1. Cell Biology
  2. Developmental Biology

Cholesterol accessibility at the ciliary membrane controls Hedgehog signaling

  1. Maia Kinnebrew
  2. Ellen Jean Iverson
  3. Bhaven B Patel
  4. Ganesh V Pusapati
  5. Jennifer H Kong
  6. Kristen A Johnson
  7. Giovanni Luchetti
  8. Kaitlyn M Eckert
  9. Jeffrey G McDonald
  10. Douglas F Covey
  11. Christian Siebold
  12. Arun Radhakrishnan  Is a corresponding author
  13. Rajat Rohatgi  Is a corresponding author
  1. Stanford University School of Medicine, United States
  2. Stanford University School of medicine, United States
  3. University of Texas Southwestern Medical Center, United States
  4. Washington University School of Medicine, United States
  5. University of Oxford, United Kingdom
https://doi.org/10.7554/eLife.50051
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Cite this article
  1. Maia Kinnebrew
  2. Ellen Jean Iverson
  3. Bhaven B Patel
  4. Ganesh V Pusapati
  5. Jennifer H Kong
  6. Kristen A Johnson
  7. Giovanni Luchetti
  8. Kaitlyn M Eckert
  9. Jeffrey G McDonald
  10. Douglas F Covey
  11. Christian Siebold
  12. Arun Radhakrishnan
  13. Rajat Rohatgi
(2019)
Cholesterol accessibility at the ciliary membrane controls Hedgehog signaling
eLife 8:e50051.
https://doi.org/10.7554/eLife.50051
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Abstract

Previously we proposed that transmission of the Hedgehog signal across the plasma membrane by Smoothened is triggered by its interaction with cholesterol (Luchetti et al., 2016). But how is cholesterol, an abundant lipid, regulated tightly enough to control a signaling system that can cause birth defects and cancer? Using toxin-based sensors that distinguish between distinct pools of cholesterol, we find that Smoothened activation and Hedgehog signaling are driven by a biochemically-defined, small fraction of membrane cholesterol, termed accessible cholesterol. Increasing cholesterol accessibility by depletion of sphingomyelin, which sequesters cholesterol in complexes, amplifies Hedgehog signaling. Hedgehog ligands increase cholesterol accessibility in the membrane of the primary cilium by inactivating the transporter-like protein Patched 1. Trapping this accessible cholesterol blocks Hedgehog signal transmission across the membrane. Our work shows that the organization of cholesterol in the ciliary membrane can be modified by extracellular ligands to control the activity of cilia-localized signaling proteins.

Data availability

All data generated or analyzed are included in Supplementary Files 1-5 in this manuscript.

Article and author information

Author details

  1. Maia Kinnebrew

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7344-8231

  2. Ellen Jean Iverson

    Department of Biochemistry, Stanford University School of medicine, Stanford, United States
    Competing interests
    No competing interests declared.

  3. Bhaven B Patel

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    Competing interests
    No competing interests declared.

  4. Ganesh V Pusapati

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    Competing interests
    No competing interests declared.

  5. Jennifer H Kong

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    Competing interests
    No competing interests declared.

  6. Kristen A Johnson

    Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    No competing interests declared.

  7. Giovanni Luchetti

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    Competing interests
    No competing interests declared.

  8. Kaitlyn M Eckert

    Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    No competing interests declared.

  9. Jeffrey G McDonald

    Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    No competing interests declared.

  10. Douglas F Covey

    Department of Developmental Biology, Washington University School of Medicine, St Louis, United States
    Competing interests
    No competing interests declared.

  11. Christian Siebold

    Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-6635-3621

  12. Arun Radhakrishnan

    Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
    For correspondence
    arun.radhakrishnan@utsouthwestern.edu
    Competing interests
    Arun Radhakrishnan, Reviewing editor, eLife.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7266-7336

  13. Rajat Rohatgi

    Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
    For correspondence
    rrohatgi@stanford.edu
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7609-8858

Funding

National Institutes of Health (GM118082)

  • Rajat Rohatgi

American Heart Association (14POST20370057)

  • Ganesh V Pusapati

American Heart Association (19POST34380734)

  • Jennifer H Kong

National Institutes of Health (GM13251801)

  • Jennifer H Kong

Ford Foundation (Pre-doctoral Fellowship)

  • Giovanni Luchetti

National Institutes of Health (GM106078)

  • Rajat Rohatgi

National Institutes of Health (HL20948)

  • Kristen A Johnson
  • Jeffrey G McDonald
  • Arun Radhakrishnan

Welch Foundation (I-1793)

  • Kristen A Johnson
  • Arun Radhakrishnan

Cancer Research UK (C20724/A14414)

  • Christian Siebold

Cancer Research UK (C20724/A26752)

  • Christian Siebold

European Research Council (647278)

  • Christian Siebold

National Science Foundation (Pre-doctoral Fellowship)

  • Maia Kinnebrew

National Science Foundation (Pre-doctoral Fellowship)

  • Ellen Jean Iverson

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Duojia Pan, UT Southwestern Medical Center and HHMI, United States

Version history

  1. Received: July 12, 2019
  2. Accepted: October 25, 2019
  3. Accepted Manuscript published: October 28, 2019 (version 1)
  4. Accepted Manuscript updated: October 30, 2019 (version 2)
  5. Version of Record published: November 12, 2019 (version 3)
  6. Version of Record updated: November 15, 2019 (version 4)

