Perturbation of membrane microdomains in GLC4 multidrug-resistant lung cancer cells--modification of ABCC1 (MRP1) localization and functionality.

The multidrug resistance-associated protein transporter ABCC1 (MRP1) is an integral plasma membrane protein involved in the multidrug resistance phenotype. It actively expels a number of cytotoxic molecules from cells. To gain insight into the modulation of the functional properties of this integral membrane protein by cholesterol, a main component of the lipid bilayer, we used multidrug-resistant GLC4/ADR cells, which overexpress MRP1. Upon altering the plasma membrane cholesterol content of these cells, membrane localization and the activity of MRP1 were analyzed. A detergent-free methodology was used to separate "light" and "heavy" plasma membrane fractions. Our data show that MRP1 was exclusively found in "light" fractions known as L0 phase membrane microdomains, together with 23% of gangliosides GM1 and 40% of caveolin-1. Depletion of the membrane cholesterol level to 40% by treatment with the cholesterol-chelating agent methyl-beta-cyclodextrin did not modify MRP1 activity, as evidenced either by the rate of efflux of pirarubicin or that of glutathione. Further cholesterol depletion below 40% yielded both a partial shift of MRP1 to the high-density fraction and a decrease of its functionality. Taken together, these data suggest that MRP1 functionality depends on its localization in cholesterol-rich membrane microdomains.