title: Inhibition of Hedgehog signaling by direct binding of cyclopamine to Smoothened.
abstract: The steroidal alkaloid cyclopamine has both teratogenic and antitumor activities arising from its ability to specifically block cellular responses to vertebrate Hedgehog signaling. We show here, using photoaffinity and fluorescent derivatives, that this inhibitory effect is mediated by direct binding of cyclopamine to the heptahelical bundle of Smoothened (Smo). Cyclopamine also can reverse the retention of partially misfolded Smo in the endoplasmic reticulum, presumably through binding-mediated effects on protein conformation. These observations reveal the mechanism of cyclopamine's teratogenic and antitumor activities and further suggest a role for small molecules in the physiological regulation of Smo.
authors.affiliation: Department of Molecular Biology and Genetics, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: James K
authors.initials: JK
authors.lastname: Chen
authors.forename: Jussi
authors.initials: J
authors.lastname: Taipale
authors.forename: Michael K
authors.initials: MK
authors.lastname: Cooper
authors.forename: Philip A
authors.initials: PA
authors.lastname: Beachy
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000633:toxicity; D001665:Binding Sites; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D053823:Hedgehog Proteins; D051379:Mice; D011485:Protein Binding; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction / Q000187:drug effects*; D000072086:Smoothened Receptor; D013723:Teratogens / Q000494:pharmacology / Q000633:toxicity; D015534:Trans-Activators / Q000502:physiology*; D014704:Veratrum Alkaloids / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D000970:Antineoplastic Agents; D053823:Hedgehog Proteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C491022:Smo protein, mouse; D000072086:Smoothened Receptor; D013723:Teratogens; D015534:Trans-Activators; D014704:Veratrum Alkaloids; C000541:cyclopamine