title: Methenyltetrahydrofolate synthetase regulates folate turnover and accumulation.
abstract: Cellular folate deficiency impairs one-carbon metabolism, resulting in decreased fidelity of DNA synthesis and inhibition of numerous S-adenosylmethionine-dependent methylation reactions including protein and DNA methylation. Cellular folate concentrations are influenced by folate availability, cellular folate transport efficiency, folate polyglutamylation, and folate turnover specifically through degradation. Folate cofactors are highly susceptible to oxidative degradation in vitro with the exception of 5-formyltetrahydrofolate, which may be a storage form of folate. In this study, we determined the effects of depleting cytoplasmic 5-formyltetrahydrofolate on cellular folate concentrations and folate turnover rates in cell cultures by expressing the human methenyltetrahydrofolate synthetase cDNA in human MCF-7 cells and SH-SY5Y neuroblastoma. Cells with increased methenyltetrahydrofolate synthetase activity exhibited: 1) increased rates of folate turnover, 2) elevated generation of p-aminobenzoylglutamate in culture medium, 3) depressed cellular folate concentrations independent of medium folic acid concentrations, and 4) increased average polyglutamate chain lengths of folate cofactors. These data indicate that folate catabolism and folate polyglutamylation are competitive reactions that influence cellular folate concentrations, and that increased methenyltetrahydrofolate synthetase activity accelerates folate turnover rates, depletes cellular folate concentrations, and may account in part for tissue-specific differences in folate accumulation.
authors.affiliation: Cornell University Graduate Field of Biochemistry, Molecular and Cellular Biology, Ithaca, New York 14853 USA>
authors.forename: Montserrat C
authors.initials: MC
authors.lastname: Anguera
authors.forename: Jae Rin
authors.initials: JR
authors.lastname: Suh
authors.forename: Haifa
authors.initials: H
authors.lastname: Ghandour
authors.forename: Ilya M
authors.initials: IM
authors.lastname: Nasrallah
authors.forename: Jacob
authors.initials: J
authors.lastname: Selhub
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Stover
mesh_terms: D001692:Biological Transport; D015152:Blotting, Northern; D015153:Blotting, Western; D019731:Carbon-Nitrogen Ligases / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003593:Cytoplasm / Q000378:metabolism; D019175:DNA Methylation; D018076:DNA, Complementary / Q000378:metabolism; D005492:Folic Acid / Q000378:metabolism*; D006801:Humans; D002955:Leucovorin / Q000378:metabolism; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D011099:Polyglutamic Acid / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry; D013997:Time Factors; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
chemical_list: D018076:DNA, Complementary; D012333:RNA, Messenger; D011099:Polyglutamic Acid; D012436:S-Adenosylmethionine; D005492:Folic Acid; D019731:Carbon-Nitrogen Ligases; C021557:5,10-methenyltetrahydrofolate synthetase; D002955:Leucovorin; D010100:Oxygen