HETEROLOGOUS EXPRESSION SYSTEMS FOR P-GLYCOPROTEIN - ESCHERICHIA-COLI, YEAST, AND BACULOVIRUS

Chemotherapy, though it remains one of the front-line weapons used to treat human cancer, is often ineffective due to drug resistance mechan isms manifest in tumor cells. One common pattern of drug resistance, c haracterized by simultaneous resistance to multiple amphipathic, but o therwise structurally dissimilar anticancer drugs, is termed multidrug resistance. Multidrug resistance in various model systems, covering t he phylogenetic range from bacteria to man, can be conferred by mammal ian P-glycoproteins (PGPs), often termed multidrug transporters. PGPs are 170-kD polytopic membrane proteins, predicted to consist of two ho mologous halves, each with six membrane spanning regions and one ATP b inding site. They are members of the ATP-binding cassette (ABC) superf amily of transporters, and are known to function biochemically as ener gy-dependent drug efflux pumps. However, much remains to be learned ab out PGP structure-function relationships, membrane topology, posttrans lational regulation, and bioenergetics of drug transport. Much of the recent progress in the study of the human and mouse PGPs has come from heterologous expression systems which offer the benefits of ease of g enetic selection and manipulation, and/or short generation times of th e organism in which PGPs are expressed, and/or high-level expression o f recombinant PGP. Here we review recent studies of PGP in E. coil, ba culovirus, and yeast systems and evaluate their utility for the study of PGPs, as well as other higher eukaryotic membrane proteins.