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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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Litynski P, Loehrer F, Linder L, Todesco L, Fowler B. Effect of low doses of 5-methyltetrahydrofolate and folic acid on plasma homocysteine in healthy subjects with or without the 677C-->T polymorphism of methylenetetrahydrofolate reductase. Eur J Clin Invest 2002; 32:662-8. [PMID: 12486865 DOI: 10.1046/j.1365-2362.2002.01055.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND The 677C-->T polymorphism of methylenetetrahydrofolate reductase can lead to increased homocysteine. Moderate increases of homocysteine can be lowered by folic acid (0.4-10 mg day-1). This study compared the effect of folic acid with 5-methyltetrahydrofolate, the active form of folate generated by this reductase, on homocysteine levels in healthy subjects and whether this is influenced by the 677C-->T polymorphism. MATERIALS AND METHODS Either 400 micrograms day-1 of [6RS] 5-methyltetrahydrofolate or 400 micrograms day-1 of folic acid were administered orally to 10 wild-type and 10 homozygous subjects. Total homocysteine and folate were determined before and after 3 and 7 weeks of treatment, and 24 weeks after stopping treatment. RESULTS After 3 and 7 weeks of treatment with 5-methyltetrahydrofolate, homocysteine levels fell from 11.6 +/- 1.5 to 9.0 +/- 2.3 and 8.7 +/- 1.8 (P < 0.005) in wild-type subjects and from 16.9 +/- 6.8 to 12.3 +/- 4.3 and 11.6 +/- 4.4 mumol/L, mean +/- SD (P < 0.005) in homozygous subjects, proving biological availability of 5-methyltetrahydrofolate irrespective of the 677C-->T genotype. After folic acid for 3 and 7 weeks, values fell from 12.6 +/- 3.3 to 9.2 +/- 2.9 and 9.2 +/- 2.7 (P < 0.005) and from 15.6 +/- 4.9 to 11.7 +/- 3.9 and 9.1 +/- 2.4 mumol L-1, mean +/- SD (P < 0.005) in wild-type and homozygous subjects, respectively. Six months after stopping treatment, homocysteine levels remained lower than pretreatment levels, with statistical significance, only in homozygous subjects treated with 5-methyltetrahydrofolate (12.1 +/- 2.5 vs. 16.9 +/- 6.8, P < 0.01). CONCLUSIONS 5-methyltetrahydrofolate showed comparable efficacy in reducing homocysteine as folic acid. A prolonged effect 6 months after ceasing treatment with 5-methyltetrahydrofolate in homozygous subjects represents a further phenotypic effect of the 677TT methylenetetrahydrofolate reductase genotype.
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Affiliation(s)
- P Litynski
- University Children's Hospital, Basel, Switzerland
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Abstract
Mediated internalization of folates is required for cellular macromolecular biosynthesis. Multiple carrier-mediated mechanisms have been identified that can fulfill this role in a variety of mammalian cell types, including neoplastic cells, with and without proliferative potential. The absorption of dietary folates also relies on the function of a carrier-mediated system in mature luminal epithelium of small intestine. The various carrier-mediated systems can be distinguished by their preferences for various folate compounds as permeants as well as by differences in temperature and pH dependence. The widely studied one-carbon, reduced-folate transport system is mediated by a transporter encoded by the newly discovered RFC-1 (reduced-folate carrier) gene. The characteristics of this gene in rodent and human cells are similar, consistent with the close similarity between these species of folate transport mediated by this transporter. However, differences occur in the form of tissue-specific expression, alternate splicing, and 5' end mRNA heterogeneity, as well as in promoter utilization regulating transcription. RFC-1 gene expression also appears to regulate luminal epithelial cell folate absorption in small intestine. However, the properties of RFC-1-mediated folate transport in these cells is anomalous when compared with that seen in nonabsorptive cell types. Detailed mechanisms as to the regulation of RFC-1 transcription are now emerging along with other information on structure and function of the transporter and its alteration following mutation.
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Affiliation(s)
- F M Sirotnak
- Program in Molecular Pharmacology and Experimental Therapeutics, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.
