1
|
Babcock S, Calvo KR, Hasserjian RP. Pediatric myelodysplastic syndrome. Semin Diagn Pathol 2023; 40:152-171. [PMID: 37173164 DOI: 10.1053/j.semdp.2023.04.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 04/10/2023] [Accepted: 04/12/2023] [Indexed: 05/15/2023]
Affiliation(s)
| | - Katherine R Calvo
- Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD, USA
| | | |
Collapse
|
2
|
Mir A, Almudhry M, Alghamdi F, Albaradie R, Ibrahim M, Aldurayhim F, Alhedaithy A, Alamr M, Bawazir M, Mohammad S, Abdelhay S, Bashir S, Housawi Y. SLC gene mutations and pediatric neurological disorders: diverse clinical phenotypes in a Saudi Arabian population. Hum Genet 2021; 141:81-99. [PMID: 34797406 DOI: 10.1007/s00439-021-02404-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Accepted: 11/12/2021] [Indexed: 12/12/2022]
Abstract
The uptake and efflux of solutes across a plasma membrane is controlled by transporters. There are two main superfamilies of transporters, adenosine 5'-triphosphate (ATP) binding cassettes (ABCs) and solute carriers (SLCs). In the brain, SLC transporters are involved in transporting various solutes across the blood-brain barrier, blood-cerebrospinal fluid barrier, astrocytes, neurons, and other brain cell types including oligodendrocytes and microglial cells. SLCs play an important role in maintaining normal brain function. Hence, mutations in the genes that encode SLC transporters can cause a variety of neurological disorders. We identified the following SLC gene variants in 25 patients in our cohort: SLC1A2, SLC2A1, SLC5A1, SLC6A3, SLC6A5, SLC6A8, SLC9A6, SLC9A9, SLC12A6, SLC13A5, SLC16A1, SLC17A5, SLC19A3, SLC25A12, SLC25A15, SLC27A4, SLC45A1, SLC46A1, and SLC52A3. Eight patients harbored pathogenic or likely pathogenic mutations (SLC5A1, SLC9A6, SLC12A6, SLC16A1, SLC19A3, and SLC52A3), and 12 patients were found to have variants of unknown clinical significance (VOUS); these variants occurred in 11 genes (SLC1A2, SLC2A1, SLC6A3, SLC6A5, SLC6A8, SLC9A6, SLC9A9, SLC13A5, SLC25A12, SLC27A4, and SLC45A1). Five patients were excluded as they were carriers. In the remaining 20 patients with SLC gene variants, we identified 16 possible distinct neurological disorders. Based on the clinical presentation, we categorized them into genes causing intellectual delay (ID) or autism spectrum disorder (ASD), those causing epilepsy, those causing vitamin-related disorders, and those causing other neurological diseases. Several variants were detected that indicated possible personalized therapies: SLC2A1 led to dystonia or epilepsy, which can be treated with a ketogenic diet; SLC6A3 led to infantile parkinsonism-dystonia 1, which can be treated with levodopa; SLC6A5 led to hyperekplexia 3, for which unnecessary treatment with antiepileptic drugs should be avoided; SLC6A8 led to creatine deficiency syndrome type 1, which can be treated with creatine monohydrate; SLC16A1 led to monocarboxylate transporter 1 deficiency, which causes seizures that should not be treated with a ketogenic diet; SLC19A3 led to biotin-thiamine-responsive basal ganglia disease, which can be treated with biotin and thiamine; and SLC52A3 led to Brown-Vialetto-Van-Laere syndrome 1, which can be treated with riboflavin. The present study examines the prevalence of SLC gene mutations in our cohort of children with epilepsy and other neurological disorders. It highlights the diverse phenotypes associated with mutations in this large family of SLC transporter proteins, and an opportunity for personalized genomics and personalized therapeutics.
Collapse
Affiliation(s)
- Ali Mir
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia.
| | - Montaha Almudhry
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Fouad Alghamdi
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Raidah Albaradie
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Mona Ibrahim
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Fatimah Aldurayhim
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Abdullah Alhedaithy
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Mushari Alamr
- Genetic and Metabolic Department, King Fahad Specialist Hospital, Dammam, Kingdom of Saudi Arabia
| | - Maryam Bawazir
- Genetic and Metabolic Department, King Fahad Specialist Hospital, Dammam, Kingdom of Saudi Arabia
| | - Sahar Mohammad
- Department of Pediatric, King Fahad Specialist Hospital, Dammam, Kingdom of Saudi Arabia
| | - Salma Abdelhay
- Department of Pediatric, King Fahad Specialist Hospital, Dammam, Kingdom of Saudi Arabia
| | - Shahid Bashir
- Department of Pediatric Neurology, Neuroscience Center, King Fahad Specialist Hospital, Ammar Bin Thabit Street, Dammam, 31444, Kingdom of Saudi Arabia
| | - Yousef Housawi
- Genetic and Metabolic Department, King Fahad Specialist Hospital, Dammam, Kingdom of Saudi Arabia
| |
Collapse
|
3
|
Do HQ, Bassil CM, Andersen EI, Jansen M. Impact of nanodisc lipid composition on cell-free expression of proton-coupled folate transporter. PLoS One 2021; 16:e0253184. [PMID: 34793461 PMCID: PMC8601550 DOI: 10.1371/journal.pone.0253184] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Accepted: 10/31/2021] [Indexed: 01/19/2023] Open
Abstract
The Proton-Coupled Folate Transporter (PCFT) is a transmembrane transport protein that controls the absorption of dietary folates in the small intestine. PCFT also mediates uptake of chemotherapeutically used antifolates into tumor cells. PCFT has been identified within lipid rafts observed in phospholipid bilayers of plasma membranes, a micro environment that is altered in tumor cells. The present study aimed at investigating the impact of different lipids within Lipid-protein nanodiscs (LPNs), discoidal lipid structures stabilized by membrane scaffold proteins, to yield soluble PCFT expression in an E. coli lysate-based cell-free transcription/translation system. In the absence of detergents or lipids, we observed PCFT quantitatively as precipitate in this system. We then explored the ability of LPNs to support solubilized PCFT expression when present during in-vitro translation. LPNs consisted of either dimyristoyl phosphatidylcholine (DMPC), palmitoyl-oleoyl phosphatidylcholine (POPC), or dimyristoyl phosphatidylglycerol (DMPG). While POPC did not lead to soluble PCFT expression, both DMPG and DMPC supported PCFT translation directly into LPNs, the latter in a concentration dependent manner. The results obtained through this study provide insights into the lipid preferences of PCFT. Membrane-embedded or solubilized PCFT will enable further studies with diverse biophysical approaches to enhance the understanding of the structure and molecular mechanism of folate transport through PCFT.
