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Farrell CC, Khanna S, Hoque MT, Plaga A, Basset N, Syed I, Biouss G, Aufreiter S, Marcon N, Bendayan R, Kim YI, O'Connor DL. Low-dose daily folic acid (400 μg) supplementation does not affect regulation of folate transporters found present throughout the terminal ileum and colon of humans: a randomized clinical trial. Am J Clin Nutr 2024; 119:809-820. [PMID: 38157986 DOI: 10.1016/j.ajcnut.2023.12.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/23/2023] [Accepted: 12/26/2023] [Indexed: 01/03/2024] Open
Abstract
BACKGROUND Folic acid supplementation during the periconceptional period reduces the risk of neural tube defects in infants, but concern over chronic folic acid exposure remains. An improved understanding of folate absorption may clarify potential risks. Folate transporters have been characterized in the small intestine, but less so in the colon of healthy, free-living humans. The impact of folic acid fortification or supplementation on regulation of these transporters along the intestinal tract is unknown. OBJECTIVE The objective was to characterize expression of folate transporters/receptor (FT/R) and folate hydrolase, glutamate carboxypeptidase II (GCPII), from the terminal ileum and throughout the colon of adults and assess the impact of supplemental folic acid. METHODS In this 16-wk open-labeled randomized clinical trial, adults consumed a low folic acid-containing diet, a folate-free multivitamin, and either a 400 μg folic acid supplement or no folic acid supplement. Dietary intakes and blood were assessed at baseline, 8 wk, and 16 wk (time of colonoscopy). Messenger RNA (mRNA) expression and protein expression of FT/R and GCPII were assessed in the terminal ileum, cecum, and ascending and descending colon. RESULTS Among 24 randomly assigned subjects, no differences in dietary folate intake or blood folate were observed at baseline. Mean ± SD red blood cell folate at 16 wk was 1765 ± 426 and 911 ± 242 nmol/L in the 400 and 0 μg folic acid group, respectively (P < 0.0001). Reduced folate carrier, proton-coupled folate transporter, and folate-receptor alpha expression were detected in the terminal ileum and colon, as were efflux transporters of breast cancer resistance protein and multidrug resistance protein-3. Other than a higher mRNA expression of FR-alpha and GCPII in the 400 μg supplement group in the ascending colon, no treatment differences were observed (P < 0.02). CONCLUSIONS Folate transporters are present throughout the terminal ileum and colon; there is little evidence that a low dose of folic acid supplementation affects colonic absorption. This trial was registered at clinicaltrials.gov as NCT03421483.
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Affiliation(s)
- Colleen C Farrell
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Siya Khanna
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Md Tozammel Hoque
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada
| | - Aneta Plaga
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Nancy Basset
- Division of Gastroenterology, Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada
| | - Ishba Syed
- Division of Gastroenterology, Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada
| | - George Biouss
- Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada; Developmental and Stem Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Susanne Aufreiter
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Norman Marcon
- Division of Gastroenterology, Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada
| | - Reina Bendayan
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada
| | - Young-In Kim
- Division of Gastroenterology, Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada; Keenan Research Centre for Biomedical Science of St. Michael's Hospital, Toronto, Ontario, Canada
| | - Deborah L O'Connor
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Translational Medicine Program, The Hospital for Sick Children, Toronto, Ontario, Canada.
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Gurler G, Belder N, Beker MC, Sever-Bahcekapili M, Uruk G, Kilic E, Yemisci M. Reduced folate carrier 1 is present in retinal microvessels and crucial for the inner blood retinal barrier integrity. Fluids Barriers CNS 2023; 20:47. [PMID: 37328777 DOI: 10.1186/s12987-023-00442-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Accepted: 05/18/2023] [Indexed: 06/18/2023] Open
Abstract
BACKGROUND Reduced folate carrier 1 (RFC1; SLC19a1) is the main responsible transporter for the B9 family of vitamins named folates, which are essential for normal tissue growth and development. While folate deficiency resulted in retinal vasculopathy, the expression and the role of RFC1 in blood-retinal barrier (BRB) are not well known. METHODS We used whole mount retinas and trypsin digested microvessel samples of adult mice. To knockdown RFC1, we delivered RFC1-targeted short interfering RNA (RFC1-siRNA) intravitreally; while, to upregulate RFC1 we delivered lentiviral vector overexpressing RFC1. Retinal ischemia was induced 1-h by applying FeCl3 to central retinal artery. We used RT-qPCR and Western blotting to determine RFC1. Endothelium (CD31), pericytes (PDGFR-beta, CD13, NG2), tight-junctions (Occludin, Claudin-5 and ZO-1), main basal membrane protein (Collagen-4), endogenous IgG and RFC1 were determined immunohistochemically. RESULTS Our analyses on whole mount retinas and trypsin digested microvessel samples of adult mice revealed the presence of RFC1 in the inner BRB and colocalization with endothelial cells and pericytes. Knocking down RFC1 expression via siRNA delivery resulted in the disintegration of tight junction proteins and collagen-4 in twenty-four hours, which was accompanied by significant endogenous IgG extravasation. This indicated the impairment of BRB integrity after an abrupt RFC1 decrease. Furthermore, lentiviral vector-mediated RFC1 overexpression resulted in increased tight junction proteins and collagen-4, confirming the structural role of RFC1 in the inner BRB. Acute retinal ischemia decreased collagen-4 and occludin levels and led to an increase in RFC1. Besides, the pre-ischemic overexpression of RFC1 partially rescued collagen-4 and occludin levels which would be decreased after ischemia. CONCLUSION In conclusion, our study clarifies the presence of RFC1 protein in the inner BRB, which has recently been defined as hypoxia-immune-related gene in other tissues and offers a novel perspective of retinal RFC1. Hence, other than being a folate carrier, RFC1 is an acute regulator of the inner BRB in healthy and ischemic retinas.
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Affiliation(s)
- Gokce Gurler
- The Institute of Neurological Sciences and Psychiatry, Hacettepe University, Ankara, Turkey
| | - Nevin Belder
- Biotechnology Institute, Ankara University, Ankara, Turkey
| | | | | | - Gokhan Uruk
- The Institute of Neurological Sciences and Psychiatry, Hacettepe University, Ankara, Turkey
| | - Ertugrul Kilic
- Neuroscience and Neurotechnology Center of Excellence (NÖROM), Ankara, Turkey
- Physiology, Istanbul Medeniyet University, Istanbul, Turkey
| | - Muge Yemisci
- The Institute of Neurological Sciences and Psychiatry, Hacettepe University, Ankara, Turkey.
- Faculty of Medicine, Department of Neurology, Hacettepe University, Ankara, Turkey.
- Neuroscience and Neurotechnology Center of Excellence (NÖROM), Ankara, Turkey.
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Gilmore JC, Hoque MT, Dai W, Mohan H, Dunk C, Serghides L, Bendayan R. Interaction between dolutegravir and folate transporters and receptor in human and rodent placenta. EBioMedicine 2021; 75:103771. [PMID: 34954655 PMCID: PMC8715299 DOI: 10.1016/j.ebiom.2021.103771] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 10/27/2021] [Accepted: 12/07/2021] [Indexed: 12/17/2022] Open
Abstract
Background Due to the critical role of folates in neurodevelopment, it is important to understand potential interactions between anti-HIV drugs used during pregnancy, and folate delivery pathways in the placenta. This study investigates the effect of dolutegravir (DTG) exposure on the functional expression of the reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and folate receptor-α (FRα) in the placenta. Methods Human placental cell lines, human placental explants, and a pregnant mouse model treated with clinically relevant concentrations of DTG were used. Gene and protein expression were assessed by qPCR, immunoblot and immunohistochemical assays. Folate transport function was measured by applying radioisotope-based transport assays. Findings In placental cells, clinically relevant DTG exposure for 3h or 6h was associated with a modest but significant reduction in the expression of RFC and PCFT both at the mRNA and protein levels, as well as decreased uptake of RFC and PCFT substrates [3H]-methotrexate and [3H]-folic acid, respectively. In pregnant mice, DTG administration was associated with an increase in both placental RFC and PCFT mRNA expression, accompanied by a decrease in placental FRα mRNA under folate-deficient dietary conditions. Interpretation These findings demonstrate a potential interaction between DTG and folate transport pathways in the placenta, particularly in vivo, under folate deficient conditions, potentially impacting folate delivery to the foetus in the context of DTG-based ART during pregnancy. Funding Funded by Ontario HIV Treatment Network, grant #506657; and Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health, award #R01HD104553.