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Roy K, Mitsugi K, Sirlin S, Shane B, Sirotnak FM. Different antifolate-resistant L1210 cell variants with either increased or decreased folylpolyglutamate synthetase gene expression at the level of mRNA transcription. J Biol Chem 1995; 270:26918-22. [PMID: 7592937 DOI: 10.1074/jbc.270.45.26918] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
L1210 cell variants selected in the presence of the lipophilic dihydrofolate reductase inhibitor, metoprine, expressed increased levels of one-carbon, reduced folate transport inward (Sirotnak, F. M., Moccio, D. M., and Yang, C.-H. (1984) J. Biol. Chem. 259, 13139-13144). Growth of one of these variants (L1210/R69), with metoprine in the presence of decreasing concentrations of 1,L5-CHO-folateH4 (natural diastereoisomer of 5-formyl-tetrahydrofolate), resulted in the selection of other variants (L1210/R82, R83, and R84) with further reduction in one-carbon, reduced folate transport and in two cases (L1210/R83 and R84) with 3-8-fold increased folylpolyglutamate synthetase (FPGS) activity and folate compound polyglutamate formation in situ. Metoprine resistance was further increased, and the requirement for exogenous folate during growth was decreased as well in these variants. The increase in FPGS activity observed in L1210/R83 and R84 was characterized by 3- and 8-fold increases in value for Vmax with no change in Km and the same increase in a 60-61-kDa protein as shown by immunoblotting. Northern blotting revealed the same increases in these two variants in the level of a 2.3-kilobase FPGS mRNA when compared with control, while Southern blotting of genomic DNA did not reveal any increase in FPGS gene-copy number or restriction polymorphisms. Also, no difference in stability of FPGS mRNA was found between parental and variant cells. In contrast, nuclear run-on assays revealed differences among these cell types in the rate of FPGS mRNA transcription that correlated with increased FPGS activity, protein, and mRNA level in the variants. Similar studies with a transport-defective, methotrexate-resistant L1210 cell variant (L1210/R25) documented a 2-3-fold decrease in FPGS activity, protein, and mRNA levels that was accounted for by a decrease in FPGS mRNA transcription. These results provide the first examples of constitutively altered transcriptional regulation of FPGS activity associated with acquired resistance to antifolates.
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Affiliation(s)
- K Roy
- Program in Molecular Pharmacology and Therapeutics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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Egan MG, Sirlin S, Rumberger BG, Garrow TA, Shane B, Sirotnak FM. Rapid decline in folylpolyglutamate synthetase activity and gene expression during maturation of HL-60 cells. Nature of the effect, impact on folate compound polyglutamate pools, and evidence for programmed down-regulation during maturation. J Biol Chem 1995; 270:5462-8. [PMID: 7890662 DOI: 10.1074/jbc.270.10.5462] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
These studies in HL-60 cells examined the regulation of folylpolyglutamate synthetase (FPGS) activity at the level of gene expression during terminal maturation. Following addition of 210 mM Me2SO to cultures of HL-60 cells at a concentration that induces maturation of 85-90% of the cells, FPGS activity, but not folylpolyglutamate hydrolase (FPGH) activity, was reduced 2-7-fold within 1-5 days. The initial decline in FPGS activity preceded any effect of Me2SO on rate of growth and the increase in appearance of nitro blue tetrazolium-positive cells, a marker of cellular maturation, and the decrease after 5 days of exposure to Me2SO was solely accounted for by a 7-fold decrease in value for Vmax. The same time and concentration dependence for Me2SO was shown for the decline in FPGS activity, increase in nitro blue tetrazolium-positive cells, and decline in the level of a 2.1-kilobase FPGS mRNA during exposure to this inducer. This decline in FPGS mRNA was reversible when Me2SO was removed from the culture medium but only until that time when an appreciable number of cells were committed to terminal maturation. Following growth of HL-60 cells with [3H]MTX, used as a model folate compound, a large reduction in its intracellular polyglutamate pools was shown during maturation which quantitatively reflected the decline in FPGS activity as well as folate transport inward (Sirotnak, F.M., Jacobson, D.M., and Yang, C-H. (1986) J. Biol. Chem. 261, 11150-11156). Other data showed that folate status or obviation of the folate requirement during growth of these cells strongly influenced the rapidity of the onset of maturation following exposure to inducer. Overall, these results show that FPGS activity in HL-60 cells is a marker for proliferative capacity and that the underlying basis for the decline in FPGS activity during maturation is altered cognate gene expression which is manifested as early reversible and late irreversible phases. They also suggest that the coordinate reduction observed in folate transport, FPGS activity, dihydrofolate reductase, and probably other folate related enzymes by limiting macromolecular biosynthesis may be early programmed events in the maturation process that influence the switch from proliferation to senescence in these cells.
