RESEARCH ARTICLE TGF-b uses a novel mode of receptor activation to phosphorylate SMAD1/5 and induce epithelial-to-mesenchymal transition Anassuya Ramachandran1, Pedro Viza´ n1†, Debipriya Das1‡, Probir Chakravarty2, Janis Vogt3, Katherine W Rogers4, Patrick Mu¨ ller4, Andrew P Hinck5, Gopal P Sapkota3, Caroline S Hill1* 1Developmental Signalling Laboratory, The Francis Crick Institute, London, United Kingdom; 2Bioinformatics and Biostatistics Facility, The Francis Crick Institute, London, United Kingdom; 3Medical Research Council Protein Phosphorylation and Ubiquitylation Unit, University of Dundee, Dundee, United Kingdom; 4Friedrich Miescher Laboratory of the Max Planck Society, Tu¨ bingen, Germany; 5Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, United States Abstract The best characterized signaling pathway downstream of transforming growth factor b (TGF-b) is through SMAD2 and SMAD3. However, TGF-b also induces phosphorylation of SMAD1 *For correspondence: and SMAD5, but the mechanism of this phosphorylation and its functional relevance is not known.
[email protected] Here, we show that TGF-b-induced SMAD1/5 phosphorylation requires members of two classes of type I receptor, TGFBR1 and ACVR1, and establish a new paradigm for receptor activation where Present address: †Center for TGFBR1 phosphorylates and activates ACVR1, which phosphorylates SMAD1/5. We demonstrate Genomic Regulation, Barcelona, ‡ the biological significance of this pathway by showing that approximately a quarter of the TGF-b- Spain; Flow Cytometry, The Francis Crick Institute, London, induced transcriptome depends on SMAD1/5 signaling, with major early transcriptional targets ID United Kingdom being the genes. Finally, we show that TGF-b-induced epithelial-to-mesenchymal transition requires signaling via both the SMAD3 and SMAD1/5 pathways, with SMAD1/5 signaling being Competing interests: The essential to induce ID1.