Human mutations in methylenetetrahydrofolate dehydrogenase 1 impair nuclear de novo thymidylate biosynthesis

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-01, Vol.112 (2), p.400-405
• Main Authors: Field, Martha S., Kamynina, Elena, Watkins, David, Rosenblatt, David S., Stover, Patrick J.
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution; Anemia; Anemia, Megaloblastic - genetics; Anemia, Megaloblastic - metabolism; Biological Sciences; Biosynthesis; Cell Line; Cell Nucleus - metabolism; Codon, Nonsense; Deoxyribonucleic acid; DNA; DNA Damage; Fibroblasts - metabolism; Humans; Metabolic Networks and Pathways; Metabolism; Methylenetetrahydrofolate Dehydrogenase (NADP) - chemistry; Methylenetetrahydrofolate Dehydrogenase (NADP) - deficiency; Methylenetetrahydrofolate Dehydrogenase (NADP) - genetics; Minor Histocompatibility Antigens; Mutant Proteins - chemistry; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutation; Phenotype; Point Mutation; Severe Combined Immunodeficiency - genetics; Severe Combined Immunodeficiency - metabolism; Thymidine Monophosphate - biosynthesis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1414555112

Significance These studies have identified that human genetic mutations, which impair the function of the folate-dependent enzyme methylene tetrahydrofolate dehydrogenase I (MTHFD1), depress rates of de novo thymidylate synthesis, elevate uracil levels in human DNA, and increase genome instability. These findings provide insights into the role of MTHFD1 and thymidylate biosynthesis in the etiology of SCID and megaloblastic anemia. An inborn error of metabolism associated with mutations in the human methylenetetrahydrofolate dehydrogenase 1 ( MTHFD1 ) gene has been identified. The proband presented with SCID, megaloblastic anemia, and neurologic abnormalities, but the causal metabolic impairment is unknown. SCID has been associated with impaired purine nucleotide metabolism, whereas megaloblastic anemia has been associated with impaired de novo thymidylate (dTMP) biosynthesis. MTHFD1 functions to condense formate with tetrahydrofolate and serves as the primary entry point of single carbons into folate-dependent one-carbon metabolism in the cytosol. In this study, we examined the impact of MTHFD1 loss of function on folate-dependent purine, dTMP, and methionine biosynthesis in fibroblasts from the proband with MTHFD1 deficiency. The flux of formate incorporation into methionine and dTMP was decreased by 90% and 50%, respectively, whereas formate flux through de novo purine biosynthesis was unaffected. Patient fibroblasts exhibited enriched MTHFD1 in the nucleus, elevated uracil in DNA, lower rates of de novo dTMP synthesis, and increased salvage pathway dTMP biosynthesis relative to control fibroblasts. These results provide evidence that impaired nuclear de novo dTMP biosynthesis can lead to both megaloblastic anemia and SCID in MTHFD1 deficiency.