The expression of the glycosyl phosphatidylinositol (GPI)-anchored protein CD24 correlates with poor prognosis in a variety of carcinomas. However, little is known about the cellular mechanisms of the CD24-mediated effects. In this study, we present evidence that CD24 affects the lateral localization of beta 1 integrin. Using stably CD24-transfected A125 and MDA-MB-435S carcinoma cells we show that CD24 augments PI-dependent cell motility and stimulates transmigration and invasion across a monolayer of endothelial cells. Furthermore, as demonstrated by sucrose density gradient centrifugation and Western Blot analysis, CD24 recruits PI integrin into lipid raft domains. We suggest that CD24 acts as a gate-keeper for lipid rafts, thereby regulating the activity of integrins and other proteins. (c) 2007 Elsevier Inc. All rights reserved.