Foxc1 and Foxc2 regulate an arterial cell fate by mediating the VEGF‐Notch signaling pathways

Vascular endothelial growth factor (VEGF) signaling and its downstream Notch pathway play critical roles in arterial‐venous cell fate determinations during development. We have recently reported that Foxc1 and Foxc2 , two closely related Fox transcription factors, are central regulators of arterial cell specification during vascular development. Significantly, compound Foxc1; Foxc2 mutants exhibit arteriovenous malformations and lack of the induction of arterial markers. The goal of this study is to elucidate the molecular mechanisms by which Foxc transcriptional factors regulate arterial gene expression in vitro . Overexpression of Foxc genes in endothelial cells directly induces expression of arterial markers, Dll4 and Hey2, through Foxc binding elements (FBEs) on their promoters, while the VEGF‐activated PI3K/Akt and ERK pathways modulate the transcriptional activity of Foxc proteins. Furthermore, we found that the Notch intracellular domain (NICD) and Foxc2, not Fox1, synergistically regulate Hey2 gene expression. Taken together, our results demonstrate that Foxc transcriptional factors act downstream of VEGF signaling to activate multiple steps of the Dll4‐Notch‐Hey2 cascade during arterial cell specification.