1
|
Wright NJ, Fedor JG, Zhang H, Jeong P, Suo Y, Yoo J, Hong J, Im W, Lee SY. Methotrexate recognition by the human reduced folate carrier SLC19A1. Nature 2022; 609:1056-1062. [PMID: 36071163 DOI: 10.1038/s41586-022-05168-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Accepted: 08/01/2022] [Indexed: 02/01/2023]
Abstract
Folates are essential nutrients with important roles as cofactors in one-carbon transfer reactions, being heavily utilized in the synthesis of nucleic acids and the metabolism of amino acids during cell division1,2. Mammals lack de novo folate synthesis pathways and thus rely on folate uptake from the extracellular milieu3. The human reduced folate carrier (hRFC, also known as SLC19A1) is the major importer of folates into the cell1,3, as well as chemotherapeutic agents such as methotrexate4-6. As an anion exchanger, RFC couples the import of folates and antifolates to anion export across the cell membrane and it is a major determinant in methotrexate (antifolate) sensitivity, as genetic variants and its depletion result in drug resistance4-8. Despite its importance, the molecular basis of substrate specificity by hRFC remains unclear. Here we present cryo-electron microscopy structures of hRFC in the apo state and captured in complex with methotrexate. Combined with molecular dynamics simulations and functional experiments, our study uncovers key determinants of hRFC transport selectivity among folates and antifolate drugs while shedding light on important features of anion recognition by hRFC.
Collapse
Affiliation(s)
- Nicholas J Wright
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Justin G Fedor
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Han Zhang
- Departments of Biological Sciences, Chemistry and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | | | - Yang Suo
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Jiho Yoo
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.,College of Pharmacy, Chung-Ang University, Seoul, Republic of Korea
| | - Jiyong Hong
- Department of Chemistry, Duke University, Durham, NC, USA
| | - Wonpil Im
- Departments of Biological Sciences, Chemistry and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.
| |
Collapse
|
2
|
Newstead S. Structural basis for recognition and transport of folic acid in mammalian cells. Curr Opin Struct Biol 2022; 74:102353. [PMID: 35303537 PMCID: PMC7612623 DOI: 10.1016/j.sbi.2022.102353] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 01/29/2022] [Accepted: 02/08/2022] [Indexed: 12/19/2022]
Abstract
Structural studies on mammalian vitamin transport lag behind other metabolites. Folates, also known as B9 vitamins, are essential cofactors in one-carbon transfer reactions in biology. Three different systems control folate uptake in the human body; folate receptors function to capture and internalise extracellular folates via endocytosis, whereas two major facilitator superfamily transporters, the reduced folate carrier (RFC; SLC19A1) and proton-coupled folate transporter (PCFT; SLC46A1) control the transport of folates across cellular membranes. Targeting specific folate transporters is being pursued as a route to developing new antifolates with improved pharmacology. Recent structures of the proton-coupled folate transporter, PCFT, revealed key insights into antifolate recognition and the mechanism of proton-coupled transport. Combined with previously determined structures of folate receptors and new predictions for the structure of the RFC, we are now able to develop a structure-based understanding of folate and antifolate recognition to accelerate efforts in antifolate drug development.
Collapse
Affiliation(s)
- Simon Newstead
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
| |
Collapse
|
3
|
Koniev O, Wagner A. Developments and recent advancements in the field of endogenous amino acid selective bond forming reactions for bioconjugation. Chem Soc Rev 2015; 44:5495-551. [PMID: 26000775 DOI: 10.1039/c5cs00048c] [Citation(s) in RCA: 390] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Bioconjugation methodologies have proven to play a central enabling role in the recent development of biotherapeutics and chemical biology approaches. Recent endeavours in these fields shed light on unprecedented chemical challenges to attain bioselectivity, biocompatibility, and biostability required by modern applications. In this review the current developments in various techniques of selective bond forming reactions of proteins and peptides were highlighted. The utility of each endogenous amino acid-selective conjugation methodology in the fields of biology and protein science has been surveyed with emphasis on the most relevant among reported transformations; selectivity and practical use have been discussed.
