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 f actor (vWF) gene was investigated in human umbilical vein endothelial cells (HUVECs) and HeLa cells. A fragment spanning -89 to +244 nucleot ides (nt), containing the first exon, is active in HUVECs only but not in HeLa cells. The activity of this promoter is sharply reduced by mu tagenesis of the GATA binding site at +221, Extension of the upstream sequences from nt -89 to -142 and to -496 results in progressive reduc tion of the activity of the -89 to +244 promoter identifying a negativ e regulatory element between nt -142 and -89. A factor present in nucl ear 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 supers hift experiments identified Oct-1 as the transcription factor that bin ds to vWF and VCAM-1 silencer elements. These results indicate that Oc t-1 acts as a transcriptional repressor of promoters of genes expresse d in endothelial cells, (C) 1998 by The American Society of Hematology .