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Suominen L, Sjöstedt N, Vellonen KS, Gynther M, Auriola S, Kidron H. In vitro identification of decreased function phenotype ABCG2 variants. Eur J Pharm Sci 2023; 188:106527. [PMID: 37451410 DOI: 10.1016/j.ejps.2023.106527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 07/09/2023] [Accepted: 07/11/2023] [Indexed: 07/18/2023]
Abstract
Reduced activity of efflux transporter ABCG2, caused e.g., by inhibition or decreased function genetic variants, can increase drug absorption and plasma levels. ABCG2 has one clinically significant single nucleotide variant Q141K (c.421C>A), which leads to decreased protein levels and transport activity. In addition to Q141K, ABCG2 has over 500 rare (<1% minor allele frequency) nonsynonymous variants, but their functionality remains unknown. We studied the transport activity and abundance of 30 rare ABCG2 variants. The variants were transiently expressed in HEK293 cells. Transport activity and protein abundance were measured from inside-out crude membrane vesicles. Results were normalised to the reference ABCG2, while Q141K was used to categorise variants into decreased and normal function phenotypes based on their apparent transport activity. Fourteen variants (G80E, D128V, T434M, Q437R, C438R, C438W, C438Y, L479S, P480L, S486N, T512N, S519P, G553D and K647E) had similar or lower apparent transport activity than Q141K and thus were categorised as having a decreased function phenotype. Protein abundance could not explain all of the observed changes in transport activity: Only six variants (D128V, Q437R, C438R, S519P, G553D, and K647E) had similar or lower abundance compared to Q141K. The decreased function variants may increase systemic drug exposure and therefore cause interindividual variability in pharmacokinetics. In the future, in vitro phenotype classification may help to design personalised drug treatments.
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Affiliation(s)
- Laura Suominen
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland
| | - Noora Sjöstedt
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland
| | | | - Mikko Gynther
- School of Pharmacy, University of Eastern Finland, Kuopio FI-70210, Finland
| | - Seppo Auriola
- School of Pharmacy, University of Eastern Finland, Kuopio FI-70210, Finland
| | - Heidi Kidron
- Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland.
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2
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A Structure-Based View on ABC-Transporter Linked to Multidrug Resistance. Molecules 2023; 28:molecules28020495. [PMID: 36677553 PMCID: PMC9862083 DOI: 10.3390/molecules28020495] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Revised: 11/29/2022] [Accepted: 12/16/2022] [Indexed: 01/06/2023] Open
Abstract
The discovery of the first ATP-binding cassette (ABC) transporter, whose overexpression in cancer cells is responsible for exporting anticancer drugs out of tumor cells, initiated enormous efforts to overcome tumor cell multidrug resistance (MDR) by inhibition of ABC-transporter. Because of its many physiological functions, diverse studies have been conducted on the mechanism, function and regulation of this important group of transmembrane transport proteins. In this review, we will focus on the structural aspects of this transporter superfamily. Since the resolution revolution of electron microscope, experimentally solved structures increased rapidly. A summary of the structures available and an overview of recent structure-based studies are provided. More specifically, the artificial intelligence (AI)-based predictions from AlphaFold-2 will be discussed.
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3
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Mehendale-Munj S, Sawant S. Breast Cancer Resistance Protein: A Potential Therapeutic Target for Cancer. Curr Drug Targets 2021; 22:420-428. [PMID: 33243119 DOI: 10.2174/1389450121999201125200132] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 10/05/2020] [Accepted: 10/14/2020] [Indexed: 11/22/2022]
Abstract
Breast Cancer Resistance Protein (BCRP) is an efflux transporter responsible for causing multidrug resistance (MDR). It is known to expel many potent antineoplastic drugs, owing to its efflux function. Efflux of chemotherapeutics because of BCRP develops resistance to many drugs, leading to failure in cancer treatment. BCRP plays an important role in physiology by protecting the organism from xenobiotics and other toxins. It is a half-transporter affiliated to the ATP- binding cassette (ABC) superfamily of transporters, encoded by the gene ABCG2 and functions in response to adenosine triphosphate (ATP). Regulation of BCRP expression is critically controlled at molecular levels, which help in maintaining the balance of xenobiotics and nutrients inside the body. Expression of BCRP can be found in brain, liver, lung cancers and acute myeloid leukemia (AML). Moreover, it is also expressed at high levels in stem cells and many cell lines. This frequent expression of BCRP has an impact on the treatment procedures and, if not scrutinized, may lead to the failure of many cancer therapies.
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Affiliation(s)
- Sonali Mehendale-Munj
- Department of Pharmaceutical Chemistry, Vivekanand Education Society's College of Pharmacy, Hashu Advani Memorial Complex, Behind Collector's Colony, Chembur (E), Mumbai 400074, Affiliated to University of Mumbai, Maharashtra, India
| | - Shivangi Sawant
- Department of Pharmaceutical Chemistry, Vivekanand Education Society's College of Pharmacy, Hashu Advani Memorial Complex, Behind Collector's Colony, Chembur (E), Mumbai 400074, Affiliated to University of Mumbai, Maharashtra, India
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4
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Khunweeraphong N, Kuchler K. The first intracellular loop is essential for the catalytic cycle of the human ABCG2 multidrug resistance transporter. FEBS Lett 2020; 594:4059-4075. [PMID: 33169382 PMCID: PMC7756363 DOI: 10.1002/1873-3468.13994] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 09/03/2020] [Indexed: 12/16/2022]
Abstract
The human multidrug transporter ABCG2 is required for physiological detoxification and mediates anticancer drug resistance. Here, we identify pivotal residues in the first intracellular loop (ICL1), constituting an intrinsic part of the transmission interface. The architecture includes a triple helical bundle formed by the hot spot helix of the nucleotide‐binding domain, the elbow helix, and ICL1. We show here that the highly conserved ICL1 residues G462, Y463, and Y464 are essential for the proper cross talk of the closed nucleotide‐binding domain dimer with the transmembrane domains. Hence, ICL1 acts as a molecular spring, triggering the conformational switch of ABCG2 before substrate extrusion. These data suggest that the ABCG2 transmission interface may offer therapeutic options for the treatment of drug‐resistant malignancies.
