KLF2 suppresses TGF-beta signaling in endothelium through induction of Smad7 and inhibition of AP-1.
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.


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.
Boon
Reinier A
RA
Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
Fledderus
Joost O
JO
Volger
Oscar L
OL
van Wanrooij
Eva J A
EJ
Pardali
Evangelia
E
Weesie
Frank
F
Kuiper
Johan
J
Pannekoek
Hans
H
ten Dijke
Peter
P
Horrevoets
Anton J G
AJ
D015153:Blotting, Western; D002478:Cells, Cultured; D015536:Down-Regulation; D042783:Endothelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051906:Smad7 Protein / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014471:Umbilical Veins / Q000166:cytology
D051741:Kruppel-Like Transcription Factors; D051906:Smad7 Protein; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta