Up-regulation of vascular endothelial growth factor receptor Flt-1 after endothelial denudation: role of transcription factor Egr-1.

Vascular endothelial growth factor (VEGF) is highly expressed in vascular remodeling processes and accelerates reendothelialization after mechanical denudation. Two VEGF tyrosine kinase receptors have been reported-fms-like-tyrosine kinase-1 (Flt-1) and kinase domain region (KDR). Little is known about the regulation of the expression of these receptors after vascular injury. Herein, we have analyzed the expression of Flt-1 after mechanical denudation of primary cultures of endothelial cells, which has been considered a useful in vitro model to study endothelium responses to vascular injury. After denudation, the Flt-1 protein and mRNA levels are clearly up-regulated, and transient transfection experiments showed a strong induction of the flt-1 promoter-dependent transcription. Analysis of the flt-1 promoter sequence revealed the presence of a putative binding site for the early growth response factor-1 (Egr-1) at positions -24 to -16. Electrophoretic mobility shift and supershift assays showed that Egr-1 was able to bind to this DNA sequence, and cotransfection of the flt-1 promoter reporter plasmid with an Egr-1 expression vector resulted in enhancement of its transcriptional activity. Furthermore, the mutation of the Egr-1 binding site markedly reduced the denudation-induced flt-1 promoter activity. These data demonstrate that Flt-1 is up-regulated after endothelial denudation and that Egr-1 plays a relevant role in this process.