title: Negative regulation of Hedgehog signaling by liver X receptors.
abstract: Hedgehog (Hh) signaling is indispensable in embryonic development, and its dysregulated activity results in severe developmental disorders as shown by genetic models of naturally occurring mutations in animal and human pathologies. Hh signaling also functions in postembryonic development and adult tissue homeostasis, and its aberrant activity causes various human cancers. Better understanding of molecular regulators of Hh signaling is of fundamental importance in finding new strategies for pathway modulation. Here, we identify liver X receptors (LXRs), members of the nuclear hormone receptor family, as previously unrecognized negative regulators of Hh signaling. Activation of LXR by specific pharmacological ligands, TO901317 and GW3965, inhibited the responses of pluripotent bone marrow stromal cells and calvaria organ cultures to sonic Hh, resulting in the inhibition of expression of Hh-target genes, Gli1 and Patched1, and Gli-dependent transcriptional activity. Moreover, LXR ligands inhibited sonic Hh-induced differentiation of bone marrow stromal cells into osteoblasts. Elimination of LXRs by small interfering RNA inhibited ligand-induced inhibition of Hh target gene expression. Furthermore, LXR ligand did not inhibit Hh responsiveness in mouse embryonic fibroblasts that do not express LXRs, whereas introduction of LXR into these cells reestablished the inhibitory effects. Daily oral administration of TO901317 to mice after 3 d significantly inhibited baseline Hh target-gene expression in liver, lung, and spleen. Given the importance of modulating Hh signaling in various physiological and pathological settings, our findings suggest that pharmacological targeting of LXRs may be a novel strategy for Hh pathway modulation.
authors.affiliation: Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
authors.forename: Woo-Kyun
authors.initials: WK
authors.lastname: Kim
authors.forename: Vicente
authors.initials: V
authors.lastname: Meliton
authors.forename: Kye Won
authors.initials: KW
authors.lastname: Park
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hong
authors.forename: Peter
authors.initials: P
authors.lastname: Tontonoz
authors.forename: Pawel
authors.initials: P
authors.lastname: Niewiadomski
authors.forename: James A
authors.initials: JA
authors.lastname: Waschek
authors.forename: Sotirios
authors.initials: S
authors.lastname: Tetradis
authors.forename: Farhad
authors.initials: F
authors.lastname: Parhami
mesh_terms: D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D001854:Bone Marrow Cells / Q000166:cytology; D002454:Cell Differentiation / Q000187:drug effects; D002923:Cilia / Q000187:drug effects / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D053823:Hedgehog Proteins / Q000378:metabolism*; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D008024:Ligands; D000071518:Liver X Receptors; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D009924:Organ Culture Techniques; D057093:Orphan Nuclear Receptors / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012886:Skull / Q000187:drug effects / Q000378:metabolism; D017154:Stromal Cells / Q000187:drug effects / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D000071676:Zinc Finger Protein GLI1; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
chemical_list: D001565:Benzoates; D001596:Benzylamines; D053823:Hedgehog Proteins; D006845:Hydrocarbons, Fluorinated; D008024:Ligands; D000071518:Liver X Receptors; D009025:Morpholines; D015513:Oncogene Proteins; D057093:Orphan Nuclear Receptors; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011687:Purines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D013449:Sulfonamides; D015534:Trans-Activators; D000071676:Zinc Finger Protein GLI1; C473027:GW 3965; C000606236:PTCH1 protein, human; C000606240:Ptch1 protein, mouse; C465570:Shh protein, mouse; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C470893:purmorphamine