title: The small GTPases Rab5 and RalA regulate intracellular traffic of P-glycoprotein.
abstract: P-glycoprotein (P-gp) is a plasma membrane glycoprotein that can cause multidrug resistance (MDR) of cancer cells by acting as an ATP-dependent drug efflux pump. The regulatory effects of the small GTPases Rab5 and RalA on the intracellular trafficking of P-gp were investigated in HeLa cells. As expected, overexpressed enhanced green fluorescent protein (EGFP)-tagged P-gp (P-gp-EGFP) is mainly localised to the plasma membrane. However, upon cotransfection of either dominant negative Rab5 (Rab5-S34N) or constitutively active RalA (RalA-G23V) the intracellular P-gp-EGFP levels increased approximately 9 and 13 fold, respectively, compared to control P-gp-EGFP cells. These results suggest that Rab5 and RalA regulate P-gp trafficking between the plasma membrane and an intracellular compartment. In contrast, coexpression of constitutively active Rab5 (Rab5-Q79L) or dominant negative RalA (RalA-S28N) had no effect on the localisation of P-gp-EGFP. Furthermore, the intracellular accumulation of daunorubicin, a substrate for P-gp, increased significantly with an increased intracellular localisation of P-gp-EGFP. These results imply that it may be possible to overcome MDR by controlling the plasma membrane localisation of P-gp.
authors.affiliation: Faculty of Pharmacy, The University of Sydney, NSW 2006, Australia.
authors.forename: Dong
authors.initials: D
authors.lastname: Fu
authors.forename: Ellen M
authors.initials: EM
authors.lastname: van Dam
authors.forename: Adam
authors.initials: A
authors.lastname: Brymora
authors.forename: Iain G
authors.initials: IG
authors.lastname: Duggin
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Robinson
authors.forename: Basil D
authors.initials: BD
authors.lastname: Roufogalis
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003630:Daunorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple; D006801:Humans; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020725:ral GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D000903:Antibiotics, Antineoplastic; D011993:Recombinant Fusion Proteins; C492198:RALA protein, human; D020696:rab5 GTP-Binding Proteins; D020725:ral GTP-Binding Proteins; D003630:Daunorubicin