Vascular endothelial growth factor induces MEF2C and MEF2-dependent activity in endothelial cells

Vascular endothelial growth factor is a key regulator of physiological and pathologic angiogenesis. Although much is known about the major upstream signaling pathways of VEGF in endothelial cells, less is known about key transcription factors involved in VEGF action. The transcription factor myocyte enhancer factor (MEF)-2C is thought to play an important role in vasculogenesis and angiogenesis during vascular development. The purpose of this study was to investigate the regulation of MEF2C expression and MEF2-dependent activity in endothelial cells by VEGF.

Expression of MEF2C in human retinal endothelial cells and human umbilical vein endothelial cells was assayed by real-time PCR and Western blot. VEGF regulation of MEF2-dependent transcription was studied using an MEF2-luciferase reporter construct containing three copies of a high-affinity MEF2 binding site. The effect of MEF2 on endothelial cell migration was evaluated using a dominant-negative MEF2C mutant.

VEGF induced MEF2C expression in a dose- and time-dependent fashion. This induction was completely abrogated by the inhibition of protein kinase C and was partially blocked by the inhibition of PKC-beta and PKC-delta. In addition to regulating MEF2C expression, VEGF stimulated transcription from an MEF2-dependent promoter. VEGF stimulation of transcription was significantly reduced by the inhibition of calcineurin, CaMKII, p38 MAPK, and PKC, but not by the inhibition of ERK1/2 or BMK1/ERK5. Transfection of a dominant-negative mutant of MEF2C significantly inhibited VEGF-stimulated endothelial cell migration.

These results implicate VEGF as a key regulator of MEF2C and suggest that MEF2 may be an important mediator of VEGF in endothelial cells.