Collapse
Affiliation(s)
- Hoa Quynh Do
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Carla M. Bassil
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- The Clark Scholar Program, Texas Tech University, Lubbock, TX, United States of America
| | - Elizabeth I. Andersen
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Michaela Jansen
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| |
Collapse
|
4
|
Man Y, Xu T, Adhikari B, Zhou C, Wang Y, Wang B. Iron supplementation and iron-fortified foods: a review. Crit Rev Food Sci Nutr 2021; 62:4504-4525. [PMID: 33506686 DOI: 10.1080/10408398.2021.1876623] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
About one-third of the world population is suffering from iron deficiency. Delivery of iron through diet is a practical, economical, and sustainable approach. Clinical studies have shown that the consumption of iron-fortified foods is one of the most effective methods for the prevention of iron deficiency. However, supplementing iron through diet can cause undesirable side-effects. Thus, it is essential to develop new iron-rich ingredients, iron-fortified products with high bioavailability, better stability, and lower cost. It is also essential to develop newer processing technologies for more effective fortification. This review compared the iron supplementation strategies used to treat the highly iron-deficient population and the general public. We also reviewed the efficacy of functional (iron-rich) ingredients that can be incorporated into food materials to produce iron-fortified foods. The most commonly available foods, such as cereals, bakery products, dairy products, beverages, and condiments are still the best vehicles for iron fortification and delivery.Scope of reviewThe manuscript aims at providing a comprehensive review of the latest publications that cover three aspects: administration routes for iron supplementation, iron-rich ingredients used for iron supplementation, and iron-fortified foods.
Collapse
Affiliation(s)
- Yaxing Man
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, PR China
| | - Tiantian Xu
- Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, PR China
| | - Benu Adhikari
- School of Science, RMIT University, Melbourne, Australia
| | - Cunshan Zhou
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, PR China
| | - Yuchuan Wang
- School of Food Engineering, Jiangnan University, Wuxi, PR China
| | - Bo Wang
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, PR China
| |
Collapse
|
5
|
Tozawa Y, Abdrabou SSMA, Nogawa-Chida N, Nishiuchi R, Ishida T, Suzuki Y, Sano H, Kobayashi R, Kishimoto K, Ohara O, Imai K, Naruto T, Kobayashi K, Ariga T, Yamada M. A deep intronic mutation of c.1166-285 T > G in SLC46A1 is shared by four unrelated Japanese patients with hereditary folate malabsorption (HFM). Clin Immunol 2019; 208:108256. [DOI: 10.1016/j.clim.2019.108256] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 08/29/2019] [Accepted: 09/02/2019] [Indexed: 02/07/2023]
|
6
|
Radziejewska A, Chmurzynska A. Folate and choline absorption and uptake: Their role in fetal development. Biochimie 2018; 158:10-19. [PMID: 30529042 DOI: 10.1016/j.biochi.2018.12.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 12/04/2018] [Indexed: 12/29/2022]
Abstract
SCOPE In this review, we attempt to assess how choline and folate transporters affect fetal development. We focus on how the expression of these transporters in response to choline and folate intake affects transport effectiveness. We additionally describe allelic variants of the genes encoding these transporters and their phenotypic effects. METHODS AND RESULTS We made an extensive review of recent articles describing role of choline and folate - with particularly emphasize on their transporters - in fetal development. Folate and choline are necessary for the proper functioning of the cell and body. During pregnancy, the requirements of these nutrients increase because of elevated maternal demand and the rapid division of fetal cells. The concentrations of folate and choline in cells depend on food intake, the absorption of nutrients, and the cellular transport system, which is tissue-specific and developmentally regulated. Relatively few studies have investigated the role of choline transporters in fetal development. CONCLUSIONS In this review we show relations between functioning of folate and choline transporters and fetal development.
Collapse
Affiliation(s)
- Anna Radziejewska
- Institute of Human Nutrition and Dietetics, Poznań University of Life Sciences, Poland
| | - Agata Chmurzynska
- Institute of Human Nutrition and Dietetics, Poznań University of Life Sciences, Poland.
| |
Collapse
|
7
|
Matherly LH, Hou Z, Gangjee A. The promise and challenges of exploiting the proton-coupled folate transporter for selective therapeutic targeting of cancer. Cancer Chemother Pharmacol 2018; 81:1-15. [PMID: 29127457 PMCID: PMC5756103 DOI: 10.1007/s00280-017-3473-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 10/20/2017] [Indexed: 12/17/2022]
Abstract
This review considers the "promise" of exploiting the proton-coupled folate transporter (PCFT) for selective therapeutic targeting of cancer. PCFT was discovered in 2006 and was identified as the principal folate transporter involved in the intestinal absorption of dietary folates. The recognition that PCFT was highly expressed in many tumors stimulated substantial interest in using PCFT for cytotoxic drug targeting, taking advantage of its high level transport activity under the acidic pH conditions that characterize many tumors. For pemetrexed, among the best PCFT substrates, transport by PCFT establishes its importance as a clinically important transporter in malignant pleural mesothelioma and non-small cell lung cancer. In recent years, the notion of PCFT-targeting has been extended to a new generation of tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine compounds that are structurally and functionally distinct from pemetrexed, and that exhibit near exclusive transport by PCFT and potent inhibition of de novo purine nucleotide biosynthesis. Based on compelling preclinical evidence in a wide range of human tumor models, it is now time to advance the most optimized PCFT-targeted agents with the best balance of PCFT transport specificity and potent antitumor efficacy to the clinic to validate this novel paradigm of highly selective tumor targeting.
