Intracellular TGF-beta Receptor Blockade Abrogates Smad-dependent Fibroblast Activation in Vitro and in Vivo

J Invest Dermatol. 2006 Aug;126(8):1733-44. doi: 10.1038/sj.jid.5700303. Epub 2006 Jun 1.


Fibrosis, the hallmark of scleroderma, is characterized by excessive synthesis of collagen and extracellular matrix proteins and accumulation of myofibroblasts. Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, cytokine production, and myofibroblast transdifferentiation, is implicated in fibrosis. Profibrotic TGF-beta responses are induced primarily via the type I activin-like receptor kinase 5 (ALK5) TGF-beta receptor coupled to Smad signal transducers. Here, we investigated the effect of blocking ALK5 function with SM305, a novel small-molecule kinase inhibitor, on fibrotic TGF-beta responses. In normal dermal fibroblasts, SM305 abrogated the ligand-induced phosphorylation, nuclear import, and DNA-binding activity of Smad2/3 and Smad4, and inhibited Smad2/3-dependent transcriptional responses. Furthermore, SM305 blocked TGF-beta-induced extracellular matrix gene expression, cytokine production, and myofibroblast transdifferentiation. In unstimulated scleroderma fibroblasts, SM305 caused a variable and modest reduction in type I collagen levels, and failed to abrogate constitutive nuclear accumulation of Smad2/3, or alter the proportion of smooth muscle actin stress fiber-positive fibroblasts. In vivo, SM305 prevented TGF-beta-induced Smad2/3 phosphorylation type I collagen (COL1)A2 promoter activation in dermal fibroblasts. Taken together, these results indicate that SM305 inhibits intracellular TGF-beta signaling through selective interference with ALK5-mediated Smad activation, resulting in marked suppression of profibrotic responses induced by TGF-beta in vivo and in vitro.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biopsy
  • Cell Division / drug effects
  • Cells, Cultured
  • Dermis / cytology
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • Humans
  • In Vitro Techniques
  • Mice
  • Mice, Transgenic
  • Protein Kinase Inhibitors / pharmacology*
  • Pyrazoles / pharmacology*
  • Quinolines / pharmacology*
  • Receptors, Transforming Growth Factor beta / antagonists & inhibitors*
  • Receptors, Transforming Growth Factor beta / metabolism
  • Scleroderma, Systemic / drug therapy*
  • Scleroderma, Systemic / metabolism*
  • Scleroderma, Systemic / pathology
  • Smad Proteins / metabolism*
  • Smad2 Protein / metabolism
  • Smad3 Protein / metabolism
  • Smad4 Protein / metabolism


  • HTS 466284
  • Protein Kinase Inhibitors
  • Pyrazoles
  • Quinolines
  • Receptors, Transforming Growth Factor beta
  • SMAD2 protein, human
  • SMAD3 protein, human
  • SMAD4 protein, human
  • Smad Proteins
  • Smad2 Protein
  • Smad3 Protein
  • Smad4 Protein