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Affiliation(s)
- Narakorn Khunweeraphong
- Max Perutz Labs Vienna, Center for Medical Biochemistry, Campus Vienna Biocenter, Medical University of Vienna, Austria.,St. Anna Children's Cancer Research Institute-CCRI, Vienna, Austria
| | - Karl Kuchler
- Max Perutz Labs Vienna, Center for Medical Biochemistry, Campus Vienna Biocenter, Medical University of Vienna, Austria
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5
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Eckenstaler R, Benndorf RA. 3D structure of the transporter ABCG2-What's new? Br J Pharmacol 2020; 177:1485-1496. [PMID: 31985041 PMCID: PMC7060357 DOI: 10.1111/bph.14991] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Revised: 12/20/2019] [Accepted: 01/07/2020] [Indexed: 12/13/2022] Open
Abstract
ABCG2 belongs to the ABC transporter superfamily and functions as a poly-specific efflux pump. As it can transport a broad spectrum of substrates out of cells, ABCG2 is thought to alter the pharmacokinetics of drugs applied to treat certain diseases. Especially, its potential to induce resistance to chemotherapy is currently the object of intense research. To foster understanding of mechanisms relevant for substrate recognition and selection of ABCG2 substrates and to finally develop selective therapeutic modulators (e.g. inhibitors) of ABCG2 transport activity, it is important to further explore the precise 3D structure of the transporter. While efforts to elucidate the three-dimensional structure of ABCG2 using X-ray crystal structure analysis have not been successful so far, high-resolution cryo-electron microscopy-based investigations have revealed exciting new insights into the structure and function of the transporter. In this review, we will focus on these seminal publications to summarize the current understanding of tertiary and quaternary structure, homodimerization or oligomerization, and functions of the ABCG2 transporter protein.
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Affiliation(s)
| | - Ralf A Benndorf
- Institute of Pharmacy, Martin-Luther-University, Halle, Germany
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6
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Chaiswing L, St. Clair WH, St. Clair DK. Redox Paradox: A Novel Approach to Therapeutics-Resistant Cancer. Antioxid Redox Signal 2018; 29:1237-1272. [PMID: 29325444 PMCID: PMC6157438 DOI: 10.1089/ars.2017.7485] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Accepted: 01/05/2018] [Indexed: 02/06/2023]
Abstract
SIGNIFICANCE Cancer cells that are resistant to radiation and chemotherapy are a major problem limiting the success of cancer therapy. Aggressive cancer cells depend on elevated intracellular levels of reactive oxygen species (ROS) to proliferate, self-renew, and metastasize. As a result, these aggressive cancers maintain high basal levels of ROS compared with normal cells. The prominence of the redox state in cancer cells led us to consider whether increasing the redox state to the condition of oxidative stress could be used as a successful adjuvant therapy for aggressive cancers. Recent Advances: Past attempts using antioxidant compounds to inhibit ROS levels in cancers as redox-based therapy have met with very limited success. However, recent clinical trials using pro-oxidant compounds reveal noteworthy results, which could have a significant impact on the development of strategies for redox-based therapies. CRITICAL ISSUES The major objective of this review is to discuss the role of the redox state in aggressive cancers and how to utilize the shift in redox state to improve cancer therapy. We also discuss the paradox of redox state parameters; that is, hydrogen peroxide (H2O2) as the driver molecule for cancer progression as well as a target for cancer treatment. FUTURE DIRECTIONS Based on the biological significance of the redox state, we postulate that this system could potentially be used to create a new avenue for targeted therapy, including the potential to incorporate personalized redox therapy for cancer treatment.
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Affiliation(s)
- Luksana Chaiswing
- Department of Toxicology and Cancer Biology, University of Kentucky-Lexington, Lexington, Kentucky
| | - William H. St. Clair
- Department of Radiation Medicine, University of Kentucky-Lexington, Lexington, Kentucky
| | - Daret K. St. Clair
- Department of Toxicology and Cancer Biology, University of Kentucky-Lexington, Lexington, Kentucky
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7
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Residues contributing to drug transport by ABCG2 are localised to multiple drug-binding pockets. Biochem J 2018; 475:1553-1567. [PMID: 29661915 PMCID: PMC5934980 DOI: 10.1042/bcj20170923] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 03/28/2018] [Accepted: 04/16/2018] [Indexed: 01/09/2023]
Abstract
Multidrug binding and transport by the ATP-binding cassette transporter ABCG2 is a factor in the clinical resistance to chemotherapy in leukaemia, and a contributory factor to the pharmacokinetic profiles of many other prescribed drugs. Despite its importance, the structural basis of multidrug transport, i.e. the ability to transport multiple distinct chemicals, has remained elusive. Previous research has shown that at least two residues positioned towards the cytoplasmic end of transmembrane helix 3 (TM3) of the transporter play a role in drug transport. We hypothesised that other residues, either in the longitudinal span of TM3, or a perpendicular slice through the intracellular end of other TM helices would also contribute to drug binding and transport by ABCG2. Single-point mutant isoforms of ABCG2 were made at ∼30 positions and were analysed for effects on protein expression, localisation (western blotting, confocal microscopy) and function (flow cytometry) in a mammalian stable cell line expression system. Our data were interpreted in terms of recent structural data on the ABCG protein subfamily and enabled us to propose a surface-binding site for the drug mitoxantrone (MX) as well as a second, buried site for the same drug. Further mutational analysis of residues that spatially separate these two sites prompts us to suggest a molecular and structural pathway for MX transport by ABCG2.