Collapse
Affiliation(s)
- Larry H Matherly
- Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, 421 East Canfield Street, Detroit, MI, 48201, USA.
- Department of Oncology, Wayne State University School of Medicine, Detroit, MI, 48201, USA.
- Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI, 48201, USA.
| | - Zhanjun Hou
- Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, 421 East Canfield Street, Detroit, MI, 48201, USA
- Department of Oncology, Wayne State University School of Medicine, Detroit, MI, 48201, USA
| | - Aleem Gangjee
- Division of Medicinal Chemistry, Graduate School of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA, 15282, USA
| |
Collapse
|
8
|
Role of Intramuscular Levofolinate Administration in the Treatment of Hereditary Folate Malabsorption: Report of Three Cases. JIMD Rep 2017; 39:7-12. [PMID: 28685492 DOI: 10.1007/8904_2017_39] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 05/17/2017] [Accepted: 06/09/2017] [Indexed: 01/19/2023] Open
Abstract
Hereditary folate malabsorption is a rare autosomal recessive disorder caused by impaired active folate transport across membranes and into the central nervous system due to loss-of-function mutations in proton-coupled folate transporter (PCFT). Newborns with this condition have initially normal folate stores, but as they are unable to absorb dietary folate and use rapidly their stores because of their growth demands, symptoms appear in the early infancy. Significant neurological morbidity usually follows the initial non-specific clinical presentation and delayed initiation of treatment. High dose oral and parenteral folinic acid treatment have been previously reported in literature to improve the clinical outcome without achieving optimal cerebrospinal fluid (CSF) folate levels though. The active isomer of 5-formyltetrahydrofolate, also known as levofolinic acid, is available for administration. We report our experience in achieving normal (age dependent) CSF 5-Methyltetrahydrofolate (5-MTHF) levels following daily intramuscular administration of levofolinic acid in three patients with HFM. Follow-up assessment with repeated lumbar punctures has shown a stabilization of 5-MTHF levels within normal range. Clinical features and brain MRI findings had as well either improvement or stabilization. To the best of our knowledge, we provide as well for the first time data in regard to the im levofolinate treatment dosage.
Collapse
|
9
|
Date SS, Fiori MC, Altenberg GA, Jansen M. Expression in Sf9 insect cells, purification and functional reconstitution of the human proton-coupled folate transporter (PCFT, SLC46A1). PLoS One 2017; 12:e0177572. [PMID: 28493963 PMCID: PMC5426777 DOI: 10.1371/journal.pone.0177572] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Accepted: 04/28/2017] [Indexed: 01/05/2023] Open
Abstract
The proton-coupled folate transporter (PCFT) provides an essential uptake route for the vitamin folic acid (B9) in mammals. In addition, it is currently of high interest for targeting chemotherapeutic agents to tumors due to the increased folic acid requirement of rapidly dividing tumor cells as well as the upregulated PCFT expression in several tumors. To understand its function, determination of its atomic structure and molecular mechanism of transport are essential goals that require large amounts of functional PCFT. Here, we present a high-level heterologous expression system for human PCFT using a recombinant baculovirus and Spodoptera frugiperda (Sf9) insect cells. We demonstrate folate transport functionality along the PCFT expression, isolation, and purification process. Importantly, purified PCFT transports folic acid after reconstitution. We thus succeeded in overcoming heterologous expression as a major bottleneck of PCFT research. The availability of an overexpression system for human PCFT provides the basis for future biochemical, biophysical and structural studies.
Collapse
Affiliation(s)
- Swapneeta S. Date
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
| | - Mariana C. Fiori
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
| | - Guillermo A. Altenberg
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
| | - Michaela Jansen
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States of America
- * E-mail:
| |
Collapse
|
10
|
Zhao R, Aluri S, Goldman ID. The proton-coupled folate transporter (PCFT-SLC46A1) and the syndrome of systemic and cerebral folate deficiency of infancy: Hereditary folate malabsorption. Mol Aspects Med 2016; 53:57-72. [PMID: 27664775 DOI: 10.1016/j.mam.2016.09.002] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 09/18/2016] [Indexed: 02/07/2023]
Abstract
The proton-coupled folate transporter (PCFT-SLC46A1) is the mechanism by which folates are absorbed across the brush-border membrane of the small intestine. The transporter is also expressed in the choroid plexus and is required for transport of folates into the cerebrospinal fluid. Loss of PCFT function, as occurs in the autosomal recessive disorder "hereditary folate malabsorption" (HFM), results in a syndrome characterized by severe systemic and cerebral folate deficiency. Folate-receptor alpha (FRα) is expressed in the choroid plexus, and loss of function of this protein, as also occurs in an autosomal recessive disorder, results solely in "cerebral folate deficiency" (CFD), the designation for this disorder. This paper reviews the current understanding of the functional and structural properties and regulation of PCFT, an electrogenic proton symporter, and contrasts PCFT properties with those of the reduced folate carrier (RFC), an organic anion antiporter, that is the major route of folate transport to systemic tissues. The clinical characteristics of HFM and its treatment, based upon the thirty-seven known cases with the clinical syndrome, of which thirty have been verified by genotype, are presented. The ways in which PCFT and FRα might interact at the level of the choroid plexus such that each is required for folate transport from blood to cerebrospinal fluid are considered along with the different clinical presentations of HFM and CFD.
