed that the absorbance value at A(490 nm) of the Rab23‑transfected group was reduced in comparison with the control group. The number of colonies formed in the breast cancer cells was significantly reduced and BrdU labeling was weakened in the group transfected with Rab23. The results of FCM showed that overexpression of Rab23 protein caused cell cycle arrest in the G1 phase and a decrease in the S phase population as well as induction of apoptosis. Furthermore, Rab23 decreased Gli1 and Gli2 mRNA levels when compared with the control group. Our results indicate that Rab23 is expressed in breast cancer cells, and ectopic expression of Rab23 inhibits the growth and proliferation as well as induces cell apoptosis in breast cancer cells. These effects may be due to the inhibition by Rab23 of Gli1 and Gli2 mRNA expression. These results suggest that Rab23 is a potential target for the treatment of breast cancer.

Probing for a deeper understanding of rhabdomyosarcoma: insights from complementary model systems

Rhabdomyosarcoma (RMS) is a mesenchymal malignancy composed of neoplastic primitive precursor cells that exhibit histological features of myogenic differentiation. Despite intensive conventional multimodal therapy, patients with high-risk RMS typically suffer from aggressive disease. The lack of directed therapies against RMS emphasizes the need to further uncover the molecular underpinnings of the disease. In this Review, we discuss the notable advances in the model systems now available to probe for new RMS-targetable pathogenetic mechanisms, and the possibilities for enhanced RMS therapeutics and improved clinical outcomes.

Disruption of Scube2 Impairs Endochondral Bone Formation

Signal peptide-CUB-EGF domain-containing protein 2 (SCUBE2) belongs to a secreted and membrane-tethered multidomain SCUBE protein family composed of three members found in vertebrates and mammals. Recent reports suggested that zebrafish scube2 could facilitate sonic hedgehog (Shh) signaling for proper development of slow muscle. However, whether SCUBE2 can regulate the signaling activity of two other hedgehog ligands (Ihh and Dhh), and the developmental relevance of the SCUBE2-induced hedgehog signaling in mammals remain poorly understood. In this study, we first showed that as compared with SCUBE1 or SCUBE3, SCUBE2 is the most potent modulator of IHH signaling in vitro. In addition, gain and loss-of-function studies demonstrated that SCUBE2 exerted an osteogenic function by enhancing Ihh-stimulated osteoblast differentiation in the mouse mesenchymal progenitor cells. Consistent with these in vitro studies and the prominent roles of Ihh in coordinating skeletogenesis, genetic ablation of Scube2 (-/-) caused defective endochondral bone formation and impaired Ihh-mediated chondrocyte differentiation and proliferation as well as osteoblast differentiation of -/- bone-marrow mesenchymal stromal-cell cultures. Our data demonstrate that Scube2 plays a key regulatory role in Ihh-dependent endochondral bone formation.

The significance of sonic hedgehog immunohistochemical expression in colorectal carcinoma

Colorectal carcinoma is a significant source of major morbidity and mortality. Sonic hedgehog (Shh) is expressed in normal gastrointestinal tract mucosa and in many malignancies. The purpose of the present study is to investigate the relationship between Shh immunoexpression in CRC and clinicopathological characteristics. Paraffin blocks of 155 primary CRCs and 37 nodal metastases were retrieved and tissue microarrays were constructed. Immunohistochemistry was performed using anti-Shh antibody. Immunostaining was scored and results were analysed in relation to the clinicopathological parameters. Shh was overexpressed in primary CRC (p = 0.02) and in nodal metastasis (p = 0.004). There was no difference between Shh immunoexpression in primary CRC and in nodal metastasis (p = 0.941). High Shh immunoexpression was associated with well differentiated tumours (p = 0.004). However, there was no association with other clinicopathological parameters. Shh overexpression was not associated disease free survival (log-rank = 0.079, p = 0.778). Shh is overexpressed in well differentiated CRC. However, Shh is not associated with other clinicopathological and prognostic factors. Loss of Shh may be associated with proliferation and loss of differentiation in CRC. Further molecular studies are required to address the potential importance of Shh signalling in CRC and to test Shh inhibitors and activators as potential therapeutic targets in CRC.

Secreted HHIP1 interacts with heparan sulfate and regulates Hedgehog ligand localization and function

Vertebrate Hedgehog (HH) signaling is controlled by several ligand-binding antagonists including Patched-1 (PTCH1), PTCH2, and HH-interacting protein 1 (HHIP1), whose collective action is essential for proper HH pathway activity. However, the molecular mechanisms used by these inhibitors remain poorly understood. In this paper, we investigated the mechanisms underlying HHIP1 antagonism of HH signaling. Strikingly, we found evidence that HHIP1 non-cell-autonomously inhibits HH-dependent neural progenitor patterning and proliferation. Furthermore, this non-cell-autonomous antagonism of HH signaling results from the secretion of HHIP1 that is modulated by cell type-specific interactions with heparan sulfate (HS). These interactions are mediated by an HS-binding motif in the cysteine-rich domain of HHIP1 that is required for its localization to the neuroepithelial basement membrane (BM) to effectively antagonize HH pathway function. Our data also suggest that endogenous, secreted HHIP1 localization to HS-containing BMs regulates HH ligand distribution. Overall, the secreted activity of HHIP1 represents a novel mechanism to regulate HH ligand localization and function during embryogenesis.

Overweight in mice and enhanced adipogenesis in vitro are associated with lack of the hedgehog coreceptor boc

Obesity arises from a combination of genetic, environmental, and behavioral factors. However, the processes that regulate white adipose tissue (WAT) expansion at the level of the adipocyte are not well understood. The Hedgehog (HH) pathway plays a conserved role in adipogenesis, inhibiting fat formation in vivo and in vitro, but it has not been shown that mice with reduced HH pathway activity have enhanced adiposity. We report that mice lacking the HH coreceptor BOC displayed age-related overweight and excess WAT. They also displayed alterations in some metabolic parameters but normal food intake. Furthermore, they had an exacerbated response to a high-fat diet, including enhanced weight gain and adipocyte hypertrophy, livers with greater fat accumulation, and elevated expression of genes related to adipogenesis, lipid metabolism, and adipokine production. Cultured Boc(-/-) mouse embryo fibroblasts showed enhanced adipogenesis relative to Boc(+/+) cells, and they expressed reduced levels of HH pathway target genes. Therefore, a loss-of-function mutation in an HH pathway component is associated with WAT accumulation and overweight in mice. Variant alleles of such HH regulators may contribute to WAT accumulation in human individuals with additional genetic or lifestyle-based predisposition to obesity.

