Graded fibronectin receptor aggregation in migrating cells

Abstract

We have examined the distribution of the integrin fibronectin receptor in migrating NIH 3T3 fibroblasts to test the hypothesis that cell locomotion involves regional differences of adhesive receptor aggregation. A distinct asymmetry of fibronectin receptor aggregation was observed on the surface of migrating NIH 3T3 fibroblasts. Direct current electric fields were used to stimulate directional cell migration and thus allow the quantitative correlation of receptor asymmetries to the direction of cell locomotion. Digital particle analysis of fluorescent confocal micrographs demonstrates that the leading half of cells has a higher proportion of receptors contained in small clusters than does the trailing half. Conversely, larger receptor aggregates are more prevalent in the rear of the cell than in the front. We have also observed a gradient of extracellular fibronectin fibril assembly, similar to that described for the fibronectin receptor. Extracellular fibronectin appears in progressively larger fibrils across the ventral cell surface from front to rear, with dense meshworks often deposited as a trail behind the cell. Large fibronectin receptor clusters toward the rear of the cell generally do not correlate with focal contacts, and are thus most likely aggregated by cell surface‐bound fibronectin fibrils and not by adhesion to the substratum. These results suggest that spatial variations in the degree of adhesive receptor aggregation are created in fibroblasts during the processes of migration and matrix synthesis. © 1996 Wiley‐Liss Inc.

Physiological electrical fields modify cell behaviour

“…lntegrin receptor distribution on fibroblasts was also influenced by an applied electric field. A greater proportion of fibronectin receptors was present in small clusters on the leading half of a cathodally migrating cell, whilst most receptors for fibronectin on the trailing half of fibroblasts were present in large clusters (52). Our working hypothesis therefore involves cathodal distribution of EGF receptors as a key element in cathodal migration of CECs.…”

Electric Field–directed Cell Motility Involves Up-regulated Expression and Asymmetric Redistribution of the Epidermal Growth Factor Receptors and Is Enhanced by Fibronectin and Laminin

“…Both AC and DC fields redistribute cell surface receptors (including the EGFR) and the actin cytoskeleton (Poo and Robinson, 1977;Luther et al, 1983;Giugni et al, 1987;McCaig and Dover, 1991;Cho et al, 1994Cho et al, , 1996Brown and Loew, 1996), although the mechanisms differ, because redistribution in an AC field is not along the field vector (Cho et al, 1996). We propose that EGFR redistribution cathodally leads to localized actin polymerization at the EGFR-plasma membrane interface and that these events respectively trigger and mediate cathodal-directed CEC migration.…”

“…EF-directed, faster migration of CECs on FN or LAM also may involve polarized focal contact disassembly and integrin receptor redistribution (see above). We have no data on integrin expression in migratory CECs, although the ␣5␤1 FN receptor redistributed on fibroblasts in a DC EF, with smaller aggregates accumulating cathodally and larger aggregates accumulating anodally (Brown and Loew, 1996). Also, the LAM receptor ␣6␤4 redistributes and spreads out in wounded corneal epithelium (in an endogenous, wound-induced EF) to break up and decrease focal adhesion in preparation for cell migration (Gipson and Inatomi, 1995).…”