Collapse
Affiliation(s)
- Rongbao Zhao
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Srinivas Aluri
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA
| | - I David Goldman
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA.
| |
Collapse
|
11
|
Functional and mechanistic roles of the human proton-coupled folate transporter transmembrane domain 6-7 linker. Biochem J 2016; 473:3545-3562. [PMID: 27514717 DOI: 10.1042/bcj20160399] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 08/11/2016] [Indexed: 12/15/2022]
Abstract
The proton-coupled folate transporter (PCFT; SLC46A1) is a folate-proton symporter expressed in solid tumors and is used for tumor-targeted delivery of cytotoxic antifolates. Topology modeling suggests that the PCFT secondary structure includes 12 transmembrane domains (TMDs) with TMDs 6 and 7 linked by an intracellular loop (positions 236-265) including His247, implicated as functionally important. Single-cysteine (Cys) mutants were inserted from positions 241 to 251 in Cys-less PCFT and mutant proteins were expressed in PCFT-null (R1-11) HeLa cells; none were reactive with 2-aminoethyl methanethiosulfonate biotin, suggesting that the TMD6-7 loop is intracellular. Twenty-nine single alanine mutants spanning the entire TMD6-7 loop were expressed in R1-11 cells; activity was generally preserved, with the exception of the 247, 250, and 251 mutants, partly due to decreased surface expression. Coexpression of PCFT TMD1-6 and TMD7-12 half-molecules in R1-11 cells partially restored transport activity, although removal of residues 252-265 from TMD7-12 abolished transport. Chimeric proteins, including a nonhomologous sequence from a thiamine transporter (ThTr1) inserted into the PCFT TMD6-7 loop (positions 236-250 or 251-265), were active, although replacement of the entire loop with the ThTr1 sequence resulted in substantial loss of activity. Amino acid replacements (Ala, Arg, His, Gln, and Glu) or deletions at position 247 in wild-type and PCFT-ThTr1 chimeras resulted in differential effects on transport. Collectively, our findings suggest that the PCFT TMD6-7 connecting loop confers protein stability and may serve a unique functional role that depends on secondary structure rather than particular sequence elements.
Collapse
|
12
|
Date SS, Chen CYC, Chen Y, Jansen M. Experimentally optimized threading structures of the proton-coupled folate transporter. FEBS Open Bio 2016; 6:216-30. [PMID: 27047750 PMCID: PMC4794783 DOI: 10.1002/2211-5463.12041] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 01/13/2016] [Accepted: 01/29/2016] [Indexed: 12/18/2022] Open
Abstract
The proton‐coupled folate transporter (PCFT, SLC46A1) transports folic acid across the plasma membrane, together with an excess of protons such that the net charge translocation is positive. We developed 3D structural models of PCFT threaded onto the X‐ray structures of major facilitator superfamily (MFS) members that were identified as close structural homologues. The model of PCFT threaded onto the glycerol‐3‐phosphate transporter (GlpT) structure is consistent with detailed accessibility studies in the absence of extracellular substrate and at pH 7.4 presented here, and additionally with a multitude of other mutagenesis and functional studies. Characteristic MFS structural features are preserved in this PCFT model, such as 12 transmembrane helices divided into two pseudosymmetric bundles, and a high density of positive charges on the periphery of the cytoplasmic site that allow interactions with negatively charged lipid head‐groups. Under the experimental conditions, PCFT predominantly samples the resting state, which in this case is inward‐open. Several positions lining the substrate cavity have been identified. Motif A, a helix‐turn‐helix motif that is a hallmark of MFS transporters between transmembrane segments II and III is oriented appropriately to interact with residues from transmembrane segments IV as well as XI upon conformational transition to the outward‐open state. A charge‐relay system between three charged residues as well as apposing glycines in two α‐helices, both contributed to by motif A, become engaged when PCFT is modeled on the outward‐open state of a putative proton‐driven transporter (YajR).
Collapse
Affiliation(s)
- Swapneeta S Date
- Department of Cell Physiology and Molecular Biophysics School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA; Center for Membrane Protein Research School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA
| | - Cheng-Yen Charles Chen
- Center for Membrane Protein Research School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA; Medical Student Summer Research Program School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA
| | - Yidong Chen
- Center for Membrane Protein Research School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA; Medical Student Summer Research Program School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA
| | - Michaela Jansen
- Department of Cell Physiology and Molecular Biophysics School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA; Center for Membrane Protein Research School of Medicine Texas Tech University Health Sciences Center Lubbock TX USA
| |
Collapse
|
13
|
Molero-Luis M, Serrano M, O’Callaghan MM, Sierra C, Pérez-Dueñas B, García-Cazorla A, Artuch R. Clinical, etiological and therapeutic aspects of cerebral folate deficiency. Expert Rev Neurother 2015; 15:793-802. [DOI: 10.1586/14737175.2015.1055322] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
|
14
|
Erlacher M, Grünert SC, Cseh A, Steinfeld R, Salzer U, Lausch E, Nosswitz U, Dückers G, Niehues T, Ehl S, Niemeyer CM, Speckmann C. Reversible pancytopenia and immunodeficiency in a patient with hereditary folate malabsorption. Pediatr Blood Cancer 2015; 62:1091-4. [PMID: 25504888 DOI: 10.1002/pbc.25364] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 10/27/2014] [Indexed: 01/19/2023]
Abstract
Mutations in SLC46A1 result in a defect of the proton coupled folate transporter (PCFT) and are the basis of hereditary folate malabsorption (HFM). Patients with HFM frequently present with neurodevelopmental delay and megaloblastic anemia. Some cases may be complicated by additional lymphopenia and immunodeficiency. We report a patient with a new homozygous mutation in the SLC46A1 gene. The boy presented with early-onset pancytopenia and secondary immunodeficiency. We provide clinical and molecular observations that extend the phenotypic description of HFM and highlight diagnostic as well as therapeutic pitfalls in this rare condition.