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Affiliation(s)
- M G Egan
- Program in Molecular Pharmacology and Therapeutics, Memorial Sloan-Kettering Cancer Center, New York, New York
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Brigle KE, Spinella MJ, Westin EH, Goldman ID. Increased expression and characterization of two distinct folate binding proteins in murine erythroleukemia cells. Biochem Pharmacol 1994; 47:337-45. [PMID: 8304978 DOI: 10.1016/0006-2952(94)90025-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We previously identified two membrane-bound folate binding proteins, FBP1 and FBP2, in murine L1210 leukemia cells. We now report on the development of two variant murine erythroleukemia cell lines that were used for direct comparison and biochemical characterization of the two murine folate binding proteins. Based on the results of northern analysis and the mobilities of affinity-labeled proteins on polyacrylamide gels, these cell lines exhibit specific up-regulated expression of FBP1 or FBP2. The affinities of the folate binding proteins for various (anti)folates were determined based upon the ability of the compounds to inhibiting of [3H]folic acid. The two proteins exhibited considerably different affinities and stereospecificities and, in general, FBP2 consistently bound each test compound with lesser affinity than FBP1. Both proteins displayed greatest affinity for folic acid, 5-methyltetrahydrofolate, and the antifolates CB3717 and 5,10-dideazatetrahydrofolate (DDATHF). Conversely, the proteins exhibited poor affinity for the dihydrofolate reductase inhibitors methotrexate and aminopterin. For 5-formyltetrahydrofolate, FBP1 had high affinity for the (6S) diastereoisomer, whereas FBP2 showed preference for the non-physiologic (6R) diasterceoisomer. The binding properties of FBP1 and FBP2 overexpressed in these cell lines closely paralleled those of their respective human homologs. These lines provide a model system in which to examine the biochemical characteristics of the individual folate binding proteins without the potential problems associated with expression of proteins in dissimilar cell lines.
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Affiliation(s)
- K E Brigle
- Department of Medicine, Virginia Commonwealth University, Medical College of Virginia, Richmond 23298
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Pizzorno G, Cashmore A, Moroson B, Cross A, Smith A, Marling-Cason M, Kamen B, Beardsley G. 5,10-Dideazatetrahydrofolic acid (DDATHF) transport in CCRF-CEM and MA104 cell lines. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)54035-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Sirotnak FM, Otter GM, Piper JR, DeGraw JI. Analogs of tetrahydrofolate directed at folate-dependent purine biosynthetic enzymes. Characteristics of mediated entry and transport-related resistance in L1210 cells for 5,10-dideazatetrahydrofolate and two 10-alkyl derivatives. Biochem Pharmacol 1988; 37:4775-7. [PMID: 3202909 DOI: 10.1016/0006-2952(88)90351-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- F M Sirotnak
- Memorial Sloan-Kettering, Cancer Center, New York, NY 10021
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Mullin RJ, Keith BR, Duch DS. Distribution and metabolism of calcium leucovorin in normal and tumor tissue. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1988; 244:25-38. [PMID: 3266825 DOI: 10.1007/978-1-4684-5607-3_3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- R J Mullin
- Department of Medicinal Biochemistry, Wellcome Research Laboratories, Research Triangle Park, NC 27709
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Sirotnak FM, Goutas LJ, Jacobsen DM, Mines LS, Barrueco JR, Gaumont Y, Kisliuk RL. Carrier-mediated transport of folate compounds in L1210 cells. Initial rate kinetics and extent of duality of entry routes for folic acid and diastereomers of 5-methyltetrahydrohomofolate in the presence of physiological anions. Biochem Pharmacol 1987; 36:1659-67. [PMID: 3593392 DOI: 10.1016/0006-2952(87)90051-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Comparison of the kinetic parameters for influx of highly purified [3H]folic acid versus [3H]methotrexate in L1210 cells under anionic buffer conditions showed a marked discordancy. In addition, the kinetics for influx of [3H]folic acid were unchanged in variant L1210 cells defective in [3H]methotrexate transport. In these variant cells, the Vmax for methotrexate was reduced 17-fold and the Km was increased 3-fold. The results show that [3H]folic acid influx is mediated by a system which has a low affinity, but a 20-fold higher capacity, for folate compounds than the classical high-affinity system mediating [3H]methotrexate