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Affiliation(s)
- Julian C Gilmore
- Department of Pharmaceutical Sciences, University of Toronto, Toronto, Canada
| | - Md Tozammel Hoque
- Department of Pharmaceutical Sciences, University of Toronto, Toronto, Canada
| | - Wanying Dai
- Department of Pharmaceutical Sciences, University of Toronto, Toronto, Canada
| | - Haneesha Mohan
- Toronto General Hospital Research Institute, University Health Network, Toronto Canada
| | - Caroline Dunk
- Toronto General Hospital Research Institute, University Health Network, Toronto Canada
| | - Lena Serghides
- Toronto General Hospital Research Institute, University Health Network, Toronto Canada; Department of Immunology and Institute of Medical Sciences, University of Toronto, Toronto, Canada
| | - Reina Bendayan
- Department of Pharmaceutical Sciences, University of Toronto, Toronto, Canada.
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Shulpekova Y, Nechaev V, Kardasheva S, Sedova A, Kurbatova A, Bueverova E, Kopylov A, Malsagova K, Dlamini JC, Ivashkin V. The Concept of Folic Acid in Health and Disease. Molecules 2021; 26:molecules26123731. [PMID: 34207319 PMCID: PMC8235569 DOI: 10.3390/molecules26123731] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 06/12/2021] [Accepted: 06/17/2021] [Indexed: 12/18/2022] Open
Abstract
Folates have a pterine core structure and high metabolic activity due to their ability to accept electrons and react with O-, S-, N-, C-bounds. Folates play a role as cofactors in essential one-carbon pathways donating methyl-groups to choline phospholipids, creatine, epinephrine, DNA. Compounds similar to folates are ubiquitous and have been found in different animals, plants, and microorganisms. Folates enter the body from the diet and are also synthesized by intestinal bacteria with consequent adsorption from the colon. Three types of folate and antifolate cellular transporters have been found, differing in tissue localization, substrate affinity, type of transferring, and optimal pH for function. Laboratory criteria of folate deficiency are accepted by WHO. Severe folate deficiencies, manifesting in early life, are seen in hereditary folate malabsorption and cerebral folate deficiency. Acquired folate deficiency is quite common and is associated with poor diet and malabsorption, alcohol consumption, obesity, and kidney failure. Given the observational data that folates have a protective effect against neural tube defects, ischemic events, and cancer, food folic acid fortification was introduced in many countries. However, high physiological folate concentrations and folate overload may increase the risk of impaired brain development in embryogenesis and possess a growth advantage for precancerous altered cells.
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Affiliation(s)
- Yulia Shulpekova
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Vladimir Nechaev
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Svetlana Kardasheva
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Alla Sedova
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Anastasia Kurbatova
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Elena Bueverova
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
| | - Arthur Kopylov
- Biobanking Group, Branch of Institute of Biomedical Chemistry “Scientific and Education Center”, 119121 Moscow, Russia;
| | - Kristina Malsagova
- Biobanking Group, Branch of Institute of Biomedical Chemistry “Scientific and Education Center”, 119121 Moscow, Russia;
- Correspondence: ; Tel.: +7-499-764-9878
| | | | - Vladimir Ivashkin
- Department of Internal Diseases Propedeutics, Sechenov University, 119121 Moscow, Russia; (Y.S.); (V.N.); (S.K.); (A.S.); (A.K.); (E.B.); (V.I.)
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Palladino E, Van Mieghem T, Connor KL. Diet Alters Micronutrient Pathways in the Gut and Placenta that Regulate Fetal Growth and Development in Pregnant Mice. Reprod Sci 2021; 28:447-461. [PMID: 32886339 DOI: 10.1007/s43032-020-00297-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 08/10/2020] [Indexed: 11/30/2022]
Abstract
Maternal malnutrition and micronutrient deficiencies can alter fetal development. However, the mechanisms underlying these relationships are poorly understood. We used a systems physiology approach to investigate diet-induced effects on maternal gut microbes and folate/inositol transport in the maternal/fetal gut and placenta. Female mice were fed a control diet (CON) diet, undernourished (UN, restricted by 30% of CON intake) or a high-fat diet (HF, 60% kcals fat) during pregnancy to model normal pregnancy, fetal growth restriction or maternal metabolic dysfunction, respectively. At gestational day 18.5, we assessed circulating folate levels by microbiological assay, relative abundance of gut lactobacilli by G3PhyloChip™, and folate/inositol transporters in placenta and maternal/fetal gut by qPCR/immunohistochemistry. UN and HF-fed mothers had lower plasma folate concentrations vs. CON. Relative abundances of three lactobacilli taxa were higher in HF vs. UN and CON. HF-fed mothers had higher gut proton coupled folate transporter (Pcft) and reduced folate carrier 1 (Rfc1), and lower sodium myo-inositol co-transporter 2 (Smit2), mRNA expression vs. UN and CON. HF placentae had increased folate receptor beta (Frβ) expression vs. UN. mRNA expression of Pcft, folate receptor alpha (Frα), and Smit2 was higher in gut of HF fetuses vs. UN and CON. Transporter protein expression was not different between groups. Maternal malnutrition alters abundance of select gut microbes and folate/inositol transporters, which may influence maternal micronutrient status and delivery to the fetus, impacting pregnancy/fetal outcomes.
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Affiliation(s)
- Elia Palladino
- Carleton University (Health Sciences), Ottawa, Ontario, Canada
| | - Tim Van Mieghem
- Mount Sinai Hospital (Obstetrics and Gynaecology), Toronto, Ontario, Canada
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Sid V, Siow YL, Shang Y, Woo CW, O K. High-fat diet consumption reduces hepatic folate transporter expression via nuclear respiratory factor-1. J Mol Med (Berl) 2018; 96:1203-1213. [PMID: 30178194 DOI: 10.1007/s00109-018-1688-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 08/03/2018] [Accepted: 08/17/2018] [Indexed: 12/13/2022]
Abstract
Folate is an essential micronutrient for biological function. The liver, a primary organ for folate metabolism and storage, plays an important role in folate homeostasis. Proton-coupled folate transporter (PCFT) and reduced folate carrier (RFC) are the major folate transporters responsible for folate uptake at basolateral membrane of hepatocytes. Low serum folate levels are frequently associated with obesity. We investigated the mechanism that regulated folate status in a mouse model with diet-induced obesity. Mice (C57BL/6J) were fed a high-fat diet (60% kcal fat) for 8 weeks. Mice displayed increased hepatic lipid accumulation and decreased folate levels in the liver and serum compared to mice fed a normal chow diet (10% kcal fat). High-fat diet-fed mice had low expression of PCFT and RFC and decreased nuclear respiratory factor-1 (NRF-1)/DNA-binding activity. Treatment with NRF-1 siRNA or palmitic acid reduced folate transporter expression in hepatocytes. Inhibition of NRF-1 mediated folate transporter expression significantly reduced intracellular folate levels. These results suggest that chronic consumption of high-fat diets impairs folate transporter expression via NRF-1-dependent mechanism, leading to reduced hepatic folate storage. Understanding the regulation of folate homeostasis in obesity may have an important implication in current guideline of folate intake. KEY MESSAGES: Serum and liver folate levels are decreased in diet-induced obese mice. Chronic high-fat diet consumption impairs expression of hepatic PCFT and RFC. NRF-1 regulates hepatic folate transporters expression and folate levels.
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Affiliation(s)
- Victoria Sid
- St. Boniface Hospital Research Centre, Winnipeg, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada
| | - Yaw L Siow
- St. Boniface Hospital Research Centre, Winnipeg, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada
- Agriculture and Agri-Food Canada, Winnipeg, Canada
| | - Yue Shang
- St. Boniface Hospital Research Centre, Winnipeg, Canada
- Department of Animal Science, University of Manitoba, Winnipeg, Canada
| | - Connie W Woo
- Department of Pharmacology and Pharmacy, The University of Hong Kong, Hong Kong, SAR, China.
| | - Karmin O
- St. Boniface Hospital Research Centre, Winnipeg, Canada.
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Canada.
