title: BMP-7/TGF-β1 signalling in myoblasts: components involved in signalling and BMP-7-dependent blockage of TGF-β-mediated CTGF expression.
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.
authors.affiliation: The Institute of Clinical Chemistry and Pathobiochemistry, RWTH University Hospital, Pauwelsstr. 30, D-52074 Aachen, Germany. smeurer@ukaachen.de
authors.forename: Steffen K
authors.initials: SK
authors.lastname: Meurer
authors.forename: Marcel
authors.initials: M
authors.lastname: Esser
authors.forename: Lidia
authors.initials: L
authors.lastname: Tihaa
authors.forename: Ralf
authors.initials: R
authors.lastname: Weiskirchen
mesh_terms: D055419:Bone Morphogenetic Protein 7 / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D032446:Myoblasts / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D051898:Smad1 Protein / Q000378:metabolism; D051902:Smad5 Protein / Q000378:metabolism; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D055419:Bone Morphogenetic Protein 7; C526317:CCN2 protein, human; C497399:SMAD1 protein, human; C497797:SMAD5 protein, human; D051898:Smad1 Protein; D051902:Smad5 Protein; D053773:Transforming Growth Factor beta1; D055513:Connective Tissue Growth Factor