title: Toxic effects of TCDD on osteogenesis through altering IGFBP-6 gene expression in osteoblasts.
abstract: Since 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has reproductive and developmental toxicity as an estrogen antagonist, we investigated the effects of TCDD on osteogenesis in rat skeleton and the human female-responsive osteoblastic osteosarcoma cell line SaOS-2. Rat fetuses were exposed to 5, 10, or 15 microg/kg TCDD on gestation day (GD) 10. TCDD dose-dependently induced single or multiple rat fetal skeletal development malformations in vivo. In vitro, 10 nM TCDD significantly inhibited cell proliferation in the presence of 1 microM 17-beta-estradiol (E2) in SaOS-2 cells. Insulin-like growth factor binding protein 6 (IGFBP-6), as a crucial regulator in IGF system, plays an important role in osteogenesis and bone function. TCDD (15 microg/kg) induced a dramatic 3-fold increase in IGFBP-6 mRNA expression in rat fetal calvaria on GD 21. On the other hand, the concurrent treatment of 10 nM TCDD and 1 muM E2 resulted in a significant increase in IGFBP-6 mRNA and protein after 24 h in SaOS-2 cells, but TCDD and (or) E2 had no effect on the mRNA level of cytosolic aromatic hydrocarbon receptor. The functional estrogen-responsive element (ERE) [5'-CCT TCA CCT G-3'] (-9 to +1) in the IGFBP-6 promoter region was identified in this study for the first time as the ER genomic binding site. Collectively, these results suggest that TCDD can alter the expression of IGFBP-6 gene and exerts growth-inhibitory effects on osteogenesis. In addition, TCDD exhibits an anti-estrogenic effect through its interference with the binding of activated estrogen-liganded ER to the functional ERE in IGFBP-6 gene promoter.
authors.affiliation: Department of Orthopedic Surgery, First Affiliated Hospital, China Medical University, Shenyang, Liaoning, P.R. China. g572@sina.com
authors.forename: Lei
authors.initials: L
authors.lastname: Guo
authors.forename: Yu-Yan
authors.initials: YY
authors.lastname: Zhao
authors.forename: Yan-Yan
authors.initials: YY
authors.lastname: Zhao
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Sun
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
authors.forename: Shi-Liang
authors.initials: SL
authors.lastname: Zhang
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004622:Embryo, Mammalian / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005333:Fetus / Q000187:drug effects; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D006801:Humans; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000235:genetics*; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D012516:Osteosarcoma / Q000473:pathology; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D012886:Skull / Q000187:drug effects / Q000196:embryology
chemical_list: D018976:Insulin-Like Growth Factor Binding Protein 6; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D004958:Estradiol