Modulation of selenoprotein P expression by TGF-beta(1) is mediated by Smad proteins.
Selenoprotein P (SeP) is a selenium-rich plasma protein which accounts for more than 50% this study, the effect of TGF-beta(1) on the expression of SeP in the human liver cell line HepG2 was investigated. Western analysis revealed a dose-dependent reduction of SeP content in cell supernatant. RT-PCR analysis of SeP-mRNA expression demonstrated a marked inhibition and a reporter gene under control of the SeP promoter was negatively regulated by TGF-beta(1). Smad proteins are the transcriptional mediators of TGF-beta signaling. A putative Smad-binding element (SBE) is present in the SeP promoter. In electrophoretic-mobility-shift assays, TGF-beta(1) enhanced the binding of nuclear proteins to this SBE. Overexpression of Smad3 and 4 resulted in a downregulation of SeP-promoter activity whereas deletion of the SBE led to a loss of TGF-beta(1) responsiveness. We conclude that SeP expression is modulated by the binding of Smad3/4 complexes to a functional SBE in the SeP promoter.
Mostert
V
V
Abteilung Experimentelle Toxikologie, Medizinisches Institut für Umwelthygiene, Heinrich-Heine-Universität, Auf'm Hennekamp 50, 40225 Düsseldorf, Germany.
Dreher
I
I
Köhrle
J
J
Wolff
S
S
Abel
J
J
D001483:Base Sequence; D006528:Carcinoma, Hepatocellular; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008113:Liver Neoplasms; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012643:Selenium / Q000378:metabolism; D051149:Selenoprotein P; D051140:Selenoproteins; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D011506:Proteins; D011993:Recombinant Fusion Proteins; D051149:Selenoprotein P; D051140:Selenoproteins; D016212:Transforming Growth Factor beta; D008156:Luciferases; D012643:Selenium