Collapse
Affiliation(s)
- Oleksandr Koniev
- Laboratory of Functional Chemo-Systems (UMR 7199), Labex Medalis, University of Strasbourg, 74 Route du Rhin, 67401 Illkirch-Graffenstaden, France.
| | | |
Collapse
|
4
|
Abscisic acid sensor RCAR7/PYL13, specific regulator of protein phosphatase coreceptors. Proc Natl Acad Sci U S A 2014; 111:5741-6. [PMID: 24706923 DOI: 10.1073/pnas.1322085111] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The plant hormone abscisic acid (ABA) acts both as a developmental signal and as an integrator of environmental cues such as drought and cold. ABA perception recruits an ABA-binding regulatory component [regulatory component of ABA receptor (RCAR)/PYR1/PYL] and an associated protein phosphatase 2C (PP2C). Phytohormone binding inactivates the phosphatase activity of the coreceptor, permitting phosphorelay of the ABA signal via downstream protein kinases. RCARs and PP2C coreceptors are represented by small protein families comprising 14 and 9 members in Arabidopsis, respectively. The specificity of the RCAR-PP2C interaction and the constraints contributing to specific combinations are poorly understood. In this contribution, we analyzed RCAR7/PYL13, which is characterized by three variant amino acid residues in the conserved ABA-binding pocket. RCAR7 regulated the phosphatase activity of the PP2Cs ABI1, ABI2, and PP2CA in vitro at nanomolar ABA levels; however, it was unable to regulate the structurally related hypersensitive to ABA 1 (HAB1). Site-directed mutagenesis of HAB1 established ABA-dependent regulation by RCAR7. Conversion of the noncanonical amino acid residues of RCAR7 into the consensus ABA-binding pocket did not perceptibly change receptor function. Ectopic expression of RCAR7 in Arabidopsis resulted in ABA hypersensitivity affecting gene regulation, seed germination, and stomatal closure. The RCAR7 loss-of-function mutant revealed no changes in ABA responses, similar to the RCAR9 knockout line, whereas the combined deficiency of RCAR7 and RCAR9 resulted in ABA-insensitive seed germination. The study shows a role of RCAR7 in early plant development, proves its ABA receptor function, and identifies structural constraints of RCAR7-PP2C interaction.
Collapse
|
5
|
Matherly LH, Wilson MR, Hou Z. The major facilitative folate transporters solute carrier 19A1 and solute carrier 46A1: biology and role in antifolate chemotherapy of cancer. Drug Metab Dispos 2014; 42:632-49. [PMID: 24396145 PMCID: PMC3965896 DOI: 10.1124/dmd.113.055723] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 01/06/2014] [Indexed: 01/19/2023] Open
Abstract
This review summarizes the biology of the major facilitative membrane transporters, the reduced folate carrier (RFC) (Solute Carrier 19A1) and the proton-coupled folate transporter (PCFT) (Solute Carrier 46A1). Folates are essential vitamins, and folate deficiency contributes to a variety of health disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates the intestinal absorption of dietary folates and appears to be important for transport of folates into the central nervous system. Clinically relevant antifolates for cancer, such as methotrexate and pralatrexate, are transported by RFC, and loss of RFC transport is an important mechanism of methotrexate resistance in cancer cell lines and in patients. PCFT is expressed in human tumors, and is active at pH conditions associated with the tumor microenvironment. Pemetrexed is an excellent substrate for both RFC and PCFT. Novel tumor-targeted antifolates related to pemetrexed with selective membrane transport by PCFT over RFC are being developed. In recent years, there have been major advances in understanding the structural and functional properties and the regulation of RFC and PCFT. The molecular bases for methotrexate resistance associated with loss of RFC transport and for hereditary folate malabsorption, attributable to mutant PCFT, were determined. Future studies should continue to translate molecular insights from basic studies of RFC and PCFT biology into new therapeutic strategies for cancer and other diseases.
