title: Mechanism of inhibition of the tumor suppressor Patched by Sonic Hedgehog.
abstract: The Hedgehog cell-cell signaling pathway is crucial for animal development, and its misregulation is implicated in numerous birth defects and cancers. In unstimulated cells, pathway activity is inhibited by the tumor suppressor membrane protein, Patched. Hedgehog signaling is triggered by the secreted Hedgehog ligand, which binds and inhibits Patched, thus setting in motion the downstream events in signal transduction. Despite its critical importance, the mechanism by which Hedgehog antagonizes Patched has remained unknown. Here, we show that vertebrate Patched1 inhibition is caused by direct, palmitate-dependent interaction with the Sonic Hedgehog ligand. We find that a short palmitoylated N-terminal fragment of Sonic Hedgehog binds Patched1 and, strikingly, is sufficient to inhibit it and to activate signaling. The rest of Sonic Hedgehog confers high-affinity Patched1 binding and internalization through a distinct binding site, but, surprisingly, it is not absolutely required for signaling. The palmitate-dependent interaction with Patched1 is specifically impaired in a Sonic Hedgehog mutant causing human holoprosencephaly, the most frequent congenital brain malformation, explaining its drastically reduced potency. The palmitate-dependent interaction is also abolished in constitutively inhibited Patched1 point mutants causing the Gorlin cancer syndrome, suggesting that they might adopt a conformation distinct from the wild type. Our data demonstrate that Sonic Hedgehog signals via the palmitate-dependent arm of a two-pronged contact with Patched1. Furthermore, our results suggest that, during Hedgehog signaling, ligand binding inhibits Patched by trapping it in an inactive conformation, a mechanism that explains the dramatically reduced activity of oncogenic Patched1 mutants.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Hanna
authors.initials: H
authors.lastname: Tukachinsky
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Kostadin
authors.initials: K
authors.lastname: Petrov
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Miyako
authors.initials: M
authors.lastname: Watanabe
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115 asalic@hms.harvard.edu.
authors.forename: Adrian
authors.initials: A
authors.lastname: Salic
mesh_terms: D016475:3T3 Cells; D000818:Animals; D004705:Endocytosis / Q000187:drug effects; D053823:Hedgehog Proteins / Q000378:metabolism*; D016142:Holoprosencephaly / Q000378:metabolism / Q000473:pathology; D006801:Humans; D054878:Lipoylation; D051379:Mice; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D009857:Oncogenes; D019308:Palmitic Acid / Q000378:metabolism; D000072079:Patched Receptors / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D053823:Hedgehog Proteins; D000072079:Patched Receptors; D010455:Peptides; C509239:SHH protein, human; D019308:Palmitic Acid
keywords: Hedgehog; Patched; lipid; palmitate; signaling