SEARCH · PubMed Health

Results for “Smoothened Receptor”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed2000

The seven-transmembrane receptor smoothened cell-autonomously induces multiple ventral cell types.

Sonic Hedgehog (Shh) is a secreted protein that controls cell fate and mitogenesis in the developing nervous system. Here we show that a constitutively active form of Smoothened (Smo-M2) mimics concentration-dependent actions of Shh in the developing neural tube, including activation of ventral marker genes (HNF3beta, patched, Nkx2.2, netrin-1), suppression of dorsal markers (Pax-3, Gli-3, Ephrin A5) and induction of ventral neurons (dopaminergic, serotonergic) and ventrolateral motor neurons (Islet-1+, Islet-2+, HB9+) and interneurons (Engrailed-1+, CHX10+). Furthermore, Smo-M2's patterning activities were cell autonomous, occurring exclusively in cells expressing Smo-M2. These findings suggest that Smo is a key signaling component in the Hh receptor and that Shh patterns the vertebrate nervous system as a morphogen, rather than through secondary relay signals.

Amino Acid Substitution↗

PubMed1999

Sonic hedgehog signaling by the patched-smoothened receptor complex.

BACKGROUND: The Hedgehog (Hh) family of secreted proteins is involved in a number of developmental processes as well as in cancer. Genetic and biochemical data suggest that the Sonic hedgehog (Shh) receptor is composed of at least two proteins: the tumor suppressor protein Patched (Ptc) and the seven-transmembrane protein Smoothened (Smo). RESULTS: Using a biochemical assay for activation of the transcription factor Gli, a downstream component of the Hh pathway, we show here that Smo functions as the signaling component of the Shh receptor, and that this activity can be blocked by Ptc. The inhibition of Smo by Ptc can be relieved by the addition of Shh. Furthermore, oncogenic forms of Smo are insensitive to Ptc repression in this assay. Mapping of the Smo domains required for binding to Ptc and for signaling revealed that the Smo-Ptc interaction involves mainly the amino terminus of Smo, and that the third intracellular loop and the seventh transmembrane domain are required for signaling. CONCLUSIONS: These data demonstrate that Smo is the signaling component of a multicomponent Hh receptor complex and that Ptc is a ligand-regulated inhibitor of Smo. Different domains of Smo are involved in Ptc binding and activation of a Gli reporter construct. The latter requires the third intracellular loop and the seventh transmembrane domain of Smo, regions often involved in coupling to G proteins. No changes in the levels of cyclic AMP or calcium associated with such pathways could be detected following receptor activation, however.

Amino Acid Sequence↗

PubMed1997

Hedgehog and its patched-smoothened receptor complex: a novel signalling mechanism at the cell surface.

Pattern formation and morphogenesis depend on the careful execution of complex genetic programs, which are conserved in multicellular organisms. An important signal in some of these programs in Drosophila and vertebrates is the secreted Hedgehog (Hh) protein, which primarily functions as an inducer of morphogenetic signals. The Hh signal plays a decisive role in such critical developmental processes as neurulation and somite and limb formation. The Hh signalling pathway exhibits a novel mechanism of signal reception and transduction. In the absence of the Hh signal, the membrane protein Patched (Ptc) represses the constitutive signalling activity of a second membrane protein, Smoothened (Smo), by virtue of its ability to form a Ptc-Smo complex. Hence, mutations within the ptc gene that result in the failure of Ptc to inhibit Smo lead to constitutive activity of the Hh signalling pathway and to cancer, such as basal cell carcinoma. For activation of Hh-target genes, the N-terminal signalling domain of Hh binds to the Ptc-Smo receptor complex to activate two parallel signalling pathways. Furthermore, Hh limits its own range of action by impeding its diffusion through (i) covalent linkage of its N-terminal signalling moiety to cholesterol, mediated by the cholesterol transferase activity of its C-terminal moiety, and (ii) induction of, and sequestration by, its antagonist, Ptc.

Animals↗

PubMed2001

Sonic hedgehog restricts adhesion and migration of neural crest cells independently of the Patched- Smoothened-Gli signaling pathway.

