BMP-7/TGF-β1 Signalling in Myoblasts: Components Involved in Signalling and BMP-7-dependent Blockage of TGF-β-mediated CTGF Expression

Eur J Cell Biol. Jun-Jul 2012;91(6-7):450-63. doi: 10.1016/j.ejcb.2011.09.004. Epub 2011 Nov 17.

Abstract

We and others have recently described the antagonistic role of Bone morphogenetic protein-7 (BMP-7) in TGF-β signalling and myogenic differentiation. To specify the underlying mechanism(s), we here analysed the expression and function of the individual components mediating TGF-β1 and BMP-7 responses. We found that BMP-7 at a concentration of 25 ng/ml induces signalling exclusively via ALK2 and ALK3 leading to the activation of Smad1 and Smad5 and subsequent expression of Id proteins. In contrast, low doses of TGF-β1 (0.1 ng/ml) lead to an exclusive activation of ALK5 and phosphorylation of Smad2 and Smad3 that regulate specific target genes including connective tissue growth factor (CTGF). CTGF is rapidly induced by TGF-β1 already 1h after stimulation and reduced by BMP-7 application. Smad1/Smad5 or Id1/2 overexpression reduced the TGF-β1-mediated expression of CTGF. However, although siRNA-mediated knock down of Alk2/3 or Smad1/5 counteracts the BMP-7 effect on basal CTGF expression there was no consistent reversion of the observed BMP-7 effect on TGF-β1-mediated CTGF expression. Moreover, ALK5 inhibition using the SB431542 inhibitor significantly affected CTGF expression only at later time points whereas ERK1/2 inhibition completely abrogated CTGF expression. These findings point towards a regulatory role of BMP-7 that relies on modulation of Mitogen-activated protein kinases rather than mechanisms that are exclusively driven by differential Smad activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bone Morphogenetic Protein 7 / genetics
  • Bone Morphogenetic Protein 7 / metabolism*
  • Cell Differentiation / physiology
  • Cells, Cultured
  • Connective Tissue Growth Factor / biosynthesis*
  • Connective Tissue Growth Factor / genetics
  • Connective Tissue Growth Factor / metabolism
  • Humans
  • Myoblasts / metabolism
  • Phosphorylation
  • Signal Transduction
  • Smad1 Protein / metabolism
  • Smad5 Protein / metabolism
  • Transfection
  • Transforming Growth Factor beta1 / genetics
  • Transforming Growth Factor beta1 / metabolism*

Substances

  • Bone Morphogenetic Protein 7
  • CCN2 protein, human
  • SMAD1 protein, human
  • SMAD5 protein, human
  • Smad1 Protein
  • Smad5 Protein
  • Transforming Growth Factor beta1
  • Connective Tissue Growth Factor