Expression of VEGFR-2/KDR and VEGFR-1/flt-1 in various tumor cell lines.

(A) RT-PCR of VEGF, VEGFR-1, and VEGFR-2 in a panel of human tumor cell lines. The cDNA was prepared and amplified using gene-specific primers as described in “Materials and methods.” Amplified products of the predicted sizes (VEGF, 535 and 403 base pairs; VEGFR-1, 498 base pairs; VEGFR-2, 709 base pairs) are observed in all of the cells in the upper row. In the lower row are cells that failed to show expression of one or all of the components tested. (B) KS Y-1, M21, Hey, U937, HL-60, and HuT 78 cells were incubated with FITC-labeled VEGFR-2 antibody as described in “Materials and methods” and analyzed by flow cytometry. Cells on the upper row expressed VEGFR-1; those on the lower row did not express the receptor. (C) Immunocytochemical staining of Hoc-7 ovarian carcinoma cells and A375 melanoma cells for VEGFR-1 and VEGFR-2. For Hoc-7, brown color is signal; for A375, crimson color is signal. Specificity of immunostaining was demonstrated in both cases by lack of signal with isotype-specific controls (control).