Novel hedgehog agonists promote osteoblast differentiation in mesenchymal stem cells

Hedgehog (Hh) family members are involved in multiple cellular processes including proliferation, migration, differentiation, and cell fate determination. Recently, the novel Hh agonists Hh-Ag 1.3 and 1.7 were identified in a high-throughput screening of small molecule compounds that activate the expression of Gli1, a target of Hh signaling. This study demonstrates that Hh-Ag 1.3 and 1.7 strongly activate the expression of endogenous Gli1 and promote osteoblast differentiation in the mesenchymal stem cell line C3H10T1/2. Both compounds stimulated alkaline phosphatase activity in a dose-dependent manner, and induced osteoblast marker gene expression in C3H10T1/2 cells, which indicated that they had acquired an osteoblast identity. Of the markers, the expression of osterix/Sp7, a downstream target of runt-related transcription factor (Runx)2, was induced by Hh-Ag 1.7, which also rescued the osteoblast differentiation defect of RD-127, a mesenchymal cell line from Runx2-deficient mice. Hh-Ags also activated canonical Wnt signaling and synergized with low doses of BMP-2 to enhance osteoblastic potential. Thus, Hh-Ag 1.7 could be useful for bone healing in individuals with abnormalities in osteogenesis, such as osteoporosis patients and the elderly, and can contribute to the development of novel therapeutics for the treatment of bone fractures and defects.

Activation of Sonic Hedgehog Leads to Survival Enhancement of Astrocytes via the GRP78-Dependent Pathway in Mice Infected with Angiostrongylus cantonensis

Angiostrongylus cantonensis infection may cause elevation of ROS and antioxidants in the CSF of infected mice. Astrocytes may protect the surrounding neurons from oxidative stress-induced cell death by secreting Sonic hedgehog (Shh) via the PI3-K/AKT/Bcl-2 pathway. This study was conducted to determine the role of the Shh signaling pathway in A. cantonensis-infected BABL/c mice by coculturing astrocytes with living fifth-stage larvae or soluble antigens. The Shh pathway was activated with corresponding increases in the level of the Shh. Glial fibrillary acidic protein (GFAP) and Shh were increased in astrocyte cocultured with living fifth-stage larvae or soluble antigens. The survival of astrocytes pretreated with Shh was significantly elevated in cocultures with the antigens but reduced by its inhibitor cyclopamine. The expression of GRP78 and Bcl-2 was significantly higher in astrocytes pretreated with recombinant Shh. These findings suggest that the expression of Shh may inhibit cell death by activating Bcl-2 through a GRP78-dependent pathway.

Distinct structural requirements for CDON and BOC in the promotion of Hedgehog signaling

Proper levels of Hedgehog (HH) signaling are essential during embryonic development and adult tissue homeostasis. A central mechanism to control HH pathway activity is through the regulation of secreted HH ligands at the plasma membrane. Recent studies have revealed a collective requirement for the cell surface co-receptors GAS1, CDON and BOC in HH signal transduction. Despite their requirement in HH pathway function, the mechanisms by which these proteins act to promote HH signaling remain poorly understood. Here we focus on the function of the two structurally related co-receptors, CDON and BOC. We utilized an in vivo gain-of-function approach in the developing chicken spinal cord to dissect the structural requirements for CDON and BOC function in HH signal transduction. Notably, we find that although CDON and BOC display functional redundancy during HH-dependent ventral neural patterning, these molecules utilize distinct molecular mechanisms to execute their HH-promoting effects. Specifically, we define distinct membrane attachment requirements for CDON and BOC function in HH signal transduction. Further, we identify novel and separate extracellular motifs in CDON and BOC that are required to promote HH signaling. Together, these data suggest that HH co-receptors employ distinct mechanisms to mediate HH pathway activity.

GLI2 inhibition abrogates human leukemia stem cell dormancy

BACKGROUND

Dormant leukemia stem cells (LSC) promote therapeutic resistance and leukemic progression as a result of unbridled activation of stem cell gene expression programs. Thus, we hypothesized that 1) deregulation of the hedgehog (Hh) stem cell self-renewal and cell cycle regulatory pathway would promote dormant human LSC generation and 2) that PF-04449913, a clinical antagonist of the GLI2 transcriptional activator, smoothened (SMO), would enhance dormant human LSC eradication.

METHODS

To test these postulates, whole transcriptome RNA sequencing (RNA-seq), microarray, qRT-PCR, stromal co-culture, confocal fluorescence microscopic, nanoproteomic, serial transplantation and cell cycle analyses were performed on FACS purified normal, chronic phase (CP) chronic myeloid leukemia (CML), blast crisis (BC) phase CML progenitors with or without PF-04449913 treatment.

RESULTS

Notably, RNA-seq analyses revealed that Hh pathway and cell cycle regulatory gene overexpression correlated with leukemic progression. While lentivirally enforced GLI2 expression enhanced leukemic progenitor dormancy in stromal co-cultures, this was not observed with a mutant GLI2 lacking a transactivation domain, suggesting that GLI2 expression prevented cell cycle transit. Selective SMO inhibition with PF-04449913 in humanized stromal co-cultures and LSC xenografts reduced downstream GLI2 protein and cell cycle regulatory gene expression. Moreover, SMO inhibition enhanced cell cycle transit and sensitized BC LSC to tyrosine kinase inhibition in vivo at doses that spare normal HSC.

CONCLUSION

In summary, while GLI2, forms part of a core HH pathway transcriptional regulatory network that promotes human myeloid leukemic progression and dormant LSC generation, selective inhibition with PF-04449913 reduces the dormant LSC burden thereby providing a strong rationale for clinical trials predicated on SMO inhibition in combination with TKIs or chemotherapeutic agents with the ultimate aim of obviating leukemic therapeutic resistance, persistence and progression.

[Role of the Sonic Hedgehog pathway in thoracic cancers]

INTRODUCTION

Sonic Hedgehog (Shh) pathway is physiologically activated during embryogenesis and development. It plays a role in idiopathic lung fibrosis and is also activated in several solid cancers.

