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Abstract
Ligands of the Hedgehog (HH) pathway are paracrine signaling molecules that coordinate tissue development in metazoans. A remarkable feature of HH signaling is the repeated use of cholesterol in steps spanning ligand biogenesis, secretion, dispersal, and reception on target cells. A cholesterol molecule covalently attached to HH ligands is used as a molecular baton by transfer proteins to guide their secretion, spread, and reception. On target cells, a signaling circuit composed of a cholesterol transporter and sensor regulates transmission of HH signals across the plasma membrane to the cytoplasm. The repeated use of cholesterol in signaling supports the view that the HH pathway likely evolved by coopting ancient systems to regulate the abundance or organization of sterol-like lipids in membranes.
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Affiliation(s)
- Christian Siebold
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, United Kingdom;
| | - Rajat Rohatgi
- Departments of Biochemistry and Medicine, Stanford University School of Medicine, Stanford, California, USA;
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Nguyen TD, Truong ME, Reiter JF. The Intimate Connection Between Lipids and Hedgehog Signaling. Front Cell Dev Biol 2022; 10:876815. [PMID: 35757007 PMCID: PMC9222137 DOI: 10.3389/fcell.2022.876815] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 05/13/2022] [Indexed: 01/19/2023] Open
Abstract
Hedgehog (HH) signaling is an intercellular communication pathway involved in directing the development and homeostasis of metazoans. HH signaling depends on lipids that covalently modify HH proteins and participate in signal transduction downstream. In many animals, the HH pathway requires the primary cilium, an organelle with a specialized protein and lipid composition. Here, we review the intimate connection between HH signaling and lipids. We highlight how lipids in the primary cilium can create a specialized microenvironment to facilitate signaling, and how HH and components of the HH signal transduction pathway use lipids to communicate between cells.
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Affiliation(s)
- Thi D. Nguyen
- Department of Biochemistry and Biophysics, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, United States
| | - Melissa E. Truong
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States
| | - Jeremy F. Reiter
- Department of Biochemistry and Biophysics, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, United States,Chan Zuckerberg Biohub, San Francisco, CA, United States,*Correspondence: Jeremy F. Reiter,
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3
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Liu YC, Wierbowski BM, Salic A. Hedgehog pathway modulation by glypican 3-conjugated heparan sulfate. J Cell Sci 2022; 135:274739. [PMID: 35142364 PMCID: PMC8977055 DOI: 10.1242/jcs.259297] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 02/04/2022] [Indexed: 11/20/2022] Open
Abstract
Glypicans are a family of cell surface heparan sulfate proteoglycans that play critical roles in multiple cell signaling pathways. Glypicans consist of a globular core, an unstructured stalk modified with sulfated glycosaminoglycan chains, and a glycosylphosphatidylinositol anchor. Though these structural features are conserved, their individual contribution to glypican function remains obscure. Here, we investigate how glypican 3 (GPC3), which is mutated in Simpson-Golabi-Behmel tissue overgrowth syndrome, regulates Hedgehog signaling. We find that GPC3 is necessary for the Hedgehog response, surprisingly controlling a downstream signal transduction step. Purified GPC3 ectodomain rescues signaling when artificially recruited to the surface of GPC3-deficient cells but has dominant-negative activity when unattached. Strikingly, the purified stalk, modified with heparan sulfate but not chondroitin sulfate, is necessary and sufficient for activity. Our results demonstrate a novel function for GPC3-associated heparan sulfate and provide a framework for the functional dissection of glycosaminoglycans by in vivo biochemical complementation. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Yulu Cherry Liu
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.,Department of Biology, Hood College, Frederick, MD 21701, USA
| | | | - Adrian Salic
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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Huang P, Wierbowski BM, Lian T, Chan C, García-Linares S, Jiang J, Salic A. Structural basis for catalyzed assembly of the Sonic hedgehog-Patched1 signaling complex. Dev Cell 2022; 57:670-685.e8. [PMID: 35231446 PMCID: PMC8932645 DOI: 10.1016/j.devcel.2022.02.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 01/13/2022] [Accepted: 02/04/2022] [Indexed: 01/04/2023]
Abstract
The dually lipidated Sonic hedgehog (SHH) morphogen signals through the tumor suppressor membrane protein Patched1 (PTCH1) to activate the Hedgehog pathway, which is fundamental in development and cancer. SHH engagement with PTCH1 requires the GAS1 coreceptor, but the mechanism is unknown. We demonstrate a unique role for GAS1, catalyzing SHH-PTCH1 complex assembly in vertebrate cells by direct SHH transfer from the extracellular SCUBE2 carrier to PTCH1. Structure of the GAS1-SHH-PTCH1 transition state identifies how GAS1 recognizes the SHH palmitate and cholesterol modifications in modular fashion and how it facilitates lipid-dependent SHH handoff to PTCH1. Structure-guided experiments elucidate SHH movement from SCUBE2 to PTCH1, explain disease mutations, and demonstrate that SHH-induced PTCH1 dimerization causes its internalization from the cell surface. These results define how the signaling-competent SHH-PTCH1 complex assembles, the key step triggering the Hedgehog pathway, and provide a paradigm for understanding morphogen reception and its regulation.
