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MBC in Press, published online ahead of print November 19, 2008
Mol. Biol. Cell 10.1091/mbc.E08-07-0785

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Submitted on July 31, 2008
Revised on October 21, 2008
Accepted on November 6, 2008

Sterols Are Mainly in the Cytoplasmic Leaflet of the Plasma Membrane and the Endocytic Recycling Compartment in CHO Cells

Mousumi Mondal, Bruno Mesmin, Sushmita Mukherjee, and Frederick R. Maxfield

Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065

Monitoring Editor: Sandra L. Schmid

The transbilayer distribution of many lipids in the plasma membrane and in endocytic compartments is asymmetric, and this has important consequences for signaling and membrane physical properties. The transbilayer distribution of cholesterol in these membranes is not properly established. Using fluorescent sterols, dehydroergosterol and cholestatrienol, and a variety of fluorescence quenchers, we studied the transbilayer distribution of sterols in the plasma membrane (PM) and the endocytic recycling compartment (ERC) of a CHO cell line. A membrane impermeant quencher, 2,4,6-trinitrobenzene sulfonic acid, or lipid-based quenchers that are restricted to the exofacial leaflet of the plasma membrane only reduce the fluorescence intensity of these sterols in the plasma membrane by 15–32%. When the same quenchers have access to both leaflets, they quench 70–80% of the sterol fluorescence. Sterol fluorescence in the ERC is also quenched efficiently in the permeabilized cells. In microinjection experiments, delivery of quenchers into the cytosol efficiently quenched the fluorescent sterols associated with the PM and with the ERC. Quantitative analysis indicates that 60–70% of the PM sterol is in the cytoplasmic leaflet. This means that cholesterol constitutes ~40 mol% of cytoplasmic leaflet lipids, which may have important implications for intracellular cholesterol transport and membrane domain formation.

Address correspondence to: Frederick R. Maxfield (frmaxfie{at}med.cornell.edu)






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