The human ATP-binding cassette (ABC) transporter superfamily

The ATP-binding cassette (ABC) transporter superfamily contains membrane proteins that translocate a variety of substrates across extra- and intra-cellular membranes. Genetic variation in these genes is the cause of or contributor to a wide variety of human disorders with Mendelian and complex inheritance, including cystic fibrosis, neurological disease, retinal degeneration, cholesterol and bile transport defects, anemia, and drug response. Conservation of the ATP-binding domains of these genes has allowed the identification of new members of the superfamily based on nucleotide and protein sequence homology. Phylogenetic analysis is used to divide all 48 known ABC transporters into seven distinct subfamilies of proteins. For each gene, the precise map location on human chromosomes, expression data, and localization within the superfamily has been determined. These data allow predictions to be made as to potential functions or disease phenotypes associated with each protein. In this paper, we review the current state of knowledge on all human ABC genes in inherited disease and drug resistance. In addition, the availability of the complete Drosophila genome sequence allows the comparison of the known human ABC genes with those in the fly genome. The combined data enable an evolutionary analysis of the superfamily. Complete characterization of all ABC from the human genome and from model organisms will lead to important insights into the physiology and the molecular basis of many human disorders.

The Human ATP-Binding Cassette (ABC) Transporter Superfamily

Mammalian drug efflux transporters of the ATP binding cassette (ABC) family: an overview.

The human Dubin-Johnson syndrome and its animal model, the TR − rat, are characterized by a chronic conjugated hyperbilirubinemia. TR − rats are defective in the canalicular multispecific organic anion transporter (cMOAT), which mediates hepatobiliary excretion of numerous organic anions. The complementary DNA for rat c moat , a homolog of the human multidrug resistance gene (h MRP1 ), was isolated and shown to be expressed in the canalicular membrane of hepatocytes. In the TR − rat, a single-nucleotide deletion in this gene resulted in a reduced messenger RNA level and absence of the protein. It is likely that this mutation accounts for the TR − phenotype.

https://science.sciencemag.org/content/sci/271/5252/1126.full.pdf

Congenital jaundice in rats with a mutation in a multidrug resistance-associated protein gene.

Multidrug Resistance Proteins (MRPs), together with the cystic fibrosis conductance regulator (CFTR/ABCC7) and the sulfonylurea receptors (SUR1/ABCC8 and SUR2/ABCC9) comprise the 13 members of the ...

Transmembrane transport of endo- and xenobiotics by mammalian ATP-binding cassette multidrug resistance proteins

The multidrug-resistance associated protein MRP is a 180- to 195-kDa membrane protein associated with resistance of human tumor cells to cytotoxic drugs. We have investigated how MRP confers drug resistance in SW-1573 human lung carcinoma cells by generating a subline stably transfected with an expression vector containing MRP cDNA. MRP-overexpressing SW-1573 cells are resistant to doxorubicin, daunorubicin, vincristine, VP-16, colchicine, and rhodamine 123, but not to 4'-(9-acridinylamino)methanesulfon-m-anisidide or taxol. The intracellular accumulation of drug (daunorubicin, vincristine, and VP-16) is decreased and the efflux of drug (daunorubicin) is increased in the transfectant. The decreased accumulation of daunorubicin is abolished by permeabilization of the plasma membrane with digitonin, showing that MRP can lower the intracellular daunorubicin level against a concentration gradient. Anti-MRP antisera predominantly stain the plasma membrane of MRP-overexpressing cells. We conclude that MRP is a plasma membrane drug-efflux pump.

https://www.pnas.org/content/pnas/91/19/8822.full.pdf

The human multidrug resistance-associated protein MRP is a plasma membrane drug-efflux pump.

The P-glycoprotein-mediated relative decrease in cytosolic free drug concentration is similar for several anthracyclines with varying lipophilicity