- Department of Animal Science, University of Manitoba, Winnipeg, Canada.
- Laboratory of Integrative Biology, CCARM, St. Boniface Hospital Research Centre, 351 Tache Avenue, Winnipeg, Manitoba, R2H 2A6, Canada.
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Mann A, Portnoy E, Han H, Inbar D, Blatch D, Shmuel M, Ben-Hur T, Eyal S, Ekstein D. Folate homeostasis in epileptic rats. Epilepsy Res 2018; 142:64-72. [PMID: 29571151 DOI: 10.1016/j.eplepsyres.2018.03.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 03/09/2018] [Accepted: 03/15/2018] [Indexed: 12/28/2022]
Abstract
Folate is involved in metabolic processes and it has been implicated in both aggravation and amelioration of seizures. The aim of the current work was to study the effect of chronic temporal lobe epilepsy (TLE) on the plasma and brain concentrations of folate and on its uptake carriers in the brain - the reduced folate carrier (RFC), folate receptor α (FRα) and proton coupled folate transporter (PCFT). We utilized the rat lithium pilocarpine model for TLE. Approximately two months following status epilepticus, rats with spontaneous recurrent seizures (SRS) were sacrificed for brain and plasma folate concentration analyses and folate uptake carrier expression studies. RT-PCR and western blot analyses were utilized for quantification of folate carriers' mRNAs and proteins, respectively. The distribution of folate carriers in the brain was studied using immunohistochemistry. In the SRS rats we found lower plasma concentrations (10 ± 0.9 in control vs. 6.6 ± 1.6 ng/ml in SRS, P < 0.05), but preserved cortical and increased hippocampal levels of folate (0.5 ± 0.1 in control vs. 0.9 ± 0.2 ng/mg in SRS, P = 0.055). Hippocampus - to - plasma ratio of folate concentration was 3-fold higher in the SRS group, compared with the controls (0.13 ± 0.03 vs. 0.04 ± 0.02, respectively; P < 0.01). mRNA and protein levels of the folate uptake carriers did not differ between SRS rats and controls. However, immunofluorescent staining quantification revealed that the emission intensity of both RFC and FRα was elevated 8-fold and 4-fold, respectively, in hippocampal CA1 neurons of SRS rats, compared to controls (P < 0.01). PCFT was unquantifiable. If corroborated by complementary research in humans, the findings of this study may be utilized clinically for supplemental therapy planning, in imaging the epileptic focus, and for drug delivery into the epileptic brain. Further studies are required for better elucidating the clinical and mechanistic significance of altered folate balances in the epileptic brain.
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Affiliation(s)
- Aniv Mann
- Institute for Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, 91120 Israel.
| | - Emma Portnoy
- Institute for Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, 91120 Israel.
| | - Hadas Han
- Institute for Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, 91120 Israel.
| | - Dorrit Inbar
- Department of Neurology, Agnes Ginges Center for Human Neurogenetics, Hadassah Hebrew University Medical Center, Jerusalem, 91120, Israel.
| | - Dana Blatch
- Department of Neurology, Agnes Ginges Center for Human Neurogenetics, Hadassah Hebrew University Medical Center, Jerusalem, 91120, Israel.
| | - Miriam Shmuel
- Institute for Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, 91120 Israel.
| | - Tamir Ben-Hur
- Department of Neurology, Agnes Ginges Center for Human Neurogenetics, Hadassah Hebrew University Medical Center, Jerusalem, 91120, Israel.
| | - Sara Eyal
- Institute for Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, 91120 Israel.
| | - Dana Ekstein
- Department of Neurology, Agnes Ginges Center for Human Neurogenetics, Hadassah Hebrew University Medical Center, Jerusalem, 91120, Israel.
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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.
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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.
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Stapf M, Pömpner N, Teichgräber U, Hilger I. Heterogeneous response of different tumor cell lines to methotrexate-coupled nanoparticles in presence of hyperthermia. Int J Nanomedicine 2016; 11:485-500. [PMID: 26893557 PMCID: PMC4745830 DOI: 10.2147/ijn.s94384] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Today, the therapeutic efficacy of cancer is restricted by the heterogeneity of the response of tumor cells to chemotherapeutic drugs. Since those therapies are also associated with severe side effects in nontarget organs, the application of drugs in combination with nanocarriers for targeted therapy has been suggested. Here, we sought to assess whether the coupling of methotrexate (MTX) to magnetic nanoparticles (MNP) could serve as a valuable tool to circumvent the heterogeneity of tumor cell response to MTX by the combined treatment with hyperthermia. To this end, we investigated five breast cancer cell lines of different origin and with different mutational statuses, as well as a bladder cancer cell line in terms of their response to exposure to MTX as a free drug or after its coupling to MNP as well as in presence/absence of hyperthermia. We also assessed whether the effects could be connected to the cell line-specific expression of proteins related to the uptake and efflux of MTX and MNP. Our results revealed a very heterogeneous and cell line-dependent response to an exposure with MTX-coupled MNP (MTX–MNP), which was almost comparable to the efficacy of free MTX in the same cell line. Moreover, a cell line-specific and preferential uptake of MTX–MNP compared with MNP alone was found (probably by receptor-mediated endocytosis), agreeing with the observed cytotoxic effects. Opposed to this, the expression pattern of several cell membrane transport proteins noted for MTX uptake and efflux was only by tendency in agreement with the cellular toxicity of MTX–MNP in different cell lines. Higher cytotoxic effects were achieved by exposing cells to a combination of MTX–MNP and hyperthermal treatment, compared with MTX or thermo-therapy alone. However, the heterogeneity in the response of the tumor cell lines to MTX could not be completely abolished – even after its combination with MNP and/or hyperthermia – and the application of higher thermal dosages might be necessary.
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Affiliation(s)
- Marcus Stapf
- Institute of Diagnostic and Interventional Radiology, Department of Experimental Radiology, Jena University Hospital, Friedrich-Schiller University, Jena, Germany
| | - Nadine Pömpner
- Institute of Diagnostic and Interventional Radiology, Department of Experimental Radiology, Jena University Hospital, Friedrich-Schiller University, Jena, Germany
| | - Ulf Teichgräber
- Institute of Diagnostic and Interventional Radiology, Department of Experimental Radiology, Jena University Hospital, Friedrich-Schiller University, Jena, Germany
| | - Ingrid Hilger
- Institute of Diagnostic and Interventional Radiology, Department of Experimental Radiology, Jena University Hospital, Friedrich-Schiller University, Jena, Germany
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DNA methylation and expression of the folate transporter genes in colorectal cancer. Tumour Biol 2015; 36:5581-90. [PMID: 25697897 DOI: 10.1007/s13277-015-3228-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 02/05/2015] [Indexed: 12/20/2022] Open
Abstract
Folate has a central role in the cell metabolism. This study aims to explore the DNA methylation pattern of the folate transporter genes FOLR1, PCFT, and RFC1 as well as the corresponding protein expressions in colorectal cancer (CRC) tissue and adjacent non-cancerous mucosa (ANCM). Our results showed statistically significant differences in the DNA-methylated fraction of all three genes at several gene regions; we identified three differentially methylated CpG sites in the FOLR1 gene, five CpG sites in the PCFT gene, and six CpG sites in the RFC1 gene. There was a pronounced expression of the FRα and RFC proteins in both the CRC and ANCM tissues, though the expression was attenuated in cancer compared to the paired ANCM tissues. The PCFT protein was undetectable or expressed at a very low level in both tissue types. Higher methylated fractions of the CpG sites 3-5 in the RFC1 gene were associated with a lower protein expression, suggestive of epigenetic regulation by DNA methylation of the RFC1 gene in the colorectal cancer. Our results did not show any association between the RFC and FRα protein expression and tumor stage, TNM classification, or tumor location. In conclusion, this is the first study to simultaneously evaluate both DNA methylation and protein expression of all three folate transporter genes, FOLR1, PCFT, and RFC1, in colorectal cancer. The results encourage further investigation into the possible prognostic implications of folate transporter expression and DNA methylation.
