Fig. 2. The hierarchy of integrin-specific signals. Integrin vß3 selectively associates with and enhances signaling by RTK receptors. It also activates several pathways including NF-B, calcium influx and possibly others yet to be identified. Integrins vß3, 5ß1 and 1 ß1 interact with caveolin and stimulate Shc phosphorylation and possibly other events. Integrins vß3 and 5ß1 also activate PI3K. Integrin 2ß1 stimulates p38 MAP kinase, which may inhibit cyclin D1 expression in some cells. Most integrins activate FAK and Rho family GTPases on rigid ECMs that resist tension and promote focal adhesion formation. The model is meant to emphasize general trends rather than the absolute specificity of each effect.