title: The insecticide synergist piperonyl butoxide inhibits hedgehog signaling: assessing chemical risks.
abstract: The spread of chemicals, including insecticides, into the environment often raises public health concerns, as exemplified by a recent epidemiologic study associating in utero piperonyl butoxide (PBO) exposure with delayed mental development. The insecticide synergist PBO is listed among the top 10 chemicals detected in indoor dust; a systematic assessment of risks from PBO exposure, as for many toxicants unfortunately, may be underdeveloped when important biological targets that can cause toxicity are unknown. Hedgehog/Smoothened signaling is critical in neurological development. This study was designed to use novel high-throughput in vitro drug screening technology to identify modulators of Hedgehog signaling in environmental chemicals to assist the assessment of their potential risks. A directed library of 1408 environmental toxicants was screened for Hedgehog/Smoothened antagonist activity using a high-content assay that evaluated the interaction between Smoothened and βarrestin2 green fluorescent protein. PBO was identified as a Hedgehog/Smoothened antagonist capable of inhibiting Hedgehog signaling. We found that PBO bound Smoothened and blocked Smoothened overexpression-induced Gli-luciferase reporter activity but had no effect on Gli-1 downstream transcriptional factor-induced Gli activity. PBO inhibited Sonic Hedgehog ligand-induced Gli signaling and mouse cerebellar granular precursor cell proliferation. Moreover, PBO disrupted zebrafish development. Our findings demonstrate the value of high-throughput target-based screening strategies that can successfully evaluate large numbers of environmental toxicants and identify key targets and unknown biological activity that is helpful in properly assessing potential risks.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Jiangbo
authors.initials: J
authors.lastname: Wang
authors.forename: Jiuyi
authors.initials: J
authors.lastname: Lu
authors.forename: Robert A
authors.initials: RA
authors.lastname: Mook
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: Shengli
authors.initials: S
authors.lastname: Zhao
authors.forename: Larry S
authors.initials: LS
authors.lastname: Barak
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Freedman
authors.forename: H Kim
authors.initials: HK
authors.lastname: Lyerly
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
mesh_terms: D000818:Animals; D047108:Embryonic Development / Q000187:drug effects; D017930:Genes, Reporter; D053823:Hedgehog Proteins / Q000378:metabolism*; D008156:Luciferases / Q000235:genetics; D010574:Pesticide Synergists / Q000633:toxicity*; D010882:Piperonyl Butoxide / Q000633:toxicity*; D018570:Risk Assessment; D015398:Signal Transduction / Q000187:drug effects*; D014704:Veratrum Alkaloids / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology
chemical_list: D053823:Hedgehog Proteins; D010574:Pesticide Synergists; D014704:Veratrum Alkaloids; D008156:Luciferases; D010882:Piperonyl Butoxide; C000541:cyclopamine