Critical role of serum response factor in pulmonary myofibroblast differentiation induced by TGF-beta.
Transforming growth factor-beta (TGF-beta) is a cytokine implicated in wound healing and in the pathogenesis of pulmonary fibrosis. TGF-beta stimulates myofibroblast differentiation characterized by expression of contractile smooth muscle (SM)-specific proteins such as SM-alpha-actin. In the present study, we examined the role of serum response factor (SRF) in the mechanism of TGF-beta-induced pulmonary myofibroblast differentiation of human lung fibroblasts (HLF). TGF-beta stimulated SM-alpha-actin expression in HLF, which paralleled with a profound induction of SRF expression and activity. Inhibition of SRF by the pharmacologic SRF inhibitor (CCG-1423), or via adenovirus-mediated transduction of SRF short hairpin RNA (shSRF), blocked the expression of both SRF and SM-alpha-actin in response to TGF-beta without affecting Smad-mediated signaling of TGF-beta. However, forced expression of SRF on its own did not promote SM-alpha-actin expression, whereas expression of the constitutively transactivated SRF fusion protein (SRF-VP16) was sufficient to induce SM-alpha-actin expression, suggesting that both expression and transactivation of SRF are important. Activation of protein kinase A (PKA) by forskolin or iloprost resulted in a significant inhibition of SM-alpha-actin expression induced by TGF-beta, and this was associated with inhibition of both SRF expression and activity, but not of Smad-mediated gene transcription. In summary, this is the first direct demonstration that TGF-beta-induced pulmonary myofibroblast differentiation is mediated by SRF, and that inhibition of myofibroblast differentiation by PKA occurs through down-regulation of SRF expression levels and SRF activity, independent of Smad signaling.
Sandbo
Nathan
N
Section of Pulmonary and Critical Care Medicine, University of Chicago, 5841 S. Maryland Ave., MC 6076, Chicago, IL 60618, USA. nsandbo@medicine.bsd.uchicago.edu
Kregel
Steven
S
Taurin
Sebastien
S
Bhorade
Sangeeta
S
Dulin
Nickolai O
NO
D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006801:Humans; D008168:Lung / Q000166:cytology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D026362:Serum Response Factor / Q000378:metabolism*; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology*
D000199:Actins; D034741:RNA, Small Interfering; D026362:Serum Response Factor; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases