Oct-1 is involved in the transcriptional repression of the von willebrand factor gene promoter.

The negative regulation of transcription of the human von Willebrand factor (vWF) gene was investigated in human umbilical vein endothelial cells (HUVECs) and HeLa cells. A fragment spanning -89 to +244 nucleotides (nt), containing the first exon, is active in HUVECs only but not in HeLa cells. The activity of this promoter is sharply reduced by mutagenesis of the GATA binding site at +221. Extension of the upstream sequences from nt -89 to -142 and to -496 results in progressive reduction of the activity of the -89 to +244 promoter identifying a negative regulatory element between nt -142 and -89. A factor present in nuclear extracts from endothelial and nonendothelial cells binds to an AT-rich sequence located between nt -133 and -125. Mutagenesis of the AT-rich sequence interferes with nuclear protein binding and restores the activity of the -142 to +244 fragment to the level of the -89 to +244 promoter. Binding of the nuclear protein to the vWF AT-rich sequence in mobility shift assays is inhibited by competition with a consensus Oct-1 binding site and with a silencer octamer-like sequence from the vascular cell adhesion molecule-1 (VCAM-1) promoter. Subsequent supershift experiments identified Oct-1 as the transcription factor that binds to vWF and VCAM-1 silencer elements. These results indicate that Oct-1 acts as a transcriptional repressor of promoters of genes expressed in endothelial cells.