In the vertebrate embryo, neural cell types are organized spatially along the dorsoventral axis of the neural tube and differ by expression of cell-intrinsic determinants and by their adhesive and locomotory properties. Thus, dorsally, neural crest cells (NCC) show a strong propensity to disperse and migrate, whereas cells situated ventrally are highly cohesive and poorly motile. Members of the bone morphogenetic proteins have been shown to exert a dual role in the specification of dorsal neuroepithelial cells and in the dispersion of NCCs. To test whether Sonic hedgehog (Shh), another signaling molecule involved in the patterning of the ventral neural tube, might also contribute to the control of the adhesive and migratory potential of neuroepithelial cells, we analyzed the effect of ectopic Shh on NCC dispersion from neural tube explants cultured in vitro. The addition of Shh to the migration substrate of NCC caused inhibition of their dispersion. The effect of Shh on cell migration was reversible and was not accounted for by alterations of the specification, delamination, proliferation, and survival of NCCs but could be essentially attributed to a decreased cell-substrate adhesion mediated by integrins. In addition, Shh activity on cell migration was mediated by a specific N-terminal region of the molecule and was independent from the signaling cascade elicited by the Patched-Smoothened receptor and involving the Gli transcription factors. Our study therefore reveals an unanticipated role for Shh in regulating adhesion and migration of neuroepithelial cells that is discernable from its inductive, mitogenic, and trophic functions.

Animals↗

PubMed2000

Posttranscriptional regulation of smoothened is part of a self-correcting mechanism in the Hedgehog signaling system.

Hedgehog signaling, mediated through its Patched-Smoothened receptor complex, is essential for pattern formation in animal development. Activating mutations within Smoothened have been associated with basal cell carcinoma, suggesting that smoothened is a protooncogene. Thus, regulation of Smoothened levels might be critical for normal development. We show that Smoothened protein levels in Drosophila embryos are regulated posttranscriptionally by a mechanism dependent on Hedgehog signaling but not on its nuclear effector Cubitus interruptus. Hedgehog signaling upregulates Smoothened levels, which are otherwise downregulated by Patched. Demonstrating properties of a self-correcting system, the Hedgehog signaling pathway adjusts the concentrations of Smoothened and Patched to each other and to that of the Hedgehog signal, which ensures that activation of Hedgehog target genes by Smoothened signaling becomes strictly dependent on Hedgehog.

Animals↗

PubMed2004

The upregulated expression of sonic hedgehog in motor neurons after rat facial nerve axotomy.

Nerve injury leads to the induction of a large number of genes to repair the damage and to restore synaptic transmission. We have attempted to identify molecules whose mRNA expression is altered in response to facial nerve axotomy. Here we report that facial nerve axotomy upregulates Sonic hedgehog (Shh) and its receptor Smoothened (Smo) in facial motor neurons of adult rats, whereas facial nerve axotomy does not upregulate mRNA of Shh or Smo in neonatal rats. We tested whether overexpression of Shh in facial motor neurons of axotomized neonatal rats may promote neuronal survival. Adenovirus-mediated overexpression of Shh, but not that of beta-galactosidase, transiently rescues axotomy-induced neuronal cell death for 3-5 d after axotomy. Finally, the pharmacological inhibitor of Shh signaling, cyclopamine, induces motor neuron death in adult rats after axotomy. These results suggest that Shh plays a regulatory role in nerve injury.

Adenoviridae↗

PubMed2003

Distribution of Indian hedgehog and its receptors patched and smoothened in human chronic pancreatitis.

Indian hedgehog (IHH) and its receptors patched (PTC) and smoothened (SMO) belong to the hedgehog family of signaling molecules, which are essential for a variety of patterning events during mammalian tIssue development. IHH plays a role in pancreas organogenesis and differentiation, as well as in the regulation of insulin production. In the present study, the expression of IHH and its receptors was analyzed in normal human pancreatic and chronic pancreatitis (CP) tIssues using Northern blotting, immunohistochemistry and Western blotting, and was correlated with clinicopathological parameters. In addition, the effects of inhibition and stimulation of the hedgehog signaling pathway on cell growth were determined in TAKA-1 normal pancreatic ductal cells. IHH mRNA was expressed in the normal human pancreas and CP tIssues, with slightly higher expression levels in CP. Using immunohistochemistry, IHH and its receptors were localized mainly in the islet cells of the normal pancreas. In CP, IHH and its receptors were present in the cells forming tubular complexes and in the islets with a different signal pattern compared with the islets in the normal pancreas. Correlation between diabetic and non-diabetic CP patients revealed no significant difference in IHH, SMO, or PTC immunoreactivity. Inhibition of hedgehog signaling in TAKA-1 pancreatic ductal cells using cyclopamine significantly reduced their growth through cell cycle arrest, while stimulation of the IHH pathway enhanced the growth of these cells. In conclusion, IHH and its receptors are expressed in the normal human pancreas and in CP, yet with a different distribution and cellular localization. IHH signaling may be involved in the pathogenesis of CP, i.e. in the formation and proliferation of tubular complexes and in islet cell dysfunction.

