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 bet ween EGFR and integrins we chose two cell lines for a more detailed an alysis: the highly metastatic rat mammary carcinoma clone MTLn3 that s howed increased adhesion to a panel of ECM proteins in the presence of 10 ng/ml EGF and the nonmetastatic human vulva carcinoma cell line A4 31 which showed a decreased adhesion under the same conditions. These EGF-mediated stimulatory or inhibitory effects on adhesion were observ ed within a few minutes. On human A431 cells the inhibitory effect was blocked by an EGFR-specific antibody that interferes with ligand bind ing. In cell adhesion assays performed in the presence of divalent cat ions 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 integr in antibodies revealed that A431 cells adhere to collagen via alpha(1) beta(1) and alpha(2) beta(1), and that adhesion to fibronectin is med iated predominantly through alpha(5) beta(1). The interaction of MTLn3 cells with fibronectin was in part RGD dependent, indicating the invo lvement of either alpha(3) beta(1) or alpha(5) beta(1). Addition of EG F in these assays showed that affecting the integrin extracellular dom ains 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 stimula tory manner.