The binding of integrins to extracellular matrix triggers signals that promote cell spreading. We previously demonstrated that expression of the integrin beta 1 cytoplasmic domain in the context of a chimeric transmembrane receptor with the Tac subunit of the interleukin-2 receptor (Tac-beta 1) inhibits cell spreading. To study the mechanism whereby Tac-beta 1 inhibits cell spreading, we examined the effect of Tac-beta 1 on early signaling events following integrin engagement namely FAK and Src signaling. We infected primary fibroblasts with adenoviruses expressing Tac or Tac-beta 1 and found that Tac-beta 1 prevented FAK activation by inhibiting the phosphorylation of FAK at Tyr-397. In contrast, Sre activation was maintained, as phosphorylation of Src at Tyr-419 and Tyr-530 were not responsive to expression of Tac-beta 1. Importantly, adhesion-induced tyrosine phosphorylation of the Src substrates p130Cas and paxillin was inhibited, indicating that Src signaling was blocked by Tac-beta 1. These Src-dependent signaling events were found to require FAK signaling. Our results suggest that Tac-beta 1 inhibits cell spreading, at least in part, by preventing the phosphorylation of FAK at Tyr-397 and the assembly of signaling complexes necessary for phosphorylation of p130Cas and other downstream effectors. (C) 2008 Elsevier Inc. All rights reserved.