Adult↗

PubMed2002

Bioinformatics and type II G-protein-coupled receptors.

The best known family B, or Type II, G-protein-coupled receptors (GPCRs) recognize peptides as ligands. The receptors for corticotrophin-releasing factor, parathyroid hormone and secretin typify this group. However, there are only 15 such GPCRs. Many other receptors share sequence homology and have been assigned to this family. The ten 'Frizzled' and one 'Smoothened' receptors show the lowest sequence homology and are not necessarily G-protein coupled. Drosophila genetics have enabled our understanding of their biology. In contrast, relatively little is known about the largest group with family B, the 33 'large amino termini' or large N-terminal family B seven-transmembrane (LNB 7TM) receptors. This review highlights the similarities found between family B receptors and provides a classification of LNB 7TM receptors.

Animals↗

PubMed2003

A dual role for Sonic hedgehog in regulating adhesion and differentiation of neuroepithelial cells.

In vertebrates, the nervous system arises from a flat sheet of epithelial cells, the neural plate, that gradually transforms into a hollow neural tube. This process, called neurulation, involves sequential changes in cellular interactions that are precisely coordinated both spatially and temporally by the combined actions of morphogens. To gain further insight into the molecular events regulating cell adhesion during neurulation, we investigated whether the adhesive and migratory capacities of neuroepithelial cells might be modulated by Sonic hedgehog (Shh), a signaling molecule involved in the control of cell differentiation in the ventral neural tube. When deposited onto extracellular matrix components in vitro, neural plates explanted from avian embryos at early neurulation readily dispersed into monolayers of spread cells, thereby revealing their intrinsic ability to migrate. In the presence of Shh added in solution to the culture medium, the explants still exhibited the same propensity to disperse. In contrast, when Shh was immobilized to the substrate or produced by neuroepithelial cells themselves after transfection, neural plate explants failed to disperse and instead formed compact structures. Changes in the adhesive capacities of neuroepithelial cells caused by Shh could be accounted for by inactivation of surface beta1-integrins combined with an increase in N-cadherin-mediated cell adhesion. Furthermore, immobilized Shh promoted differentiation of neuroepithelial cells into motor neurons and floor plate cells with the same potency as soluble Shh. However, the effect of Shh on the neuroepithelial cell adhesion was discernible and apparently independent from its differentiation effect and was not mediated by the signaling cascade elicited by the Patched-Smoothened receptor and involving the Gli transcription factors. Thus, our experiments indicate that Shh is able to control sequentially adhesion and differentiation of neuroepithelial cells through different mechanisms, leading to a coordinated regulation of the various cell interactions essential for neural tube morphogenesis.

Animals↗

PubMed2000

Sonic hedgehog promotes G(1) cyclin expression and sustained cell cycle progression in mammalian neuronal precursors.

Sonic hedgehog (Shh) signal transduction via the G-protein-coupled receptor, Smoothened, is required for proliferation of cerebellar granule neuron precursors (CGNPs) during development. Activating mutations in the Hedgehog pathway are also implicated in basal cell carcinoma and medulloblastoma, a tumor of the cerebellum in humans. However, Shh signaling interactions with cell cycle regulatory components in neural precursors are poorly understood, in part because appropriate immortalized cell lines are not available. We have utilized primary cultures from neonatal mouse cerebella in order to determine (i) whether Shh initiates or maintains cell cycle progression in CGNPs, (ii) if G(1) regulation by Shh resembles that of classical mitogens, and (iii) whether individual D-type cyclins are essential components of Shh proliferative signaling in CGNPs. Our results indicate that Shh can drive continued cycling in immature, proliferating CGNPs. Shh treatment resulted in sustained activity of the G(1) cyclin-Rb axis by regulating levels of cyclinD1, cyclinD2, and cyclinE mRNA transcripts and proteins. Analysis of CGNPs from cyclinD1(-/-) or cyclinD2(-/-) mice demonstrates that the Shh proliferative pathway does not require unique functions of cyclinD1 or cyclinD2 and that D-type cyclins overlap functionally in this regard. In contrast to many known mitogenic pathways, we show that Shh proliferative signaling is mitogen-activated protein kinase independent. Furthermore, protein synthesis is required for early effects on cyclin gene expression. Together, our results suggest that Shh proliferative signaling promotes synthesis of regulatory factor intermediates that upregulate or maintain cyclin gene expression and activity of the G(1) cyclin-Rb axis in proliferating granule neuron precursors.