STATE OF THE ART

Shh pathway is reactivated in thoracic cancers, as small cell lung carcinoma, non-small cell lung carcinoma and malignant pleural mesothelioma. Shh pathway is associated with cancer stem cells and seems to have a crucial role in tumor proliferation, aggressiveness and chemoresistance in these cancers. This review describes the activation mode of Shh pathway in thoracic cancers and its role in small cell lung carcinoma, non-small cell lung carcinoma and malignant pleural mesothelioma, using in vitro and in vivo models. Notably, data from literature show that inhibition of Shh pathway has an antitumor action and sensitizes to chemotherapy.

PERSPECTIVES

These results incite to develop targeted therapies against Shh pathway in the treatment of thoracic cancers.

Shaping of the tumor microenvironment: Stromal cells and vessels

Lymphomas develop and progress in a specialized tissue microenvironment such as bone marrow as well as secondary lymphoid organs such as lymph node and spleen. The lymphoma microenvironment is characterized by a heterogeneous population of stromal cells, including fibroblastic reticular cells, nurse-like cells, mesenchymal stem cells, follicular dendritic cells, and inflammatory cells such as macrophages, T- and B-cells. These cell populations interact with the lymphoma cells to promote lymphoma growth, survival and drug resistance through multiple mechanisms. Angiogenesis is also recognized as an important factor associated with lymphoma progression. In recent years, we have learned that the interaction between the malignant and non-malignant cells is bidirectional and resembles, at least in part, the pattern seen between non-neoplastic lymphoid cells and the normal microenvironment of lymphoid organs. A summary of the current knowledge of lymphoma microenvironment focusing on the cellular components will be reviewed here.

Hedgehog signaling pathway is active in GBM with GLI1 mRNA expression showing a single continuous distribution rather than discrete high/low clusters

Hedgehog (Hh) signaling pathway is a valid therapeutic target in a wide range of malignancies. We focus here on glioblastoma multiforme (GBM), a lethal malignancy of the central nervous system (CNS). By analyzing RNA-sequencing based transcriptomics data on 149 clinical cases of TCGA-GBM database we show here a strong correlation (r = 0.7) between GLI1 and PTCH1 mRNA expression--as a hallmark of the canonical Hh-pathway activity in this malignancy. GLI1 mRNA expression varied in 3 orders of magnitude among the GBM patients of the same cohort showing a single continuous distribution-unlike the discrete high/low-GLI1 mRNA expressing clusters of medulloblastoma (MB). When compared with MB as a reference, the median GLI1 mRNA expression in GBM appeared 14.8 fold lower than that of the "high-Hh" cluster of MB but 5.6 fold higher than that of the "low-Hh" cluster of MB. Next, we demonstrated statistically significant up- and down-regulation of GLI1 mRNA expressions in GBM patient-derived low-passage neurospheres in vitro by sonic hedgehog ligand-enriched conditioned media (shh-CM) and by Hh-inhibitor drug vismodegib respectively. We also showed clinically achievable dose (50 μM) of vismodegib alone to be sufficient to induce apoptosis and cell cycle arrest in these low-passage GBM neurospheres in vitro. Vismodegib showed an effect on the neurospheres, both by down-regulating GLI1 mRNA expression and by inducing apoptosis/cell cycle arrest, irrespective of their relative endogenous levels of GLI1 mRNA expression. We conclude from our study that this single continuous distribution pattern of GLI1 mRNA expression technically puts almost all GBM patients in a single group rather than discrete high- or low-clusters in terms of Hh-pathway activity. That is suggestive of therapies with Hh-pathway inhibitor drugs in this malignancy without a need for further stratification of patients on the basis of relative levels of Hh-pathway activity among them.

Effects and mechanisms of blocking the hedgehog signaling pathway in human gastric cancer cells

Excessive activation of the hedgehog (Hh) signaling pathway is important in a variety of human cancer cell types, including gastric cancer. However, the underlying mechanisms of the Hh signaling pathway in inducing gastric tumorigenesis and its downstream target genes are largely unknown. In the present study, the inhibitory effect of cyclopamine on the Hh signaling pathway was investigated in the human gastric cancer AGS cell line. It was identified that cyclopamine treatment inhibited the proliferation, migration and invasion of the AGS cells in a dose- and time-dependent manner, and resulted in the downregulation of a number of key Hh signaling pathway-associated factors [glioma-associated oncogene homolog 1, C-X-C chemokine receptor type 4 and transforming growth factor (TGF)-β1] at the RNA and protein levels. Furthermore, the secretion of TGF-β1 was significantly reduced following the administration of cyclopamine to the AGS cells. The results of the present study provided insight into the mechanisms by which the Hh signaling pathway regulates gastric cancer formation and identified the Hh signaling pathway as a potential novel therapeutic target in human gastric cancer.

Sonic hedgehog signaling in the lung. From development to disease

Over the past two decades, the secreted protein sonic hedgehog (SHH) has emerged as a critical morphogen during embryonic lung development, regulating the interaction between epithelial and mesenchymal cell populations in the airway and alveolar compartments. There is increasing evidence that the SHH pathway is active in adult lung diseases such as pulmonary fibrosis, asthma, chronic obstructive pulmonary disease, and lung cancer, which raises two questions: (1) What role does SHH signaling play in these diseases? and (2) Is it a primary driver of the disease or a response (perhaps beneficial) to the primary disturbance? In this review we aim to fill the gap between the well-studied period of embryonic lung development and the adult diseased lung by reviewing the hedgehog (HH) pathway during the postnatal period and in adult uninjured and injured lungs. We elucidate the similarities and differences in the epithelial-mesenchymal interplay during the fibrosis response to injury in lung compared with other organs and present a critical appraisal of tools and agents available to evaluate HH signaling.

The role of reactive oxygen species in mesenchymal stem cell adipogenic and osteogenic differentiation: a review

Mesenchymal stromal cells (MSCs) are promising candidates for tissue engineering and regenerative medicine. The multipotent stem cell component of MSC isolates is able to differentiate into derivatives of the mesodermal lineage including adipocytes, osteocytes, chondrocytes, and myocytes. Many common pathways have been described in the regulation of adipogenesis and osteogenesis. However, stimulation of osteogenesis appears to suppress adipogenesis and vice-versa. Increasing evidence implicates a tight regulation of these processes by reactive oxygen species (ROS). ROS are short-lived oxygen-containing molecules that display high chemical reactivity toward DNA, RNA, proteins, and lipids. Mitochondrial complexes I and III, and the NADPH oxidase isoform NOX4 are major sources of ROS production during MSC differentiation. ROS are thought to interact with several pathways that affect the transcription machinery required for MSC differentiation including the Wnt, Hedgehog, and FOXO signaling cascades. On the other hand, elevated levels of ROS, defined as oxidative stress, lead to arrest of the MSC cell cycle and apoptosis. Tightly regulated levels of ROS are therefore critical for MSC terminal differentiation, although the precise sources, localization, levels and the exact species of ROS implicated remain to be determined. This review provides a detailed overview of the influence of ROS on adipogenic and osteogenic differentiation in MSCs.