Collapse
Affiliation(s)
- Miriam Erlacher
- Department of Pediatrics and Adolescent Medicine, University Medical Center, Freiburg, Germany
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Torres A, Newton SA, Crompton B, Borzutzky A, Neufeld EJ, Notarangelo L, Berry GT. CSF 5-Methyltetrahydrofolate Serial Monitoring to Guide Treatment of Congenital Folate Malabsorption Due to Proton-Coupled Folate Transporter (PCFT) Deficiency. JIMD Rep 2015; 24:91-6. [PMID: 26006721 PMCID: PMC4582027 DOI: 10.1007/8904_2015_445] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Revised: 04/11/2015] [Accepted: 04/16/2015] [Indexed: 01/19/2023] Open
Abstract
Hereditary folate malabsorption is characterized by folate deficiency with impaired folate transport into the central nervous system (CNS). This disease is characterized by megaloblastic anemia of early appearance, combined immunodeficiency, seizures, and cognitive impairment. The anemia and immunologic disease are responsive but neurological signs are refractory to folic-acid treatment. We report a 7-year-old girl who has congenital folate deficiency and SLC46A1 gene mutation who is unable to transport folate from her gut to the circulatory system and consequently from the blood to the cerebrospinal fluid (CSF). As a result she developed undetectable 5-methyltetrahydrofolate levels in her plasma and CSF and became immunocompromised and quite ill. Intramuscular treatment with 5-formyltetrahydrofolate (folinic acid) was therapeutic at her presentation and has been successful preventing other signs and symptoms of hereditary folate malabsorption even at relatively low CSF levels. Although difficult, early detection and diagnosis of cerebral folate deficiency are important because folinic acid at a pharmacologic dose may normalize outcome in PCFT gene defects, as well as bypass autoantibody-blocked folate receptors and enter the cerebrospinal fluid by way of the reduced folate carrier. This route elevates the 5-methyltetrahydrofolate level within the central nervous system and can prevent the neuropsychiatric disorder. CSF levels of 5-methyltetrahydrofolate between 18 and 46 nmol/L may be sufficient to eradicate CNS disease.
Collapse
Affiliation(s)
- A Torres
- Department of Pediatrics, Division of Pediatric Neurology, Boston Medical Center, Boston University Medical School, Boston, MA, USA
| | - S A Newton
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - B Crompton
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - A Borzutzky
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - E J Neufeld
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - L Notarangelo
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - G T Berry
- Department of Neurology, Divisions of Hematology and Genetics and Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
| |
Collapse
|
16
|
|
17
|
Abstract
The properties of intestinal folate absorption were documented decades ago. However, it was only recently that the proton-coupled folate transporter (PCFT) was identified and its critical role in folate transport across the apical brush-border membrane of the proximal small intestine established by the loss-of-function mutations identified in the PCFT gene in subjects with hereditary folate malabsorption and, more recently, by the Pcft-null mouse. This article reviews the current understanding of the properties of PCFT-mediated transport and how they differ from those of the reduced folate carrier. Other processes that contribute to the transport of folates across the enterocyte, along with the contribution of the enterohepatic circulation, are considered. Important unresolved issues are addressed, including the mechanism of intestinal folate absorption in the absence of PCFT and regulation of PCFT gene expression. The impact of a variety of ions, organic molecules, and drugs on PCFT-mediated folate transport is described.
Collapse
Affiliation(s)
- Michele Visentin
- Departments of Molecular Pharmacology and Medicine, Albert Einstein College of Medicine, Bronx, New York 10461; , , ,
| | | | | | | |
Collapse
|
18
|
Wilson MR, Hou Z, Matherly LH. Substituted cysteine accessibility reveals a novel transmembrane 2-3 reentrant loop and functional role for transmembrane domain 2 in the human proton-coupled folate transporter. J Biol Chem 2014; 289:25287-95. [PMID: 25053408 DOI: 10.1074/jbc.m114.578252] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The proton-coupled folate transporter (PCFT) is a folate-proton symporter highly expressed in solid tumors that can selectively target cytotoxic antifolates to tumors under acidic microenvironment conditions. Predicted topology models for PCFT suggest that the loop domain between transmembrane domains (TMDs) 2 and 3 resides in the cytosol. Mutations involving Asp-109 or Arg-113 in the TMD2-3 loop result in loss of activity. By structural homology to other solute carriers, TMD2 may form part of the PCFT substrate binding domain. In this study we mutated the seven cysteine (Cys) residues of human PCFT to serine, creating Cys-less PCFT. Thirty-three single-Cys mutants spanning TMD2 and the TMD2-3 loop in a Cys-less PCFT background were transfected into PCFT-null HeLa cells. All 33 mutants were detected by Western blotting, and 28 were active for [(3)H]methotrexate uptake at pH 5.5. For the active residues, we performed pulldown assays with membrane-impermeable 2-aminoethyl methanethiosulfonate-biotin and streptavidin beads to determine their aqueous-accessibilities. Multiple residues in TMD2 and the TMD2-3 loop domain reacted with 2-aminoethyl methanethiosulfonate-biotin, establishing aqueous accessibilities. Pemetrexed pretreatment inhibited biotinylation of TMD2 mutants G93C and F94C, and biotinylation of these residues inhibited methotrexate transport activity. Our results suggest that the TMD 2-3 loop domain is aqueous-accessible and forms a novel reentrant loop structure. Residues in TMD2 form an aqueous transmembrane pathway for folate substrates, and Gly-93 and Phe-94 may contribute to a substrate binding domain. Characterization of PCFT structure is essential to understanding the transport mechanism including the critical determinants of substrate binding.
