title: Overexpression of latent transforming growth factor-beta binding protein 1 (LTBP-1) in dioxin receptor-null mouse embryo fibroblasts.
abstract: The aryl hydrocarbon receptor (AhR) is a transcriptional regulator of genes involved in xenobiotic metabolism. Increasingly clear is also the role of the AhR in the control of cell growth and proliferation. By analyzing differential patterns of gene expression between wild-type (AhR+/+) and null (AhR-/-) mouse embryo fibroblasts (MEF), we have identified latent transforming growth factor-beta binding protein 1 (LTBP-1) as a negatively AhR-regulated gene in the absence of xenobiotics. Ltbp-1 mRNA and protein expression were markedly increased in AhR-/- MEF. Furthermore, secreted LTBP-1 was elevated in the culture medium and the extracellular matrix of AhR-null MEF. Actinomycin D inhibited Ltbp-1 mRNA overexpression, suggesting regulation at the transcriptional level. AhR activation by dioxin (TCDD) downregulated Ltbp-1, again suggesting an AhR-regulated mechanism. Treatment of AhR+/+ MEF with transforming growth factor-beta(TGF-beta) downregulated AhR and, simultaneously, increased Ltbp-1, further supporting the role of this receptor in LTBP-1 expression. AhR-/- conditioned medium had higher levels of active and total TGF-beta activity, suggesting a role for LTBP-1 in maintaining extracellular TGF-beta concentrations. TGF-beta did not appear to directly regulate Ltbp-1 given that addition of TGFbeta neutralizing antibody or TGFbeta protein to AhR-/- MEF had no effect on Ltbp-1 expression. AhR-/- MEF had lower levels of matrix metalloproteinase 2 (MMP-2) activity, which could not be attributable to MMP-2 mRNA downregulation or MMP-inhibitors Timp-1 and Timp-2 overexpression. These data identify LTBP-1 as one of the few AhR-regulated genes not involved in xenobiotic metabolism and also support the implication of the AhR in controlling TGFbeta activity and cell proliferation.
authors.affiliation: Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s/n, 06071-Badajoz, Spain.
authors.forename: Belen
authors.initials: B
authors.lastname: Santiago-Josefat
authors.forename: Sonia
authors.initials: S
authors.lastname: Mulero-Navarro
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Dallas
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Fernandez-Salguero
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D047908:Intracellular Signaling Peptides and Proteins; D053779:Latent TGF-beta Binding Proteins; D045726:Metalloproteases / Q000096:biosynthesis; D051379:Mice; D011480:Protease Inhibitors / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000378:metabolism; D019716:Tissue Inhibitor of Metalloproteinase-2 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053779:Latent TGF-beta Binding Proteins; C509033:Ltbp1 protein, mouse; D011480:Protease Inhibitors; D018336:Receptors, Aryl Hydrocarbon; D019715:Tissue Inhibitor of Metalloproteinase-1; D016212:Transforming Growth Factor beta; D019716:Tissue Inhibitor of Metalloproteinase-2; D045726:Metalloproteases