Resveratrol inhibits the hedgehog signaling pathway and epithelial-mesenchymal transition and suppresses gastric cancer invasion and metastasis

The hedgehog (Hh) signaling pathway is vital to vertebrate development, the homeostatic process and tumorigenesis. Epithelial-mesenchymal transition (EMT) is a cellular process during which epithelial cells become mesenchymal-appearing cells, which in turn promotes cancer metastasis and invasion. Resveratrol is a natural polyphenolic compound found in grapes, a variety of berries, peanuts and other plants. Numerous studies have demonstrated that the Hh signaling pathway is able to regulate the EMT, and that resveratrol can suppress carcinoma invasion and metastasis. In addition, certain studies have indicated that resveratrol can inhibit the Hh signaling pathway and EMT in cancers other than gastric cancer. The purpose of the present study was to investigate the inhibitory effect of resveratrol on the Hh signaling pathway and EMT in gastric cancer in vitro. Gastric cancer SGC-7901 cells were treated with resveratrol or cyclopamine at different concentrations. The viability of the cells was assessed using an MTT assay. The expression of Gli-1, a key component of the Hh signaling pathway, and Snail, E-cadherin and N-cadherin, key components of EMT, was detected by reverse transcription polymerase chain reaction (RT-PCR) and western blotting. The invasion and metastasis of the cells were observed by performing a cell scratch test. The RT-PCR and western blotting showed a decrease in Gli-1, Snail and N-cadherin expression, and an increase in E-cadherin expression in the resveratrol and cyclopamine group compared with the control group, suggesting that resveratrol inhibited the Hh pathway and EMT, as did cyclopamine. The MTT assay indicated that the viability of the SGC-7901 cells was significantly decreased in a concentration-dependent manner following resveratrol and cyclopamine treatment. The cell scratch test showed slower cell invasion and metastasis in the resveratrol and cyclopamine groups. These findings indicated that resveratrol was able to inhibit the Hh signaling pathway and EMT, and suppress invasion and metastasis in gastric cancer in vitro.

Topological analysis of Hedgehog acyltransferase, a multipalmitoylated transmembrane protein

Hedgehog proteins are secreted morphogens that play critical roles in development and disease. During maturation of the proteins through the secretory pathway, they are modified by the addition of N-terminal palmitic acid and C-terminal cholesterol moieties, both of which are critical for their correct function and localization. Hedgehog acyltransferase (HHAT) is the enzyme in the endoplasmic reticulum that palmitoylates Hedgehog proteins, is a member of a small subfamily of membrane-bound O-acyltransferase proteins that acylate secreted proteins, and is an important drug target in cancer. However, little is known about HHAT structure and mode of function. We show that HHAT is comprised of ten transmembrane domains and two reentrant loops with the critical His and Asp residues on opposite sides of the endoplasmic reticulum membrane. We further show that HHAT is palmitoylated on multiple cytosolic cysteines that maintain protein structure within the membrane. Finally, we provide evidence that mutation of the conserved His residue in the hypothesized catalytic domain results in a complete loss of HHAT palmitoylation, providing novel insights into how the protein may function in vivo.

The medaka dhc2 mutant reveals conserved and distinct mechanisms of Hedgehog signaling in teleosts

Background

Primary cilia are essential for Hedgehog (Hh) signal transduction in vertebrates. Although the core components of the Hh pathway are highly conserved, the dependency on cilia in Hh signaling is considered to be lower in fish than in mice, suggesting the presence of species-specific mechanisms for Hh signal transduction.

Results

To precisely understand the role of cilia in Hh signaling in fish and explore the evolution of Hh signaling, we have generated a maternal-zygotic medaka (Oryzias latipes) mutant that lacks cytoplasmic dynein heavy chain 2 (dhc2; MZdhc2), a component required for retrograde intraflagellar transport. We found that MZdhc2 exhibited the shortened cilia and partial defects in Hh signaling, although the Hh defects were milder than zebrafish mutants which completely lack cilia. This result suggests that Hh activity in fish depends on the length of cilium. However, the activity of Hh signaling in MZdhc2 appeared to be higher than that in mouse Dnchc2 mutants, suggesting a lower requirement for cilia in Hh signaling in fish. We confirmed that Ptch1 receptor is exclusively localized on the cilium in fish as in mammals. Subsequent analyses revealed that Fused, an essential mediator for Hh signaling in Drosophila and fish but not in mammals, augments the activity of Hh signaling in fish as a transcriptional target of Hh signaling.

Conclusions

Ciliary requirement for Hh signaling in fish is lower than that in mammals, possibly due to fused-mediated positive feedback in Hh signaling. The finding of this fish-specific augmentation provides a novel insight into the evolution of Hh signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0057-x) contains supplementary material, which is available to authorized users.

The Hedgehog pathway: role in cell differentiation, polarity and proliferation

Hedgehog (Hh) is first described as a genetic mutation that has "spiked" phenotype in the cuticles of Drosophila in later 1970s. Since then, Hh signaling has been implicated in regulation of differentiation, proliferation, tissue polarity, stem cell population and carcinogenesis. The first link of Hh signaling to cancer was established through discovery of genetic mutations of Hh receptor gene PTCH1 being responsible for Gorlin syndrome in 1996. It was later shown that Hh signaling is associated with many types of cancer, including skin, leukemia, lung, brain and gastrointestinal cancers. Another important milestone for the Hh research field is the FDA approval for the clinical use of Hh inhibitor Erivedge/Vismodegib for treatment of locally advanced and metastatic basal cell carcinomas. However, recent clinical trials of Hh signaling inhibitors in pancreatic, colon and ovarian cancer all failed, indicating a real need for further understanding of Hh signaling in cancer. In this review, we will summarize recent progress in the Hh signaling mechanism and its role in human cancer.