Collapse
Affiliation(s)
| | - Zhanjun Hou
- From the Department of Oncology and the Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan 48201
| | - Larry H Matherly
- From the Department of Oncology and the Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan 48201 Department of Pharmacology, Wayne State University School of Medicine and
| |
Collapse
|
19
|
Impact of folate therapy on combined immunodeficiency secondary to hereditary folate malabsorption. Clin Immunol 2014; 153:17-22. [DOI: 10.1016/j.clim.2014.03.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2013] [Revised: 03/19/2014] [Accepted: 03/21/2014] [Indexed: 01/19/2023]
|
20
|
Chiabrando D, Vinchi F, Fiorito V, Mercurio S, Tolosano E. Heme in pathophysiology: a matter of scavenging, metabolism and trafficking across cell membranes. Front Pharmacol 2014; 5:61. [PMID: 24782769 PMCID: PMC3986552 DOI: 10.3389/fphar.2014.00061] [Citation(s) in RCA: 275] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 03/18/2014] [Indexed: 01/19/2023] Open
Abstract
Heme (iron-protoporphyrin IX) is an essential co-factor involved in multiple biological processes: oxygen transport and storage, electron transfer, drug and steroid metabolism, signal transduction, and micro RNA processing. However, excess free-heme is highly toxic due to its ability to promote oxidative stress and lipid peroxidation, thus leading to membrane injury and, ultimately, apoptosis. Thus, heme metabolism needs to be finely regulated. Intracellular heme amount is controlled at multiple levels: synthesis, utilization by hemoproteins, degradation and both intracellular and intercellular trafficking. This review focuses on recent findings highlighting the importance of controlling intracellular heme levels to counteract heme-induced oxidative stress. The contributions of heme scavenging from the extracellular environment, heme synthesis and incorporation into hemoproteins, heme catabolism and heme transport in maintaining adequate intracellular heme content are discussed. Particular attention is put on the recently described mechanisms of heme trafficking through the plasma membrane mediated by specific heme importers and exporters. Finally, the involvement of genes orchestrating heme metabolism in several pathological conditions is illustrated and new therapeutic approaches aimed at controlling heme metabolism are discussed.
Collapse
Affiliation(s)
- Deborah Chiabrando
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin Turin, Italy
| | - Francesca Vinchi
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin Turin, Italy
| | - Veronica Fiorito
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin Turin, Italy
| | - Sonia Mercurio
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin Turin, Italy
| | - Emanuela Tolosano
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin Turin, Italy
| |
Collapse
|
21
|
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
|
22
|
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
|
23
|
Duddempudi PK, Goyal R, Date SS, Jansen M. Delineating the extracellular water-accessible surface of the proton-coupled folate transporter. PLoS One 2013; 8:e78301. [PMID: 24205192 PMCID: PMC3799626 DOI: 10.1371/journal.pone.0078301] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 09/16/2013] [Indexed: 11/19/2022] Open
Abstract
The proton-coupled folate transporter (PCFT) was recently identified as the major uptake route for dietary folates in humans. The three-dimensional structure of PCFT and its detailed interplay with function remain to be determined. We screened the water-accessible extracellular surface of HsPCFT using the substituted-cysteine accessibility method, to investigate the boundaries between the water-accessible surface and inaccessible buried protein segments. Single-cysteines, engineered individually at 40 positions in a functional cysteine-less HsPCFT background construct, were probed for plasma-membrane expression in Xenopus oocytes with a bilayer-impermeant primary-amine-reactive biotinylating agent (sulfosuccinimidyl 6-(biotinamido) hexanoate), and additionally for water-accessibility of the respective engineered cysteine with the sulfhydryl-selective biotinylating agent 2-((biotinoyl)amino)ethyl methanethiosulfonate. The ratio between Cys-selective over amine-selective labeling was further used to evaluate three-dimensional models of HsPCFT generated by homology / threading modeling. The closest homologues of HsPCFT with a known experimentally-determined three-dimensional structure are all members of one of the largest membrane protein super-families, the major facilitator superfamily (MFS). The low sequence identity - 14% or less – between HsPCFT and these templates necessitates experiment-based evaluation and model refinement of homology / threading models. With the present set of single-cysteine accessibilities, the models based on GlpT and PepTSt are most promising for further refinement.
Collapse
Affiliation(s)
- Phaneendra Kumar Duddempudi
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Raman Goyal
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Swapneeta Sanjay Date
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Michaela Jansen
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
- * E-mail:
| |
Collapse
|
24
|
Duddempudi PK, Nakashe P, Blanton MP, Jansen M. The monomeric state of the proton-coupled folate transporter represents the functional unit in the plasma membrane. FEBS J 2013; 280:2900-15. [PMID: 23601781 DOI: 10.1111/febs.12293] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 03/10/2013] [Accepted: 04/16/2013] [Indexed: 01/20/2023]
Abstract
Folic acid is an essential vitamin required for de novo biosynthesis of nucleotides and amino acids. The proton-coupled folate transporter (PCFT; SLC46A1) has been identified as the major contributor for intestinal folate uptake. It is also involved in folate transport across the blood-brain barrier and into solid tumors. PCFT belongs to the major facilitator superfamily. Major facilitator superfamily members can exist in either monomeric or homo-oligomeric form. Here, we utilized blue native polyacrylamide gel electrophoresis (BN/PAGE) and crosslinking with bi-functional chemicals to investigate the quaternary structure of human PCFT after heterologous expression in Xenopus laevis oocytes and CHO cells. PCFT was expressed in the plasma membrane in both expression systems. The functionality of the utilized PCFT construct was confirmed in oocytes by folic acid induced currents at acidic pH. For both the oocyte and CHO expression system [(3)H]folic acid uptake studies indicated that PCFT was functional. To analyze the oligomeric state of PCFT in the plasma membrane, plasma membranes were isolated by polymerization with colloidal silica and polyacrylic acid and subsequent centrifugation. The digitonin-solubilized non-denatured PCFT migrated during BN/PAGE as a monomer, as judged by comparison with a membrane protein (5-HT(3A) receptor) of known pentameric assembly that was used to create a molecular sizing ladder. The chemical crosslinkers glutaraldehyde and dimethyl adipimidate were not able to covalently link potential higher order PCFT structures to form oligomers that were stable following SDS treatment. Together, our results demonstrate that plasma-membrane PCFT functions as a monomeric protein.
