Intracellular signaling of osteogenic protein-1 through Smad5 activation

J Cell Physiol. 1998 Nov;177(2):355-63. doi: 10.1002/(SICI)1097-4652(199811)177:2<355::AID-JCP17>3.0.CO;2-8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antibody Specificity
  • Bone Morphogenetic Protein 7
  • Bone Morphogenetic Protein Receptors, Type I
  • Bone Morphogenetic Proteins / metabolism
  • Bone Morphogenetic Proteins / physiology*
  • Cell Line
  • DNA-Binding Proteins / biosynthesis
  • DNA-Binding Proteins / immunology
  • DNA-Binding Proteins / metabolism*
  • Female
  • Humans
  • Immune Sera / chemistry
  • Intracellular Fluid / physiology*
  • Molecular Sequence Data
  • Osteoblasts
  • Phosphoproteins / biosynthesis
  • Phosphoproteins / immunology
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism
  • Rats
  • Receptors, Growth Factor / metabolism
  • Signal Transduction / physiology*
  • Smad Proteins
  • Smad1 Protein
  • Smad5 Protein
  • Smad8 Protein
  • Trans-Activators / biosynthesis
  • Trans-Activators / immunology
  • Trans-Activators / metabolism*
  • Transcription, Genetic / drug effects
  • Transforming Growth Factor beta / physiology


  • BMP7 protein, human
  • Bmp7 protein, rat
  • Bone Morphogenetic Protein 7
  • Bone Morphogenetic Proteins
  • DNA-Binding Proteins
  • Immune Sera
  • Phosphoproteins
  • Receptors, Growth Factor
  • SMAD1 protein, human
  • SMAD5 protein, human
  • SMAD8 protein, human
  • Smad Proteins
  • Smad1 Protein
  • Smad1 protein, rat
  • Smad5 Protein
  • Smad5 protein, rat
  • Smad8 Protein
  • Smad9 protein, rat
  • Trans-Activators
  • Transforming Growth Factor beta
  • Protein-Serine-Threonine Kinases
  • BMPR1B protein, human
  • Bone Morphogenetic Protein Receptors, Type I