Role of Rho/ROCK and p38 MAP kinase pathways in transforming growth factor-beta-mediated Smad-dependent growth inhibition of human breast carcinoma cells in vivo

J Biol Chem. 2005 Jan 14;280(2):1024-36. doi: 10.1074/jbc.M403960200. Epub 2004 Nov 1.


TGF-beta is a multifunctional cytokine known to exert its biological effects through a variety of signaling pathways of which Smad signaling is considered to be the main mediator. At present, the Smad-independent pathways, their interactions with each other, and their roles in TGF-beta-mediated growth inhibitory effects are not well understood. To address these questions, we have utilized a human breast cancer cell line MCF10CA1h and demonstrate that p38 MAP kinase and Rho/ROCK pathways together with Smad2 and Smad3 are necessary for TGF-beta-mediated growth inhibition of this cell line. We show that Smad2/3 are indispensable for TGF-beta-mediated growth inhibition, and that both p38 and Rho/ROCK pathways affect the linker region phosphorylation of Smad2/3. Further, by using Smad3 mutated at the putative phosphorylation sites in the linker region, we demonstrate that phosphorylation at Ser203 and Ser207 residues is required for the full transactivation potential of Smad3, and that these residues are targets of the p38 and Rho/ROCK pathways. We demonstrate that activation of the p38 MAP kinase pathway is necessary for the full transcriptional activation potential of Smad2/Smad3 by TGF-beta, whereas activity of Rho/ROCK is necessary for both down-regulation of c-Myc protein and up-regulation of p21waf1 protein, directly interfering with p21waf1 transcription. Our results not only implicate Rho/ROCK and p38 MAPK pathways as necessary for TGF-beta-mediated growth inhibition, but also demonstrate their individual contributions and the basis for their cooperation with each other.

MeSH terms

  • Breast Neoplasms / enzymology
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • DNA-Binding Proteins / metabolism*
  • Down-Regulation / drug effects
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • MAP Kinase Signaling System / drug effects*
  • Oncogene Protein p55(v-myc) / metabolism
  • Phosphorylation / drug effects
  • Protein Serine-Threonine Kinases / metabolism*
  • Retinoblastoma Protein / metabolism
  • Smad2 Protein
  • Smad3 Protein
  • Trans-Activators / metabolism*
  • Transforming Growth Factor beta / pharmacology*
  • p38 Mitogen-Activated Protein Kinases / metabolism*
  • rho-Associated Kinases


  • DNA-Binding Proteins
  • Intracellular Signaling Peptides and Proteins
  • Oncogene Protein p55(v-myc)
  • Retinoblastoma Protein
  • SMAD2 protein, human
  • SMAD3 protein, human
  • Smad2 Protein
  • Smad3 Protein
  • Trans-Activators
  • Transforming Growth Factor beta
  • Protein Serine-Threonine Kinases
  • rho-Associated Kinases
  • p38 Mitogen-Activated Protein Kinases