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8
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Jackson SM, Manolaridis I, Kowal J, Zechner M, Taylor NMI, Bause M, Bauer S, Bartholomaeus R, Bernhardt G, Koenig B, Buschauer A, Stahlberg H, Altmann KH, Locher KP. Structural basis of small-molecule inhibition of human multidrug transporter ABCG2. Nat Struct Mol Biol 2018; 25:333-340. [PMID: 29610494 DOI: 10.1038/s41594-018-0049-1] [Citation(s) in RCA: 227] [Impact Index Per Article: 37.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Accepted: 02/12/2018] [Indexed: 01/16/2023]
Abstract
ABCG2 is an ATP-binding cassette (ABC) transporter that protects tissues against xenobiotics, affects the pharmacokinetics of drugs and contributes to multidrug resistance. Although many inhibitors and modulators of ABCG2 have been developed, understanding their structure-activity relationship requires high-resolution structural insight. Here, we present cryo-EM structures of human ABCG2 bound to synthetic derivatives of the fumitremorgin C-related inhibitor Ko143 or the multidrug resistance modulator tariquidar. Both compounds are bound to the central, inward-facing cavity of ABCG2, blocking access for substrates and preventing conformational changes required for ATP hydrolysis. The high resolutions allowed for de novo building of the entire transporter and also revealed tightly bound phospholipids and cholesterol interacting with the lipid-exposed surface of the transmembrane domains (TMDs). Extensive chemical modifications of the Ko143 scaffold combined with in vitro functional analyses revealed the details of ABCG2 interactions with this compound family and provide a basis for the design of novel inhibitors and modulators.
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Affiliation(s)
- Scott M Jackson
- Institute of Molecular Biology and Biophysics, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Ioannis Manolaridis
- Institute of Molecular Biology and Biophysics, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Julia Kowal
- Institute of Molecular Biology and Biophysics, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Melanie Zechner
- Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Nicholas M I Taylor
- Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, Basel, Switzerland.,Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Manuel Bause
- Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg, Germany
| | - Stefanie Bauer
- Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg, Germany
| | - Ruben Bartholomaeus
- Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Guenther Bernhardt
- Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg, Germany
| | - Burkhard Koenig
- Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg, Germany
| | - Armin Buschauer
- Faculty of Chemistry and Pharmacy, University of Regensburg, Regensburg, Germany
| | - Henning Stahlberg
- Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, Basel, Switzerland
| | - Karl-Heinz Altmann
- Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
| | - Kaspar P Locher
- Institute of Molecular Biology and Biophysics, Department of Biology, ETH Zurich, Zurich, Switzerland.
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9
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Structure-function relationships in ABCG2: insights from molecular dynamics simulations and molecular docking studies. Sci Rep 2017; 7:15534. [PMID: 29138424 PMCID: PMC5686161 DOI: 10.1038/s41598-017-15452-z] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 10/25/2017] [Indexed: 12/29/2022] Open
Abstract
Efflux pumps of the ATP-binding cassette transporters superfamily (ABC transporters) are frequently involved in the multidrug-resistance (MDR) phenomenon in cancer cells. Herein, we describe a new atomistic model for the MDR-related ABCG2 efflux pump, also named breast cancer resistance protein (BCRP), based on the recently published crystallographic structure of the ABCG5/G8 heterodimer sterol transporter, a member of the ABCG family involved in cholesterol homeostasis. By means of molecular dynamics simulations and molecular docking, a far-reaching characterization of the ABCG2 homodimer was obtained. The role of important residues and motifs in the structural stability of the transporter was comprehensively studied and was found to be in good agreement with the available experimental data published in literature. Moreover, structural motifs potentially involved in signal transmission were identified, along with two symmetrical drug-binding sites that are herein described for the first time, in a rational attempt to better understand how drug binding and recognition occurs in ABCG2 homodimeric transporters.
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10
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László L, Sarkadi B, Hegedűs T. Jump into a New Fold-A Homology Based Model for the ABCG2/BCRP Multidrug Transporter. PLoS One 2016; 11:e0164426. [PMID: 27741279 PMCID: PMC5065228 DOI: 10.1371/journal.pone.0164426] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 09/23/2016] [Indexed: 12/03/2022] Open
Abstract
ABCG2/BCRP is a membrane protein, involved in xenobiotic and endobiotic transport in key pharmacological barriers and drug metabolizing organs, in the protection of stem cells, and in multidrug resistance of cancer. Pharmacogenetic studies implicated the role of ABCG2 in response to widely used medicines and anticancer agents, as well as in gout. Its Q141K variant exhibits decreased functional expression thus increased drug accumulation and decreased urate secretion. Still, there has been no reliable molecular model available for this protein, as the published structures of other ABC transporters could not be properly fitted to the ABCG2 topology and experimental data. The recently published high resolution structure of a close homologue, the ABCG5-ABCG8 heterodimer, revealed a new ABC transporter fold, unique for ABCG proteins. Here we present a structural model of the ABCG2 homodimer based on this fold and detail the experimental results supporting this model. In order to describe the effect of mutations on structure and dynamics, and characterize substrate recognition and cholesterol regulation we performed molecular dynamics simulations using full length ABCG2 protein embedded in a membrane bilayer and in silico docking simulations. Our results show that in the Q141K variant the introduced positive charge diminishes the interaction between the nucleotide binding and transmembrane domains and the R482G variation alters the orientation of transmembrane helices. Moreover, the R482 position, which plays a role the substrate specificity of the transporter, is located in one of the substrate binding pockets identified by the in silico docking calculations. In summary, the ABCG2 model and in silico simulations presented here may have significant impact on understanding drug distribution and toxicity, as well as drug development against cancer chemotherapy resistance or gout.
