Intracellular signaling of osteogenic protein-1 through Smad5 activation.
Smad proteins play pivotal roles in the intracellular signaling of the multifunctional transforming growth factor-beta (TGF-beta) family members downstream of serine/threonine kinase type I and type II receptors. Smad2 and Smad3 are specific mediators of TGF-beta and activin, while Smadl and Smad5 are involved in bone morphogenetic protein-2 (BMP-2) and BMP-4 signaling. Here we report that osteogenic protein-1 (OP-1), also termed BMP-7, binds predominantly to BMPR-IB in the rat osteoprogenitor-like cell line, ROB-C26. Smad1, Smad5, and Smad8, but not Smad2 and Smad3, were found to stably interact with the kinase-deficient BMPR-IB after it was phosphorylated by the BMPR-II kinase. In ROB-C26 cells, which express Smad2, Smad3, Smad4, and Smad5, OP-1 was found to stimulate the phosphorylation of Smad5. Whereas transfection of wild-type Smad5 enhanced the OP-1-induced response, transfection of wild-type Smad2 had no effect on OP-1 signaling. A Smad5-2SA mutant, in which the two most carboxy-terminal serine residues were mutated to alanine residues, was found to act as a dominant negative inhibitor of OP-1-induced responses upon its transfection into various cell types, including ROB-C26 cells, in contrast to ectopic expression of a Smad2-2SA mutant which was without effect. Smad5, therefore, is a key component in the intracellular signaling of OP-1.
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
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Tamaki
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Souchelnytskyi
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Itoh
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Nakao
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Sampath
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Heldin
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ten Dijke
D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D055419:Bone Morphogenetic Protein 7; D052005:Bone Morphogenetic Protein Receptors, Type I; D019485:Bone Morphogenetic Proteins / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D005260:Female; D006801:Humans; D007106:Immune Sera / Q000737:chemistry; D007424:Intracellular Fluid / Q000502:physiology*; D008969:Molecular Sequence Data; D010006:Osteoblasts; D010750:Phosphoproteins / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017978:Receptors, Growth Factor / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins; D051898:Smad1 Protein; D051902:Smad5 Protein; D051904:Smad8 Protein; D015534:Trans-Activators / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000502:physiology
C525819:BMP7 protein, human; C525821:Bmp7 protein, rat; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D007106:Immune Sera; D010750:Phosphoproteins; D017978:Receptors, Growth Factor; C497399:SMAD1 protein, human; C497797:SMAD5 protein, human; C107514:SMAD9 protein, human; D051785:Smad Proteins; D051898:Smad1 Protein; C497400:Smad1 protein, rat; D051902:Smad5 Protein; C497799:Smad5 protein, rat; D051904:Smad8 Protein; C109462:Smad9 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; C498214:BMPR1B protein, human; D052005:Bone Morphogenetic Protein Receptors, Type I