Assembly of actin filaments induced by sequestration of membrane cholesterol in transformed cells

Abstract

Cholesterol is one of the major lipid components of plasma membrane and it plays an important role in various signaling processes in mammalian cells. Our study focused on the role of membrane cholesterol in organization and dynamics of actin cytoskeleton. Experiments were performed on cultured transformed cells characterized by weakly developed actin network and reduced stress fibers--human embryonic kidney HEK293 cells, epidermoid larynx carcinoma HEp2 cells and mouse fibroblasts 3T3-SV40. Using F-actin labeling with rhodamine-phalloidin, actin cytoskeleton rearrangements were analyzed after sequestration of membrane cholesterol by cyclic oligosaccharide methyl-beta-cyclodextrin, and polyene macrolide antibiotic filipin. In cells treated with methyl-beta-cyclodextrin or filipin, similar processes of actin cytoskeleton reorganization involving filament assembly were revealed. In carcinoma HEp2 cells and fibroblasts 3T3-SV40, cholesterol-sequestering reagents induced intensive stress fiber formation and enhanced cell spreading which corresponded to reversion of transformed phenotype. The rearrangements of cytoskeleton are likely initiated by disruption of lipid raft integrity that is critically dependent on the level of the membrane cholesterol.