title: Transforming growth factor beta signaling through Smad1 in human breast cancer cells.
abstract: Previous results have suggested that Smad1 transduces signals in response to bone morphogenetic proteins (BMPs), but not in response to transforming growth factor beta (TGF-beta). Here we investigated the ability of TGF-beta to regulate Smad1 phosphorylation, hetero-oligomerization with Smad4, translocation to the nucleus, and transcriptional activation of 3TP-luciferase reporter activity in TGF-beta- and BMP-responsive Hs578T human breast cancer cells. We demonstrate that Smad1 was rapidly phosphorylated in vivo in response to both TGF-beta3 and BMP2 as determined using an antibody against the epitope-tagged Smad1 being expressed. In addition, both TGF-beta3 and BMP2 increased Smad1-Smad4 hetero-oligomerization in Hs578T cells. Visualization of Smad1 nuclear translocation with the aid of green fluorescent protein (GFP) in live cells demonstrated nuclear accumulation of GFP-Smad1 fluorescence in response to either TGF-beta or BMP2 stimulation. After ligand stimulation, approximately 60-70% of transfected cells displayed prominent nuclear fluorescence. Expression of Smad1 in Hs578T cells increased the activity of the TGF-beta-responsive reporter 3TP-Lux. Moreover, TGF-beta treatment further potentiated the effect of Smad1 on 3TP-luciferase activity. Collectively, our results demonstrate that TGF-beta as well as BMP can signal through Smad1.
authors.affiliation: Department of Pharmacology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: J
authors.initials: J
authors.lastname: Yue
authors.forename: R S
authors.initials: RS
authors.lastname: Frey
authors.forename: Q
authors.initials: Q
authors.lastname: Zhu
authors.forename: K M
authors.initials: KM
authors.lastname: Mulder
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000502:physiology*; D005260:Female; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D051785:Smad Proteins; D051898:Smad1 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; C497399:SMAD1 protein, human; C497796:SMAD4 protein, human; D051785:Smad Proteins; D051898:Smad1 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D004247:DNA; D008156:Luciferases