Animals↗

PubMed2003

Wnts and Hedgehogs: lipid-modified proteins and similarities in signaling mechanisms at the cell surface.

This review compares the signaling mechanisms of the Wnt and the Hedgehog proteins. Although Wnts and Hedgehogs are unrelated proteins, they are both modified by lipids, possibly through the action of enzymes that are related to each other. At the surface of target cells, the reception of Wnt and Hedgehog signals is regulated by several molecules, some of which, in particular the Frizzled and Smoothened receptors, are related to each other. Several other aspects of Wnt and Hedgehog transport and signaling are discussed, as well as the possible origin of these pathways.

Animals↗

PubMed1996

smoothened encodes a receptor-like serpentine protein required for hedgehog signalling.

Members of the Hedgehog family of secreted proteins control a number of important inductive interactions in the development of both vertebrates and Drosophila, but little is known about the ways in which their signalling activities are transduced. In Drosophila, hedgehog is one of the segment-polarity genes, mutations of which disrupt the pattern and polarity of individual embryonic segments and their adult derivatives; several of these genes have been implicated in transduction of the hedgehog signal. Here we show that the segment-polarity gene smoothened is required for the response of cells to hedgehog signalling during the development of both the embryonic segments and imaginal discs. Sequence analysis of the smoothened transcription unit reveals a single open reading frame encoding a protein with seven putative transmembrane domains. This structure is typical of G-protein-coupled receptors, suggesting that the Smoothened protein may act as a receptor for the Hedgehog ligand.

Alleles↗

PubMed2000

Erythroid differentiation in vitro is blocked by cyclopamine, an inhibitor of hedgehog signaling.

Adult hematopoietic differentiation is a developmental process that employs many of the same molecular mechanisms as embryogenesis. To explore the possibility that hedgehog signaling is involved in the control of hematopoietic differentiation, we screened a panel of human leukemia cell lines for the expression of Patched1 and Smoothened, the receptor and coreceptor for hedgehog ligands. Expression was found in multiple cell lines, and Patched1 expression was detected in normal marrow. Induction of myeloid differentiation in cell lines downregulated expression of both genes. When normal marrow mononuclear cells were grown in semisolid medium in the presence of 10 microM cyclopamine, development of colonies of granulocytic/monocytic lineage was unaffected in terms of both number and morphology. The number of erythroid colonies, however, was significantly reduced (P < 0.01). Furthermore, hemoglobinization was substantially delayed relative to controls in those erythroid colonies that did form. Incubation of hematopoietic progenitors with Shh-N and GM-CSF resulted in increased granulocyte/monocyte colonies (P < 0.01); the increase was blocked by cyclopamine. Incubation of hematopoietic progenitors with Shh-N and stem cell factor resulted in larger erythroid colonies. These results suggest that elements of the hedgehog signaling pathway are involved in the control of hematopoietic differentiation.

Cell Differentiation↗

PubMed2000

Analysis of PTCH/SMO/SHH pathway genes in medulloblastoma.

Inactivation of the PTCH tumor suppressor gene occurs in a subset of sporadic medulloblastomas, suggesting that alterations in the PTCH pathway may be important in the development of this tumor. In order to address the frequency of genetic alterations affecting genes in this pathway, we used a combination of loss of heterozygosity (LOH) analysis, single-stranded conformational polymorphism (SSCP) analysis, and direct sequencing of DNA samples from sporadic primitive neuroectodermal tumors (PNETs). To identify alterations in the PTCH gene, we performed LOH analysis on 37 tumor DNA samples. Of those with matched constitutional DNA samples, one demonstrated LOH. Of those without matched constitutional DNA, six were homozygous with all markers. All exons of the PTCH gene were sequenced in these seven tumors, and three mutations were found. To identify alterations in the SHH and SMO genes, we analyzed all exons of both genes in 24 tumors with SSCP and sequenced any exons that showed aberrant band patterns. No mutations were found in either SHH or SMO in any tumor. We also identified the following genes as candidate tumor suppressors based on their roles in controlling hh/ptc signaling in Drosophila: EN-1 and EN-2, deletion of which results in a lack of cerebellar development in mice; SMAD family members 1-7, and protein kinase A subunits RIalpha, RIbeta, RIIbeta, Calpha, and Cbeta. Each of these genes was investigated in a panel of 24 matched constitutional and tumor DNA samples. Our search revealed no mutations in any of these genes. Thus, PTCH is the only gene in this complex pathway that is mutated with notable frequency in PNET. Genes Chromosomes Cancer 27:44-51, 2000.

