Membrane raft microdomains mediate front-rear polarity in migrating cells

The acquisition of spatial and functional asymmetry between the rear and th e front of the cell is a necessary step for cell chemotaxis, Insulin-like g rowth factor-I (IGF-I) stimulation of the human adenocarcinoma MCF-7 induce s a polarized phenotype characterized by asymmetrical CCR5 chemokine recept or redistribution to the leading cell edge, CCR5 associates with membrane r aft microdomains, and its polarization parallels redistribution of raft mol ecules, including the raft-associated ganglioside GM1, glycosylphosphatidyl -inositol-anchored green fluorescent protein and ephrinB1, to the leading e dge. The non-raft proteins transferrin receptor and a mutant ephrinB1 are d istributed homogeneously in migrating MCF-7 cells, supporting the raft loca lization requirement for polarization. IGF-I stimulation of cholesterol-dep leted cells induces projection of multiple pseudopodia over the entire cell periphery, indicating that raft disruption specifically affects the acquis ition of cell polarity, but not IGF-I-induced protrusion activity. Choleste rol depletion inhibits MCF-7 chemotaxis, which is restored by replenishing cholesterol. Our results indicate that initial segregation between raft and non-raft membrane proteins mediates the necessary redistribution of specia lized molecules for cell migration.