Fibronectin and integrin α5β1 support endothelial cell survival. (a–c) HUVECs were maintained in suspension (SUS) or on fibronectin-coated (Fn) or poly-L-lysine–coated (PLL) plates. (a) The percentage of annexin V–positive cells on poly-L-lysine– or fibronectin-coated dishes was determined at regular intervals from 0 to 8 hours. (b) Cell lysates prepared after 4 hours of attachment were immunoblotted to detect intact (116 kDa) and cleaved PARP (85 kDa). The ratio of intact to cleaved PARP was determined by densitometry. Cl., cleaved. (c) Soluble DNA extracted from cells attached to poly-L-lysine or fibronectin was electrophoresed on 1.6% agarose gels. Relative DNA cleavage was determined by densitometry. (d–f) HUVECs were plated on fibronectin, anti-α5β1, or control Ab-coated plates. (d) The percentage of annexin V–positive cells was determined from 0 to 8 hours. (e) Cell lysates were immunoblotted to detect intact and cleaved PARP. (f) DNA fragmentation was evaluated as in c. cIgG, control immunoglobulin.