Figure 4.

Thrombospondins compete with VCAM-1 for binding to α4β1 integrin. (A) NH₂-terminal regions of TSP1 and TSP2 inhibit binding of soluble VCAM-1 to activated T cells. ¹²⁵I-labeled S7D–VCAM-1 was used as a probe to bind either resting or TS2/16- (0.5 μg/ml) activated Jurkat T cells. NoC1 and NoC2 (10 μg/ml) were used to antagonize the binding of ¹²⁵I-S7D–VCAM-1 (500,000 cpm) to α4β1 integrin on T cells. The α4-specific antagonist (4-((2-methylphenyl)aminocarbonyl)aminophenyl)acetyl-LDVP (phLDVP, 1 μM) was used as a positive control for α4β1 integrin blocking. S7D–VCAM-1 binding is presented as mean ± SD, n = 3. (B) Jurkat cell adhesion on wells coated using 1 μg/ml S7D–VCAM-1 was determined using the colorimetric assay in the presence of the indicated concentrations of TSP1, 100 μM of the TSP1 peptide acAELDVP, or 260 nM S7D–VCAM-1.