Transforming Growth Factor-β Induction of Smooth Muscle Cell Phenotpye Requires Transcriptional and Post-transcriptional Control of Serum Response Factor

Abstract

Transforming growth factor-␤ induces a smooth muscle cell phenotype in undifferentiated mesenchymal cells. To elucidate the mechanism(s) of this phenotypic induction, we focused on the molecular regulation of smooth muscle-␥-actin, whose expression is induced at late stages of smooth muscle differentiation and developmentally restricted to this lineage. Transforming growth factor-␤ induced smooth muscle-␥-actin protein, cytoskeletal localization, and mRNA expression in mesenchymal cells. Smooth muscle-␥-actin promoter-luciferase reporter activity was enhanced by transforming growth factor-␤, and deletion analysis revealed that CArG box 2 in the promoter was necessary for this transcriptional activation. CArG motifs bind transcriptional activator serum response factor; gel shift analyses revealed increased binding of serum response factor-containing complexes to this site in response to transforming growth factor-␤, paralleled by increased serum response factor protein expression. Serum response factor expression was found to be up-regulated by transforming growth factor-␤ via transcriptional activation of the gene and post-transcriptional regulation. Using mesenchymal cells stably transfected with wild type or dominant-negative serum response factor, we demonstrated that its expression is sufficient for induction of a smooth muscle phenotype in mesenchymal cells and is necessary for transforming growth factor-␤-mediated smooth muscle induction.

Primary and immortalized mouse epicardial cells undergo differentiation in response to TGFβ

“…Up-regulation of smooth muscle proteins by endothelial cell conditioned medium was blocked by preincubation with neutralizing antisera to TGF␤. Subsequent studies showed TGF␤-mediated induction of the late phenotypic marker smooth muscle ␥-actin by means of serum response factor (Hirschi et al, 2002). TGF␤ also induces smooth muscle cell differentiation in both embryonic stem cells (Sinha et al, 2004) and neural crest stem cells (Chen and Lechleider, 2004).…”

Sphingosylphosphorylcholine induces differentiation of human mesenchymal stem cells into smooth-muscle-like cells through a TGF-β-dependent mechanism

“…It is well established that most SMCspecific differentiation marker genes are dependent on the SRF/myocardin-dependent pathway (Miano, 2003;Wang and Olson, 2004), and that the onset of SRF expression correlates closely with SMC marker expression during development (Browning et al, 1998;Croissant et al, 1996). TGF-␤ induces the expression of SRF, which in turn activates CArG-dependent SMC differentiation (Hirschi et al, 2002;Kawai-Kowase et al, 2004). Furthermore, mouse embryos lacking myocardin die during the early stage of smooth muscle development and fail to express multiple smooth muscle marker genes in embryonic dorsal aorta and other vascular structures .…”

mSmile is Necessary for Bronchial Smooth Muscle and Alveolar Myofibroblast Development

“…Transforming growth factor-b (TGF-b) is known to induce the myofibroblast phenotype both in vitro (Desmouliere et al, 1993;Hirschi et al, 2002) and in vivo (Zhou et al, 1996;Sime et al, 1997). We examined the ability of wild-type and mSmile mutant MEF to differentiate into myofibroblasts in response to TGF-b.…”