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Affiliation(s)
- Laura László
- Molecular Biophysics Research Group and Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
| | - Balázs Sarkadi
- Molecular Biophysics Research Group and Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
- Research Centre for Natural Sciences, Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary
| | - Tamás Hegedűs
- Molecular Biophysics Research Group and Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
- * E-mail:
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11
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Role of cysteine residues in the redox-regulated oligomerization and nucleotide binding to EhRabX3. Mol Biochem Parasitol 2016; 208:84-90. [PMID: 27485554 DOI: 10.1016/j.molbiopara.2016.06.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 05/22/2016] [Accepted: 06/28/2016] [Indexed: 11/20/2022]
Abstract
The enteric protozoan parasite, Entamoeba histolytica, an etiological agent of amebiasis, is involved in the adhesion and destruction of human tissues. Worldwide, the parasite causes about 50 million cases of amebiasis and 100,000 deaths annually. EhRabX3, a unique amoebic Rab GTPase with tandem G-domains, possesses an unusually large number of cysteine residues in its N-terminal domain. Crystal structure of EhRabX3 revealed an intra-molecular disulfide bond between C39 and C163 which is critical for maintaining the 3-dimensional architecture and biochemical function of this protein. The remaining six cysteine residues were found to be surface exposed and predicted to be involved in inter-molecular disulfide bonds. In the current study, using biophysical and mutational approaches, we have investigated the role of the cysteine residues in the assembly of EhRabX3 oligomer. The self-association of EhRabX3 is found to be redox sensitive, in vitro. Furthermore, the oligomeric conformation of EhRabX3 failed to bind and exchange the guanine nucleotide, indicating structural re-organization of the active site. Altogether, our results provide valuable insights into the redox-dependent oligomerization of EhRabX3 and its implication on nucleotide binding.
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12
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Liu Y, Li Q, Zhou L, Xie N, Nice EC, Zhang H, Huang C, Lei Y. Cancer drug resistance: redox resetting renders a way. Oncotarget 2016; 7:42740-42761. [PMID: 27057637 PMCID: PMC5173169 DOI: 10.18632/oncotarget.8600] [Citation(s) in RCA: 116] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 03/28/2016] [Indexed: 02/05/2023] Open
Abstract
Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.
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Affiliation(s)
- Yuan Liu
- State Key Laboratory for Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center of Biotherapy, Chengdu, P. R. China
- Department of Neurology, The Affiliated Hospital of Hainan Medical College, Haikou, Hainan, P. R. China
| | - Qifu Li
- Department of Neurology, The Affiliated Hospital of Hainan Medical College, Haikou, Hainan, P. R. China
| | - Li Zhou
- State Key Laboratory for Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center of Biotherapy, Chengdu, P. R. China
| | - Na Xie
- State Key Laboratory for Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center of Biotherapy, Chengdu, P. R. China
| | - Edouard C. Nice
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Haiyuan Zhang
- Department of Neurology, The Affiliated Hospital of Hainan Medical College, Haikou, Hainan, P. R. China
| | - Canhua Huang
- State Key Laboratory for Biotherapy and Cancer Center, West China Hospital, Sichuan University, and Collaborative Innovation Center of Biotherapy, Chengdu, P. R. China
| | - Yunlong Lei
- Department of Biochemistry and Molecular Biology, and Molecular Medicine and Cancer Research Center, Chongqing Medical University, Chongqing, P. R. China
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13
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Hasanabady MH, Kalalinia F. ABCG2 inhibition as a therapeutic approach for overcoming multidrug resistance in cancer. J Biosci 2016; 41:313-24. [DOI: 10.1007/s12038-016-9601-5] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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14
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Srivastava VK, Chandra M, Saito-Nakano Y, Nozaki T, Datta S. Crystal Structure Analysis of Wild Type and Fast Hydrolyzing Mutant of EhRabX3, a Tandem Ras Superfamily GTPase from Entamoeba histolytica. J Mol Biol 2015; 428:41-51. [PMID: 26555751 DOI: 10.1016/j.jmb.2015.11.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Revised: 10/30/2015] [Accepted: 11/04/2015] [Indexed: 10/22/2022]
Abstract
The enteric protozoan parasite, Entamoeba histolytica, is the causative agent of amoebic dysentery, liver abscess and colitis in human. Vesicular trafficking plays a key role in the survival and virulence of the protozoan and is regulated by various Rab GTPases. EhRabX3 is a catalytically inefficient amoebic Rab protein, which is unique among the eukaryotic Ras superfamily by virtue of its tandem domain organization. Here, we report the crystal structures of GDP-bound fast hydrolyzing mutant (V71A/K73Q) and GTP-bound wild type EhRabX3 at 3.1 and 2.8Å resolutions, respectively. Though both G-domains possess "phosphate binding loop containing nucleoside triphosphate hydrolases fold", only the N-terminal domain binds to guanine nucleotide. The relative orientation of the N-terminal domain and C-terminal domain is stabilized by numerous inter-domain interactions. Compared to other Ras superfamily members, both the GTPase domains displayed large deviation in switch II perhaps due to non-conservative substitutions in this region. As a result, entire switch II is restructured and moved away from the nucleotide binding pocket, providing a rationale for the diminished GTPase activity of EhRabX3. The N-terminal GTPase domain possesses unusually large number of cysteine residues. X-ray crystal structure of the fast hydrolyzing mutant of EhRabX3 revealed that C39 and C163 formed an intra-molecular disulfide bond. Subsequent mutational and biochemical studies suggest that C39 and C163 are critical for maintaining the structural integrity and function of EhRabX3. Structure-guided functional investigation of cysteine mutants could provide the physiological implications of the disulfide bond and could allow us to design potential inhibitors for the better treatment of intestinal amebiasis.