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11
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Hu J, Wang B, Sahyoun NR. Application of the Key Events Dose-response Framework to Folate Metabolism. Crit Rev Food Sci Nutr 2015; 56:1325-33. [DOI: 10.1080/10408398.2013.807221] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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12
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Liu T, Singh R, Rios Z, Bhushan A, Li M, Sheridan PP, Bearden SE, Lai JCK, Agbenowu S, Cao S, Daniels CK. Tyrosine phosphorylation of HSC70 and its interaction with RFC mediates methotrexate resistance in murine L1210 leukemia cells. Cancer Lett 2014; 357:231-241. [PMID: 25444929 DOI: 10.1016/j.canlet.2014.11.036] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2014] [Revised: 11/14/2014] [Accepted: 11/14/2014] [Indexed: 10/24/2022]
Abstract
We previously identified and characterized a 66-68 kDa membrane-associated, tyrosine phosphorylated protein in murine leukemia L1210 cells as HSC70 which is a methotrexate (MTX)-binding protein. In order to further characterize the functional role of HSC70 in regulating MTX resistance in L1210 cells, we first showed that HSC70 colocalizes and interacts with reduced folate carrier (RFC) in L1210 cells by confocal laser scanning microscopy and Duolink in situ proximity ligation assay. The tyrosine phosphorylation status of HSC70 found in the membrane fraction was different from the parental L1210/0 and cisplatin (CDDP)-MTX cross resistant L1210/DDP cells. In MTX-binding assays, HSC70 from L1210/DDP cells showed less affinity for MTX-agarose beads than that of L1210/0 cells. In addition, genistein (a tyrosine phosphorylation inhibitor) significantly enhanced the resistance of L1210/0 cells to MTX. Moreover, site-directed mutation studies indicated the importance of tyrosine phosphorylation of HSC70 in regulating its binding to MTX. These findings suggest that tyrosine phosphorylation of HSC70 regulates the transportation of MTX into the cells via the HSC70-RFC system and contributes to MTX resistance in L1210 cells.
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Affiliation(s)
- Tuoen Liu
- Department of Internal Medicine, Division of Oncology, Washington University School of Medicine, St. Louis, MO, United States
| | - Ratan Singh
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, United States
| | - Zechary Rios
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, United States
| | - Alok Bhushan
- Department of Pharmaceutical Sciences, Jefferson School of Pharmacy, Thomas Jefferson University, Philadelphia, PA, United States
| | - Mengxiong Li
- Gynecological Department, Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong Province, China
| | - Peter P Sheridan
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States; The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID, United States
| | - Shawn E Bearden
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States; The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID, United States
| | - James C K Lai
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, United States; The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID, United States
| | - Senyo Agbenowu
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, United States
| | - Shousong Cao
- Chifeng Saliont Pharmaceutical Co., Ltd., 228 North Qinghe Road, Hongshan District, Chifeng, Inner Mongolia Autonomous Region 024000, China.
| | - Christopher K Daniels
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, Idaho State University, Pocatello, ID, United States; The ISU Biomedical Research Institute, Idaho State University, Pocatello, ID, United States.
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13
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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.
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Affiliation(s)
- Michele Visentin
- Departments of Molecular Pharmacology and Medicine, Albert Einstein College of Medicine, Bronx, New York 10461; , , ,
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14
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Post-transcriptional regulation of the human reduced folate carrier as a novel adaptive mechanism in response to folate excess or deficiency. Biosci Rep 2014; 34:BSR20140065. [PMID: 24949876 PMCID: PMC4122975 DOI: 10.1042/bsr20140065] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The RFC (reduced folate carrier) is the principal mechanism by which folates and clinically used antifolates are delivered to mammalian cells. hRFC (human RFC) is subject to complex transcriptional controls and exists as homo-oligomer. To explore the post-transcriptional regulation of hRFC by exogenous folates, hRFC-null HeLa cells were stably transfected with hRFC under control of a constitutive promoter. hRFC transcripts and the total membrane protein increased with increasing LCV [(6R,S)5-formyl tetrahydrofolate (leucovorin)] with a maximum at 20 nM LCV, attributable to reduced turnover of hRFC transcripts. hRFC homo-oligomerization was unaffected by increasing LCV. Cell surface hRFC paralleled [3H]methotrexate transport and increased from 0.5 to 2 nM LCV, and then decreased (~2-fold) with increasing LCV up to 20 nM. hRFC was localized to the cell surface at low LCV concentrations (0.5–1.5 nM). However, at higher LCV concentrations, significant intracellular hRFC was localized to the ER (endoplasmic reticulum), such that at 20 nM LCV, intracellular hRFC was predominated. Our results demonstrate a novel post-transcriptional regulation of hRFC involving: (i) increased hRFC transcripts and proteins, accompanying increased extracellular folates, attributable to differences in hRFC transcript stabilities; and (ii) increased retention of hRFC in the ER under conditions of folate excess, because of impaired intracellular trafficking and plasma membrane targeting. A novel regulation of the physiologically/pharmacologically important human reduced folate carrier was demonstrated in response to increasing extracellular folates, involving: (i) increased transcripts and total protein, reflecting increased transcript stabilities; and (ii) increased endoplasmic reticulum trapping, due to impaired intracellular trafficking.
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15
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Zhao R, Goldman ID. The proton-coupled folate transporter: physiological and pharmacological roles. Curr Opin Pharmacol 2014; 13:875-80. [PMID: 24383099 DOI: 10.1016/j.coph.2013.09.011] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Recent studies have identified the proton-coupled folate transporter (PCFT) as the mechanism by which folates are absorbed across the apical brush-border membrane of the small intestine and across the basolateral membrane of the choroid plexus into the cerebrospinal fluid. Both processes are defective when there are loss-of-function mutations in this gene as occurs in the autosomal recessive disorder hereditary folate malabsorption. Because this transporter functions optimally at low pH, antifolates are being developed that are highly specific for PCFT in order to achieve selective delivery to malignant cells within the acidic environment of solid tumors. PCFT has a spectrum of affinities for folates and antifolates that narrows and increases at low pH. Residues have been identified that play a role in folate and proton binding, proton coupling, and oscillation of the carrier between its conformational states.
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16
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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.
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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.)
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17
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Knockdown of endogenous myostatin promotes sheep myoblast proliferation. In Vitro Cell Dev Biol Anim 2013; 50:94-102. [PMID: 24052475 DOI: 10.1007/s11626-013-9689-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 09/06/2013] [Indexed: 02/06/2023]
Abstract
Myostatin (MSTN), is a known negative regulator of myogenesis. Silencing of the function of MSTN could result in increasing muscle mass in mice. To determine the function of endogenous MSTN expression on proliferation of sheep myoblasts, a short-hairpin RNA-targeting sheep MSTN was constructed into lentiviral vector to silence endogenous MSTN expression. We demonstrated that silencing of endogenous MSTN gene with up to approximately 73.3% reduction by short hairpin RNA (shRNA) resulted in significant increase (overall 28.3%) of proliferation of primary ovine myoblasts. The upregulation of proliferation was accompanied by the decrease expression of MyoD (-37.6%, p = 0.025), myogenin (-33.1%, p = 0.049), p21 (-49.3%, p = 0.046), and Smad3 (-50.0%, p = 0.007). Silencing of myostatin using shRNA may provide a feasible approach to improve meat productivity in farm animals.
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18
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Structures of human folate receptors reveal biological trafficking states and diversity in folate and antifolate recognition. Proc Natl Acad Sci U S A 2013; 110:15180-8. [PMID: 23934049 DOI: 10.1073/pnas.1308827110] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Antifolates, folate analogs that inhibit vitamin B9 (folic acid)-using cellular enzymes, have been used over several decades for the treatment of cancer and inflammatory diseases. Cellular uptake of the antifolates in clinical use occurs primarily via widely expressed facilitative membrane transporters. More recently, human folate receptors (FRs), high affinity receptors that transport folate via endocytosis, have been proposed as targets for the specific delivery of new classes of antifolates or folate conjugates to tumors or sites of inflammation. The development of specific, FR-targeted antifolates would be accelerated if additional biophysical data, particularly structural models of the receptors, were available. Here we describe six distinct crystallographic models that provide insight into biological trafficking of FRs and distinct binding modes of folate and antifolates to these receptors. From comparison of the structures, we delineate discrete structural conformations representative of key stages in the endocytic trafficking of FRs and propose models for pH-dependent conformational changes. Additionally, we describe the molecular details of human FR in complex with three clinically prevalent antifolates, pemetrexed (also Alimta), aminopterin, and methotrexate. On the whole, our data form the basis for rapid design and implementation of unique, FR-targeted, folate-based drugs for the treatment of cancer and inflammatory diseases.
