Induction of human LTBP-3 promoter activity by TGF-beta1 is mediated by Smad3/4 and AP-1 binding elements.
Latent TGF-beta binding proteins (LTBPs) are extracellular matrix glycoproteins, which are essential for the targeting and activation of TGF-betas. LTBP-3 regulates the bioavailability of TGF-beta especially in the bone. To understand the regulation of LTBP-3 expression, we have isolated and characterized the promoter region of human LTBP-3 gene. The GC-rich TATA-less promoter contained several transcription initiation sites and putative binding sites for multiple sequence specific transcription factors including Sp1, AP-1, c-Ets, MZF-1, Runx1 and members of the GATA-family. Reporter gene analyses of the promoter indicated that it was more active in MG-63 than in Saos-2 osteosarcoma cells, suggesting that it is regulated as the endogenous gene. TGF-beta1 stimulated the transcriptional activity of LTBP-3 promoter in MG-63 cells, while certain other bone-derived growth factors and hormones were ineffective. TGF-beta1 increased LTBP-3 mRNA levels accordingly. Analyses of deletion constructs of the promoter and mutational deletion of specific transcription factor binding sites indicated that Smad3/4 and AP-1 binding sites mediated the TGF-beta1 response. The involvement of AP-1 activity was further indicated by decreased TGF-beta responsiveness of the LTBP-3 promoter in the presence of a MEK/Erk signaling pathway inhibitor. Our results suggest an important new role for TGF-beta1 in the regulation of its binding protein, LTBP-3.
Kantola
Anna K
AK
Department of Virology, Haartman Institute and Helsinki University Hospital, University of Helsinki, Biomedicum Rm A506, P.O.Box 63, Haartmaninkatu 8, 00014 Helsinki, Finland.
Keski-Oja
Jorma
J
Koli
Katri
K
D001483:Base Sequence; D045744:Cell Line, Tumor; D004247:DNA; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D053779:Latent TGF-beta Binding Proteins; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012689:Sequence Homology, Nucleic Acid; D051900:Smad3 Protein / Q000378:metabolism / Q000502:physiology*; D051901:Smad4 Protein / Q000378:metabolism / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000378:metabolism / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C509038:LTBP3 protein, human; D053779:Latent TGF-beta Binding Proteins; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; C508960:TGFB1 protein, human; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004247:DNA; D020930:MAP Kinase Kinase Kinases