Signaling by epidermal growth factor differentially affects integrin-mediated adhesion of tumor cells to extracellular matrix proteins.

The adhesion of different epidermal growth factor (EGF) receptor (EGFR) expressing cell lines to various extracellular matrix (ECM) proteins is influenced by EGF. To investigate a putative receptor crosstalk between EGFR and integrins we chose two cell lines for a more detailed analysis: the highly metastatic rat mammary carcinoma clone MTLn3 that showed increased adhesion to a panel of ECM proteins in the presence of 10 ng/ml EGF and the nonmetastatic human vulva carcinoma cell line A431 which showed a decreased adhesion under the same conditions. These EGF-mediated stimulatory or inhibitory effects on adhesion were observed within a few minutes. On human A431 cells the inhibitory effect was blocked by an EGFR specific antibody that interferes with ligand binding. In cell adhesion assays performed in the presence of divalent cations MTLn3 and A431 cells exhibited the typical behavior described for integrin-dependent matrix adhesion: Mn2+ enhanced binding to collagen IV and fibronectin whereas Ca2+ inhibited adhesion to collagen IV but not to fibronectin. Adhesion-inhibition assays with anti-human integrin antibodies revealed that A431 cells adhere to collagen via alpha 1 beta 1 and alpha 2 beta 1, and that adhesion to fibronectin is mediated predominantly through alpha 5 beta 1. The interaction of MTLn3 cells with fibronectin was in part RGD dependent, indicating the involvement of either alpha 3 beta 1 or alpha 5 beta 1. Addition of EGF in these assays showed that affecting the integrin extracellular domains by addition of either bivalent cations, RGD peptides, or function-blocking integrin antibodies did not prevent the effects mediated by EGF. We conclude that signals downstream of EGFR can modulate integrin-mediated adhesion to ECM proteins in both an inhibitory and a stimulatory manner.