Transforming growth factor β-induced phosphorylation of Smad3 is required for growth inhibition and transcriptional induction in epithelial cells

• DOI: 10.1073/pnas.94.20.10669
• Publication Date: 2002-07-26T14:35:50Z
• Authors: Xuedong Liu; Yin Sun; Stefan N. Constan...; Edmund Karam; Robert A. Weinberg; Harvey F. Lodish
• Keywords: Smad2 Protein; R-SMAD; Decapentaplegic

Drosophila Mad proteins are intracellular signal transducers of decapentaplegic (dpp), the transforming growth factor β (TGF-β)/bone morphogenic protein (BMP) homolog. Studies in which mammalian Smad homologs were transiently overexpressed cultured cells have implicated Smad2 TGF-β signaling, but physiological relevance Smad3 signaling by receptors has not been established. Here we stably expressed at controlled levels epithelial using a novel approach that combines highly efficient retroviral gene transfer and quantitative cell sorting. We show upon treatment becomes rapidly phosphorylated SSVS motif its very C terminus. Either attachment an epitope tag to terminus or replacement these three serine residues with alanine abolishes TGF-β-induced phosphorylation; act dominant-negative fashion block antiproliferative effect mink lung cells. A C-terminal serines replaced aspartic acids is also dominant inhibitor can activate plasminogen activator 1 (PAI-1) transcription ligand-independent when nuclear localization forced transient overexpression. Phosphorylation activated receptor complex essential step transduction for both inhibition proliferation activation PAI-1 promoter.