Regulation of biglycan gene expression by transforming growth factor-beta requires MKK6-p38 mitogen-activated protein Kinase signaling downstream of Smad signaling.
Several signaling pathways have been implicated in mediating TGF-beta1-induced extracellular matrix production and fibrosis. We have shown recently that induction of biglycan (BGN) expression by TGF-beta1 depended on a functional Smad pathway (Chen, W.-B., Lenschow, W., Tiede, K., Fischer, J. W., Kalthoff, H., and Ungefroren, H. (2002) J. Biol. Chem. 277, 36118-36128). Here, we present evidence that the ability of TGF-beta 1 to induce BGN mRNA, in addition to Smads, requires p38 MAPK signaling, because 1) pharmacological inhibitors of p38 dose-dependently inhibited the TGF-beta effect without significantly affecting the transcriptional activity of a constitutively active mutant of the TGF-beta type I receptor or Smad2 phosphorylation at concentrations up to 10 microm, 2) the up-regulation of BGN mRNA was preceded by a delayed increase in the phosphorylation of p38 and its upstream activator MKK6 in TGF-beta 1-treated PANC-1 cells, 3) inhibition of the p38 pathway by stable retroviral transduction with a dominant negative mutant of either p38 or MKK6 reduced TGF-beta 1-induced BGN mRNA expression, and 4) overexpression of wild-type p38 or MKK6, but not MKK3, augmented the TGF-beta 1 effect on BGN mRNA. We further demonstrate that the (delayed) p38 activation by TGF-beta 1 is downstream of Smads and requires a functional Smad pathway, because blocking TGF-beta-induced p38 activity with SB202190 had no effect on Smad2 phosphorylation, but blocking Smad signaling by forced expression of Smad7 abolished TGF-beta1 induction of p38 activation and, as shown earlier, BGN mRNA expression; finally, re-expression of Smad4 in Smad4-null CFPAC-1 cells restored TGF-beta-induced p38 phosphorylation and, as demonstrated previously, BGN mRNA accumulation. These results clearly show that TGF-beta induction of BGN expression in pancreatic cells requires activation of MKK6-p38 MAPK signaling downstream of Smad signaling and provide a mechanistic clue to the up-regulation of BGN seen in inflammatory response-related fibrosis and desmoplasia.
Ungefroren
Hendrik
H
Research Unit Molecular Oncology, Clinic for General Surgery and Thoracic Surgery, Christian-Albrechts-University, 24105 Kiel, Germany. hungefroren@email.uni-kiel.de
Lenschow
Wolfgang
W
Chen
Wen-Bin
WB
Faendrich
Fred
F
Kalthoff
Holger
H
D001483:Base Sequence; D058578:Biglycan; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D016326:Extracellular Matrix Proteins; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D048669:MAP Kinase Kinase 6; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D011509:Proteoglycans / Q000235:genetics*; D015398:Signal Transduction; D051785:Smad Proteins; D015534:Trans-Activators / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
C546884:BGN protein, human; D058578:Biglycan; D017931:DNA Primers; D004268:DNA-Binding Proteins; D016326:Extracellular Matrix Proteins; D011509:Proteoglycans; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048669:MAP Kinase Kinase 6; C482566:MAP2K6 protein, human