title: The human multidrug resistance P-glycoprotein is inactive when its maturation is inhibited: potential for a role in cancer chemotherapy.
abstract: The human multidrug resistance P-glycoprotein (P-gp) contributes to the phenomenon of multidrug resistance during cancer and AIDS chemotherapy. A potential novel strategy to circumvent the effects of P-gp during chemotherapy is to prevent maturation of P-gp during biosynthesis so that the transporter does not reach the cell surface. Here we report that immature, core-glycosylated P-gp that is prevented from reaching the cell surface by processing mutations or by proteasome inhibitors such as lactacystin or MG-132 exhibited no detectable drug-stimulated ATPase activity. Disulfide cross-linking analysis also showed that the immature P-gp did not exhibit ATP-induced conformational changes as found in the mature enzyme. In addition, the immature P-gp was more sensitive to trypsin than the mature enzyme. These results suggest that P-gp is unlikely to be functional immediately after synthesis. These differences in the structural and enzymatic properties of the mature and core-glycosylated, immature P-gp could potentially be used during chemotherapy, and should result in the search for compounds that can specifically inhibit the maturation of P-gp.
authors.affiliation: MRC Group in Membrane Biology, Department of Medicine and Department of Biochemistry, University of Toronto, Ontario M5S 1A8, Canada.
authors.forename: T W
authors.initials: TW
authors.lastname: Loo
authors.forename: D M
authors.initials: DM
authors.lastname: Clarke
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000187:drug effects; D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000163:Acquired Immunodeficiency Syndrome / Q000188:drug therapy; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001692:Biological Transport; D002462:Cell Membrane / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000502:physiology*; D006031:Glycosylation; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000187:drug effects; D009369:Neoplasms / Q000188:drug therapy; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation / Q000187:drug effects; D017510:Protein Folding; D011498:Protein Precursors / Q000096:biosynthesis* / Q000187:drug effects; D011499:Protein Processing, Post-Translational
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D011498:Protein Precursors; C067713:lactacystin; D000255:Adenosine Triphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine