Expression and functional significance of vascular endothelial growth factor receptors in human tumor cells

Vascular endothelial growth factor (VEGF) is one of the key factors in tumor neoangiogenesis, acting through its receptors KDR (VEGFR-2) and fit-1 (VEGFR-1) expressed on endothelial cells. Our data demonstrate that VEGFR-1 and to a lesser extent VEGFR-2 are expressed in a number of human tumor tissues and derived cells in culture. VEGFR-1 protein is expressed in 26 of 42 glioma tissues, 22 of which show a coexpression of VEGFR-1 with VEGFR-2; 1 glioma tissue expresses exclusively VEGFR-2. In the derived glioma cell cultures, we found VEGFR-1 mRNA expression in 6 of 11 cultures, with one coexpressing VEGFR-1 and VEGFR-2. Of four established glioma cell lines, two expressed VEGFR-1. In addition VEGFR-1 protein expression was demonstrated in 30 of 37 tumor tissues of squamous cell carcinomas of the head and neck, with VEGFR-2 coexpression in 15 tissues and an expression of VEGFR-2 alone in 1 tissue. Derived tumor cell cultures showed mRNA expression of VEGFR-1 alone in seven of seven cases. Established melanoma cell lines expressed VEGFR-1 mRNA in four of five lines, with VEGFR-2 coexpression in two lines. Concerning the functional significance of VEGF receptor expression, VEGF treatment of VEGFR-1-expressing tumor cells induced the inhibition of cell proliferation by 25 to 55% and the inhibition of tumor cell migration by 29 to 55%. Thus our data indicate that the coexpression of VEGF and VEGFR-1 in tumor cells could have an inhibitory effect on tumor cell proliferation and migration, a mechanism possibly induced as a response to a deficiency in nutrient and oxygen supply.