Modulation of the TGFbeta/Smad signaling pathway in mesangial cells by CTGF/CCN2

• Published in: Experimental cell research 2005-07, Vol.307 (2), p.305-314
• Main Authors: Wahab, Nadia Abdel, Weston, Benjamin S, Mason, Roger M
• Format: Article
• Language: English
• Subjects: Cell Cycle Proteins - genetics; Cells, Cultured; Collagen Type III - genetics; Connective Tissue Growth Factor; Cyclin-Dependent Kinase Inhibitor p15; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Early Growth Response Transcription Factors; Gene Expression - drug effects; Glomerular Mesangium - cytology; Glomerular Mesangium - physiology; Humans; Immediate-Early Proteins - genetics; Immediate-Early Proteins - pharmacology; Immediate-Early Proteins - physiology; Intercellular Signaling Peptides and Proteins - genetics; Intercellular Signaling Peptides and Proteins - pharmacology; Intercellular Signaling Peptides and Proteins - physiology; Kruppel-Like Transcription Factors; Oligoribonucleotides, Antisense - pharmacology; Phosphorylation - drug effects; Plasminogen Activator Inhibitor 1 - genetics; Recombinant Proteins - pharmacology; Signal Transduction - physiology; Smad Proteins; Smad2 Protein; Smad3 Protein; Smad7 Protein; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic - drug effects; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - pharmacology; Transforming Growth Factor beta - physiology; Tumor Suppressor Proteins - genetics
• ISSN: 0014-4827

Transforming growth factor-beta (TGFbeta) drives fibrosis in diseases such as diabetic nephropathy (DN). Connective tissue growth factor (CTGF; CCN2) has also been implicated in this, but the molecular mechanism is unknown. We show that CTGF enhances the TGFbeta/Smad signaling pathway by transcriptional suppression of Smad 7 following rapid and sustained induction of the transcription factor TIEG-1. Smad 7 is a known antagonist of TGFbeta signaling and TIEG-1 is a known repressor of Smad 7 transcription. CTGF enhanced TGFbeta-induced phosphorylation and nuclear translocation of Smad 2 and Smad 3 in mesangial cells. Antisense oligonucleotides directed against TIEG-1 prevented CTGF-induced downregulation of Smad 7. CTGF enhanced TGFbeta-stimulated transcription of the SBE4-Luc reporter gene and this was markedly reduced by TIEG-1 antisense oligonucleotides. Expression of the TGFbeta-responsive genes PAI-1 and Col III over 48 h was maximally stimulated by TGFbeta+CTGF compared to TGFbeta alone, while CTGF alone had no significant effect. TGFbeta-stimulated expression of these genes was markedly reduced by both CTGF and TIEG-1 antisense oligonucleotides, consistent with the endogenous induction of CTGF by TGFbeta. We propose that under pathological conditions, where CTGF expression is elevated, CTGF blocks the negative feedback loop provided by Smad 7, allowing continued activation of the TGFbeta signaling pathway.