Myo1c regulates lipid raft recycling to control cell spreading, migration and Salmonella invasion

Abstract

A balance between endocytosis and membrane recycling regulates the composition and dynamics of the plasma membrane. Internalization and recycling of cholesterol and sphingolipid-enriched lipid rafts is an actin-dependent process that follows a specialized Arf6-dependent recycling pathway. Here we identify the first motor protein, myosin1c (Myo1c) that drives the formation of recycling tubules emanating from the perinuclear recycling compartment. We demonstrate that the single headed Myo1c is a lipid raft-associated motor protein, specifically involved in recycling of lipid raft-associated GPI-linked cargo proteins and their delivery to the cell surface. While Myo1c overexpression increases the levels of these raft proteins at the cell surface, in cells depleted of Myo1c function by RNA interference or by over-expression of a dominant-negative mutant, these tubular transport carriers of the recycling pathway are lost and GPI-linked raft markers are trapped in the perinuclear recycling compartment. Intriguingly, Myo1c selectively promotes delivery of only lipid raft membranes back to the cell surface and is not required for recycling of cargo such as the transferrin receptor using parallel pathways. The profound defect in lipid raft trafficking in Myo1c knockdown cells has a dramatic impact on cell spreading, cell migration and cholesterol-dependent Salmonella invasion; processes that require lipid raft transport to the cell surface to deliver signalling components and the extra membrane essential for cell surface expansion and remodelling. Thus, Myo1c plays a crucial role in the recycling of lipid raft membrane and proteins that regulate plasma membrane plasticity, cell motility and pathogen entry.