Collapse
Affiliation(s)
- Phaneendra K Duddempudi
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | | | | | | |
Collapse
|
25
|
Kirsch SH, Herrmann W, Obeid R. Genetic defects in folate and cobalamin pathways affecting the brain. Clin Chem Lab Med 2013. [DOI: 10.1515/cclm-2012-0673] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
26
|
Desmoulin SK, Hou Z, Gangjee A, Matherly LH. The human proton-coupled folate transporter: Biology and therapeutic applications to cancer. Cancer Biol Ther 2012; 13:1355-73. [PMID: 22954694 PMCID: PMC3542225 DOI: 10.4161/cbt.22020] [Citation(s) in RCA: 116] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
This review summarizes the biology of the proton-coupled folate transporter (PCFT). PCFT was identified in 2006 as the primary transporter for intestinal absorption of dietary folates, as mutations in PCFT are causal in hereditary folate malabsorption (HFM) syndrome. Since 2006, there have been major advances in understanding the mechanistic roles of critical amino acids and/or domains in the PCFT protein, many of which were identified as mutated in HFM patients, and in characterizing transcriptional control of the human PCFT gene. With the recognition that PCFT is abundantly expressed in human tumors and is active at pHs characterizing the tumor microenvironment, attention turned to exploiting PCFT for delivering novel cytotoxic antifolates for solid tumors. The finding that pemetrexed is an excellent PCFT substrate explains its demonstrated clinical efficacy for mesothelioma and non-small cell lung cancer, and prompted development of more PCFT-selective tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine antifolates that derive their cytotoxic effects by targeting de novo purine nucleotide biosynthesis.
Collapse
Affiliation(s)
- Sita Kugel Desmoulin
- Cancer Biology Graduate Program in Cancer Biology, Department of Oncology, Wayne State University School of Medicine; Detroit, MI USA
| | | | | | | |
Collapse
|
27
|
Gonen N, Assaraf YG. Antifolates in cancer therapy: Structure, activity and mechanisms of drug resistance. Drug Resist Updat 2012; 15:183-210. [DOI: 10.1016/j.drup.2012.07.002] [Citation(s) in RCA: 269] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2012] [Revised: 06/25/2012] [Accepted: 07/11/2012] [Indexed: 01/19/2023]
|
28
|
Shin DS, Zhao R, Fiser A, Goldman DI. Functional roles of the A335 and G338 residues of the proton-coupled folate transporter (PCFT-SLC46A1) mutated in hereditary folate malabsorption. Am J Physiol Cell Physiol 2012; 303:C834-42. [PMID: 22843796 DOI: 10.1152/ajpcell.00171.2012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The proton-coupled folate transporter (PCFT-SLC46A1) mediates intestinal folate absorption and folate transport across the choroid plexus, processes defective in hereditary folate malabsorption (HFM). This paper characterizes the functional defect, and the roles of two mutated PCFT residues, associated with HFM (G338R and A335D). The A335D-PCFT and other mutations at this residue result in an unstable protein; when expression of a mutant protein was preserved, function was always retained. The G338R and other charged mutants resulted in an unstable protein; substitutions with small neutral and polar amino acids preserved protein but with impaired function. Pemetrexed and methotrexate (MTX) influx kinetics mediated by the G338C mutant PCFT revealed marked (15- to 20-fold) decreases in K(t) and V(max) compared with wild-type PCFT. In contrast, there was only a small (∼2-fold) decrease in the MTX influx K(i) and an increase (∼3-fold) in the pemetrexed influx K(i) for the G338C-PCFT mutant. Neither a decrease in pH to 4.5, nor an increase to 7.4, restored function of the G338C mutant relative to wild-type PCFT excluding a role for this residue in proton binding or proton coupling. Homology modeling localized the A335 and G338 residues embedded in the 9th transmembrane, consistent with the inaccessibility of the A335C and G338C proteins to MTS reagents. Hence, the loss of intrinsic G338C-PCFT function was due solely to impaired oscillation of the carrier between its conformational states. The data illustrate how alterations in carrier cycling can impact influx K(t) without comparable alterations in substrate binding to the carrier.
Collapse
Affiliation(s)
- Daniel Sanghoon Shin
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | | | | | | |
Collapse
|
29
|
Zhao R, Shin DS, Fiser A, Goldman ID. Identification of a functionally critical GXXG motif and its relationship to the folate binding site of the proton-coupled folate transporter (PCFT-SLC46A1). Am J Physiol Cell Physiol 2012; 303:C673-81. [PMID: 22785121 DOI: 10.1152/ajpcell.00123.2012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The proton-coupled folate transporter (PCFT) mediates intestinal folate absorption, and loss-of-function mutations in this gene result in the autosomal recessive disorder hereditary folate malabsorption. The current study, focused on a structure-functional analysis of this transporter, identified Gly-189 and Gly-192 (a GxxG motif) located in the fifth transmembrane domain as residues that could not be replaced with alanine without a loss of function. In contrast, function was preserved when Gly-56 and Gly-59 (the other conservative GXXG motif in human PCFT) were replaced with alanine. Similarly, Gly-93 and Gly-97, which constitute the only conserved GXXXG dimerization motif in human PCFT, tolerated alanine substitution. To explore the role of this region in folate binding, the residues around Gly-189 and Gly-192 were analyzed by the substituted cysteine accessibility method. Both I188C and M193C mutants were functional and were inhibited by membrane-impermeable sulfhydryl-reactive reagents; this could be prevented with PCFT substrate, but the protection was sustained at 0°C only for the I188C mutant, consistent with localization of Ile-188 in the PCFT folate binding pocket. The functional role of residues around Gly-189 and Gly-192 is consistent with a molecular structural model in which these two residues along with Ieu-188 are accessible to the PCFT aqueous translocation pathway.
