Abstract 1365: Forkhead Transcription Factors, Foxc1 and Foxc2, Directly Regulate VCAM-1 Gene Expression in Endothelial Cells
Objectives - Although it is known that the induction of vascular cell adhesion molecule 1 (VCAM-1) in endothelial cells promotes leukocyte-endothelium interaction at sites of atheroma initiation leading to the development of atherosclerosis, the precise molecular mechanisms underlying transcriptional regulation of the VCAM-1 gene are incompletely understood. Foxc1 and Foxc2, closely related forkhead transcription factors, have been shown to play important roles in embryonic blood vessel development and endothelial functions in postnatal life. We investigated their potential regulation of VCAM-1 gene expression.
Methods and Results - We found that transcripts of VCAM-1 are significantly upregulated by overexpressing Foxc in endothelial cells. Importantly, consistent with this finding, there are three Foxc-binding elements (FBEs) conserved between mouse and human in the VCAM-1 promoter region, and we confirmed by gel shift and chromatin immunoprecipitation (ChIP) assays that Foxc proteins can bind to these FBEs in vitro and in vivo. Luciferase assays using a series of deletion and mutant constructs for the VCAM-1 promoter further demonstrate that Foxc1 and Foxc2 regulate the promoter activity of VCAM-1 via the FBEs. Furthermore, we also found that using an in vitro adhesion assay with monocytic THP-1 cells, endothelial cells overexpressing Foxc genes show increased adhesiveness for monocytes as compared to mock-transfected cells. Most importantly, endothelial cells isolated from adult Foxc2 heterozygous mutant mice show a significant reduction in VCAM-1 transcription compared to wild-type endothelial cells.
Conclusions - Our results indicate that Foxc transcription factors directly regulate VCAM-1 gene expression in endothelial cells and that they may play a pivotal role in the development of atherosclerosis.