ARS | Publication request: REGULATION OF FOLATE-MEDIATED ONE-CARBON METABOLISM BY 10-FORMYLTETRAHYDROFOLATE DEHYDROGENASE

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 17, 2006
Publication Date: July 7, 2006
Reprint URL: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstract&list_uids=16627483&query_hl=6&itool=pubmed_docsum
Citation: Anguera, M.C., Ghandour, H., Chiang, E., Selhub, J., Shane, B., Stover, P.J. 2006. Regulation of folate-mediated one-carbon metabolism by 10-formyltetrahydrofolate dehydrogenase. Journal of Biological Chemistry. 281(27):18335-42.

Interpretive Summary: The vitamin folic acid has many functions in the cell (body), many of which use different enzymes which act on various forms of the vitamin. Because of this multiplicity of enzymes and forms, an important area of research is to learn how these forms are regulated. In this study we were particularly interested in one enzyme, 10-formyltetrahydrofolate dehydrogenase (FDH). We inserted the gene of this enzyme into cells which do not normally have this enzyme. We found that such an insertion caused the cells to decrease their folate content, as well as to cause change in the character of these folates.

Technical Abstract: 10-formyltetrahydrofolate dehydrogenase (FDH) catalyzes the conversion of 10-formyltetrahydrofolate to tetrahydrofolate (THF) in mammalian liver and brain. Several functions for FDH have been ascribed including: 1) the inhibition of purine biosynthesis by depleting 10-formylTHF pools, 2) the regulation of cellular folate concentrations by sequestering THF and 3) the stimulation of THF-activated one-carbon unit synthesis by channeling folate cofactors to serine hydroxymethyltransferase (SHMT) and C1-tetrahydrofolate synthase (MTHFD1). However, none of these functions have been demonstrated in vivo. To elucidate the role of FDH in folate-mediated one-carbon metabolism, the effects of FDH expression on cellular folate concentrations and one-carbon metabolism were investigated in SH-SY5Y neuroblastoma, a cell line that does not contain detectable levels of FDH protein. Expression of the human FDH cDNA at low levels increased the formylTHF/THF ratio nearly 10-fold and depleted cellular folate concentrations by 57% compared to nontransfected cells. Neuroblastoma expressing higher levels of FDH protein had 65% lower cellular folate concentrations, elevated levels of unsubstituted THF and increased rates of folate catabolism compared to nontransfected cells. FDH expression increased the flux of one-carbon units derived from cytoplasmic SHMT into methionine and thymidylate by 60% but did not affect significantly the enrichment of exogenous formate into methionine, serine or purines. We conclude that FDH, when expressed at low levels, facilitates the incorporation of one-carbon units into the THF-activated one-carbon pool, whereas high levels of FDH expression deplete the pool of folate-activated one-carbon units by catalyzing the conversion of 10-formylTHF to THF. FDH does not increase cellular folate concentrations by sequestering THF in neuroblastoma.