Collapse
Affiliation(s)
- Rongbao Zhao
- Depts. of Medicine and Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | | | | | | |
Collapse
|
30
|
Hou Z, Kugel Desmoulin S, Etnyre E, Olive M, Hsiung B, Cherian C, Wloszczynski PA, Moin K, Matherly LH. Identification and functional impact of homo-oligomers of the human proton-coupled folate transporter. J Biol Chem 2011; 287:4982-95. [PMID: 22179615 DOI: 10.1074/jbc.m111.306860] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The proton-coupled folate transporter (PCFT; SLC46A1) is a proton-folate symporter that is abundantly expressed in solid tumors and normal tissues, such as duodenum. The acidic pH optimum for PCFT is relevant to intestinal absorption of folates and could afford a means of selectively targeting tumors with novel cytotoxic antifolates. PCFT is a member of the major facilitator superfamily of transporters. Because major facilitator superfamily members exist as homo-oligomers, we tested this for PCFT because such structures could be significant to PCFT mechanism and regulation. By transiently expressing PCFT in reduced folate carrier- and PCFT-null HeLa (R1-11) cells and chemical cross-linking with 1,1-methanediyl bismethanethiosulfonate and Western blotting, PCFT species with molecular masses approximating those of the PCFT dimer and higher order oligomers were detected. Blue native polyacrylamide gel electrophoresis identified PCFT dimer, trimer, and tetramer forms. PCFT monomers with hemagglutinin and His(10) epitope tags were co-expressed in R1-11 cells, solubilized, and bound to nickel affinity columns, establishing their physical associations. Co-expressing YPet and ECFP*-tagged PCFT monomers enabled transport and fluorescence resonance energy transfer in plasma membranes of R1-11 cells. Combined wild-type (WT) and inactive mutant P425R PCFTs were targeted to the cell surface by surface biotinylation/Western blots and confocal microscopy and functionally exhibited a "dominant-positive" phenotype, implying positive cooperativity between PCFT monomers and functional rescue of mutant by WT PCFT. Our results demonstrate the existence of PCFT homo-oligomers and imply their functional and regulatory impact. Better understanding of these higher order PCFT structures may lead to therapeutic applications related to folate uptake in hereditary folate malabsorption, and delivery of PCFT-targeted chemotherapy drugs for cancer.
Collapse
Affiliation(s)
- Zhanjun Hou
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Mangold S, Blau N, Opladen T, Steinfeld R, Wessling B, Zerres K, Häusler M. Cerebral folate deficiency: a neurometabolic syndrome? Mol Genet Metab 2011; 104:369-72. [PMID: 21737328 DOI: 10.1016/j.ymgme.2011.06.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 06/07/2011] [Accepted: 06/07/2011] [Indexed: 11/19/2022]
Abstract
BACKGROUND Cerebral folate deficiency (CFD) is increasingly recognized in various neurological conditions, raising the question of whether it might represent a clear-cut clinical syndrome. METHODS Retrospective analysis of patients with low cerebral spinal fluid (CSF) 5-methyltetrahydrofolate (5MTHF) values was performed. RESULTS 58 pediatric patients with low (-2nd to -3rd standard deviation) and 45 patients with very low 5MTHF values (<3rd standard deviation) were identified, including 22 patients with defined underlying neurological conditions. The leading symptoms were mental retardation (n=84), motor retardation (n=75), epilepsy (n=53), ataxia (n=44) and pyramidal tract signs (n=37). There was no relationship between 5MTHF levels and the severity of clinical disease, the duration of clinical disease, distinct neurological symptoms and antiepileptic drug treatment, respectively. Genetical analysis for mutations in the folate receptor 1 gene proved normal in all 16 children studied. CONCLUSIONS For the majority of patients CFD is not a clear-cut neurometabolic syndrome but the common result of different genetic, metabolic or unknown processes. Nevertheless, CFD may represent a treatable disease-modifying factor which should therefore be addressed in prospective studies.
Collapse
Affiliation(s)
- Sarah Mangold
- Department of Pediatrics, University Hospital RWTH Aachen, Germany.
| | | | | | | | | | | | | |
Collapse
|
32
|
Zhao R, Shin DS, Diop-Bove N, Ovits CG, Goldman ID. Random mutagenesis of the proton-coupled folate transporter (SLC46A1), clustering of mutations, and the bases for associated losses of function. J Biol Chem 2011; 286:24150-8. [PMID: 21602279 PMCID: PMC3129196 DOI: 10.1074/jbc.m111.236539] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 04/25/2011] [Indexed: 01/19/2023] Open
Abstract
Loss-of-function mutations in the proton-coupled folate transporter (PCFT, SLC46A1) result in the autosomal recessive disorder, hereditary folate malabsorption (HFM). Identification and characterization of HFM mutations provide a wealth of information on the structure-function relationship of this transporter. In the current study, PCR-based random mutagenesis was employed to generate unbiased loss-of-function mutations of PCFT, simulating the spectrum of alterations that might occur in the human disorder. A total of 26 mutations were generated and 4 were identical to HFM mutations. Eleven were base deletion or insertion mutations that led to a frameshift and, along with similar HFM mutations, are predominantly localized to two narrow regions of the pcft gene at the 5'-end. Base substitution mutations identified in the current study and HFM patients were largely distributed across the pcft gene. Elimination of the ATG initiation codon by a one-base substitution (G > A) did not result in a complete lack of translation at the same codon consistent with rare non-ATG translation initiation. Among six missense mutants evaluated, three mutant PCFTs were not detected at the plasma membrane, one mutation resulted in decreased binding to folate substrate, and one had a reduced rate of conformational change associated with substrate translocation. The remaining PCFT mutant had defects in both processes. These results broaden understanding of the regions of the pcft gene prone to base insertion and deletion and inform further approaches to the analysis of the structure-function of PCFT.
Collapse
Affiliation(s)
- Rongbao Zhao
- Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
| | | | | | | | | |
Collapse
|