Cholesterol distribution in plasma membranes of β1 integrin-expressing and β1 integrin-deficient fibroblasts

The effect of integrin receptors on the level and transmernbrane localization of cholesterol molecules was investigated in PI integrin-expressing (beta 1) and beta 1 integrin-deficient (beta 1 null) cells. We found that the content of specific raft components-cholesterol, sphingomyelin, and caveolin-was increased in integrin-expressing cells. Integrin presence affected as well the transmembrane distribution of cholesterol-a higher percent was found in the plasma membrane outer monolayer of beta 1 compared to beta 1 null cells. Sphingomyelin depletion reduced the presence of cholesterol in the outer membrane monolayer of both cell lines, but the differences in cholesterol asymmetry, observed between beta 1 and beta 1 null cells before sphingomyelinase treatment were preserved. These findings implied that integrin receptors affected the non-random transmembrane distribution of cholesterol. Finally, a higher percent of detergent-resistant membranes was obtained from beta 1 integrin-expressing cells, suggesting that the presence of these receptors in the membranes influenced the formation and/or stabilization of lipid raft domains. (c) 2005 Elsevier Inc. All rights reserved.