P-Glycoprotein (P-gp) and multidrug resistance protein (MRP) are plasma membrane associated proteins which can confer multidrug resistance (MDR) to cancer cells by lowering the intracellular amount of drug. Although clinical trials with MDR-reverting agents have been initiated, not much attention has been paid to blood components which may modulate the activity of P-gp or MRP. The present investigation was performed to identify and characterize blood components which may influence the drug content and the drug cytotoxicity of MDR cells. Human plasma, from healthy volunteers, was tested for its effects on the daunorubicin (DNR) accumulation and cytotoxicity in the MDR cell lines SW-1573/2R160 (2R160) and GLC4/ADR containing P-gp and MRP, respectively. The data were compared to the effects observed in wild-type cells. MDR-modifying plasma components were isolated by extraction procedures and characterized using ultrafiltration, high-performance liquid chromatography (HPLC) and mass spectrometry. An increase in the proportion of plasma in the culture medium led to a reduction of the ratio between the DNR content of wild-type and corresponding MDR cells. At 100% plasma we observed an increase in the cellular DNR content of 2R160 cells, which was 10-30% (median 18%) of the maximum possible increase induced by well-known MDR-reverting agents, such as verapamil (for GLC4/ADR cells: 10-20%, median 15%). The DNR cytotoxicity in MDR cells also increased with an increasing amount of plasma included in the culture media. There was neither an increase in the cellular DNR content nor an effect on the DNR cytotoxicity in wild-type cells. Plasma extract analysis by HPLC showed a major peak which increased the DNR content of MDR cells. The HPLC column retention time of this fraction was identical to that of a standard of cortisol and it was further confirmed to be cortisol using mass spectrometry. Moreover, inclusion of a standard of cortisol in culture media induced a similar effect. We analyzed the data for one of the plasma pools and found that blood cortisol was responsible for the MDR-modulating effect only for 35% of the effect of 100% plasma. Other plasma components were responsible for the remaining modulation effect on MDR cells. In conclusion, the DNR pumping activity of P-gp and MRP is inhibited by human plasma, resulting in 10-30% of the maximum possible increase in cellular drug content. Based on cellular pharmacokinetic calculations this percentage will most likely increase at clinical levels of drug resistance (reaching 40-50%). In one sample blood cortisol accounted for 35% of the effect of plasma on the DNR content in MDR 2R160 cells. These data show the need for additional studies to test plasma samples for their MDR modulating effects before the administration of MDR-reverting agents in chemotherapy. The data suggest that the effectiveness of chemotherapeutic drugs may be enhanced when administered in accordance with the circadian peak of endogenous corticoids.

Multidrug resistance-modifying components in human plasma with potential clinical significance.

Multidrug-resistant, human non-small-cell lung carcinoma SW-1573/2R120 (2R120) cells, not containing the drug efflux pump P-glycoprotein (Pgp), have reduced initial daunorubicin (DN) accumulation rates and decreased cellular steady-state drug concentrations. Previously we found indications of the presence of a plasma membrane "vacuum cleaner", pumping DN directly from the membrane, and reported evidence of active DN pumping using digitonin. Further evidence of active DN pumping is now provided via a different methodology and the active drug pump flux is estimated. Cells were exposed to a flowing medium containing the cytotoxic agent DN. After reaching a steady state, in which net DN uptake equals net DN efflux, high concentration pulses of vincristine (VCR) were injected into the flowing medium. A rapid increase in cellular DN content was observed, while only a minimal effect was seen in SW-1573 wild-type cells. After passage of the VCR pulse, the extra accumulated DN was effluxed against a concentration gradient. Upon increasing the VCR concentration, a maximum pump inhibition was reached which was similar to the effect of cellular energy depletion. Similar effects were observed for Pgp-containing SW-1573/2R160 (2R160) cells as well as non-Pgp MDR human small-cell lung carcinoma GLC4/ADR cells. With increasing extracellular DN concentrations, saturation of the VCR-induced DN influx was observed (DN medium concentration 2.5 microM at 1/2 Vmax). At an extracellular DN concentration of 5 microM, higher concentrations of VCR were needed to reach the maximum effect in 2R120 cells than at 0.5 microM DN. This is an indication of competitive interaction between DN and VCR for the putative DN efflux system. In summary, we found indications of inhibition of active DN efflux by VCR and DN efflux against a concentration gradient in non-Pgp MDR 2R120 and GLC4/ADR cells. These features are consistent with the presence of a multidrug transporter, different from Pgp, in the plasma membrane of these cells.

H.S. Mülder

Papers

The human multidrug resistance-associated protein MRP is a plasma membrane drug-efflux pump.

The P-glycoprotein-mediated relative decrease in cytosolic free drug concentration is similar for several anthracyclines with varying lipophilicity

Multidrug resistance-modifying components in human plasma with potential clinical significance.

Daunorubicin efflux against a concentration gradient in non-P-glycoprotein multidrug-resistant lung-cancer cells