influx. Since the latter system also exhibits very low affinity for [3H]folic acid, it would not be expected to contribute significantly to the total influx of [3H]folic acid. The high-capacity system for [3H]folic acid influx is different from that believed to mediate pterin influx in L1210 cells since it was not inhibited by adenine, a potent inhibitor of pterin influx. However, exposure of cells to [3H]folic acid in a nonanionic buffer resulted in marked stimulation of initial influx, and a fraction of influx under these conditions was inhibited by methotrexate. These results suggest that anions modulate the extent of multiplicity of [3H]folic acid influx by their known effects on the high-affinity, reduced folate/methotrexate system. The diastereomers, at carbon 6, of [14C]5-methyltetrahydrohomofolate shared both transport systems. The influx Km for the natural diastereomer was one-half that of the unnatural form for both transport systems. Both diastereomers showed a much greater differential in affinity between the two transport systems than did [3H]folic acid. Our results suggest that an analog which could be effectively transported by the low-affinity/high-capacity route may be useful in the treatment of tumors resistant to methotrexate due to a defective high-affinity/low capacity influx system. We also found that incubation of L1210 cells with [3H]folic acid or the natural diastereomer [14C]5-methyltetrahydrohomofolate for 10 min resulted in the formation of a nonexchangeable fraction of radioactivity amounting to 20-40% of the total accumulation. This non-exchangeable fraction may be explained by the accumulation of metabolites other than polyglutamates. Preloading of cells with methotrexate prior to incubation with [3H]folic acid prevented the accumulation of radioactivity as a nonexchangeable fraction.
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Luhrs CA, Sadasivan E, da Costa M, Rothenberg SP. The isolation and properties of multiple forms of folate binding protein in cultured KB cells. Arch Biochem Biophys 1986; 250:94-105. [PMID: 3767384 DOI: 10.1016/0003-9861(86)90705-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The folate binding proteins (FBPs) of KB cells which were cultured in normal (N) and folate-deficient (D) medium have been characterized. The 200,000 g supernate of lysed cells contained two FBPs which could be separated by DEAE-Bio-Gel A chromatography, indicating that they differ in ionic charge although they could not be separated by gel filtration through Sephadex G-100 (apparent Mr approximately 40,000). Two species of FBP, a major form of apparent Mr approximately 160,000 and a minor form of apparent Mr approximately 40,000, were identified by gel filtration through Sephadex G-150 in the membrane component of the cells after solubilization with Triton X-100. An additional FBP was isolated and purified by affinity chromatography from the medium in which these cells were cultured. By gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the apparent Mr of this FBP was approximately 44,000. The association constants for pteroylglutamic acid of the FBPs in the 200,000 g cell lysate supernate, culture medium, and Triton-solubilized membrane were similar and the relative affinity of folate analogs for the FBP, vis-à-vis pteroylglutamic acid, was similar for all species. An antiserum raised to the purified FBP from the culture medium precipitated the FBPs in the 200,000 g cell lysate supernate, Triton-solubilized membrane, and culture medium, indicating antigenic homology among these FBPs. There was no unsaturated FBP in the 200,000 g cell lysate supernate or medium when KB cells were cultured in N medium. However, when cells were cultured in D medium, the unsaturated FBP of the 200,000 g cell supernate and culture medium was substantial (9.2 and 14.1 pmol/mg protein, respectively). Unsaturated FBP was detected in the membrane of normal cells but this also increased when these cells were cultured in D medium (4.5 to 756 pmol/mg protein), indicating that the FBPs of these cellular compartments are normally saturated by folate. After 16 weeks of culture in D medium, the total folate binding capacity of the membrane-associated FBP was twofold greater than that of normal KB cells, indicating the induction of FBP.
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Alteration of folate analogue transport following induced maturation of HL-60 leukemia cells. Early decline in mediated influx, relationship to commitment, and functional dissociation of entry and exit routes. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67361-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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