Collapse
Affiliation(s)
- Larry H Matherly
- Department of Oncology (L.H.M., M.R.W., Z.H.) and Department of Pharmacology (L.H.M.), Wayne State University School of Medicine, Detroit, Michigan; and Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan (L.H.M., Z.H.)
| | | | | |
Collapse
|
6
|
Hou Z, Matherly LH. Biology of the major facilitative folate transporters SLC19A1 and SLC46A1. CURRENT TOPICS IN MEMBRANES 2014; 73:175-204. [PMID: 24745983 DOI: 10.1016/b978-0-12-800223-0.00004-9] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
This chapter focuses on the biology of the major facilitative membrane folate transporters, the reduced folate carrier (RFC), and the proton-coupled folate transporter (PCFT). Folates are essential vitamins, and folate deficiency contributes to a variety of heath disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates intestinal absorption of dietary folates. Clinically relevant antifolates such as methotrexate (MTX) are transported by RFC, and the loss of RFC transport is an important mechanism of MTX resistance. PCFT is abundantly expressed in human tumors and is active under pH conditions associated with the tumor microenvironment. Pemetrexed (PMX) is an excellent substrate for PCFT as well as for RFC. Novel tumor-targeted antifolates related to PMX with selective membrane transport by PCFT over RFC are being developed. The molecular picture of RFC and PCFT continues to evolve relating to membrane topology, N-glycosylation, energetics, and identification of structurally and functionally important domains and amino acids. The molecular bases for MTX resistance associated with loss of RFC function, and for the rare autosomal recessive condition, hereditary folate malabsorption (HFM), attributable to mutant PCFT, have been established. From structural homologies to the bacterial transporters GlpT and LacY, homology models were developed for RFC and PCFT, enabling new mechanistic insights and experimentally testable hypotheses. RFC and PCFT exist as homo-oligomers, and evidence suggests that homo-oligomerization of RFC and PCFT monomeric proteins may be important for intracellular trafficking and/or transport function. Better understanding of the structure and function of RFC and PCFT should facilitate the rational development of new therapeutic strategies for cancer as well as for HFM.
Collapse
Affiliation(s)
- Zhanjun Hou
- Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan, USA; Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan, USA.
| | - Larry H Matherly
- Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan, USA; Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan, USA; Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan, USA.
| |
Collapse
|
7
|
Liu T, Dean A, Ashwini S, Sheridan PP, Bhushan A, Lai JCK, Cao S, Daniels CK. Identification and characterization of a 66-68-kDa protein as a methotrexate-binding protein in murine leukemia L1210 cells. Cell Stress Chaperones 2013; 18:223-34. [PMID: 23090015 PMCID: PMC3581622 DOI: 10.1007/s12192-012-0376-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Revised: 09/20/2012] [Accepted: 09/21/2012] [Indexed: 01/07/2023] Open
Abstract
We previously observed an unidentified, tyrosine-phosphorylated, membrane-associated, 66-68-kDa protein which was present in the L1210 murine leukemia cells but not present, at least in the tyrosine-phosphorylated form, in cisplatin-methotrexate (CDDP-MTX) cross-resistant L1210/DDP cells. We purified and characterized this 66-68-kDa protein by affinity chromatography purification using its two identified properties, tyrosine phosphorylation and MTX-binding, and yielded a single band of 66-68 kDa. The purified protein was subjected to trypsin digestion and the isolated peptide fragments were sequenced and yielded two partial peptide sequences: VEIIANDQ and VTNAVVTVPAYFNDSQRQA. The two peptide sequences were used to search for the mouse genome at the national center for biotechnology information (NCBI) database for Open Reading Frame Sequence (ORFs) containing these peptides using the TBLASTN function. A single gene was identified containing both sequences, the HSPa8 gene, which codes for the heat shock family protein, HSC70. We further demonstrated that HSC70 is a MTX-binding protein using a binding assay with MTX-agarose beads followed by Western blotting. The HSC70 also existed in various cancer cell lines and showed binding to MTX. Additionally, the HSC70 protein, cloned from the L1210 murine leukemia cells, was expressed and purified from E. coli cells using a polyhistidine-tag purification system and it also showed the binding properties with MTX. DnaK, the HSC70 homologue in E. coli, also binds to MTX. By using the purified truncated HSC70 domains, we identified the adenosine triphosphatase (ATPase) domain of HSC70 that can bind to MTX. Thus, we have tentatively characterized a new, novel property of HSC70 as a MTX-binding protein.