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Affiliation(s)
- Vijay Kumar Srivastava
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal 462023, India
| | - Mintu Chandra
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal 462023, India
| | - Yumiko Saito-Nakano
- Department of Parasitology, National Institute of Infectious Diseases Shinjuku-ku, Tokyo 162-8640, Japan
| | - Tomoyoshi Nozaki
- Department of Parasitology, National Institute of Infectious Diseases Shinjuku-ku, Tokyo 162-8640, Japan
| | - Sunando Datta
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal 462023, India,.
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15
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Characterization of native PfABCG protein in Plasmodium falciparum. Biochem Pharmacol 2015; 97:137-46. [DOI: 10.1016/j.bcp.2015.06.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 06/29/2015] [Indexed: 01/26/2023]
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16
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Szafraniec MJ, Szczygieł M, Urbanska K, Fiedor L. Determinants of the activity and substrate recognition of breast cancer resistance protein (ABCG2). Drug Metab Rev 2014; 46:459-74. [DOI: 10.3109/03602532.2014.942037] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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17
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Isom CE, Turner JL, Lessner DJ, Karr EA. Redox-sensitive DNA binding by homodimeric Methanosarcina acetivorans MsvR is modulated by cysteine residues. BMC Microbiol 2013; 13:163. [PMID: 23865844 PMCID: PMC3729527 DOI: 10.1186/1471-2180-13-163] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2013] [Accepted: 07/12/2013] [Indexed: 11/16/2022] Open
Abstract
Background Methanoarchaea are among the strictest known anaerobes, yet they can survive exposure to oxygen. The mechanisms by which they sense and respond to oxidizing conditions are unknown. MsvR is a transcription regulatory protein unique to the methanoarchaea. Initially identified and characterized in the methanogen Methanothermobacter thermautotrophicus (Mth), MthMsvR displays differential DNA binding under either oxidizing or reducing conditions. Since MthMsvR regulates a potential oxidative stress operon in M. thermautotrophicus, it was hypothesized that the MsvR family of proteins were redox-sensitive transcription regulators. Results An MsvR homologue from the methanogen Methanosarcina acetivorans, MaMsvR, was overexpressed and purified. The two MsvR proteins bound the same DNA sequence motif found upstream of all known MsvR encoding genes, but unlike MthMsvR, MaMsvR did not bind the promoters of select genes involved in the oxidative stress response. Unlike MthMsvR that bound DNA under both non-reducing and reducing conditions, MaMsvR bound DNA only under reducing conditions. MaMsvR appeared as a dimer in gel filtration chromatography analysis and site-directed mutagenesis suggested that conserved cysteine residues within the V4R domain were involved in conformational rearrangements that impact DNA binding. Conclusions Results presented herein suggest that homodimeric MaMsvR acts as a transcriptional repressor by binding Ma PmsvR under non-reducing conditions. Changing redox conditions promote conformational changes that abrogate binding to Ma PmsvR which likely leads to de-repression.
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Affiliation(s)
- Catherine E Isom
- Department of Microbiology and Plant Biology, University of Oklahoma, 770 Van Vleet Oval, Norman, OK, 73019, USA
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18
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Mo W, Qi J, Zhang JT. Different roles of TM5, TM6, and ECL3 in the oligomerization and function of human ABCG2. Biochemistry 2012; 51:3634-41. [PMID: 22497316 DOI: 10.1021/bi300301a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ABCG2 is a member of the ATP-binding cassette transporter superfamily, and its overexpression causes multidrug resistance (MDR) in cancer chemotherapy. ABCG2 may also protect cancer stem cells by extruding cytotoxic materials. ABCG2 has previously been shown to exist as a high-order homo-oligomer consisting of possibly 8-12 subunits, and the oligomerization domain was mapped to the C-terminal domain, including TM5, ECL3, and TM6. In this study, we further investigate this domain in detail for the role of each segment in the oligomerization and drug transport function of ABCG2 using domain swapping and site-directed mutagenesis. We found that none of the three segments (TM5, TM6, and ECL3) is essential for the oligomerization activity of ABCG2 and that any one of these three segments in the full-length context is sufficient to support ABCG2 oligomerization. While TM5 plays an important role in the drug transport function of ABCG2, TM6 and ECL3 are replaceable. Thus, each segment in the TM5-ECL3-TM6 domain plays a distinctive role in the oligomerization and function of ABCG2.
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Affiliation(s)
- Wei Mo
- Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, Indiana 46202, United States
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19
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Haider AJ, Briggs D, Self TJ, Chilvers HL, Holliday ND, Kerr ID. Dimerization of ABCG2 analysed by bimolecular fluorescence complementation. PLoS One 2011; 6:e25818. [PMID: 21991363 PMCID: PMC3185054 DOI: 10.1371/journal.pone.0025818] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Accepted: 09/11/2011] [Indexed: 12/18/2022] Open
Abstract
ABCG2 is one of three human ATP binding cassette transporters that are functionally capable of exporting a diverse range of substrates from cells. The physiological consequence of ABCG2 multidrug transport activity in leukaemia, and some solid tumours is the acquisition of cancer multidrug resistance. ABCG2 has a primary structure that infers that a minimal functional transporting unit would be a homodimer. Here we investigated the ability of a bimolecular fluorescence complementation approach to examine ABCG2 dimers, and to probe the role of individual amino acid substitutions in dimer formation. ABCG2 was tagged with fragments of venus fluorescent protein (vYFP), and this tagging did not perturb trafficking or function. Co-expression of two proteins bearing N-terminal and C-terminal fragments of YFP resulted in their association and detection of dimerization by fluorescence microscopy and flow cytometry. Point mutations in ABCG2 which may affect dimer formation were examined for alterations in the magnitude of fluorescence complementation signal. Bimolecular fluorescence complementation (BiFC) demonstrated specific ABCG2 dimer formation, but no changes in dimer formation, resulting from single amino acid substitutions, were detected by BiFC analysis.
