α5β1 integrin is gradually activated in dedifferentiating chondrocytes, possibly by RRAS. (a) Chondrocytes were cultured in monolayers for 2 days (D2) or 7 days (D7), and cell attachment was evaluated at respective time points on noncoated plates (Non-coat) or plates coated with fibronectin or BSA. (b) Attachment to fibronectin-coated plates was evaluated using 7-day cultured chondrocytes after incubation with a function blocking anti-α5β1 integrin antibody (JBS5; 1 μg/ml) or control IgG (Control; 1 μg/ml). (c) Constitutively active (CA) or dominantly negative (DN) mutants of small GTPases were overexpressed in monolayer-cultured chondrocytes by adenoviral gene transfer, and adhesion to fibronectin-coated plates was evaluated. Results are mean ± standard error of the mean of four (a), (b) or five (c) independent experiments, each in duplicate. **P <0.01.