Collapse
Affiliation(s)
- Tuoen Liu
- />Department of Internal Medicine, Division of Oncology, Washington University School of Medicine, St. Louis, MO USA
| | - Allison Dean
- />Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT USA
| | - Saint Ashwini
- />Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, 970 South 5th Avenue, Campus Box 8334, Pocatello, ID 83209 USA
| | - Peter P. Sheridan
- />Department of Biological Sciences, Idaho State University, Pocatello, ID USA
- />The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID USA
| | - Alok Bhushan
- />Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, 970 South 5th Avenue, Campus Box 8334, Pocatello, ID 83209 USA
- />The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID USA
| | - James C. K. Lai
- />Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, 970 South 5th Avenue, Campus Box 8334, Pocatello, ID 83209 USA
- />The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID USA
| | - Shousong Cao
- />Department of Medicine, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263 USA
| | - Christopher K. Daniels
- />Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, 970 South 5th Avenue, Campus Box 8334, Pocatello, ID 83209 USA
- />The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID USA
| |
Collapse
|
8
|
Substrate-specific binding and conformational changes involving Ser313 and transmembrane domain 8 of the human reduced folate carrier, as determined by site-directed mutagenesis and protein cross-linking. Biochem J 2010; 430:265-74. [PMID: 20557288 PMCID: PMC2947195 DOI: 10.1042/bj20100181] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
RFC (reduced folate carrier) is the major transporter for reduced folates and antifolates [e.g. MTX (methotrexate)]. RFC is characterized by two halves, each with six TMD (transmembrane domain) α helices connected by a hydrophilic loop, and cytoplasmic N- and C-termini. We previously identified TMDs 4, 5, 7, 8, 10 and 11 as forming the hydrophilic cavity for translocation of (anti)folates. The proximal end of TMD8 (positions 311–314) was implicated in substrate binding from scanning-cysteine accessibility methods; cysteine replacement of Ser313 resulted in loss of transport. In the present study, Ser313 was mutated to alanine, cysteine, phenylalanine and threonine. Mutant RFCs were expressed in RFC-null R5 HeLa cells. Replacement of Ser313 with cysteine or phenylalanine abolished MTX transport, whereas residual activity was preserved for the alanine and threonine mutants. In stable K562 transfectants, S313A and S313T RFCs showed substantially decreased Vmax values without changes in Kt values for MTX compared with wild-type RFC. S313A and S313T RFCs differentially impacted binding of ten diverse (anti)folate substrates. Cross-linking between TMD8 and TMD5 was studied by expressing cysteine-less TMD1–6 (N6) and TMD7–12 (C6) half-molecules with cysteine insertions spanning these helices in R5 cells, followed by treatment with thiol-reactive homobifunctional cross-linkers. C6–C6 and N6–N6 cross-links were seen for all cysteine pairs. From the N6 and C6 cysteine pairs, Cys175/Cys311 was cross-linked; cross-linking increased in the presence of transport substrates. The results of the present study indicate that the proximal end of TMD8 is juxtaposed to TMD5 and is conformationally active in the presence of transport substrates, and TMD8, including Ser313, probably contributes to the RFC substrate-binding domain.
