Multidrug resistance-related protein 1 (MRP1) function and localization depend on cortical actin.

MRP1 (ABCC1) is known to be localized in lipid rafts. Here we show in two different cell lines that localization of Mrp1/MRP1 (Abcc1/ABCC1) in lipid rafts and its function as an efflux pump are dependent on cortical actin. Latrunculin B disrupts both cortical actin and actin stress fibers. This results in partial loss of actin and Mrp1/MRP1 (Abcc1/ABCC1) from detergent-free lipid raft fractions, partial internalization of Mrp1/MRP1 (Abcc1/ABCC1), and reduction of Mrp1/MRP1 (Abcc1/ABCC1)-mediated efflux. Pretreatment with nocodazole prevents latrunculin B-induced loss of cortical actin and all effects of latrunculin B on Mrp1 (Abcc1) localization and activity. However, pretreatment with tyrphostin A23 does not prevent latrunculin B-induced loss of cortical actin, lipid raft association, and efflux activity, but it does prevent latrunculin B-induced internalization of Mrp1 (Abcc1). Cytochalasin D disrupts actin stress fibers but not cortical actin and this inhibitor much less affects Mrp1/MRP1 (Abcc1/ABCC1) localization in lipid rafts, internalization, and efflux activity. In conclusion, cortical actin disruption results in reduced Mrp1/MRP1 (Abcc1/ABCC1) activity concomitant with a partial shift of Mrp1/MRP1 (Abcc1/ABCC1) out of lipid raft fractions and partial internalization of the ABC transporter. The results suggest that reduced Mrp1 (Abcc1) function is correlated to the loss of lipid raft association but not internalization of Mrp1 (Abcc1).