bFGF-induced MAP kinase activation requires JAM-1 and α_vβ₃. (A) HUVECs expressing various JAM-1 constructs were stimulated with bFGF, as indicated, and were processed to observe the amount of phospho-ERK1/2 and total ERK1/2. (B) Serum-starved JAM-1–overexpressing HUVECs were preincubated with PBS (control) or indicated antibodies, stimulated with bFGF, and then processed as in panel A. (C) Quantitation of the amount of phospho-ERK1/2 from panel B by densitometry. Anti-α_vβ₃ and anti–JAM-1 significantly inhibit ERK1/2 activity (*P < .05).