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19
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Post-hatching ontogeny of intestinal proton-coupled folate transporter and reduced folate carrier in broiler chickens. Animal 2013; 7:1659-64. [DOI: 10.1017/s1751731113001213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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20
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Wani NA, Kaur J. Adaptive transport of folic acid across renal epithelia in folate-deficient rats. J Physiol Sci 2012; 62:461-8. [PMID: 22865158 PMCID: PMC10717754 DOI: 10.1007/s12576-012-0223-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Accepted: 07/16/2012] [Indexed: 01/01/2023]
Abstract
Folate (vitamin B(9)) is an essential vitamin for a wide spectrum of biochemical reactions; however, unlike bacteria and plants, mammals are devoid of folate biosynthesis and thus must obtain this cofactor from exogenous sources. The activities of folate transporters on the kidneys play an important role in conserving folate excretion and reabsorption across the apical membrane of the renal proximal tubules. The different transport system activities may become identifiable in response to external stimuli, such as folate availability and exposure to chemotherapeutic agents. We have explored the effect of folate deficiency on the activity and expression of folate transporters in rat kidneys. Wistar rats were fed a folate-containing diet (2 mg folic acid kg(-1) diet) or a folic acid-free diet over a 3-month period, and mechanisms of folate transport were studied in renal brush border membrane vesicles and basolateral membrane vesicles. The renal folate uptake process is saturable and pH dependent, and it involves the folate receptor and reduced folate carrier (RFC) systems and possibly the proton coupled folate transporter (PCFT) system. We found that folate deficiency increased the renal brush border membrane and basolateral folate uptake by increasing the number of transporter molecules. The observed up-regulation of mRNA expression was also associated with a significant increase in RFC and PCFT expression at the protein level.
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Affiliation(s)
- Nissar Ahmad Wani
- Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, 160 012 India
| | - Jyotdeep Kaur
- Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, 160 012 India
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21
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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.
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Affiliation(s)
- Sita Kugel Desmoulin
- Cancer Biology Graduate Program in Cancer Biology, Department of Oncology, Wayne State University School of Medicine; Detroit, MI USA
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22
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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]
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23
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The critical role of myostatin in differentiation of sheep myoblasts. Biochem Biophys Res Commun 2012; 422:381-6. [DOI: 10.1016/j.bbrc.2012.04.151] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 04/27/2012] [Indexed: 12/27/2022]
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24
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Simon KW, Ma H, Dombkowski AA, Cabelof DC. Aging alters folate homeostasis and DNA damage response in colon. Mech Ageing Dev 2012; 133:75-82. [DOI: 10.1016/j.mad.2012.01.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2011] [Revised: 12/16/2011] [Accepted: 01/13/2012] [Indexed: 10/14/2022]
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25
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Zhao R, Diop-Bove N, Visentin M, Goldman ID. Mechanisms of membrane transport of folates into cells and across epithelia. Annu Rev Nutr 2011; 31:177-201. [PMID: 21568705 DOI: 10.1146/annurev-nutr-072610-145133] [Citation(s) in RCA: 236] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Until recently, the transport of folates into cells and across epithelia has been interpreted primarily within the context of two transporters with high affinity and specificity for folates, the reduced folate carrier and the folate receptors. However, there were discrepancies between the properties of these transporters and characteristics of folate transport in many tissues, most notably the intestinal absorption of folates, in terms of pH dependency and substrate specificity. With the recent cloning of the proton-coupled folate transporter (PCFT) and the demonstration that this transporter is mutated in hereditary folate malabsorption, an autosomal recessive disorder, the molecular basis for this low-pH transport activity is now understood. This review focuses on the properties of PCFT and briefly addresses the two other folate-specific transporters along with other facilitative and ATP-binding cassette (ABC) transporters with folate transport activities. The role of these transporters in the vectorial transport of folates across epithelia is considered.
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Affiliation(s)
- Rongbao Zhao
- Departments of Medicine and Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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26
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Hinken M, Halwachs S, Kneuer C, Honscha W. Subcellular localization and distribution of the reduced folate carrier in normal rat tissues. Eur J Histochem 2011; 55:e3. [PMID: 21556118 PMCID: PMC3167344 DOI: 10.4081/ejh.2011.e3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 12/03/2010] [Accepted: 12/13/2010] [Indexed: 11/23/2022] Open
Abstract
The reduced folate carrier (Rfc1; Slc19a1) mediated transport of reduced folates and antifolate drugs such as methotrexate (MTX) play an essential role in physiological folate homeostasis and MTX cancer chemotherapy. As no systematic reports are as yet available correlating Rfc1 gene expression and protein levels in all tissues crucial for folate and antifolate uptake, storage or elimination, we investigated gene and protein expression of rat Rfc1 (rRfc1) in selected tissues. This included the generation of a specific anti-rRfc1 antibody. Rabbits were immunised with isolated rRfc1 peptides producing specific anti-rRfc1 antiserum targeted to the intracellular C-terminus of the carrier. Using RT-PCR analysis, high rRfc1 transcript levels were detected in colon, kidney, brain, thymus, and spleen. Moderate rRfc1 gene expression was observed in small intestine, liver, bone marrow, lung, and testes whereas transcript levels were negligible in heart, skeletal muscle or leukocytes. Immunohistochemical analyses revealed strong carrier expression in the apical membrane of tunica mucosa epithelial cells of small intestine and colon, in the brush-border membrane of choroid plexus epithelial cells or in endothelial cells of small vessels in brain and heart. Additionally, high rRfc1 protein levels were localized in the basolateral membrane of renal tubular epithelial cells, in the plasma membrane of periportal hepatocytes, and sertoli cells of the testes. Taken together, our results demonstrated that rRfc1 is expressed almost ubiquitously but to very different levels. The predominant tissue distribution supports the essential role of Rfc1 in physiological folate homeostasis. Moreover, our results may contribute to understand antifolate pharmacokinetics and selected organ toxicity associated with MTX chemotherapy.
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Affiliation(s)
- M Hinken
- Institute of Pharmacology, Pharmacy and Toxicology, Universität Leipzig, Germany.
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27
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The effect of folate status on the uptake of physiologically relevant compounds by Caco-2 cells. Eur J Pharmacol 2010; 640:29-37. [DOI: 10.1016/j.ejphar.2010.04.056] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/19/2010] [Accepted: 04/23/2010] [Indexed: 12/25/2022]
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28
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Becker ML, Leeder JS. Developmental pharmacogenetics in pediatric rheumatology: utilizing a new paradigm to effectively treat patients with juvenile idiopathic arthritis with methotrexate. HUMAN GENOMICS AND PROTEOMICS : HGP 2010; 2010:257120. [PMID: 20981233 PMCID: PMC2958653 DOI: 10.4061/2010/257120] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Accepted: 05/20/2010] [Indexed: 01/27/2023]
Abstract
Although methotrexate is widely used in clinical practice there remains significant lack of understanding of its mechanisms of action and the factors that contribute to the variability in toxicity and response seen clinically. In addition to differences in drug administration, factors that affect pharmacokinetics and pharmacodynamics such as genetic variation may explain individual differences in drug biotransformation. However, the pediatric population has an additional factor to consider, namely the ontogeny of gene expression which may result in variation throughout growth and development. We review the current understanding of methotrexate biotransformation and the concept of ontogeny, with further discussion of how to implement a developmental pharmacogenomics approach in future studies.
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Affiliation(s)
- Mara L. Becker
- Division of Clinical Pharmacology and Toxicology, Children's Mercy Hospitals and Clinics, University of Missouri Kansas City, 2401 Gillham Road, Kansas City, MO 64108, USA
| | - J. Steven Leeder
- Division of Clinical Pharmacology and Toxicology, Children's Mercy Hospitals and Clinics, University of Missouri Kansas City, 2401 Gillham Road, Kansas City, MO 64108, USA
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29
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Abstract
Strong epidemiological evidence indicates that derangement of single-carbon metabolism has detrimental effects for proper CNS functioning. Conversely, a role for folate supplementation in the treatment and prevention of neurodegenerative and neuropsychiatric disorders remains to be established. In this issue of the JCI, in an elegant series of experiments in rodents, Iskandar and colleagues demonstrate a crucial role of folate in the regeneration of afferent spinal neurons after injury. Probing sequential steps in folate metabolism, from cellular entry to DNA methylation, the authors show that axonal regeneration relies upon the integrity of DNA methylation pathways. These findings provide the first demonstration of an epigenetic mechanism contributing to neurorepair and suggest that manipulation of the methylation milieu may offer promising new therapeutic avenues to promote regeneration.