Copyright

© 2019, Kinnebrew et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Maia Kinnebrew
  2. Ellen Jean Iverson
  3. Bhaven B Patel
  4. Ganesh V Pusapati
  5. Jennifer H Kong
  6. Kristen A Johnson
  7. Giovanni Luchetti
  8. Kaitlyn M Eckert
  9. Jeffrey G McDonald
  10. Douglas F Covey
  11. Christian Siebold
  12. Arun Radhakrishnan
  13. Rajat Rohatgi
(2019)
Cholesterol accessibility at the ciliary membrane controls Hedgehog signaling
eLife 8:e50051.
https://doi.org/10.7554/eLife.50051

Categories and tags

Further reading

    1. Cell Biology
    2. Developmental Biology

    Patched 1 reduces the accessibility of cholesterol in the outer leaflet of membranes

    Maia Kinnebrew, Giovanni Luchetti ... Rajat Rohatgi
    Research Advance Updated

    A long-standing mystery in vertebrate Hedgehog signaling is how Patched 1 (PTCH1), the receptor for Hedgehog ligands, inhibits the activity of Smoothened, the protein that transmits the signal across the membrane. We previously proposed (Kinnebrew et al., 2019) that PTCH1 inhibits Smoothened by depleting accessible cholesterol from the ciliary membrane. Using a new imaging-based assay to directly measure the transport activity of PTCH1, we find that PTCH1 depletes accessible cholesterol from the outer leaflet of the plasma membrane. This transport activity is terminated by binding of Hedgehog ligands to PTCH1 or by dissipation of the transmembrane potassium gradient. These results point to the unexpected model that PTCH1 moves cholesterol from the outer to the inner leaflet of the membrane in exchange for potassium ion export in the opposite direction. Our study provides a plausible solution for how PTCH1 inhibits SMO by changing the organization of cholesterol in membranes and establishes a general framework for studying how proteins change cholesterol accessibility to regulate membrane-dependent processes in cells.

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    Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

    Giovanni Luchetti, Ria Sircar ... Rajat Rohatgi
    Research Article Updated

    Cholesterol is necessary for the function of many G-protein coupled receptors (GPCRs). We find that cholesterol is not just necessary but also sufficient to activate signaling by the Hedgehog (Hh) pathway, a prominent cell-cell communication system in development. Cholesterol influences Hh signaling by directly activating Smoothened (SMO), an orphan GPCR that transmits the Hh signal across the membrane in all animals. Unlike many GPCRs, which are regulated by cholesterol through their heptahelical transmembrane domains, SMO is activated by cholesterol through its extracellular cysteine-rich domain (CRD). Residues shown to mediate cholesterol binding to the CRD in a recent structural analysis also dictate SMO activation, both in response to cholesterol and to native Hh ligands. Our results show that cholesterol can initiate signaling from the cell surface by engaging the extracellular domain of a GPCR and suggest that SMO activity may be regulated by local changes in cholesterol abundance or accessibility.

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    Glucagon-like peptide-1 receptor activation stimulates PKA-mediated phosphorylation of Raptor and this contributes to the weight loss effect of liraglutide

    Thao DV Le, Dianxin Liu ... Julio E Ayala
    Research Article Updated

    The canonical target of the glucagon-like peptide-1 receptor (GLP-1R), Protein Kinase A (PKA), has been shown to stimulate mechanistic Target of Rapamycin Complex 1 (mTORC1) by phosphorylating the mTOR-regulating protein Raptor at Ser791 following β-adrenergic stimulation. The objective of these studies is to test whether GLP-1R agonists similarly stimulate mTORC1 via PKA phosphorylation of Raptor at Ser791 and whether this contributes to the weight loss effect of the therapeutic GLP-1R agonist liraglutide. We measured phosphorylation of the mTORC1 signaling target ribosomal protein S6 in Chinese Hamster Ovary cells expressing GLP-1R (CHO-Glp1r) treated with liraglutide in combination with PKA inhibitors. We also assessed liraglutide-mediated phosphorylation of the PKA substrate RRXS*/T* motif in CHO-Glp1r cells expressing Myc-tagged wild-type (WT) Raptor or a PKA-resistant (Ser791Ala) Raptor mutant. Finally, we measured the body weight response to liraglutide in WT mice and mice with a targeted knock-in of PKA-resistant Ser791Ala Raptor. Liraglutide increased phosphorylation of S6 and the PKA motif in WT Raptor in a PKA-dependent manner but failed to stimulate phosphorylation of the PKA motif in Ser791Ala Raptor in CHO-Glp1r cells. Lean Ser791Ala Raptor knock-in mice were resistant to liraglutide-induced weight loss but not setmelanotide-induced (melanocortin-4 receptor-dependent) weight loss. Diet-induced obese Ser791Ala Raptor knock-in mice were not resistant to liraglutide-induced weight loss; however, there was weight-dependent variation such that there was a tendency for obese Ser791Ala Raptor knock-in mice of lower relative body weight to be resistant to liraglutide-induced weight loss compared to weight-matched controls. Together, these findings suggest that PKA-mediated phosphorylation of Raptor at Ser791 contributes to liraglutide-induced weight loss.