Cerebellar Neoplasms↗

PubMed2004

Reading ratios.

Explore the source record for details and available documents.

Animals↗

PubMed2001

Retinoic acid specifically downregulates Fgf4 and inhibits posterior cell proliferation in the developing mouse autopod.

Retinoic acid, when administered to pregnant mice on d 11.0 of gestation, causes limb skeletal abnormalities consisting of reduced digital number, shortening of the long bones and delayed ossification. We show here that these effects are correlated with a decrease in cell proliferation within 5 h of retinoic acid administration, specifically in the posterior half of the distal limb bud mesenchyme, from which the distal skeletal elements are generated. There is a specific downregulation of Fgf4, a gene known to be involved in limb bud outgrowth and expressed only in the posterior part of the apical ectodermal ridge; Fgf8, which is expressed throughout the apical ectodermal ridge, is unaffected. The reduction in Fgf4 expression is not accompanied by downregulation of Shh, nor of its receptor and downstream target gene Ptc, suggesting that the skeletal reduction defects induced by retinoic acid are mediated specifically by FGF4-induced skeletogenic mesenchymal cell proliferation.

Animals↗

PubMed2003

A genetic screen for hedgehog targets involved in the maintenance of the Drosophila anteroposterior compartment boundary.

The development of multicellular organisms requires the establishment of cell populations with different adhesion properties. In Drosophila, a cell-segregation mechanism underlies the maintenance of the anterior (A) and posterior (P) compartments of the wing imaginal disc. Although engrailed (en) activity contributes to the specification of the differential cell affinity between A and P cells, recent evidence suggests that cell sorting depends largely on the transduction of the Hh signal in A cells. The activator form of Cubitus interruptus (Ci), a transcription factor mediating Hh signaling, defines anterior specificity, indicating that Hh-dependent cell sorting requires Hh target gene expression. However, the identity of the gene(s) contributing to distinct A and P cell affinities is unknown. Here, we report a genetic screen based on the FRT/FLP system to search for genes involved in the correct establishment of the anteroposterior compartment boundary. By using double FRT chromosomes in combination with a wing-specific FLP source we screened 250,000 mutagenized chromosomes. Several complementation groups affecting wing patterning have been isolated, including new alleles of most known Hh-signaling components. Among these, we identified a class of patched (ptc) alleles exhibiting a novel phenotype. These results demonstrate the value of our setup in the identification of genes involved in distinct wing-patterning processes.

Animals↗

PubMed1999

The hedgehog morphogen and gradients of cell affinity in the abdomen of Drosophila.

The adult abdomen of Drosophila is a chain of anterior (A) and posterior (P) compartments. The engrailed gene is active in all P compartments and selects the P state. Hedgehog enters each A compartment across both its anterior and posterior edges; within A its concentration confers positional information. The A compartments are subdivided into an anterior and a posterior domain that each make different cell types in response to Hedgehog. We have studied the relationship between Hedgehog, engrailed and cell affinity. We made twin clones and measured the shape, size and displacement of the experimental clone, relative to its control twin. We varied the perceived level of Hedgehog in the experimental clone and find that, if this level is different from the surround, the clone fails to grow normally, rounds up and sometimes sorts out completely, becoming separated from the epithelium. Also, clones are displaced towards cells that are more like themselves: for example groups of cells in the middle of the A compartment that are persuaded to differentiate as if they were at the posterior limit of A, move posteriorly. Similarly, clones in the anterior domain of the A compartment that are forced to differentiate as if they were at the anterior limit of A, move anteriorly. Quantitation of these measures and the direction of displacement indicate that there is a U-shaped gradient of affinity in the A compartment that correlates with the U-shaped landscape of Hedgehog concentration. Since affinity changes are autonomous to the clone we believe that, normally, each cell's affinity is a direct response to Hedgehog. By removing engrailed in clones we show that A and P cells also differ in affinity from each other, in a manner that appears independent of Hedgehog. Within the P compartment we found some evidence for a U-shaped gradient of affinity, but this cannot be due to Hedgehog which does not act in the P compartment.

Abdomen↗