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Affiliation(s)
- Golo Kronenberg
- Klinik und Poliklinik für Neurologie and Center for Stroke Research Berlin, Charité-Universitätsmedizin Berlin, Berlin, Germany
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30
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Iskandar BJ, Rizk E, Meier B, Hariharan N, Bottiglieri T, Finnell RH, Jarrard DF, Banerjee RV, Skene JHP, Nelson A, Patel N, Gherasim C, Simon K, Cook TD, Hogan KJ. Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation. J Clin Invest 2010; 120:1603-16. [PMID: 20424322 DOI: 10.1172/jci40000] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Accepted: 02/24/2010] [Indexed: 01/07/2023] Open
Abstract
The folate pathway plays a crucial role in the regeneration and repair of the adult CNS after injury. Here, we have shown in rodents that such repair occurs at least in part through DNA methylation. In animals with combined spinal cord and sciatic nerve injury, folate-mediated CNS axon regeneration was found to depend on injury-related induction of the high-affinity folate receptor 1 (Folr1). The activity of folate was dependent on its activation by the enzyme dihydrofolate reductase (Dhfr) and a functional methylation cycle. The effect of folate on the regeneration of afferent spinal neurons was biphasic and dose dependent and correlated closely over its dose range with global and gene-specific DNA methylation and with expression of both the folate receptor Folr1 and the de novo DNA methyltransferases. These data implicate an epigenetic mechanism in CNS repair. Folic acid and possibly other nontoxic dietary methyl donors may therefore be useful in clinical interventions to promote brain and spinal cord healing. If indeed the benefit of folate is mediated by epigenetic mechanisms that promote endogenous axonal regeneration, this provides possible avenues for new pharmacologic approaches to treating CNS injuries.
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Affiliation(s)
- Bermans J Iskandar
- Department of Neurological Surgery, University of Wisconsin, Madison, Wisconsin 53792, USA.
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Basolateral efflux mediated by multidrug resistance-associated protein 3 (Mrp3/Abcc3) facilitates intestinal absorption of folates in mouse. Pharm Res 2010; 27:665-72. [PMID: 20148291 DOI: 10.1007/s11095-009-0047-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2009] [Accepted: 12/27/2009] [Indexed: 12/21/2022]
Abstract
PURPOSE This study investigated the role of an ABC transporter, Mrp3/Abcc3 in intestinal folate absorption. METHODS Plasma concentrations of folic acid and leucovorin, given orally, were determined in wild-type and Mrp3 ( -/- ) mice. Mucosal-to-serosal transport was determined in the everted intestinal sacs. The plasma concentrations of endogenous 5-methyltetrahydrofolic acid, homocysteine and vitamin B(12), and mRNA levels of hepatic and intestinal folate metabolizing enzymes were compared between wild-type and Mrp3 ( -/- ) mice. RESULTS C ( max ) and area-under plasma concentration-time curve of folic acid were 3.0- and 2.3-fold lower in Mrp3 ( -/- ) mice compared with wild-type mice, whereas the total body clearance was unchanged. Absorption of leucovorin was significantly delayed in Mrp3 ( -/- ) mice. Mucosal-to-serosal transport of folic acid and leucovorin was significantly decreased in the duodenum of Mrp3 ( -/- ) mice, where their PS ( serosal ) was decreased to 6.3 and 22% of that in wild-type mice, respectively. PS ( serosal ) of 5-methyltetrahydrofolic acid was moderately decreased in Mrp3 ( -/- ) mice. There was no obvious abnormality in folate homeostasis in Mrp3 ( -/- ) mice. CONCLUSIONS Mrp3 accounts for the serosal efflux of folic acid and leucovorin, while it makes a moderate contribution to the serosal efflux of 5-methyltetrahydrofolic acid in mice. Mrp3 dysfunction does not disrupt folate homeostasis in mouse.
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Jing M, Tactacan G, Rodriguez-Lecompte J, Kroeker A, House J. Molecular cloning and tissue distribution of reduced folate carrier and effect of dietary folate supplementation on the expression of reduced folate carrier in laying hens. Poult Sci 2009; 88:1939-47. [DOI: 10.3382/ps.2009-00032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Diop-Bove NK, Wu J, Zhao R, Locker J, Goldman ID. Hypermethylation of the human proton-coupled folate transporter (SLC46A1) minimal transcriptional regulatory region in an antifolate-resistant HeLa cell line. Mol Cancer Ther 2009; 8:2424-31. [PMID: 19671745 DOI: 10.1158/1535-7163.mct-08-0938] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
This laboratory recently identified a novel proton-coupled folate transporter (PCFT) that mediates intestinal folate absorption and transport of folates into the central nervous system. The present study focuses on the definition of the minimum transcriptional regulatory region of this gene in HeLa cells and the mechanism(s) underlying the loss of PCFT expression in the methotrexate-resistant HeLa R1-11 cell line. The PCFT transcriptional regulatory controls were localized between -42 and +96 bases from the transcriptional start site using a luciferase-reporter gene system. The promoter is a G + C rich region of 139 nucleotides contained in a CpG island. HeLa R1-11 cells have no mutations in the PCFT open reading frame and its promoter; the transcription/translation machinery is intact because transient transfections in HeLa R1-11 and wild-type HeLa cells produced similar luciferase activities. Hypermethylation at CpG sites within the minimal transcriptional regulatory region was shown in HeLa R1-11 cells as compared with the parental PCFT-competent HeLa cells, using bisulfite conversion and sequence analysis. Treatment with 5-aza-2'-deoxycytidine resulted in a substantial restoration of transport and PCFT mRNA expression and small but significant decreases in methylation in the promoter region. In vitro methylation of the transfected reporter plasmid inhibited luciferase gene expression. Cytogenetics/fluorescence in situ hybridization indicated a loss of half the PCFT gene copies in HeLa R1-11 as compared with PCFT-competent HeLa cells. Taken together, promoter silencing through methylation and gene copy loss accounted for the loss of PCFT activity in antifolate-resistant HeLa R1-11 cells.
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Affiliation(s)
- Ndeye Khady Diop-Bove
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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Shafizadeh TB, Halsted CH. Postnatal ontogeny of intestinal GCPII and the RFC in pig. Am J Physiol Gastrointest Liver Physiol 2009; 296:G476-81. [PMID: 19033540 DOI: 10.1152/ajpgi.00446.2007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In humans and pigs, hydrolysis of dietary polyglutamyl folates is carried out by intestinal brush border folate hydrolase [glutamate carboxypeptidase II (GCPII)], whereas the transport of the monoglutamyl folate derivatives occurs via the intestinal brush border reduced folate carrier (RFC). The study objective was to measure the expression of intestinal GCPII and RFC during postnatal development of pigs and their effects on plasma and liver folate concentrations. Duodenum, jejunum, ileum, liver, and plasma samples were collected from female Yorkshire pigs at birth, 24 h, 1 wk, 3 wk, and 6 mo (n=6 at each time point). GCPII mRNA transcripts and protein (normalized using beta-actin), and enzyme activity (normalized per mg mucosal protein) were highest in all segments of small intestine at birth and were undetectable in ileum after 1 wk, whereas jejunal protein and activity predominated at 6 mo. RFC mRNA transcripts were present in all segments of small intestine at birth and declined significantly throughout development to 6 mo. Conversely, RFC protein increased twofold during the first 24 h and remained constant throughout development in all segments of small intestine. Liver RFC mRNA transcripts were detected at birth but were reduced by 6 mo. Liver folate concentration increased throughout postnatal development, whereas plasma folate levels increased during the first 24 h but decreased over time, reflecting the pattern of RFC expression in small intestine. These findings show that intestinal GCPII and intestinal and hepatic RFC all exhibit ontogenic changes in the pig that are reflected in postnatal folate status.
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Affiliation(s)
- Tracy B Shafizadeh
- Department of Internal Medicine, University of California, Davis, CA, USA.
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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.