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Affiliation(s)
- Pengxiang Huang
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | | | - Tengfei Lian
- Laboratory of Membrane Proteins and Structural Biology, Biochemistry and Biophysics Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Charlene Chan
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | | | - Jiansen Jiang
- Laboratory of Membrane Proteins and Structural Biology, Biochemistry and Biophysics Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Adrian Salic
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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New advances of DNA/RNA methylation modification in liver fibrosis. Cell Signal 2021; 92:110224. [PMID: 34954394 DOI: 10.1016/j.cellsig.2021.110224] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 12/15/2021] [Accepted: 12/20/2021] [Indexed: 11/23/2022]
Abstract
Liver fibrosis is a complex pathological process caused by multiple pathogenic factors,such as ethanol, viruses, toxins, drugs or cholestasis, and it can eventually develop into liver cirrhosis without effective treatment. Activation of hepatic stellate cells (HSCs) is a pivotal cellular event in the pathogenesis of liver fibrosis. However, the pathogenesis of liver fibrosis has not been fully elucidated. DNA/RNA methylation can regulate gene expression without alteration in its sequence, and numerous studies have shown the involvement of DNA methylation in the activation of HSCs and then promote the progression of liver fibrosis. In addition, RNA methylation has recently been reported to play a regulatory role in this process. In this review, we focus on the aberrant DNA/RNA methylation of selected genes and explore their functional mechanism in regulating HSCs activation and liver fibrogenesis. All of these findings will enhance our understanding of DNA/RNA methylation and their roles in liver fibrosis and provide the basis to identify effective therapeutic targets.
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Loo CKC, Pearen MA, Ramm GA. The Role of Sonic Hedgehog in Human Holoprosencephaly and Short-Rib Polydactyly Syndromes. Int J Mol Sci 2021; 22:ijms22189854. [PMID: 34576017 PMCID: PMC8468456 DOI: 10.3390/ijms22189854] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 09/03/2021] [Accepted: 09/09/2021] [Indexed: 12/18/2022] Open
Abstract
The Hedgehog (HH) signalling pathway is one of the major pathways controlling cell differentiation and proliferation during human development. This pathway is complex, with HH function influenced by inhibitors, promotors, interactions with other signalling pathways, and non-genetic and cellular factors. Many aspects of this pathway are not yet clarified. The main features of Sonic Hedgehog (SHH) signalling are discussed in relation to its function in human development. The possible role of SHH will be considered using examples of holoprosencephaly and short-rib polydactyly (SRP) syndromes. In these syndromes, there is wide variability in phenotype even with the same genetic mutation, so that other factors must influence the outcome. SHH mutations were the first identified genetic causes of holoprosencephaly, but many other genes and environmental factors can cause malformations in the holoprosencephaly spectrum. Many patients with SRP have genetic defects affecting primary cilia, structures found on most mammalian cells which are thought to be necessary for canonical HH signal transduction. Although SHH signalling is affected in both these genetic conditions, there is little overlap in phenotype. Possible explanations will be canvassed, using data from published human and animal studies. Implications for the understanding of SHH signalling in humans will be discussed.
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Affiliation(s)
- Christine K. C. Loo
- South Eastern Area Laboratory Services, Department of Anatomical Pathology, NSW Health Pathology, Prince of Wales Hospital, Sydney, NSW 2031, Australia
- Correspondence: ; Tel.: +61-2-93829015
| | - Michael A. Pearen
- Hepatic Fibrosis Group, Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Brisbane, QLD 4006, Australia; (M.A.P.); (G.A.R.)
| | - Grant A. Ramm
- Hepatic Fibrosis Group, Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Brisbane, QLD 4006, Australia; (M.A.P.); (G.A.R.)
- Faculty of Medicine, The University of Queensland, Brisbane, QLD 4006, Australia
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Ho EK, Stearns T. Hedgehog signaling and the primary cilium: implications for spatial and temporal constraints on signaling. Development 2021; 148:dev195552. [PMID: 33914866 PMCID: PMC8126410 DOI: 10.1242/dev.195552] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The mechanisms of vertebrate Hedgehog signaling are linked to the biology of the primary cilium, an antenna-like organelle that projects from the surface of most vertebrate cell types. Although the advantages of restricting signal transduction to cilia are often noted, the constraints imposed are less frequently considered, and yet they are central to how Hedgehog signaling operates in developing tissues. In this Review, we synthesize current understanding of Hedgehog signal transduction, ligand secretion and transport, and cilia dynamics to explore the temporal and spatial constraints imposed by the primary cilium on Hedgehog signaling in vivo.
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Affiliation(s)
- Emily K. Ho
- Department of Developmental Biology, Stanford School of Medicine, Stanford, CA 94305, USA
| | - Tim Stearns
- Department of Biology, Stanford University, Stanford, CA 94305, USA
- Department of Genetics, Stanford School of Medicine, Stanford, CA 94305, USA
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