Receptor expression modulates the specificity of transforming growth factor-β signaling pathways

• Published in: Genes to cells : devoted to molecular & cellular mechanisms Vol. 14; no. 4; pp. 469 - 482
• Main Authors: Murakami, Masaru, Kawachi, Hiroyuki, Ogawa, Kenji, Nishino, Yoshii, Funaba, Masayuki
• Format: Journal Article
• Language: English
• Published: Malden, USA Malden, USA : Blackwell Publishing Inc 01.04.2009; Blackwell Publishing Inc
• Subjects: Activin Receptors, Type I - genetics; Activin Receptors, Type I - metabolism; Animals; Blotting, Western; Bone Morphogenetic Protein 2 - pharmacology; Cell Line; Cell Line, Tumor; Cercopithecus aethiops; COS Cells; Dose-Response Relationship, Drug; Gene Expression; HeLa Cells; Humans; Imidazoles - pharmacology; Immunoprecipitation; Mice; Phosphorylation - drug effects; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Pyridines - pharmacology; Receptors, Transforming Growth Factor beta - genetics; Receptors, Transforming Growth Factor beta - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Signal Transduction; Smad Proteins, Receptor-Regulated - genetics; Smad Proteins, Receptor-Regulated - metabolism; Transforming Growth Factor beta1 - pharmacology
• ISSN: 1356-9597; 1365-2443
• DOI: 10.1111/j.1365-2443.2009.01283.x

In current models of transforming growth factor-β (TGF-β) family signaling, type II receptors activate specific activin receptor-like kinase (ALK) type I receptors. These serine/threonine kinases activate ligand-dependent receptor regulated (R)-Smad by phosphorylating carboxy-terminal serines. We found that the receptor expression levels affected the phosphorylation and activation of the two R-Smad subclasses, activin/TGF-β-specific (AR-Smad) and bone morphogenetic protein (BMP)-specific (BR-Smad). Co-expressing constitutively active type I and type II receptors in COS7 cells resulted in the phosphorylation of both R-Smad subclasses in a ligand-independent manner. This was verified using in vitro kinase assays. In untransfected B16 melanoma cells, TGF-β1 and BMP-2 induced phosphorylation of both R-Smad subclasses, and TGF-β1 up-regulated the inhibitor of differentiation (Id) gene, which is usually regulated by BMP. By contrast, BMP-2 up-regulated plasminogen activator inhibitor-1 (PAI-1), which is an AR-Smad-regulated gene. Except for ALK4 and ALK6, levels of type I and type II receptor mRNAs were higher in B16 cells than in HeLa and HepG2 cells, in which TGF-β1 and BMP-2 induced phosphorylation of only the expected R-Smad. These results help to explain the diverse effects of this ligand family.