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Idriss HT, Hannun YA, Boulpaep E, Basavappa S. Regulation of volume-activated chloride channels by P-glycoprotein: phosphorylation has the final say! J Physiol 2000; 524 Pt 3:629-36. [PMID: 10790147 PMCID: PMC2269906 DOI: 10.1111/j.1469-7793.2000.00629.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
P-glycoprotein (Pgp) is a transmembrane transporter causing efflux of a number of chemically unrelated drugs and is responsible for resistance to a variety of anticancer drugs during chemotherapy. Pgp overexpression in cells is also associated with volume-activated chloride channel activity; Pgp is thought to regulate such activity. Reversible phosphorylation is a possible mechanism for regulating the transport and chloride channel regulation functions of Pgp. Protein kinase C (PKC) is a good candidate for inducing such phosphorylation. Hierarchical multiple phosphorylation (e.g. of different serines and with different PKC isoforms) may shuttle the protein between its different states of activity (transport or channel regulation). Cell volume changes may trigger phosphorylation of Pgp at sites causing inhibition of transport. The possible regulation of chloride channels by Pgp and the potential involvement of reversible phosphorylation in such regulation is reviewed.
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Affiliation(s)
- H T Idriss
- School of Biomedical Sciences, Centre for Biomolecular Sciences, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, Scotland, UK.
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2
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Wang L, Chen L, Walker V, Jacob TJ. Antisense to MDR1 mRNA reduces P-glycoprotein expression, swelling-activated C1- current and volume regulation in bovine ciliary epithelial cells. J Physiol 1998; 511 ( Pt 1):33-44. [PMID: 9679161 PMCID: PMC2231096 DOI: 10.1111/j.1469-7793.1998.033bi.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Native ciliary epithelial cells from the ciliary epithelium of the eye exhibit anti-P-glycoprotein (P-gp) immunofluorescence. We have used an antisense 'knock-down' approach to investigate the relationship between P-gp and the volume-activated chloride current (IC1,swell) and its role in volume regulation. An antisense oligonucleotide to the human multidrug resistance (MDR1) gene, taken up by the cells in a dose-dependent manner, reduced P-gp immunofluorescence, inhibited IC1,swell and significantly increased the latency of activation of IC1,swell. Increasing the hypotonic stress did not result in an increased activation of ICl,swell. MDR1 antisense 'knock-down' also reduced the ability of the cells to volume regulate following a hypotonic challenge. These cells are known to express at least two volume-activated chloride channels, and the data suggest that P-gp is involved in the activation pathway of a subset of channels that contribute to whole-cell IC1,swell and participate in volume regulation.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/analysis
- ATP Binding Cassette Transporter, Subfamily B, Member 1/biosynthesis
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- Animals
- Cattle
- Cells, Cultured
- Chlorides/metabolism
- Cilia/physiology
- Epithelial Cells/drug effects
- Epithelial Cells/physiology
- Gene Expression Regulation/drug effects
- Humans
- Hypotonic Solutions
- Membrane Potentials
- Oligodeoxyribonucleotides, Antisense/pharmacokinetics
- Oligodeoxyribonucleotides, Antisense/pharmacology
- Patch-Clamp Techniques
- RNA, Messenger/genetics
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Affiliation(s)
- L Wang
- School of Molecular and Medical Biosciences, University of Wales, Cardiff CF1 3US, UK
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3
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Aziz SM, Worthen DR, Yatin M, Ain KB, Crooks PA. A unique interaction between polyamine and multidrug resistance (P-glycoprotein) transporters in cultured Chinese hamster ovary cells transfected with mouse mdr-1 gene. Biochem Pharmacol 1998; 56:181-7. [PMID: 9698071 DOI: 10.1016/s0006-2952(98)00132-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We have shown that a functional link exists between the polyamine transporter and the multi-drug resistance (MDR) efflux transporter (P-glycoprotein, P-gp) in MDR-positive cancer cells. To further explore the nature of this interaction, we have examined the effect of reduced polyamine transport activity on cellular expression and activity of P-gp acquired by either selection or transfection. Chinese hamster ovary (CHO) cells and their polyamine transport-deficient mutants (CHOMGBG) were transfected with mouse mdr-1b gene. The activity of P-gp in these cells was quantified by measuring cellular accumulation of radiolabeled taxol and etoposide in the presence and absence of the P-gp modulator SDZ PSC-833 (valspodar; a semisynthetic undecapeptide derived from cyclosporin D). The mdr-1b-transfected CHO cells accumulated 2- to 3-fold less taxol and etoposide than the controls, an accumulation defect reversed by the potent MDR modulator PSC-833. Despite expression of P-gp on the surface of mdr-1b-transfected CHOMGBG cells, this classic MDR phenotype was not observed. Similarly, CHO cells, but not CHOMGBG cells, showed MDR activity after selection with doxorubicin as determined by reduced accumulation of radiolabeled taxol. Treatment with 50 microM of reduced polymer of spermine and glutaraldehyde, a selective blocker of the polyamine transport system, reduced MDR activity in mdr-1-transfected CHO cells and restored cellular accumulation of etoposide and taxol to control levels, effects not observed in mdr-1-transfected CHOMGBG cells. Notably, mdr-1-transfected CHO cells were 4- to 16-fold more resistant to the cytotoxic effects of the P-gp substrates doxorubicin, taxol, and etoposide than were the mdr-1-transfected CHOMGBG cells. CHO cells transfected with the mdr-1 gene exhibited a 23% reduction in cellular uptake of [14C]spermidine compared with untransfected controls; spermidine accumulation in CHOMGBG cells was no different than that in untransfected controls. These data suggest that the existence of a functioning polyamine transport system may be a requirement for MDR transporter activity, while the expression of functioning P-gp appears to reduce polyamine transporter activity.
