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Blood. 2002 Dec 1;100(12):4019-25. Epub 2002 Aug 1.

Differential regulation of the von Willebrand factor and Flt-1 promoters in the endothelium of hypoxanthine phosphoribosyltransferase-targeted mice.

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Department of Molecular Medicine, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.


An important limitation of standard transgenic assays is that multiple copies of the transgene are inserted randomly into the mouse genome, resulting in line-to-line variation in expression. One way to control for these variables is to target a single copy of the transgene to a defined locus of the mouse genome by homologous recombination. In the present study, we have used such an approach to target the promoters of 2 different genes, namely von Willebrand factor (VWF) and Flt-1, to the hypoxanthine phosphoribosyltransferase (Hprt) gene locus. Consistent with previous findings in standard transgenic animals, we report that the VWF promoter contains information for expression in a subset of endothelial cells in the heart, skeletal muscle, and brain. In contrast, the Flt-1 promoter directs expression in all vascular beds except for the liver. The Flt-1 transgene was active in the endothelium of tumor xenografts, whereas the VWF promoter was not. Under in vitro conditions, conditioned medium from tumor cells resulted in a significant up-regulation of Flt-1 mRNA and promoter activity, but no change in VWF levels. Taken together, these results suggest that (1) Hprt locus targeting is a valuable tool for studying vascular bed-specific gene regulation, (2) the VWF and Flt-1 promoters are regulated by distinct transcriptional mechanisms in the intact endothelium, and (3) tumor angiogenesis results in the differential activation of endothelial cell-specific promoters.

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