MDR3 P-glycoprotein, a phosphatidylcholine translocase, transports several cytotoxic drugs and directly interacts with drugs as judged by interference with nucleotide trapping.
The human MDR3 gene is a member of the multidrug resistance (MDR) gene family. The MDR3 P-glycoprotein is a transmembrane protein that translocates phosphatidylcholine. The MDR1 P-glycoprotein related transports cytotoxic drugs. Its overexpression can make cells resistant to a variety of drugs. Attempts to show that MDR3 P-glycoprotein can cause MDR have been unsuccessful thus far. Here, we report an increased directional transport of several MDR1 P-glycoprotein substrates, such as digoxin, paclitaxel, and vinblastine, through polarized monolayers of MDR3-transfected cells. Transport of other good MDR1 P-glycoprotein substrates, including cyclosporin A and dexamethasone, was not detectably increased. MDR3 P-glycoprotein-dependent transport of a short-chain phosphatidylcholine analog and drugs was inhibited by several MDR reversal agents and other drugs, indicating an interaction between these compounds and MDR3 P-gp. Insect cell membranes from Sf9 cells overexpressing MDR3 showed specific MgATP binding and a vanadate-dependent, N-ethylmaleimide-sensitive nucleotide trapping activity, visualized by covalent binding with [alpha-(32)P]8-azido-ATP. Nucleotide trapping was (nearly) abolished by paclitaxel, vinblastine, and the MDR reversal agents verapamil, cyclosporin A, and PSC 833. We conclude that MDR3 P-glycoprotein can bind and transport a subset of MDR1 P-glycoprotein substrates. The rate of MDR3 P-glycoprotein-mediated transport is low for most drugs, explaining why this protein is not detectably involved in multidrug resistance. It remains possible, however, that drug binding to MDR3 P-glycoprotein could adversely affect phospholipid or toxin secretion under conditions of stress (e.g. in pregnant heterozygotes with one MDR3 null allele).
Smith
A J
AJ
Division of Molecular Biology and Center for Biomedical Genetics, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
van Helvoort
A
A
van Meer
G
G
Szabo
K
K
Welker
E
E
Szakacs
G
G
Varadi
A
A
Sarkadi
B
B
Borst
P
P
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics / Q000378:metabolism*; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D016764:Cell Polarity; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D003524:Cyclosporins / Q000494:pharmacology; D003603:Cytotoxins / Q000378:metabolism*; D003630:Daunorubicin / Q000378:metabolism; D004077:Digoxin / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology; D006801:Humans; D007559:Ivermectin / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D017239:Paclitaxel / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera / Q000166:cytology; D013552:Swine; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism
D018435:ATP Binding Cassette Transporter, Subfamily B; D018528:ATP-Binding Cassette Transporters; D003524:Cyclosporins; D003603:Cytotoxins; D004364:Pharmaceutical Preparations; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; D014747:Vinblastine; D007559:Ivermectin; D004077:Digoxin; D016572:Cyclosporine; D000255:Adenosine Triphosphate; C095122:multidrug resistance protein 3; D014700:Verapamil; D017239:Paclitaxel; C070272:valspodar; D003630:Daunorubicin