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Affiliation(s)
- S M Aziz
- Department of Pharmacy Services and Division of Oncology and Hematology, Henry Ford Hospital, Detroit, MI 48202-2689, USA
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Bray PG, Ward SA. A comparison of the phenomenology and genetics of multidrug resistance in cancer cells and quinoline resistance in Plasmodium falciparum. Pharmacol Ther 1998; 77:1-28. [PMID: 9500157 DOI: 10.1016/s0163-7258(97)00083-1] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Plasmodium falciparum is the causative agent of the most deadly form of human malaria. Chemotherapy traditionally has been the main line of defense against this parasite, and chloroquine, the drug of choice, has been one of the most successful drugs ever developed. Unfortunately, the evolution and spread of resistance to chloroquine and other quinoline-containing drugs means that these compounds are now virtually useless in many endemic areas. Future prospects for the use of quinoline compounds improved considerably when it was demonstrated that chloroquine resistance could be circumvented in vitro by a number of structurally and functionally unrelated compounds such as verapamil and desipramine. The phenomenon of resistance reversal by compounds such as verapamil is also a key feature of drug resistance in mammalian cells, and this has raised the possibility that the underlying mechanisms of drug resistance of the two cell types could be similar. This hypothesis has prompted a large number of studies into the genetics and biochemistry of resistance to quinoline-containing drugs in P. falciparum. Both the genetic and the biochemical studies have raised issues of controversy and stimulated much debate. These issues are discussed in this review, in the context of a comparison with the genetics and biochemistry of multidrug resistance in mammalian cells.
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Affiliation(s)
- P G Bray
- Department of Pharmacology and Therapeutics, University of Liverpool, UK
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5
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Kourie JI. ATP-sensitive voltage- and calcium-dependent chloride channels in sarcoplasmic reticulum vesicles from rabbit skeletal muscle. J Membr Biol 1997; 157:39-51. [PMID: 9141357 DOI: 10.1007/s002329900214] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Chloride channels in the sarcoplasmic reticulum (SR) are thought to play an essential role in excitation-contraction (E-C) coupling by balancing charge movement during calcium release and uptake. In this study the nucleotide-sensitivity of Cl- channels in the SR from rabbit skeletal muscle was investigated using the lipid bilayer technique. Two distinct ATP-sensitive Cl- channels that differ in their conductance and kinetic properties and in the mechanism of ATP-induced channel inhibition were observed. The first, a nonfrequent 150 pS channel was inhibited by trans (luminal) ATP, and the second, a common 75 pS small chloride (SCl) channel was inhibited by cis (cytoplasmic) ATP. In the case of the SCl channel the ATP-induced reversible decline in the values of current (maximal current amplitude, Imax and integral current, I') and kinetic parameters (frequency of opening FO, probability of the channel being open PO, mean open TO and closed Tc times) show a nonspecific block of the voltage- and Ca2+-dependent SCl channel. ATP was a more potent blocker from the cytoplasmic side than from the luminal side of the channel. The SCl channel block was not due to Ca2+ chelation by ATP, nor to phosphorylation of the channel protein. The inhibitory action of ATP was mimicked by the nonhydrolyzable analogue adenylylimidodiphosphate (AMP-PNP) in the absence of Mg2+. The inhibitory potency of the adenine nucleotides was charge dependent in the following order ATP4- > ADP3- > > > AMP2-. The data suggest that ATP-induced effects are mediated via an open channel block mechanism. Modulation of the SCl channel by [ATP]cis and [Ca2+]cis indicates that (i) this channel senses the bioenergetic state of the muscle fiber and (ii) it is linked to the ATP-dependent cycling of the Ca2+ between the SR and the sarcoplasm.
