Integrin involvement in keratocyte locomotion

Keratocytes are useful in the study of locomotion because they move rapidly (up to 1 micron/second) while maintaining an almost uniform shape, speed and direction. The smooth gliding motion of the keratocyte requires a precise coordination between adhesion, contractility, and retraction. To ask what role integrins play in keratocyte adhesion and locomotion, either RGD peptides or an anti-beta1 integrin mAb that binds to an ectodomain epitope and inhibits adhesion formation was added to the culture media of moving keratocytes. The response to these reagents depended on three interrelated factors: the dose of RGD/mAb, the apparent adhesion strength of the keratocyte to the substratum and the cell speed. High doses cause keratocytes to quickly and irreversibly round up. At intermediate RGD/mAb doses, keratocytes reestablish adhesion after treatment and briefly resume locomotion until partial detachment recurs. At the lowest doses, disruption of beta1 integrin-mediated adhesion formation destabilizes the lamella, temporarily preventing lamellar extension and forward movement of the cell. With increasing culture time, there is an increase in apparent adhesion and a corresponding marked decrease in locomotory velocity. Under these conditions, high doses of RGD/mAb do not cause keratocytes to detach or even produce detectable lamellar instabilities. We postulate that RGD/mAb competitively inhibits new beta1 integrin mediated adhesion formation that is required to support the rates of lamellar extension necessary for rapid locomotion.