title: P-Glycoprotein is not present in mitochondrial membranes.
abstract: Recent reports have indicated the presence of P-glycoprotein in crude mitochondrial membrane fractions, leading to the assumption that P-glycoprotein is present in mitochondrial membranes, and may be involved in transport across these membranes. To determine the validity of this claim, two cell lines overexpressing endogenous P-glycoprotein were investigated. Using various centrifugation steps, mitochondria were purified from these cells and analyzed by Western blot reaction with the anti-P-glycoprotein antibody C219 and organelle-specific antibodies. While P-glycoprotein is present in crude mitochondrial fractions, these fractions are contaminated with plasma membranes. Further purification of the mitochondria to remove plasma membranes revealed that P-glycoprotein is not expressed in mitochondria of the KB-V1 (vinblastine-resistant KB-3-1 cells) or MCF-7(ADR) (adriamycin-resistant MCF-7 cells) cell lines. To further substantiate these findings, we used confocal microscopy and the anti-P-glycoprotein antibody 17F9. This demonstrated that in intact cells, P-glycoprotein is not present in mitochondria and is primarily localized to the plasma membrane. These findings are consistent with the role of P-glycoprotein in conferring multidrug resistance by decreasing cellular drug accumulation. Therefore, contrary to previous speculation, P-glycoprotein does not confer cellular protection by residing in mitochondrial membranes.
authors.affiliation: Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH/DHHS, Bethesda, MD 20892-4256, USA.
authors.forename: Jill K
authors.initials: JK
authors.lastname: Paterson
authors.forename: Michael M
authors.initials: MM
authors.lastname: Gottesman
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000378:metabolism*; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005456:Fluorescent Dyes