title: Balancing BMP signaling through integrated inputs into the Smad1 linker.
abstract: FGF and other Ras/MAPK pathway activators counterbalance BMP action during neurogenesis, bone formation, and other aspects of vertebrate development and homeostasis. BMP receptors signal through C-terminal phosphorylation and nuclear translocation of the transcription factor Smad1, whereas MAPKs catalyze inhibitory phosphorylation in the Smad1 linker region. Here we show that linker phosphorylation restricts Smad1 activity by enabling Smad1 recognition by the HECT-domain ubiquitin ligase Smurf1. Besides causing Smad1 polyubiquitination, Smurf1 binding inhibits the interaction of Smad1 with the nuclear translocation factor Nup214. Consequently, MAPK-dependent Smurf1 binding leads Smad1 alternatively to degradation or cytoplasmic retention. Smad1 linker phosphorylation and Smurf1 act as interdependent inputs to control BMP signaling during mouse osteoblast differentiation and Xenopus neural development. Linker phosphorylation is triggered also by BMP, providing feedback control. The interplay between linker phosphorylation, Smurf-dependent ubiquitination, and nucleoporin exclusion enables regulation of BMP action by diverse signals and biological contexts.
authors.affiliation: Cancer Biology and Genetics Program, Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
authors.forename: Gopal
authors.initials: G
authors.lastname: Sapkota
authors.forename: Claudio
authors.initials: C
authors.lastname: Alarcón
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Spagnoli
authors.forename: Ali H
authors.initials: AH
authors.lastname: Brivanlou
authors.forename: Joan
authors.initials: J
authors.lastname: Massagué
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D005346:Fibroblast Growth Factors / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008934:Mitogens / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D051898:Smad1 Protein / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D014981:Xenopus
chemical_list: D019485:Bone Morphogenetic Proteins; D008934:Mitogens; D028861:Nuclear Pore Complex Proteins; D051898:Smad1 Protein; D025801:Ubiquitin; D005346:Fibroblast Growth Factors; C120925:SMURF1 protein, Xenopus; C492381:Smurf1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D000071679:Glycogen Synthase Kinase 3 beta; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3