The heterotrimeric kinesin-2 complex interacts with and regulates GLI protein function

GLI transport to the primary cilium and nucleus is required for proper Hedgehog (HH) signaling; however, the mechanisms that mediate these trafficking events are poorly understood. Kinesin-2 motor proteins regulate ciliary transport of cargo, yet their role in GLI protein function remains unexplored. To examine a role for the heterotrimeric KIF3A-KIF3B-KAP3 kinesin-2 motor complex in regulating GLI activity, we performed a series of structure-function analyses using biochemical, cell signaling and in vivo approaches that define novel specific interactions between GLI proteins and two components of this complex, KAP3 and KIF3A. We find that all three mammalian GLI proteins interact with KAP3 and we map specific interaction sites in both proteins. Furthermore, we find that GLI proteins interact selectively with KIF3A, but not KIF3B, and that GLI interacts synergistically with KAP3 and KIF3A. Using a combination of cell signaling assays and chicken in ovo electroporation, we demonstrate that KAP3 interactions restrict GLI activator function but not GLI repressor function. These data suggest that GLI interactions with KIF3A-KIF3B-KAP3 complexes are essential for proper GLI transcriptional activity.

Comparative analysis of genes regulated by Dzip1/iguana and hedgehog in zebrafish

BACKGROUND

The zebrafish genetic mutant iguana (igu) has defects in the ciliary basal body protein Dzip1, causing improper cilia formation. Dzip1 also interacts with the downstream transcriptional activators of Hedgehog (Hh), the Gli proteins, and Hh signaling is disrupted in igu mutants. Hh governs a wide range of developmental processes, including stabilizing developing blood vessels to prevent hemorrhage. Using igu mutant embryos and embryos treated with the Hh pathway antagonist cyclopamine, we conducted a microarray to determine genes involved in Hh signaling mediating vascular stability.

RESULTS

We identified 40 genes with significantly altered expression in both igu mutants and cyclopamine-treated embryos. For a subset of these, we used in situ hybridization to determine localization during embryonic development and confirm the expression changes seen on the array.

CONCLUSIONS

Through comparing gene expression changes in a genetic model of vascular instability with a chemical inhibition of Hh signaling, we identified a set of 40 differentially expressed genes with potential roles in vascular stabilization.

Regulation of human PTCH1b expression by different 5' untranslated region cis-regulatory elements

PTCH1 gene codes for a 12-pass transmembrane receptor with a negative regulatory role in the Hedgehog-Gli signaling pathway. PTCH1 germline mutations cause Gorlin syndrome, a disorder characterized by developmental abnormalities and tumor susceptibility. The autosomal dominant inheritance, and the evidence for PTCH1 haploinsufficiency, suggests that fine-tuning systems of protein patched homolog 1 (PTC1) levels exist to properly regulate the pathway. Given the role of 5' untranslated region (5'UTR) in protein expression, our aim was to thoroughly explore cis-regulatory elements in the 5'UTR of PTCH1 transcript 1b. The (CGG)n polymorphism was the main potential regulatory element studied so far but with inconsistent results and no clear association between repeat number and disease risk. Using luciferase reporter constructs in human cell lines here we show that the number of CGG repeats has no strong impact on gene expression, both at mRNA and protein levels. We observed variability in the length of 5'UTR and changes in abundance of the associated transcripts after pathway activation. We show that upstream AUG codons (uAUGs) present only in longer 5'UTRs could negatively regulate the amount of PTC1 isoform L (PTC1-L). The existence of an internal ribosome entry site (IRES) observed using different approaches and mapped in the region comprising the CGG repeats, would counteract the effect of the uAUGs and enable synthesis of PTC1-L under stressful conditions, such as during hypoxia. Higher relative translation efficiency of PTCH1b mRNA in HEK 293T cultured hypoxia was observed by polysomal profiling and Western blot analyses. All our results point to an exceptionally complex and so far unexplored role of 5'UTR PTCH1b cis-element features in the regulation of the Hedgehog-Gli signaling pathway.

Decoding Ci: from partial degradation to inhibition

Hedgehog is a morphogen, which is widely involved in the regulation of cell proliferation, differentiation and tissue patterning during development in both vertebrate and invertebrate, such as in coordination of eye, brain, gonad, gut and tracheal development. In invertebrate, Cubitus interruptus (Ci) modification process is the last identified step before transcriptional activation in the Hh signaling pathway. Ci can form a truncated repressor (Ci(R) /Ci75) or act as an activator (Ci(A) /Ci155) based on Hh gradient to regulate the expressions of target genes. The activity of Ci is mediated by different mechanisms, including processing, trafficking and degradation. While in vertebrate, Glioblastomas (Glis), homologs of Ci, play similar but more complex roles in the regulation of mammals Hh pathway. Hh signaling is responsible for a wide variety of processes during embryonic development and adult tissue homeostasis. Malfunction of Hh signaling could cause various diseases including birth defects and cancers. Enormous efforts were made in the past decades to explore the Hh pathway regulation and the results have provided us important insights into disease diagnosis and therapeutic treatment. In this review, we focus on a small branch of Hh pathway regulation based on studies in the Drosophila system, mainly about Ci degradation, aiming to explain how Ci is modified by different ubiquitin ligases due to the strong or moderate Hh signals and then been subjected to complete or partial degradation by proteasomes. Overall, we intend to offer an overview on how Ci responds to and relays Hh signals in a precise manner to control target genes expressions and ensures proper Hh signal transduction.

Role of SOX2 in foregut development in relation to congenital abnormalities

The uptake of the two essential ingredients for life, oxygen and nutrients, occurs primarily through the oral cavity, but these two lifelines need to be separated with high accuracy once inside the body. The two systems, the gas exchange pulmonary system and the gastro-intestinal feeding system, are derived from the same primitive embryonic structure during development, the foregut, which need to be separated before birth. In certain newborns, this separation occurs not or insufficiently, leading to life threatening conditions, sometimes incompatible with life. The development of the foregut, trachea and lungs is influenced and coordinated by a multitude of signaling cascades and transcription factors. In this review, we will highlight the development of the foregut and pulmonary system and focus on associated congenital abnormalities in light of known genetic alterations with specific attention to the transcription factor SOX2.

