Both the basic and RGD region mediate Tat-promoted vascular cell growth. (A) shows the proliferative response of KS (▪) and IC-HUVE (□) cells to Tat peptides, Tat (1 ng/mL), or FN (30 ng/mL). In the left panel, Tat peptides were used at concentrations equimolar to Tat. In the right panel, Tat peptides were serially diluted to determine the dose-dependency of their effect. (B) shows peptide competition experiments of KS (left panel, ▪) and IC-HUVE (right panel, □) cell growth. Cells were preincubated with an excess of Tat peptides (5 μg/mL each) and then stimulated to growth with Tat (1 ng/mL), as described above. Preincubation of the cells with buffer was the negative control. For (A) and (B), experiments were performed by cell counting. Data (from 3 experiments, each in duplicate) are expressed as the percentage increase of cell growth over the number of cells grown in the absence of mitogens (basal cell growth). This was 1 × 10⁴ cells/well for KS cells and 1.2 × 10⁴cells/well for HUVE cells and was given a 0% increase value. Results were also reproduced by the ³[H]-thymidine uptake method (data not shown).