title: Probing the role of homomeric and heteromeric receptor interactions in TGF-beta signaling using small molecule dimerizers.
abstract: BACKGROUND
  Transforming growth factor Beta (TGF-Beta) arrests many cell types in the G1 phase of the cell and upregulates plasminogen activator inhibitor 1 (PAI-1). The type 1 (TGF-Beta RI) an II (TGF-Beta RII) TGF-Beta receptors mediate these and other effects of TGF-Beta on target cells. TGF-Beta initially binds to TGF-Beta RII and subsequently TGF-Beta RI is recruited to form a heteromeric complex. TGF-Beta RI phosphorylates the downstream effectors Smad2 and Smad3, leading to their translocation into the nucleus. Here, we explored the role of receptor oligomerization in TGF-Beta signaling.
  
  
  RESULTS
  We constructed fusion proteins containing receptor cytoplasmic tails linked to binding domains for small-molecule dimerizers. In COS-1 cells, recruitment of a soluble TGF-Beta RII tail to a myristoylated TGF-Beta RI tail promoted Smad2 nuclear translocation. In mink lung cells, homo-oligomerization of a myristoylated TGF-Beta Ri tail in presence of a myristoylated TGF-Beta RII tail activated the PAI-1 promoter. Oligomerization of an acidic mutant of the TGF-Beta RI tail in absence of TGF-Beta RII activated the PAI-A promoter and inhibited the growth of mink lung cells.
  
  
  CONCLUSIONS
  Non-toxic, small molecules designed to oligomerize cytoplasmic tails of TGF-Beta receptors at the plasma membrane can activate TGF-Beta signaling. Although TGF-Beta normally signals through two receptors that are both necessary for signaling, in one small-molecule system, a dimerizer activates signaling through a single type of receptor that is sufficient to induce TGF-Beta signaling. These methods of activating TGF-Beta signaling could be extended to signaling pathways of other TGF-Beta superfamily members such as activin and the bone morphogenetic proteins.
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: B R
authors.initials: BR
authors.lastname: Stockwell
authors.forename: S L
authors.initials: SL
authors.lastname: Schreiber
mesh_terms: D030201:Activin Receptors, Type I; D000818:Animals; D019556:COS Cells; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D015335:Molecular Probes / Q000378:metabolism*; D009226:Myristates / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D008164:Luminescent Proteins; D015335:Molecular Probes; D009226:Myristates; D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II