Attachment of A-431 cells on immobilized antibodies to the EGF receptor promotes cell spreading and reorganization of the microfilament system

EGF-like sequences, inherent in a number of extracellular matrix proteins, participate in cell adhesion. It is possible that interactions of these seq uences with EGF receptors (EGFR) affect actin filament organization. It was shown previously [Khrebtukova et al., 1991. Exp. Cell Res. 194:48-55] that antibodies specific to EGFR induce capping of these receptors and redistri bution of cytoskeletal proteins in A-431 cells. Here we report that A-431 c ells attach and spread on solid substrata coated with antibodies to EGFR, e ven in the absence of serum. Thus, EGFR can act as an adhesion protein and promote microfilament reorganization. Binding of the cells to the EGFR-anti body resulted in the formation of a unique cell shape characterized by nume rous, actin-based filopodia radiating from the cell body, but without membr ane ruffles. There was also a conspicuous circular belt of actin-containing fibers inside the cell margin, and many irregular actin aggregates in the perinuclear area. The morphologies and actin distributions in A-431 cells s pread on fibronectin or laminin 2/4 were very different. On fibronectin, ce lls had polygonal shapes with numerous stress-fibers and thick actin-contai ning fibers along the cell edges. On laminin-covered substrata, the cells b ecame fusiform and acquired broad leading lamellae with ruffles. In these c ells, there were also a few bundles of filaments running the whole length o f the cell body, and shorter bundles extending through the leading lamellae tot-yards the membrane ruffles in the cell edge. These effects and those s een with immobilized EGF suggest that different ligand/receptor complexes i nduce specific reorganizations of the microfilament system. Cell Motil. Cyt oskeleton 48:24-36, 2001. (C) 2001 Wiley-Liss, Inc.