KLF2 Suppresses TGF- Signaling in Endothelium Through Induction of Smad7 and Inhibition of AP-1

Boon RA, Fledderus JO, Volger OL, van Wanrooij EJ, Pardali E, Weesie F, Kuiper J, Pannekoek H, Ten Dijke P, Horrevoets AJ
Source: Arterioscler Thromb Vasc Biol
Publication Date: (2007)
Issue: 27(3): 532-9
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Endothelial, umbilical vein, human (HUVEC)
Species: human
Tissue Origin: vein
Nucleofector® I/II/2b
OBJECTIVE: The flow-responsive Kruppel-like factor 2 (KLF2) is crucial for maintaining endothelial cell quiescence. Here, we describe its detailed effects on transforming growth factor-beta (TGF-beta) signaling, which normally has proatherogenic effects on endothelium. METHODS AND RESULTS: In-depth analysis of genome-wide expression data shows that prolonged lentiviral-mediated overexpression of KLF2 in human umbilical vein endothelial cells (HUVECs) diminishes the expression of a large panel of established TGF-beta-inducible genes. Both baseline and TGF-beta-induced expression levels of plasminogen activator inhibitor 1 (PAI-1) and thrombospondin-1 are greatly diminished by KLF2. Using a combination of ectopic expression, small interfering RNA-mediated knockdown, and promoter activity assays, we show that KLF2 partly inhibits the phosphorylation and subsequent nuclear accumulation of Smad2, thereby suppressing the TGF-beta-induced Smad4-mediated transcriptional activity. This is achieved through TGF-beta-independent induction of inhibitory Smad7. Additionally, a full inhibition of TGF-beta signaling is functionally achieved through a simultaneous suppression of activator protein 1 (AP-1), which is an essential cofactor for TGF-beta-dependent transcription of many genes. CONCLUSIONS: The concerted mechanism by which KLF2 inhibits TGF-beta signaling through induction of inhibitory Smad7 and attenuation of AP-1 activity provides a novel mechanism by which KLF2 contributes to sustaining a quiescent, atheroprotective status of vascular endothelium.