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Affiliation(s)
- Ameena J. Haider
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Deborah Briggs
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Tim J. Self
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Hannah L. Chilvers
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Nicholas D. Holliday
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Ian D. Kerr
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
- * E-mail:
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20
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Liu JY, Li Z, Li H, Zhang JT. Critical residue that promotes protein dimerization: a story of partially exposed Phe25 in 14-3-3σ. J Chem Inf Model 2011; 51:2612-25. [PMID: 21870863 DOI: 10.1021/ci200212y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Many proteins exist and function as oligomers. While hydrophobic interactions have been recognized as the major driving force for oligomerization, detailed molecular mechanisms for the assembly are unknown. Here, we used 14-3-3σ as a model protein and investigated the role of hydrophobic residues at the dimeric interface using MD simulations and coimmunoprecipitations. We found that a half-exposed and half-buried residue in the interface, Phe(25), plays a more important role in promoting homodimerization than the hydrophobic core residues by organizing both favorable hydrophobic and hydrophilic interactions. Phe(25) is critical in packing and stabilizing hydrophobic core residues. We conclude that the structural stability of hydrophobic cores is critical for a stable homodimer complex and this stable property can be bestowed by residues outside of hydrophobic core. The important organizing activity of Phe(25) for homodimerization of 14-3-3σ originates from its unique physical location, rigidity, size, and hydrophobicity. Thus, hydrophobic residues that are not deeply buried at the oligomeric interface may play important but different roles from the buried core residues and they may promote oligomerization by organizing co-operativity of core and other residues for favorable hydrophobic and electrostatic interactions.
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Affiliation(s)
- Jing-Yuan Liu
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana 46202, United States
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21
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Ni Z, Bikadi Z, Shuster DL, Zhao C, Rosenberg MF, Mao Q. Identification of proline residues in or near the transmembrane helices of the human breast cancer resistance protein (BCRP/ABCG2) that are important for transport activity and substrate specificity. Biochemistry 2011; 50:8057-66. [PMID: 21854076 DOI: 10.1021/bi200573t] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The human breast cancer resistance protein (BCRP/ABCG2) confers multidrug resistance and mediates the active efflux of drugs and xenobiotics. BCRP contains one nucleotide-binding domain (NBD) followed by one membrane-spanning domain (MSD). We investigated whether prolines in or near the transmembrane helices are essential for BCRP function. Six proline residues were substituted with alanine individually, and the mutants were stably expressed in Flp-In(TM)-293 cells at levels comparable to that of wild-type BCRP and predominantly localized on the plasma membrane of the cells. While P392A showed a significant reduction (35-50%) in the efflux activity of mitoxantrone, BODIPY-prazosin, and Hoechst 33342, P485A exhibited a significant decrease of approximately 70% in the efflux activity of only BODIPY-prazosin. Other mutants had no significant changes in the efflux activities of these substrates. Drug resistance profiles of the cells expressing the mutants correlated well with the efflux data. ATPase activity was not substantially affected for P392A or P485A compared to that of wild-type BCRP. These results strongly suggest Pro(392) and Pro(485) are important in determining the overall transport activity and substrate selectivity of BCRP, respectively. Prazosin differentially affected the binding of 5D3, a conformation-sensitive antibody, to wild-type BCRP, P392A, or P485A in a concentration-dependent manner. In contrast, mitoxantrone had no significant effect on 5D3 binding. Homology modeling indicates that Pro(392) may play an important role in the communication between the MSD and NBD as it is predicted to be located at the interface between the two functional domains, and Pro(485) induces flexible hinges that may be essential for the broad substrate specificity of BCRP.
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Affiliation(s)
- Zhanglin Ni
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, Washington 98195-7610, USA
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22
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Papale GA, Hanson PJ, Sahoo D. Extracellular disulfide bonds support scavenger receptor class B type I-mediated cholesterol transport. Biochemistry 2011; 50:6245-54. [PMID: 21675794 DOI: 10.1021/bi2005625] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Scavenger receptor class B type I (SR-BI) binds high-density lipoprotein (HDL) and mediates the selective uptake of cholesteryl esters (CE). Although the extracellular domain of SR-BI is critical for function, the structural characteristics of this region remain elusive. Using sulfhydryl labeling strategies, we report the novel finding that all six cysteine (Cys) residues in the extracellular domain of SR-BI are involved in disulfide bond formation that is intramolecular by nature. We hypothesized that an SR-BI conformation stabilized by extracellular disulfide bonds is a prerequisite for SR-BI-mediated cholesterol transport. Thus, single-Cys mutant SR-BI receptors (C251S-, C280S-, C321S-, C323S-, C334S-, and C384S-SR-BI), as well as Cys-less SR-BI, a mutant SR-BI receptor void of all Cys residues, were created, and plasma membrane localization was confirmed. Functional assays revealed that C280S-, C321S-, C323S-, and C334S-SR-BI and Cys-less SR-BI mutant receptors displayed weakened HDL binding and subsequent selective uptake of HDL-CE. However, only C323S-SR-BI and Cys-less SR-BI were unable to mediate wild-type levels of efflux of free cholesterol (FC) to HDL. None of the Cys mutations disrupted SR-BI's ability to redistribute plasma membrane FC. Taken together, the intramolecular disulfide bonds in the extracellular domain of SR-BI appear to maintain the receptor in a conformation integral to its cholesterol transport functions.
