Dihydrofolate Reductase Function
Primary Enzymatic Function
Dihydrofolate reductase (DHFR) catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate (THF), which is essential for DNA synthesis, repair, and cellular replication. 1, 2
Critical Metabolic Roles
DNA Synthesis and Cell Proliferation
- DHFR regenerates tetrahydrofolate by reducing dihydrofolate using NADPH as a cofactor, making it essential for maintaining the cellular folate pool 2, 3
- Tetrahydrofolate and its one-carbon adducts are required for de novo synthesis of purines and thymidylate, which are fundamental building blocks of DNA 2, 3
- The enzyme enables synthesis of glycine, methionine, and serine through one-carbon metabolism pathways 2
- Dihydrofolates must be reduced to tetrahydrofolates before they can function as carriers of one-carbon groups in nucleotide synthesis 1
Folate Metabolism Integration
- DHFR is expressed primarily in the liver and converts synthetic folic acid (pteroylglutamic acid) into biologically active tetrahydrofolate, though this enzymatic activity is relatively limited 4
- The enzyme works in concert with other folate-dependent enzymes, particularly thymidylate synthase, which uses 5,10-methylenetetrahydrofolate to convert uracil to thymine 4
- DHFR activity is essential for maintaining adequate intracellular concentrations of 5,10-MTHF, preventing uracil misincorporation into DNA 4
Clinical Significance
Therapeutic Target
- DHFR inhibition depletes tetrahydrofolate, thereby slowing DNA synthesis and cell proliferation, making it an effective target for cancer chemotherapy 1, 5
- Methotrexate inhibits DHFR, interfering with DNA synthesis, repair, and cellular replication in rapidly proliferating tissues such as malignant cells, bone marrow, and intestinal mucosa 1
- The enzyme has been studied extensively as a drug target for bacterial, protozoal, and fungal infections, as well as neoplastic and autoimmune diseases 3
Genetic Variations
- Polymorphisms in the DHFR gene affect mRNA levels and enzyme expression, influencing folate status, disease susceptibility (including spina bifida and cancer), and response to antifolate medications like methotrexate 5
- Changes in DHFR expression levels can affect susceptibility to folate-dependent diseases and sensitivity to anti-cancer drugs 5
Secondary DHFR Enzyme
- Humans possess a second dihydrofolate reductase enzyme (DHFRL1) located in mitochondria, which has lower specific activity and higher Km for dihydrofolate compared to cytoplasmic DHFR 6
- DHFRL1 can complement DHFR-negative phenotypes but appears optimized for mitochondrial folate metabolism with its lowered substrate affinity 6
Pathophysiological Consequences of Deficiency
- Limited DHFR activity leads to accumulation of uracil, imbalanced deoxyuridine monophosphate:deoxythymidine monophosphate ratios, and misincorporation of uracil into cellular DNA 4
- Inadequate DHFR function results in increased DNA deletions, chromosomal instability, and impaired DNA integrity 4
- DHFR inhibition causes disruption of purine and thymidylate biosynthesis and DNA replication, leading to cell death 2