Collapse
|
9
|
Hayashi K, Ono K, Suzuki H, Sawada M, Moriya M, Sakamoto W, Yogo T. High-frequency, magnetic-field-responsive drug release from magnetic nanoparticle/organic hybrid based on hyperthermic effect. ACS APPLIED MATERIALS & INTERFACES 2010; 2:1903-11. [PMID: 20568697 DOI: 10.1021/am100237p] [Citation(s) in RCA: 161] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Magnetic nanoparticles (MNPs) generate heat when a high-frequency magnetic field (HFMF) is applied to them. Induction heat is useful not only for hyperthermia treatment but also as a driving force for drug-release. beta-Cyclodextrin (CD) can act as drug container because of its inclusion properties. Drugs incorporated in the CD can thus be released through the use of induction heating, or hyperthermic effects, by applying a HFMF. In this study, we have synthesized folic acid (FA) and CD-functionalized superparamagnetic iron oxide nanoparticles, FA-CD-SPIONs, by chemically modifying SPIONs derived from iron(III) allylacetylacetonate. FA is well-known as a targeting ligand for breast cancer tumor and endows the SPIONs with cancer-targeting capability. Immobilization of FA and CD on spinel iron oxide nanoparticles was confirmed by Fourier transform IR (FTIR) and X-ray photoelectron spectroscopy (XPS). The FA-CD-SPIONs have a hydrodynamic diameter of 12.4 nm and prolonged stability in water. They are superparamagnetic with a magnetization of 51 emu g(-1) at 16 kOe. They generate heat when an alternating current (AC) magnetic field is applied to them and have a specific absorption rate (SAR) of 132 W g(-1) at 230 kHz and 100 Oe. Induction heating triggers drug release from the CD cavity on the particle - a behavior that is controlled by switching the HFMF on and off. The FA-CD-SPIONs are noncytotoxic for cells. Thus, FA-CD-SPIONs can serve as a novel device for performing drug delivery and hyperthermia simultaneously.
Collapse
Affiliation(s)
- Koichiro Hayashi
- Division of Nanomaterials Science, EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
| | | | | | | | | | | | | |
Collapse
|
10
|
Dridi L, Haimeur A, Ouellette M. Structure-function analysis of the highly conserved charged residues of the membrane protein FT1, the main folic acid transporter of the protozoan parasite Leishmania. Biochem Pharmacol 2009; 79:30-8. [PMID: 19660435 DOI: 10.1016/j.bcp.2009.07.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Revised: 07/24/2009] [Accepted: 07/27/2009] [Indexed: 10/20/2022]
Abstract
The main plasma membrane folate transporter FT1 of Leishmania belongs to the novel FBT family which is part of the major facilitator superfamily. We have investigated the role of the 10 most conserved charged amino acids of FBTs by site directed mutagenesis. The functions of the mutated proteins were tested for their capacity to transport FA, to sensitize methotrexate resistant cells to methotrexate, for protein production, and for protein localisation. Of the 10 conserved charged amino acids that were mutated to neutral amino acids, all had effects on FT1 transport activities. Only four of the 10 initial mutants (K116L, K133L, R497L, and D529V) retained between 15% and 50% of FT1 activity. The R497 residue was shown to be involved in substrate binding. When the charged conserved residues at position 124, 134, 179, 514, 537 and 565 were changed to neutral amino acids, this led to inactive proteins but the generation of new mutants D124E, R134K, D514E and D537E regained between 20% and 50% of wild-type FT1 activity suggesting that the charge is important for protein function. The mutated protein D179E had, under our standard experimental conditions, no activity, while E565D was completely inactive. The differential activity of the mutated proteins was due either to changes in the apparent K(m) or V(max). Mutagenesis experiments have revealed that charged amino acids were essential for FT1 stability or activity and led to a plausible model for the transport of folic acid through FT1.
Collapse
Affiliation(s)
- Larbi Dridi
- Centre de Recherche en Infectiologie du CHUL, Université Laval, 2705 Boul, Laurier, Québec, Québec G1V4G2, Québec, Canada
| | | | | |
Collapse
|
11
|
Membrane transporters and folate homeostasis: intestinal absorption and transport into systemic compartments and tissues. Expert Rev Mol Med 2009; 11:e4. [PMID: 19173758 DOI: 10.1017/s1462399409000969] [Citation(s) in RCA: 254] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Members of the family of B9 vitamins are commonly known as folates. They are derived entirely from dietary sources and are key one-carbon donors required for de novo nucleotide and methionine synthesis. These highly hydrophilic molecules use several genetically distinct and functionally diverse transport systems to enter cells: the reduced folate carrier, the proton-coupled folate transporter and the folate receptors. Each plays a unique role in mediating folate transport across epithelia and into systemic tissues. The mechanism of intestinal folate absorption was recently uncovered, revealing the genetic basis for the autosomal recessive disorder hereditary folate malabsorption, which results from loss-of-function mutations in the proton-coupled folate transporter gene. It is therefore now possible to piece together how these folate transporters contribute, both individually and collectively, to folate homeostasis in humans. This review focuses on the physiological roles of the major folate transporters, with a brief consideration of their impact on the pharmacological activities of antifolates.