Cdo suppresses canonical Wnt signalling via interaction with Lrp6 thereby promoting neuronal differentiation

Canonical Wnt signalling regulates expansion of neural progenitors and functions as a dorsalizing signal in the developing forebrain. In contrast, the multifunctional co-receptor Cdo promotes neuronal differentiation and is important for the function of the ventralizing signal, Shh. Here we show that Cdo negatively regulates Wnt signalling during neurogenesis. Wnt signalling is enhanced in Cdo-deficient cells, leading to impaired neuronal differentiation. The ectodomains of Cdo and Lrp6 interact via the Ig2 repeat of Cdo and the LDLR repeats of Lrp6, and the Cdo Ig2 repeat is necessary for Cdo-dependent Wnt inhibition. Furthermore, the Cdo-deficient dorsal forebrain displays stronger Wnt signalling activity, increased cell proliferation and enhanced expression of the dorsal markers and Wnt targets, Pax6, Gli3, Axin2. Therefore, in addition to promoting ventral central nervous system cell fates with Shh, Cdo promotes neuronal differentiation by suppression of Wnt signalling and provides a direct link between two major dorsoventral morphogenetic signalling pathways.

Distinct cellular origin and genetic requirement of Hedgehog-Gli in postnatal rhabdomyosarcoma genesis

Dysregulation of the Hedgehog (Hh)-Gli signaling pathway is implicated in a variety of human cancers, including basal cell carcinoma (BCC), medulloblastoma (MB) and embryonal rhabdhomyosarcoma (eRMS), three principle tumors associated with human Gorlin syndrome. However, the cells of origin of these tumors, including eRMS, remain poorly understood. In this study, we explore the cell populations that give rise to Hh-related tumors by specifically activating Smoothened (Smo) in both Hh-producing and -responsive cell lineages in postnatal mice. Interestingly, we find that unlike BCC and MB, eRMS originates from the stem/progenitor populations that do not normally receive active Hh signaling. Furthermore, we find that the myogenic lineage in postnatal mice is largely Hh quiescent and that Pax7-expressing muscle satellite cells are not able to give rise to eRMS upon Smo or Gli1/2 overactivation in vivo, suggesting that Hh-induced skeletal muscle eRMS arises from Hh/Gli quiescent non-myogenic cells. In addition, using the Gli1 null allele and a Gli3 repressor allele, we reveal a specific genetic requirement for Gli proteins in Hh-induced eRMS formation and provide molecular evidence for the involvement of Sox4/11 in eRMS cell survival and differentiation.

CDO, an Hh-coreceptor, mediates lung cancer cell proliferation and tumorigenicity through Hedgehog signaling

Hedgehog (Hh) signaling plays essential roles in various developmental processes, and its aberrant regulation results in genetic disorders or malignancies in various tissues. Hyperactivation of Hh signaling is associated with lung cancer development, and there have been extensive efforts to investigate how to control Hh signaling pathway and regulate cancer cell proliferation. In this study we investigated a role of CDO, an Hh co-receptor, in non-small cell lung cancer (NSCLC). Inhibition of Hh signaling by SANT-1 or siCDO in lung cancer cells reduced proliferation and tumorigenicity, along with the decrease in the expression of the Hh components. Histological analysis with NSCLC mouse tissue demonstrated that CDO was expressed in advanced grade of the cancer, and precisely co-localized with GLI1. These data suggest that CDO is required for proliferation and survival of lung cancer cells via Hh signaling.

Perturbations to the hedgehog pathway in sea urchin embryos

The Hedgehog pathway has been shown to be an important developmental signaling pathway in many organisms (Ingham and McMahon. Genes Dev 15:3059-3087, 2001). Recently that work has been extended to developing echinoderm embryos (Walton et al. Dev Biol 331(1):26-37, 2009). Here we describe several methods to perturb the Hedgehog signaling pathway in the sea urchin. These include microinjection of Morpholinos and mRNA constructs as well as treatments with small molecule inhibitors. Finally we provide simple methods for assaying Hedgehog phenotypes in the sea urchin embryo.

Genistein decreases the breast cancer stem-like cell population through Hedgehog pathway

Introduction

The existence of breast cancer stem-like cells (BCSCs) has profound implications for cancer prevention. Genistein, a predominant isoflavone found in soy products, has multiple robust anti-tumor effects in various cancers, especially in the breast and prostate cancer. In this study, we aimed to evaluate genistein inhibition of BCSCs and its potential mechanism by culturing MCF-7 breast cancer cells and implanting these cells into nude mice.

Methods

Cell counting, colony formation and cell apoptosis analysis were used to evaluate the effect of genistein on breast cancer cells’ growth, proliferation and apoptosis. We then used mammosphere formation assay and CD44CD24 staining to evaluate the effect of genistein on BCSCs in vitro. A nude mice xenograft model was employed to determine whether genistein could target BCSCs in vivo, as assessed by real-time polymerase chain reaction (PCR) and immunohistochemical staining. The potential mechanism was investigated utilizing real-time PCR, western blotting analysis and immunohistochemical staining.

Results

Genistein inhibited the MCF-7 breast cancer cells’ growth and proliferation and promoted apoptosis. Both in vitro and in vivo genistein decreased breast cancer stem cells, and inhibited breast cancer stem-like cells through down-regulation of the Hedgehog-Gli1 Signaling Pathway.

Conclusions

We demonstrated for the first time that genistein inhibits BCSCs by down-regulating Hedgehog-Gli1 signaling pathway. These findings provide support and rationale for investigating the clinical application of genistein in treating breast cancer, and specifically by targeting breast cancer stem cells.

Back to the drawing board: Re-thinking the role of GLI1 in pancreatic carcinogenesis

Aberrant activation of the transcription factor GLI1, a central effector of the Hedgehog (HH) pathway, is associated with several malignancies, including pancreatic ductal adenocarcinoma (PDAC), one of most deadly human cancers. GLI1 has been described as an oncogene in PDAC, making it a promising target for drug therapy. Surprisingly, clinical trials targeting HH/GLI1 axis in advanced PDAC were unsuccessful, leaving investigators questioning the mechanism behind these failures. Recent evidence suggests the loss of GLI1 in the later stages of PDAC may actually accelerate disease. This indicates GLI1 may play a dual role in PDAC, acting as an oncogene in the early stages of disease and a tumor-suppressor in the late stages.

Back to the drawing board: Re-thinking the role of GLI1 in pancreatic carcinogenesis

Aberrant activation of the transcription factor GLI1, a central effector of the Hedgehog (HH) pathway, is associated with several malignancies, including pancreatic ductal adenocarcinoma (PDAC), one of most deadly human cancers. GLI1 has been described as an oncogene in PDAC, making it a promising target for drug therapy. Surprisingly, clinical trials targeting HH/GLI1 axis in advanced PDAC were unsuccessful, leaving investigators questioning the mechanism behind these failures. Recent evidence suggests the loss of GLI1 in the later stages of PDAC may actually accelerate disease. This indicates GLI1 may play a dual role in PDAC, acting as an oncogene in the early stages of disease and a tumor-suppressor in the late stages.