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Affiliation(s)
- J I Kourie
- Muscle Research Group, Division of Neuroscience, John Curtin School of Medical Research, ANU, PO Box 334, Canberra City, ACT, 2601 Australia
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Abstract
P-glycoprotein turns out not to be 'VSOAC', a known channel activated by cell swelling; it does seem to influence cell-volume recovery after swelling, but the physiological importance of this effect is presently unclear.
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Affiliation(s)
- J J Wine
- Cystic Fibrosis Research Laboratory, Stanford University, California 94305-2130, USA
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7
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Basavappa S, Ellory JC. The role of swelling-induced anion channels during neuronal volume regulation. Mol Neurobiol 1996; 13:137-53. [PMID: 8938648 DOI: 10.1007/bf02740638] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Regulation of cell volume is an essential function of most mammalian cells. In the cells of the central nervous system, maintenance of cell osmolarity and, hence, volume, is particularly crucial because of the restrictive nature of the skull. Cell volume regulation involves a variety of pathways, with considerable differences between cell types. One common pathway activated during hypo-osmotic stress involves chloride (Cl-) channels. However, hypo-osmotically stimulated anion permeability can be regulated by a diverse array of second messengers. Although neuronal swelling can occur in a number of pathological and nonpathological conditions, our understanding of neuronal volume regulation is limited. This article summarizes our current understanding of the role of anion channels during neuronal volume regulation.
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Affiliation(s)
- S Basavappa
- University Laboratory of Physiology, University of Oxford, UK
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Luckie DB, Krouse ME, Law TC, Sikic BI, Wine JJ. Doxorubicin selection for MDR1/P-glycoprotein reduces swelling-activated K+ and Cl- currents in MES-SA cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C1029-36. [PMID: 8928730 DOI: 10.1152/ajpcell.1996.270.4.c1029] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
To test the hypothesis that P-glycoprotein enhances swelling currents through regulation of volume-sensitive Cl- channels [recently termed VSOAC (volume-sensitive osmolyte and anion channel)], a human uterine sarcoma cell line (MES-SA) and its doxorubicin-selected counterpart (Dx5) were studied. P-glycoprotein mRNA and protein levels were detected only in Dx5 cells. However, whole cell patch-clamp experiments showed that swollen Dx5 cells (n = 5) produced smaller VSOAC currents than MES-SA cells (n = 4; 106 +/- 26 pA/pF vs. 232 +/- 76 pA/pF at 90 mV). In radioisotopic efflux experiments, both swelling-activated 125I (Cl-) currents (n = 15) and 86Rb (K+) currents (n = 8) were found to be two-to fourfold smaller in the Dx5 (high P-glycoprotein) cells. Inhibitors of P-glycoprotein showed no specificity for the doxorubicin-selected cells (Dx5). Dideoxyforskolin (100 microM) blocked swelling-activated 125I efflux equally in both cell lines, whereas 100 microM verapamil had no effect. Thus, in this cell line, selection for P-glycoprotein expression is associated with reduced swelling currents. These findings suggest that P-glycoprotein expression does not directly facilitate VSOAC.
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Affiliation(s)
- D B Luckie
- Cystic Fibrosis Research Laboratory, Stanford University, California 94305, USA
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Affiliation(s)
- Q al-Awqati
- College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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Morin XK, Bond TD, Loo TW, Clarke DM, Bear CE. Failure of P-glycoprotein (MDR1) expressed in Xenopus oocytes to produce swelling-activated chloride channel activity. J Physiol 1995; 486 ( Pt 3):707-14. [PMID: 7473231 PMCID: PMC1156558 DOI: 10.1113/jphysiol.1995.sp020846] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. P-glycoprotein, the protein product of the multidrug resistance (MDR1) gene, has ATP-dependent transporter activity. It has been suggested that P-glycoprotein may also function as a volume-regulated chloride channel or chloride channel regulator. To assess the chloride channel function of P-glycoprotein, we examined swelling-activated chloride conductances in Xenopus oocytes injected with human MDR1 cRNA. 2. Functional expression of P-glycoprotein in Xenopus oocytes was confirmed using Western blot analysis and by assessing transport of the P-glycoprotein substrate, calcein AM. 3. Endogenous, swelling-activated chloride conductances were virtually absent by the time P-glycoprotein expression was confirmed. Thus, this expression system afforded the advantage of assessing putative MDR1-associated chloride currents in the absence of background currents. 4. The currents activated by hypotonic shock (50%) in both MDR1-injected and control (water-injected) oocytes were not significantly different. The swelling response was due in part to the activation of a potassium-selective conductance which could be inhibited by barium. No chloride-selective currents were activated by hypotonic shock in the presence or absence of barium. Therefore, we conclude that P-glycoprotein expression does not produce a swelling-activated chloride conductance in the Xenopus oocyte expression system.
