Rap1 promotes adhesion to laminin via the BCAM/LU receptor. (A) Rap1 promotes adhesion to laminin via the BCAM/LU receptor. SS RBCs were treated with 100 μM 8CPT-2-Me for 20 minutes and then flowed over chambers coated with either 0.75 μg laminin or 0.75 μg laminin blocked by precoating the immobilized laminin with 3 μg soluble BCAM/LU in 75 μL of PBS for 3 hours at 37°C in a flow adhesion assay. Results shown are expressed as mean ± SE from 2 separate experiments. (B) Soluble VCAM does not block adhesion to laminin. Immobilized laminin (0.75 μg) either was not precoated or precoated with 50 μg/mL soluble VCAM-1. SS RBCs were treated with 100 μM 8CPT-2-Me for 20 minutes. The cell suspension, while still in the presence of 8CPT-2-Me at the aforementioned concentration, was flowed across 0.75 μg laminin in a flow adhesion assay. Results are expressed as mean ± SE from 2 separate experiments. (C) The BCAM/LU receptor mediates adhesion to laminin stimulated via Epac/Rap1. SS RBCs were either untreated or preincubated with either 25 μg/mL BCAM adhesion-blocking antibody or an equivalent concentration of IgG control antibody for 1 hour. The RBCs or RBC/antibody mixture were then treated with 100 μM 8CPT-2-Me for 20 minutes and, while still in the presence of antibody and 8CPT-2-Me at the aforementioned concentrations, flowed over channels coated with 0.75 μg laminin in a flow adhesion assay. Results shown are expressed as mean ± SE from 4 separate experiments.