| Summary: | <p>Cell attachment to the extracellular matrix (ECM) engages integrin signaling into the cell, but part of the signaling response also stem from cell spreading (<abbr bid="B3">3</abbr>). To analyze specific integrin signaling-mediated responses independent of cell spreading, we developed a method engaging integrin signaling by use of an immobilized anti-integrin monoclonal antibody (mab) directed against the fibronectin (FN) receptor integrin &agr;5&bgr;1. ECV 304 cells were plated onto FN or immobilized mab JBS5 (anti-integrin &agr;5&bgr;1) or onto poly-L-lysin (P-L-L), which mediates integrin-independent attachment. Cells attached and spread on FN, while cells on JBS5 or P-L-L attached but did not spread. Importantly, plating onto FN or mab JBS5 gave rise to identical integrin-induced responses, including a down-regulation of the cyclin-dependent kinase (Cdk2) inhibitors p21<sup>CIP1</sup> and p27<sup>KIP1</sup>, while attachment to P-L-L did not. We conclude that engagement of the FN-receptor integrin &agr;5&bgr;1 induces integrin signaling regulating the Cdk2-inhibitors independent of cell spreading and present a method for how integrin signaling can be analyzed separate from the effects of cell spreading.
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