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Mahabir S, Ettinger S, Johnson L, Baer DJ, Clevidence BA, Hartman TJ, Taylor PR. Measures of adiposity and body fat distribution in relation to serum folate levels in postmenopausal women in a feeding study. Eur J Clin Nutr 2008; 62:644-50. [PMID: 17457338 PMCID: PMC3236439 DOI: 10.1038/sj.ejcn.1602771] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Revised: 02/21/2007] [Accepted: 03/02/2007] [Indexed: 01/12/2023]
Abstract
OBJECTIVE To assess the associations between serum folate concentration and measures of adiposity in postmenopausal women. DESIGN This study was conducted as a cross-sectional analysis within the control segment of a randomized, crossover trial in which postmenopausal women (n=51) consumed 0 g (control), 15 g (one drink) and 30 g (two drinks) alcohol (ethanol)/day for 8 weeks as part of a controlled diet. Subjects in one treatment arm were crossed-over to another arm after a 2- to 5-week washout period. Body mass index (BMI) was measured, and dual energy X-ray absorptiometry (DEXA) scan administered to the women during the control (0 g alcohol) treatment, and a blood sample from this group was collected at baseline and week 8 of each diet period and analyzed for folate, B12, homocysteine and methylmalonic acid. SETTING This study was conducted at the Beltsville Human Nutrition Research Center, MD, USA. RESULTS In multivariate analysis, women who were overweight had a 12% lower, and obese women had a 22% lower serum folate concentrations compared to normal weight women (P-trend=0.02). Vitamin B12 also decreased with increasing BMI (P-trend=0.08). Increased BMI, percent body fat, and absolute amounts of central and peripheral fat were all significantly associated with decreased serum folate, but were unrelated to serum B12, homocysteine or methylmalonic acid. CONCLUSIONS Our data show that adiposity is associated with lower serum folate levels in postmenopausal women. With obesity at epidemic proportions, these data, if confirmed by prospective or randomized controlled studies, have important public health implications.
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Affiliation(s)
- S Mahabir
- Department of Epidemiology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
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Patterson D, Graham C, Cherian C, Matherly LH. A humanized mouse model for the reduced folate carrier. Mol Genet Metab 2008; 93:95-103. [PMID: 17983788 PMCID: PMC2271060 DOI: 10.1016/j.ymgme.2007.09.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2007] [Revised: 09/20/2007] [Accepted: 09/20/2007] [Indexed: 12/26/2022]
Abstract
The ubiquitously expressed reduced folate carrier (RFC) or SLC19A1 is recognized to be an essential transport system for folates in mammalian cells and tissues. In addition to its generalized role as a folate transporter, RFC provides specialized tissue functions including absorption across intestinal/colonic epithelia, transport across the basolateral membrane of renal proximal tubules, transplacental transport of folates, and folate transport across the blood-brain barrier. The human RFC (hRFC) gene is regulated by five major upstream non-coding regions (designated A1/A2, A, B, C, and D), each transcribed from a unique promoter. Altogether, at least 14 distinct hRFC transcripts can be envisaged in which different 5' untranslated regions (UTRs) are fused to a common splice acceptor region (positions -1 to -49) within the first coding exon with a common 1776bp coding sequence. The 5' non-coding regions are characterized by alternate transcription start sites, multiple splice forms, and selective tissue distributions. Alternate 5' UTRs impact mRNA stabilities and translation efficiencies, and result in synthesis of modified hRFC proteins translated from upstream AUGs. In this report, we describe production and characterization of transgenic mice (TghRFC1) containing a functional hRFC gene and of humanized mice in which the mRFC gene is inactivated and an active hRFC gene has been introduced. The mice appear to be healthy and to breed well. Analysis of tissue specificity of expression in both the TghRFC1 and humanized hRFC mice by real-time RT-PCR demonstrates that the hRFC gene is expressed with a specificity closely resembling that seen in human tissues. For the humanized hRFC mice, levels of B and A1/A2 5' UTRs predominated in all mice/tissues, thus resembling results in normal human tissues. Lower levels of A and C 5' UTRs were also detected. The availability of humanized mouse models for hRFC will permit investigators to address critical unanswered questions pertinent to human health and disease. These include the ability to analyze the hRFC gene in vivo, to control dietary and other environmental conditions that may impact levels of gene expression, and to control the genetics of the mice in order to assess the effects of hRFC gene alterations on tissue folate uptake and distribution, none of which can be easily achieved in human populations.
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Affiliation(s)
- David Patterson
- Eleanor Roosevelt Institute, Department of Biological Sciences, University of Denver, 1899 Gaylord Street, Denver, CO 80206, USA.
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Qiu A, Min SH, Jansen M, Malhotra U, Tsai E, Cabelof DC, Matherly LH, Zhao R, Akabas MH, Goldman ID. Rodent intestinal folate transporters (SLC46A1): secondary structure, functional properties, and response to dietary folate restriction. Am J Physiol Cell Physiol 2007; 293:C1669-78. [PMID: 17898134 DOI: 10.1152/ajpcell.00202.2007] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This laboratory recently identified a human gene that encodes a novel folate transporter [Homo sapiens proton-coupled folate transporter (HsPCFT); SLC46A1] required for intestinal folate absorption. This study focused on mouse (Mus musculus) PCFT (MmPCFT) and rat (Rattus norvegicus) PCFT (RnPCFT) and addresses their secondary structure, specificity, tissue expression, and regulation by dietary folates. Both rodent PCFT proteins traffic to the cell membrane with the NH(2)- and COOH-termini accessible to antibodies targeted to these domains only in permeabilized HeLa cells. This, together with computer-based topological analyses, is consistent with a model in which rodent PCFT proteins likely contain 12 transmembrane domains. Transport of [(3)H]folates was optimal at pH 5.5 and decreased with increasing pH due to an increase in K(m) and a decrease in V(max). At pH 7.0, folic acid and methotrexate influx was negligible, but there was residual (6S)5-methyltetrahydrofolate transport. Uptake of folates in PCFT-injected Xenopus oocytes was electrogenic and pH dependent. Folic acid influx K(m) values of MmPCFT and RnPCFT, assessed electrophysiologically, were 0.7 and 0.3 microM at pH 5.5 and 1.1 and 0.8 microM at pH 6.5, respectively. Rodent PCFTs were highly specific for monoglutamyl but not polyglutamyl methotrexate. MmPCFT mRNA was highly expressed in the duodenum, proximal jejunum, liver, and kidney with lesser expression in the brain and other tissues. MmPCFT protein was localized to the apical brush-border membrane of the duodenum and proximal jejunum. MmPCFT mRNA levels increased approximately 13-fold in the proximal small intestine in mice fed a folate-deficient vesus folate-replete diet, consistent with the critical role that PCFT plays in intestinal folate absorption.
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Affiliation(s)
- Andong Qiu
- Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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Matherly LH, Hou Z, Deng Y. Human reduced folate carrier: translation of basic biology to cancer etiology and therapy. Cancer Metastasis Rev 2007; 26:111-28. [PMID: 17334909 DOI: 10.1007/s10555-007-9046-2] [Citation(s) in RCA: 195] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
This review attempts to provide a comprehensive overview of the biology of the physiologically and pharmacologically important transport system termed the "reduced folate carrier" (RFC). The ubiquitously expressed RFC has unequivocally established itself as the major transport system in mammalian cells and tissues for a group of compounds including folate cofactors and classical antifolate therapeutics. Loss of RFC expression or function may have potentially profound pathophysiologic consequences including cancer. For chemotherapeutic antifolates used for cancer such as methotrexate or pemetrexed, synthesis of mutant RFCs or loss of RFC transcripts and proteins results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and insufficient substrate for polyglutamate synthesis. Since RFC was first cloned in 1994, tremendous advances have been made in understanding the complex transcriptional and posttranscriptional regulation of RFC, in identifying structurally and functionally important domains and amino acids in the RFC molecule as a prelude to establishing the mechanism of transport, and in characterizing the molecular defects in RFC associated with loss of transport in antifolate resistant cell line models. Many of the insights gained from laboratory models of RFC portend opportunities for modulating carrier expression in drug resistant tumors, and for designing a new generation of agents with improved transport by RFC or substantially enhanced transport by other folate transporters over RFC. Many of the advances in the basic biology of RFC in cell line models are now being directly applied to human cancers in the clinical setting, most notably pediatric acute lymphoblastic leukemia and osteogenic sarcoma.
