REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR RECEPTOR KDR IN-VITRO BY A SOLUBLE FACTOR IN CONFLUENT ENDOTHELIAL-CELLS

Hypoxia regulates the expression of both vascular endothelial growth f actor (VEGF) and its receptor (KDR). We have shown that cell density r egulates VEGF expression in colon cancer and hypothesized that a simil ar mechanism regulates KDR in endothelial cells. Human umbilical vein endothelial cells were grown as sparse and confluent monolayers. North ern blot analysis revealed that KDR and VEGF mRNA expression in conflu ent cells was more than two-fold greater than in sparse cells. In cont rast, flt-1 expression increased only slightly in cells grown to confl uence. Cells were then plated at various concentrations and subjected to semi-quantitative PCR; KDR mRNA expression increased as cell densit y increased. Serum-free conditioned medium from cells grown to conflue ncy for 48 h was added to sparsely plated cells, and KDR expression in the sparse cells increased twofold. We conclude that cell density reg ulates KDR endothelial cell expression via an unidentified soluble fac tor.