Synergistic effect of Indian hedgehog and bone morphogenetic protein-2 gene transfer to increase the osteogenic potential of human mesenchymal stem cells

Introduction

To stimulate healing of large bone defects research has concentrated on the application of mesenchymal stem cells (MSCs).

Methods

In the present study, we induced the overexpression of the growth factors bone morphogenetic protein 2 (BMP-2) and/or Indian hedgehog (IHH) in human MSCs by adenoviral transduction to increase their osteogenic potential. GFP and nontransduced MSCs served as controls. The influence of the respective genetic modification on cell metabolic activity, proliferation, alkaline phosphatase (ALP) activity, mineralization in cell culture, and osteogenic marker gene expression was investigated.

Results

Transduction had no negative influence on cell metabolic activity or proliferation. ALP activity showed a typical rise-and-fall pattern with a maximal activity at day 14 and 21 after osteogenic induction. Enzyme activity was significantly higher in groups cultured with osteogenic media. The overexpression of BMP-2 and especially IHH + BMP-2 resulted in a significantly higher mineralization after 28 days. This was in line with obtained quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analyses, which showed a significant increase in osteopontin and osteocalcin expression for osteogenically induced BMP-2 and IHH + BMP-2 transduced cells when compared with the other groups. Moreover, an increase in runx2 expression was observed in all osteogenic groups toward day 21. It was again more pronounced for BMP-2 and IHH + BMP-2 transduced cells cultured in osteogenic media.

Conclusions

In summary, viral transduction did not negatively influence cell metabolic activity and proliferation. The overexpression of BMP-2 in combination with or without IHH resulted in an increased deposition of mineralized extracellular matrix, and expression of osteogenic marker genes. Viral transduction therefore represents a promising means to increase the osteogenic potential of MSCs and the combination of different transgenes may result in synergistic effects.

Potential smoothened inhibitor from traditional Chinese medicine against the disease of diabetes, obesity, and cancer

Nowadays, obesity becomes a serious global problem, which can induce a series of diseases such as type 2 diabetes mellitus, cancer, cardiovascular disease, metabolic syndrome, and stoke. For the mechanisms of diseases, the hedgehog signaling pathway plays an important role in body patterning during embryogenesis. For this reason, smoothened homologue (Smo) protein had been indicated as the drug target. In addition, the small-molecule Smo inhibitor had also been used in oncology clinical trials. To improve drug development of TCM compounds, we aim to investigate the potent lead compounds as Smo inhibitor from the TCM compounds in TCM Database@Taiwan. The top three TCM compounds, precatorine, labiatic acid, and 2,2′-[benzene-1,4-diylbis(methanediyloxybenzene-4,1-diyl)]bis(oxoacetic acid), have displayed higher potent binding affinities than the positive control, LY2940680, in the docking simulation. After MD simulations, which can optimize the result of docking simulation and validate the stability of H-bonds between each ligand and Smo protein under dynamic conditions, top three TCM compounds maintain most of interactions with Smo protein, which keep the ligand binding stable in the binding domain. Hence, we propose precatorine, labiatic acid, and 2,2′-[benzene-1,4-diylbis(methanediyloxybenzene-4,1-diyl)]bis(oxoacetic acid) as potential lead compounds for further study in drug development process with the Smo protein.

The transcription factor GLI1 modulates the inflammatory response during pancreatic tissue remodeling

Pancreatic cancer, one of the deadliest human malignancies, is almost uniformly associated with a mutant, constitutively active form of the oncogene Kras. Studies in genetically engineered mouse models have defined a requirement for oncogenic KRAS in both the formation of pancreatic intraepithelial neoplasias, the most common precursor lesions to pancreatic cancer, and in the maintenance and progression of these lesions. Previous work using an inducible model allowing tissue-specific and reversible expression of oncogenic Kras in the pancreas indicates that inactivation of this GTPase at the pancreatic intraepithelial neoplasia stage promotes pancreatic tissue repair. Here, we extend these findings to identify GLI1, a transcriptional effector of the Hedgehog pathway, as a central player in pancreatic tissue repair upon Kras inactivation. Deletion of a single allele of Gli1 results in improper stromal remodeling and perdurance of the inflammatory infiltrate characteristic of pancreatic tumorigenesis. Strikingly, this partial loss of Gli1 affects activated fibroblasts in the pancreas and the recruitment of immune cells that are vital for tissue recovery. Analysis of the mechanism using expression and chromatin immunoprecipitation assays identified a subset of cytokines, including IL-6, mIL-8, Mcp-1, and M-csf (Csf1), as direct GLI1 target genes potentially mediating this phenomenon. Finally, we demonstrate that canonical Hedgehog signaling, a known regulator of Gli1 activity, is required for pancreas recovery. Collectively, these data delineate a new pathway controlling tissue repair and highlight the importance of GLI1 in regulation of the pancreatic microenvironment during this cellular process.

Targeted treatment for sonic hedgehog-dependent medulloblastoma

Novel treatment options, including targeted therapies, are needed for patients with medulloblastoma (MB), especially for those with high-risk or recurrent/relapsed disease. Four major molecular subgroups of MB have been identified, one of which is characterized by activation of the sonic hedgehog (SHH) pathway. Preclinical data suggest that inhibitors of the hedgehog (Hh) pathway could become valuable treatment options for patients with this subgroup of MB. Indeed, agents targeting the positive regulator of the pathway, smoothened (SMO), have demonstrated efficacy in a subset of patients with SHH MB. However, because of resistance and the presence of mutations downstream of SMO, not all patients with SHH MB respond to SMO inhibitors. The development of agents that target these resistance mechanisms and the potential for their combination with traditional chemotherapy and SHH inhibitors will be discussed. Due to its extensive molecular heterogeneity, the future of MB treatment is in personalized therapy, which may lead to improved efficacy and reduced toxicity. This will include the development of clinically available tests that can efficiently discern the SHH subgroup. The preliminary use of these tests in clinical trials is also discussed herein.