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Affiliation(s)
- Gabriella A Papale
- Department of Medicine, Division of Endocrinology, Metabolism and Clinical Nutrition, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, United States
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23
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Mo W, Zhang JT. Human ABCG2: structure, function, and its role in multidrug resistance. INTERNATIONAL JOURNAL OF BIOCHEMISTRY AND MOLECULAR BIOLOGY 2011; 3:1-27. [PMID: 22509477 PMCID: PMC3325772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 03/25/2011] [Indexed: 05/31/2023]
Abstract
Human ABCG2 is a member of the ATP-binding cassette (ABC) transporter superfamily and is known to contribute to multidrug resistance (MDR) in cancer chemotherapy. Among ABC transporters that are known to cause MDR, ABCG2 is particularly interesting for its potential role in protecting cancer stem cells and its complex oligomeric structure. Recent studies have also revealed that the biogenesis of ABCG2 could be modulated by small molecule compounds. These modulators, upon binding to ABCG2, accelerate the endocytosis and trafficking to lysosome for degradation and effectively reduce the half-life of ABCG2. Hence, targeting ABCG2 stability could be a new venue for therapeutic discovery to sensitize drug resistant human cancers. In this report, we review recent progress on understanding the structure, function, biogenesis, as well as physiological and pathophysiological functions of ABCG2.
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Affiliation(s)
- Wei Mo
- Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine Indianapolis, IN 46202, USA
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24
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Jacobs A, Emmert D, Wieschrath S, Hrycyna CA, Wiese M. Recombinant Synthesis of Human ABCG2 Expressed in the Yeast Saccharomyces cerevisiae: an Experimental Methodological Study. Protein J 2011; 30:201-11. [DOI: 10.1007/s10930-011-9321-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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25
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Ni Z, Bikadi Z, Rosenberg MF, Mao Q. Structure and function of the human breast cancer resistance protein (BCRP/ABCG2). Curr Drug Metab 2010; 11:603-17. [PMID: 20812902 DOI: 10.2174/138920010792927325] [Citation(s) in RCA: 189] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 08/13/2010] [Indexed: 12/22/2022]
Abstract
The human breast cancer resistance protein (BCRP/ABCG2) is the second member of the G subfamily of the large ATP-binding cassette (ABC) transporter superfamily. BCRP was initially discovered in multidrug resistant breast cancer cell lines where it confers resistance to chemotherapeutic agents such as mitoxantrone, topotecan and methotrexate by extruding these compounds out of the cell. BCRP is capable of transporting non-chemotherapy drugs and xenobiotiocs as well, including nitrofurantoin, prazosin, glyburide, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. BCRP is frequently detected at high levels in stem cells, likely providing xenobiotic protection. BCRP is also highly expressed in normal human tissues including the small intestine, liver, brain endothelium, and placenta. Therefore, BCRP has been increasingly recognized for its important role in the absorption, elimination, and tissue distribution of drugs and xenobiotics. At present, little is known about the transport mechanism of BCRP, particularly how it recognizes and transports a large number of structurally and chemically unrelated drugs and xenobiotics. Here, we review current knowledge of structure and function of this medically important ABC efflux drug transporter.
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Affiliation(s)
- Zhanglin Ni
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Health Science Building H272, 1959 NE Pacific Street, Seattle, Washington 98195-7610, USA
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26
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Polgar O, Ierano C, Tamaki A, Stanley B, Ward Y, Xia D, Tarasova N, Robey RW, Bates SE. Mutational analysis of threonine 402 adjacent to the GXXXG dimerization motif in transmembrane segment 1 of ABCG2. Biochemistry 2010; 49:2235-45. [PMID: 20088606 DOI: 10.1021/bi902085q] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ABCG2 is an ATP-binding cassette half-transporter important in normal tissue protection, drug distribution, and excretion. ABCG2 requires homodimerization for function, though the mechanism for dimerization has not been elucidated. We conducted mutational analysis of threonine 402, three residues from the GXXXG motif in TM1, to study its potential role in ABCG2 dimerization (TXXXGXXXG). Single mutations to leucine (T402L) or arginine (T402R) did not have a significant impact on the ABCG2 protein. On the other hand, combining the T402 mutations with the GXXXG glycine to leucine mutations (T402L/G406L/G410L and T402R/G406L/G410L) resulted in a substantially reduced level of expression, altered glycosylation, degradation by a proteosome-independent pathway, and partial retention in the endoplasmic reticulum as suggested by immunostaining, Endo H sensitivity, and MG132 and bafilomycin failed effect. The T402L/G406L/G410L mutant when incubated with the ABCG2 substrate MX showed a shift on immunoblot analysis to the band representing the fully mature glycoprotein. The T402R/G406L/G410L mutant carrying the more drastic substitution was found to primarily localize intracellularly. The same set of mutations also displayed impaired dimerization in the TOXCAT assay for TM1 compared to that of the wild type. Homology modeling of ABCG2 places the TXXXGXXXG motif at the dimer interface. These studies are consistent with a role for the extended TXXXGXXXG motif in ABCG2 folding, processing, and/or dimerization.
