Cholesterol Dictates the Freedom of EGF Receptors and HER2 in the plane of the membrane

¹ Pacific Northwest National Laboratory

^* To whom correspondence should be addressed. E-mail: galya.orr{at}pnl.gov.

Submitted on November 11, 2004
Revised on January 18, 2005
Accepted on 10 May 2005

	Abstract

The flow of information through the EGF receptor (EGFR) is shaped by molecular interactions in the plasma membrane. The EGFR is associated with lipid rafts, but their role in modulating receptor mobility and subsequent interactions is unclear. To investigate the role of nanoscale rafts in EGFR dynamics, we used single-molecule fluorescence imaging to track individual receptors and their dimerization partner, HER2, in the membrane of human mammary epithelial cells. We found that the motion of both receptors was interrupted by dwellings within nanodomains. EGFR was significantly less mobile than HER2. This difference was likely due to F-actin because its depolymerization led to similar diffusion patterns between the EGFR and HER2. Manipulations of membrane cholesterol content dramatically altered the diffusion pattern of both receptors. Cholesterol depletion led to almost complete confinement of the receptors, whereas cholesterol enrichment extended the boundaries of the restricted areas. Interestingly, F-actin depolymerization partially restored receptor mobility in cholesterol depleted membranes. Our observations suggest that membrane cholesterol provides a dynamic environment that facilitates the free motion of EGFR and HER2, possible by modulating the dynamic state of F-actin. The association of the receptors with lipid rafts could therefore promote their rapid interactions only upon ligand stimulation.

Key Words: actin cytoskeleton, confined diffusion, lipid rafts, membrane nanodomains, receptor dimerization, single-molecule fluorescence

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