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Affiliation(s)
- X K Morin
- Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada
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11
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Abstract
Chloride channels are present in a variety of intracellular organelles (Golgi, endosomes, endoplasmic reticulum, and sarcoplasmic reticulum) where they serve largely to shunt the membrane potential created by other ion-translocating processes. Electrophysiological studies have shown that the Cl- channels of the endoplasmic and sarcoplasmic reticula facilitate the efflux of Ca2+. In the Golgi and some endosomes, the open Cl- channels (probably the cystic fibrosis transmembrane conductance regulator) favor accumulation of H+.
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Affiliation(s)
- Q al-Awqati
- College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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12
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Abstract
The overexpression of the P-glycoprotein, the MDR1 gene product, has been linked to the development of resistance to multiple cytotoxic natural product anticancer drugs in certain cancers and cell lines derived from tumors. P-glycoprotein, a member of the ATP-binding cassette (ABC) superfamily of transporters, is believed to function as an ATP-dependent drug efflux pump with broad specificity for chemically unrelated hydrophobic compounds. We review here recent studies on the purification and reconstitution of P-glycoprotein to elucidate the mechanism of drug transport. P-glycoprotein from the human carcinoma multidrug resistant cell line, KB-V1, was purified by sequential chromatography on anion exchange followed by a lectin (wheat germ agglutinin) column. Proteoliposomes reconstituted with pure protein exhibited high levels of drug-stimulated ATPase activity as well as ATP-dependent [3H]vinblastine accumulation. Both the ATPase and vinblastine transport activities of the reconstituted P-glycoprotein were inhibited by vanadate. In addition, the vinblastine transport was inhibited by verapamil and daunorubicin. These studies provide strong evidence that the human P-glycoprotein functions as an ATP-dependent drug transporter. The development of the reconstitution system and the availability of recombinant protein in large amounts due to recent advances in overexpression of P-glycoprotein in a heterologous expression system should facilitate a better understanding of the function of this novel protein.
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Affiliation(s)
- S V Ambudkar
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Abstract
The multidrug resistance P-glycoprotein (P-gp) is an active drug transporter which can expel hydrophobic compounds from cells. Expression of P-gp has many effects on cells and tissues and the physiological function, or functions, of P-gp are still unclear. Recently, expression of P-gp has been associated with altered activity of chloride channels which play a role in regulating cell volume of response to osmotic shock or nutrient uptake. The nature and physiological role of this association has been a subject of some debate. In this article, mechanisms by which P-gp might influence cell volume-activated chloride currents is discussed, and the potential physiological role of this regulation considered.
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Affiliation(s)
- C F Higgins
- Nuffield Department of Clinical Biochemistry, University of Oxford, John Radcliffe Hospital, UK
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Higgins CF. Volume-activated chloride currents associated with the multidrug resistance P-glycoprotein. J Physiol 1995; 482:31S-36S. [PMID: 7730973 PMCID: PMC1334234 DOI: 10.1113/jphysiol.1995.sp020562] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The ability to regulate volume is an important property of most, if not all cells. In epithelial cells, amongst others, cell volume-activated chloride channels are central to this response. The molecular identities of these channels are not yet known. Expression of the human multidrug resistance P-glycoprotein (P-gp) has been associated with cell volume-regulated chloride currents, although the nature of this association is the subject of debate. Recent data indicate that P-gp acts by regulating the activation of an endogenous channel protein. In this review, evidence associating P-gp with cell volume-activated chloride currents, and the possible mechanisms by which this might be achieved, are discussed.
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Affiliation(s)
- C F Higgins
- Nuffield Department of Clinical Biochemistry, University of Oxford, John Radcliffe Hospital
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Kirk J, Kirk K. Inhibition of volume-activated I- and taurine efflux from HeLa cells by P-glycoprotein blockers correlates with calmodulin inhibition. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)43891-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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