Boc modifies the spectrum of holoprosencephaly in the absence of Gas1 function

Holoprosencephaly is a heterogeneous developmental malformation of the central nervous system characterized by impaired forebrain cleavage, midline facial anomalies and wide phenotypic variation. Indeed, microforms represent the mildest manifestation, associated with facial anomalies but an intact central nervous system. In many cases, perturbations in sonic hedgehog signaling are responsible for holoprosencephaly. Here, we have elucidated the contribution of Gas1 and an additional hedgehog co-receptor, Boc during early development of the craniofacial midline, by generating single and compound mutant mice. Significantly, we find Boc has an essential role in the etiology of a unique form of lobar holoprosencephaly that only occurs in conjunction with combined loss of Gas1. Whilst Gas1(-/-) mice have microform holoprosencephaly characterized by a single median maxillary central incisor, cleft palate and pituitary anomalies, Boc(-/-) mice have a normal facial midline. However, Gas1(-/-); Boc(-/-) mutants have lobar holoprosencephaly associated with clefting of the lip, palate and tongue, secondary to reduced sonic hedgehog transduction in the central nervous system and face. Moreover, maxillary incisor development is severely disrupted in these mice, arresting prior to cellular differentiation as a result of apoptosis in the odontogenic epithelium. Thus, Boc and Gas1 retain an essential function in these tooth germs, independent of their role in midline development of the central nervous system and face. Collectively, this phenotype demonstrates both redundancy and individual requirements for Gas1 and Boc during sonic hedgehog transduction in the craniofacial midline and suggests BOC as a potential digenic locus for lobar holoprosencephaly in human populations.

Lentivirus-mediated delivery of sonic hedgehog into the striatum stimulates neuroregeneration in a rat model of Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative disorder in which the nigrostriatal pathway, consisting of dopaminergic neuronal projections from the substantia nigra to the striatum, degenerates. Viral transduction is currently the most promising in vivo strategy for delivery of therapeutic proteins into the brain for treatment of PD. Sonic hedgehog (Shh) is necessary for cell proliferation, differentiation and neuroprotection in the central nervous system. In this study, we investigated the effects of overexpressed N-terminal product of SHH (SHH-N) in a PD model rat. A lentiviral vector containing SHH-N was stereotactically injected into the striatum 24 h after a striatal 6-OHDA lesion. We found that overexpressed SHH-N attenuated behavioral deficits and reduced the loss of dopamine neurons in the substantia nigra and the loss of dopamine fibers in the striatum. In addition, fluoro-ruby-labeled nigrostriatal projections were also repaired. Together, our results demonstrate the feasibility and efficacy of using the strategy of lentivirus-mediated Shh-N delivery to delay nigrostriatal pathway degeneration. This strategy holds the potential for therapeutic application in the treatment of PD.

New insight into hedgehog signaling in hematological malignancies

The hedgehog (Hh) signaling pathway is well established as being evolutionarily conserved across vertebrates, and is involved in organogenesis, hematopoiesis, embryogenesis and homeostasis of adult tissues. At a microscopic level, the Hh signaling pathway controls the proliferation, apoptosis, cell-cycle and differentiation programs of stem and progenitor cells. Increasing evidence suggests that aberrant activation of the Hh signaling pathway is related to neoplasm, including solid tumors and hematologic malignancies. Currently the Hh signaling pathway has become one of the most studied potential therapeutic targets in hematological malignancies. In this review, we focus on findings related to Hh signaling in the initiation, maintenance, progression and chemoresistance of hematological malignancies, looking forward to better targeted treatment strategies.

Signaling domain of Sonic Hedgehog as cannibalistic calcium-regulated zinc-peptidase

Sonic Hedgehog (Shh) is a representative of the evolutionary closely related class of Hedgehog proteins that have essential signaling functions in animal development. The N-terminal domain (ShhN) is also assigned to the group of LAS proteins (LAS = Lysostaphin type enzymes, D-Ala-D-Ala metalloproteases, Sonic Hedgehog), of which all members harbor a structurally well-defined Zn2+ center; however, it is remarkable that ShhN so far is the only LAS member without proven peptidase activity. Another unique feature of ShhN in the LAS group is a double-Ca2+ center close to the zinc. We have studied the effect of these calcium ions on ShhN structure, dynamics, and interactions. We find that the presence of calcium has a marked impact on ShhN properties, with the two calcium ions having different effects. The more strongly bound calcium ion significantly stabilizes the overall structure. Surprisingly, the binding of the second calcium ion switches the putative catalytic center from a state similar to LAS enzymes to a state that probably is catalytically inactive. We describe in detail the mechanics of the switch, including the effect on substrate co-ordinating residues and on the putative catalytic water molecule. The properties of the putative substrate binding site suggest that ShhN could degrade other ShhN molecules, e.g. by cleavage at highly conserved glycines in ShhN. To test experimentally the stability of ShhN against autodegradation, we compare two ShhN mutants in vitro: (1) a ShhN mutant unable to bind calcium but with putative catalytic center intact, and thus, according to our hypothesis, a constitutively active peptidase, and (2) a mutant carrying additionally mutation E177A, i.e., with the putative catalytically active residue knocked out. The in vitro results are consistent with ShhN being a cannibalistic zinc-peptidase. These experiments also reveal that the peptidase activity depends on pH.

Effects of quercetin on hedgehog signaling in chronic myeloid leukemia KBM7 cells

OBJECTIVE

To investigate the effects of quercetin on Hedgehog (Hh) signaling in chronic myeloid leukemia KBM7 cells.

METHODS

The KBM7 cells were treated with 50, 100 and 200 μmol/L quercetin for 48 h respectively. And then the trypan blue assay was used to examine the proliferative inhibition of quercetin. Apoptotic cells and cell cycle were measured by flow cytometry. The mRNA and protein expression were detected by quantitative real-time polymerase chain reaction (PCR) and Western blot, respectively.

RESULTS

Quercetin significantly inhibited KBM7 cell proliferation, induced cell apoptosis, and blocked cell cycle at G1 phase, which were in dose-dependent manners. The mRNA and protein expression of Smoothened and Glioma1 (Gli1), the members of Hh pathway decreased after treatment with quercetin. The Bcl-2 and Cyclin D1, targets of Hh signaling, also decreased after treatment with quercetin, respectively. Quercetin also could increase p53 and Caspase-3 expression. Bcr-abl mRNA copies decreased, but no changes of phosphorylated Bcr-abl and Bcr-abl proteins were observed, after treatment with quercetin.

CONCLUSION

Quercetin could inhibit Hh signaling and its downstream targets in the KBM7 cells. And it might be one of mechanisms of inducing apoptosis and inhibiting cell cycle by quercetin.