Tat RGD region provides vascular cells with the adhesion signal required by the cells to respond to mitogens. KS (▪) and IC-HUVE (□) cells were preincubated with RGD or mutated KGE peptides (1 μg/each) or with anti-5β1 and/or anti-vβ3 antibodies (4 μg/mL) and were then stimulated with Tat (1 ng/mL; upper left panel). No effects of the competitor peptides or antibodies were observed on cells grown in the absence of stimuli (upper right panel). Anti-CD34 or anti-vβ5 MoAbs (4 μg/mL) were used as control antibodies (CR-Ab) for KS cells. Anti-factor VIII-related antigen MoAbs (4 μg/mL) were used as control antibodies (CR-Ab) for HUVE cells. TNF- (10 ng/mL) or ECGS (45 μg/mL) were used as control mitogens (CR mitogen) for KS and IC-HUVE cells, respectively (lower left panel). The preincubation of the cells with antibody or peptide dilution buffer was the negative control. In the upper panels and in the lower left panel, KS and IC-HUVE cells were seeded onto gelatin-coated plates. In the lower right panel, IC-HUVE cells were seeded onto plates coated with Tat (5 μg/mL), and then they were stimulated to grow with ECGS (45 μg/mL) in the presence or absence of anti-5β1, -vβ3, or -vβ5 antibodies (4 μg/mL). Results (from 3 experiments, each in duplicate) are expressed as the percentage increase of cell growth relative to the growth of cells preincubated with buffer and stimulated with Tat, TNF-, or ECGS (assumed as 100% of cell growth increase).