TGF-beta-signaling with small molecule FKBP12 antagonists that bind myristoylated FKBP12-TGF-beta type I receptor fusion proteins

Chem Biol. 1998 Jul;5(7):385-95. doi: 10.1016/s1074-5521(98)90072-2.


Background: Growth arrest in many cell types is triggered by transforming growth factor beta (TGF-beta), which signals through two TGF-beta receptors (type I, TGF-beta RI, and type II, TGF-beta). In the signaling pathway, TGF-beta binds to the extracellular domain of TGF-betaRII, which can then transphosphorylate TGF-betaRI in its glycine/serine (GS)-rich box. Activated TGF-betaRI phosphorylates two downstream effectors, Smad2 and Smad3, leading to their translocation into the nucleus. Cell growth is arrested and plasminogen activator inhibitor 1 (PAI-1) is upregulated. We investigated the role of the immunophilin FKBP12, which can bind to the GS box of TGF-betaRI, in TGF-beta signaling.

Results: Overexpression of myristoylated TGF-betaRI and TGF-betaRII cytoplasmic tails caused constitutive nuclear translocation of a green-fluorescent-protein-Smad2 construct in COS-1 cells, and constitutive activation of a PAI-1 reporter plasmid in mink lung cells. Fusing FKBP12 to TGF-betaRI resulted in repression of autosignaling that could be alleviated by FK506M or rapamycin (two small molecules that can bind to FKBP12). Mutation of the FKBP12-binding site in the FKBP1-TGF-betaRI fusion protein restored constitutive signaling. An acidic mutation in the FKBP12-TGF-betaRI protein allowed FKBP12 antagonists to activate signaling in the absence of TGF-betaRII. Further mutations in the TGF-betaRI FKBP12-binding site resulted in TGF-beta signaling that was independent of both TGF-betaRII and FKBP12 antagonists.

Conclusions: Fusing FKBP12 to TGF-betaRI results in a novel receptor that is activated by small molecule FKBP12 antagonists. These results suggest that FKBP12 binding to TGF-betaRI is inhibitory and that FKBP12 plays a role in inhibiting TGF-beta superfamily signals.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Activin Receptors, Type I*
  • Animals
  • COS Cells / drug effects
  • Carrier Proteins / antagonists & inhibitors*
  • Carrier Proteins / genetics
  • DNA-Binding Proteins / antagonists & inhibitors*
  • DNA-Binding Proteins / genetics
  • Fluorescent Antibody Technique
  • Heat-Shock Proteins / antagonists & inhibitors*
  • Heat-Shock Proteins / genetics
  • Immunosuppressive Agents / pharmacology
  • Lung / drug effects
  • Lung / metabolism
  • Mink
  • Polyenes / pharmacology
  • Protein Serine-Threonine Kinases / drug effects
  • Protein Serine-Threonine Kinases / metabolism*
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptors, Transforming Growth Factor beta / drug effects
  • Receptors, Transforming Growth Factor beta / metabolism*
  • Recombinant Fusion Proteins / drug effects
  • Recombinant Fusion Proteins / metabolism*
  • Repressor Proteins
  • Signal Transduction*
  • Sirolimus
  • Tacrolimus / pharmacology
  • Tacrolimus Binding Proteins
  • Transforming Growth Factor beta / drug effects
  • Transforming Growth Factor beta / physiology*


  • Carrier Proteins
  • DNA-Binding Proteins
  • Heat-Shock Proteins
  • Immunosuppressive Agents
  • Polyenes
  • Receptors, Transforming Growth Factor beta
  • Recombinant Fusion Proteins
  • Repressor Proteins
  • Transforming Growth Factor beta
  • Protein Serine-Threonine Kinases
  • Activin Receptors, Type I
  • Receptor, Transforming Growth Factor-beta Type I
  • Tacrolimus Binding Proteins
  • Sirolimus
  • Tacrolimus