Collapse
|
12
|
Hou Z, Matherly LH. Oligomeric structure of the human reduced folate carrier: identification of homo-oligomers and dominant-negative effects on carrier expression and function. J Biol Chem 2008; 284:3285-3293. [PMID: 19019821 DOI: 10.1074/jbc.m807206200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ubiquitously expressed reduced folate carrier (RFC) is the major transport system for folate cofactors in mammalian cells and tissues. Previous considerations of RFC structure and mechanism were based on the notion that RFC monomers were sufficient to mediate transport of folate and antifolate substrates. The present study examines the possibility that human RFC (hRFC) exists as higher order homo-oligomers. By chemical cross-linking, transiently expressed hRFC in hRFC-null HeLa (R5) cells with the homobifunctional cross-linker 1,3-propanediyl bis-methanethiosulfonate and Western blotting, hRFC species with molecular masses of hRFC homo-oligomers were identified. Hemagglutinin- and Myc epitope-tagged hRFC proteins expressed in R5 cells were co-immunoprecipitated from both membrane particulate and surface-enriched membrane fractions, indicating that oligomeric hRFC is expressed at the cell surface. By co-expression of wild type and inactive mutant S138C hRFCs, combined with surface biotinylation and confocal microscopy, a dominant-negative phenotype was demonstrated involving greatly decreased cell surface expression of both mutant and wild type carrier caused by impaired intracellular trafficking. For another hRFC mutant (R373A), expression of oligomeric wild type-mutant hRFC was accompanied by a significant and disproportionate loss of wild type activity unrelated to the level of surface carrier. Collectively, our results demonstrate the existence of hRFC homo-oligomers. They also establish the likely importance of these higher order hRFC structures to intracellular trafficking and carrier function.
Collapse
Affiliation(s)
- Zhanjun Hou
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Larry H Matherly
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201; Cancer Biology Graduate Program, Wayne State University School of Medicine, Detroit, Michigan 48201; Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201.
| |
Collapse
|
13
|
Matherly LH, Hou Z. Structure and function of the reduced folate carrier a paradigm of a major facilitator superfamily mammalian nutrient transporter. VITAMINS AND HORMONES 2008; 79:145-84. [PMID: 18804694 DOI: 10.1016/s0083-6729(08)00405-6] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Folates are essential for life and folate deficiency contributes to a host of health problems including cardiovascular disease, fetal abnormalities, neurological disorders, and cancer. Antifolates, represented by methotrexate, continue to occupy a unique niche among the modern day pharmacopoeia for cancer along with other pathological conditions. This article focuses on the biology of the membrane transport system termed the "reduced folate carrier" or RFC with a particular emphasis on RFC structure and function. The ubiquitously expressed RFC is the major transporter for folates in mammalian cells and tissues. Loss of RFC expression or function portends potentially profound physiological or developmental consequences. For chemotherapeutic antifolates used for cancer, loss of RFC expression or synthesis of mutant RFC protein with impaired function results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and low levels of substrate for polyglutamate synthesis. The functional properties for RFC were first documented nearly 40 years ago in murine leukemia cells. Since 1994, when RFC was first cloned, tremendous advances in the molecular biology of RFC and biochemical approaches for studying the structure of polytopic membrane proteins have led to an increasingly detailed picture of the molecular structure of the carrier, including its membrane topology, its N-glycosylation, identification of functionally and structurally important domains and amino acids, and helix packing associations. Although no crystal structure for RFC is yet available, biochemical and molecular studies, combined with homology modeling, based on homologous bacterial major facilitator superfamily transporters such as LacY, now permit the development of experimentally testable hypotheses designed to establish RFC structure and mechanism.
Collapse
Affiliation(s)
- Larry H Matherly
- Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
| | | |
Collapse
|