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Affiliation(s)
- Larry H Matherly
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, The Cancer Biology Graduate Program, Detroit, MI 48201, USA.
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Zhao R, Goldman ID. The molecular identity and characterization of a Proton-coupled Folate Transporter--PCFT; biological ramifications and impact on the activity of pemetrexed. Cancer Metastasis Rev 2007; 26:129-39. [PMID: 17340171 DOI: 10.1007/s10555-007-9047-1] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Membrane transport of folates is essential for the survival of all mammalian cells and transport of antifolates is an important determinant of antifolate activity. While a major focus of attention has been on transport mediated by the reduced folate carrier and folate receptors, a very prominent carrier-mediated folate transport activity has been recognized for decades with a low-pH optimum and substrate specificity distinct from that of the reduced folate carrier which operates most efficiently at neutral pH. This low-pH transporter represents the mechanism by which folates are absorbed in the small intestine and it is also widely expressed in other human tissues and solid tumors. Recently, this laboratory discovered the molecular identity of this transporter which is genetically unrelated to the reduced folate carrier. This transporter is proton-coupled, electrogenic, and manifests a substrate specificity that is similar to that of the low-pH transport activity previously described in mammalian cells. The key role this transporter plays in intestinal folate absorption has been confirmed by the demonstration of a mutation in this gene in the rare autosomal recessive disorder, hereditary folate malabsorption. This article reviews (1) the characteristics and prevalence of the low-pH folate transport activity, (2) its relationship to, and properties of, the recently identified Proton-Coupled Folate Transporter (PCFT), (3) the physiological and pharmacological roles of this transporter, particularly with respect to pemetrexed, and (4) the historical controversy, now resolved, on the mechanism of intestinal folate absorption.
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Affiliation(s)
- Rongbao Zhao
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Zhao R, Min SH, Qiu A, Sakaris A, Goldberg GL, Sandoval C, Malatack JJ, Rosenblatt DS, Goldman ID. The spectrum of mutations in the PCFT gene, coding for an intestinal folate transporter, that are the basis for hereditary folate malabsorption. Blood 2007; 110:1147-52. [PMID: 17446347 PMCID: PMC1939898 DOI: 10.1182/blood-2007-02-077099] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hereditary folate malabsorption (HFM) is a rare autosomal recessive disorder caused by impaired intestinal folate absorption and impaired folate transport into the central nervous system. Recent studies in 1 family revealed that the molecular basis for this disorder is a loss-of-function mutation in the PCFT gene encoding a proton-coupled folate transporter. The current study broadens the understanding of the spectrum of alterations in the PCFT gene associated with HFM in 5 additional patients. There was no racial, ethnic, or sex pattern. A total of 4 different homozygous mutations were detected in 4 patients; 2 heterozygous mutations were identified in the fifth patient. Mutations involved 4 of the 5 exons, all at highly conserved amino acid residues. A total of 4 of the mutated transporters resulted in a complete loss of transport function, primarily due to decreased protein stability and/or defects in membrane trafficking, while 2 of the mutated carriers manifested residual function. Folate transport at low pH was markedly impaired in transformed lymphocytes from 2 patients. These findings further substantiate the role that mutations in PCFT play in the pathogenesis of HFM and will make possible rapid diagnosis and treatment of this disorder in infants, and prenatal diagnosis in families that carry a mutated gene.
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Affiliation(s)
- Rongbao Zhao
- Departments of Medicine, Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Abstract
Down syndrome (DS) is the most common genetic cause of significant intellectual disability in the human population, occurring in roughly 1 in 700 live births. The ultimate cause of DS is trisomy of all or part of the set of genes located on chromosome 21. How this trisomy leads to the phenotype of DS is unclear. The completion of the DNA sequencing and annotation of the long arm of chromosome 21 was a critical step towards understanding the genetics of the phenotype. However, annotation of the chromosome continues and the functions of many genes on chromosome 21 remain uncertain. Recent findings about the structure of the human genome and of chromosome 21, in particular, and studies on mechanisms of gene regulation indicate that various genetic mechanisms may be contributors to the phenotype of DS and to the variability of the phenotype. These include variability of gene expression, the activity of transcription factors both encoded on chromosome 21 and encoded elsewhere in the genome, copy number polymorphisms, the function of conserved nongenic regions, microRNA activities, RNA editing, and perhaps DNA methylation. In this manuscript, we describe current knowledge about these genetic complexities and their likely importance in the context of DS. We identify gaps in current knowledge and suggest priorities to fill these gaps.
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Affiliation(s)
- David Patterson
- Eleanor Roosevelt Institute, University of Denver, Denver, Colorado 80206, USA.
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Butler C, Knox AJ, Bowersox J, Forbes S, Patterson D. The production of transgenic mice expressing human cystathionine beta-synthase to study Down syndrome. Behav Genet 2006; 36:429-38. [PMID: 16541333 DOI: 10.1007/s10519-006-9046-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2005] [Accepted: 12/17/2005] [Indexed: 10/24/2022]
Abstract
Down syndrome (DS) is the most common genetic cause of significant cognitive disability. We hypothesize that by identifying metabolic alterations associated with cognitive impairment, it may be possible to develop medical or dietary interventions to ameliorate cognitive disabilities in persons with DS. Evidence suggests that one-carbon/transsulfuration (1C-TS) metabolism is abnormal in persons with DS. Cystathionine beta-synthase (CBS) plays a critical role in this metabolic system. The gene for CBS is on human chromosome 21, and there is evidence of elevated CBS enzyme activity in tissues and cells from individuals with DS. To analyze the possible role of CBS in Down syndrome, we have produced several lines of transgenic mice expressing the human CBS gene. We describe the use of Florescence Situ Hybridization (FISH) analysis to characterize the transgene insertion site for each line. Our initial expression analysis of each transgenic line by RT-PCR shows that the tissue specificity of human CBS mRNA levels in these mice may differ from the tissue specificity of mouse CBS mRNA levels in the same animals. These mice will be invaluable for assessing the regulation of the CBS gene and the role of CBS in cognition. They can also be used to develop therapies that target abnormalities in 1C-TS metabolism to improve cognition in persons with DS.
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Affiliation(s)
- Christine Butler
- The Eleanor Roosevelt Institute at the University of Denver, CO 80206, USA
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Payton SG, Liu M, Ge Y, Matherly LH. Transcriptional regulation of the human reduced folate carrier A1/A2 promoter: Identification of critical roles for the USF and GATA families of transcription factors. ACTA ACUST UNITED AC 2005; 1731:115-24. [PMID: 16225938 DOI: 10.1016/j.bbaexp.2005.08.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Revised: 08/25/2005] [Accepted: 08/25/2005] [Indexed: 10/25/2022]
Abstract
The human reduced folate carrier (hRFC) gene has a complex regulation involving 6 alternatively spliced non-coding exons and promoters (A1/A2, A, B, C, D, and E). The hRFC-A1/A2 promoter is unique in that it transcribes a novel transcript with an in-frame AUG in non-coding exon A1/A2 that encodes a modified hRFC protein with altered transport function. In this report, we characterize the hRFC-A1/A2 promoter in HepG2 human hepatoma cells. By transfecting HepG2 cells with 5' and 3' deletion constructs, a transcriptionally important 270 bp region was identified. Gel shift assays identified transcription factor binding to three E-box elements and one GATA site within this region. These elements were verified by transfections of mutant constructs into HepG2 cells. Cotransfections in Drosophila Mel-2 cells confirmed promoter activation by USF1 and GATA1. A physical association between USF1 and GATA1 was demonstrated by their co-immunoprecipitation. By real time PCR analysis of transfected HepG2 cells, USF1 and GATA1 increased endogenous hRFC-A1/A2 transcripts. Altogether, our results demonstrate a transcriptionally important region in the hRFC-A1/A2 promoter including E-box and GATA elements, and a transactivation by USF1 and GATA1 proteins. Our results further establish the complexity of hRFC regulation, as a means of ensuring adequate folate cofactor transport for cell proliferation.
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Affiliation(s)
- Scott G Payton
- Department of Pharmacology, Barbara Ann Karmanos Cancer Institute, and Wayne State University School of Medicine, Detroit, MI 48201, USA
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