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Affiliation(s)
- Orsolya Polgar
- Medical Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Building 10, Room 13N240, Bethesda, Maryland 20892, USA
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27
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Ni Z, Mark ME, Cai X, Mao Q. Fluorescence resonance energy transfer (FRET) analysis demonstrates dimer/oligomer formation of the human breast cancer resistance protein (BCRP/ABCG2) in intact cells. INTERNATIONAL JOURNAL OF BIOCHEMISTRY AND MOLECULAR BIOLOGY 2010; 1:1-11. [PMID: 20622991 PMCID: PMC2901148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Accepted: 01/28/2010] [Indexed: 05/29/2023]
Abstract
The human breast cancer resistance protein (BCRP/ABCG2) is a half ATP-binding cassette (ABC) efflux transporter that plays an important role in drug resistance and disposition. Although BCRP is believed to function as a homodimer or homooligomer, this has not been demonstrated in vivo in intact cells. Therefore, in the present study, we investigated dimer/oligmer formation of BCRP in intact cells. Wild-type BCRP and the mutant C603A were attached to cyan or yellow fluorescence protein and expressed in HEK293 cells by transient transfection. Protein levels, cell surface expression, and efflux activities of wild-type and mutant BCRP were determined by immunoblotting, 5D3 antibody binding, and flow cytometric efflux assay, respectively. Dimer/oligomer formation of BCRP in intact cells was analyzed using fluorescence resonance energy transfer (FRET) microscopy. Wild-type BCRP and C603A were expressed in HEK293 cells at comparable levels. C603A was predominantly expressed in the plasma membrane as was wild-type protein. Furthermore, C603A retained the same mitoxantrone efflux activity and the ability of dimer/oligmer formation as wild-type BCRP. Finally, cross-linking experiments yielded data consistent with the FRET analysis. In conclusion, we have, for the first time, demonstrated that BCRP can form a dimer/oligomer in vivo in intact cells using the FRET technique. We have also shown that Cys(603) alone does not seem to be essential for dimer/oligomer formation of BCRP.
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Affiliation(s)
- Zhanglin Ni
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, Washington 98195-7610, USA
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28
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Mo W, Zhang JT. Oligomerization of human ATP-binding cassette transporters and its potential significance in human disease. Expert Opin Drug Metab Toxicol 2009; 5:1049-63. [PMID: 19637987 DOI: 10.1517/17425250903124371] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Human ATP-binding cassette transporters (ABC transporter) belong to an extremely important superfamily of membrane transporters. They use energy from ATP hydrolysis to transport a wide variety of substrates across the cellular membrane. Due to the physiological and pharmacological importance of their diverse substrates, ABC transporters have been shown to have close relationship with various human diseases such as cystic fibrosis and multi-drug resistance in cancer chemotherapy. While it has been thought traditionally that functional ABC transporters exist as monomeric full or dimeric half transporters, emerging evidence indicates that some ABC transporters oligomerize on cellular membranes and this oligomerization seems to have functional relevance. Therefore, this oligomerization process might be a promising drug target for ABC transporter-related human diseases, especially in overcoming multi-drug resistance in cancer chemotherapy. In this review, we perform a critical analysis of the past studies on the oligomerization of ABC transporters.
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Affiliation(s)
- Wei Mo
- Indiana University School of Medicine, Indianapolis, 46202, USA
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29
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McDevitt CA, Collins R, Kerr ID, Callaghan R. Purification and structural analyses of ABCG2. Adv Drug Deliv Rev 2009; 61:57-65. [PMID: 19124053 DOI: 10.1016/j.addr.2008.07.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Accepted: 07/23/2008] [Indexed: 01/24/2023]
Abstract
ABCG2 is best known as a multidrug transporter capable of conferring resistance to cancer cells. However, the protein is also inherently expressed in numerous barrier tissues and intriguingly within hematopoietic stem cells. Unlike its partners ABCB1 and ABCC1, there is considerably less information available on the molecular mechanism of ABCG2. The transporter has a distinct topology and is presumed to function as a homodimer. However, a number of biochemical studies have presented data to suggest that the protein adopts higher order oligomers. This review focuses on this controversial issue with particular reference to findings from low resolution structural data. In addition, a number of molecular models of ABCG2 based on high resolution structures of bacterial ABC transporters have recently become available and are critically assessed. ABCG2 is a structurally distinct member of the triumvirate of human multidrug transporters and continues to evade description of a unifying molecular mechanism.
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Affiliation(s)
- Christopher A McDevitt
- Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Oxford, OX3 9DU, United Kingdom
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30
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Kuo MT. Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities. Antioxid Redox Signal 2009; 11:99-133. [PMID: 18699730 PMCID: PMC2577715 DOI: 10.1089/ars.2008.2095] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.
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Affiliation(s)
- Macus Tien Kuo
- Department of Molecular Pathology (Unit 951), The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
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31
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McDevitt CA, Crowley E, Hobbs G, Starr KJ, Kerr ID, Callaghan R. Is ATP binding responsible for initiating drug translocation by the multidrug transporter ABCG2? FEBS J 2008; 275:4354-62. [PMID: 18657189 DOI: 10.1111/j.1742-4658.2008.06578.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
ABCG2 confers resistance to cancer cells by mediating the ATP-dependent outward efflux of chemotherapeutic compounds. Recent studies have indicated that the protein contains a number of interconnected drug binding sites. The present investigation examines the coupling of drug binding to ATP hydrolysis. Initial drug binding to the protein requires a high-affinity interaction with the drug binding site, followed by transition and reorientation to the low-affinity state to enable dissociation at the extracellular face. [3H]Daunomycin binding to the ABCG2 R482G isoform was examined in the nucleotide-bound and post-hydrolytic conformations. Binding of [3H]daunomycin was displaced by ATP analogues, indicating transition to a low-affinity conformation prior to hydrolysis. The low-affinity state was observed to be retained immediately post-hydrolysis. Therefore, the dissociation of phosphate and/or ADP is likely to be responsible for resetting of the transporter. The data indicate that, like ABCB1 and ABCC1, the 'power stroke' for translocation in ABCG2 R482G is the binding of nucleotide.
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Affiliation(s)
- Christopher A McDevitt
- Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, UK
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